QoS with TDM phones (CS1000E)

[DutchExport]

We have two WAN connected CS1000E PBX's with TDM phones (no IP phones) on both sides. The vendor that installed the PBX tells me that the voice traffic between both will be marked CS5 instead of EF (expedited forwarding) and that this is how it works with TDM phones (IP phones will do EF for voice media). We have an outstanding question with Nortel about this, however no satisfactory answer yet! Haven't been able to find any specific documentation concerning TDM and QoS, only IP telephony related (IP phones). This seems very odd to me that the voice media gets the same priority as the system control traffic with the PBX's, obviously I can remark the voice to EF.....but like to understand the WHY? first. Anybody???

 

[pronei]

If you are using H323 or SIP trunks to connect the 2 sites, QoS would be recommended, however I run almost all my sites without QoS as my network traffic never even spikes anywhere near bandwidth capacity.

Anyway, if you're using VOIP trunks to connect the 2 PBX's QoS would be useful to you, especially if the link between the 2 sites is heavily saturated.

If you're using just a simple DTI/PRI to connect the 2 PBX's, you will not need QoS.

 

[DutchExport]

Two PBX systems are communicating across a MPLS network, which does require QoS to deal with congestion and priority (LLQ). My question relates to the DSCP marking for voice media across the trunk (Nortel proprietary) between both CS1000E's.

 

[pronei]

I've only used Diffserv EF when I'm concerned with traffic congestion in an IP end to end solution.

I am assuming you have only an NRS configured and a CPPM Signaling Server or COTS server connected to each CS1000E.

Using TDM, the only voice traffic you are going to have is from ELAN to ELAN running through the signaling servers only.

Did your vendor perform any kind of MPLS traffic study to support Precedence 5 (CS5) tagging?

Perhaps your MPLS circuit is just not busy enough to warrant QoS data structuring, or you are not spanning VLANs across your MPLS circuit or you just had a vendor who didn't quite understand how QoS works.

 

[DutchExport]

Actually I am the network engineer responsible for the configuration of QoS in our network. What I don't understand is that fact that the vendor claims that in a TDM configuration the voice media is always marked CS5 across the trunk. While I can certainly mark this to up to EF on my routers, I am wondering if this is something you can specify on the trunks in the Nortel configuration (Element Manager)? This is not really a problem just something that I would like to understand as I will pump the traffic to EF on our MPLS network even if the standard is CS5....doesn't make any sense to me why you would want to share control, signaling and voice media in a non-priority queue.

 

[pronei]

You can not specify on the trunks however, you can specific in the node configuration.

All your voip routes will be configured with a Node ID.

The config for that Node ID can be found in Element Manager.

There you will be able to specify 802.1q tagging and priorities for your control and voice packets.

 

[pronei]

Check NTPs
NN43100-500
NN43001-260

Those will help explain QoS in a Nortel environment.

 

[teekow]

all voip rtp traffic is marked by default as EF (dscp 46) and all signaling is CS5 (dscp 40)......it can be changed to other values, but it would be odd to do that........one thing you don't mention is how the CS1000E's are connected. I assume it is via virtual trunks and not a T1. If so, then your traffic is probably being marked as EF and that is what you should be setting up your routers to prioritize. The easiest thing to do is mirror the switch port from your CS1000E and start a sniffer trace to see what the packets are marked as.

good luck
rob

 

[phones1]

tdm/ IP qos: you may be running tdm @ both end but using ip inbetween. in the node config you specify the DSCP (46 voice payload 40 for messaging) you can also enable 802.1 p/q. this by default is set to 6. your data network needs to A: recognise the DCSP value (layer3) or trust the 802.1 value & route to the appropiate Que. The CS doesn't mark the packets as CS5 nor would it ever mak it as EF.

Remember if it doesn't work hit it harder

Scott UK

 

[Zwinter]

You could have your MPLS provider mark the VoIP traffic by the access list at the CE router. I am running various VoIP configurations across NA and have experienced many QOS problems.

 

[DutchExport]

We mark the traffic and the provider trusts our DSCP markings through the MPLS network.

Latest response from the installer:

Where the issue lies is that you are not seeing Diffserv 46, and we are using TDM phones, rather than IP phones. It is our belief, and XXXXX has had a discussion with Nortel of this, that the TDM sets are being marked at Diffserv 40 because they are not originating from IP sets. Nortel’s policy is they handle 40 and 46 equally in their policy.

Does this make any sense?

 

[pbxn]

In your OTM/TM, what are the codec's set to? Is it G.711 or G.729?
In the NTP's it lists Expected QoS levels under the G.729.
Here is how my main site is setup.

G.729AB, Fax (it also shows the .711 but 729 is actually checked)
Control Pkts 46 (this is the CS3 values)
Voice Pkts 24 (I believe this is where you will find DSCP EF)
Voice Payload
30
60
120

 

[DutchExport]

Codecs configured are 711 and T38 FAX.

I have access to OTM, however if you are referring to the 'VGW and IP phone codec profile' and its codec options none of them relate to QoS. Where do I configure this relationship??

 

[pbxn]

In your OTM, look for ITG related items. Open your main site, and there should be I think 4 ITG related choices. You may have to open each one dependent on how your ITG's are configured.

 

[DutchExport]

Sorry I said OTM but meant 'CS1000 Element Manager'.

 

[DutchExport]

While I have the ITG options in OTM they show up empty when selecting them. The vendor told me it's because this has been taking out of the newer versions as ITG is no longer used??? They had no explanation on what replaced it.

 

[pbxn]

Huh?
I think your vendor is trying to sell you lake front property in the middle of the desert.
I have a 4.5 rls. switch with ITG's configured, and I am running on TM 3.0 (next upgrade from OTM)
All my remote sites run off of ITG's cards and I do all my management changes through my TM. I think they (your vendor) never took the time to configure your OTM with the ITG info.
If you know your ITG IP address', mask's, etc you may want to try to add a site in your OTM.

 

[xtract]

only few use ITG now for the new system as they already has signalling server to run NRS,it is better to use IP Peer instead of ITG trunking

 

[DutchExport]

That makes sense from what I am seeing in OTM. With that being the case though where do you tie together codecs and users (IP or TDM phones)with certain QoS markings? I still have a hard time believing that Nortel marks TDM-to-TDM (in essence media gateway to media gateway) voice traffic with DSCP 40 instead of 46 (Vendor tells me that is because Nortel think of these as 'legacy' equipment, however none of the documents state this).

 

[PBX77]

You say that these are two CS1000 switches. That’s a pretty large network. Is it really two Switches, or one switch across a campus? That would make sense that you don’t have ITG cards if it is one Switch that is connected across a campus, utilizing campus distributed MG1000E’s.

ITG’s can still be used, but are not a preferred method, as the Signaling Server and media gateways are more efficient at distributing the traffic across the network and don’t use trunks. These really are two different design concepts, one using ITG which is the old method, and one using Media Gateways and the Signaling Server which is the newer method and more efficient and preferred method.