asterisk users - Dec 2009 - E1 Channel Numbering - Your Comments.

All

This is a small issue that I stumbled onto that has to do with the
channel numbering on an E1 connection into an Asterisk Zaptel/DAHDI
system.

As most of us already know an E1 has 32 channels of which 30(1-15
17-31) are B-channels and 1 (16) is a D-Channel.  The 32nd channel is
not presented in Asterisk Zaptel/DAHDI.  There are other
configurations but this is the most common.

*** Everything currently works and the community is humming along with
the current implementation. ***

Is it or would it be worth the time to note the 32nd channel of the
E1?  I noticed this issue on a 4 port card with 4 E1s.  I quickly
expected the last B-channel at 127 where it was actually at 124 (my
first time with E1s).  As telcom lingo goes I have seen this 32nd
channel referred to as "time slot 0" and as "framing
channel" and
expect there to be other names as well.

As an example, the current method:

bchan=1-15
dchan=16
bchan=17-31
...
bchan=32-46
dchan=47
bchan=48-62
...
bchan=63-77
dchan=78
bchan=79-93
...
bchan=94-108
dchan=109
bchan=110-124

and an example of my first thoughts:

bchan=1-15
dchan=16
bchan=17-31
uchan=32
...
bchan=33-47
dchan=48
bchan=49-63
uchan=64
...
bchan=65-79
dchan=80
bchan=81-95
uchan=96
...
bchan=97-111
dchan=112
bchan=113-127
uchan=128

I quickly grabbed the "uchan" to mean "Unused" or
"Unallocated".  I am
going to assume that there are some better ideas and names for this.
One thought was "Framing" or "fchan" which does not exactly
describe
the channel.  I did notice that depending on your locale the channel
had several names.


What are your ideas?




~
Andrew "lathama" Latham
lathama at gmail.com

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Andrew Latham wrote:
> and an example of my first thoughts:
> 
> bchan=1-15
> dchan=16
> bchan=17-31
> uchan=32
Well, you've missed an important point: the DAHDI drivers for E1 cards
would have to be modified to make this 32nd channel in each span
actually exist, before any configuration in chan_dahdi.conf would be
relevant.

If that was done, there wouldn't actually be any changes required in
chan_dahdi.conf at all; if you wished to, you could put in a comment for
each 32nd channel to indicate that you are intentionally skipping it,
but there is no need to make chan_dahdi actually aware of that channel
at all.

-- 
Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
skype: kpfleming | jabber: kpfleming at digium.com
Check us out at www.digium.com & www.asterisk.org

On Tue, 2009-12-08 at 14:47 -0300, Andrew Latham wrote:
> As most of us already know an E1 has 32 channels of which 30(1-15
> 17-31) are B-channels and 1 (16) is a D-Channel.  The 32nd channel is
> not presented in Asterisk Zaptel/DAHDI.  There are other
> configurations but this is the most common.
As an aside, I've seen different documentation in various places that
shows this "sync" channel as being channel zero (coming before the
first
bearer channel), not the 32nd channel.  I'm not familiar enough with E1s
myself to be able to say definitively that this is the case, but thought
I'd throw this out there for discussion (and hopefully more
enlightenment).

--
Jared Smith
Digium, Inc.