Another QoS mechanism that is useful for slower link speeds is LFI which will fragment larger payload to specified fragment sizes and then interleave the smaller payloads in among the fragments, reducing then the serialization delay.

There are three primary LFI mechanisms supported by Cisco are as follows:

  • Multitlink PPP (MLP) : used on PPP links
  • FRF.12 : used on Voice over IP over Frame-Relay (VoIPovFR) links
  • FRF.11 Annex C : used on voice ov Frame-Relay (VoFR) links

In MLP mode , then you define the maximum serialisation delay that you wnat on your link and under FRF.12, you define the maximum size of the fragment that you want on your link.