Overprovisioning Delivery Bandwidth

By overprovisioning delivery bandwidth, we can also reduce the need to provide traffic
control mechanisms, which in turn absorb signaling bandwidth. As we start to
reduce the amount of delivery bandwidth available, we start to have to prioritize
bandwidth access—that is, provide good service to some users at the expense of other
users. Service quality becomes less consistent.
We revisit this issue when we study traffic shaping protocols in Part IV on network
software, but essentially the whole problem boils down to the fact that bursty bandwidth
is expensive bandwidth. Supporting bursty bandwidth across the radio physical
layer requires static and dynamic rate matching, which in turn absorbs signaling bandwidth,
hopefully minimizing the need to overprovision delivery bandwidth. The
OVSF code structure provides a variable allocation of code domain power—the
amount of RF power is matched to the variable information rate.

In the network, the cost of bursty bandwidth is correlated to the fact that we either
have to overprovision transmission resources or overprovision router buffer bandwidth
(or both), or we need to deploy a transport layer that can handle highly asynchronous
traffic in a deterministic fashion.
In 3GPP1, we manage highly asynchronous traffic by implementing ATM (cell
switching) across the access network. In 3GPP2, the problem is managed by overprovisioning.
3GPP1 uses smart thin pipes. 3GPP2 uses fat dumb pipes. Either way, additional
delivery cost is incurred.
Traffic in the network has traditionally been managed by a circuit switch. Adefined
route is established between two points, and the traffic is connected using a hardware
connection—a physical change of transistor state in the switch. This is inflexible but
fast and consistent. An alternative is to packet-route the traffic. Here a packet header is
read by the router, and the router software decides where the packet should be sent.
This process introduces delay and delay variability—that is, it is flexible, but slow (relative
to circuit switching) and inconsistent. 351