Is Low MTU (ie 320) for VoIP over Frame-relay can be used to avoid serialization delay for large data packets?

Question

In order to provide voice quality for VoIP, is FR fragmentation equivalent to lowering the MTU size for the serial subinterface of a Frame relay subinterface?
Is there any isues like stop communications, using Low MTU ?

Answer 1

If the router belongs to any of the
platform listed below, then use
FRF12 for you fragmentation. The MTU size
lowering also works but this can cause a high over
head as it can't be specified on a per dlci level.
With multiple dlci i.e. subinterfaces use per dlci fragmentation.. this helps reduce the overhead of changing the MTU size of the physical interface.
Snip config example.( __Must be configured on both side of the termination___)
PHONE [phone]---ROUTERA ----DLCI 100----ROUTERB ---PHONE [phone]
ROUTER A
dial-peer voice 1 voip
destination-pettern 2T
session target ipv4:10.10.10.2
int ser 0/0
encap frame-relay
frame-relay traffic-shaping
no ip address
interface serial0/0.1 point-to-point
ip add 10.10.10.1 255.255.255.252
frame-relay interface-dlci 100
class voice
map-class frame-relay voice
frame cir 64000
frame bc 640
frame mincir 64000
frame-relay ip rtp priority 16384 16383 48
frame fragment 80
frame fair-queue 64 256 0
ROUTER B
dial-peer voice 3 voip
destination-pettern 3T
session target ipv4:10.10.10.1
int ser 0/0
encap frame-relay
frame-relay traffic-shaping
no ip address
interface serial0/0.1 point-to-point
ip add 10.10.10.2 255.255.255.252
frame-relay interface-dlci 100
class voice
map-class frame-relay voice
frame cir 64000
frame bc 640
frame mincir 64000
frame-relay ip rtp priority 16384 16383 48
frame fragment 80
frame fair-queue 64 256 0
This should help if your router is
c2600, c3600, mc3810, c7200, c1750
all running the right level of IOS.
12.1(5)T and above should work well.