SRST, ISDN PRI

[cooper_69]

Customer reports that when the WAN link fails calls to PSTN get dropped because ISDN PRI drops and reassoicates with SRST.

Souldn't there be a seemless failover to SRST for calls incomming/outgoing to PSTN

[Brandon Buffin · Accepted solution]

I'm assuming your gateway is using MGCP. If so, this is expected behavior. During normal operation, an MGCP PRI backhauls the D channel to Callmanager. When the WAN goes down, so does the D channel. When the D channel drops, so do your calls. It then has to reestablish the D channel with the local gateway. Take a look at the following link.

http://supportwiki.cisco.com/ViewWiki/index.php/Calls_drop_when_switching_from_MGCP_to_SRST_mode_or_rehoming_from_SRST_to_MGCP

Hope this helps.

Brandon

[cooper_69]

Hi Brandon,

It sure does. Thanks!

1 more q. Does it make sense to change the architecture to distributed from Centralized with remote branches and cluster at a remote branch because of the dropped calls? or would it make sense to implement H323? I know that there are a lot of factors that need to be answered to properly re-design this network that uses both Call Manger and legacy PBX but purely from dropped calls during WAN outage argument.

CCIE-V, RIGHT on!

[Brandon Buffin]

I think a centralized approach is best when possible. A move to H.323 would help with the issue of call preservation. However, as you noted, you would need to consider other factors such as the number of branches that you have, increased configuration required, staff comfort level with H.323, PBX interoperability, etc.

Hope this helps.

Brandon