Posted: September 10th, 2023

ITEC851 Mobile Data Networks Assignment 1 Medium Access Control

ITEC851 Mobile Data Networks
Assignment 1
Due: Tuesday (Week 8) – 1
st of October, 2019: 2024 – Online Assignment Homework Writing Help Service By Expert Research Writers, 6 pm (Via Turnitin).
Total Marks: 70
Weighting (Value): 10%
This assignment has been designed to test the following areas:
 Medium Access Control
 Wireless LAN
 Mobile IP
1. (18 marks) A CDMA system includes two stations X and Y. The Walsh codes for
stations X and Y are (-1 1 -11 -1 1 -11) and (-1 -111 -1 -111) respectively.
a. Show the output at the receiver, if X transmits a data bit 1 and Y does not
transmit (2 marks)
b. Show the output at the receiver, if X transmits a data bit 0 and Y does not
transmit (2 marks)
c. Show the output at the receiver, if X transmits a data bit 1 and Y transmits
a data bit 1. Assume the received power from both X and Y is the same (2
marks)
d. Show the output at the receiver, if X transmits a data bit 0 and Y transmits
a data bit 1. Assume the received power from both X and Y is the same (2
marks)
e. Show the output at the receiver, if X transmits a data bit 1 and Y transmits
a data bit O. Assume the received power from both X and Y is the same (2
marks)
f. Show the output at the receiver, if X transmits a data bit 0 and Y transmits
a data bit O. Assume the received power from both X and Y is the same (2
marks)
g. Show the output at the receiver, if X transmits a data bit 1 and Y transmits
a data bit 1. Assume the received power from Y is twice the received power
from X; this can be represented by showing the received signal component
from X as consisting of elements of magnitude 1(+1, -1) and the received
signal component from Y as consisting of elements of magnitude 2 (+2, – 2)
(3 marks)
h. Show the output at the receiver, if X transmits a data bit 0 and B transmits
a data bit 1. Assume the received power from Y is twice the received power
from X (3 marks)
2. [6 marks] The dual busy tone multiple access (DBTMA) scheme splits the single
common channel into two sub-channels: a data channel and a control channel.
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Data packets are transmitted on the data channel. Control packets (RTS/CTS) are
transmitted on the control channel. Explain the rationale behind this design
principle. Identify and explain two key limitations of this scheme. (300 words)
3. [12 marks]
a. [4 marks] Identify and explain two main causes of collision in 802.11
mobile ad hoc networks. (200 words)
b. [8 marks] It is argued that using the fragmentation scheme of CSMA/CA
for data transmission results in performance improvement. Explain why?
Highlight and briefly explain a few deficiencies of this approach to data
transmission. (300 words)
4. [14 marks]
a. [8 marks] Assume there is a bidirectional transmission (e.g. DATA/ACK or
RTS/CTS/DATA/ACK) using the 802.11 protocol between a pair of nodes.
In this scenario, is it possible for a node that is currently an exposed node
to any one node in this transmitter-receiver pair, to be a hidden node when
the roles of the transmitting and receiving nodes are switched? If yes, then
explain how with the aid of an example. If no, then explain why. (400
words)
b. [6 marks] Highlight and explain the key limitations of the binary
exponential back-off (BEB) algorithm that is used in CSMA/CA. Explain
how the multiplicative increase and linear decrease (MILD) algorithm used
in the MACAW protocol can address these deficiencies. Explain why the
MILD algorithm may also suffer from performance degradation. (400
words)
5. [8 marks] Consider a novel Mobile IP scheme in which a mobile station announces
its permanent (home) IP address to agents in foreign networks. These agents, in
turn, announce this information to other routers using their regular routing
protocol update messages. What are some benefits and drawbacks of this scheme
when compared to the IETF Mobile IP scheme? (300 Words)
6. [12 marks] (Refer to figure 1) An organization has deployed a campus network
using cellular IP. The cellular IP network extends the wired infrastructure of the
campus as shown in figure 1 below. The gateways in cellular IP connect their
respective wireless segments to the wired segment. Each Base Station in the
wireless segment provides layer 3 functionality (in other words, they act as IP
forwarding engines). The campus network supports multicast routing. All the
components in the wireless part strictly adhere to cellular IP standard. Assume
that this campus network deploys a Source Based Multicast Routing scheme – a
protocol that builds source based multicast distribution trees (Refer to the
appendix for a brief explanation on Source Based Multicast Routing).
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Figure 1
A visiting mobile node MN enters the wireless network and initially gets
registered to its home network via BS1-G1 and acquires a Care of Address (CoA –
an address from the campus network address space). The CoA assigned to the MN
