Towards a Robust Protocol Stack for Diverse Wireless Networks
description
Transcript of Towards a Robust Protocol Stack for Diverse Wireless Networks
![Page 1: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/1.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS, A, AMHERST • MHERST • Department of Computer Science Department of Computer Science
Towards a Robust Protocol Stack for Diverse Wireless Networks
Arun Venkataramani(in collaboration with Ming Li, Devesh Agrawal, Deepak Ganesan, Aruna
Balasubramanian, Brian Levine, Xiaozheng Tie at UMass Amherst)
![Page 2: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/2.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 2
Wireless network landscape today
Diverse wireless networks coexistAdapt TCP/IP stack in different ways
WLAN Mesh MANET DTN
Little mobility High mobilitySome mobility
Cellular
![Page 3: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/3.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 3
Interconnecting diverse networks?
Vision: A simple robust protocol stack to interconnect diverse wireless networks.
DTNWLAN Mesh MANET
Little mobility High mobilitySome mobility
Cellular
![Page 4: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/4.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 4
Why does TCP/IP not suffice?
E2E route disruptions cause unavailability
DTNWLAN Mesh MANET
Little mobility High mobilitySome mobility
Cellular
![Page 5: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/5.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 5
Why does TCP/IP not suffice?
Gap between what you buy vs. get
DTNWLAN Mesh MANET
Little mobility High mobilitySome mobility
Cellular
Advertised capacity: 11Mbps
![Page 6: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/6.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 6
Principle: Design for high uncertainty
Observe what works at an extreme point in the design space--always-partitioned DTNs--for insights into a robust design.
![Page 7: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/7.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 7
Outline
Motivation
Block transport
Replication routing
Research challenges
![Page 8: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/8.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 8
E2E Feedback
1. E2E Transport
E2E rate control is error-prone
E2E retransmissions are wasteful
Rate ControlRate
Control
DestSource Congestion? Link loss?
Loss Rate
RTT
![Page 9: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/9.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 9
1. E2E Transport
E2E rate control is error-prone
E2E retransmissions are wasteful
Source DestRedundant
Transmissions
E2E Retransmissions
P
![Page 10: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/10.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 11
2. Packet as Unit of Control
Channel accessLink layer ARQ
Listen Backoff RTS/CTS
![Page 11: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/11.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 12
2. Packet as Unit of Control
Channel access Link layer ARQ
Timeout Backoff Timeout Backoff
![Page 12: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/12.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 13
3. Complex Cross-Layer Interaction
Transport
Link
Link-layer ARQ/backoff hurts TCP rate control
Highly Variable RTT
Link ARQ Link ARQ Link ARQ
Rate ControlRate
Control
![Page 13: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/13.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 14
Hop: Clean-Slate Transport Protocol
End-To-End
Packets
Complexity
Hop-by-Hop
Blocks
Minimize interaction
Block-switched networks: A new paradigm for wireless networks, Li et al. [NSDI 2009]
![Page 14: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/14.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 15
Hop Design
Reliable Block Transfer
ACK Withholding
Micro-block Prioritization
Virtual Retransmission
Backpressure
Per-hopMulti-hop
![Page 15: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/15.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 16
Reliable Per-Hop Block Transfer
B-SYN Request for B-ACK
B-ACK Packet bitmap
Mechanisms
Burst mode (TXOP)
Block ACK based ARQ
Benefits
Amortizes control overhead
CSMA TXOP
![Page 16: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/16.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 17
Hop Design
Reliable Block Transfer
ACK Withholding
Micro-block Prioritization
Virtual Retransmission
Backpressure
Per-hopMulti-hop
![Page 17: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/17.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 18
MechanismLeverages in-network cachingRe-transmits blocks only when unavailable in cache
BenefitsFewer transmissionsLow overheadSimple
Virtual Retransmission (VTX)
B-SYNB-ACK
A B
E
C
D
DATA
![Page 18: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/18.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 19
MechanismLeverages in-network cachingRe-transmits blocks only when unavailable in cache
BenefitsFewer transmissionsLow overheadSimple
Virtual Retransmission (VTX)
A B
E
D
B-SYNVTX
B-ACK
B-SYNVTX B-SYN with VTX flag set
VTX TimerE2E ACK
B-SYNVTX Timer
![Page 19: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/19.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 20
Hop Design
Reliable Block Transfer
ACK Withholding
Micro-block Prioritization
Virtual Retransmission
Backpressure
Per-hopMulti-hop
![Page 20: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/20.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 21
MechanismLimits outstanding blocks per-flow at forwarder
Backpressure
A B C D E
Source Dest
Slow
Limit on outstanding blocks=2
B-SYN
Hold B-ACK
B-SYNB-SYN
![Page 21: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/21.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 22
MechanismLimits outstanding blocks per-flow at forwarder
BenefitsImproves network utilization
Backpressure
A B C
D E
Source
Dest
F G
Dest
Aggregate goodput without backpressure: 6Mbps
20Mbps 10Mbps 20Mbps
20Mbps
20Mbps1Mbps
![Page 22: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/22.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 23
MechanismLimits #outstanding blocks per-flow at forwarder
BenefitsImproves network utilization
Backpressure
A B C
D E
Source
Dest
F G
Dest
Aggregate goodput with backpressure: 10Mbps
20Mbps 10Mbps 20Mbps
20Mbps
20Mbps1Mbps
Limit of Outstanding Blocks=1
