강좌파일 - 한국정보과학회 정보통신소사이어티
Download
Report
Transcript 강좌파일 - 한국정보과학회 정보통신소사이어티
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
Routing Functions in
Mesh Networks
2007년 5월 18일
이상환
[email protected]
국민대학교
Contents
Introduction
Link Quality Metric
WMN Routing Protocols
ETX, ETT, WCETT
LQSR, BAF, ExOR
Feasibility for All-Wireless Offices
100+ users
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
2/58
What is Wireless Mesh Network
(WMN)?
Nodes are static
Wireless channel for node to node transmission
Also called Static Wireless Network
External interference, channel fading, inclement
weather
Quality of a link varies frequently over time
Many links may be in degraded state at any given time
Multi-hop transmission
The path from source to destination can be multi-hop
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
3/58
Multi-hop Wireless Networks
Static
Mobile
Motivating
scenario
Community
wireless
networks
Battlefield
networks
Cause of
Tx Failure
Bad Link Quality
Node Movement
Improving
network capacity
Handling mobility,
node failures,
limited power.
Key
challenge
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
4/58
Why New Routing Protocols?
Routing protocols for wireless ad-hoc
networks can be applied to WMN
TBRPF, DSR, AODV, DSDV, etc
Need research for several reasons
New performance metric
Limited scalability
Cross-layer interaction
Different requirements on power and mobility
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
5/58
Features of Routing Protocol (1)
Multiple Performance Metrics
Hop-count is not an effective routing metric.
Other performance metrics, e.g., link quality
and round trip time (RTT), must be considered.
Scalability
Routing setup in large network is time
consuming.
Node and link states on the path may change.
Scalability of routing protocol is critical in
WMNs
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
6/58
Features of Routing Protocol (2)
Robustness
WMNs must be robust to link failures or congestion.
Routing protocols need to be fault tolerant with link failures
and can achieve load balancing
Adaptive support of both mesh routers and mesh clients
Mesh routers : minimal mobility, no constraint of power
consumption, routing is simpler
Mesh clients : mobility, power efficiency, routing is
complicated
Need to design a routing protocol that can adaptively
support both mesh routers and mesh clients.
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
7/58
Performance Metric
Throughput ([6])
How many packets are transmitted successfully
better
Better
29 PC Testbed
UDP throughput
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
8/58
Can We Do Better?
DSDV :
Shortest Path in Hop
count
Routing protocol
‘Best’
‘Best’ for each pair
is highest measured
throughput of 10
promising static
routes.
There must be some
protocol to achieve
this.
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
9/58
2 Phase Path Selection Strategy
Phase 1 : Link Quality Metric
Phase 2 : Path Quality Metric
Assign the quality of individual link
Combine link quality metrics on the path
Challenges
Multi-hop performance degradation
Lossy links
Asymmetric links
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
10/58
Challenge 1 : more hops, less
throughput
1
2
3
4
5
6
Throughput over # of hops
1 hop = 1
2 hop = 1/2
3 hop = 1/3
•Links in route share radio spectrum
MAC Interference among a chain of nodes. The Solid-line circle denotes transmission range
(200m approx) and the dotted line circle denotes the interference range (550m approx)
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
11/58
Challenge 2: many links are lossy
One-hop broadcast delivery ratios
‘Good’
‘Bad’
Smooth link distribution complicates link classification.
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
12/58
Challenge 3 : many links are
asymmetric
Broadcast
delivery ratios
in both link
directions.
Very asymmetric link.
Many links are good in one direction, but lossy in the other.
