1. Network: Non Traditional Routing
Y. Richard Yang
4/4/2011

2. Recap: Traditional Routing Protocols
Proactive protocols
distance vector
e.g., DSDV
link state
link reversal
e.g., partial link reversal, TORA
Reactive (on-demand) protocols
DSR
AODV A E D C B F 2 1 3 5

3. Summary: Traditional Routing
Implicit assumptions in traditional routing
a graph representation of underlying network
point-to-point graph, edges with costs
select a lowest-cost route for a src-dest pair
commit to a specific route before forwarding
each node forwards a received packet as it is to next hop

4. Motivating Scenarios

5. Motivating Scenario
Src A sends 1 packet to dst B; src B sends packet 3 to dst A
The network needs to transmit 4 packets
Motivating question: can we do better? p1 p1 1 2 3 p3 p3

6. Key Question
How to explore path diversity and wireless broadcast opportunities?

7. Outline Admin. Non-traditional routing motivation
network coding: exploiting network broadcast

8. Opportunistic Network Coding
If R has both packets 1 and 3, it can combine them and explore coding and broadcast nature of wireless p1 p1 1 2 3 p3 p3

9. Opportunistic Coding: Basic Idea
Each node looks at the packets available in its buffer, and those its neighbors’ buffers
It selects a set of packets, computes the XOR of the selected packets, and broadcasts the XOR

10. Opportunistic Coding

11. Outline Admin. Non-traditional routing motivation
network coding: exploiting network broadcast
opportunistic routing: broadcast and path div.

12. Key Issue in Opportunistic Routing
Key Issue: opportunistic forwarding may lead to duplicates.

13. Extreme Opportunistic Routing (ExOR)
Basic idea: avoid duplicates by scheduling
Instead of choosing a fix sequential path (e.g., src->B->D->dst), the source chooses a list of forwarders (a forwarder list in the packets) using ETX-like metric
a background process collects ETX information via periodic link-state flooding
Forwarders are prioritized by ETX-like metric to the destination

14. ExOR: Forwarding Group packets into batches
The highest priority forwarder transmits when the batch ends
The remaining forwarders transmit in prioritized order
each forwarder forwards packets it receives yet not received by higher priority forwarders
status collected by batch map

15. Batch Map
Batch map indicates, for each packet in a batch, the highest-priority node known to have received a copy of that packet

16. ExOR: Example N2 N0 N3 N1

17. ExOR: Stopping Rule
A nodes stops sending the remaining packets in the batch if its batch map indicates over 90% of this batch has been received by higher priority nodes
the remaining packets transferred with traditional routing

18. Evaluations 65 Node pairs 1.0MByte file transfer
1 Mbit/s bit rate
1 KByte packets
EXOR bacth size 100
1 kilometer

19. Evaluation: 2x Overall Improvement
1.0
0.8
0.6
Cumulative Fraction of Node Pairs
0.4
0.2
ExOR
Traditional
spend a little more time on the 240 x say this is just for the median, and it’s a factor of 2!
200
400
600
800
Throughput (Kbits/sec)
Median throughputs: Kbits/sec for ExOR,
121 Kbits/sec for Traditional

20. OR uses links in parallel
possible question – why are there only 7 forwarders.(just say we thin out...)
ExOR
7 forwarders
18 links
Traditional Routing
3 forwarders
4 links

21. OR moves packets farther
58% of Traditional Routing transmissions
0.6
ExOR
Traditional Routing
Fraction of Transmissions
0.2
25% of ExOR transmissions
0.1
lower is better. right circle – using lots of longer links, sum them up and it’s 25%. so, like ex 1, using lots of long links. zeros: before many packets made no progress, with exor at least some.
100
200
300
400
500
600
700
800
900
1000
Distance (meters)
ExOR average: 422 meters/transmission
Traditional Routing average: 205 meters/tx

22. Comments: ExOR Pros Cons
takes advantage of link diversity (the probabilistic reception) to increase the throughput
does not require changes in the MAC layer
can cope well with unreliable wireless medium
Cons
scheduling is hard to scale in large networks
overhead in packet header (batch info)
batches increase delay

23. Outline Admin. Non-traditional routing motivation
network coding: exploiting network broadcast
opportunistic routing
ExOR
MORE

24. MORE: MAC-independent Opportunistic Routing & Encoding
Basic idea:
Replace node coordination with network coding
Trading structured scheduler for random packets combination
Previous network coding technique is for inter-flow
MORE is for intra-flow network coding

25. Basic Idea: Source Chooses a list of forwarders (e.g., using ETX)
Breaks up file into K packets (p1, p2, …, pK)
Generate random packets
MORE header includes the code vector [cj1, cj2, …cjK] for coded packet pj’

26. Basic Idea: Forwarder Check if in the list of forwarders
Check if linearly independent of new packet with existing packet
Re-coding and forward

27. Basic Idea: Destination
Decode
Send ACK back to src if success

28. Key Practical Question: How many packets does a forwarder send?
Compute zi: the expected number of times that forwarder i should forward each packet

29. Computes zs
Єij: loss probability of the link between i and j
Compute zs so that at least one forwarder that is closer to destination is expected to have received the packet :

