1. Simple Efficient and Extensible Mesh
May 2005
doc.: IEEE /0398r0
May 2005
Simple Efficient and Extensible Mesh
Date:
Authors:
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Texas Instruments Inc.
Texas Intruments Inc.

2. Outline Proposal Objectives Proposal Overview Summary
May 2005
Outline
Proposal Objectives
Proposal Overview
Overall architecture
QoS and access
Discovery/Association
Routing
Powersave mechanism
Security
Summary
Texas Instruments Inc.

3. Proposal Objectives (1/3)
May 2005
Proposal Objectives (1/3)
Functionality
Support functional requirements (obvious)
Better functionality for ad-hoc networking than IBSS
Balance between functionality and simplicity
Enough functionality that does not spawn too many PARs too soon
But not too heavy so it delays standardization
Simplicity and extensibility
Simple algorithms that enable quick product cycles
Easy manageability
As much re-use of current protocols as possible
Simple hooks to enable further addition of functionality
Texas Instruments Inc.

4. Proposal Objectives (2/3)
May 2005
Proposal Objectives (2/3)
MAC and QoS support
Compatible with E
EDCA extensions for mesh environment
Map HCCA into mesh without synchronization requirements among mesh points
Routing
Flexible routing protocol that can be adapted to most environments
Possibly parameterized tuning to various environments
Possibility of additional protocols in future
Power Save Support
Enable power efficient ad-hoc network operation
Fix holes in powersave scheme
Avoid complexity in sleep wake cycle operation
Routing and other mechanisms be power aware
Texas Instruments Inc.

5. Proposal Objectives (3/3)
May 2005
Proposal Objectives (3/3)
Enable advanced technologies
Multi-channel multi-radio operation
Hooks for such optimizations
Flexible
Mitigation of hidden and exposed nodes problems
Hooks for independent solutions to the problem using multiple radios etc.
Security:
Enable both centralized and distributed scenarios
Pre-shared secret
Authentication server through a mesh portal
Adapt/Reuse i as much as possible
Measurement/Control
Possibility of (Hooks for) exclusive control channels
Texas Instruments Inc.

6. Outline Proposal Goals Proposal Overview (A top down approach) Summary
May 2005
Outline
Proposal Goals
Proposal Overview (A top down approach)
Overall architecture
QoS and access
Discovery/Association
Routing
Powersave mechanism
Security
Summary
Texas Instruments Inc.

7. A Multi-Radio Mesh Point Architecture
May 2005
A Multi-Radio Mesh Point Architecture
To higher layers
Multi-radio mesh operation
(possibly transparent: for all Meshs working only on single channels)
Radio 1:
11s + BSS
Stack
Radio 2:
11s + BSS
Stack
Radio 3:
11s + BSS
Stack
Texas Instruments Inc.

8. Hooks for Multi-radio Optimizations
May 2005
Hooks for Multi-radio Optimizations
Independent and identical mesh stacks on different radios, all controlled by a multi-radio controller
Operation of multi-radio controller left open
Multi-radio controller may be configured to set up from 1 to N number of different meshs, if N is the number of radios on the MP
E.g. 3 radio
1 mesh with 3 radios
2 meshs: one with single radio, other with 2 radios
3 meshs: single radio each
Provide hooks in the form of the above architecture
Texas Instruments Inc.

9. Mesh Stack for a Radio Interface
May 2005
Mesh Stack for a Radio Interface
Each radio’s stack is as follows
Discovery, association, and link management
Configuration and management: Includes QoS management
Measurements / CTRL
Measurements and CTRL
Security protocol
Topology learning/Routing protocol and Forwarding
Mesh MAC
Including QoS, Powersave, and any Encryption
DCF
PHY
Non DCF compatible measurements/control are only used in a channel with no legacy devices, and possibly in multi-radio enhanced operation
Texas Instruments Inc.

10. Mesh and Legacy MAC Architecture
May 2005
Mesh and Legacy MAC Architecture
BSS and Mesh MAC may be independently turned on or off
When both MACs are ‘on’ they interact to coexist
Interaction does not effect legacy air interface (thus backwards compatible)
Mesh scheduling
BSS scheduling
11n
MAC
Measurements / CTRL
Measurements/CTRL
HCF
Controlled
Access
(HCCA)
Mesh
Minimal
Contention
Access (MMCA)
HCF
Contention
Access
(EDCA)
Mesh
EDCA
HCCA-MMCA access resolution
Mesh-BSS prioritized access resolution
Distributed Coordination Function (DCF)
PHY
11a/11b/11g/11j PHY
11n
PHY
Texas Instruments Inc.

11. May 2005
doc.: IEEE /0398r0
May 2005
Mesh EDCA
For an N hop flow, the effective PHY rate of 1/N and statistically same access latency as a single hop connection is achieved.
ACs are preserved across hops.
Packets carry the expected value of number of hops for their flows (N).
Higher basic values of CWmin and CWmax
Backoff is chosen by dividing the current CW by N. This gives statistically N times access to N-hop traffic compared to single hop traffic in the same AC.
All traffic reaching a MP from a particular link is logically queued separately within the same AC. Note that logical queues are not too difficult in software. Thus, the winner of EDCA TXOP is the logical queue within all ACs that has the minimum backoff value. If expected maximum neighbors = 5, maximum (5*4=20) logical queues are contending within a MP.
Texas Instruments Inc.
Texas Intruments Inc.