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
13/58
Contents
Introduction
Link Quality Metric
ETX, ETT, WCETT
WMN Routing Protocols
LQSR, BAF, ExOR
Feasibility for All-Wireless Offices
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
14/58
A straw-man route metric (1)
Product of link delivery ratio along path
B
100%
100%
C
A
51%
Product:
Actual throughput:
A-B-C = 100%
A-C = 51%
A-B-C : ABABAB = 2 tx
A-C : AAAAAAAA = 1.96 tx
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
15/58
A straw-man route metric (2)
Maximize bottleneck throughput
B
Delivery ratio = 100%
50%
C
A
51%
51%
D
Bottleneck throughput:
Actual throughput:
A-B-C = 50%
A-D-C = 51%
A-B-C : ABBABBABB = 3 tx
A-D-C : AADDAADD = 4 tx
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
16/58
A straw-man route metric (3)
Maximize end-to-end delivery ratio
B
100%
51%
C
A
50%
End-to-end delivery ratio:
Actual throughput:
A-B-C = 51%
A-C = 50%
A-B-C : ABBABBABB = 3 tx
A-C : AAAAAAAA = 2 tx
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
17/58
Expected Transmission Count ([5])
Minimize total transmissions per packet
Link throughput 1/ Link ETX
Delivery Ratio
Link ETX
Throughput
100%
1
100%
50%
2
50%
33%
3
33%
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
18/58
Calculating Link ETX
Assuming 802.11 link-layer acknowledgments
(ACKs) and retransmissions:
P(TX success) = P(Data success) ⅹP(ACK success)
Link ETX = 1 / P(TX success)
= 1 / [ P(Data success) ⅹ P(ACK success) ]
Estimating link ETX:
P(Data success) ≈ measured fwd delivery ratio rfwd
P(ACK success) ≈ measured rev delivery ratio rrev
Link ETX ≈ 1 / (rfwd ⅹ rrev)
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
19/58
Measuring Delivery Ratios
Each node broadcasts small link probes
(134 bytes), once per second
Nodes remember probes received over
past 10 seconds
Reverse delivery ratios estimated as
rrev pkts received / pkts sent
Forward delivery ratios obtained from
neighbors (piggybacked on probes)
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
20/58
Route ETX
Route ETX = Sum of link ETXs
Route ETX Throughput
1
100%
2
50%
2
50%
3
33%
5
20%
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
21/58
ETX Properties
Advantages
ETX predicts throughput for short routes (1, 2, and 3 hops)
ETX quantifies loss, asymmetry, throughput reduction of
longer routes
Caveats
ETX link probes are susceptible to MAC unfairness and
hidden terminals
ETX estimates are based on measurements of a single link
probe size (134 bytes)
Route ETX measurements change under load
Loss rate of broadcast probe packets is not the same as loss
rate of data packets
Under-estimates data loss ratios, over-estimates ACK loss
ratios
ETX assumes all links run at one bit-rate
Does not take data rate or link load into account
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
22/58
Per-hop RTT ([6])
Node periodically pings each of its neighbors
Unicast probe/probe-reply pair
RTT samples are averaged using TCP-like low-pass filter
Path with least sum of RTTs is selected
Advantages
Easy to implement
Accounts for link load and bandwidth
Also accounts for link loss rate
802.11 retransmits lost packets up to 7 times
Lossy links will have higher RTT
Disadvantages
Expensive
Self-interference due to queuing
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
23/58
Per-hop Packet-Pair ([6])
Node periodically sends two back-to-back
probes to each neighbor
First probe is small, second is large
Neighbor measures delay between the arrival of
the two probes; reports back to the sender
Sender averages delay samples using low-pass
filter
Path with least sum of delays is selected
Advantages
Self-interference due to queuing is not a problem
Implicitly takes load, bandwidth and loss rate into
account
Disadvantages
More expensive than RTT
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
24/58
Considering Multiple Channel
ETX assumes single channel
Source
One bit-rate
Self Interference among links
Mesh Router
Destination
No
simultaneous
transmission
Simultaneous
transmission
Source
Mesh Router
Destination
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
25/58
Existing Routing Metrics are
Inadequate
2 Mbps
18 Mbps
18 Mbps
Destination
Mesh Router
Source
11 Mbps
11 Mbps
Shortest path: 2 Mbps
Path with fastest links: 9 Mbps
Best path: 11 Mbps
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
26/58
Link Metric: Expected Transmission
Time (ETT, [7])
Link loss rate = p
Expected number of transmissions
1
ETX
1- p
Packet size = S, Link bandwidth = B
Each transmission lasts for S/B
S
Similar to airtime
ETT * ETX
metric in 802.11s
B
Lower ETT implies better link
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
27/58
ETT: Illustration
11 Mbps
5% loss
Source
18 Mbps
10% loss
50%
Destination
1000 Byte Packet
ETT : 0.77 ms
ETT
ETT :: 0.89
0.40ms
ms
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
28/58
Combining Link Metric into Path
Metric Proposal 1
Add ETTs of all links on the path
Use the sum as path metric
SETT = Sum of ETTs of links on path
(Lower SETT implies better path)
Pro: Favors short paths
Con: Does not favor channel diversity
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
29/58
SETT does not favor channel
diversity
6 Mbps
No Loss
6 Mbps
No Loss
1.33ms
1.33ms
Mesh Router
Source
Destination
1.33ms
1.33ms
6 Mbps
No Loss
6 Mbps
No Loss
Path
Throughput
SETT
Red-Blue
6 Mbps
2.66 ms
Red-Red
3 Mbps
2.66 ms
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
30/58
Impact of Interference
Interference reduces throughput
Throughput of a path is lower if many links
are on the same channel
Path metric should be worse for non-diverse
paths
Assumption: All links that are on the same
channel interfere with one another
Pessimistic for long paths
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
31/58
Combining Link Metric into Path
Metric : Proposal 2
Group links on a path according to channel
Add ETTs of links in each group
Find the group with largest sum.
