Transcript Addressing, Routing, and Forwarding

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
Router
C
Traditional Routing requires 4 time slots
Current Wireless
Router
C
Traditional Routing requires 4 time slots
Network Coding
Router
C
XOR =
Traditional Routing requires 4 time slots
Network Coding
Router
C
Traditional Routing requires 4 time slots
Network Coding
Router
C
XOR
=
XOR
Traditional Routing requires 4 time slots
With Network Coding need only 3 time slots
 Higher throughput
=
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.
COPE Coding Opportunities
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
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.
Analog Network Coding
Instead of router mixing packets…
Exploit that the wireless channel naturally mixes
signals
Analog Network Coding (ANC)
Analog Network Coding
Router
C
Analog Network Coding
Router
C
Interference
1) Phil and David transmit simultaneously
Analog Network Coding
Router
C
1) Phil and David transmit simultaneously
2) Router amplifies and broadcasts interfered signal
Analog Network Coding
Router
C
1) Phil and David transmit simultaneously
2) Router amplifies and broadcasts interfered signal
3) Phil subtracts known signal from interfered signal
Analog Network Coding
Router
C
1) Dina Network
and RobertCoding
transmitrequires
simultaneously
Analog
2 time slots
2) Router amplifies
and broadcasts
interfered signal
Higher
throughput
3) Dina subtracts known signal from interfered signal
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
Hidden Terminal Scenario
C
Src
C
R1
C
R2
C
Dst
Hidden Terminal Scenario
C
Src
P1
C
R1
C
R2
C
Dst
Hidden Terminal Scenario
C
Src
P2
C
R1
C
R2
P1
1) Src and R2 transmit simultaneously
C
Dst
Hidden Terminal Scenario
C
Src
C
R2
C
R1
P1
C
Dst
P2
1) Src and R2 transmit simultaneously
2) R1 subtracts P1, which he relayed earlier to
recover P2 that he wants
Hidden Terminal Scenario
C
Src
C
R2
C
R1
P1
C
Dst
P2
R2 and Src are hidden terminals
Today : Simultaneous transmission  Collision
ANC : Simultaneous transmission  Success!
Hidden Terminal Scenario
C
Src
C
R1
C
R2
C
Dst
Other Benefits of ANC:
First step toward addressing hidden terminals
ANC extends network coding to new scenarios
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.
b.
c.
d.
Low cost, Low power, Light weight
Densely deployed
Prone to failures
Two ways of deployment: randomly, pre-determined
4. Objectives:
1.
2.
3.
Monitor Activities
Gather and fuse information
Communicate it to special node “Base Station”.
Computer Revolution
Original IBM PC (1981)
MICAZ Mote (2005)
4.77 MHz
4 MHz
16-256 KB RAM
128 KB RAM
160 KB Floppies
512 KB Flash
~ $6K (today)
~ $35
~ 64 W
~14 mW
25 lb, 19.5 x 5.5 x 16 inch
0.5 oz, 2.25 x 1.25 x 0.25 inch
Sensor Node Hardware Platform
Software Platform
WSN Applications
WSN Applications
WSN Applications
WSN Applications
WSN Applications
WSN protocols
Protocol Requirements:
1.
2.
3.
4.
5.
Energy Efficient (Maximize node lifetime)
Self Configuring
Scalable
Redundant
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.
2.
3.
4.
5.
Collisions
Overhearing
Idle Listening
Control Packets overhead
Over emitting
WSN Protocol Research
Questions?