1. CS541 Advanced Networking 1 Dynamic Channel Assignment and Routing in Multi-Radio Wireless Mesh Networks Neil Tang 3/10/2009

2. CS541 Advanced Networking 2 Outline  References  Channel Assignment Methods  Problem Definition  Link Layer (Channel Assignment) Protocol  Routing metric and protocol  Simulation Results

3. CS541 Advanced Networking 3 References Kyasanur-MC2R06: P. Kyasanur and N. H. Vaidya, Routing and link-layer protocols for multi-channel multi-interface ad hoc wireless networks, ACM SIGMOBILE Mobile Computing and Communications Review, Vol.10, No.1, 2006, pp. 31 – 43. Draves-MobiCom06: R. Draves, J. Padhye, and B. Zill, Routing in multi- radio, multi-hop wireless mesh networks, ACM Mobicom’2004, pp. 114- 128.

4. CS541 Advanced Networking 4 Channel Assignment Methods  Static  Dynamic  Hybrid

5. CS541 Advanced Networking 5 Assumptions  MAC layer: 802.11  Multiple available channels: IEEE 802.11a and 802.11b standard specify 12 and 3 non-overlapping channels respectively. The number of available channels is larger than the number of radios in a node.  Channel switching delay: a few millisecond.  Node: each node has multiple radios (NICs), each of which can be tuned to one of the available channels.  Traffic: Unicast communications and a connection request with a source-destination pair may arrive at any time.

6. CS541 Advanced Networking 6 Problem Definition  Problem: A source-destination route and a corresponding channel assignment.  Optimization goals: 1) High channel utilization. 2) Network connectivity is ensured. 3) Allow implementation on existing 802.11 hardware.

7. CS541 Advanced Networking 7 Interface Assignment  Fixed interfaces: Some K out of M interfaces at each node are assigned for long intervals of time to some K channels.  Switchable interfaces: The remaining M − K interfaces are dynamically assigned to any of the remaining M − K channels (over short time scales), based on data traffic.

8. CS541 Advanced Networking 8 Link Layer Protocol  Each node maintains a NeighborTable containing the fixed channels being used by its neighbors.  Each channel is associated with a packet queue. If an unicast packet is received at the link layer for transmission, the fixed channel of the destination of the packet is looked up in the NeighborTable, and the packet is added to the corresponding channel queue.  Broadcast (e.g., route discovery, Hello) is conducted over every channel.

9. CS541 Advanced Networking 9 Link Layer Protocol  When the switchable interface is switched to a new channel, it is always switched to the channel with the oldest queued data.  The switchable interface changes channels only when there are packets queued for another channel, and one of the following two conditions hold: 1) The switchable interface is on a channel with an empty queue. 2) The switchable interface has been on a channel for more than MaxSwitchTime duration.

10. CS541 Advanced Networking 10 Link Layer Protocol  Nodes also maintain a ChannelUsageList containing a count of the number of nodes in its two-hop neighborhood using each channel.  Periodically, each node broadcasts a “Hello” packet on every channel. The Hello packet contains the fixed channel being used by the node, and its current NeighborTable.  If the number of other nodes using the same fixed channel as itself is large, then a node with some probability p (set to 0.4 in simulations) changes its fixed channel to a less used channel.

11. CS541 Advanced Networking 11 Strength and Weakness  Transmitter-receiver synchronization is not needed.  High channel utilization and low interference.  Scalable.  High broadcast overhead.  Interface utilization and throughput?

12. CS541 Advanced Networking 12 Switching Cost

13. CS541 Advanced Networking 13 Switching Cost  InterfaceUsage(j): the fraction of the time a switchable interface was transmitting on channel j.  p s (j): the probability the switchable interface will be on a different channel (i ≠ j) when a packet arrives on channel j.  Switching cost:

14. CS541 Advanced Networking 14 Routing Metric For hop i, channel j :

15. CS541 Advanced Networking 15 Measure ETX

16. CS541 Advanced Networking 16 Routing Protocol  DSR is the baseline solution.  The RREQ packet sent by a node X over a channel i contains the ETT, switching cost, and channels used on all previous hops, as well as the switching cost of channel i at node X.  An intermediate node re-broadcasts the RREQ if 1) The sequence number in the RREQ is being seen for the first time. 2) The cost of the already discovered (partial) path in the RREQ is smaller than the cost seen in all earlier RREQs with the same sequence number, if any.  When the destination receives an RREQ, it responds with a route reply (RREP) only if the cost of the received RREQ is smaller than other RREQs (containing the same sequence number) seen till then.

17. CS541 Advanced Networking 17 Simulation Results