ISR4k (srst)

[raid_t]

Dear experts,

Maybe this is answered here but couldn't find it.

Have two simple questions on licensing ISR4k on a branch that connects to CUCM at HQ.

1. Is CME-UL required with as many licenses as you purchase for SRST endpoints?

2. Does the SRST require to purchase either FXO or T1 ports for fallback to work?

Thanks in advance!

[Jaime Valencia]

See table 2

https://www.cisco.com/c/en/us/products/collateral/unified-communications/unified-survivable-remote-site-telephony/data_sheet_c78-678873.html

Whether you need a T1 or FXO for your SRST router is up to you, if you want PSTN connectivity over TDM while on SRST, you obviously need one. SRST itself doesn't require any TDM connectivity to work and make only internal calls.

[Roger Kallberg]

I assume you have a SIP connection with your telco provider for PSTN, hence your question about if you need to have a TDM connection for PSTN in SRST. The answer to that is no you don’t need to have this. As Java wrote the SRST functionality have no relation to any PSTN connection, but you would not be able to make or receive any calls from external parties without any connection with PSTN.

[raid_t]

Hi Roger,

If the Central Site is the only site that has sip trunk to PSTN and this main site is connected with other remote sites via MPLS/WAN, do the Remote routers require SIP trunk licenses?

[Roger Kallberg]

There are no license for SIP trunks. However for the router to handle calls between two IP call legs it would require CUBE licensing. These are sessions based and is rights to use type.

[raid_t]

So how many legs would be in this scenario?

Would I have to have cube licenses for the router/phones for calling to/at the remote site?

[raid_t]

Hi Roger,
Can you please shed some light here to better understand it?

Thanks in advance.

[Roger Kallberg]

It’s not absolutely so that you will need to have Cube licenses for two CMEs to communicate with each other. That’s a bit of a grey area. A CME will actually act as a Cube for calls between two SIP phones that are registered to the CME. As such it has the needed functionality for this as part of the CME. Cube functionality is not more than the router handling calls between two IP call legs. For each call from one CME to the other you would have two call legs, these are counted as one in session in Cube.

[raid_t]

Have one last question while on this.

Imagine a common scenario with Centralized Call Control at HQ. For SRST at Remote sites when the WAN is down, to enable inbound/outbound external calls, it more common to have local SIP trunk for each Remote to PSTN or PRI/FXO circuits?

What would be common on these cases?

Thanks in advance!

[Roger Kallberg · Accepted solution]

For SRST local PSTN breakout is a requirement to be able to handle ingress and egress calls. For this a SIP or digital connection, like for example T1 or E1, is preferred. Analog connection should be last resort only as this is the least preferable option.