[cisco-voip] SIP Fail over

[Erik Anderson]

Morning Folks,

We have implemented a new SIP solution with Level 3 and found that we have
outbound calling failover issues. When a CUBE loses its ability to talk to
its Level 3 Peer, but can still talk to CUCM outbound calls will still
connect to the CUBE, but fail connecting to Level 3. In turn CUCM still
thinks the call is connected since the CUCM SIP trunk remains up to the
CUBE.



Architecture Notes:



4 Locations with 1 CUBE Each

4 CUCM SIP Trunks with each connecting to one of the 4 CUBEs

4 CUCM Route Groups with Various CUBE/SIP Trunks assigned a Distribution
Algorithm of Top Down

Each CUBE has 2 SIP Peers

Each CUBE can only talk to its respective SIP peer via its local Level 3
Transport to reduce call control latency by not allowing it to use the
DMVPN backup network

Level 3 does not support SIP Options Ping

CUCM Trunks have SIP Options Ping enabled



Call Flows:



Working Flow:



Phone ----> SLRG ----> Route Group Member #1 ----> CUBE SIP TRUNK ---->
CUBE ----> Level 3 Transport ----> Level 3 SIP Peer #1/#2 ----> Call
Completes





CUBE Failure:



Phone ----> SLRG ---->

         Route Group Member #1 ----> CUBE SIP TRUNK --X--> CUBE (CUCM Cant
Reach CUBE)



        CUCM Routes Call to Next Route Group Member



                              Route Group Member #2 ----> CUBE SIP TRUNK
----> CUBE ----> Level 3 Transport ----> Level 3 SIP Peer #1/#2 ----> Call
Completes



Level 3 Transport Failure/SIP Server Failure:



Phone ----> SLRG ---->

         Route Group Member #1 ----> CUBE SIP TRUNK ----> CUBE --X--> Level
3 Transport (CUBE Cant Reach Level 3 SIP Server)



        CUCM Thinks Call Connects since the CUBE accepts the call, Phone
gets dead air, never tries the next RG Member





My idea to fix this is to use an IPSLA to ping the pingable address on the
Level 3 SIP Servers. If both address are unreachable then shutdown the CUCM
Dial-Peers. This doesn’t sounds like the best way of fixing it, but it
should work.



If any has any other better ideas please let me know.
-- 
Erik Anderson
Telecom Manager
Some Random Corp.
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