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CSCI 415 Computer Networks
Homework 4
Due 03/12/08
Saad Mneimneh
Hunter College of CUNY
Problem 1: Sliding window algorithm
The sliding window algorithm with unbounded sequence numbers is given in
the notes. Upon receiving an
RN
, the sender checks if
RN > SN
and slides
the window. Similarly, upon receiving an
SN
, the receiver checks if
SN
=
RN
and slides the window. Describe the modiﬁcations needed (if any) for these two
rules when the sequence numbers are sent modulo
p
(bounded).
Problem 2: Modulus without FIFO
Assume that a sliding window algorithm is used but the FIFO property does
not hold. Instead, consider only frames that are sent and received (possibly
with error). If a frame is the
i
th
frame sent and the
j
th
frame received, then

i

j
 ≤
K
. Note that when
K
= 0, we have the FIFO property.
Here’s an example scenario with
K
= 3.
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
(a) Show that if the receiver receives
SN
at time
t
, then
RN
(
t
)

n

K
≤
SN
≤
RN
(
t
) +
n

1
(b) Show that if the sender receives
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This note was uploaded on 03/27/2010 for the course CSCI 415 taught by Professor Saadmneimneh during the Spring '08 term at CUNY Hunter.
 Spring '08
 SaadMneimneh
 Computer Networks

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