Cisco Support Community
Community Member

Qos Over frame Relay

Dear support,

I have two routers connected togather back-to-back and configured as frame-relay connection .

One is Cisco2503 with IOS 12.2 (3) and the other is Cisco 2501 with 12.1 (1).

I mad the configuration of the Qos on the 2503 successfully but on the 2501, the FR.12 didn't work ( i mean the router refused the command ) and the two routers didn't see it each other until i deleted the "fragment command from the 2503 router" why is that ????

the router 2501 has 8 MB flash and 4 mb DRAM, does he want an upgrade for the IOS ( with its memory conf. what IOS is suitable )??

If i didn't use the FR.12 command , the Qos of the voice over ip will be harmed ???

Why the routers didn't see each other when enabling the Fr.12 on one of them??

I have another problem, i want to make the router suffers from data transfer and i test the quality of voice in that situation , how can i monitor from the router the quality of voice and how can make the router suffers from data transfer ( i mean, the router gives request time out and the voice is very clear !! )

Please i need ur help on this case very badely ...

thanks a lot ,..waiting for ur reply

Cisco Employee

Re: Qos Over frame Relay


According to feature navigator (, FRF.12 on the 2500 is not supported until 12.1(2)T. The fragment command needs to be on both routers. If you are running voice and data at speeds of

Hope this helps.

Community Member

Re: Qos Over frame Relay

After upgrading the IOS of the router and applying the FR.12 feature on both sites,will the Qos of voice work perfectly on a link 64kbps frame-relay with huge ammount of data ( database application running o nboth sites ) ?

Cisco Employee

Re: Qos Over frame Relay

I would get more bandwidth for this type of application. If you are doing database operations over a 64k pipe, you are asking for trouble(IMHO).

But if you REALLY want to put voice on there too it can be done. You will either need a seperate PVC for the voice traffic to to proritize the voice traffic over the data traffic in the output queueing scheme. Use the 'ip rtp priority' command to do this. You will need to fragment down to 80bytes on this speed will be very slow for data.

Community Member

Re: Qos Over frame Relay

i am using the LLQ method ( matching with the access-list command using the H.323 udp ports and signaling 1720 port )with cRTP on the serial and fragmentation FR.12 , exact like the example of the Qos over frame-relay documentation..Is it enough for the voice to have nice quality in the real traffic time of the database??

Another problem, when doing traffic shaping and fragmentation FR.12 and pinging during a data transfer, it suppose to give the same ammount of time in each ping signal but i found that the pinging time varies between very larg ammount and return to low time, why ??? I tryied the fragmentation on the PPP Qos of voice example and it was really great..

Community Member

Re: Qos Over frame Relay

The more consistant time would be for the traffic in the priority queue. The pings may be in the default queue and contending with the data transfer. In your message you said you were placing the H.323 UDP ports and the 1720 signaling port traffic. Your ping traffic probably is not in the prioirty queue.

Community Member

Re: Qos Over frame Relay

If I remember correctly, I had to be at 12.1(5T) before I could get the QoS to work. I would recommend the upgrade. As for why they did work together. The fragmentation on both ends has to match for them to communicate. You've sliced large packets in to little pieces and the other side needs to know what size so they can be reassembled.

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