QoS question

[gserghiou]

Hi all,

My workplace is moving to a new building, and they are having a new telephony system installed. This system will communicate with another system via a FR connection.

The FR will be 2Mbps but this will serve for both data and telephony needs. I guess´voice traffic´ will flow from one IP address (first tel system) to a second IP address (second tel system). I assume that an RJ 45 cable will connect the tel systems to a switch, and that in turn to the router.

The setup , in term of cisco hardware will be the following :

Site A:

-------

tel system ->cisco 2950 switch ->cisco 1721 router ->FR

Site B:

-------

tel system ->cisco 2950 switch ->cisco 3745 router ->FR

I would like to limit the bandwidth available to the telephone system traffic, and at the same time give it highest priority so that voice conversations dont jitter.

Is it necessary to configure both the switches and routers at both ends or just the routers ??

Also any tips or amterial (URL) of how to do this would be appreciated.

Thanks,

George

[Georg Pauwen]

Hello,

you might want to try LLQ in order to prioritize your voice traffic.

The configuration would look like this:

interface Serial0

frame-relay interface-dlci 102

class VoFR

!

map-class frame-relay VoFR

service-policy output VoIP

!

class-map match-all Voice

match access-group Voice_Priority

!

policy-map VoIP

class Voice

priority percent 25

!

ip access-list extended Voice_Priority

permit tcp any any eq 1720

permit udp any any range 16384 32767

I am not 100% sure if that is the complete syntax. Make sure you have this configured on both sides of the Frame Relay link.

One other thing: which IP Telephony system are you using ? I am asking because Cisco IP Phones by default mark their traffic with precedence 5. If you use Cisco phones, you dould also match the traffic on precedence instead of the access list, provided that nothing else has a precedence of 5.

Your best source of information is the CCO online documentation, check this link (you might need a CCO login):

Cisco IOS Voice Configuration Library

http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123cgcr/vcl.htm

Regards,

GP

[gserghiou]

Hi GP,

The telephony system is a Siemens HiPath 3750.

Two Siemens VoIP cards will be installed on the two telephony systems so that they can communicate their voice traffic as IP traffic.

I have spoken to the technician who is to install the new system and he is not sure how and if the packets are marked for priority.

He is actually going on a 3-day course on this subject and he should be able to help me more when he comes back.

Nevertheless, suppose that I dont worry about what type of packet it is, so that i can prioritise it, can i assign priority to an IP Address, so that each packet arriving with a specific source or destination IP address get the priority ??

Also can i configure something similar to the switch, to prioritize traffic on a particular interface(the interface that the tel system will connect on ?)

I hope i make my question clear to you,

Thanks,

George

[Georg Pauwen]

Hello George,

if you want to prioritize traffic from a source IP to a destination IP, you can use the same principle, just add the IP addresses to the access-list that is matched in the class, instead of the udp ports.

As I said, I do not know if the Siemens phones default their traffic to a precedence value, but if so, you can use the interface command 'mls qos trust cos' to tell the switch to just accept any precedence value it receives.

HTH,

GP