Authors Medium Mark Lindsey SMTS at ECG

Wireshark Memory Bloat on VoIP capture files

Wireshark is a really neat tool for analyzing phone calls. But when you load a 100 MB capture file of VoIP calls, you need much more than 100 MB of RAM. But how much more? Here's a data point from which you can make a line: a 326.15 MB PCAP file contained lots of SIP, and a little RTP. This wasn't a raw capture file; I had thrown away a lot of the RTP and RTCP. The file compressed to 121.1...


BroadSoft Connections 2008: the obvious ideas are all here

From the flight from Phoenix, AZ to Raleigh, NC: The BroadSoft Connections 2008 conference completed today. This is my third time at Connections. The stated goal of the show is networking and dealmaking. The former is difficult to measure, but I suppose I did some of that. I know the latter occurred, and the work will occupy me for a while. BroadSoft spent some time advertising the "xtend" pla...


How important is a lab system?

How important is it to have a lab replicating your production (VoIP) environment? Conventional wisdom says that everybody has a lab: some people just host their production users on it. Having a lab incurs a lot of additional cost and work: -- You have to buy the lab equipment, and the software. -- You have to install and integrate the lab system. -- You have to keep it up to date and secure. ...


This CDR has been brought to you from the letters B, F, and the symbol #

TWICE in the past month, I've bumped into CDRs from SS7 equipment in Atlanta that include alphabetic characters and pound signs in the calling party number (ANI) field of the CDR. One of the calls was from 5176#0B600. (That's a phone number.) What's going on here?


Voicemail peak-hour oversubscription ratio (48:1)

If I'm a phone company and I have 100 subscribers, and every one of them has voicemail, how many people will be calling into the voicemail system at any one time? Back in the old days, they'd provision trunks into the voicemail system between the Class-5 switch and the voicemail system. They'd have to know how many trunks to provision to let all the subscribers both receive voicemails, and call...


The cat in Aastra 2.2 SIP Software

The Aastra 57i 2.2 software has this ASCII art embedded: | ("`-''-/").___..--''"`-._ | Line (`6_ 6 ) `-. ( ).`-.__.`) | Manager (_Y_.)' ._ ) `._ `. ``-..-' | _..`--'_..-_/ /--'_.' ,' | (il),-'' (li),' ((!.-' Is it a Cat? Or is it a Pig?


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...