200 OK

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?

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 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?

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...

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 ...

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...

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 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."

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...

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):

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...

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...

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...

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...

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...