Protocol Performance

You also need to be able to qualify protocol performance. We add traffic shaping protocols
to manage the allocation of radio and network resources when demand on those
resources at times exceeds supply. Traffic shaping protocols, however, absorb bandwidth,
which means they can make matters worse. One solution is to overprovision
radio and network bandwidth so that peak demands can always be serviced. However,
as bandwidth becomes increasingly bursty, this becomes more difficult. The burstier
the bandwidth, the higher the peak loads you need to accommodate and the more you
will have to overprovision.
So you use traffic shaping protocols. Figure 14.1 shows the protocol stack. The properties
of the offered traffic (bandwidth quantity and quality requirements) may be
determined at the application layer. For example, the MPEG encoder output may
describe what radio layer and network layer QoS is needed, or QoS may be determined
at the presentation layer. XML, for instance, defines the QoS requirements needed for
transaction processing. It is an information protocol and as such is able to determine
and request QoS needs.

Moving down the protocol stack, session persistency may be defined by RSVP, Diffserv,
MPLS, and SIP (all of which we study in Chapter 17). Whether the traffic stream
is isochronous or non-isochronous is determined in the transport layer and network
layer (TCP/IP). Finally, radio admission is contingent on the MAC layer and allocation
of physical radio resources. Admission control is congestion-driven in the network and
interference-driven over the radio physical layer.
It is the job of the protocols in the protocol stack to preserve session value—specifically,
session consistency in a persistent session and session properties, particularly the timedependent
properties of a rich media exchange. 337