Page 124 of 378 ITG Engineering Guidelines
553-3001-202 Standard 1.00 April 2000
Reduce hop count
End-to-end delay can be reduced significantly by reducing hop count,
especially on hops that traverse WAN links. Thes e are some of the ways to
reduce hop count:
• Attach the T-LAN directly to th e WAN router
• Improve meshing. Add links to help improve meshing; adding a link
from router1 to router4 in the previous example might
cause the routing protocol to use that new link, ther eby redu cing the hop
count by two.
• Node reduction. You can connect colocated nodes into one larger and
more powerful router.
These guidelines affect the whole i ntranet, as they tam per with network
architecture, design and policies. To proce ed with this involves considering
cost, political and IP design issues, topics which are bey ond the s cope of thi s
document.
Adjust jitter buffer size
The jitter buffer parameters directly affect the end-to-end del ay. Lowering the
voice playout settings decrease s one-way del ay, but the de crease c omes at th e
cost of giving less waiting time for voice packets that arrive late. Refer to
“ITG Trunk DSP profile settings” on page135 for guidelines for re-sizing the
jitter buffer.
Reduce packet errors
Packet errors in intranets are general ly correl ated with conges tion somewhe re
in the network. Bottleneck links occur where the packet errors are high
because packets get dropped when t hey arriv e faster t han the link can transm it
them. The task of upgrading highly utilized links can remove the source of
packet errors on a particular flow. Also an effort to reduce hop count gives
fewer opportunities for routers and links to drop packets.
Other causes of packet errors not related to queueing delay are as follows:
• Poor link quality. The underlying circuit may have transmission
problems, high line error rates, subject to freque nt outages, etc. Note that
the circuit may be provisioned on top of other services, such as X.25,
frame relay or ATM. Check with the service provider for information.