Beyond the Central Office

Within the telecommunications business, no common carrier or diversified service provider
can exist in splendid isolation. An isolated network is like the old narrow-gauge railways built
in mountainous areas that could not connect to major railways; a communications networks
unconnected with the outside is just as limited.
The following sections explore the various relationships that a broadband wireless service
provider must forge with other service providers in order to serve the needs of customers.
Certainly some service providers can be nothing but competitors, but many relationships
between network operators are mutually beneficial.
Ultimately, setting up a successful broadband wireless access involves a great deal more
than erecting base station towers and signing up subscribers, although certainly both processes
are essential. It involves more than establishing link budgets for all the airlinks and
frequency coordination throughout the network, though these tasks also are essential. Preeminently,
the network operator has to decide how desired content and applications are going
to be moved across the network, and that will be determined by the nature of the connections
with other networks.
In many cases, a metro network with a wireless broadband component will also have wireline
elements. The wireless network may extend the reach of a cable television, a DSL network,
or even a fiber-optic network, or the network may be truly hybrid, with wireline and wireless
parts coexisting in a rough parity. In either case, the wireless portion of the network must be
joined with one or more wireline segments.
Many 802.16 base station controller/routers have DSL and fiber-optic ports to facilitate
such connections, but if the network operator is actually operating rather than interconnecting
with a wireline network, a complete complement of appropriate hardware devices will be
required. In the case of optical networks, optical transponders and optoelectonic converters
will be needed, and in the case of DSL, DSL modem cards and aggregation devices will be necessary;
however, obviously, any discussion of the intricacies of DSL, hybrid fiber coax, or
optical network operation is far beyond the scope of this book.
Essentially, all such networks would be unified with a wireless broadband network
through the higher layers of the network, primarily at layer 3, the layer where IP routing takes
place, since all these systems would be accessible via routers. In most cases, direct translations
from one physical platform to another where routers are bypassed are not possible.
In some cases, the wireless broadband network operator will have no choice but to use a
synchronous optical network (SONET) interface to off-load traffic onto a SONET ring for transport
to an Internet exchange point or a class 4 or 5 telephone switch (or both). Such equipment
would usually be installed and owned by the service provider selling the connection to the ring.
IP and Ethernet connections to optical rings are also possible and are cheaper and simpler to
install and administer, but they are still fairly uncommon in most optical rings, because, for
good or ill, SONET still remains the established standard.