Requirements for ESS mesh network development November 2003 Requirements for ESS mesh network development David E. Hudak, Karlnet, Inc. dhudak@karlnet.com David E. Hudak, Karlnet, Inc.

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 802.11 LAN functions David E. Hudak, Karlnet, Inc.

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.

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.

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 802.11 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.

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.

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.

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.

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.

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.

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.

Additonal LAN functions November 2003 Additonal LAN functions 802.11 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.

Conclusions Frame mesh discussion in terms of November 2003 Conclusions Frame mesh discussion in terms of Services to be provided (unicast delivery, broadcast delivery, 802.11 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.