LFI – Fragmentation

Fragmentation may be necessary for latency-sensitive traffic
Serialization delay = frame-size (bits) / link-bw (bps)

1500byte frame(12,000bits) takes 12,000/65,000 seconds to serialize or roughly 214ms
1500*8 = 12000/56000 = .214 * 1000 (1000ms in 1 sec)= 214ms

LFI is a feature of MLPPP, i.e. = PPPoFR

FRF.12 done with frame-relay map class:
Map-class frame-relay mlp
– Frame-relay cir 64000
– Frame-relay bc 640
– Frame-relay be 0
– Frame-relay fragmentation (#bytes)
– No frame-relay adaptive-shaping

Common fragmentation sizes (These are geared for 10ms packet size *VOICE*):
– 64k -> 80 byte fragments
– 128k -> 160 byte fragments
– 512k -> 640 byte fragments
– 768k -> 1000 byte fragments

Make sure to consider length of the data-link headers and trailers when choosing the size of the fragments:
1500-byte packet has 9 bytes of FR header and trailer, makes 1509-byte frame, FRF.12 adds 2 bytes of header to manage fragments, which makes fragments 511 bytes each in length…

MLP LFI (mutlilink ppp):
Max-delay * bandwidth
bandwidth = bandwidth interface command
Max-delay = ppp multilink fragment-delay
56kbps with 10ms max-delay, 56000 * .01 = 560 bits / 8 = 70bytes

MLP LFI config:
interface Multilink10
ip address
ppp multilink
ppp multilink fragment delay 10
ppp multilink interleave
ppp multilink group 10
interface Serial0/0
bandwidth 56
no ip address
encapsulation ppp
ppp multilink
ppp multilink group 10

FRF.12 config:
interface Serial0/0
bandwidth 128
ip address
encapsulation frame-relay
no fair-queue
frame-relay class shape-all-64
frame-relay traffic-shaping
map-class frame-relay shape-all-64
frame-relay fragment 160 (in bytes) (128kbps implies 10ms of serialization delay)
frame-relay traffic-rate 64000 64000
frame-relay fair-queue


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