Mid Term ReviewMid Term Review

Mid TermMid Term

• Tue, April 1– Open Book– Open papers– Open laptop

• In class exam– Duration 1hour 15 minutes

• Exam level– Not too easy, not too hard– 20% of total grade

SyllabusSyllabus

• Topic covered till March 27 (inclusive)– Basic Networking– Wireless MAC (channel, rate, antenna, 802.11 …)– Misbehavior, Channel diagnosis– WLANs, Vehicular Nets, Cellular + Ad Hoc– Ad Hoc Routing, Mesh Routing– Delay Tolerant Networks– Sensor MAC, Routing– Sensor aggregation, congestion control– Basic TCP, Wireless TCP

• Beneficial for you to attend wireless TCP classes

Approximate Exam FormatApproximate Exam Format

• Around 5 questions

• Q1. -- Set of true/false statements – You will need to justify your answer in one sentence

• Q2 to Q5 -- Topic questions with sub-parts– You may need to work out small problems– You may need to argue and/or identify flaws– You may need to give examples/counter-examples

• Questions should not require you to know paper details– You will not be asked how ESRT distinguishes between HC, LC– However, need to understand event-based congestion control

Some Focus TopicsSome Focus Topics

• Understand Elementary Basics– Transmission time, propagation delay, Q delay– CSMA/CD Vs CSMA/CA, slotted/unslotted ALOHA– Layering– Dijkstra’s, bellman ford routing on graphs– UDP/TCP, Transport schemes (stop&wait, GBN, SRQ …)

• Understand 802.11 well– Carrier sensing, Backoff, Hidden/Exposed terminals– RTS/CTS, ACK, NAV, Spatial Reuse

• Understand tradeoffs between CSMA/TDMA– Graph coloring as TDMA abstraction

Some Focus TopicsSome Focus Topics

• Directional Antennas, Multiple Channels– Beams, channels - their impact on spatial reuse– Deafness, HT, Capture, Overlapping channels

• Rate Control (RC)– Channel characteristic, Tradeoffs– Thrghput/Time fairness, Problem w/ ARF, RBAR, OAR

• Broadcast, Misbehavior, Gossip– Issues with flooding, geographic flooding – Dominated sets, Why Gossip? Smart Gossip? Issues

Some Focus TopicsSome Focus Topics

• Routing– Understand DSR, Directed Diffusion, GLS well– Routing metrics - impact on performance– Reactive vs proactive routing - when good/bad– Why ETX? Why ExOR? Tradeoffs

• Delay Tolerance– Understand the use of mobility, tradeoffs– Understand assumptions -- mobility model, density

Some Focus TopicsSome Focus Topics

• Sensor Networks– MAC: Energy Efficiency

• Why not 802.11, Tradeoffs with SMAC, TMAC• Pros/Cons with additional radio

– Routing:• Directed Diffusion behavior, issues

– Aggregation, Congestion control• Tree-based aggregation, fault-tolerance, agg.

Functions• Impact of agg. Function on energy savings• Congestion control for events - why ESRT

works/fails

Some Example QuestionsSome Example Questions

• P = prop delay, T = transmit time, L = pkt size, CS range = 2*R.– You want to ensure that every node carrier senses every

transmission on your WLAN. What is the max commuication radius of the WLAN AP.

• (T/F): Deafness can be solved by transmitting an omnidirectional RTS/CTS (but performance will be affected)

• (T/F): When the channel quality is constant, ARF performs better than RBAR (I am open to explaining to you ARF or RBAR, if necessary)

Some Example QuestionsSome Example Questions

• You are given a graph, G. Also you are told that pi > pj if i>j (I.e., p1 < p2 < p3 …). You are also told which node is the gossip originator.– (a) You will be asked to assign most efficient probabilities

to each node in G– (b) You will have to kill 3 nodes. Which 3 will you kill and

retain max reliability?– (c) Write an algorithm that takes as input N and Gp, and

shows which N nodes should be killed.

• Order the following aggregation functions in terms of energy consumption:– median, avg, min, max, mode

Some Example QuestionsSome Example Questions

• A DTN protocol X is described. You are asked:– Order which mobility model will perform best, worst

• Random walk, random waypoint, manhattan, brownian(I am open to explaining the mobility models if necessary)

– What is the problem when X runs over Rand Waypnt– Modify X to make it suitable for RW

Some Non-ExamplesSome Non-Examples

• What is the size of PLCP header?• When may DRAND not converge to a

schedule?• What is the interference function in the

paper on “partially overlapping channels …”

• How is the expected zone defined in LAR protocol?

These type of questions will not be askedThese type of questions will not be asked

Question?

BTW, Jorge Cham is coming to campus (in case you read PhD comics)

April 5, Page auditorium.

AnnouncementsAnnouncements

• Best Awards– Likely to be awarded by Cisco

• Mid-term (open book, open papers)– Tue, April 3– Do you want a review / discussion ?

• Proposal 2:– Talk about solutions– Include your proposal 1