This and the next posts are an adoption of my old 2017 series from another blog. The factual material may be obsolete. I’m keeping the posts here for historical reasons, and also because I find the narrative of the story somewhat curious. Some minor stylistic changes were applied. Obsolete links updated as needed.
ARP is one of the most widely used protocols in modern networks. Its history goes back to early 80s into the times of DARPA backed internetworking experiments. The very first RFC 826 that defined the protocol is dated November 1982 (it’s 35 years old at the time of writing). Despite the age, it’s still a backbone of local IPv4 network connectivity. Even in 2017 (the year I draft this post), it’s still very hard to find a IPv6-only network node, especially outside cloud environments. But that’s IPv4, so how does ARP fit into the picture?
To understand the goal of ARP, let’s first look at how network nodes are connected. The general model can be described as a set of hosts, each having one or more Network Interface Controller (NIC) cards connected to a common data link fabric. This fabric comes in different flavors (Ethernet, IEEE 802.11 aka WiFi, or FireWire). Irrespective of particular fabric flavor, all of them provide similar capabilities. One of the features that are expected from all of them is some form of endpoint addressing, ideally globally unique, so that network hosts connected to a shared medium can distinguish each other and address transferred data to specific peers. Ethernet and IEEE 802.11 are probably the most popular data link layers in the world, and since they are largely identical in terms of NIC addressing, in next discussions we will assume Ethernet fabric unless explicitly said otherwise.
For Ethernet, each NIC card produced in the world gets a unique 48-bit long hardware address allocated by a vendor under IEEE supervision that guarantees that no hardware address is allocated to two NIC cards. Uniqueness is to ensure that whichever hardware you plug into your network, it will never clash in address space with any other card also attached to the network. An example of a EUI-48 address would be, in commonly used notation, f4:5c:89:89:cd:54. These addresses are widely known as MAC addresses, and so I will also use this term moving forward.
It all means that your NIC already has a unique address, so why do you even need IP addresses? Sadly, people are bad at memorizing 48 randomized bits, so an easier scheme would be handy. Another problem is whenever your NIC dies and you replace it with a new one, the new card will have another unique address, and so you would need to advertise the new MAC address to all your network peers that may need to access your host.
And so engineers were looking for a better scheme to address network hosts. One of those successful alternative addressing proposals was IPv4. In this scheme, IPv4 addresses are defined 32-bit long. Still a lot, but the crucial point is that now you could pick addresses for your NIC cards. With that freedom, you could pick the same bit prefix for all your hosts, distinguishing them by a shorter number of trailing bits, and memorize just those unique bits, and configure your networking software to use the same prefix for network communication with other hosts. Then whenever you want to address a host, you pass unique trailing bits assigned to the host into your networking stack and allow it to produce the resulting address by prepending the common prefix.
The only problem with this approach is that now you have two address schemes: MAC addresses and IP addresses, with no established mapping between them. Of course, in small networks, you could maintain static IP-to-MAC mappings in sync on every host, but that is error prone and doesn’t scale well.
And that’s where ARP comes in to the stage. Instead of maintaining static mappings across hosts, the protocol allows to dynamically disseminate the information on the wire.
Quoting the abstract of RFC 826:
Presented here is a protocol that allows dynamic distribution of the information needed to build tables to translate an address A in protocol P’s address space into a 48.bit Ethernet address.
And that’s exactly what we need.
While the abstract and even the RFC title talk about Ethernet, the mechanism rendered so successful that it was later expanded to other data links, including e.g. FireWire.
The protocol introduces both ARP packet format as well as its state machine. Sadly, the RFC doesn’t contain a visual scheme for ARP packets, but we can consult the protocol Wikipedia page.
The RFC describes an address translation (ARP) table for each host storing IP-to-MAC mappings. It also defines two operations: a REQUEST and a REPLY. Whenever a host wants to contact an IP address for which there is no mapping in the local ARP table, the host sends a REQUEST ARP packet to broadcast destination MAC address asking the question “Who has the IP address?” Then it’s expected that the host carrying the IP address will send a REPLY ARP packet back with its own MAC address set in “Sender hardware address” field. The original host will then update its ARP table with a new IP-to-MAC mapping and will use the newly learned value as a destination MAC address for all communication with the IP address.
One thing to clarify before we move forward: this is all true assuming both interacting hosts are on the same layer-2 network segment, without an IP gateway (router) in between. If hosts are located in different segments, then connection between them is established through a router. In this case, a host willing to communicate with a host in another segment will determine that fact by inspecting its IP routing table. Since the destination IP address then would not belong to the local network IP prefix, the host will instead send the data to the default router IP address. (Of course, at this point the host may also determine that its ARP table doesn’t contain an entry for the gateway IP address yet, in which case it will use ARP to learn about the router MAC address.)
One interesting aspect of the original RFC is that it doesn’t define a mechanism to update existing ARP table entries with new MAC addresses. Back in 1982, it was probably widely assumed that mobile IP stations roaming across network segments changing devices used to connect to outside world on the fly (think about how your smartphone seamlessly switches from WiFi to LTE) were not a too realistic use case. But even then, in “Related issue” section of the document, some ideas on how it could be implemented if needed were captured.
One suggestion was for every host to define “aging time” for its ARP entries. If a peer host is detected as unreachable (probably because there was no incoming traffic using both the MAC and IP addresses stored in ARP table), the originating host could remove the corresponding ARP entry from its table after it’s “aged”. This mechanism is indeed used in most modern ARP implementations, with 60 seconds being the common default for Linux systems (can be overridden using gc_stale_time sysctl setting).
It means that your connectivity to a roaming IP host will heal itself after a minute of temporary down time. While that’s great, some use cases would benefit from a more rapid reaction of hosts to network changes.
And that’s where gratuitous ARP comes into play.
Gratuitous ARP is an ARP packet that was never asked for (hence its alternative name - unsolicited ARP). RFC 826, “Related issue” section, mentions an algorithm to update existing ARP table entries in the network based on unsolicited ARP packets. But it’s only RFC 2002, “IP Mobility support” from year 1996 that made it part of a standard and introduced the very term “gratuitous ARP”.
RFC 2002 discusses protocol enhancements for IP networks to allow for IP devices roaming across networks without introducing significant connectivity delays or disruptions. Among other things, it defines the algorithm to be used to update existing ARP table entries with new MAC addresses. For this matter, it adopts the proposal from RFC 826, where a host can broadcast a gratuitous ARP packet into a network, and its peers then update their tables with the new MAC address sent, restoring connectivity even before old ARP entries expire.
There are two main use cases for gratuitous ARP. One is to quickly switch between multiple devices on the same host. Another is to move services exposed through an IP address from one host to another transparently to network peers.
This last scenario may happen either as part of a planned action on behalf of an Ops team managing a service, or triggered by a self-healing mechanism used in networks to guarantee availability of services in case of software or network failures. One piece of popular software that allows to fail over IP addresses from one host to another is keepalived which uses the VRRP protocol to negotiate between hosts which node should carry IP addresses managed by the software.
In OpenStack Neutron, gratuitous ARP is how floating IP addresses roam between ports; they also help with failing over IP addresses between HA router instances.
To recollect, the primary use for gratuitous ARP in OpenStack Neutron L3 agent is to update network peers about the new location of a “floating” IP address (“elastic” in AWS-speak) when it’s disassociated from one port and then associated to another port with a different MAC address. Without issuing a gratuitous ARP on new association, it may take significant time before a reused floating IP address mapping is updated as a result of the “aging” process.
Gratuitous ARP is also used by the L3 agent to implement HA for Neutron routers. Whenever a new HA router instance becomes “master”, it adds IP addresses managed by Neutron to its interfaces and issues a set of gratuitous ARP packets into attached networks to advertise the new location. Network peers then update their ARP tables with new MAC addresses from those packets and in this way don’t need to wait for old entries to expire before connectivity would be restored. The switch to the new router instance is then a lot smoother.
There are two distinct implementations for gratuitous ARP in OpenStack Neutron, one for each distinct router deployment mode: legacy and HA. The difference comes primarily from the fact that legacy router data plane is fully realized by the L3 agent, while HA routers “outsource” IP address management to
keepalived daemon spawned by the agent. (The third deployment mode - DVR - is largely covered by those two, where specific implementation depends on whether DVR routers are also HA or not; for this reason I won’t mention DVR going forward).
Let’s consider each distinct deployment mode separately, starting with legacy.
Legacy mode is what once was the only mode supported by OpenStack Neutron. In this mode, the L3 agent itself implements the whole data plane, creating network namespaces for routers, creating ports, plugging them into the external
br-ex bridge, and adding fixed and floating IP addresses to router ports. Besides that, the agent also issues gratuitous ARP packets into attached networks when a new IP address is added to one of its ports. This is to update network peers about the new mappings. Peers may use those unsolicited updates either to update any existing ARP entries with a new MAC address, or to “warm up” their tables with IP-to-MAC mappings even before the very first IP datagram is issued to the router IP address (this is something that Linux kernel does when arp_accept sysctl setting is enabled for the receiving interface).
When the L3 agent sends gratuitous ARP packets for an IP address, this is what you can find in the agent log file:
2017-04-28 20:53:11.264 14176 DEBUG neutron.agent.linux.utils [-] Running command (rootwrap daemon): ['ip', 'netns', 'exec', 'qrouter-726095be-5916-489b-be05-860e2f19d556', 'ip', '-4', 'addr', 'add', '10.1.0.1/26', 'scope', 'global', 'dev', 'qr-864545b9-5f', 'brd', '10.1.0.63'] execute_rootwrap_daemon /opt/stack/new/neutron/neutron/agent/linux/utils.py:108
And then later:
2017-04-28 20:53:11.425 14176 DEBUG neutron.agent.linux.utils [-] Running command (rootwrap daemon): ['ip', 'netns', 'exec', 'qrouter-726095be-5916-489b-be05-860e2f19d556', 'arping', '-A', '-I', 'qr-864545b9-5f', '-c', '3', '-w', '4.5', '10.1.0.1'] execute_rootwrap_daemon /opt/stack/new/neutron/neutron/agent/linux/utils.py:108
As you have probably figured out, the first snippet shows the agent adding a new IPv4 address
10.1.0.1 to an internal router
qr-864545b9-5f port, and the second snippet is where the agent sends gratuitous ARP packets advertising the new IP address into the network to which the
qr-864545b9-5f port is attached to (this is achieved by calling the
arping tool from iputils package with the right arguments).
Let’s have a look at each of the arguments passed into
The very first option is -A, and it’s used to issue gratuitous (broadcast) ARP packets. Without the option, the tool would send unicast ARP REQUEST packets for the IP address, and would wait for a REPLY (the unicast mode may be useful when you need to check if there are any other hosts in the network carrying the same IP address, or to sanity check an existing IP-to-MAC mapping). The packets sent are of REPLY type. (If we would use -U instead, it would send REQUEST packets.)
The next option is -I, and it specifies the interface to issue the packets on.
The -c option defines the number of ARP packets to issue into the network. There is always a 1 second interval between the packets. Since we call it with -c 3, it issues three packets in two second time span.
The next option is -w 4.5 and it means that we will wait for 4.5 seconds (or better, 4 seconds because the tool doesn’t recognize floating part of the argument) before exiting it. In general, the tool will exit after two seconds, but when the interface used to send packets is gone while the tool is running, it may block its execution since it will never be able to successfully send all three packets. The option guarantees that the thread running the tool will eventually make progress.
The very last argument is the IP address to advertise. A single port may carry multiple IPv4 addresses, so it’s crucial to define which of those addresses should be advertised.
HA support is a relatively new addition to OpenStack Neutron routers. To use HA for Neutron routers, one should configure Neutron API controller to expose l3-ha API extension, at which point users are able to create highly available routers.
For those routers, data plane is managed both by the L3 agent as well as the
keepalived daemon that the agent spawns for every HA router it manages. The agent first prepares the router namespace, its ports, rules for NAT translation; but then it falls back to the
keepalived daemon which manages IP addresses on ports. For this matter, the agent generates a configuration file listing all managed IP addresses and passes it into
keepalived. The daemon then starts, negotiates with other
keepalived processes implementing the HA router who is going to be its “master” (for this matter, VRRP is used), and if it’s indeed “master”, it triggers state transition machinery, which, among other things, will add managed IP addresses specified in the configuration file to appropriate router ports. It will also send gratuitous ARP packets into the network to update peers about the location of those IP addresses. If you then inspect your system log, you may find the following messages there:
May 2 13:19:47 host-192-168-24-12 Keepalived: Starting Keepalived v1.2.13 (07/01,2016)
May 2 13:19:47 host-192-168-24-12 Keepalived: Starting VRRP child process, pid=307083
May 2 13:19:47 host-192-168-24-12 Keepalived_vrrp: Netlink reflector reports IP 169.254.192.6 added
May 2 13:19:47 host-192-168-24-12 Keepalived_vrrp: Netlink reflector reports IP fe80::f816:3eff:fe5f:d44b added
May 2 13:19:47 host-192-168-24-12 Keepalived_vrrp: Registering Kernel netlink reflector
May 2 13:19:47 host-192-168-24-12 Keepalived_vrrp: Registering Kernel netlink command channel
May 2 13:19:47 host-192-168-24-12 Keepalived_vrrp: Registering gratuitous ARP shared channel
May 2 13:19:47 host-192-168-24-12 Keepalived_vrrp: Opening file '/var/lib/neutron/ha_confs/b7fece4b-ea95-4eb6-b7b8-dc060325d1bc/keepalived.conf'.
May 2 13:19:47 host-192-168-24-12 Keepalived_vrrp: Configuration is using : 64829 Bytes
May 2 13:19:47 host-192-168-24-12 Keepalived_vrrp: Using LinkWatch kernel netlink reflector...
May 2 13:19:47 host-192-168-24-12 Keepalived_vrrp: VRRP_Instance(VR_1) Entering BACKUP STATE
May 2 13:19:47 host-192-168-24-12 Keepalived_vrrp: VRRP_Instance(VR_1) removing protocol Virtual Routes
May 2 13:19:47 host-192-168-24-12 Keepalived_vrrp: VRRP sockpool: [ifindex(16), proto(112), unicast(0), fd(10,11)]
May 2 13:19:54 host-192-168-24-12 Keepalived_vrrp: VRRP_Instance(VR_1) Transition to MASTER STATE
May 2 13:19:56 host-192-168-24-12 Keepalived_vrrp: VRRP_Instance(VR_1) Entering MASTER STATE
May 2 13:19:56 host-192-168-24-12 Keepalived_vrrp: VRRP_Instance(VR_1) setting protocol VIPs.
May 2 13:19:56 host-192-168-24-12 Keepalived_vrrp: VRRP_Instance(VR_1) setting protocol E-VIPs.
May 2 13:19:56 host-192-168-24-12 Keepalived_vrrp: VRRP_Instance(VR_1) setting protocol Virtual Routes
May 2 13:19:56 host-192-168-24-12 Keepalived_vrrp: VRRP_Instance(VR_1) Sending gratuitous ARPs on ha-e09aa535-6f for 169.254.0.1
May 2 13:19:56 host-192-168-24-12 Keepalived_vrrp: VRRP_Instance(VR_1) Sending gratuitous ARPs on qg-6cf347df-28 for 10.0.0.219
May 2 13:19:56 host-192-168-24-12 Keepalived_vrrp: VRRP_Instance(VR_1) Sending gratuitous ARPs on qr-3ee577eb-4f for 10.100.0.1
May 2 13:19:56 host-192-168-24-12 Keepalived_vrrp: VRRP_Instance(VR_1) Sending Unsolicited Neighbour Adverts on qr-3ee577eb-4f for fe80::f816:3eff:fe9a:c17
May 2 13:19:56 host-192-168-24-12 Keepalived_vrrp: VRRP_Instance(VR_1) Sending Unsolicited Neighbour Adverts on qg-6cf347df-28 for fe80::f816:3eff:fec7:861a
May 2 13:19:56 host-192-168-24-12 Keepalived_vrrp: Netlink reflector reports IP fe80::f816:3eff:fe9a:c17 added
May 2 13:19:56 host-192-168-24-12 Keepalived_vrrp: Netlink reflector reports IP fe80::f816:3eff:fec7:861a added
Here we can see
keepalived transitioning to master state and immediately issuing gratuitous updates after VIP addresses are set for managed interfaces. (A careful reader will also notice that it also issues something called
Unsolicited Neighbour Adverts which is a similar mechanism for IPv6 addresses, but I won’t go there.)
It would seem like it’s good for the job. Sadly, the reality is uglier than one could hope.
As we’ve learned during our testing of the HA feature, sometimes
keepalived forgot to send gratuitous ARP packets. It always happened when an existing
keepalived instance was asked to reload its configuration file because some Neutron API operations triggered router updates that affected the file contents. An example of an update could be e.g. adding a new floating IP address to a port, or disassociating one. In this case, Neutron L3 agent would generate a new configuration file and then send SIGHUP signal to the running
keepalived instance, hoping that it will catch the changes, converge the data plane to latest configuration, and finally issue gratuitous ARP updates. It did not.
Investigation, largely carried by John Schwarz, uncovered it was not an issue with latest
keepalived releases, but the one from RHEL7 repositories. Bisecting releases, we’ve found out that the very first
keepalived release that was not exposing the buggy behavior was 1.3.20. Popular distributions (RHEL7, Ubuntu Xenial) were still shipping older versions of the daemon (1.2.13 for RHEL7 and 1.2.19 for Xenial).
Though the issue was technically in
keepalived, we needed to adopt OpenStack to the buggy releases shipped with platforms we support. First considered option was just fully restarting
keepalived, which would correctly trigger the gratuitous ARP machinery. The problem with this approach was that full restart temporarily stops the VRRP thread that sends master health checks, and with unfortunate timing, it sometimes results in an unnecessary “master” to “backup” flip, operation that is both computationally costly as well as data plane disruptive.
Since we couldn’t just upgrade
keepalived, it meant that Neutron L3 agent would need to play some role in issuing gratuitous ARP packets, not relying on the daemon to do the right job. For this matter, Neutron patch was introduced. What the patch does is it calls to
arping tool whenever a new IPv4 address is added to an interface managed by
keepalived. A new address added indicates that VRRP negotiation resulted in the locally running
keepalived instance transitioning to ”master”; or it means a new floating IP address was added in the configuration file just reloaded by the daemon. At this point it makes sense to advertise the newly added addresses on the wire using gratuitous ARP, something that in an ideal world
keepalived would do for us.
We already had the neutron-keepalived-state-change helper daemon running inside HA router network namespaces that monitors router interfaces for new IP addresses to detect transitions between
keepalived states and then sends the information back to neutron-server. To avoid introducing a new daemon just to issue gratuitous ARP packets, we figured it’s easier to reuse the existing one.
Of course, issuing gratuitous ARP packets from outside of
keepalived introduced some complications.
For one, the whole setup became slightly racy. For example, what happens when
keepalived decides to forfeit its mastership in the middle of
neutron-keepalived-state-change sending gratuitous ARP packets? Will we continue sending those packets into the network even after
keepalived removed VIP addresses from its interfaces? Thanks to net.ipv4.ip_nonlocal_bind sysctl knob, it shouldn’t be a concern. Its default value (0) means that userspace tools (including
arping) won’t be able to send an ARP packet for an IPv4 address that is not on the interface. If we hit the race, the worst that could happen is that
arping would hang, failing to send more gratuitous ARP packets into the network, logging the “bind: Cannot assign requested address” error message on its stderr. Since we set a hard time limit for the tool execution (remember the -w 4.5 CLI arguments discussed above), it should be fine. To stay on safe side, we would just set the sysctl knob inside each new router namespace to 0 to override whatever custom value the platform may have for the setting.
There are still two complications with that though.
First, as it turned out, the
ip_nonlocal_bind knob was set to 1 for DVR
fip namespaces, and for a reason. So we needed to make sure that it’s set to
0 in all router namespaces except
fip. Another issue that we surfaced was specific to RHEL7 kernel where the
ip_nonlocal_bind knob was not network namespace aware, so changing it in one of namespaces affected all other routers. It was fixed in later RHEL7 kernels, and in the meantime, we could only hope that no one ever hosts both DVR
fip and HA
qrouter namespaces on the same node, for they would clash.
Not completely related to gratuitous ARP, but since it’s also about
SIGHUP handler, I figured I will mention this issue here too.
Some testing revealed that when multiple HA router updates arrived to Neutron L3 agent in quick succession,
keepalived sometimes forfeits its mastership, flipping to “backup” with no apparent reason. Consequent network disruption until a new
keepalived ”master” instance is elected included.
Further investigation, also led by John Schwarz, revealed that it always happens when you would send multiple
SIGHUP signals to
keepalived, irrespective to whether there were any changes to its configuration files.
It was clearly a bug in the daemon, but at this point we were used to work around its quirks, so it hasn’t taken a lot of time to come up with a special signal throttler for
keepalived. What it does is it introduces 3 second delays between consequent SIGHUP signals sent to
keepalived instances. Why 3 seconds? No particular reason, except that it worked (anything below 2 seconds didn’t), and it seemed like a good idea to give
keepalived a chance to send at least a single health check VRRP message between reload requests, so we made it slightly longer than the default health check interval which is 2 seconds for Neutron.
So how do I know that an HA router actually sent gratuitous ARP packets without having access to a live machine? Let’s say all I have is log files for Neutron services.
For those packets that are sent by
keepalived itself, it logs a message per advertised IP address in syslog, as seen in a snippet provided earlier.
As for packets issued by
neutron-keepalived-state-change daemon, corresponding messages were originally logged in a file that was located in a directory that also contained other files needed for the router, including
keepalived configuration and state files. The problem here is that once a HA router is unscheduled from an L3 agent, it stops
keepalived and cleans up both the router namespace as well as all files used by the router, including log files for
neutron-keepalived-state-change. It means that after the router is gone, you can’t get your hands on the daemon log file. You are left in darkness as to whether it even called to
To facilitate post-cleanup debugging, in Pike release cycle we’ve made the daemon to log to system log in addition to its own log file. With the patch, we can now see the daemon messages in system journal, including those corresponding to
Apr 28 20:56:00 ubuntu-xenial-rax-ord-8650506 neutron-keepalived-state-change: 2017-04-28 20:56:00.338 20945 DEBUG neutron.agent.linux.utils [-] Running command: ['sudo', 'ip', 'netns', 'exec', 'qrouter-433765a8-f084-4fbd-9aea-447835c32b09@testceeee6ac', 'arping', '-A', '-I', 'qg-c317683_6ac', '-c', '3', '-w', '4.5', '10.0.0.215'] create_process /opt/stack/new/neutron/neutron/agent/linux/utils.py:92
Apr 28 20:56:00 ubuntu-xenial-rax-ord-8650506 sudo: stack : TTY=unknown ; PWD=/ ; USER=root ; COMMAND=/sbin/ip netns exec qrouter-433765a8-f084-4fbd-9aea-447835c32b09@testceeee6ac arping -A -I qg-c317683_6ac -c 3 -w 4.5 10.0.0.215
Apr 28 20:56:02 ubuntu-xenial-rax-ord-8650506 neutron-keepalived-state-change: 2017-04-28 20:56:02.430 20945 DEBUG neutron.agent.linux.utils [-] Exit code: 0 execute /opt/stack/new/neutron/neutron/agent/linux/utils.py:153
Now whenever you have a doubt whether gratuitous ARP packets were sent by a Neutron HA router, just inspect syslog. You should hopefully find there relevant messages, either from
keepalived itself or from
neutron-keepalived-state-change calling to
You can find a continuation of this post, of sort, here.


