cs601 assignment no 4

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Assignment No. 04 Fall 2010 CS601- Data Communication Total Marks: 15
Due Date: 18/01/2011

Instructions
Please read the following instructions carefully before solving & submitting assignment: It should be clear that your assignment will not get any credit (zero marks) if:
• The assignment is submitted after due date.
• The submitted assignment does not open or file corrupt.
• The assignment is copied (from other student or ditto copy from handouts or internet).
• Student ID is not mentioned in the assignment File or name of file is other than student ID.
• The assignment file must be MS word .doc file.
For any query about the assignment, contact at cs601@vu.edu.pk

Marks: 20

Question 1: [10]
Compare digital services with analog services. Give at least 5 points for each? Question 2: [5]
A signal travels through a transmission medium and its power is reduces to one forth calculate the Attenuation?
Lectures Covered: This assignment covers Lecture # 27- 32 Deadline
Your assignment must be uploaded/submitted till Tuesday 18th Jan, 2011.

[Xpert]

These are two solutions given by vu student. Please make changes.

[Xpert]

ANS
Telephone companies started providing their subscription with analog services using analog network.
Later on Digital services were took their place. Nowadays carriers are thinking about changing their service lines digital too.
Analog services
These services are of two kinds
1-switch analog services
2-Analog leased services
1- Analog services are poor, slow and unreliable.
2- They often encountered problem during a call.
3- The net work it joins is called PSTN.
4- Its bandwidth is usually lies between 0 to 4000Hz.
5- It uses twisted pair cable to connect subscriber’s phone to the network via exchange.
6- It is cheaper then Digital services.
7- In these services call is conveyed through switched lines or dedicated lines.
Digital services
These services are largely offered nowadays because these are less sensitive of noise than analog.
These services are of three kinds.
1-switched/56
2-DDS
3-DS
1- Digital services provide better sound quality, fast and reliable services.
2- These are less sensitive than analog because signals are digital and noise is analog so can be separated easily.
3- Provide data rate 56 kbps to 128 Mbps.
4- Use twisted pair cable, coaxial cable and fiber optical.
5- These are expensive.




Q2.
ANS

Let us consider a signal with an initial intensity of I, that travels through a medium and the final intensity is F. I have considered an electromagnetic signal moving through an appropriate medium.
The attenuation is expressed in terms of decibels and given by the formula:
Attenuation = 10* log (I / F)
In the question the signal travelling through the transmission medium loses 3/4 of its power.
If the initial power was I, the final power is I/4.
Substituting this in the formula for attenuation we get:
Attenuation = 10 * log (I / (I/4))
=> 10* log (4I/I)
=> 10* log 4
=> 10*0.6020
=> 6.02
Therefore the attenuation is 6.02 dB.