LLQ And VoIP over Frame Relay

[dgrizzard]

I will be putting in a 1720 in a new office that will be using a voip connection back to our meridian 1 PBX. I've been looking over various forums and documents on cisco.com and I cant seem to get either the right configuration(conflicting examples) or a good example of what I'll need to do in my case. Can someone give me an config example of what I'll need to do or point me to a good example? Here will be the current config of the 1720 in respect to the interfaces with no access-lists or anything else setup as of yet, and I'll be using eigrp. If you would like to email me directly, pls email dgrizzard at floridaortho dot com.

!
interface Serial0
description SouthBrandon PT Circuit
no ip address
encapsulation frame-relay IETF
shutdown
no fair-queue
service-module t1 timeslots 1-24
frame-relay lmi-type ansi
!
interface Serial0.1 multipoint
description Frame Relay link to Telecom
ip address x.x.x.x x.x.x.x
ip directed-broadcast
no arp frame-relay
frame-relay map ip x.x.x.x 16 broadcast
frame-relay interface-dlci 16

Also regarding some of the commands in the config(since our current IT staff inherited all the routers setup already this will be our first new router setup on the network) what does the frame-relay interface-dlci XXX command do, and what significance is the number(is it just a grouping like with ac-groups?).


Also, what do these commands do?

service-module t1 timeslots 1-24
frame-relay lmi-type ansi

TIA,
Daniel

 

[jneiberger]

The service-module command tells your internal CSU/DSU that it is connected to a full T1 circuit, i.e. all 24 channels.

LMI is the management protocol used between frame relay endpoints and frame relay switches, and there are a couple of flavors. In this case, you're specifically instructing your router to use ANSI LMI when talking to its frame relay switch.

Here's a pretty good link from CCO:

http://www.cisco.com/warp/public/788/voice-qos/voip-ov-fr-qos.html

That pretty much describes what you need to do:

1. Configure LLQ in order to provide a high priority, low latency queue for voice traffic

2. Configure IP RTP header compression (be careful here. If you're using Nortel VoIP gear, some of their older software breaks cRTP)

3. Configure Frame Relay Traffic Shaping so that you *never* burst above your Committed Information Rate, at least if you want to maximize voice quality. Anything over your CIR might experience additional queueing and delays within the frame relay cloud. It's best to stay under your CIR.

4. Unless you have a reason to do so, I'd suggest using a point-to-point subinterface instead of a multipoint subinterface. In fact, although I'm not sure of this, you probably need to do that anyway in order to apply the LLQ and FRTS config and get the results you expect. Possibly not, but you might as well do it.

 

[dgrizzard]

Thanks, it looks like that configuration checked out ok, the only things that wont work it looks like are the IP RTP header compression since Im using 12.0(3). Wont know if it works completely until I actually hook everything up at the office, but so far so good.

Also, regarding commited burst(bc), this office will start of with a frac. T1 of 768k CIR. What would be a good BC to use, and what would be a good priority speed in kbps for voice-traffic? I'll be using a nortel 9150 remote office that will connect with our meridian 1, so all voip traffic will just come from that device, with about 5-8 phones in that office for right now.

TIA again

 

[jneiberger]

12.0(3)?? I don't think that IOS supports LLQ. You'd better make sure of that. If you can't do LLQ or cRTP then you might be happy with the end result. You could try priority queueing but that can causes more headaches than it solves.

If you have a 768k CIR, you could use these settings assuming that you won't have all eight phones in use at the same time:

class-map match-any voicecalls
match access-group name voicelist
!
policy-map voice
class voicecalls
priority 192
class class-default
fair-queue
random-detect
!
map-class frame-relay VoIP-768k
no frame-relay adaptive-shaping
frame-relay cir 768000
frame-relay bc 7680
frame-relay be 0
frame-relay mincir 768000
service-policy output voice
!
interface Serial0/0
frame-relay traffic-shaping
!
interface Serial0/0.1 point-to-point
frame-relay interface-dlci 16
class VoIP-768k
!
ip access-list extended voicelist
permit ip host [ip address of Nortel system]

 

[dgrizzard]

I followed the directions on the CCO pretty much exactly, and all the commands work except the first set, it was a little different. For class-map match-any "name" the match-any part wasn't a valid command so it was just class-map "name".I dont know if that means the LLQ worked or not, maybe you could tell me?

Also, with the:

ip access-list extended voicelist
permit ip host [ip address of Nortel system]

Is that going on my serial subinterface?

TIA

 

[jneiberger]

The access list is used to build your class-map. It defines the IP address of your voice system.

If you were able to enter the "priority" command in your policy map then you are configuring LLQ. I didn't think LLQ became available until 12.1. Weird.

 

[dgrizzard]

Ah I see about the access-list voicelist now, I was using the 102 103 numbering, confused me for a second. I got it now. Thanks again for the help, I'll know in the next month or 2 if everything works right

 

[dgrizzard]

One more question... in what you suggested you have the priority at 192, if Im using G.711 then I'll be using 64kbps per call/fax transmission, so for 5 simultaneous calls minimum would I want to set the priority to 320 since all originating voip transmissions come from just one device?

TIA

 

[jneiberger]

If you're going to use G.711 then you would want to increase the size of the priority queue. But do you really need G.711? G.729 sounds very nearly as good as G.711 without the huge bandwidth hit.

 

[dgrizzard]

I'll test out G.711 and G.729A/Fax to see if there is any noticeable quality difference, thanks again.