Back to the index.
Go to part 2 >>
Return loss bridge. (part 1)
A "return loss bridge" is a device to measure the difference in dB
between the forward power to a load, and the power reflected by the load.
The measured "return loss" tells us how well the load is matched to a reference impedance (most times the reference is 50 Ω).
A High return loss, let's say 20 dB or more, means the match is quite good, and very little power is reflected.
By some people the return loss is presented as a negative number, others (including me) present the return loss as a positive number.
A typical application of the return loss bridge is the measurement of resonance frequency and bandwidth of antenna's.
The return loss is related to the VSWR and Reflection coefficient.
I will not discuss VSWR and reflection coefficient here, but just give some converted values in the following table
|infinite||0||1 : 1||0|
|30||0.100||1.065 : 1||0.032|
|25||0.316||1.119 : 1||0.056|
|20||1.00||1.222 : 1||0.100|
|18||1.58||1.288 : 1||0.126|
|16||2.51||1.377 : 1||0.158|
|14||3.98||1.499 : 1||0.200|
|12||6.31||1.671 : 1||0.251|
|10||10.0||1.925 : 1||0.316|
|8||15.8||2.323 : 1||0.398|
|6||25.1||3.010 : 1||0.501|
|5||31.6||3.570 : 1||0.562|
|4||39.8||4.419 : 1||0.631|
|3||50.1||5.848 : 1||0.708|
|2||63.1||8.724 : 1||0.794|
|1||79.4||17.391 : 1||0.891|
|0||100||infinite : 1||1|
Circuit diagram of the return loss bridge.
Figure 1: circuit diagram of a return loss bridge.
Other circuits are possible, but this is the circuit I use.
The bridge has 4 ports (connectors).
- IN, input to be connected to a signal generator (for instance a tracking generator of a spectrum analyser).
- REF, reference port, connect a high precision 50 Ω RF terminator resistor to this port.
- TEST, connect here the device from which you want to measure the return loss.
- OUT, output to spectrum analyser, or other type of RF detector.
Note, the REF and TEST port are interchangeable in function.
Resistor R1 and REF form a voltage divider, giving a voltage at point A.
Resistor R2 and TEST form another voltage divider, giving a voltage at point B.
The output line, which is a piece of coax cable, measures the voltage between A and B, and delivers this to the output port.
The output line has ferrite cores around, this turns the output line into a wideband "current balun", converting the balanced signal between point A and B into a unbalanced signal at the output port.
The output line passes "differential mode currents" without attenuation, these are currents which are equal in amplitude in centre and screen of the coax, but with opposite direction.
"Differential mode currents" produce no magnetic field outside the coax, the magnetic field of the current in centre conductor and screen cancel out each other, and therefore differential mode current is not influenced by the ferrite cores around the coax cable.
"Common mode currents" in the coax however will meet a high impedance through the addition of the ferrite cores, and therefore the amplitude of common mode currents will stay (very) low.
"Common mode current" is any current in the screen of the coax, which not has it's equal and opposite return current, in the centre conductor.
Through this all, the unbalanced 50 Ω load connected to the output, appears as a 50 Ω "floating" load between point A and B.
Although the common mode impedance of the output line is very high, let's say several thousand Ohms, it is not infinite, and this impedance is in parallel with (in this case) the TEST port.
A second piece of coax (the "balance line") with the same number of ferrite cores is placed parallel to the REF port, to keep maximum balance between the REF and TEST port.
The use of the balance line is especially important at lower frequencies where the impedance of the ferrite cores reduces.
For the balance line, only the shielding of the coax is used, the centre conductor is not connected.
You might as well use a solid wire, but then use the same diameter as the output (coax) line, to keep the capacitance also in balance.
The use of the return loss bridge
A return loss bridge is often used together with a spectrum analyser with tracking generator.
The tracking generator is then connected to the IN port, and the spectrum analyser input connected to the OUT port.
At the begin of a measurement, first make a measurement with maximum unbalance in the bridge, this is with the TEST port open (not connected), or with the TEST port shorted.
The signal level you measure is the 0 dB reference trace for the return loss, this trace should be flat on all frequencies.
Then connect the "device under test" to the TEST port, and measure again the signal level.
The difference in dB with the 0 dB reference trace is then the "return loss".
Go to part 2 >>
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Bin Tops are GPS enabled devices which can be attached to any bin including large waste containers that are capable of detecting waste fill level and send real time data to Cloud Collection Connect. Fill level sensors helps in reducing number of collections and collection cost.
How Bin Top works?
- Bin Top can be attached to any type of bin irrespective of size. The ultrasonic fill level sensors within the device detect the waste level.
- The data send will be monitored by cloud based system.
- Once the waste reaches peak level, data send by the sensor will notify the collection agents. This will prevent the waste spillage from the bins and getting accumulated around the bin.
- Bin Tops are equipped with anti theft and GPS tracking facilities, which helps to track the devices.
- No need of replacing your current bin, instead install Bin Tops and prevent waste overflow and litter accumulation.


