Transcript Capacity Modeling for Wireless Networks

Doc.: IEEE 11-03-0712-01-0wng
September 2003
Performance of an 802.11
Home Network Mesh Testbed
September 15, 2003
W. Steven Conner
Intel Corporation
([email protected])
Submission
Slide 1
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Outline
 Overview of 802.11 ESS Mesh
 Performance evaluation of a wireless home
network testbed
 Lowering the barriers to 802.11 mesh
deployment
 Recommendation to start 802.11 Mesh SG/TG
 Summary
Submission
Slide 2
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Overview: 802.11 Mesh Architectures
Peer-to-Peer Mesh
(Ad Hoc Mode)
Infrastructure Mode ESS
with WDS Backhaul
WDS Links
Ad Hoc Links
Hybrid Infrastructure/
Ad Hoc Mesh
Ad Hoc Links
Ad Hoc or
WDS Links
Submission
Slide 3
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Overview: 802.11 ESS Mesh
 Mesh is not limited to highly mobile networks
with no infrastructure
 Also has application in many fixed-infrastructure
environments
 Extended range and coverage, without requiring
additional wires (convenient deployment, cost)
 Enhanced redundancy, reliability
 Potential throughput improvement
 Example networks where ESS Mesh is useful:
 Home networks, hotspot networks, etc.
Submission
Slide 4
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Question: Does it Make Sense to
Deploy a Wireless ESS Mesh for a
Home Network?
71
70
B
73
A
Office
Den
72
74
C
Back
Yard
Living
Room
D
77
Submission
75
76
Lower Level
Upper Level
Slide 5
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Overview: Experimental evaluation of
an 802.11b home mesh network
71
70
B
73
A
Office
Den
72
74
C
Back
Yard
D
77
Living
Room
75
76
Lower Level
Upper Level
 Experiments performed in my house (~2000 sq. ft.) in Hillsboro, OR (August, 2003)
 Topology: 8 Client Laptops and 4 AP routers
 In a real home network scenario, some of the laptops would likely be replaced by other 802.11
enabled devices (e.g., DVRs, media servers, stereo systems, etc.)
 Traffic: Experiments assume network traffic is not limited to Internet surfing on a
broadband link
 Clients share significant amount of data within the home (e.g., A/V content sharing, photo
storage, data backup, etc.)
Submission
Slide 6
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Testbed Configurations
Configuration 1
 Traditional 1-hop BSS
 802.11b, auto-rate, 15mW
 BSS emulated with ad-hoc
mode
 All clients communicate
directly with AP-A
Configuration 2
 Multi-hop ESS Mesh
 802.11b, 11Mbps, 15mW
 ESS emulated with ad-hoc mode
- Centrally configured minimum-airtimemetric routing (zero overhead)
 Clients communicate with best AP
to join wireless ESS mesh
Submission
Slide 7
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Individual Node Throughput
Multi-Hop ESS Individual Node Throughput
6
6
5
5
4
70 (O)
3
73 (D)
5.182
75 (L)
2
77 (B)
1
Throughput (Mbps)
Throughput (Mbps)
Non-Mesh BSS Individual Node Throughput
1.7X

3.1X

4
3
Connected!
70 (O)
73 (D)
5.179
75 (L)
2
77 (B)
2.679
2.686
1.8
1
1.572
0.85
0
0
Office
Submission
Living Room
Den
0
Backyard
Office
Slide 8
Living Room
Den
Backyard
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Multi-Node Throughput
Non-Mesh BSS Aggregate Throughput
5.338
6
5
1.768
2.878
4
3
1.798
0.976
2
0.992
1
70 (O)
71 (O)
1.994
0.664
0.646
1.772
0.91
0.684
72 (O)
73 (D)
1.520
0.504
0.494
0.522
75 (D)
76 (D)
Aggregate Throughput (Mbps)
Aggregate Throughput (Mbps)
6
Multi-Hop ESS Aggregate Throughput
0
5.322
5
1.7525
1.3X

