Avaya 555-245-600 사용자 설명서

*0.01 second (10 ms)/8 bits/byte = 480 bytes. As the circuit size diminishes, however, care 
should be taken to never reduce the MTU below 200 bytes. Below that size, telephony signaling 
and bearer (voice) packets can also be fragmented, which reduces the link efficiency and 
degrades voice performance.

Link Fragmentation and Interleaving (LFI) is an enhancement to Multilink PPP (MLP) that 
fragments packets at the Layer 2 (PPP) level. Fragmenting at the IP layer, as with MTU 
reduction, forces the addition of a new 20-byte IP header and an 8-byte PPP header. However, 
fragmenting at the data link (PPP) layer only forces generation of an 8-byte PPP header, which 
greatly increases the efficiency of the link. 
Avaya recommends use of LFI functionality instead of MTU manipulation when transmitting IP 
Telephony packets over PPP links. As with MTU, Avaya recommends sizing packets so that the 
serialization delay is approximately 10 ms or less.

FRF.12 is a Frame Relay standard for fragmentation. It works for Frame Relay in the same way 
that LFI works for PPP, with similar increases in efficiency over MTU manipulation. When 
implementing a Frame Relay network, Avaya recommends using FRF.12 for fragmentation, and 
sizing the fragments so the serialization delay is no more than 10 ms.

RTP header compression is a mechanism that reduces the protocol overhead that is associated 
with IP Telephony audio packets. It is a function of the network, and not a function of the IP 
Telephony application. Along with the benefits of using RTP header compression, there are also 
cautions. 

on page 329 shows the anatomy of a 20-ms 

G.729 audio packet, which is recommended for use across limited bandwidth WAN links. Notice 
that two-thirds of the packet is consumed by overhead (IP, UDP, and RTP), and only one-third is 
used by the actual audio.