Links on same channel interfere
This is the “bottleneck” group
Too many links, or links with high ETT (“poor quality”
links)
Use this largest sum as the path metric
Lower value implies better path
“Bottleneck Group ETT” (BG-ETT)
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
32/58
BG-ETT Example
6 Mbps
6 Mbps
1.33 ms
6 Mbps
6 Mbps
1.33 ms
1.33 ms
1.33 ms
Path
Throughput
Blue Sum
Red Sum
BG-ETT
All Red
1.5 Mbps
0
5.33 ms
5.33 ms
1 Blue
2 Mbps
1.33 ms
4 ms
4 ms
Red-Blue
3 Mbps
2.66 ms
2.66 ms
2.66 ms
BG-ETT favors high-throughput, channel-diverse paths.
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
33/58
BG-ETT does not favor short paths
S
S
D
6 Mbps
6 Mbps
6 Mbps
1.33 ms
1.33 ms
1.33 ms
6 Mbps
6 Mbps
6 Mbps
1.33 ms
1.33 ms
1.33 ms
2 Mbps
4 ms
Path
Throughput
Blue Sum
Red Sum
BG-ETT
3-Hop
2 Mbps
0
4 ms
4 ms
4-Hop
2 Mbps
4 ms
4 ms
4 ms
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
34/58
D
Path Metric: Putting it all
together
SETT favors short paths
BG-ETT favors channel diverse paths
Weighted Cumulative ETT (WCETT)
WCETT = (1-β) * SETT + β * BG-ETT
β is a tunable parameter
Higher value: More preference to channel diversity
Lower value: More preference to shorter paths
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
35/58
How to measure loss rate and
bandwidth?
Loss rate measured using broadcast
probes
Similar to ETX
Updated every second
Bandwidth estimated using periodic
packet-pairs
Updated every 5 minutes
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
36/58
Contents
Introduction
Link Quality Metric
ETX, ETT, WCETT
WMN Routing Protocols
LQSR, BAF, ExOR
Feasibility for All-Wireless Offices
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
37/58
Multi-Radio Link Quality Source
Routing (MR-LQSR, [7])
Implemented in a source-routed, link-state
protocol
Nodes discovers links to its neighbors; Measure
quality of those links
Link information floods through the network
Each node has “full knowledge” of the topology
Sender selects “best path”
Derived from DSR : RREQ, RREP
Packets are source routed using this path
http://research.microsoft.com/mesh/
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
38/58
Blacklist Aided Forwarding ([8])
Disseminate base topology infrequently globally
Convey short-term state of degraded links as far
as necessary
Links with higher short-term cost w.r.t. base topology
Ensure loop-free forwarding to reachable destinations
Updating of links with better short-term cost is
not essential
Base topology reflects the long-term state of each link
Usage of such links doesn’t cause loops even without
link state updates
A scheme based on LOLS approach
Blacklist-Aided Forwarding
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
39/58
Blacklist Aided Forwarding (2)
Each packet carries a blacklist
Each node maintains a blacklist cache
A set of degraded links and their short-term costs
Adjacent degraded links
From forwarding failures or periodic probes
Non-adjacent degraded links
From blacklists of arriving packets
Purged after a refresh interval
Forwarding based on both destination and
blacklist
(p.dest, p.blist)
(next hop, p.blist)
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
40/58
Forwarding under BAF
Imagine forwarding packets in two modes
Packets normally forwarded in greedy mode
Switched to recovery mode upon hitting a
deadend
Next hop along the path with decreasing long-term
cost to destination
In recovery mode, each packet carries a blacklist
Nexthop chosen after excluding the packet’s blacklist
Switched back to greedy mode on forward
progress
When next hop is closer to the destination than any
node visited so far
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
41/58
Updating of a Packet’s Blacklist
Blacklist initialized to empty at the packet’s
