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Silver

QOS & H.323 Trunk

Hello All,

I have integrated a CCM 5.1 (Main Office) with an Avaya S8400 G3 (Branch Office)using H.323 trunk connected directly from CCM to Avaya PBX over the WAN (T1). Everything seems to work fine except the audio quality. The average round trip ping reply is btw 100-120 which is quiet acceptable. We are using Cisco 2800 series routers in both ends. There's no Voice Vlan configured in the branch office. I though QOS may help to improve the situation. How am I going to prioritize the Voice traffic over data with H.323 Trunk? Any idea/config sample would be appreciated.

Thaks,

33 REPLIES

Re: QOS & H.323 Trunk

Silver

Re: QOS & H.323 Trunk

Wow, that was a pretty deep QOS training class my friend.

So back to my case, as I am using direct H.323 trunk, is the following what I need to configure in both end routers?

H323:

access-list 121 permit tcp any host 1.1.1.1 range 1718 1720

access-list 121 permit tcp any host 1.1.1.1 range 11000 - 11999

class-map match-any voice-rtp-nbar

match protocol rtp audio

Thanks,

Re: QOS & H.323 Trunk

Yes you would do something like this:

class-map match-any voice-rtp-nbar

match protocol rtp audio

class-map match-any voice-signaling

match access-group 121

policy-map

class voice-rtp-nbar

priority percent 40

class voice-signaling

priority percent 5

That would give you a pretty basic voice QoS. Depending on your link bandwidth, how many phones etc, you would want to play with those values.

-nick

Silver

Re: QOS & H.323 Trunk

Thanks Nick,

As of monday, I am starting to integrate another site which is anotehr Avaya S8400 G3. The site is connected to the Main site through Frame relay (FR). At the branch site we have a Catalyst 3750 L3 capable which is connected to the provider FR router. Can I use the same QOS config in the Catalyst 3750 as well? If not, what would be the best way to implement QOS in the 3750 end?

Thanks,

Re: QOS & H.323 Trunk

On the 3750 I would just use Auto QoS. Generally unless you have a large switched network and you're moving a lot of traffic, switch QoS will not affect much.

But no, the 3750 will use switched MLS QoS, and not routed QoS.

-nick

Re: QOS & H.323 Trunk

Hi Nick

why you used LLQ for signalling while garnteed bandwidth should be enough and better for signalling as it is not sensitive as VOIP ?

thanks

Re: QOS & H.323 Trunk

A few things on this:

1) For simplicity's sake.

2) I tend to see a lot of implementations where voice is the only important data going over the link, especially for remote sites. In this case, it may be better to prioritize the voice traffic.

3) Depending on your other data, voice signaling may still be more important, and some of the signaling is more delay sensitive that you would expect. Example: Pressing transfer on a IP phone requires a number of messages to be passed, including to/from the gateway for a PSTN call, and the cumulative delay of these messages equals the delay on the IP phone when the user gets a response.

4) For troubleshooting voice problems, I prefer not to spare any chance

If you're in a situation where the difference between a bandwidth command and a priority command is making a significant difference, you most likely need a fatter uplink anyways.

-nick

Silver

Re: QOS & H.323 Trunk

Hello Nick,

I was going to implement the QOS solution that you provided below. In the Cisco side we have a 2821 (data) router and in the Avaya side we have a 2610 (data) router. The IOS in the 2610 is : IOS (tm) C2600 Software (C2600-IS-M), Version 12.1(11), RELEASE SOFTWARE (fc1). I was thinking of upgrading the IOS to the c2600-advipservicesk9-mz.124-15.T8 in order to get better flexibility in implementing the modular QOS. The bandwidth btw HQ and Branch office is 10M. I am planning to have 5 simultaneous H.323 calls over the WAN. Do you think I can use the exact config that you sent me or do I need to play a bit with the priority percentage?

The Bandwidth utilization is over 90% all the time. Do you think implementing QOS will help to provide better voice quality?

QOS Config

class-map match-any voice-rtp-nbar

match protocol rtp audio

class-map match-any voice-signaling

match access-group 121

policy-map

class voice-rtp-nbar

priority percent 40

class voice-signaling

priority percent 5

Thanks,

MK

Re: QOS & H.323 Trunk

Hi MK,

Hopefully with a 10M connection you won't need much QoS at all. QoS should only really kick in when there is congestion, and you'll need a lot of traffic to fill up a 10 Mb pipe.

If you do G.711 you'll want to allocate around 80kb/sec per call.

For 5 calls this is 200 Kb/sec.

Thus, you would change your 'priority percent 40' to 'priority 200'.

You can also change your signaling to 'priority 15'.

For that few phones you shouldn't need to allocate 4 MB/sec, etc.

hth,

nick

Silver

Re: QOS & H.323 Trunk

I am sorry nick, I made a big mistake here. The bandwidth is a T1 and not 10M. Sorry for the mistake. Does it change the config a lot?

Do you recommand the upgrade to the new IOS version that I mentionned above?

Thanks,

MK

Re: QOS & H.323 Trunk

Hi MK,

I highly suggest moving from 12.1 code to 12.4 code. The commands we're discussing don't even exist in that code.

I would keep the same priority commands followed by the kbps.

If you want some more exact values, you can use the bandwidth calculator:

http://tools.cisco.com/Support/VBC/do/CodecCalc1.do

hth,

nick

Silver

Re: QOS & H.323 Trunk

Thanks Nick,

Let's say we have only one VLAN and all data and Voice are in the same VLAN. If a packet is not classified and marked in the switch, how a router knows which packet is voice and which one is data. My question may sound stupid but the reason that I am asking this is because I don't have access to the switches in the Branch office (more than 500 switches). All I have is access to the router. Would that be possible to priorotize a packet only in layer 3 without doing any layer 2 classification and marking. If so, how the router knows which packet is voice and which is data?

