Applying LFI on Multilink PPP for Real-Time Traffic(VOIP)

LFI stands for Link Fragmentation and interleaving is not of QoS mechanism. However, it is help for real-time traffic such as VOIP on small size of link. LFI on Multilink PPP allows large packets to be fragmented into a small size to fit a minimum delay requirement for real-time traffic. Also, interleaving function provides a special transmit queue for the high priority traffic can be sent earlier than others.

1. Configuring LFI on Multilink PPP

Router-LFI-1#conf t
Router-LFI-1(config)# interface multilink 1
Router-LFI-1(config-if)# ppp multilink fragment delay 10 ; 10ms for VOIP delay requirement
Router-LFI-1(config-if)# ppp multilink interleave
Router-LFI-1(config-if)# ip address 1.1.1.1 255.255.255.0
Router-LFI-1(config-if)# bandwidth 1536 ; Specify for auto fragmentation calculation
Router-LFI-1(config-if)# ppp multilink endpoint hostname

Router-LFI-1(config-if)# interface serial1/0
Router-LFI-1(config-if)# encapsulation ppp
Router-LFI-1(config-if)# ppp multilink group 1

 

 

interface Multilink1
 bandwidth 1536
 ip address 1.1.1.1 255.255.255.0
 ppp multilink
 ppp multilink fragment delay 10
 ppp multilink interleave
 ppp multilink group 1
end
 

interface Serial1/0
 no ip address
 encapsulation ppp
 serial restart-delay 0
 ppp multilink
 ppp multilink group 1
end
 

 ** setup on both side of router

 2. Verifying

Router-LFI-1# sh ppp multilink active

Multilink1, bundle name is Router-LFI-2
  Endpoint discriminator is Router-LFI-2
  Bundle up for 00:00:27, total bandwidth 1544, load 1/255
  Receive buffer limit 12000 bytes, frag timeout 1000 ms
  Interleaving disabled
    0/0 fragments/bytes in reassembly list
    0 lost fragments, 0 reordered
    0/0 discarded fragments/bytes, 0 lost received
    0x6 received sequence, 0x6 sent sequence
  Member links: 1 active, 0 inactive (max not set, min not set)
    Se1/0, since 00:00:27, 1930 weight, 1496 frag size
 
Router-LFI-1# sh int multilink 1
Multilink1 is up, line protocol is up
  Hardware is multilink group interface
  Internet address is 1.1.1.1/24
  MTU 1500 bytes, BW 1536 Kbit, DLY 100000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation PPP, LCP Open, multilink Open
  Open: IPCP, CDPCP, loopback not set
  Keepalive set (10 sec)
  DTR is pulsed for 2 seconds on reset
  Last input 00:00:41, output never, output hang never
  Last clearing of "show interface" counters 00:26:24
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     37 packets input, 8104 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     37 packets output, 8318 bytes, 0 underruns
     0 output errors, 0 collisions, 2 interface resets
     0 unknown protocol drops
     0 output buffer failures, 0 output buffers swapped out
     0 carrier transitions
Router-LFI-1#

Router-LFI-1# sh ppp multilink interface multilink 1

Multilink1, bundle name is Router-LFI-2
  Endpoint discriminator is Router-LFI-2
  Bundle up for 00:07:37, total bandwidth 1544, load 1/255
  Receive buffer limit 12000 bytes, frag timeout 1000 ms
  Interleaving disabled
    0/0 fragments/bytes in reassembly list
    0 lost fragments, 0 reordered
    0/0 discarded fragments/bytes, 0 lost received
    0xD received sequence, 0xD sent sequence
  Member links: 1 active, 0 inactive (max not set, min not set)
    Se1/0, since 00:07:37, 1930 weight, 1496 frag size