642-642 QOS VIDEO TRAINING: Link Efficiency Tools

Link Efficiency Tools


Two Major Types:

Payload Compression – Through CODECs and traditional compression types:

TCP Header Compression

-Compress TCP headers

RTP Header Compression (cRTP)

– Compress RTP Headers – Suppresses/caches information in header of 40 byte to 2-4 bytes.

Enabling Header Compression

Voice Activity Detection – Any silence on the line and no data will be sent.

Header Compression has to be enabled.

show voice call summary (Will show the codec being used also)

Create a class map to match RTP – MATCHRTP

Create a policy map called COMPRESSVOICE to use the class Match RTP and enable compression:

compression header ip rtp

Under the physical interface apply the service policy:

service-policy output COMPRESSVOICE

*Has to be set at both ends!

show ip rtp header-compression (int optional)

Offers lots of statistics such as efficiency

show policy-map int Serial0/0

Compress voice details also found here such as the hit ratio.

Link Fragmentation + Interleaving (LFI)


Serialisation Delay – Delay from router to the wire of 214ms on a 56k Serial line


Enabling LFI

PPP and Frame Relay only not HDLC

ATM connections already does this for us.

Homework on multilink interfaces? Creating a group and bundling physical interfaces into 1 logical group.

ppp multilink fragment delay VALUE (Router will work out the size of the packet based on this value)

ppp multilink interleave (Will not splice in voice, just cut up into fragments)

show ppp multilink

Frame Relay interfaces use a map class configuration:

map-class frame-relay NAME

frame-relay fragment SIZE (is not as clever as a PPP style cfg, you have to set the size of the fragments manually using the chart as a reference)