Cell Relay Archive

[Prem Shankar Sharma <prem@trillium.com>]

Hi Prasad,

 

 

-----Original Message-----
From: Prasad Venkatesh [mailto:prasad.hebbar@ind.alcatel.com]
Sent: Thursday, July 06, 2000 7:26 AM
To: cell-relay
Subject: CR: Crankback in PNNI

Hi

I have a doubt related to PNNI crankback handling.

A ---- B ___1_____C
       |____2_____|
       |          |
       |____D_____|

If node B receives a DTL  from A to reach C ( A-B-C) without port being specified in the DTL, node B will try both outgoing links 1 and 2.
But if both the links are not in a position to forward the call, then what will be the crankback info
sent back to A.  How do we specify to A that both the links are not able to handle the call so that A will consider A-B-D-C as the next path. This problem is arising because A does not specify port in the DTL.

How do we handle this case ?  

 

For this case, as the port is not specified in DTL, the crankback blocked transit type 

should be set to "blocked link" and preceding, succeeding and link id need to be filled

in correctly. Here the link id would be 0.

Once the crankback info. reaches the originator of DTL (here node A), all the links

between preceding and succeeding node (i.e. node B and node C) would be blocked

for that particular call because of port id being 0. Then the alternate routing at A won't

consider links between nodes B and C for route computation, and hence the path ABDC

could be provided. [Port id has a special significance and in when present in DTL, could

be assumed to refer to any/all the links between the nodes.]

 

Hope this helps.

Thanks.

Prem