Frame Relay Forum specification FRF.12 defines how to fragment large Frame Relay packets into smaller packets. This is necessary on slower WAN links that are also carrying voice or video data. Voice and video data are both very sensitive to delay, whereas "normal" data packets just need to get to the far end intact.
If a large data packet is sent out over a slow WAN link it could "hog up" the link and cause unacceptable amounts of delay for either the voice or video stream. For example, on a 64K Frame Relay link, if a 1500 byte data packet has just been sent, it will take almost 200 milliseconds to transmit. Voice circuits can tolerate (at most) 150 milliseconds of delay before quality suffers.
To enable the FRF.12 Fragmentation, click the Advanced button when setting up a Frame Relay Data Link. This will bring up the Advanced Frame Relay options window. Click on the Use FRF.12 Fragmentation box, then set both the Max TX PDU Size and Max RX PDU Size.
Note that smaller PDU sizes help audio quality, but can reduce total throughput of the system.
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