E1 PRI Group Timeslots

[DAVID L GARCIA VARGAS]

Hi, 

Im triying to configure a E1 with the PRI group timeslots command as follow: 

controller E1 0/0/0

    line-termination 75-ohm
    pri-group timeslots 1-30

Then, I'm using interface serial0/0/0:15 to configure signalling.

Right know everything is working fine, but I'm a little confused.

As fas as I know, E1 have 32 timeslots or channels (1 to 32), where the fisrt channel is TS0 and the last one is TS31. Signalling should always go on channel 16, which is TS15.

My question is, in the controller configuration, shouldnt be "pri-group timeslots 1-31" instead of 1-30? ...  

If I have pri-group timeslots 1-30 does it means that I only configured 29 voice channels? because TS15 is not going to be usefull 

When I do a show voice port summary, I still see 30 channels =S

                                           IN       OUT
PORT            CH   SIG-TYPE   ADMIN OPER STATUS   STATUS   EC
=============== == ============ ===== ==== ======== ======== ==
0/0/0:15        01  isdn-voice  up    dorm none     none     y 
0/0/0:15        02  isdn-voice  up    dorm none     none     y 
0/0/0:15        03  isdn-voice  up    dorm none     none     y 
0/0/0:15        04  isdn-voice  up    dorm none     none     y 
0/0/0:15        05  isdn-voice  up    dorm none     none     y 
0/0/0:15        06  isdn-voice  up    dorm none     none     y 
0/0/0:15        07  isdn-voice  up    dorm none     none     y 
0/0/0:15        08  isdn-voice  up    dorm none     none     y 
0/0/0:15        09  isdn-voice  up    dorm none     none     y 
0/0/0:15        10  isdn-voice  up    dorm none     none     y 
0/0/0:15        11  isdn-voice  up    dorm none     none     y 
0/0/0:15        12  isdn-voice  up    dorm none     none     y 
0/0/0:15        13  isdn-voice  up    dorm none     none     y 
0/0/0:15        14  isdn-voice  up    dorm none     none     y 
0/0/0:15        15  isdn-voice  up    dorm none     none     y 
0/0/0:15        17  isdn-voice  up    dorm none     none     y 
0/0/0:15        18  isdn-voice  up    dorm none     none     y 
0/0/0:15        19  isdn-voice  up    dorm none     none     y 
0/0/0:15        20  isdn-voice  up    dorm none     none     y 
0/0/0:15        21  isdn-voice  up    dorm none     none     y 
0/0/0:15        22  isdn-voice  up    dorm none     none     y 
0/0/0:15        23  isdn-voice  up    dorm none     none     y 
0/0/0:15        24  isdn-voice  up    dorm none     none     y 
0/0/0:15        25  isdn-voice  up    dorm none     none     y 
0/0/0:15        26  isdn-voice  up    dorm none     none     y 
0/0/0:15        27  isdn-voice  up    dorm none     none     y 
0/0/0:15        28  isdn-voice  up    dorm none     none     y 
0/0/0:15        29  isdn-voice  up    dorm none     none     y 
0/0/0:15        30  isdn-voice  up    up   none     none     y 

Thank you

[Jaime Valencia]

PRI provides a varying number of channels depending on the standards in the country of implementation. In North America and Japan it consists of 23xB (B channels(be/s). In Europe and Australia it is 30xB + 1xD on an E1 2.048 Mbit/s. One timeslot on the E1 is used for synchronization purposes and is not considered to be a B or D channel.

http://en.wikipedia.org/wiki/Primary_Rate_Interface

[DAVID L GARCIA VARGAS]

Hi Jaime, 

I know that... I also know how the signalling works

My question is about the timsslots when configuring the pri-group for E1 ISDN PRI

[Jaime Valencia]

And that snip answers your questions. 32 channels total, only 30 B channels, 1 D, one for sync

How many B channels you'll use is what you configure as pri-group timeslots.

[DAVID L GARCIA VARGAS]

So what will be the difference between:

pri-group timeslots 1-31

and

pri-group timeslots 1-30 ?

 E1 should give me 30 channels anyway

[Jaime Valencia]

1-31 should be used with NFAS, but it's rare to see that. You usually see that with T1s.

[acampbell · Accepted solution]

David,

Imagine you had only bought 20 usable channels from your service provider

You would configure like this:-

!
controller E1 0/0/0
line-termination 75-ohm
pri-group timeslots 1-21
!

Timeslot 16 is as you know for signalling so we need to add an additional timeslot to compensate for timeslot 16

Usable channels 1-15, 17-21 = 20

So for the full 30 usable channels:-

!
controller E1 0/0/0
line-termination 75-ohm
pri-group timeslots 1-31
!

This link may help you
http://www.cisco.com/en/US/docs/ios/12_2/dial/configuration/guide/dafchant_support_TSD_Island_of_Content_Chapter.html#wp1001062

Hope this helps

Regards Alex

[Nishant Savalia · Accepted solution]

Hi David,

Regarding your query,

When I do a show voice port summary, I still see 30 channels =S "the sequence then voice-port 16 you can not see, so total number of B channels is still 29.

0/0/0:15        14  isdn-voice  up    dorm none     none     y 
0/0/0:15        15  isdn-voice  up    dorm none     none     y 
0/0/0:15        17  isdn-voice  up    dorm none     none     y 
0/0/0:15        18  isdn-voice  up    dorm none     none     y 

you will always see the (number of channels -1 ) you have configured in output of "show voice port summary".

Regards,

Nishant Savalia