Cool Topics in Networking CS144 Review Session 8 November 20, 2009 Samir Selman

Announcements Lab 5 : Due Thursday Dec 3 Final Exam: Wednesday, December 9 12:15pm - 3:15pm For those of you submitting late, contact us before your deadline if you need an additional extension. Tell us: – Where you are – How much more time you need

Today’s Cool Topics 1.Network Coding 2.Wireless Sensor Networks

Current Wireless Router C

Current Wireless Traditional Routing requires 4 time slots C

Router Current Wireless Traditional Routing requires 4 time slots C

XOR = Router Traditional Routing requires 4 time slots Network Coding C

Router Traditional Routing requires 4 time slots C

Network Coding XOR = = Router Traditional Routing requires 4 time slots With Network Coding need only 3 time slots  Higher throughput C

I - COPE  Sachin Katti, Hariharan Rahul, Wenjun Hu, Dina Katabi, Muriel Medard, and Jon Crowcroft, "XORs In The Air: Practical Wireless Network Coding," ACM SIGCOMM, 2006."XORs In The Air: Practical Wireless Network Coding,"

COPE Coding Opportunities

II- Opportunistic Routing Traditional routing chooses next hop before transmitting a packet. Poor Link Quality => Probability of chosen next hop receiving packet is low Solution: Opportunistic Routing allows any node that overhears the transmission and is closer to the destination to participate in forwarding the packet Challenge: Multiple nodes might hear a packet broadcast and unnecessarily forward the same packet.

EXOR EXOR solves this issue by tying the MAC to the Routing and imposing a strict schedule on the routers. The scheduler goes in rounds. Forwarders transmit in order, and only one forwarder is allowed to transmit at a given time. Other nodes listen to learn which packets were overheard by other nodes. Problem: This strict scheduling prevents forwarders from exploiting spatial reuse (even when multiple packets can be received by their respective receivers).

MORE  Szymon Chachulski, Michael Jennings, Sachin Katti, and Dina Katabi, "Trading Structure for Randomness in Wireless Opportunistic Routing," ACM SIGCOMM, 2007"Trading Structure for Randomness in Wireless Opportunistic Routing,"

MORE MORE solves the problem with Opportunistic Coding without tying Routing to the MAC. Instead it uses Network Coding + Randomness. Basically nodes randomly mix packets before forwarding them. This ensures the routers hearing the same transmission do not forward the same packet.

MORE - Examples Unicast Case Src sends P1,P2 Dest luckily overhears P1. Router doesn’t know what dest received (P1). In any case R can forward P1 + 2P2 Dest now has two received packets P1 P1 + 2P2 Dest can solve 2 eqns with 2 unknowns to retrieve P2. Conclusion: R only forwarded one packet instead of two =>Higher throughput

MORE - Examples Multicast Case Without Network Coding, src has to retransmit the union of the lost packets ( 4 pkts ). With Network coding can retransmit only 2 randomly coded pkts and allow all destinations to decode their respective packets. Src retransmits pa = p1+ p2 + p3 + p4, and pb= p1 + 2p2 + 3p3 + 4p4.

Analog Network Coding  Sachin Katti, Shyamnath Gollakota, and Dina Katabi, "Embracing Wireless Interference: Analog Network Coding," ACM SIGCOMM, 2007."Embracing Wireless Interference: Analog Network Coding,"

Analog Network Coding (ANC) Instead of router mixing packets… Exploit that the wireless channel naturally mixes signals Analog Network Coding

Router C

Analog Network Coding 1)Phil and David transmit simultaneously Interference C

Router Analog Network Coding 1)Phil and David transmit simultaneously 2)Router amplifies and broadcasts interfered signal C

Router Analog Network Coding 1)Phil and David transmit simultaneously 2)Router amplifies and broadcasts interfered signal 3)Phil subtracts known signal from interfered signal C

Router Analog Network Coding 1)Dina and Robert transmit simultaneously 2)Router amplifies and broadcasts interfered signal 3)Dina subtracts known signal from interfered signal Analog Network Coding requires 2 time slots  Higher throughput Analog Network Coding requires 2 time slots  Higher throughput C

It Is More Than Going From 3 To 2! Philosophical shift in dealing with interference Strategically exploit interference instead of avoiding it Promises new ways of dealing with hidden terminals

C C CC Hidden Terminal Scenario R1 R2 Src Dst

P1 Hidden Terminal Scenario C C CC R1 R2 Src Dst

P2 Hidden Terminal Scenario P1 1)Src and R 2 transmit simultaneously C C CC R1 R2 Src Dst

Hidden Terminal Scenario 1)Src and R 2 transmit simultaneously 2)R 1 subtracts P 1, which he relayed earlier to recover P 2 that he wants P1 P2 C C CC R1 R2 Src Dst

Hidden Terminal Scenario R2 and Src are hidden terminals Today : Simultaneous transmission  Collision ANC : Simultaneous transmission  Success! P1 P2 C C CC R1 R2 Src Dst

Hidden Terminal Scenario Other Benefits of ANC: First step toward addressing hidden terminals ANC extends network coding to new scenarios Other Benefits of ANC: First step toward addressing hidden terminals ANC extends network coding to new scenarios C C CC R1 R2 Src Dst

Wireless Sensor Networks 1.A sensor network is an Ad-hoc network composed of densely populated tiny electronic sensing devices. 2.Basic function of the network is to observe some phenomenon. 3.Characteristics: a.Low cost, Low power, Light weight b.Densely deployed c.Prone to failures d.Two ways of deployment: randomly, pre-determined 4.Objectives: 1.Monitor Activities 2.Gather and fuse information 3.Communicate it to special node “Base Station”.

Computer Revolution 0.5 oz, 2.25 x 1.25 x 0.25 inch 25 lb, 19.5 x 5.5 x 16 inch ~14 mW~ 64 W ~ $35~ $6K (today) 512 KB Flash160 KB Floppies 128 KB RAM KB RAM 4 MHz4.77 MHz MICAZ Mote (2005)Original IBM PC (1981)

Sensor Node Hardware Platform

Software Platform

WSN Applications

WSN protocols Protocol Requirements: 1.Energy Efficient (Maximize node lifetime) 2.Self Configuring 3.Scalable 4.Redundant 5.Efficient (less computation, less memory requirements, less energy consumption…) 6.Robust

Energy Efficiency I.Sources of Energy Consumption: 1.Communications (Transmitting & Receiving) 2.Computations 3.Sensing II.Sources of Energy Wastage in Communications: 1.Collisions 2.Overhearing 3.Idle Listening 4.Control Packets overhead 5.Over emitting

WSN Protocol Research

Questions?