Wednesday, May 31, from 10.00 to 10.20 alarm sirens will be activated throughout the country for a period of three minutes. Residents have no reason to worry because it is a routine siren check.
The State Fire and Rescue Service (SFRS) will perform an alarm siren check throughout Latvia, starting them for three minutes, as well as check the performance of contracts concluded between SFRSand electronic media (radio, TV).
In cases where alerts to citizens on natural or technogenic disasters and their potential hazards are needed to be distributed as quickly as possible, alarm sirens may be activated. Each year the SFRS shall carry out an alarm siren test required to verify the technical readiness of the early warning system, the technical condition of alarm sirens, possible damage or disturbance in the operation of sirens, as well as the performance of the contracts concluded between SFRS and electronic media (radio, TV), which will inform the public in the event of a threat.
If you do not hear them during an alarm siren check, do not worry, as in emergency cases where sirens are not heard or deployed, other types of communication may be used, such as passing information to the public through the speakers of the operational services and their liaison partners. SFRS calls on the hotel administration to inform its foreign guests about the upcoming alarm siren test so as not to cause unnecessary worry.
Will be sent by mobile operators to Ukrainian civilians on the territory of Latvia to SMS with information that an alert siren test will take place on 31 May.
There are 164 alarm sirens installed in Latvia, which are so arranged that the sound signal transmitted is heard within a radius of approximately 1.5 kilometres (siren hearing is affected by the height of the siren deployment, the special features of the territorial building, noise caused by the city's daily transport and production facilities, meteorological conditions). VUGD recalls that if residents have not previously been alerted to the siren check, citizens should switch on televisions and radios (Latvian social media – “Latvian TV” channels LTV1 and LTV7 or “Latvian radio” broadcasting channels) or other devices such as mobile broadcasts. or applications, information on the reason for the activation of alarm sirens and the necessary behaviour of the population.
Other information: SFRS Prevention and Public Information Division, E-mail: firstname.lastname@example.org