![Page 23: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/23.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 24
Hop Design
Reliable Block Transfer
ACK Withholding
Micro-block Prioritization
Virtual Retransmission
Backpressure
Per-hopMulti-hop
![Page 24: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/24.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 25
Mechanism:
Receiver withholds all but one BACK
Benefit:Low overheadLess conservativeSimple
Ack Withholding
A C B
B-SYNB-ACK
DATA
B-SYN
B-ACKDATA
Withhold B-ACK
![Page 25: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/25.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 26
Hop Design
Reliable Block Transfer
ACK Withholding
Micro-block Prioritization
Virtual Retransmission
Backpressure
Per-hopMulti-hop
![Page 26: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/26.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 27
Micro-block Prioritization
MechanismsSender piggybacks small blocks to B-SYNReceiver prioritizes small block’s B-ACK
BenefitsLow delay for small blocks
SSH FTP
B-SYN
B-ACKDATA
B-SYN64B 1MB
Sender SenderReceiver
![Page 27: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/27.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 28
20 nodes on the 2nd floor of UMass CS building
Apple Mac Mini1.8GHz, 2GB RAM, Atheros 802.11 a/b/g card
Testbed
![Page 28: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/28.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 29
Single-flow Single-hop Performance
Hop achieves significant gains over TCP
HopTCP
28x
1.6x
1.2x
![Page 29: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/29.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 30
Single-flow Multi-hop Performance
HopTCP
2.7x
2.3x
1.9x
Hop achieves significant gains over TCP
![Page 30: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/30.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 31
Graceful Degradation with Loss
Emulated link layer losses at the receiver
TCP breaks down at moderate loss rates
HopTCP
![Page 31: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/31.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 32
Scalability to High Load
30 concurrent flows
Hop is much fairer than TCP
Meangoodput
HopTCP
Hop-by-hop TCP
150x
20x
2x
![Page 32: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/32.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 33
Hop Performance Breakdown
![Page 33: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/33.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 35
Low Delay for Small Transfers
AP
1 small transfer competing with 4 large
Small transfer size (KB)
Hop lowers delay across all file sizes
![Page 34: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/34.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 40
Related WorkFixing E2E rate-control
Separating loss/congestion [Snoop, WTCP, Westwood+, ATCP, TCP-ELFN][Snoop, WTCP, Westwood+, ATCP, TCP-ELFN]
Network-assisted rate control [ATP, NRED, IFRC, WCP][ATP, NRED, IFRC, WCP]
Hop circumvents rate control
BackpressureATM, theoretical work [Tassiulas et al.][Tassiulas et al.]
Tree/chain sensor data aggregation [Fusion, Flush][Fusion, Flush]
Reliable point-to-point transport [RAIN, CXCC, Horizon][RAIN, CXCC, Horizon]
Hop reduces backpressure overhead using blocksBatching
Common optimization at link [802.11e/802.11n, WiLDNet, Kim08, [802.11e/802.11n, WiLDNet, Kim08,
CMAP]CMAP], transport [Delayed-ACK, DTN2.5][Delayed-ACK, DTN2.5], and network [ExOR][ExOR] layersHop leverages batching across layers
![Page 35: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/35.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 41
Outline
Motivation
Block transport
Replication routing
Research challenges
![Page 36: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/36.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 42
Replication routing
PX Z
Y
P
P
W
P
Replication reduces delay under topology uncertainty
![Page 37: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/37.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 43
Routing as resource allocation problem
RAPID Protocol (X,Y):
1. Control channel: Exchange metadata
2. Direct Delivery: Deliver packets destined to each other
3. Replication: Replicate in decreasing order of marginal utility
4. Termination: Until all packets replicated or nodes out of range
YX
Change in utility
Packet size
Problem: Which packets to replicate given limited bandwidth to optimize a specified metric?
DTN routing as a resource allocation problem, Balasubramanian et al. [SIGCOMM 2007]
![Page 38: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/38.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 44
Objective: Minimize average delay
Define U(i) = -(T + D) T = time since created, D = expected remaining time to deliver
Simplistic assumptionsuniform exponential meeting with mean ¸global view
Utility computation example
D = ¸
iX
D = ¸/2
iY
D =¸/3
iW
Z
![Page 39: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/39.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 45
Utility computation example (cont’d)
Replicate i
Metric: Min average delay
Deadline of i < TDeadline of j = T1 > T
Metric: Maximize #packets delivered within deadline
Replicate j
iX
j
Y j
W Z
![Page 40: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/40.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 46
Deployment on DieselNet
![Page 41: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/41.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 47
Results based on DieselNet traces
![Page 42: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/42.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 48
Outline
Motivation
Block transport
Replication routing
Research challenges
![Page 43: Towards a Robust Protocol Stack for Diverse Wireless Networks](https://reader035.fdocuments.in/reader035/viewer/2022062519/568152ba550346895dc0dc9f/html5/thumbnails/43.jpg)
UUNIVERSITY OF NIVERSITY OF MMASSACHUSETTSASSACHUSETTS A AMHERST • MHERST • Department of Computer Science Department of Computer Science 49
C1: When to replicate? Replication useful under
Topology uncertainty Delay optimization Light load scenarios
WLAN Mesh MANET DTN
Low uncertaintyForwarding suffices
High uncertaintyReplication useful
X1
X2
Xk
src dst
relays
Xi = r.v. for delay of path iForwarding delay = mini(E[Xi])Replication delay = E[mini(Xi)]
Claim: Delay benefit of replication is unbounded.