1. Performance of an 802.11 Home Network Mesh Testbed
September 15, 2003
W. Steven Conner
Intel Corporation

2. Outline Overview of 802.11 ESS Mesh
Performance evaluation of a wireless home network testbed
Lowering the barriers to mesh deployment
Recommendation to start Mesh SG
Summary

3. Overview: 802.11 Mesh Architectures
Ad Hoc Links
Peer-to-Peer Mesh
(Ad Hoc Mode)
Infrastructure ESS
with WDS Backhaul
WDS Links
Ad Hoc Links
Ad Hoc or
WDS Links
Hybrid Infrastructure/
Ad Hoc Mesh

4. Overview: 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.

5. Question: Does it Make Sense to Deploy a Wireless ESS Mesh for a Home Network?70 71 72 73 74 75 76 77
Upper Level
Office
Lower Level
Living
Room
Den
Back
Yard B A C D

6. Overview: Experimental evaluation of an 802.11b home mesh network
Upper Level
Office
Lower Level
Living
Room
Den
Back
Yard B C D A 70 71 72 73 74 75 76 77
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 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.)

7. Testbed Configurations
Traditional 1-hop BSS
802.11b, auto-rate, 15mW
BSS emulated with ad-hoc mode
All clients communicate directly with AP-A
Out of range
Configuration 2
Multi-hop ESS Mesh
802.11b, 11Mbps, 15mW
ESS emulated with ad-hoc mode
Centrally configured minimum-airtime-metric routing (zero overhead)
Clients communicate with best AP to join wireless ESS mesh

8. Individual Node Throughput
Non-Mesh BSS Individual Node Throughput
Multi-Hop ESS Individual Node Throughput
1.7X 
3.1X 
Connected!
Out of range

9. Multi-Node Throughput
Non-Mesh BSS Aggregate Throughput
5.338
2.878
1.994
1.520
Multi-Hop ESS Aggregate Throughput
5.322
3.910
3.880
3.284
1.3X 
1.9X 
2.1X 
Out of range

10. Multi-Node Throughput cont.
Aggregate Throughput with 8 Clients
2.1X 
3.709
1.719
Out of range

11. Client-to-Client Throughput
Non-Mesh BSS Client-to-Client Throughput
Multi-Hop ESS Client-to-Client Throughput
3.4X 
2.4X 
Out of range
Note: Direct client-to-client links can help here as well

12. Non-Mesh BSS End-to-End Latency
Network Latency
Non-Mesh BSS End-to-End Latency
Multi-Hop ESS End-to-End Latency
~ 2ms increase per hop
Out of range
Highly dependent on implementation

13. 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 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 works today, why do we need additional standards support?

14. Barriers to 802.11 Mesh Deployment
Interoperability
Security
Configuration / Management
Lack of Hooks for Statistics/Control
Radio and metric aware routing
MAC Performance

15. 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 i for mesh
Improving Configuration / Management
Statistics and Control Hooks need to be exposed between MAC and “mesh layer”
Leverage/extend k for mesh

16. A few notable examples:
Research indicates 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 multi-hop chain3
[1] Kaixin Xu, M. Gerla, and Sang Bae, "How effective is the IEEE RTS/CTS handshake in ad hoc networks?" IEEE Globecom'02, 2002, pp
[2] Shugong Xu and Tarek Saadawi – “Does the IEEE MAC Protocol Work Well in Multihop Wireless Ad Hoc Networks?” IEEE Communications Magazine, June 2001, pp
[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 , July 2001.

17. 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
Multi-hop scheduling/scalability are significant issues

18. Lowering the Barriers to 802.11 Mesh Deployment
Proposed Parallel Efforts:
Standardize Multi-Hop ESS
Radio/Metric-Aware L2 Routing
Interoperability
Security
Configuration / Management
Enhance MAC Performance for Mesh
Scalability
Scheduling (managing collisions/ interference)
New Mesh Study/Task Group
Leverage i/k where possible
Influence current/ future MAC enhancement efforts to improve scalability of for mesh

19. Recommendation to WNG for Starting a Mesh Study Group
Scope: Develop an Infrastructure-Mode 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/metric-aware unicast routing
Multiple-radios: Include support for optional multiple-radios per router
Usage Models: Initially focus on home and small-scale hotspot networks

20. Backup

21. 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 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 !

22. Fixing the MAC for Mesh
We know there are issues with the current MAC, but what about e?
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., n)