Based on a Cisco environment with the new technology Cisco Jabber Guest, NTW allowed usage of video communication in real-time at the highest level for the first time in 2014. Using this innovative solution, customers are able to transmit voice and video live in HD quality and communicate securely. This is the first usage of video interpreting as a flexible and cost-efficient service. Especially in health care and for asylum seekers this solution has proven to be invaluable.
Connected to your operator in a matter of seconds
The video solution promises the transfer to a qualified interpreter in 7 seconds on average. All applying privacy protection laws are observed. Delivering highest quality is top priority, this also extends to the interpreters: each one has a college degree and additional training in health care, judiciary, management and welfare. At the moment, more than 30 languages are provided – with more to come.
Innovative technology: Cisco Jabber Guest and NTWcall Routing
NTWcall Routing provides a clear administration and real-time display of available languages and interpreters. The customer – e.g. a doctor – selects the desired language (and interpreter, if wanted) and immediately the conversation can be interpreted directly on the PC, iPad, Cisco DX80, etc.. All data transfer between interpreter and customer is securely encrypted and never routed via a private network. At the same time, NTW allows automated invoicing of video interpreter services for the operating company.
Additional applications of video interpreters
The flexible and cost-efficient video interpreter solution is not only in high demand for health care and asylum seekers. Already, it finds more and more application in other fields as well: communal institutions and agencies, police, emergency medical services and fire brigades.
More information about video interpreting (in German): SAVD Videodolmetschen GmbH


The quality of spectral channels may be set to bad by choosing the appropriate option. If set bad, channels will not be considered when grouping channels with one of the statistical methods. However, if a range or regular binning is specified which includes these bins then this will take precedence and the quality of these channels will be set to good.
The options are:
in which case the channels to exclude from spectral fitting will be read from a calibration file.
in which case the channels from 0 to 10 and 790 to 799 will be set bad.
in which case the channels with energy between 0 and 0.2 keV or 10 and 15 keV will be set to bad.
in which case no channels will be excluded before the spectrum is grouped.


Webmail (or web-based email) is an email service that can be accessed using a standard web browser. It contrasts with email service accessible through a specialised email client software. As with any web application, webmail's main advantage over the use of a desktop email client is the ability to send and receive email anywhere from a web browser.
Access your email, calendars, contacts, tasks, chats and notes anywhere with ZNetLive's BizMail webmail interface that combines aesthetics with the full functionality of a desktop client.
Premium Anti-virus/ Anti-spam Protection:
ZnetLive provides budding businesses with: Industry-best antivirus & anti-spam that ensures 97% spam protection upon setup and installation. It also ensures mail server security with a variety of intrusion detection methods.
Communicate with your co-workers in real time with ZNetLive's BizMail instant messaging features. It allows you to use your own XMPP-compatible instant messaging desktop client like Adium, Digsby or Live Messenger or mobile clients like IM+ and IMO to have instant access to anyone within your organization.
Preserve your email and chat history with full archiving. It also provides searchable message archiving at the domain and system level for inbound and outbound email and chat, and complies with Sarbanes-Oxley (SOX), the Health Industry Portability and Accountability Act (HIPAA), and other regulatory requirements.
Easily migrate single mailbox, or an entire domain, from mail services like Gmail, Yahoo!, Office 365 / Outlook.com, Hotmail / Windows Live, Microsoft Exchange or even mail servers like Merak, iMail and MailEnable.


Fused image products are used in a variety of medical, scientific, and industrial applications. Common classes of fused fiber products are:
Fiber Optic Faceplates: Fused fiber optic structures used as the input or output face on image or cathode ray tubes. Generally round or rectangular in cross-section, with planar, cylindrical or spherical polished surfaces, faceplates provide a hermetic seal and an effective barrier to the high voltages inside the tube.
Fiber Optic Windows: Fused fiber optic structures used as the input face for solid state imaging devices such as CCDs and photodiode arrays. Typically rectangular in cross-section with planar polished surfaces, the structures are machined to conform to the package configuration of the semiconductor device. Fiber optic windows generally have extremely demanding optical specifications because of the small pixel size of the device receiving the transmitted image.
Image Conduit: Drawn or fused fiber optic structures that transmit images over distances from a few inches to a few feet. Applications are extremely varied, ranging from transferring an image from a signature card to film, to visual alignment of plotters. With quantities ranging from thousands down to a single structure for a custom machine-vision application, image conduit varies greatly in its composition and cross-section in order to be optimized for a particular application.
Light Diffusers/ Filter Plates: Fused fiber optic structures with solid-core fibers. Diffuser plates are useful for angular light discrimination and for breaking or de-focusing light beams.
When utilizing fused fiber optic products, the optical designer should consider the following parameters:
Numerical Aperture (N.A.): The sine of the half-angle at which light (in air) enters a fiber, propagates along its length, and exits at the other end. The N.A. is a function of the refractive indices of the core and cladding glasses. Common formulations include .35, .56, .66, .8, and 1.0. Other numerical apertures are available on a custom basis.
Fiber Diameter: Determines the resolving power, or resolution (expressed in Lp/mm, or pixel density), of the image bundle. Typically 6 - 8µm, fiber diameters can range from more than 100µm to a practical downward limit of 3µm.
Extramural Aborption (EMA): A light-absorbing material (usually glass) optionally introduced into the fiber optic structure. EMA absorbs stray light that exits a fiber when a ray exceeds the critical angle determined by the numerical aperture.
CHI has a well-earned reputation for responding quickly and effectively to unique design requirements for fused image products. Our focus is to provide faceplates, windows, image conduit, and custom fused fiber optics to customers needing unusual geometries and the highest optical quality. Our fused fiber optics are characterized by very low optical distortion, a minimum of optical blemishes, and a general absence of boundary defects known as fixed pattern noise, or chicken wire . With a substantial inventory of optical glasses ready for use, CHI is able to deliver the specific solution to the most challenging optical design that are available (round, hexagonal, rectangular, square, and custom)and fused.


The range of your two-way radios is greatly dependant on the terrain and location you are using them. As a rough guide we have included above the safe estimates on ranges you might achieve when using your devices. If you require additional advice on the ranges you might achieve and how to achieve them please get in touch… Call us: 01778 426777 Email us: email@example.com
The revamped DP2000e series demonstrates Motorola’s pivotal role in driving the future of digital two way radios forward. The DP2400e radio has been designed for the everyday workers who requires effective communications. Building on the success of the DP2400 handset, the DP2400e provides better coverage and clear audio delivering cost-effective connectivity to all.
A non-display radio featuring 16 channel capacity, 3 programmable buttons and available on both UHF and VHF frequencies, the DP2400e is able to operate on both analogue and Motorola’s MOTOTRBO digital system. The DP2400e has been boosted to ensure strong signal coverage and through the latest energy technology the radio delivers up to 28 hours of battery life making this perfect for businesses to stay connected. With the optional IMPRES Over-the-air Battery Management tool, it enables you to maximize the battery lifetime to ensure you get the best out of radio.
With an IP67 rating for water and dust resistance, the DP2400e digital radio is suited to harsh environments including construction and manufacturing making this radio perfect for industrial businesses.
Having the cutting edge IMPRES audio system this provides a consistent sound quality for all environments ensuring all messages are being heard loud and clear regardless of any background noise. Featuring intelligent audio, the DP2400e, has the ability for the volume to automatically adjust to compensate for background noise which again ensures that messages are transmitted clear.
The DP2400e features Lone Worker as standard ensuring that staff are monitored at all times. Having the ability to make and receive private as well as group calls means that you are able to communicate with radio users without disturbing others as well as having the ability to non-verbally communicate using the pre-programmed text messages which are sent with the push of a button.
- 1 x Motorola DP2400e Radio
- 1 x battery (PMNN4491A - Lithium Ion Battery)
- 1 x Antenna
- 1 Single-unit charger & power supply (if selected above)
- 1 x Belt Clip
- 1 x In-box documentation
- 1 x Dust cover for side connector
IP Rating – IP64 environmental sealing
Dimensions – 127.7 x 56 x 36mm
Weight – 265 grams
Frequency – VHF (136 – 174 MHz) UHF (403 – 527 MHz)
Number of Channels – 16
Radio Type – Digital & Analog
Yes! This radio is a full-power unit which works on licensed spectrum. Here’s a few important points to remember:
- Licencing is really easy and cost effective, so don’t be put off
- You only licence the frequency (channel) your radios use, not the number of radios or handsets
- If you’re buying radios to use outside of the UK, you will need to get a licence from your country’s regulatory body
- Want us to guide you through it? Call us on 01778 426777 or email firstname.lastname@example.org
Buy a licence online:
You can choose from one of the following two options to buy a licence online. Once you place your order, we’ll apply for the licence for you, which is valid for 5 years. Ofcom will then contact you directly in 5 years’ time to arrange the renewal.
Remember: you don’t need a licence per radio, just a licence per fleet of radios. One licence will usually provide enough cover for your company or site (or you as an individual if you’re buying for private use)
Simple UK Licence - £75 for 5 years
This is ideal for most users. It authorises the use of radios anywhere within the UK, on a shared bank of back-to-back (simplex) frequencies. Up to 14 UHF or VHF channels become available on digital radios (7 on analogue)
Simple Site Licence - £75 for 5 years
This is suited to users who use their radios with a repeater. It authorises radio use within 1km of a given site or location, on a shared assignment basis. Up to 34 UHF back to back channels + 6 repeater frequencies become available on digital
I already have a licence:
If you already have radios, you should already have a licence. If you’d like your new radios to work with your existing fleet, you need to send us:
- A copy of your existing Ofcom licence
- For digital radios:
- Let us know which frequencies are in which channel
- Which colour code you use
- Which digital group ID you use
- For analogue radios:
- Let us know which frequencies are in which channel
- What CTCSS/TPL/DPL tone you use
Alternatively, you can send us a programming file from one of your existing radios, or even post us one of your existing handsets so that we can make sure we match it correctly.
Note that we accept no responsibility for radios which do not work due to incorrectly provided information. We’ll program your radios for free upon order, but if they don’t work and need re-programming there will be a £10 + VAT fee per unit.
If you need help, feel free to call our team of friendly experts and we’ll guide you through.
- Call us: 01778 426777
- Email us: email@example.com
Payment & Security
Your payment information is processed securely. We do not store credit card details nor have access to your credit card information.