source
A link XY is added to the packet’s blacklist if
Packet arrives at X and the nexthop is Y and
Link XY is currently degraded
A packet’s blacklist is reset to empty if
Stays empty if forward progress w.r.t. base topology
Cost from next hop to destination is the smallest so far
Blacklist grows if necessary and reset when
possible
Minimal set of degraded links to ensure loop-freedom
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
42/58
Illustration: BAF
3, {B-E}
B
2
∞, {}
1
A
3, {B-E, A-C}
2
3
2
4
D
3
3
C
F
3
∞, {}
E
2
1
H
2
G
A packet from B to E
gets caught in a loop under Shortest Path Forwarding
traverses B-A-D-C-E under BAF
BAF can forward packets between all pairs of nodes
without informing G,F,H about A-C or B-E and A,B,C,D,E
about G-H
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
43/58
ExOR (1)
Ex Opportunistic Routing ([11])
A Link/Network Layer diversity routing
technique that uses standard radio
hardware
Achieves substantial increase in
throughput for large unicast transfers in
mesh network.
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
44/58
ExOR (2)
dst
src
A complete schedule, undelivered packet are retried in subsequent
one
A subset within a transmission batch is called Fragment (F)
After each batch destination sends packet just containing batch map
4 transmissions in total
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
45/58
Contents
Introduction
Link Quality Metric
WMN Routing Protocols
ETX, ETT, WCETT
LQSR, BAF, ExOR
Feasibility for All-Wireless Offices
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
46/58
Feasibility Evaluation
Questions
Current Approach
Can we use a wireless mesh network to support an
entire office? At what scale and performance penalty?
How do various network design choices, such as node
placement, hardware, wireless band and routing metrics
impact application performance?
Deployed testbeds
Synthetic traces
Random traffic patterns
Need more realistic evaluation
CARE : Capture, Analysis, Replay, and Evaluation ([10])
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
47/58
Layered Service Provider in
Windows XP
Socket level traffic
capture
27% missing traffic
SMB, RPC, NetBUI/NBT,
LDAP and ICMP
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
48/58
Replay
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
49/58
Result
Difference between wired
transaction and wireless transaction
10 ms delay
Performance Variation Across Repeated Runs of
Medium Traffic Period, Distant Placement, WCETT Metric
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
50/58
Is All-Wireless Office Feasible?
Up to 100+ users
19 user traces
13 orthogonal channels => 6 parallel
transmission
19 * 6 = 114 users
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
51/58
Findings of Experiments
Routing metric
Significant impact when the offered load grows close to
network capacity.
Metrics that make use of unicast probes :
Server placement
Direct effect on average path length
Crucial for achieving good performance
Hardware and IEEE 802.11 band
high overhead
contention for the medium increases
Can significantly impact delay.
Additional delay : mostly under 20ms.
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
52/58
Research Issues (1)
Scalability
Hierarchical routing protocols can only partially solve
this problem
Geographic routing relies positioning technologies.
New scalable routing protocols need to be developed.
Better Performance Metrics
New performance metrics need to be developed.
Need to integrate multiple performance metrics into a
routing protocol
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
53/58
Research Issues (2)
Routing/MAC Cross-Layer Design
Needs to interact with the MAC layer, e.g. adopting multiple
performance metrics from MAC layer.
