Committed access rate (CAR) is an older bandwidth and policing system; however, it is commonly
used in concert with bandwidth management. As noted before, like CBWFQ, committed access
rate can specify a bandwidth guarantee to an application. However, CAR also specifies a hard
upper limit to that application as well. This can be very useful when wanting to reserve bandwidth
for bursty applications. One example of this would be file transfer with Common Internet File System
(CIFS) and other protocols on a circuit with web traffic. An administrator might wish to use
CAR to allocate 128Kbps for HTTP/web traffic, which would have the same impact as saying all
934 Chapter 30 Queuing and Compression
traffic on a T-1 except HTTP/web has over 1,400Kbps available. The advantage is that an administrator
need not define each of the other applications to implement this solution.
CAR has some benefits. However, in many enterprises with a QoS strategy, CBWFQ is
leading the way, and administrators are opting to protect important applications with the
newer technique. You should evaluate CAR and CBWFQ for your specific environment.