3.910
1.9X

2.1X
3.880
4
1.27
3
1
3.284
0.786
Submission
2Office,1Den
1Office,2Den
3Den
1.336
1.314
1.048
75 (D)
76 (D)
1.775
3Office
Slide 9
72 (O)
73 (D)
1.304
1.45
1.338
0
3Office
70 (O)
71 (O)
1.228
1.795
2

2Office,1Den
1Office,2Den
3Den
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Multi-Node Throughput cont.
Aggregate Throughput with 8 Clients
2.1X

3.709
4
0.534
Throughput (Mbps)
3.5
70 (O)
0.522
3
2.5
2
1.5
1
0.5
1.719
0.517
71 (O)
72 (O)
73 (D)
0.283
0.279
0.291
0.234
0.198
0.211
0.223
0
0.412
74 (D)
0.408
75 (L)
0.457
76 (L)
0.461
77 (B)
0.398
0
Non-Mesh BSS
Submission
Multi-Hop ESS
Slide 10
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Client-to-Client Throughput
Non-Mesh BSS Client-to-Client Throughput
Multi-Hop ESS Client-to-Client Throughput
3
3.4X
3
2.4X
2
75 (L) -> 73 (D)
75 (D) -> 76 (D)
1.5
2.721
1
0.5

2.5
0.776
0.792
LR to Den
LR to LR
71 (O) -> 72 (O)
Throughput (Mbps)
Throughput (Mbps)
2.5

