VOIP over frame relay problems

[admin_2]

I have installed two 1750 routers with FR 5 Link. I can talk clearly in the beginning of the conversation and during about 8 minutes, but after that time at one side cannot hear the other one. The side with problems can not hear because the voice is so interrupted. I already read the cisco document "VoIP over Frame Relay with Quality of Service" and i have these results :

I cannot applicate the RTP header compression because the FR compresion is IETF.

I can not use Frame-Relay Fragment 80 because I cannot use FR12.

I used Frame-relay cir 64000

Frame-relay BC 640

I do not hear anything in both sides, but if I use

Fram-relay BC 64000

I have the problem in one side after a few minutes.

[#2]

First question will be if the FR link is carrying also

data packets.

If yes the fragmentation and prioritization of voice

packets is mandatory for a correct voice traffic

handling.

If no you should pay attention to the FR infrastructure and

check if the delays over the FR are constant (no jitter).