WiMax Operator's Manual

CHAPTER 4 ■ SETTING UP PHYSICAL INFRASTRUCTURE 67
to modify the Transmission Control Protocol/Internet Protocol (TCP/IP) data stream so as to
adapt it to the airlink. The design of such boxes is far from uniform, and in the first generation
of lower microwave equipment, a modified Data over Cable Service Interface Specification
(DOCSIS) cable data headend device was often employed. Today that approach is thoroughly
discredited, however, and indeed with the finalization of 802.16 and the production of equipment
embodying it, the network operator need not even consider such a makeshift. Generally,
the base station transceiver will be combined with the router/switch.
Second, the operator will also need an edge router whose output will go directly to the
radio transceiver, if the two are not combined in a single box. The size and power consumption
of this device will depend on the number of subscribers served. Most edge routers made today
are highly modular, consisting of a largish box with multiple slots taking a number of separate
blades, each of which handles a group of input/output (I/O) ports. The router is designed for a
certain maximum number of ports, and in most cases the operator chooses to buy additional
blades as needed until reaching the full capacity of the design. A fully loaded edge router will,
as a rule, take up several rack spaces and will have a power consumption in the kilowatts.
Carrier-grade edge routers cost thousands of dollars, but a small metropolitan network may be
able to get away with an enterprise-class router, which costs less than $1,000. In some cases, as
I have mentioned, the base transceiver will incorporate an edge router. Figure 4-1 shows a
Juniper edge router.
Figure 4-1. A Juniper edge router, courtesy of Juniper Networks
Some products that are primarily edge routers perform other functions as well, such as
creating services, inputting and outputting protocols other than IP, and providing switching
functions within those other transport protocols. Such “Swiss Army knife” network elements
are popularly known as godboxes and are intended to provide the network operator with lots of
choices and a high degree of flexibility.
The utility of such devices is a matter of some contention in the telecommunications
world today. Little uniformity exists in the design approaches embodied in godboxes, and any