Immediately upon my wife and I upgrading our pair of iPhone 4s’s to 6s’s, I called to complain that I was not receiving messages from my wife while on calls anymore. I was given the run-around both from Sprint and from Apple, stating that, as I already knew, you can’t do data and phone calls at the same time on Sprint’s CDMA network. BUT, you can get SMS’s while on a call and after some testing, I figured out that there was nothing wrong with our new phones receiving SMS messages. The problem was on the other end – with sending them.
With our 4s’s, both with iMessages enabled (you can confirm this from our message history), if the message wouldn’t go through (because I was on a call), her phone would convert the message to a (green) SMS and try sending it again. I’d receive it while on a call and hear the message chime over my phone call.
This does not work on an iPhone 6s, though I don’t know if it was specific to the hardware itself or if it could have had to do with a newer iOS that came with the 6s’s that couldn’t be installed on a 4s. On a 6s, Apple appears to have dumbed down message sending. It will only attempt to send a message as an SMS is the sender has no wifi or data connection. It no longer pays any mind to the receiver. If they’re on a call, the message just gets buffered somewhere and once the other person gets off their call and again connects to a data signal, whether it’s a phone carrier’s data connection or a wifi signal, they get all their buffered messages at once.
I commute to and from work on my bike. It’s an hour ride and I like to pass the time by talking on the phone. My wife invariably messages me while I’m on my call, either about dinner or wanting to know when I’m getting home or whatever. I pretty much expect to hear from her every time. I would usually hang up whatever call I was on (usually some family member) and ask Siri to read my messages to me while I rode.
I thought that when we bought the 6s’s, they would be better and more capable. I did not expect their capabilities to regress, so I’ve called to complain about this numerous times. I’ve tested with numerous iPhones and Android phones. My latest feedback to Apple is below:
Convert iMessages sent to me to SMSs during calls on sprint
I’m submitting this issue again. When my wife and I bought our iPhone 6s’s about a year ago (staying with sprint), the first thing I noticed that they could not do that our 4s’s could was automatically convert an iMessage to an SMS when the other one of us was on the phone. E.g. I ride my bike for an hour commute and I talk on the phone the whole time. With our 4s’s (on Sprint), when my wife sent me a message (with iMessage enabled), which she always does at some point during my ride, the message would get converted to an SMS and I would receive it while on the call. But with our 6s’s set up the same way, I do not get her messages until I hang up the phone, i.e. her phone does not convert the iMessages to SMS’s. We’ve been with sprint for forever and our 4s’s could do this.
In fact, some Apple support people I’ve spoken to had the same complaint about not receiving messages. Apple has been unresponsive on this issue and it’s ridiculous to have to turn off iMessages to be able to get around this issue. So I am blogging this out there to raise awareness that it doesn’t have to be this way!
Complain to Apple about this issue and have them fix their newer phones to restore the capability of converting iMessages to SMS’s the way the 4s used to do. If enough of us complain, maybe they’ll deign to get around to it.


Payment & Shipping Terms:
|DRAIN Voltage:||0.3 V To 700 V||CONTROL Voltage:||-0.3 V To 9 V|
|CONTROL Current:||100 MA||LINE SENSE Pin Voltage:||. -0.3 V To 9 V|
|CURRENT LIMIT Pin Voltage:||-0.3 V To 4.5 V|
TOP242-250 TOPSwitch-GX Family
Extended Power, Design Flexible,
EcoSmart, Integrated Off-line Switcher
TOPSwitch-GX uses the same proven topology as TOPSwitch, cost effectively integrating the high voltage power MOSFET, PWM control, fault protection and other control circuitry onto a single CMOS chip. Many new functions are integrated to reduce system cost and improve design flexibility, performance and energy efficiency. Depending on package type, either 1 or 3 additional pins over the TOPSwitch standard DRAIN, SOURCE and CONTROL terminals allow the following functions: line sensing (OV/UV, line feed-forward/DCMAX reduction), accurate externally set current limit, remote ON/OFF, synchronization to an external lower frequency, and frequency selection (132 kHz/66 kHz). All package types provide the following transparent features: Soft-start, 132 kHz switching frequency (automatically reduced at light load), frequency jittering for lower EMI, wider DCMAX, hysteretic thermal shutdown, and larger creepage packages. In addition, all critical parameters (i.e. current limit, frequency, PWM gain) have tighter temperature and absolute tolerances to simplify design and optimize system cost.
Lower System Cost, High Design Flexibility
• Extended power range for higher power applications
• No heatsink required up to 34 W using P package
• Features eliminate or reduce cost of external components
• Fully integrated soft-start for minimum stress/overshoot
• Externally programmable accurate current limit
• Wider duty cycle for more power, smaller input capacitor
• Separate line sense and current limit pins on Y/R/F packages
• Line under-voltage (UV) detection: no turn off glitches
• Line overvoltage (OV) shutdown extends line surge limit
• Line feed-forward with maximum duty cycle (DCMAX) reduction
rejects line ripple and limits DCMAX at high line
• Frequency jittering reduces EMI and EMI filtering costs
• Regulates to zero load without dummy loading
• 132 kHz frequency reduces transformer/power supply size
• Half frequency option in Y/R/F packages for video applications
• Hysteretic thermal shutdown for automatic fault recovery
• Large thermal hysteresis prevents PC board overheating
EcoSmart - Energy Efficient
• Extremely low consumption in remote off mode (80 mW at 110 VAC, 160 mW at 230 VAC)
• Frequency lowered with load for high standby efficiency
• Allows shutdown/wake-up via LAN/input port
CONTROL (C) Pin:
Error amplifier and feedback current input pin for duty cycle control. Internal shunt regulator connection to provide internal bias current during normal operation. It is also used as the connection point for the supply bypass and auto-restart/ compensation capacitor.
LINE-SENSE (L) Pin: (Y, R or F package only) Input pin for OV, UV, line feed forward with DCMAX reduction, remote ON/OFF and synchronization. A connection to SOURCE pin disables all functions on this pin.
EXTERNAL CURRENT LIMIT (X) Pin: (Y, R or F package only)
Input pin for external current limit adjustment, remote ON/OFF, and synchronization. A connection to SOURCE pin disables all functions on this pin.
MULTI-FUNCTION (M) Pin: (P or G package only) This pin combines the functions of the LINE-SENSE (L) and EXTERNAL CURRENT LIMIT (X) pins of the Y package into one pin. Input pin for OV, UV, line feed forward with DCMAX reduction, external current limit adjustment, remote ON/OFF and synchronization. A connection to SOURCE pin disables all functions on this pin and makes TOPSwitch-GX operate in simple three terminal mode (like TOPSwitch-II).


