[Asterisk-doc] Connecting to a PRI

[Julian Lyndon-Smith]

Comments inline:

Many thanks for taking the time to doc this.

Julian.

Gene Naden wrote:
> Here is my explanation of the issues involved in connecting to a PRI. I am
> open to feedback, corrections, comments. This is a text file with line
> breaks.
> 
> Gene Naden, MA
> Programmer Analyst
> GlobalTeldata II, LLC
> 4700 N. Ravenswood
> Chicago, IL 60640
> (773) 878-3161 x 223
> 
> 
> ------------------------------------------------------------------------
> 
> WHAT IS A PRI?
> 
> A PRI is a 24-channel connection to a telephone network such as the Public 
> Switched Telephone Network (PSTN). PRI is a type of ISDN (Integrated 
> Services Digital Network) connection. A PRI can carry 23 voice channels. 
> The 24-th channel is used for signalling. The voice channels are referred 
> to as B channels and the signalling channel is referred to as the D channel.

Euro ISDN PRI have 31 channels, 16th used for signalling

> 
> Because a PRI uses a four-wire local loop, d4 or esf framing, and AMI or B8ZS 
> coding, it may also be referred to at T-1. However, T-1 can be used to carry 
> either voice or digital data. 

or E1 for euroisdn

> 
> You specify the type of framing and coding when you provision the PRI with the 
> telephone company.
> 
> CONNECTING TO A PRI
> 
> To connect to a PRI you use Zapata technology. Zapata is also used for 
> connecting to POTS lines (ordinary, single channel analog phone lines) and 
> analog phones. You configure Zapata for Asterisk in the file /etc/zaptel.conf. 
> Therefore this file can have information about both PRI connections and POTS 
> line connections. See the example below.
> 
> You do not need a Channel Service Unit/Data Service Unit (CSU/DSU) to connect
> your PRI to the Asterisk computer.
> 
> The Digium cards for PRIs accept RJ45 plugs, the same type of plug used
> in Category 5 cables.
> 
> All the Digium cards for connecting to a PRI are PCI cards. Therefore, you 
> cannot use a 1U rack-mounted server if you are connecting to a PRI. The TE405P

Um, we are - most 1U servers have riser boards allowing for the card to 
be mounted sideways. Both our TE405p and TE405P are in 1U servers.

> card is an example of a PRI interface card. It has four ports and therefore
> can connect to up to four PRIs. Alternatively, one or more ports could be 
> connected to channel banks for analog phones. However, channel banks are 
> beyond the scope of this discussion.
> 
> Below is a sample Zapata configuraion file (zaptel.conf). It shows the 
> configuration for a single PRI, two analog phones and two POTS lines. 
> 
> # zaptel.conf
> 
> loadzone = us
> 
> #te405p card
> span=1,1,0,esf,b8zs
> bchan=1-23
> dchan=24
> fxols=1-23

> 
> #tdm400 card
> fxoks=97-98
> fxsks=99-100
> 
> The 23 B channels and the D channel are shown. 
> 
> The line "fxols=1-23" reflects the fact that the connection is to a PRI
> rather than a channel bank. "ls" refers to "loop start." 
> 
> The way the channel numbering works is that the first 96 channels (one 
> through 96) are for the TE405P card. The fxo and fxs channels, if any,
> must follow, rather than precede, the PRI channels. In other words,
> you cannot have fxoks=1-2, fxsks=3-4, bchan=5-27, dchan=28. If you
> do this you will get an obscure error message.
> 
> Regarding the line beginning with the word "span", there is one span
> for each port that is in use. The "span" line has the following format:
> 
> span=port number, timing, line build out, framing, coding
> 
> The port number is one because the PRI is connected to the first port on the
> card. 
> 
> The timing should be 1 for one of the ports. The line connected to that
> port provides a timing reference. If other ports are used, the timing for those
> ports should be two or zero. Two means this line is a secondary timing reference
> and zero means this line is not used as a timing reference.
> 
> Line build out reflects the length of last leg of the connection and is set to 
> zero if the length is less than 133 feet. The specific values for line build
> out are specified in the sample zaptel.conf that comes with Asterisk.
> 
> The framing and coding are discussed in "WHAT IS A PRI", above. The option "esf"
> refers to "extended super frame" and "b8zs" refers to "Bipolar with 8 Zero 
> Substitution."
> 
> TROUBLE-SHOOTING
> When the PRI card was purchased from Digium, Digium has provided free
> technical support for configuring the card.
> 
> The lights on the PRI card can be red, amber/green or green. When all is
> well they are green. 
> 
> If Asterisk aborts when you try to start it, there are several things you
> can check:
> 
> The Linux modules for your Zapata cards have to be loaded in order for the
> connections to work. You load the PRI driver, wct4xxp, before you load the
> FXS/FXO driver, wctdm. 
> 
> You also have to execute the program ztcfg to get things to work. If all is
> well, when you run ztcfg it should not produce any output. When you 
> do this, the lights should change to green, even if Asterisk has not been 
> started.
> 
> Loading of the modules may or may not be done automatically by the system.
> 
> It is possible to construct a loop-back plug to test your PRI card.
> You do this using an RJ45 plug, connecting pin one to pin four and pin 
> two to pin five. When the loop-back connector is connected to the card, the 
> light should turn green. Again, the modules have to be loaded and possibly 
> ztcfg has to have been run.
> 
> The B channels listed in zaptel.conf must agree with the channels listed in
> /etc/asterisk/zapata.conf, otherwise Asterisk may abort when you try to
> start it.
> 
> 
> ------------------------------------------------------------------------
> 
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