SRST with SIP CUBE

[glennmartindell]

Hello All,

I have a SIP to SIP CUBE router with a SIP trunk to the PSTN.   This router is also acting as an SRST gateway for the local site for about a dozen 7841 phones (SIP).   Everything is working well in both SRST and non-SRST modes except when in SRST I have the following issue:

Phone A forwards their phone to Phone B

When calling from phone C to phone A, the call forwards correctly to phone B

When calling from the PSTN to Phone A, nothing happens.   No ringback, no forwarding, no nothing.   Is there something I need to put in my config to allow forwarding from a PSTN SIP trunk to a SIP phone in SRST?

Thanks,

Glenn

[R0g22]

For G2's yes, SIP SRST co-location with CUBE is not supported. With ISR-4k, co-location support has been introduced with Fuji XE release aka 16.7.X

[joeg]

To confirm, SRST and CUBE are supported co-resident on G2 with SCCP? I was under the impression SRST and CUBE were not supported co-res regardless of SCCP or SIP on the G2's.

[R0g22]

Correct.
1. ASR and CSR don't support SRST at all with CUBE colocated.
2. ISR-G2 supports only SCCP SRST.
3. ISR-4k support SRST starting 16.7.X XE code.

[i.pletenev]

Hi everyone.

I'm a little bit confused with SCCP SRST at ISR-4K.

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@R0g22 wrote:
3. ISR-4k support SRST starting 16.7.X XE code.

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That sounds for me as Cisco supports SCCP SRST at ISR-4k with CUBE.

And here https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cusrst/admin/sccp_sip_srst/configuration/guide/SCCP_and_SIP_SRST_Admin_Guide/srst_sip_trunking.pdf Cisco says:

For Unified SRST Release 12.1 and later releases, you can deploy product instances of Cisco Unified Border Element and Unified SRST (only for SIP) on the same Cisco 4000 Series Integrated Services Router.

So could anyone clarify: is SCCP SRST supported with CUBE at ISR-4K or not?

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[Jonathan Schulenberg]

Cisco only tested/qualified SIP SRST with CUBE on ISR4k. That doesn't mean SCCP outright won't work, only that you can't ask Cisco to support it and there are almost certainly some features/scenarios that will fail.

On an editorial note: Cisco generally expects IP phones to have a lifespan of five years, only slightly longer than desktop PCs. Under that mindset you could argue that a router generational refresh shouldn't be a problem since you're also refreshing phones; all current phone models are SIP-only.

[Clifford McGlamry]

> Cisco generally expects IP phones to have a lifespan of five years

Interesting.  I haven't heard this before.  I've still got very large customers who have a LOT of 7940's and 7960's in the mix.

[Jonathan Schulenberg]

I'm so glad we're finally coming to terms with this as an industry. IP phones are computers connected to the network like any other PC, server, building automation equipment, printer, etc. They are capable of having security vulnerabilities just like any other device. Despite this, they are almost never included in the patch management process. Cisco hasn't maintained the codebase of the 7940/7960 since July 2011, in part because they literally ran out of NVRAM - I think the last release 8.1(2)SR2 had 10kb of free space left. Phones need a refresh cycle like any other IT asset. In my opinion, the End of SW Maintenance of a model is when they need to be refreshed.

CUCM 11.5 and 12.0 both deprecated phone models - they won't register after an upgrade even if they were working before. I can't speak to roadmap details on the forums but I think it's safe to assume Cisco will continue with this trend eventually. This will become especially critical when there is a server-side vulnerability - which is happening fairly often these days - and the newer version its fixed in doesn't support an ancient phone model. InfoSec will rightly demand that the CVE is patched to satisfy their security scan/audit.

[Clifford McGlamry]

Jonathan, I don't disagree at all. I was just observing there is a LOT of old stuff still out there. The viewpoint is that the phone is a dumb terminal, so until it breaks, no reason to replace it.



What strikes me as extremely odd is that Cisco is deprecating the 7070 and 7971 with v12 and already deprecated the 7935 with 11.5, yet they have completely ignored the 794X and 796X trains. I'd be very interested in their thinking on this (not to argue, just interested).

[Jonathan Schulenberg]

They started with models that were truly ancient (e.g. VIP30) or had fewer units sold; the original 79X0 sold more than the 79X1. Obviously this is a delicate topic and, to your point, requires an expectation reset across the customer base. This will change the TCO, though it also creates opportunity to pilot or expand Jabber soft phone usage. I think they were hoping to start small and build momentum behind the idea to avoid major shock.

[i.pletenev]

Update: got a confirmation from the CISCO TAC: SCCP with CUBE is supported.

I have tested a basic functionality in our lab: inbound/outbound calls with SCCP phones work fine

[Clifford McGlamry]

The issue is not SCCP and CUBE.  It's using a CUBE as an SRST gateway for both SCCP and SIP at the same time.  While SCCP isn't an issue, SIP with SRST and CUBE is. 

[Jonathan Schulenberg]

That TAC engineer is incorrect. Ask them to support their assertion with documentation; they won't be able to because it does not exist. The best authoritative reference on this topic currently available was written by the TME responsible for CUBE here: https://cisco.app.box.com/v/cube/file/281263947533 (Bookmark https://cisco.app.box.com/v/cube for future reference.)

To recap: starting in IOS XE 16.7(1) the ISR 4k routers support CUBE co-resident with SIP SRST only. Not SIP E-SRST; not SCCP SRST; and not secure SRST. The only way it is supported is if you use voice class tenant on the CUBE dial-peers. Everything else is not tested, qualified, or supported by the BU.

[Clifford McGlamry]

Wow.....without a doubt the most complicated configuration I've ever seen on an SRST or a CUBE device.  

I really hope they publish something that will break this down and make it a bit more understandable.  

[dlong8381640]

Hi Glenn, 

I have a SIP to SIP CUBE configured on a ISR 4k at one of my remote sites. I was unable to get SRST working on that CUBE, and since its not supported I was unable to get assistance from TAC. They did assist me with getting SRST configured on a separate router. 

I am now trying to merge SRST config on to the CUBE. Any change you could post your CUBE/SRST config as a reference?

Thanks,

Dylan

[Jose Carlos Zamora Araya]

Hey Dylan, 

I has been a long since your last post but I would like to share with you and every one the configuration guide for SIP SRST CUBE Collocated:

https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cusrst/admin/sccp_sip_srst/configuration/guide/SCCP_and_SIP_SRST_Admin_Guide/srst_sip_trunking.pdf