Tag Archives: VOIP

Make VoIP work on your LAN

I have a client with a local area network with about forty client PCs. A few months ago, a third-party phone vendor added an Elastix “PBX” phone server, as well as a new workgroup router. Elastix provides a graphic administrator interface to its underlying Asterix telephone private branch exchange (PBX). Elastix and Asterix run on a Linux server.

The client has complained that phone callers’ voices have been randomly distorting, incoming calls randomly terminating, and after ringing, desktop phones’ handsets randomly die. The phone vendor assured my client that the new router (an Asus RT-N66U) was not at fault, and suspected that the problems were caused by cabling problems or configuration problems with the Elastix server.

After months of frustration, the client asked me to have a look. I began with the workgroup router. I noticed that it was configured to use cut-through switching. (Asus calls this “NAT Acceleration”, which sounds like a good thing, doesn’t it?  NAT is Network Address Translation. The router apparently defaults to cut-through switching mode.) VoIP (Voice over Internet Protocol) uses UDP (User Datagram Protocol), rather than TCP/IP. UDP is used for streaming real time audio and video because of its low overhead and potentially reduced latency. It does, though, require that its underlying transport mechanism be rock solid.

Cut-through switching does NOT provide a rock solid transport mechanism! Cut-through switching is fast, but it can damage frames and forward previously damaged frames. The more conservative store and forward method ensures that all frames that traverse a switch remain undamaged. It also will not forward damaged frames. Result?  A cleaner network.

Onion layer 1

Troubleshooting system problems is like peeling an onion. You remove one layer at a time and look for changes.

For our first layer, I reconfigured the workgroup router so that it employed store and forward, rather than cut-through switching. Then I waited for user reports. Users reported that we’d fixed the distortion problem, but calls occasionally dropped and/or weren’t initiated.

Onion layer 2

Next, I activated the workgroup router’s QOS (Quality Of Service) feature. I assigned highest priority to all traffic in and out of all active ports on the Elastix server. Then I waited. Users reported that all phones now work as they should.

Problem solved.

Think before adding boxes

Adding boxes to networks often works with little tweaking. Eventually, though, services begin to fail and users complain of slow response, as traffic jams the network’s pipes. Eventually, someone must reduce unnecessary traffic, and assign priorities to different classes of network traffic. I recommend doing this before problems occur — not after.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

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FCC and VoIP

The FCC seems to favor moving our nation’s telecommunications from a circuit-switched model (using crossbar and ESS switches) to a packet-switched model using routers and VoIP (voice over internet protocol) packets. They appear to favor SIP (session initiation protocol).

Karl Auerbach, in a recent article, criticized this use of SIP. According to Mr. Auerbach, the current SIP spec is way too loose. I’ve used SIP with Asterisk-based “PBX”s, but I’m not a SIP expert. In my limited experience, SIP works fine, but its loose spec seems to make system configuration needlessly confusing.

imageIt reminds me of the RS-232 spec. It’s open to interpretation, so each manufacturer interprets it as it wishes. Result? You’re lucky if an RS-232 device works without fiddling with its connector’s pinout. The USB spec, in contrast, works reliably because it’s unambiguous.

Let’s hope that, whatever is finally chosen, our telecommunication backbone is as robust as USB, and not as flaky as RS-232.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

T-Mobile’s VoIP 9-1-1 Strategy

Yesterday, my T-Mobile home page included a link to their page titled Wi-Fi Calling and 9-1-1 Address. This describes their method of providing 911 caller geo-location information when using a T-Mobile phone that’s connected via a Wi-Fi access point. [“Wi-Fi Calling” is their tradename for VoIP (Voice over Internet Protocol).]

Like their cellular phone 9-1-1 location strategy, it doesn’t rely on the caller phone’s GPS receiver. Also like their cellular geo-location strategy, it tries the most precise method first, and falls back to progressively less precise methods. I guess that the other U.S. cellular companies employ a similar VoIP 9-1-1 strategy.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Net neutrality in a bandwidth-limited Internet

The phrase “net neutrality’ was coined by Tim Wu, the author of The Master Switch: The Rise and Fall of Information Empires, to describe a so-called open Internet in which all packets from all users are treated equally. Sounds fair, doesn’t it?

I’ve managed corporate networks since 1987. When all clients were the same, treating their packets equally made sense. As videoconferencing and VoIP (Voice over Internet Protocol) traffic joined these networks, latency caused frozen video frames and dropouts in VoIP telephone conversations — all verboten in a business environment. One cure is to implement QoS (Quality Of Service) across the enterprise. Packets that are time-sensitive are created with a QoS field that asks routers that these packets go to the front of the line when packets queue for routing. In private networks, where IT departments control which stations and apps create packets with high priority, implementing QoS works nicely.

