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Page 124 of 378
Reduce hop count
Adjust jitter buffer size
Reduce packet errors
553-3001-202
Standard 1.00
ITG Engineering Guidelines
End-to-end delay can be reduced significantly by reducing hop count,
especially on hops that traverse WAN links. These are some of the ways to
reduce hop count:
•
Attach the T-LAN directly to the WAN router
•
Improve meshing. Add links to help improve meshing; adding a link
from router1 to router4 in the previous
cause the routing protocol to use that new link, thereby reducing the hop
count by two.
•
Node reduction. You can connect colocated nodes into one larger and
more powerful router.
These guidelines affect the whole intranet, as they tamper with network
architecture, design and policies. To proceed with this involves considering
cost, political and IP design issues, topics which are beyond the scope of this
document.
The jitter buffer parameters directly affect the end-to-end delay. Lowering the
voice playout settings decreases one-way delay, but the decrease comes at the
cost of giving less waiting time for voice packets that arrive late. Refer to
"ITG Trunk DSP profile settings" on page 135 for guidelines for re-sizing the
jitter buffer.
Packet errors in intranets are generally correlated with congestion somewhere
in the network. Bottleneck links occur where the packet errors are high
because packets get dropped when they arrive faster than the link can transmit
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 frequent 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.
April 2000
97,.074:90
example might
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