12. Mesh Minimal Contention Access (MMCA)
May 2005
Mesh Minimal Contention Access (MMCA)
HCCA in BSS can access channel after PIFS and thus gets priority over any EDCA access
Problem:
In co-existing BSS-Mesh environments, BSS HCCA can starve flows in Mesh EDCA
Solution:
Map HCCA to a minimal contention access method in mesh
Can be interpreted as a fifth access category with IFS comparable to PIFS and low contention probability
Texas Instruments Inc.

13. Discovery, Association, and Link Management
May 2005
Discovery, Association, and Link Management
Beacons and Probes for discovery
All MPs not in powersave mode beacon regularly
Potentially lower beaconing frequency in powersave mode
Mutual Association between every pair of directly communicating MPs
Link Management
Measurements of various metrics for links
Link information possibly used by routing protocols
Disassociation may be explicit or implicit
Implicit => connectivity loss over a time period
Texas Instruments Inc.

14. Routing Protocol Design Motivation
May 2005
Routing Protocol Design Motivation
Mobility is expected to be low to moderate.
Network size restricted; Scale not an issue.
For larger networks hierarchical routing can be achieved and utilized through mesh portals
bridging protocols: e.g., spanning tree bridge protocol
layer 3 subnets
Expectations from a baseline routing protocol
Possibly be able to function in the widest variety of expected scenarios
Not too complicated
Efficient in terms of power, channel capacity usage, and processing
Should be good enough for basic requirements such as QoS, load balancing, alternate path selection etc., and not be a routing protocol that only provides reachability
Texas Instruments Inc.

15. Approaches to Routing Find an optimum balance between
May 2005
Approaches to Routing
Find an optimum balance between
Reactivitity and Proactivity
Begin with a reactive protocol and add proactive elements
Begin with a proactive protocol and reduce proactivity
Distance vector “simplicity” and link state “performance and capability”
Modulate the size and frequency of link state updates
Enhancements to distance vector approaches
Can we design a single routing protocol that finds “any” operating region in the broad spectrum of operating regions as described above?
Answer: Parameterized routing
Texas Instruments Inc.

16. Powersave: Motivation and Approach
May 2005
Powersave: Motivation and Approach
Motivation
IBSS powersave mechanisms are broken
Support for power aware ad-hoc networking using s (versus IBSS mode)
Approach
Use as much as possible concepts and message structures that have been previously standardized for standard infrastructure and AdHoc operation
ATIM interval
More bit
Mesh APSD
Texas Instruments Inc.

17. Powersave: Salient features
May 2005
Powersave: Salient features
Mesh PS requires mesh points to be awake only for the portion of time required for actual reception
Uses EOSP and More bits to indicate that mesh point may return to doze mode
Mesh PS allows for setup of agreed flexible and non beacon related schedules for transmission between mesh points operating in PS
Mesh PS allows for STAs to wakeup on any selected Listen Interval period rather than each beacon interval
Texas Instruments Inc.

18. Mesh Powersave versus IBSS Powersave
May 2005
Mesh Powersave versus IBSS Powersave
The proposed mesh powersave mechanism provides the following benefits compared to IBSS powersave mechanism
Drastically improve power saving for devices operating in standby mode
Drastically improve power saving for devices that source/sync packetized streaming data
Provides better QoS for streams by allowing flexible scheduling
Reducing collision between mesh points by minimizing the usage of ATIM and synchronization to beacons
Texas Instruments Inc.

19. Security (1/2) Scenario with respect to 802.11i: Proposal Overview:
May 2005
Security (1/2)
Scenario with respect to i:
Challenge: Authentication server may be absent or multiple hops away
Saving grace: Parts of mesh similar to IBSS
Proposal Overview:
Use a combination of ESS and IBSS parts of i
Data privacy: Re-use the part of i without any changes
Treat one-hop clusters in the mesh as IBSSs for authentication purposes (The whole mesh can be viewed as a group of IBSSs)
Re-use the IBSS-specific key management and authentication portions of i
Some changes required to accommodate the interconnectedness of the mesh
Texas Instruments Inc.

20. May 2005
Security (2/2)
All MPs must use a single “group” cipher suite i.e. the same security protocol for multicast/broadcast frames
All MPs must support a common subset of “pairwise” cipher suites. However, a pair of MPs may negotiate to use any common pairwise cipher suite they both support
For e.g. MP1 and MP2 can use TKIP while MP1 and MP3 use CCMP
An MP must perform security associations with all devices that it is associated with
Generate pairwise and group keys for all of its one-hop neighbors
Broadcast/multicast transmissions: Each MP defines its own group key, and distributes to all peer MPs
The mesh can use either pre-shared keys or 802.1X to authenticate MPs
Solution to authentication server being multi-hop away
Texas Instruments Inc.

21. Summary Better functionality for ad-hoc networking than IBSS
May 2005
Summary
Better functionality for ad-hoc networking than IBSS
Balance between functionality and simplicity
As much re-use of current protocols as possible
Simple hooks to enable further addition of functionality
Flexible and simple routing protocol that can be adapted to most environments
Powersave and QoS support
802.11i extensions for mesh security
Texas Instruments Inc.