Samsung Galaxy Note. First Look
Today, large companies, especially corporate giants like Samsung, do not surprise users with extraordinary products...
|First look. Sony ST21i Tapioca Microsoft Windows Phone 7: Reasons for Failure First Look at Samsung Galaxy S3 as a 2012 Flagship|
IP-telephony – thinking aloud
1. What is it for?
The first time I came across IP-telephony was in 2002 when I was in China on business. No handset of mine could tap into their networks, while phone cards and international calls seemed to be a quite steep alternative, that’s why my Thai colleague chatting via a headset and staring at his notebook provoked some interest in me. And everything turned out to be very straightforward – both his PC and notebook had Skype installed with two separate user names, so at a certain hour his wife would start up this app, and so would he, while somewhere in China’s north-east provinces. Thankfully our hosts provided us with a broadband internet connection back then.
That was the moment when I really regretted that I hadn’t registered a couple of user names beforehand, in fact, calling via Skype was easy even without a laptop at hand, since I could easily install Skype on one of the work stations, log in and chat as much as I pleased. However, giving my wife the guidelines via email proved to be quite a challenge; she was by no means a computer-geek. Well, she could launch some applications, but when it came to installing something new – alas!
That’s why as soon as I got home, I registered a Skype account outright and plunged into the paradise of wireless communication with my bills rapidly losing in weight – to the point when the savings easily made a couple of great meals in a restaurant. In fact this was what I did to reward myself for mastering such an efficient technology.
Regrettably, the country I resided in couldn’t sport any advanced online payment systems, so I had to enjoy Skype-to-Skype calls only for several years more, since depositing to my Skype-account so as to enable calls to mobile phones was quite a tricky affair. I can’t say it has really changed for the better over the years, though, but at least it is possible to get some prepaid cards and pay via an online system nowadays.
Basically, the only requirement you have to meet to get top-notch quality of voice calls over IP is a broadband connection. And it is not such a challenge to get one these days. So after I sorted out the issue with the first deposit, I made my first international call to Israel – after a 40-minute chatter I was charged less than a dollar. That was the moment when I had an epiphany: Skype was bound to stay on my desktop.
2. Any alternatives to Skype?
SIP (Session Initiation Protocol) – is an application-layer control protocol, developed by IETF MMUSIC Working Group for creating, modifying, and terminating sessions, including multimedia elements, such as voice or video, instant messaging, online-games and virtual reality.
At first Skype seemed to be the pink of perfection – clear voice calls, with a couple of tricks you could initiate a videocall (with a communicator having Cool Camera app installed acting as a web-camera). On top of that the rates were so much better than those offered by local carriers for international calls. And then I got my mitts on my first softphone for calls over SIP. While Skype could beat local carriers when it came to international calls, SIP-powered calls with the local carrier SIPNET left Skype behind hands down.
Handling these services via PC is done with the help of softphone-applications, whose major trump is the ease of use. Specifically, all the settings you have to deal with are user details, while the user interface strongly resembles a dialing pad. The extras include a phonebook that can group up contacts, video call feature and call log.
In fact, once you install this application, you can dial a sequence of digits on the pad and get connected – it is that simple. The best thing about the service is that it has been made to be intuitive and very straightforward. You don’t need to know how a switchboard works to make calls via land lines, right? Nor do you need to be a sophisticated user to make calls over Internet from your PC.
Another known SIP-carrier is Gizmo Project. Gizmo is a freeware software kit from SIPphone, running on the SIP protocol.
The user can make free calls to other desktops having this software onboard or handsets at reasonably low rates. Further more, Gizmo supports incoming calls from landline or mobile phones – 5 bucks a month and it is all yours. You also get free voice mail, conference calling and call recording abilities right after installing it on your PC.
Gizmo is compatible with other VoIP-systems running on SIP, furthermore, the company has proclaimed that it is ready to officially tie its product with any VoIP-network – having a personal SIP-number allows for calls to any handset or SIP-device of any VoIP-carrier.
Google Talk – a free voice-chat service and also a free messenger delivered by Google. On top of that you can utilize a third-party application as the client - Psi, Miranda IM etc. The only third-party client with support for voice calls is fring.
ICQ, even though with a number of significant reservations, can be considered a VoIP-client as well – voice communications are enabled only within the native network.
3. A softphone or a hardware solution?
All the above services have own software tools that allow for communications via a PC. Nevertheless, recently has market has been seeing a lot of hardware solutions resembling conventional handsets.
Employing one of these hardware solutions becomes justified if only you’re an active VoIP user – a USB-phone turns out to be much handier for serious conversations than a headset coupled with a desktop PC, especially in light of the fact that many models enable you to run a handful of VoIP-services at a time. Some offerings can easily do without a PC in sight. Some time ago we got to know about a device reminiscent of an ordinary portable flash drive, which carries a hardware SIP-client, meaning that you will need to enter your personal data once and then put in your pocket – any PC connected to the Internet will do for engaging the client, and that’s it. We are hoping to release a review on this gadget in the near term.
4. PC is all good, but what are the options for mobile device users?
The market of software solutions for mobile devices has at least a handful of utilities for making VoIP calls right from the user’s handset.
The most functionally rich app to date is fring, which already was under the scope of Mobile-Revilew once. With this application on your phone you will be able to communicate with the users of Skype, Google Talk, SIP and even ICQ.
The Call Back feature establishes a connection with the Skype server and then this server sets up a conference call between you and the person you meant to call. On the bright side is the fact that call quality has nothing to do with data speeds provided by your carrier. This method minimizes the amount of processing power required on the phone and means there are no data latency issues. However, there are two sides to the coin – any call will be charged like a SkypeOut call. Upon calling a contact from Skype you will pay for an incoming (redirected) call to your handset, and should your call aim external networks, you will be charged for voice traffic as well.
Other SIP-services are handled with the help of pretty much similar utilities - Gizmo Project, Truphone, Telphin and others have own clients for mobile devices on offer.
5. Will VoIP oust ordinary telephony?
Even if it does, it is still a long way to go. For the time being you won’t end up frustrated with voice calls over the Internet only if you have a broadband connection – as long as these networks keep spreading across the globe, the number of calls made online will remain on an upswing. At the same time, there is no such vital need in using Internet-telephony for calls within city limits or one cellular network. But as far as international calls are concerned, VoIP may save you some coins, however, again, it is all about your connection speed.
There is a clear trend of prevalence of data over voice in the carriers’ traffic, and those will reap more in this rapidly growing market, who will be able to roll out new services faster than the competition. I won’t be surprised to find VoIP-telephony among the latest benefits offered by some local carrier, in fact many have already taken certain steps towards this.
Published 26 September 2007
Have something to add?! Write us... email@example.com
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Whether you have Wi-Fi deceased zones in your house or office, the best way to solve these kinds of problems is by using a Wi fi signal booster. Often known as a range explayarse or WiFi repeater, these devices help to improve and prolong your existing wireless network to more spaces. They do this by getting an already weak Wi fi signal and amplify this before rebroadcasting it over a larger coverage space.
This helps to boost your cordless connectivity, that can then give you the speed and access you need. This is especially beneficial if you enjoy playing on line video games that need decent publish and download speeds to run smoothly. It can also help reduce ping, which is enough time it takes meant for data to go from the device online and again.
Many of these equipment have a plug-in design and style and hook up directly to your router with no need pertaining to an ethernet cable connection. Others will be larger and sit on a desk or shelf, looking more like a traditional router. The bigger products are often allowed to support more wireless connectors and offer even more internal components for a stronger signal.
The majority of Wi-Fi transmission boosters and extenders include a quick and straightforward make process. They often use a WPS button which makes it fast to pair with the router. A few devices have an ethernet interface, which will enable you to wire your ransomware protection free computer’s desktop computers or perhaps printers to the booster. This might be beneficial if you wish to keep your equipment closer to your router designed for better performance.


- Multi-core – 1.8 GHz processor or better
- 4GB RAM
- Windows 7, 8, 8.1, or 10
- 80 GB hard drive or more (160 GB highly recommended)
- Monitor with 1024 X 768 resolution or higher
- Windows compatible printer (laser printer recommended)
- Gigabit Ethernet port and router (for networking computers)**
- 1 serial port or a USB to serial adapter (only required for certain software options)
- Wired, high speed internet connection (only required for certain software/service options)
*There may be additional requirements depending on which software options have been purchased.
**We do not recommend using mixed networks (using computers running different versions of Windows on the same network).


Microsoft is making a big push to make its employees feel better about their jobs, but some workers are having a hard time letting go.
The tech giant recently released an app called M-Train, which uses the same audio and video that is found in its most popular video games.
It uses a series of headphones and a small microphone to record what employees say in a chat with the company’s human resources manager.
Microsoft is hoping the app will help them “get back to work faster, more productively and more effectively,” the company said in a blog post.
“It’s not just about listening to your coworkers,” the blog post said.
Its a powerful tool, and we’re hoping it can help you.
M-Train also works with the same set of headphones that Apple uses in its iMessage app.
Apple’s iMessage lets you record video calls with your friends and family, and the company uses the audio of your headphones to record voice messages.
However, Apple’s iMessages are designed to be used with the iPhone’s Siri feature, which allows users to speak into the microphone.
While Microsoft is trying to make Skype easier to use, it is still possible for users to record audio while in the app.


Garland Technology is a company that was founded in 2011 and has its headquarters in New York. It is dedicated to enhancing the value of customer networks by providing reliable, affordable, user-friendly, and scalable network test and monitoring solutions. These solutions include network TAPs, packet brokers, and cloud visibility offerings that help organizations optimize network performance and security. The company serves a diverse range of customers in industries such as finance, healthcare, government, and technology, and its products and services provide valuable insight into network traffic and security, helping customers identify and resolve network issues and prevent potential security threats.
Garland Technology is a leading provider of network TAP (Test Access Point) and packet broker solutions, specializing in helping businesses identify their unique environment requirements and deliver packet visibility to improve their security and monitoring solutions. With a wide range of products and services designed to meet the diverse needs of modern networks, Garland Technology provides businesses with the tools they need to capture, filter, and analyze network traffic for security and performance purposes.


|Based in Kolkata, Parash Enterprises is a manufacturer, supplier and exporter of various products used for electrical transmission like Substation Connector, Poleline Hardware & transmission line material, Cable tray & Accessories, Industrial Earthing Materials.|
Cable Tray and Accessories
The cable trays offered can efficiently hold up cables and are light, durable and strong. They are made of superior quality high purity metal and have fine finishes. They can be used with cable ladders for variety of applications. These are fabricated using the finest quality of raw materials and are resistant to corrosion. These cable trays are manufactured from steel and aluminum and are in compliance with international quality standards.
The cable trays offered are either:
- Perforated cable tray
- Ladder cable tray
- Flooring raceway and trunking cable tray
Alongwith cable trays, various kinds of cable tray accessories are also provided for effective fitting, installation and support. The accessories include premium quality Clamps, Connecting pieces, and Slotted angles for creating an effective network of cable trays and providing a suitable installation. The clamps and angles we offer are of various grades and thickness.


Schleuniger’s most versatile stripping machine, the UniStrip 2600 can process many unique applications and wire & cable types, including discrete wire from 0.03 mm² up to 16 mm² (6 – 32 AWG), power cords (even multiple-conductors with different lengths, all in one cycle), multi-conductor cables, flat cables and others. The UniStrip 2600 is fully electric and features strong, quiet drives and fast cycle times.
- Virtually unlimited range of applications
- Fully programmable – up to 1,000 memory locations
- Wire list processing
- Many unique processing functions for special applications
- SmartStrip™ technology option


Procurement procedures of the highest value
- Construction of the ERTMS/GSM for Railways communication system for majority of the Polish railways, which is a system enabling digital communication between the driver’s cab systems on trains and the traffic management system, of a value of almost PLN 3 bn.
- Implementation of a rapid passenger information system at 760 railway stations, with a procurement contract value exceeding
PLN 420 m.
- Supervision and project engineering for implementation of an ERTMS/GSM for Railways communication system, with a procurement contract value exceeding PLN 80 m.
- Provision of IP VPN (multiprotocol label switching) data transmission services with internet access for the State Forests, with a procurement contract value exceeding PLN 40 m.


