Page 64 - DCAP406_DCAP_207_Computer Networks

Unit 4: Physical Layer-2

Self Assessment Notes

Fill in the blanks:
6. The velocity of transmission of energy in free space is ........................
7. ........................ is a serious problem in microwave communication systems.

8. Satellite systems send signals high above the earth from ........................
9. The uplink frequency and the down frequency are kept different in satellite communication
systems to ........................

10. ........................ is a larger transmission line that carries data gathered from smaller lines
that interconnect with it.
11. ........................ a circular geographical area that handles cellular phones within its defined
physical boundary.
12. 10-12 GHz microwave frequency range will have maximum antenna separation in the
range of ........................ for digital transmission.

13. A cable operator usually pick ups TV signal from ........................ before distributing it to its
subscribers.

4.6 Summary

There are several kinds of transmission media. These media technologies starting from
copper wire to wireless and fiber optic has grown-up so rapidly and replacing other very
quickly in this information age. It may be seen that the Public Telephone Switched Network
(PSTN) had been evolved from the early use of coaxial cable to interconnect main centers.
Gradually, these were replaced with the use of microwave stations because of the cost of
copper and related infrastructure.

Long distance communication could be made affordable, feasible and reliable using high
microwave towers coupled with the repeater stations at specified distances. This involves
less maintenance and improved reliability because of aerial interface instead of physical
lines in the form of coaxial cables. This long distance communication was strengthened
with easy availability of omnipresent satellites in sufficient numbers. The satellite
communication has large delay problem.
Now fiber optic cables are being used as a preferred means of interconnecting main
centers together. This does not mean that these new media like fiber optic and satellite has
completely outdated conventional one. In fact, in this information age, each media is
suited to different purposes and each has their place.
Mobile communication can also be seen in the same perspective, as these services should
be available anytime at anywhere.

4.7 Keywords

Cable Modem: It works on the principle of modems and provides access to data signal sent
through the cable television infrastructure.
Cell Site: A circular geographical area that handles cellular phones within its defined physical
boundary.

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