The last post generating some buzz on Twitter so I’m going to follow it up with one more.

The command “show call active voice brief” is an engineer’s best friend when it comes to confirming jitter and other call quality issues.

Here is a sample output of the command:

GapFillWithSilence=950 ms
GapFillWithPrediction=1980 ms
GapFillWithInterpolation=0 ms
GapFillWithRedundancy=0 ms
HiWaterPlayoutDelay=350 ms
LoWaterPlayoutDelay=25 ms
ReceiveDelay=29 ms
LostPackets=0
EarlyPackets=0
LatePackets=83

If you see the following values incrementing at a high rate, then you likely have an issue:

• GapFillWithSilence = Choppy voice issues
• GapFillWithPrediction = Synthetic voice issues
• LatePackets = Jitter

Short and sweet for this lovely Wednesday morning:

Fax passthrough encodes fax traffic with in a G.711 voice codec and sends it across the VoIP network as a voice call. The call may use any codec (G.711, G.729, G.723) etc. initially and once a 2100 Hz CED tone is detected, the device (ATA, for example) tells the far end gateway to switch over to G.711 using a peer-to-peer message. This message is called a NSE message (Named Signalling Event) with in the RTP stream.

Here are the important things to know about NSE-based passthrough for fax faxes and modems:

• The 2100 Hz CED tone played from the terminating fax is the stimuli tone for initiating NSE-based passthrough for normal G3 fax devices. If the DSP on the TGW never detects this tone then the switchover to passthrough will never occur.
• Upon detecting the 2100 Hz CED tone, the TGW initiates the passthrough switchover using an NSE-192 message. The OGW responds with an NSE-192 message.
• The NSE-192 message upspeeds the codec to G.711, disables VAD, and sets the jitter buffer appropriately.
• The NSE-193 is triggered by an ANSam tone that is only found with high speed modem and SG3 fax calls. The NSE-193 signals that the echo cancellers on the voice gateways need to be disabled.

Last Friday, I read a great blog post by William Bell over at ucguerrilla.com.  The conversion of a 7960 phone into a gold-plated icon would throw many Paris Hilton’s into a fit of envy.  After reading his account, I decided to convert one of my spare Cisco 7960s into a Bat-phone.

The process is pretty straightforward once you address a few issues.

Issue number one: Paint Selection

William picked a faux gold-plated can of spray paint.  Make sure you select the type of paint that will bond to plastic.

Issue number two: Disassembly

Take some time to understand how the pieces of the 79XX phones lock together.  I found that this article was especially helpful.  The trick to disassembly is to know how the pieces slide apart from one another.  You have to use a fair amount of force in the process.  Knowing which way to pry and pull will ensure that nothing will break.

Issue number three: Spray Paint Application

Be patient in the process!  I was short on time and, as a result, got poor results with the paint.  Make sure that you work in a well-ventilated room and space out applications with plenty of time to allow the paint to dry and cure.  If I were to go back and do it over again, I’d use these as a general rule:

• No more than one application per 24 period
• Do not attempt to pain everything in one application
• Do not apply more than two coats of paint, otherwise the line buttons and soft keys will stick a little since the tolerance is so low between the pieces.

Issue number four: Understand How the Metal Spring is Positioned

I wasted some cycles getting the metal spring on the hook lever.  There’s nothing worse than getting the phone reassembled only to find that the spring came loose.  I found this YouTube video especially helpful as it provides a close-up of the spring.

Issue number four: Avoid Tight Spaces

This point can’t be stressed enough.  I applied the first coat of paint on my three-season porch.  The ventilation was poor and it gave me some nasty symptoms akin to a head cold the following day.  Remember that spray crap is wicked toxic.  Get outside for you application and avoid some chemical fallout.

The result?

I was pretty happy overall.  Yes, I made some mistakes, but it looks cool sitting in my home lab downstairs.  is the final product.

Holy cow, Batman, that's a lot of red!