remains unchanged irrespective of MN’s movements within the campus network.
In other words, MN does not need to acquire a new CoA upon moving to a wireless
segment under the same or under a different gateway.
While initially at BS1, the MN joins a multicast group G whose scope is local to this
campus network (all sources, and members reside in the campus network).
Assume that hosts H1, H3, H5, and H7 are members of this group with H1 and H7
also acting as Multicast sources. Furthermore, assume that MN itself is a source
for multicast traffic. In this scenario, explain what problems can arise in multicast
communication due to MN’s mobility. (300 Words)
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Submission
You must make an online submission on ilearn via Turnitin.
Assignments will normally be marked and returned online. There are no hardcopy
submissions for written assignments.
Ensure you submit the correct file. The submission process shows you a complete
preview of your entire assignment after you have uploaded it, but before you have
submitted it. Carefully check through every single page to ensure everything is there and
the correct version has been uploaded, and only then press CONFIRM.
Multiple submissions may be possible via Turnitin prior to the final due date and time of
an assessment task. Teaching staff will use the originality report to judge whether
plagiarism has occurred and whether penalties should apply for breaches of the
Academic Honesty Policy. Any similar text identified by Turnitin will be considered
carefully to see if it is indeed a breach of the Academic Honesty Policy.
Note
 Answers must be within the specified word limit which is an absolute word limit
and no excess will be allowed.
 Assumptions (if any) must be stated clearly in your answers.
Remember, there may not be one right answer for some of the questions. Rather,
your explanations do need to present your case clearly. The explanations you
provide do not have to be long – a concise answer is preferred to a rambling one.
Assessment
For all questions in this assignment not only the contents but also the presentation will
affect your mark. You will lose marks (and not necessarily only a small portion) if there
are problems with the presentation, particularly with clarity. This means that your
answers to each question should be a coherent statement and that the spelling and
grammar of your submission will be taken into account in assessing its presentation.
For full marks, your answers should all be clear, coherent and correct, and also strictly
within the word limits.
The questions will be marked individually, the marks totalled, and a final grade assigned
that is no more than indicated by the total marks, and no more than allowed by the
standards specified above and in the unit outline.
Plagiarism
You should be well aware of the University’s plagiarism policy. In this assignment, you
must be particularly careful to avoid plagiarising your articles or any other sources of
information. It is important that you do not attempt to write your answers by pasting
together pieces of text that you find on the Internet. You need to write your own words
and phrases that express your own ideas.
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Appendix
Source Based Multicast Routing
Consider a single sender. In source based multicast Routing, the routing process builds
shortest path trees rooted at the sender. The router delivers packets to each receiver
along the shortest path. In a nutshell, it builds a shortest path spanning tree routed at the
source to all intended destinations.
Source Based Multicast Routing (SBMR) (Refer to Figure 2)
The SBMR techniques implement the Reverse Path Multicast (RPM) algorithm. The RPM
constructs an implicit spanning tree for each source.
 It accepts a packet from a source S, on link L, if L is the shortest path toward
S (Reverse Path Check)
 Uses a unicast routing table which contains shortest paths to each node in
the network
In this technique, the first packet flooded across the internetwork. The packet scope is
restricted by a TTL value. Due to flooding, all routers in the network get a copy of the
packet. Routers not having any downstream router in a multicast tree are called leaf
routers. If a leaf router has no group members on its sub-networks, a Prune message is
sent upstream to parent router (one hop up). The prune state is maintained in every
router. This process is repeated every hop upwards. These cascaded prune messages
create/truncate the original RPM tree. Prune information only held for a certain lifetime
(soft state). A Graft message is sent to quickly recover back a previous pruned branch. It
cancels out the previously received prune message. Graft cascades reliably hop by hop
toward the source. Due to this graft and prune feature, messages are forwarded on only
by those links leading to a group member.
Figure 2

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