Telephone Switches

Dec 03,2006 00:00 by admin
Telephone services were commonly offered by the first-generation millimeter wave wireless
operators but seldom to date by networks operating in the lower microwave regions. Chapter 7
covers voice telephony and the protocols and equipment required to implement it, but here I
will venture a few words as to how telephone switches figure into the central office environment.
In traditional local exchanges, the switch was the primary piece of hardware occupying
the central office. In broadband networks where the emphasis is on data, switches are of secondary
importance and are lacking in many networks.
As I stated earlier, I do not think provisioning circuit telephone services is a good business
for a wireless broadband operator to enter, particularly a startup with limited financial
resources. Class 5 circuit switches cost millions of dollars, and, considering that most wireless
broadband networks start small and remain fairly small, acquiring at most a few thousand subscribers,
paying millions of dollars for a device that is likely to yield a few dollars per subscriber
per month simply does not make economic sense—not in a highly competitive service environment
where infrastructure equipment has a far shorter life span than in the past. The full
return on investment for a class 5 switch would require decades, by which time it would be
completely obsolete. Also, given that telephone switches are not designed to interface with
radios and that complex procedures for mapping voice channels onto airlinks, providing dial
tone and ring tones, and assigning telephone numbers are required, the prospect of doing circuit
voice appears distinctly uninviting—except perhaps in developing nations in regions
where wireline telephone services are completely unavailable (such fixed wireless telephone
services are known as wireless local loop). Cable operators, for reasons best known to themselves,
have frequently offered circuit voice, and they have had to put in complete cable
telephony hardware and software platforms to enable such services as well as the aforementioned
class 5 switches. If anything, circuit over broadband wireless is even more problematic.