Vol. 12, No. 1
News of the Field:
|New Edition of Bibliography|
History of Telecommunications Technology: An Annotated Bibliography by Christopher H. Sterling and George Shiers is due from Scarecrow Press ( Lanham, MD) in early 2000. A substantially updated and revised and reorganized edition of Shiers’s Bibliography of the History of Electronics (Scarecrow, 1972), it focuses on telecommunications and adds many new subject areas. About 1,500 entries cover general reference works, serial publications, general surveys, institutional and company history, biographies of inventors and engineers, telegraphy, telephony, electromagnetic waves, radio, electroacoustics and recording, electron tubes and solid state devices, television, newer media technologies, transmission (mobile, satellite, and fiber optics, and the Internet), and Internet resources.
Shiers (1908-1983) was a California-based technical freelance author with several books and a host of telecommunications technology history articles to his credit. Sterling is a member of the George Washington University faculty, editor of Communication Booknotes Quarterly and more than a dozen books including Stay Tuned: A Concise History of American Broadcasting.
For further information contact Shirley Lambert, editor, Scarecrow Press, 4720 Boston Way, Lanham, MD 20706, 301-459-3366; fax 301-459-2118; email@example.com.


1 × $1,500.00
The Company is incorporated in September, 2017 with the main objective of promoting Internet services and Information Technology that has been in business since 2017 and serving more than 500 satisfied customers.
We offer a range of Internet services for Individuals, Corporate and Educational Institutions.
We Are India’s First ISO Accredited Broadband Service Provider Using State Of The Art Technology And Tools To Provide Best Broadband Plans For Homes, Small To Medium Business Entities, And Big Enterprises. View Plans..
With Verizon as your wireless internet service provider and the Fios Quantum Gateway as your WiFi router, you’ll enjoy lightning fast speeds for your connected devices.View Plans..
An advanced wireless modem – modem and router in one – providing higher data speeds to your devices ensuring your Internet experience is the best it can be. View Plans..
A Suite Of Built-In Security, Privacy And Parental Control Tools That Protect And Provide Peace Of Mind.
Network Security Providers Can Also Help Monitor Device Inventories And Wireless Access Points, And Provide Up-To-Date Visibility Into The Overall Security Health Of Individual Devices And The Network As A Whole.
Our new aitcpl High-Speed Internet Gateway device is included with your plan and features the latest Wi-Fi 6 technology.
While Wi-Fi and wireless internet are often referred to interchangeably, there is a difference. Both enable wireless connectivity to the internet via radio waves. But wireless LANs refer to any local area network that a mobile user can connect to through a wireless connection, while Wi-Fi is a specific type of LAN that uses specifications in the 802.11 protocol family.
As rapid advances in wireless technology continue to revolutionize the way people connect and communicate, Verizon remains the industry leader in building next-generation networks. In October 2018, we introduced 5G Home –the first 5G-powered home internet—in certain areas of Houston, Sacramento, Los Angeles and Indianapolis, with plans to expand in other areas in 2019 and beyond. 5G represents a massive upscale of network technology. It will provide data transfer rates many times faster than a blink of an eye, high bandwidth and greater opportunities for connectivity and reliability. As the fifth generation of wireless technology, it is expected to become a game-changer for cloud gaming, augmented and virtual reality applications, robotics, and other high-bandwidth activities.
No confusing charts with multiple speed options that do who-knows-what. Customers will get the max speed the network is able to offer at their home location. We have one unlimited data service tier. Nice and simple!


Supported SIP Phones
Our Hosted PBX service platform supports many of the industries most popular SIP endpoints. With all technologies, features and functionality can vary from manufacturer. We have provisioned, tested, and utilized these phones in a day-to-day working environment to ensure a reliable user experience. We are providing our assessment solely as a reference to assist you in determining the exact phone for your business environment.
The IP 150 SIP phone is an Android based phone with HD call quality, has a 7” color touchscreen LCD, a 6 line call appearance, 3 way call conferencing, call transfer, backlit keyboard and comes with the ability to set different ringtones for different callers. Adapter required and not included.
IP Video Phone VP530
The Yealink VP530 is a further innovation of our advanced, executive-level IP Video Phone. With integrated audio, video and applications, the VP530 is a very powerful business video phone. Its large display and easy use make it an ideal all-in-one tool for today's busy business leaders, regardless of were they happen to be.
GXP2200 Enterprise IP Telephone
GXP2200 represents the future of enterprise business telephones in modern Internet age. Featuring AndroidTM Operating System 2.3 and its vast number of 3rd party applications, a 480X272 capacitive touch screen TFT LCD, dual Gigabit network ports, integrated PoE and Bluetooth.


You definitely want to go with the best long-range wireless router if you have large homes and you frequently use your router to connect several different devices that are far off. However, how can you select the Best Long Range Wireless Router 1000 Feet? If you plan on buying a wireless router then you might be wondering as to what you should look out for when selecting one. In other words, how can you tell which one is the Best Long Range Wireless Router?
It might sound quite complicated but in actuality, it is not as tricky as you might think. The most important factors to consider when buying a long-range wireless router is what type of internet connection you will have, where you will be using it, and the kind of device that you will be connecting to it. These are the three most important factors to consider when it comes to choosing a long Wi-Fi router. However, before going into these important details, there are a few more factors that should never be overlooked.
The first factor that you need to consider is whether you will be able to connect to a Wi-Fi hotspot or not. If you are in an area where there are many hotels, restaurants, coffee shops, and other forms of wireless connectivity then it would be most reasonable to opt for a Wi-Fi hotspot. However, if you live in an area where there are not many such establishments and where there is no public Wi-Fi availability then the best-recommended wireless router is one that will allow you to connect to a Wi-Fi network on a temporary basis.
The second factor is whether you want to buy a wireless router that has a built-in DVI port. Some routers have built-in DVI ports but most of them do not; therefore, if your internet services do not include DVI porting then you should consider purchasing a router that does not have DVI ports. It is also advisable to avoid using DVI ports with wireless routers because they are very expensive and complicated and may very well not work in the future.
The third factor is to consider the antennas that will be connected to the long-range Wi-Fi router. There are mainly two types of antennas to consider. First is the Bluetooth antenna. This antenna enables the long-range Wi-Fi connection to be picked up even in an area where there is no cable or any form of signal coverage. The second type is a Wi-Fi hot spot antenna.
The other factor to consider is the speed of the Wi-Fi signal. The signal speed can be measured in Gbit/s orMbps and it ranges between fifty and one hundred Gbit/s. The faster the signal the better the speed and therefore the better the internet services.
A good long-range Wi-Fi router should be able to connect to the internet even in areas where the signal strength is poor. A modem is usually used in this case. You need to find one that has a modem that supports dual-core processor technology. In order for your laptop to connect to the router properly, you need to get a device that has a USB port. The USB port will enable the device to connect to the router wirelessly.
In order to connect your laptop to the router you need to download an app. Such an app enables you to connect your laptop to the Wi-Fi network without any physical connection. It is important to install such an app after buying the device so that it enables you to set up the device properly. It is also advisable to download such an app from trusted websites to ensure that you get high quality service.


Ocean Cables Collection
Ocean cable telegraph lines were laid from shore to shore beneath the sea. The first Atlantic cable was successfully laid in 1866 by Cyrus W. Field. Submarine telegraph lines had already for some years been in operation over short distances. Coney Island and Fire Island had been successfully connected. In Europe a cable had been laid from Dover to Calais, and many others over distances less than a hundred miles. In deeper waters, also, cables had been laid, one from Newfoundland to Cape Breton and another from Spezia to Corsica.
In 1857 Mr. Field made his first attempt to lay a cable under the Atlantic from Newfoundland to Valentia in Ireland. This attempt failed, as did several others. In 1858 a cable was laid which worked at first but became silent after a few weeks. In 1865 the Great Eastern took on board a vast cable weighing 20,000 tons, and laid 1,200 miles of it, when by a sudden lurch of the ship the cable was snapped. The next year's attempt was, however, successful. The cable, 2,000 miles long, was safely stretched across the ocean, and submarine communication was an accomplished fact. Its first message was the news that a treaty had been signed by Prussia and Austria.
By 1903 there were 16 cables carrying messages through the Atlantic Ocean, besides three that are no longer used. But the greatest triumph of cable-laying was the completion of the British Pacific cable, 7,800 nautical miles long, which now connects British Columbia with Australia. In 1903 an American cable was laid to the Philippines from San Francisco by way of Hawaii. Thus, by means of the overland telegraph and the submarine cable, it is now possible to transmit a message in a few hours to almost any country on the globe.
Submarine Cables are laid on the bottom of the sea. They require not only good insulation, but great tensile strength, else they will not support their own weights when lowered from the vessel to the bottom of the sea. This tensile strength is acquired by wrapping the guttapercha insulation with a sheathing of steel wire. There now are 16 cables of this type across the Atlantic Ocean, each carrying two copper conductors. Each of these conductors is capable of transmitting about 20 words a minute.
The New Student's Reference Work (1914) pg. 300


Asynchronous Customer maintain Channels
Asynchronous Customer Support Channels
In an effort to meet evolving customer demands, Deltapath Contact Center Solution recently added new omnichannel capabilities. The brand joined forces with Comm100 in order to create the new omnichannel contact center. The new feature was designed to improve communication and includes various communication channels including website live chat, email SMS, Twitter, Facebook, WhatsApp Business, WeChat, Line, Telegram, and Instagram. Thus allowing customers to connect with the social apps they feel the most comfortable using.
David Liu, CEO at Deltapath, said: “Historically, Deltapath has been focused, not just on voice, but also on the video contact center. However, more interactions are happening outside of video and voice. We want to keep up to date with the latest customer channel preferences, which often includes an asynchronous communication style. For example, many users today generally do not want to deal with companies via phone, so we focused on bringing omnichannel into our contact center solution.”


