1. Requirements for ESS mesh network development
November 2003
Requirements for ESS mesh network development
David E. Hudak, Karlnet, Inc.
David E. Hudak, Karlnet, Inc.

2. Overview Background Mesh network Mesh Network Example 1 (MNE1)
November 2003
Overview
Background
LAN functions
LAN characteristics
Mesh network
Functional requirements
Mesh Network Example 1 (MNE1)
MNE1 assumptions
MNE1 possibilities
Additional LAN functions
David E. Hudak, Karlnet, Inc.

3. LAN characteristics Collision domain Broadcast domain
November 2003
LAN characteristics
Collision domain
Set of hosts in LAN that participate in the same media arbitration (I.e., coordination function)
For classic ethernet, collision domain is all nodes on network segment
Broadcast domain
Set of hosts in LAN that see one another’s broadcast frames
VLAN, for example, is the support of a single broadcast domain over multiple collision domains.
David E. Hudak, Karlnet, Inc.

4. November 2003
L3/L2 Interface
Functions that a L2 network has to support for an IP stack
Unicast frames
Broadcast frames
Taking multicast as a special case of broadcast
The IP stack (L3) is not aware of any underlying L2 bridging or VLAN switching that is done.
David E. Hudak, Karlnet, Inc.

5. Mesh functional requirements
November 2003
Mesh functional requirements
I propose that these requirements MUST be supported by any mesh architecture
L3 support
Provide unicast delivery service
Provide broadcast delivery service
L2 support
Match underlying physical network topology
Provide protocol support
E.g., media arbitration (coordination function)
…and more ugly stuff that I don’t want to address right now
David E. Hudak, Karlnet, Inc.

6. November 2003
MNE1: Constraints
Concurrent utilization of single channel, or “Loosely connected network”
Required method: shrink the collision domain
Transmit power control
Directional antennas
Single radio per station (decreases cost)
Single ESS
One broadcast domain, one IP subnet
David E. Hudak, Karlnet, Inc.

7. MNE1: Mesh Network Example
November 2003
MNE1: Mesh Network Example A B C A B C D E F D E F
David E. Hudak, Karlnet, Inc.

8. MNE1: Definitions Visibility Two sets are interesting
November 2003
MNE1: Definitions
Visibility
A host, a, is said to be visible from another host, b, if
a has sufficient transmit power to be heard by b, and
a and b are on the same channel
a ~ b read as “a is visible to b”
Special case: symmetric link is a set of two stations, a and b, such that (a ~ b) and (b ~ a)
Two sets are interesting
T(a) = {b, such that a ~ b} (a’s transmit set - “you can hear a”)
R(a) = {b, such that b ~ a} (a’s receive set - “a can hear you”)
Any host, a, can construct R(a) by sensing medium
Getting T(a) is trickier…
For symmetric links, T(a) = R(a)
David E. Hudak, Karlnet, Inc.

9. MNE1: Coordination function constraints
November 2003
MNE1: Coordination function constraints
An ongoing transmission restricts a station’s ability to communicate. If station a is transmitting to station b:
T(a) cannot receive due to hearing a’s transmission
R(b) cannot transmit or else b will hear a collision with a’s transmission
So, T(a) and R(b) have to be notified
David E. Hudak, Karlnet, Inc.

10. MNE1: DCF frames Using DCF, let TA = a, RA = b
November 2003
MNE1: DCF frames
Using DCF, let TA = a, RA = b
RTS(a) - observed by T(a)
CTS(b) - observed by T(b)
DATA(a) - observed by T(a)
ACK(b) - observed by T(b)
If all links are symmetric, than T(a) = R(a) and T(b) = R(b)
Therefore, DCF gives us concurrent operation
David E. Hudak, Karlnet, Inc.

11. MNE1: delivery services
November 2003
MNE1: delivery services
Stations make link announcements (starting with receive sets)
Receive sets are link state information
OSPF-style routing algorithm has to be developed
Initial cost could be simple hop-count
Supports both unicast and broadcast deliveries
David E. Hudak, Karlnet, Inc.

12. Additonal LAN functions
November 2003
Additonal LAN functions
is a session-oriented protocol
Associate/disassociate
Authenticate and key exchange
These have to be solved as well
Stations in the mesh can “proxy beacon” for the AP
All associated stations have a path back to AP
David E. Hudak, Karlnet, Inc.

13. Conclusions Frame mesh discussion in terms of
November 2003
Conclusions
Frame mesh discussion in terms of
Services to be provided (unicast delivery, broadcast delivery, protocol support)
Assumptions of network topology
Mesh is something that should be hidden from L3 (as VLAN is today)
Just because forwarding tables are computed, that does not make it IP
David E. Hudak, Karlnet, Inc.