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296 Chapter 10: Managing Network Performance with Queuing and Compression
Foundation Topics
The process that handles the movement of data through a router is protocol dependent. With the
many variations in protocol needs and activities in the typical internetworking environment,
traffic sometimes needs to be prioritized. Anytime prioritization takes place, latency is added to
the transfer time. In addition, prioritization of critical traffic can come at the expense of less
critical traffic. This chapter explains what to do when prioritization is needed and how to decide
the degree to which prioritization should be implemented.
Along with a discussion of traffic prioritization, the topic of compression is also addressed in
this chapter. Compression is a somewhat misunderstood tool. Although compression has a
number of circumstances in which it is useful, it has just as many circumstances in which it is
detrimental.
Queuing Overview
The misconception that queuing is a necessary part of any router configuration is a topic that
needs to be dealt with straight away. As mentioned earlier, implementation of any queuing
strategy results in higher delay in the network. This happens because of a higher per packet
processor requirement. In other words, each traffic type must be sorted out and dealt with
according to the defined parameters of the queue. This is the trade-off for assuring that your
critical traffic passes through the router.
Queuing is only necessary when existing traffic flow is having problems getting through the
router. If all traffic is going through properly and no packet drops are occurring, leave it alone.
Simply put, in the absence of congestion, do not implement a queuing strategy and leave the
default setting alone. Depending on the interface type and speed, a queuing strategy might
already be in place. Again, if it works, don't change it. That point cannot be stressed enough.
There are four types of queuing discussed in this chapter:
·
First in, first out (FIFO)
·
WFQ
·
Priority queuing
·
Custom queuing
Once the queuing discussion is complete, our focus shifts to data compression techniques as
well as where and when to use them.
It may seem an obvious fact, but queuing is most effectively implemented on WAN links.
Bursty traffic and low data rates can combine to create a congestive situation that can require
administrative oversight to correct. Depending on the maximum transmission units (MTUs) of
the surrounding media, queuing is most effective when applied to links with T1 (1.544 Mbps)
or E1 (2.048 Mbps) bandwidth speeds or lower.