Web or Online fax has become very well known in the last four or five years. Innumerable people have unexpectedly found this better approach for faxing and have really embraced it. Throughout a similar time period, numerous organizations, both of all shapes and sizes, are exchanging over to this new faxing innovation.
However, what precisely is internet faxing and why has it become so well known so rapidly?
Basically, Internet fax is utilizing your email framework and the web to send and get every one of your faxes. In the first place, you need to join to a web-based fax specialist co-op which goes about as a delegate to deal with all your faxing. You are given your own neighborhood or Toll-Free fax number and your faxes are sent as email connections, normally in TIFF or PDF design.
You can send your faxes in more ways than one, you can logon to your fax administration account (interface) where your faxes are put away and send your faxes from that point. Some fax administrations have a work area application for faxing or you can utilize your own email program. Furthermore you can in any case utilize a customary fax machine to send as well as accept your faxes.
An ever increasing number of people are dishing the old fax machine for their PC and the Internet. Many faxes are currently just sent and gotten by PCs through the web – bringing this normal business task into the cutting edge age.
The following are five super motivations behind why web based faxing has become so well known:
Online fax is extremely advantageous to utilize in light of the fact that it is paperless and inkless. Since there are no more paper jams or muddled inks to waste time with; it is speedy and quick. Making your faxes can likewise be more catalyst since you can set them up on your PC and afterward rapidly send them without messing with the old conventional fax machine.
Your faxes are open anyplace, whenever. Since it is online, your faxes are accessible any place you have Internet access and nowadays that is just about all over. In addition, your old faxes can be put away on the web or on your PC, so you can get to them whenever, whether it is the previous fax or one from a month ago.
Web faxing is safer than the conventional approach to faxing. Your faxes can be sent scrambled over the web and no one but you can get to them. Dissimilar to the old fax machine, where anybody can peruse your faxes, web based faxing offers significantly more security.
4. Simple to Use
Sending a fax is essentially as simple as sending an email. You essentially connect your fax as a TIFF or PDF document. Seeing your faxes is pretty much as simple as perusing any PDF record on your PC. Furthermore, all your old faxes can be put away and prepared for your utilization whenever.
5. Financially savvy
Maybe, one of the significant Fax reasons internet faxing has become so famous, is a result of the low cost. Web faxing is a lot less expensive than the former approach to faxing – – you needn’t bother with all that paper, inks and toners which you need to continually keep in stock with an ordinary office machine. Besides, you needn’t bother with an additional telephone line since every one of your exchanges occur over the Internet. Online fax administrations are generally economical, month to month designs run for around $4 to $15 every month, contingent upon your faxing necessities. On the off chance that your faxing is exceptionally least, you can get a straightforward arrangement for around $20 every year.


SUNSHINE DT-21N TOUCH MULTIMETER
Sunshine DT-21N Digital Multimeter With Touch Control for Phone Screen Repair, SUNSHINE DT-21N Multimeter Fully Automatic High Precision Color Touch Screen AC DC Voltage and Current Resistance Measurement.
- HIGH PRECISION CORE – The built-in intelligent high-speed chip enables more precise measurements while also preventing errors, burning, and overloading.
- LED DISPLAY – The high-definition LED display is touch-sensitive and easy to use.
- TEMPERATURE – When the device is turned on, the ambient temperature is displayed on the LED display immediately and updates in real-time.
- FAST MEASUREMENTS – Because the multimeter has a maximum range of 60M?, measurements are substantially faster.
- SIMULTANEOUS – The analog bar display clearly shows both the AC voltage and the frequency at the same time.
- 1 x Sunshine DT-21N Digital Multimeter With Touch Control for Phone Repair


Managing Projects → About Projects → Project Settings → Communications Page Settings → Creating Communication Rules
External communication provides a way for non-SBM users to submit items via e-mail and to communicate with SBM users on items that they have submitted.
You can create communication rules that are executed automatically in response to an external communication e-mail reply. For example, in a help desk scenario, you can create a rule that transitions the item back to the With Technician state when a reply from a non-SBM user is received.
To create a new external communication rule:
Select the Show e-mail fields check box to map e-mail fields to SBM fields. For example, you can map the Body field in the e-mail reply to your Description field in SBM. As you map fields, you can use a combination of values by selecting the check box to use e-mail fields or clearing the check box to use SBM field values.
Copyright © 2007–2018 Serena Software, Inc., a Micro Focus company. All rights reserved.


Yota (4G internet) is the first Russian high-speed wireless network based on Mobile WiMAX.
WiMAX delivers up to 10 Mbps access at any time within the coverage area. The powerful
connection is maintained even when moving at 120 km/h! WiMAX can truly claim to deliver always and everywhere.
Yota extends across Moscow, St. Petersburg and Ufa, regions with populations of over 20 million people.
The network operates under the standard IEEE 802.16e-2005 with very high frequency 2.5-2.7 GHz.
Yota has licensed the following Crystal2TM technology components for
YotaTV, YotaMusic and
More information about Yota can be found on company website:
Spb Software is the global leader in the design of Windows Mobile applications, with
R&D and design centers in Russia and Thailand, and presence in Hong Kong, Taiwan, and USA.
Spb combines a unique line of popular consumer products and cooperation with the world's leading
OEMs and carriers, such as ASUSTeK, BenQ Siemens, E-TEN, Fly, Fujitsu Siemens Computers, Gigabyte,
HTC, O2, Optimus, Palm, Pharos, SingTel, Samsung, Sony Ericsson, Swisscom Mobile, Toshiba, T-Mobile,
Spb Software has licensed Crystal Reality Crystal2TM technology components, including:
More information about Spb Software products and services can be found on company website:
Elecard is a leading provider of software and hardware solutions implemented on MPEG-2 and AVC/H.264 video compression technology.
Based on more than 15-year research of multimedia and network technologies, Elecard now offers advanced and cost-effective IPTV solution SIGMA iTV. The IPTV product line comprises AVC/H.264 encoders, VoD and TimeShift servers, DVB-IP streamers and IP-DVB encapsulators, set-top-boxes.
Consumer and professional product lines feature software products for video editing, playback, conversion, and analysis on PC.
Elecard has chosen Crystal Reality expertize in ARM processor optimization to undertake the challenging task of producing
the one of the world fastest MPEG4 ASP decoders.
More information about Elecard at


Last week, I discussed cutting the cord cable television and switching over completely to the internet. In this article, I talk about doing the same for the old telephone.
The Current Context
Remember back when long distance rates were sky-high? Well, I barely do, but I do remember they were high. Really high. Rates were a few dollars for a phone call lasting only a few minutes, even within Canada.
The reason? Largely, because the CRTC permitted only a single company to serve each area in Canada. These high rates are what happens in a monopoly market.
Granted, there were legitimate reasons for the monopolies. The infrastructure cost of creating a telephone network was enormous. But this is all history. In 1992, we got deregulation. The CRTC took down the walls and started allowing competition in the long distance market. Sure enough, long distance rates took a steep plunge.
Unfortunately, phone bills remained high! The Big Seven incumbent phone companies simply raised their local calling rates to compensate. The CRTC hadn't deregulated local phone plans, so the major phone companies were able to continue raking in revenues after a period of "rate rebalancing" in favour of higher local rates.
Finally, the CRTC did deregulate the local market in the late 1990's. Unfortunately, the local rates have still remained high, as the infrastructure cost of setting up local services has remained enormous. This fact has been true until recently -- that is, until the advent of high-quality VOIP (voice-over-IP internet phones).
With the help of the internet, it's finally time to take down the last barriers keeping the monopolies of the telecom era intact. Voice over the internet means zero infrastructure other than what's already there for the internet, leaving the market open for competition...right?
Right. Just about. There are still some regulations that are slowing VOIP uptake in Canada. For example, Skype blames these regulations for the lack of Skype-in in Canada. Canadians can make calls with Skype, but cannot get a local Skype phone number to receive calls.
Overall, I think Canadian VOIP services are merely slowed, but not halted. Other companies are taking the leap to comply with the CRTC regulations. Unlike the largely paternalistic regulation of the Broadcasting Act (thou-shalt-watch-Canadian-TV), I also actually have few qualms about these remaining VOIP regulations. Most of them are minimal and necessary. We're talking about essential services such as 911, and consumer protection measures such as requiring phone number portability.
Excellent solutions to cutting your phone cord are already here. First, the cheapest way to take advantage is of VOIP is to make internet-to-internet calls. Both Google and Skype allow you to do this for free. The rates for this in Canada are as cheap as anywhere else. In fact, there is not even the possibility for any regulation to increase rates in Canada, as the Telecommunications Act only applies to a "transmission facility". This is the wires between any two points, but not the points themselves. The internet calls of Skype and Google only operate to connect people, but the companies own only servers to accomplish this task and no phone lines.
However, internet calls probably isn't enough for most people. As handy as it is to be able to call someone from my GMail sidebar, there's a lot of people that I'm never going to see there. A phone number is necessity.
Fortunately, there has recently been a small explosion of companies offering local phone numbers. I use Vbuzzer, paying all of $5 for my Ottawa phone number and an additional $15 for absolutely unlimited calling to anywhere in 32 countries. This is just the service I happen to use -- there are other similar services available.
Most of these VOIP services use the SIP protocol. You can get an app for an Android phone called CSimpleSIP that works seamlessly to receive and dial out phone calls. I have WIFI at home and at work, so can make calls at these locations for free, avoiding costly cellphone charges in addition to already avoiding the cost of a land line.
<Snip>, coaxial cable. <Snip>, telephone cord. It's all just internet now.


Aurora-5Besides the presence of background noise and unknown frequency characteristics, the reverberation inside a room can cause an additional distortion in case of a hands-fee speech input in rooms. To cover all distortion effects as they might occur in real applications of speech recognition systems, the data base Aurora-5 has been set up in 2006. Aurora-5 is quite similar to Aurora-2. A 8 kHz version of the TIDigits is taken as basis. Special focus is put on two application scenarios. The first one is the speech input in a car where three different situations are considered. These are the usage of a close-talking microphone, the recording with a hands-free microphone and the usage of a hands-free microphone in combination with a further speech transmission over a GSM cellular network to a remote recognition system. The second scenario is the hands-free speech input in different noisy room environments, e.g. to control electronic devices like a telephone or audio/video equipment.
All noisy data of Aurora-5 have been artificially created with a tool for simulating the hands-free speech input in noisy rooms and the transmission over a cellular telephone network. A Web interface exists to experience this simulation tool . In comparison to Aurora-2 where only a subset of all available test data has been taken, Aurora-5 uses all available test data for each test set. Furthermore the variance of the distortion effects inside each test set is higher due to e.g. randomly selecting a noise segment from a whole set of noise recordings at the specific noise situation.
A set of HTK based recognition experiments is distributed with the noisy data.
A report is available containing more details about the set-up and the achieved recognition results.