Thanks,

Re: QOS & H.323 Trunk

Hi MK,

If you look at the post I linked in the first post I went over some of these things.

Basically if you can't trust that the DSCP markings are going to be maintained you can do one of two things:

1) Match on an ACL for UDP on the voice range

2) Match with NBAR 'match protocol' command.

The ACL runs the risk of matching non-voice traffic as nothing prevents other applications from using those ports (16384-32767). This is layer 3+4

NBAR takes up processor resources reading the packets, but will give you a more accurate matching. This is layer 4+7.

hth,

nick

Silver

Re: QOS & H.323 Trunk

Thanks Nick,

Here's my very last question;

I have two router is 2 different sites. One is point to point and the other one is MPLS. I guess the QOS configuration would be enough for the one with Point to point link but do we need to do anything in the provider router with the one with MPLS connection?

When we priorotize a voice packet over the data, would the packet follow the same order in the MPLS network to the destination?

Thanks,

Re: QOS & H.323 Trunk

Hi MK,

The QoS you apply on your interface is only for packets in the buffer of that interface. Once they leave that interface it is up to the provider to prevent dropping them or prioritizing them.

The only way to let the provider to know how to treat the traffic is the DSCP byte. You will want an agreement with your provider for voice marked with EF DSCP. Most providers have this ability.

hth,

nick

Silver

Re: QOS & H.323 Trunk

Thanks Nick, I appreciate your assistance :-)

Silver

Re: QOS & H.323 Trunk

Hello Nick,

I am implementing Meeting Place Express for the same above customer. The MPE will be replacing the Conference calls provided by Bell and WEBEX (Destop Sharing)provided by Cisco. Would the following QOS config be enough? Could you please advise if I need additional QOS configuration for MPE? As you advised, I am going to use NBAR. The following is the current CPU utilization.

router#sh processes cpu

CPU utilization for five seconds: 13%/12%; one minute: 15%; five minutes: 14%

Would you still recommand to use NBAR?

QOS Configuration:

class-map match-any voice-rtp-nbar

match protocol rtp audio

class-map match-any voice-signaling

match access-group 121

policy-map

class voice-rtp-nbar

priority percent 40

class voice-signaling

priority percent 5

Thanks,

MK

Re: QOS & H.323 Trunk

Hi MK,

That policy looks fine. The best way to determine an appropriate bandwidth amount is by using the online calculator:

http://tools.cisco.com/Support/VBC/do/CodecCalc1.do

The CPU utilization is fine - there is nothing to worry about until you're edging near 90%.

-nick

Silver

Re: QOS & H.323 Trunk

Nick,

My worry is about the Web Conferencing. We have 20 sites world wide and the helpdesk will be using MPE to access the desktop of the users within the company all around the world. Our T1's utilization are about 85%. My question is; do I need extra QOS setting for the WEB Conference?

Thanks,

MK

Re: QOS & H.323 Trunk

Hi MK,

This is a question I can't really answer for you. You would need to do the numbers and figure out the maximum amount of calls you would have on this T1, and then figure out how much bandwidth is needed.

If this is a T1 that supports a voice-only site with no data traffic, you can pretty safely put 90-95% for the voice priority class.

This is really dependent on what else you need to accomplish.

-nick

Silver

Re: QOS & H.323 Trunk

Nick,

My question is not about voice, I am asking for Web Conference. Do I need any additional QOS settings for Web Conference to prioritize it over regular data traffic?

Re: QOS & H.323 Trunk

This depends on how your web conference talks to your other network devices. You would want to find out if it's H323 / SIP and then classify that as signaling traffic, and ensure you have enough bandwidth for those messages.

It's probably H323 if it's an IP solution.

-nick

Silver

Re: QOS & H.323 Trunk

Yes, it is H.323. I guess, I am going to be ok with the same QOS setting. Am I mistaken?

Thanks,

MK

Re: QOS & H.323 Trunk

Hi MK,

If you're worried, you can always get a packet capture and actually see what's on the wire. Most conferencing servers are going to consist of H323 and RTP, and that's about it. Unless there are some proprietary protocols at hand, there shouldn't be other protocols to worry about.

-nick

Silver

Re: QOS & H.323 Trunk

Thanks Nick

Silver

Re: QOS & H.323 Trunk

I am sorry Nick but I have got one more question. The following QOS config has to be done in both edge routers, right?

class-map match-any voice-rtp-nbar

match protocol rtp audio

class-map match-any voice-signaling

match access-group 121

policy-map

class voice-rtp-nbar

priority percent 40

class voice-signaling

priority percent 5

H323:

access-list 121 permit tcp any host 1.1.1.1 range 1718 1720

access-list 121 permit tcp any host 1.1.1.1 range 11000 - 11999

Also, instead of 1.1.1.1 IP Address in the ACL, I need to put the CCM IP Address in the CCM side router and the Avay PBX IP Address in the Avaya side router. Is that right? I am using a direct H.323 trunk btw CCM and the Avay PBX.

MK

Re: QOS & H.323 Trunk

QoS will only really be used when there is contention for the port / tx-ring.

Best practice says you want it on both sides, as they are both protecting different sides of the circuit.

-nick

Silver

Re: QOS & H.323 Trunk

Thanks again,

So the 1.1.1.1 in ACL will be replaced by the IP Address of the CCM?

Re: QOS & H.323 Trunk

The second IP address is the destination. On the remote site you use the CCM address, and on the main site you use the avaya address.

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