Dr$.$ Ashraf S$.$ Mahmoud

Problem $1(10$ points$)$: In the context of framing, answer the following questions very briefly:

a$)(4$ points$)$ Assume byte stuffing is used. $(1)$ What is the result of stuffing the following data frame:

A$-$B$-$FLAG$-$ESC$-$ESC$-$FLAG$-$C$-$FLAG$-$FLAG$-$D

$(2)$ What is the overhead ratio? Define overhead as ratio of number of added $($not data$)$ bytes to

number of all bytes in the new stuffed frame

b$)(2$ points$)$ What would the worst overhead percentage for this byte stuffing method? Justify your

answer.

c$)(4$ points$)$ Assume bit stuffing is used and a frame, containing a $16-$bit checksum, is corrupted with

errors, where bits can be lost, inserted, or altered. If the original data field contains the string

$01111110$ somewhere around the middle of the frame, as shown

$[----$segment $1$ of frame$---01111110-----$segment $2$ of frame$--$checksum$]$

$(1)$ What kind of error can occur in the stuffed frame and make segment $1$ be interpreted as complete

frame? $(2)$ Compute the probability of accepting this new frame as a correct frame given the checksum

requirements?

Problem $2(10$ points$)$: Similar to Textbook problem $10-$ Page $252.$

Consider the original $8-$bit message represented by $0$ xE$5$ to be encoded using Hamming code.

a$)(5$ points$)$ Determine the number of parity bits needed $r$ and encode the message. Specify the

generated code word in Hex.

b$)(5$ points$)$ Assume bit $2($i$.$e$.$ B$2)$ is flipped to simulate a single bit error. Show syndrome

calculations.

#Computer Networks question$($Book NAME:COMPUTER NETWORKS. FIFTH EDITION. ANDREW S$.$ TANENBAUM$)$