SRST and dial-peer groups (dpg)

[Frank Mittrup]

Hi all,

I'm working on a new SRST configuration with E1 to the provider and SIP towads CUCM with +E164 DN. Here in the past we used COR list to avoid wrong dial-peer matching.

Now, with the new dial-peer group feature this might be more elegant but I just don't know if dial-peer groups are working in conjuction with SRST. Could not find anything in the current SRST Admin Guide:

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_41.html

This SIP section is pretty outaged as it is based on 4.1.

Concret question - can I use dpg inbound towards CUCM and SRST? If yes, how?

Any help is welcome.

Thanks,

Frank

[R0g22]

DPG should work in SRST as well. It is not something that is specifically for CUBE or a voice gateway in general.
Now when you say inbound DPG for both CUCM and SRST, can you detail out your requirement ?

[Frank Mittrup]

Hmm, clicked accidently solved - so it's not yet :-).

So, here my setup:

Matchin inbound from PSTN to dial-peer 100 and pointing with dgp to the outbound dial-peer 50. So, is there an option to also point the dpg to SRST? Think not as this dial-peers are dynamic, right?

dial-peer voice 100 pots
 description *** from PSTN ***
 translation-profile incoming from-PSTN
 destination dpg 100
 incoming called-number .
 direct-inward-dial
 
voice class dpg 100
 description Inbound Direction DialPeer 100 -> DialPeer 50
 dial-peer 50
 
dial-peer voice 50 voip
 description TO CUCM
 huntstop
 destination-pattern +
 session protocol sipv2
 session transport tcp
 session server-group 50
 voice-class codec 1
 voice-class sip options-keepalive profile 1
 dtmf-relay rtp-nte
 no vad

[R0g22]

Understood. So this is not really relevant anymore in SRST because once your phones register, they would be using the virtual dial-peers already created to route the calls. Is there a specific need for DPG ? DPG is used to force the IOS to only parse through a couple of dial-peers depending upon the incoming DP.

[Frank Mittrup]

Hi Nipun,

thanks for this discussion!

My specific need for DPG is to avoid loops. To avoid inbound calls from PSTN matching the outbound dial-peer towards PSTN (hairpining). That's how I understood dpg. I'm usually using this method in both directions and it works fine without SRST. Now with SRST I try to understand if dpg can be used as well.

If dpg does not work in conjuction with SRST, fine but this should be documented somewhere, right?

But then, what is the best way to configure SRST? Do we really need COR list again?

Thanks,

Frank

[R0g22]

If you do not have a overlapping dial-plan, there should not be any loops. COR list do not prevent loops. Yes, they would reject calls when a dial peer gets selected but why implement them when you can create a dial plan that does not cause loops in the first place.
Share your config here. I can take a look and see if there would be any loops and if we can tweak something to improve it.

[Frank Mittrup]

It's actually not about a specific config. I'm just trying to understand the new features like dpg and how to use them to define a kind of best practice template.

So, do you agree that dpg does not work in conjuction with SRST?

My dial-plan ist +E164. CUCM has e.g. +4912345xxxx and +. goes to the PSTN. In this case I need to avoid that a call +4911111xxxx comes in and get's hairpined back to the PSTN. There is always the defaul dial-peer 0 collecting all calls and distribute them to the matching dial-peers, right?

Probalbly that szenario is not really realisic on a E1 connection but on a SP SIP-Trunk you never now...

Thanks,

Frank

[R0g22 · Accepted solution]

The premise of using DPG is to select outbound dial-peers based on the incoming dial-peer and the devices defined within the DPG rather than the destination-pattern or dial string. So the way that you have your dial-peers, if the 100 DPG is selected as the incoming dial-peer, the IOS will always select DP 50 to route the call out of the router irrespective of the fact what the destination-pattern/dial string is.

Read here -
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/configuration/cube-book/multiple-outbound-dial-peer.html

Your PSTN should not be allowing any +number dialing. You would use some sort of translations to convert your non +E.164 to +E.164 numbers. With the same premise, you would use some sort of a translations to route your outbound calls after stripping the + from the called numbers.

Now what you are trying to do is have the DPG contain your SRST dial-peers which will be your phone virtual dial-peers. You cannot add virtual dial-peers/sip lines to a DPG. The IOS will throw an error.

I know I said that DPG will work in SRST and it would but it would be a different scenario all together where you are not looking to have virtual DP's in the DPG.

[Frank Mittrup]

Hi Nipun,

now it's getting interesting.

Can you provide a concret example for DPG with SRST or is this something Cisco is just coding and not yet available?

Thanks,

Frank

[R0g22]

Did you check the link in my last post ? It talks about DPG. Check Table 1 first to ensure you have the minimum IOS requirement met.

[Frank Mittrup]

Yes, I checked this.

The DPG chapter and example is unterstood at the CUBE Configuration Guide. This chapter does not talk about SRST.

You are saying: "I know I said that DPG will work in SRST and it would but it would be a different scenario all together where you are not looking to have virtual DP's in the DPG."

That's where my last question is coming from. How does the different scenario look like?

Anyhow, the thread is getting to long now that we should come to an end :-). I'm still a fan of simple statements. Can we summerize that as of now, DPG and SRST does not work?

May I can open another thread to discuss the best practice to configure SRST with todays' CUBE feature set.

[R0g22]

Sometimes simple statements don't really explain things better. I am a fan of simple statements as well. To summarize in a simple statement, DPG and SRST will work depending upon the scenario being deployed. No hard and fast rule that it won't work at all. It's just a IOS feature like SRST.

[Frank Mittrup]

"DPG and SRST will work depending upon the scenario being deployed"?

Then it would help, if you could provide an example.

My understanding is, that SRST has virtual dial-peers.

DPG use case PSTN inbound does not work, because you can't point to those dial-peers.

DPG use case SRST outbound to PSTN does also not work becasue I'm not aware on how to config a DPG for SRST.

I just see one usecase which works - you can bypass SRST.

Anyhow, thanks for this discussion.

I will work on a concete SRST config and probably discuss this on a new thread.