2
75 (L) -> 73 (D)
75 (D) -> 76 (D)
1.5
1
2.716
2.721
LR to LR
Off to Off
71 (O) -> 72 (O)
1.886
0.5
0
0
LR to Den
Off to Off
• Note: Direct client-to-client links can help here as well
Submission
Slide 11
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Network Latency
Multi-Hop ESS End-to-End Latency
9
9
8
8
7
6
5
70 (O)
73 (D)
4
75 (L)
3
2
77 (B)
4.06
4.16
3.88
Round-Trip-Time (ms)
Round-Trip-Time (ms)
Non-Mesh BSS End-to-End Latency
1
~ 2ms increase per hop
7
6
5
8.34
4
6.34
3
2
77 (B)
4.18
0
Office
Living Room
Den
Backyard
Office
Living Room
Den
Backyard
• Highly dependent on implementation
Submission
Slide 12
73 (D)
75 (L)
6.06
1
0
70 (O)
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Summary of Testbed Results
 A multi-hop ESS mesh is beneficial, even for a
relatively small-scale home network
 Multi-hop topologies:
 Can be built with standard 802.11 hardware
 Can improve network performance in comparison
to traditional 1-hop BSS networks
 These experiments used 1 radio on each AP/router; multi-radio per
AP/router would allow even better performance (multi-channel)
 Question: If mesh networking with 802.11
works today, why do we need additional
standards support?
Submission
Slide 13
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Barriers to 802.11 Mesh
Deployment
 Interoperability
 Security
 Configuration / Management
 Should require minimal effort to deploy
 Lack of hooks for statistics/control
 Radio and metric-aware routing
 MAC Performance
Submission
Slide 14
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Making Mesh Work
Key areas for IEEE Standardization:
 Interoperability
 Standardizing over-the-air messaging for mesh
 Routing:
– L2 mesh subnet for wireless backhaul
– Radio and metric-aware path selection (hop-count is not sufficient!)
 Security:
 To make it possible to secure a mesh, routers should be able to
trust each other
 Leverage/extend 802.11i for mesh
 Improving Configuration / Management
 Should require minimal effort to deploy (beyond router introduction)
 Statistics and control hooks need to be exposed between MAC and
“mesh layer”
 Leverage/extend 802.11k for mesh
Submission
Slide 15
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Research indicates 802.11 MAC performance needs
to be optimized for large scale mesh networks
A few notable examples:
 RTS/CTS does not correctly solve hidden terminal
problem in a mesh
 Tends to either sacrifice spatial reuse or allow excessive
interference1
 RTS/CTS fails to achieve good schedule in a multi-hop
chain
 RTS/CTS scheduling along a chain can cause serious TCP
fairness problems and backoff inefficiencies2
 RTS/CTS does not efficiently schedule transmissions in a multihop chain3
[1] Kaixin Xu, M. Gerla, and Sang Bae, "How effective is the IEEE 802.11 RTS/CTS handshake in ad hoc networks?" IEEE Globecom'02, 2002, pp. 72 -76.
[2] Shugong Xu and Tarek Saadawi – “Does the IEEE 802.11 MAC Protocol Work Well in Multihop Wireless Ad Hoc Networks?” IEEE Communications
Magazine, June 2001, pp 130-137.
[3] J. Li, C. Blake, D. S. De Couto, H. I. Lee, and R. Morris. Capacity of ad hoc wireless networks. In Proceedings of ACM MOBICOM, pages 61--69, July 2001.
Submission
Slide 16
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Enabling Mesh Usage Models
 Before MAC Enhancements:
 Home Network
 Small Office
 Small Hotspot
 MAC Enhancements Necessary:
 Enterprise
 Large Conference
 High Performance Home Network
 Power-users, A/V
Submission
Multi-hop scheduling/scalability
are significant issues
Slide 17
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Lowering the Barriers to
802.11 Mesh Deployment
Proposed Parallel Efforts:
 Standardize Multi-Hop ESS (AP Mesh)
New 802.11 Mesh
Study/Task Group
 Radio/Metric-Aware L2 Routing
 Interoperability
 Leverage 802.11i/k
where possible
 Security
 Configuration / Management
 Enhance MAC Performance for Mesh
 Scalability
 Scheduling (managing collisions/
interference)
Submission
Influence current/ future MAC
enhancement efforts to improve
scalability for mesh
 Leverage 802.11e/n where
possible
Slide 18
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Recommendation to WNG for
Starting a Mesh Study/Task Group
 Scope: Develop an Infrastructure-Mode 802.11 ESS
AP Mesh that Appears as a Broadcast Ethernet to
Higher Layer Protocols
 Scale: Up to 255 devices (APs and Clients)
 Security: Include support for trusted set of routers controlled by
single entity
 Routing: Include support for both broadcast and radio/metricaware unicast routing
 Multiple-radios: Include support for optional multiple-radios per
router
 Usage Models: Initially focus on home and smallscale hotspot networks
Submission
Slide 19
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Backup
Submission
Slide 20
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Is IEEE the Right Place to
Create a Mesh Standard?
 IETF/IRTF MANET groups have been working on L3 mesh standards for
years
 But… radio awareness is out-of-scope, significantly limiting opportunity for efficient use
of the wireless channel
 Major focus on large scale and high mobility (hard problems!) has significantly
prolonged the standards process
 IEEE 802.11 is a reasonable place to create a L2 mesh subnet standard
 Allows tight integration with MAC (radio awareness)
 Has the advantage of creating a mesh that looks like an ethernet to IP applications
 Improved hooks/statistics for supporting a L2 mesh can also be used to improve L3
mesh implementations
 IETF L3 mesh network can be used to interconnect multiple IEEE L2 mesh subnets
 There is recent precedent for standardizing mesh support in IEEE
 802.16a already has explicit mesh support
Yes, we need improved standard support for mesh in 802.11!
Submission
Slide 21
Intel Corporation
Doc.: IEEE 11-03-0712-01-0wng
September 2003
Fixing the 802.11 MAC for Mesh
 We know there are issues with the current 802.11
MAC, but what about 802.11e?
 EDCF should improve fairness and efficiency
 TXOPs
 Block ACK
 Direct links between clients
 Multiple queues allow traffic prioritization
 What are the implications for mesh?
 Improving MAC in IEEE:
 Option 1: Start a new study group/task group focused on MAC
support for mesh
 Option 2: Piggyback on current/future non-mesh MAC
enhancement efforts (e.g., 802.11n)
Submission
Slide 22
Intel Corporation