1. Architecture and Algorithms for an IEEE 802
Architecture and Algorithms for an IEEE based Multi-channel Wireless Mesh Network
Ashish Raniwala
Tzi-cker Chiueh
Experimental Computer Systems Lab
Stony Brook University

2. Motivation Characteristics- Characteristics - Applications - Goal -
Deployment
Characteristics-
Wireless last-hop
(AP-to-Mobile)
Wired backbone
Wireless Mesh Network
Characteristics -
Wireless backbone
Single channel
Low capacity
Applications -
Last-mile ISP connectivity
Wireless campus backbone
Hyacinth Architecture
Goal -
High-capacity wireless mesh network
Using Multiple channels
No MAC modifications
(off-the-shelf hardware)
Wires

3. Hyacinth Architecture Research Issues
Outline
Motivation
Hyacinth Architecture
Research Issues
Load-balancing Routing
Traffic-aware Channel Assignment
Throughput and Latency Gains
Hyacinth Prototype
Conclusions

4. Interconnection Network ?
Network Model
Internet
NFS
ERP
Enterprise Resources
Gateways
Interconnection Network ?
Access Net

5. Hyacinth Architecture
Internet
NFS
ERP
Enterprise Resources
Gateways
Access Net

6. Hyacinth Architecture
Wired Network 4 3 3 5 4 2 1 3 2 1 5 4 2 1 3 2
Virtual link
operating on
Channel 2
Mesh router
operating on
Channel 2 and
Channel 3

7. Connectivity Optimal Capacity
Research Issues
Interface Channel Assignment
Channel assignment => Bandwidth of virtual links
Connectivity vs. radio spectrum utilization efficiency
Workload awareness
Connectivity Optimal Capacity
Packet Routing
Routing => Traffic load on virtual links and gateways
Network-wide load balance
Interaction between routing and channel assignment
Goal: Maximize network cross-section goodput

8. Load-Balancing Routing: Problem30 20 40 10 30 10 40 50 20

9. Load-Balancing Routing: Solution
802.1D-like Gateway Discovery Protocol
Each node joins one (or more) gateways
Messages: ADVERTISE/JOIN/ACCEPT/LEAVE
Structure: Forest of trees rooted at gateway nodes.
Cache extra advertisements for failure recovery
Metrics
Hop-count
+ stable because mostly static
- load-imbalance
Gateway residual capacity
+ load balanced, adapts to traffic
- route flaps because dynamic
Path residual capacity
+ handles non-gateway bottlenecks
(1)
(2)
(3)

10. Traffic-Aware Channel Assignment: Problem70
110 60 30 40 40 30 40 30 20

11. Traffic-Aware Channel Assignment
Workload-Awareness
Why ?
Need to distribute load uniformly across channels.
How ?
1. Periodically construct a neighborhood channel-usage map
2. Re-assign channels to balance traffic load across channels
3. Coordinate with direct neighbors 10 40 30
Channel load
imbalance 10 40 30 10 40 30
Channel load
balanced

12. Traffic-Aware Channel Assignment
Channel Dependency Issue
Each node has a limited number of interfaces. Hence each interface is used to communicate with multiple neighbors.
Control Channel
- Physical: Extra NIC on dedicated channel
- Virtual: Multi-hop connectivity to neighbors C E
SOLUTION D B A
Channel Load Metrics
- Contention group size
Aggregated channel usage
Weighted sum of the two

13. Performance Evaluation: Throughput Gains
Simulation Setup
60 nodes with 4 gateway nodes
2 or 3 NICs/node, 12 channels
30 random flows to wired net
Cross-section goodput X
Results
Baseline: Single-channel net
Identical CA: 2x improvement
Centralized CA: 6-7x gains
Distributed CA: 6-7x gains
Single-NIC Multi-channel:
only marginal improvement

14. Performance Evaluation: Latency Reductions
Simulation Setup
64 nodes with 4 gateway nodes
2 NICs/node, 12 channels
HTTP traffic requests/response
Traffic intensity:0, X, 2X, 3X, 4X
Results
Reduced average delay
Saturation point: 4x users with
multi-channel networking

15. Hyacinth Channel/Route Allocation Daemon
Prototype Implementation
Hyacinth Channel/Route Allocation Daemon
User
Channels
Routes
Statistics
NDIS
Miniport
Driver
Kernel
Routing
Tables
Windows
Performance
Counters
Kernel
Optional
Wired
Interface
Hardware
Wireless
Network
Interfaces

16. Prototype Evaluation Configuration –
9 Win XP desktops, 2 gateway nodes
Two a NICs / node
FTP Throughput –
5-times improvement
Should be higher for larger testbed
Fail-over –
Node 6 fails; Node 3 switches to Node 2
< 700 msec to recover
~450 msec for changing route tables

17. IEEE 802.11 beyond AP—mobile communication
Conclusions..
IEEE beyond AP—mobile communication
Multi-channel wireless mesh backbone
Multiple commodity cards per node
Workload-aware channel assignment
Load-balancing routing
Many-fold improvement with small increase in price
Applicable to IEEE a
Ongoing Mesh Networking Research:-
Link-aware transport layer
Station-transparent mobility management
Secure routing protocol
Self-diagnosing and self-healing network management
Directional antenna: Spatial Diversity
Project site: