Authors Mark Lindsey SMTS at ECG

On Having an Opinion: Goodness/Badness vs. Pros/Cons

There are two ways of giving recommendations on technical issues:  (a) To say that something is "good" or that something is "bad".  (b) To list Pros and Cons, or else Advantages and Limitations. The most popular, and natural way is just to say what's good, or often, what's best. In my opinion Linux servers are better than Windows servers; I'm ascribing goodness to Linux servers. But I've no...


Interop Lab Testing for VoIP Devices (2008 edition)

In an Interoperation (Interop) Lab, devices are made to work together. When they seem to, the vendors of the devices claim that they "interop with" each other. This is necessary, but not sufficient, to know things will work together. Background Suppose you make telephone soft-switch or application server, such as BroadSoft BroadWorks, Sylantro, MetaSwitch, or the Alcatel-Lucent Network Gateway ...


Why won't anybody build far-end echo cancellation into their VoIP phones and ATAs?

Nobody VoIP Phone or ATA on the market offers talker far-end echo cancellation. They should. Background Some background: echo is when you hear yourself talking. It's usually the caused by the device on the other end of the call, but it's exacerbated in VoIP networks because they have long delays. Suppose you have a phone call that includes a VoIP device (such as a PolyCom SoundPoint 65...


Call Transfer Scenarios in VoIP, SIP, IMS

UPDATED: 2014 October 1: A "Semi-consultative" call transfer cases are now included. The IETF Call Control - Transfer draft seems to have the best and latest info on call transfer scenarios. But I haven't find a good summary of the cases involving transfer-like scenarios. -- Blind transfer, original recipient is facilitator: Alice calls Bob, Bob answers, Alice and Bob talk, Bob transfers to C...


AT&T "will not block or degrade [Internet] traffic."

At the metaswitch user forum, AT&T VP Joe Weinman was asked about whether AT&T would block internet traffic that they disagreed with. He said: "AT&T is a common carrier. We will not block or degrade traffic."


Deploying a new system? Want new features? Expect immaturity.

If you're a Bellhead, accustomed to the stability, processes, and reliability you get from old-line telephony companies like Nortel, Lucent, and Siemens, and you want to deploy VoIP and get neat-new-whiz- bang features, then you shouldn't expect to get the same stability and reliability. There's an intrinsic trade-off in complex systems: if you want new features, then you get new bugs, an...


Nothing sells VoIP like a woman on a telephone

It's an epidemic of conventionality: it seems like every company who's ever tried to sell something related to VoIP uses, at some point, a photo of a woman holding a telephone. Proof by Numerous Examples: Genisys: XO Communications:   From Sprint: AT&T: Covad:   From Level(3) (She's using a SIP Soft Client, of course):


VoIP RTP Packetization Interval: Maybe it's time for a smaller ptime

When a one vendor's VoIP media/trunking gateway is talking to another of the same type, it uses 5 ms packetization (ptime) by default. I.e., each RTP packet has only 5 ms of audio recorded in it. At first this sounds crazy. The efficiency is awful! The bandwidth across Ethernet for G.711 goes to 188 kbps per call per direction! It also means that a single call imposes 400 packets per seco...


Private IP Addresses in VoIP Networks Considered Harmful: Sloppiness

Over the past few years, it's become very common for VoIP carriers (i.e., telephone companies using VoIP) to use private (RFC 1918) IP addresses in their internal VoIP network. These have IPs like 192.168.0.1 or 10.0.0.1. This practice has been promoted by many of the hardware vendors. It reflects the setup many of them use in their labs. There are a number of problems this creates. One of...


Flooding packets for VoIP testing

It's sometimes useful to saturate a network with simple traffic to test your QoS measures. What you want is something that'll send a controlled amount of bandwidth. A TCP-friendly connection won't work, because TCP slows down to the available amount of bandwidth. iperf from NLANR is one such tool. However, you have to have it running on both the sender and the receiver. I couldn't find anyth...


Getting VoIP Equipment Documentation

VoIP software and hardware vendors come from two camps: There are those who hide their documentation from the general public, and those who are open. Too many hide their documentation. Even if you register on their site as a guest, you can't get it. You usually have to be a customer with a paid support agreement. This includes Sylantro, BroadSoft, MetaSwitch, Acme Packet, General Bandwidth, P...


On Network Diagrams

Update: This page desperately needed some diagrams. So I've added some. -- Mark, 2008 May 26 I'm a consultant for telcos and ISPs who do VoIP. Nearly all of my customers have diagrams. They're always Visio. We use their diagrams to help do network design changes or troubleshooting.At nearly every customer, as we start studying their diagrams in detail, they'll say, "wait, that's not right. This...


VoIP Monitoring Tools

Monitoring tools come in these categories: Reactive Passive Monitoring Comprehensive Passive Monitoring Active Probing Reactive Passive Monitoring is when you run tcpdump/wireshark to troubleshoot individual call problems. This is the most critical to have -- but managing and analyzing real-time data streams is no easy skill. Comprehensive Passive Monitoring (CPM) monitors all calls, all the t...


New Discussion Group

There's a new discussion group, "BroadWorks-Discuss" for discussing the BroadSoft BroadWorks platform. It's one of the leading VoIP carrier software platforms out there, and this mailing list is intended to let people who use it, work with it, manage it, etc., discuss things. To subscribe, email broadworks-discuss-on@e-c-group.com


Verizon does agree with Jeff Pulver – but neither realizes it

Jeff Pulver of FreeWorldDialup and Pulver.com and the VON Coalition got into it a bit with Brian Whitton of Verizon Labs at IPTComm 07 last week. Pulver argues that VoIP systems should be open, and new ideas should be tried. Brian Whitton argued that "business realities" were what caused Verizon to do the things it does -- like deploy FTTX using Voice over ATM at first. Both of them are probabl...