Nortel Meridian ITG Line 2.0 Description, Installation And Operation Manual page 82

Page 82 of 302 IP Network engineering guidelines
553-3001-204 Preliminary 0.10 August 2000
To determine which links should be considered for upgrading, first list all the
intranet links used to support the ITG traffic, which can be derived from the
traceroute output for each site pair. Then, using the intranet link utilization
report, note the highest utilized and/or the slowest links. Estimate the link
delay of suspect links using the traceroute results.
Example: a 256kbps link from router1 to router 2 has a high utilization. The
following is a traceroute output that traverses this link:
ITG_Node1% traceroute SubnetA
traceroute to SubnetA (10.3.2.7), 30 hops max, 32
byte packets
router1 (10.8.0.1) 1 ms 1 ms
router2 (10.18.0.2) 42 ms
router3 (10.28.0.3) 78 ms
router4 (10.3.0.1) 92 ms
SubnetA (10.3.2.7) 94 ms
The average rtt time on the example link is about 40 ms; the one-way link
delay is about 20 ms, of which the circuit transmission and serialization delay
are just a few milliseconds. Most of this link's delay is due to queueing.
Reducing hop count
The ITG Line 2.0 card nodes must be connected to the intranet to minimize
the number of router hops between Meridian 1s, assuming adequate
bandwidth on the WAN links for the shorter route. This will reduce the fixed
and variable IP packet delay, and improve the Voice over IP Quality of
Service. It is recommended that no more than one card utilize a particular
10BaseT LAN collision domain, provided that the preferred codec
throughout the ITG network is set to G.729 AB with 30 ms default payload
size.
Note: In a passive Ethernet hub, all ports on the hub share one 10Mbps
collision domain; in a switched Ethernet hub, each port has its own
collision domain.
1 ms
44 ms 38 ms
70 ms 81 ms
90 ms 101 ms
97 ms 95 ms