ISDN (BRI/PRI)

by | Mar 5, 2010 | Uncategorized, Written Theory

ISDN is a digital transport service that can support both Data and Voice over existing telephone wires. There are 2 types of ISDN:

  • Basic Rate ISDN – BRI : This provides 2 x 64 Kbps bearer channels and a 16 Kbps signaling channel. It represents then (2B+1D) channels , so 144Kbps
  • Primary Rate ISDN – PRI : this provides 23 or 30 x 64 Kbps beare channels depending on whether it is delivered as a T1 or an E1. It represents then (23B+1D) channels for a T1 and (30B+1D) for an E1

At Layer2, ISDN signaling is provided by the Link Access Procedure on the D channel (LAPD) which is relying on Q920/921 messages.

At Layer3, ISDN call control signaling and access to service are specified by the Q931/932 messages suchg as Setup, Alerting, Connect ,…

Now as the network is not end-to-end all the time, you can encounter that you don’t receive anymore busy tone after the destination is busy. It is normal as once the ISDN network has sent the busy tone to the IP Phone, it iniatiates a normal call clearing so a disconnect, then you can fix this on the your side by setting the following command voice call convert-discpi-to-prog to force the gateway to send the busy tone on the IP end even if the ISDN side is torn down

PSTN Emulator

by | Feb 11, 2010 | CCME, H.323, IOS

Hi ,

Just thinking how can we make a  pstn emulator in a lab …. First thought is to use a CME router with several T1/E1  , BRI cards to distribute PSTN connection back-to-back to all locations …..

Need to think about it !!!