1. Naval Research Laboratory Dynamic Backbone Subnets
ESS Mesh
Overview & Issues
James P. Hauser
Naval Research Laboratory
Dennis J. Baker
Dynamic Backbone Subnets

2. Meshing with the 802 Architecture
ANSI/IEEE Std , 1999 Edition
Interaction with other IEEE 802 layers
IEEE is required to appear to higher layers [logical link control (LLC)] as a current style IEEE 802 LAN. This requires that the IEEE network handle station mobility within the MAC sublayer. To meet reliability assumptions (that LLC makes about lower layers), it is necessary for IEEE to incorporate functionality that is untraditional for MAC sublayers.

3. Requirements Necessary for ESS Mesh to Appear as a IEEE 802 LAN
All nodes in the LAN appear to be one hop away from the vantage point of a higher layer protocol.
Any pair of nodes within the LAN may communicate with each other.
Every node may broadcast to all other nodes in the LAN.
In a hierarchical topology, such as an ESS, station mobility must be managed, i.e., as the station migrates from one BSS to another.

4. Mobility Issues Routing is the central issue in a flat topology.
In a hierarchical topology, e.g., an ESS, STA mobility is also an issue.
Mobility is facilitated by the following:
Topologically correct address, e.g., (Access Point ID + Association ID)
Use BSSID as an Access Point ID?
Use short, local, pseudonym for Access Point ID (e.g., 0,1,2,…)?
Auto assignment of local, mesh-unique Access Point IDs
Address resolution protocol(s) to map from the topologically correct address to the MAC address
Proactive / Reactive ?

5. L2.5 Routing Broadcast / Multicast / Unicast Proactive / Reactive
Convergence
Ability of a protocol to form valid routes
Affected by link dynamics
Impacts routes
Impacts operation of routing algorithm itself
Link Metrics
Capacity, Latency, Hop Count, Power Consumption, …
Link State Advertisement (LSA) Protocol

6. “Broadcast” Types ESS-Wide (All 1’s) Broadcast
Mesh-Wide (All APs) Broadcast
Non-Relayed (1 hop) Broadcast
Does an Ethernet address exist for this purpose?
Multicast Buffering Issue
Multicast buffering for traffic destined for STAs in power-save mode, but NOT for multicast traffic destined for APs

7. Control Approaches
Centralized
Distributed

8. Synchronization Beacon Coordination?
Support for synchronous protocols?
e.g., 11-03/266r1
QoS
Mesh scheduled media access?

9. AP-to-AP 802.11 Message Format Design Decisions
Use ‘Reserved’ message type/subtype?
Use Beacon Element(s) for management frames?
Use existing WDS message formats?
Encapsulation within Mesh frames?
E.g., Subnet headers specified in 11-03/266r1
Frame sequence numbers that have mesh-wide scope?