30. Compute zj for forwarder j
Only need to forward packets that are
received by j
sent by forwarders who are further from destination
not received by any forwarder who is closer to destination

31. Compute zj for forwarder j
To guarantee at least one forwarder closer to d receives the packet

32. Evaluations 20 nodes distributed in a indoor building
Path between nodes are 1 ~ 5 hops in length
Loss rate is 0% ~ 60%; average 27%

33. Throughput

34. Summary: Opportunistic Routing
Basic idea:
Take advantage of spatial diversity
Key issue
Avoid redundancy and interference
Techniques
ExOR: coordination
MORE: coordination -> random network coding

35. Opportunistic Routing  50 transmissions
Problem of MORE R1
99% (10-3 BER)
Loss 0% S D
Loss 0%
99% (10-3 BER) R2
Opportunistic Routing  50 transmissions

36. MIXIT: Revisiting Link/ Network API
PHY + LL
Deliver correct symbols to higher layer
Network
Forward correct symbols to destination R1 S P1 P1 P2 R2 P2 P1 P2

37. Key Question: What Should Each Router Forward?P1 P1 P2 R2 P2 P1 P2

38. Key Question: What Should Each Router Forward?P1 P2 P1 P1 P2 R2 P2 P1 P2 P1 P2
Forward everything  Inefficient

39. Symbol Level Network CodingP1 P2 P1 R2 P2 P1 P2
Forward random combinations of correct symbols

40. Symbol Level Network Coding… … D R2 … …
Routers create random combinations of correct symbols

41. Symbol Level Network Coding… D R2 …
Solve 2
equations
Destination decodes by solving linear equations

42. Symbol Level Network Coding… … D R2 … …
Routers create random combinations of correct symbols

43. Symbol Level Network Coding… D R2 …
Solve 2
equations
Destination decodes by solving linear equations

44. Problem: Mixed Correct and Incorrect Symbols
Original Packets

45. Destination needs to know which combinations it received
Use run length encoding
Original Packets
Coded Packet

46. Destination needs to know which combinations it received
Use run length encoding
Original Packets
Coded Packet

47. Destination needs to know which combinations it received
Use run length encoding
Original Packets
Coded Packet

48. Destination needs to know which combinations it received
Use run length encoding
Original Packets
Coded Packet

49. Destination needs to know which combinations it received
Use run length encoding

50. Evaluation Implementation on GNURadio SDR and USRP
Zigbee (IEEE ) link layer
25 node indoor testbed, random flows
Compared to:
Shortest path routing based on ETX
MORE: Packet-level opportunistic routing

51. Throughput Comparison
CDF
2.1x
MIXIT 3x
MORE
Shortest Path
Throughput (Kbps)

52. Outline
Admin.
Non-traditinoal routing
Transport overview

53. Transport Layer vs. Network Layer
Provide logical communication between app’ processes
Transport protocols run in end systems
Transport vs. network layer services:
network layer
data transfer between end systems
transport layer
data transfer between processes
relies on, enhances, network layer services
application
transport
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
logical end-end transport
network
data link
physical
network
data link
physical
application
transport
network
data link
physical

54. Transport Layer Services and Protocols
Transport services
multiplexing/demultiplexing
flow control
reliable data transfer
congestion/rate control
Transport protocols in the Internet
UDP
TCP

55. Key Challenge in Transport: Rate /Congestion Control
router 3
router 5
flow 1
5 Mbps
20 Mbps
10 Mbps
flow 2 (5 Mbps)
20 Mbps
5 Mbps
router 1
router 2
router 4
router 6
Assume
flow 2 fixed at 5 Mbps
no retransmission
the link from router 1 to router 2 has finite buffer
sending rate by flow 1 (Mbps)
throughput of flows 1 & 2 (Mbps) 5 10
when packet dropped at the link from router 2 to router 5, the upstream transmission from router 1 to router 2 used for that packet was wasted!

56. TCP Reliability/Rate Control
End-to-end, sliding window-based reliability
Use the AIMD algorithm to adjust the sliding window size dynamically
after receiving an ACK for a packet, increase cwin by 1/cwin
if any loss, reduce cwin to half
cwnd w

57. TCP/Reno: Cwin Q: Is TCP rate control effective in wireless networks?
cwnd
Loss
Loss
Time
congestion
avoidance
congestion
avoidance
congestion
avoidance
Q: Is TCP rate control effective in wireless networks?

58. TCP/Reno Throughput as a Function of Loss Rate
Given mean packet loss rate p, mean round-trip time RTT, packet size S

59. Example Assume a TCP flow with S = 1000 bits, RTT = 10 ms
Assume the link bandwidth is 11 Mbps
If there is only one flow, then the (congestion) loss rate to fully utilize the link
Assume a wireless network with packet (corruption) loss rate of 4%,
then the maximum achievable rate using TCP/Reno is 700 Kbps
If we increase RTT = 200 ms (satellite)
the rate is 35 Kbps

60. Discussion Does TCP perform really that bad in wireless? mobile host
base station
“wired“ Internet

61. Wireless Networking: Summary
send
receive
status
info
info/control
The ability to communicate is a foundational support of wireless mobile networks
Unfortunately, the capacity of such networks using current techniques is limited
Much progress has been made, but still more are coming.