[cisco-voip] SDLLinkOutOfService

[Wes Sisk]

Each ccm process is a concurrent real time process. They exchange 
messages as needed over SDL links.  In addition to that realtime 
communication there are keepalives every 10 seconds.  The real time 
synchronization makes these links the most sensitive TCP sessions in the 
network.

At the same time it is necessary to detect dead links as quickly as 
possible.  A call may be held up on node1 pending a response from 
node2.  A bandwidth reservation request on node1 must synchronize with 
all nodes as quickly as possible to avoid potential over subscription.

To that end a network outage as low as ~ 2 seconds can cause SDL link 
out of service.  The value can be even lower depending on RTT in your 
network. See:
http://www.faqs.org/rfcs/rfc793.html

These parameters are not configurable on CUCM.


At what interval is your network service monitoring network 
connectivity?  They need to get down to the order of single seconds for 
monitoring to correctly detect outages that will affect CUCM.

Regards,
Wes



On 1/25/2011 3:50 PM, steve.siltman at assurant.com wrote:
> Hey All!
>
> Quick one for you.
>
> Four of our Call Manager clusters are split between two locations. 
>  All received the SDLLinkOutOfService message.  I have no doubt that 
> we had a network issue of some sort that prevented these clusters from 
> talking to each other for a few seconds.  Our Network services area 
> was unable to find this network burp.  I want to understand this 
> message a little better.  Do you know what the timer is for the SDL 
> packets between the call manager servers and whether or not this can 
> be massaged?
>
> Thanks,
>
> -Steve
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