MUSE QoS
MUSE QoS architecture
IGMP = Internet Group Management Protocol
ASP = Application service provider
NSP = Network service provider

The Internet is anything but private. If all Internet routers accommodate QoS, is it sensible to assign the same high priority to packets carrying real-time heart surgery, HD video of Rocky XXII, and people playing online games?

The Internet will never be a boundless resource, so from a technical point of view it’s sensible to implement QoS. Who will pay for priority handling? If Netflix were to pay a premium for preferential handling of its streaming video packets, it could hurt the cable TV providers, so the cable TV industry piously supports net neutrality. Any argument against enabling QoS is purely political, and opens a Pandora’s box that revolves around the question, “What IS the Internet?”, or “What do we wish the Internet to become?”

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Call phones from Gmail using Google voice

Logo is property of Google

Google tightens link between Gmail and telephone: Great for consumers who trade service for privacy; Irrelevant for major corporations.

The walls between email, voice mail, and the telephone have been under attack for years, by a variety of companies. Google has recently added the ability for its Gmail users to place calls directly from their Gmail mailboxes. Google announced on August 25, "Starting today you can use Gmail to receive or place Google Voice calls." Here’s a short independent demo on Youtube

This seems to be aimed at the VOIP market shared by Skype and Vonage, as well as the traditional phone companies. Caveat: Before getting too excited about any Google product, remember that by using Google products, you grant them almost unlimited rights to your material.

Here is section 11 from Gmail’s Terms of Service http://www.google.com/accounts/TOS. I’ve emphasized the most troublesome term for me:

11. Content license from you

11.1 You retain copyright and any other rights you already hold in
Content which you submit, post or display on or through, the Services.
By submitting, posting or displaying the content you give Google a
perpetual, irrevocable, worldwide, royalty-free, and non-exclusive
license to reproduce, adapt, modify, translate, publish, publicly
perform, publicly display and distribute any Content which you submit,
post or display on or through, the Services
. This license is for the
sole purpose of enabling Google to display, distribute and promote the
Services and may be revoked for certain Services as defined in the
Additional Terms of those Services.

11.2 You agree that this license includes a right for Google to make
such Content available to other companies, organizations or individuals
with whom Google has relationships for the provision of syndicated
services, and to use such Content in connection with the provision of
those services.

11.3 You understand that Google, in performing the required
technical steps to provide the Services to our users, may (a) transmit
or distribute your Content over various public networks and in various
media; and (b) make such changes to your Content as are necessary to
conform and adapt that Content to the technical requirements of
connecting networks, devices, services or media. You agree that this
license shall permit Google to take these actions.

11.4 You confirm and warrant to Google that you have all the rights, power and authority necessary to grant the above license.


As I understand this section, no message in Gmail is "private". Will Google process your voice, as it does your text, and use it to build your profile so that it can direct advertising at you? Yes, probably.

While examining Gmail’s Terms of Service, note that Google may discontinue any aspect of Gmail at any time with no prior notice. This is the definition of an anti-SLA (Service Level Agreement). This is one more reason why relying upon Gmail for business messaging is reckless (emphasis is mine):

4. Provision of the Services by Google

4.1 Google has subsidiaries and affiliated legal entities around the
world (“Subsidiaries and Affiliates”). Sometimes, these companies will
be providing the Services to you on behalf of Google itself. You
acknowledge and agree that Subsidiaries and Affiliates will be entitled
to provide the Services to you.

4.2 Google is constantly innovating in order to provide the best
possible experience for its users. You acknowledge and agree that the
form and nature of the Services which Google provides may change from
time to time without prior notice to you.

4.3 As part of this continuing innovation, you acknowledge and agree
that Google may stop (permanently or temporarily) providing the
Services (or any features within the Services) to you or to users
generally at Google’s sole discretion, without prior notice to you
. You
may stop using the Services at any time. You do not need to
specifically inform Google when you stop using the Services.

4.4 You acknowledge and agree that if Google disables access to your
account, you may be prevented from accessing the Services, your account
details or any files or other content which is contained in your
account.

4.5 You acknowledge and agree that while Google may not currently
have set a fixed upper limit on the number of transmissions you may send
or receive through the Services or on the amount of storage space used
for the provision of any Service, such fixed upper limits may be set by
Google at any time, at Google’s discretion.


Gmail is well done, and I admire the constant upgrades that Google introduces, but I regard Gmail as a consumer service — not a service that’s suitable for business use. Then again, maybe Google guarantees privacy and offers service level agreements to large corporate accounts. (I’m not aware that Google does anything like this.) Such guarantees, with penalty clauses, are the only way that corporate boards and managers will (or at least should) approve Gmail for business use.

Visit my website: http://russbellew.com
Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695



I’m shocked. Shocked! China spies on Skype phone calls.