Best Efforts Networks

Best Efforts Networks
In a
best efforts network
, as illustrated in Figure 20.5, data is transmitted in the hope (an expectation)
that it will be delivered. It’s similar to the mail system. You write your letter, address it,
and put it in the mailbox. And that’s it. You hope (and expect) that it will be delivered, but it’s
out of your control. If something goes wrong with the system, your mail is undelivered. And you
may not even know that it failed to get through!
IP network
(variable latency,
jitter, best efforts,
per-hop behavior)
Si
Si
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IP phones may be directly attached to the switch, or connected to a LAN-attached PC.
Ingress routers
(packets marked for
priority queuing;
dissimilar data rates at
LAN/WAN boundary
contribute to buffer
delays and drops)
Campus switches
(variable length
frames forwarded
using best efforts
mechanisms,
modified by simple
prioritization)
Understanding the Fundamentals of QoS
643
FIGURE 2 0 . 5
Best efforts packets
Of course, if the mail system were truly unreliable, you would complain loudly and eventually
stop using it, so it can’t be all that bad or it wouldn’t still exist. But because there is no reliability
built in, we refer to it as unreliable.
Under these circumstances, there are two choices open to us. We can either live with the
unreliability, or try to do something about it.