Fragmentation
Issue 3.4.1 June 2005
323
Thus, the complete configuration for Frame Relay traffic shaping looks like:
map-class frame-relay NoBurst
no frame-relay adaptive shaping
frame-relay cir 384000! (for a 384K CIR)
frame-relay mincir 384000
frame-relay be 0
frame-relay bc 3840
interface serial 0
frame-relay class NoBurst
Fragmentation
One large cause of delay and jitter across WAN links is serialization delay, or the time that it
takes to put a packet on a wire. For example, a 1500-byte FTP packet takes approximately
214 ms to be fed onto a 56-Kbps circuit. For optimal voice performance, the maximum
serialization delay should be close to 10 ms. Thus, it can be problematic for a voice packet to
wait for a large data packet over a slow circuit. The solution to this problem is to fragment the
large data packet into smaller pieces for propagation. If a smaller voice packet comes in, it can
be squeezed between the data packet fragments and be transmitted within a short period of
time.
The sections that follow discuss some of the more common fragmentation techniques:
●
MTU
●
LFI
●
FRF.12
MTU
The maximum transmission unit (MTU) is the longest packet (in bytes) that can be transmitted
by an interface without fragmentation. Reducing the MTU on an interface forces a router to
fragment the large packet at the IP level. This allows smaller voice packets to squeeze through
in a timelier manner.
The drawback to this method is that it increases overhead and processor occupancy. For every
fragment, a new IP header must be generated, which adds 20 bytes of data. If the MTU is
1,500 bytes, the overhead is approximately 1.3%. If the MTU is shortened to 200 bytes,
however, the overhead increases to 10%. In addition, shortening the MTU to force
fragmentation increases processor utilization on both the router and the end host that needs to
reassemble the packet.
Summary of Contents for Application Solutions
Page 1: ...Avaya Application Solutions IP Telephony Deployment Guide 555 245 600 Issue 3 4 1 June 2005 ...
Page 20: ...About This Book 20 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 21: ...Issue 3 4 1 June 2005 21 Section 1 Avaya Application Solutions product guide ...
Page 22: ...22 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 106: ...Call processing 106 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 124: ...Avaya LAN switching products 124 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 139: ...Issue 3 4 1 June 2005 139 Section 2 Deploying IP Telephony ...
Page 140: ...140 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 186: ...Traffic engineering 186 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 204: ...Security 204 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 228: ...Avaya Integrated Management 228 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 274: ...Reliability and Recovery 274 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 275: ...Issue 3 4 1 June 2005 275 Section 3 Getting the IP network ready for telephony ...
Page 276: ...276 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 356: ...Network recovery 356 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 366: ...Network assessment offer 366 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 367: ...Issue 3 4 1 June 2005 367 Appendixes ...
Page 368: ...Appendixes 368 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 394: ...Access list 394 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 414: ...DHCP TFTP 414 Avaya Application Solutions IP Telephony Deployment Guide ...