Merely exchanging parameters between them is not enough,
merging certain functions of MAC and routing protocols is a
promising approach.
For multi-radio or multi-channel routing, the channel/radio
selection in the MAC layer can help the path selection in the
routing layer.
Hybrid Routing
Mesh routers and mesh clients have different constraints in
power efficiency and mobility.
Need to adaptively support mesh routers and mesh clients
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
54/58
References
[1] MACAW: A Medium Access Protocol for Wireless LANs, by V.
Bharghavan et al., ACM SIGCOMM '94
[2] Jinyang Li, charles Blake, Douglas S. J. De Couto, Hu Imm
Lee, Robert Morris, Capacity of Ad Hoc Wireless Networks. In
Mobicom 2001, Rome, Italy
[3] D. Aguayo, J. Bicket, S. Biswas, G. Judd, and R. Morris.
Link-level measurements from an 802.11b mesh network. In Proc.
ACM Sigcomm, August 2004.
[4] Kamal Jain Jitendra Padhye Venkat Padmanabhan Lili Qiu.
The impact of interference on multi-hop wireless network
performance. In Proc. ACM Mobicom, September 2003.
[5] Douglas De Couto, Daniel Aguayo, John Bicket, and Robert
Morris. A high throughput path metric for multi-hop wireless
routing. In Proc. ACM Mobicom, September 2003.
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
55/58
References
[6] Richard Draves, Jitendra Padhye, and Brian Zill. Comparison of
routing metrics for static multi-hop wireless networks. In Proc. ACM
Sigcomm, August 2004.
[7] Richard Draves Jitendra Padhye Brian Zill. Routing in Multi-Radio,
Multi-Hop Wireless Mesh Networks. In Proc. ACM Mobicom,
September 2004.
[8] Srihari Nelakuditi, Sanghwan Lee, Yinzhe Yu, Junling Wang, Zifei
Zhong, Guor-Huar Lu, and Zhi-Li Zhang, "Blacklist-Aided
Forwarding in Static Multihop Wireless Networks," In the Proceedings
of IEEE SECON'05, Santa Clara, CA, Sep 2005
[9] I. Akyildiz, X. Wang, and W. Wang. Wireless mesh networks: A
survey. In Elsevier Computer Networks, 2005.
[10] J. Eriksson, S. Agarwal, P. Bahl, and J. Padhye, “Feasibility
study of mesh networks for all-wireless offices,” in MobiSys’06,
Uppsala, Sweden, June 2006
[11] Sanjit Biswas and Robert Morris. ExOR: Opportunistic
Multi-Hop Routing for Wireless Networks. In Proc. ACM
Sigcomm, August 2005.
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
56/58
References for Slides
http://pdos.csail.mit.edu/roofnet/sigcomm-talk.ppt
http://www-faculty.cs.uiuc.edu/~jhou/cs598jh/MITroofnet_sigcomm.ppt
http://www.cse.buffalo.edu/~qiao/cse620/fall04/capacity.ppt
http://research.microsoft.com/netres/kit/Publications/Presentations/mobicom20
04.ppt
http://www-faculty.cs.uiuc.edu/~jhou/cs598jh/routing4.ppt
http://research.microsoft.com/netres/kit/Publications/Presentations/sigcomm20
04.ppt
http://www.cs.cmu.edu/~srini/15-849E/S06/lectures/12-metrics.ppt
http://pdos.csail.mit.edu/grid/mobicom03-mark-II.ppt
http://www.cs.utexas.edu/~lili/classes/F05/slides/etx.ppt
http://www.cs.ucsb.edu/~avijit/ExOR.ppt
http://netweb.usc.edu/cs558/Slides/gaurav.ppt
http://www.cs.utexas.edu/~lili/classes/F05/slides/2P.ppt
http://lion.cs.uiuc.edu/group_seminar_slides/Mesh-2P-Chunyu-2005-0723.ppt
http://www2.cs.uh.edu/~rzheng/course/COSC7397/sp07/cunqing.ppt
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
57/58
Questions?
Thanks you
한국정보과학회 정보통신연구회 창립 20주년 기념 단기강좌
58/58