A Routing Protocol for Utilizing Multiple Channels in Multi-Hop Wireless Networks with a Single Transceiver

1. A Routing Protocol for Utilizing Multiple Channels in Multi-Hop Wireless Networks with a Single Transceiver Jungmin So & Nitin Vaidya (Technical Report Oct ’04) Presented by: Naveen Manicka

2. Agenda • Problems with Wireless Ad Hoc networks • Issues with multiple channel routing • Assigning channels to nodes • Assigning channels to flows • Channel load balancing • Multi-Channel Routing Protocol (MCRP) • Node States • Route Discovery • Channel Selection • Packet Forwarding & Channel Switching • Force Mechanism • Route Maintenance • Performance Evaluation • Related work • Conclusion & Future Work

3. Issues with Wireless Ad Hoc Networks • Number of users inversely proportional to performance • Single channel is shared by all users • IEEE 802.11 Infrastructure mode provides multiple non-overlapping channels • Ad Hoc mode – most MAC and routing protocols assume network uses single channel • Single transceiver nodes • Transmit or Receive • Need to agree on a channel to communicate with another node

4. Assumptions in the paper • Each node with single transceiver • Each node capable of switching channels (delay < 80μs) • MAC protocol - IEEE 802.11 DCF • Network Layer determines when and which channel to switch to • Goal – Design a routing protocol that utilizes multiple channels without changing the MAC protocol.

5. Issues in multi-channel routing • Routing protocol must perform channel assignment as well as route discovery. • 2 approaches to channel assignment • Assigning channel to node • Assigning channel to flow

6. Assigning channel to node • Channel assigned to node regardless of traffic patterns • Nodes can send packets by switching to channel of the receiver. • Works well with both proactive and reactive routing. • Benefit – Route establishment de-coupled with channel assignment • Issue – Deafness problem -> Channel deadlock

7. Deafness Problem • 2 flows - A to C & D to E • A & D on Channel 1, B is on 2 and C & E are on 3 • B switches to 3 to transmit packet from A to C and later returns to 2 • While B is on 3, D tries to transmit to B on 2 -> Packet is lost ---- Deafness Problem • IEEE 802.11 DCF waits for a random delay and retransmits : Drops packets after several retransmissions : Notifies link as broken • Channel Deadlock can occur when another node tries to transmit to D on 1 and series of nodes wait on the receivers channel

8. Assigning channels to flows • All nodes in the route are assigned common channel • Nodes do not need to know the next hop channel and do not need to switch to it to transmit. • Works well with reactive protocols, but difficult to maintain routes proactively. • Channel assignment is coupled with route establishment • Benefit - Deafness problem can be avoided • Issue – Routing protocol becomes complicated

9. Assigning Channels to flows • Constraints to allow nodes to switch channels • 2 consecutive nodes in a path cannot switch channels • A node must notify its neighbors in a path whenever it switches channels • A node can only switch between a small number of channels (such as two), although many more channels are available. • Nodes may not switch channels too frequently, such as per-packet basis • First 2 constraints avoid Deafness Problem & last 2 are for performance reasons • Channel switching allows more freedom in selecting routes and assigning channels : Worst case – All flows share a common channel i.e performance does not fall below single channel protocol.

10. Channel Load Balancing • Single channel routing protocols – Routes selected based on metrics like hop distance, signal strength, degree of stability and expected transmission time. • Multi-channel routing protocol – Balancing load between available channels also important • 3 flows on node-disjoint routes • Assigning different channels to the flows requires channel load info • Send HELLO messages on all channels in round robin fashion • Trade-off between overhead and accuracy in collected info

11. MCRP – Multi Channel Routing Protocol • On-demand routing protocol • Similar to AODV • Benefits from multiple channels without changing MAC protocol • Improves network performance by allocating different channels to different flows • Guarantees route establishment if the route can be established in a single channel network with same topology. • Worst case performance compares to single channel protocol • Allows nodes to switch channels based on constraints

12. MCRP – Multi Channel Routing Protocol • Node States • free: The node does not have any flows and may freely switch to other channels. • locked: The node has a flow on a certain channel. • switching: The node is involved in multiple flows on different channels. • hard-locked: The node has a flow on a certain channel, and it cannot be made a switching node.

13. MCRP – Multi Channel Routing Protocol • Node States C – Switching node A, E, F & I – Locked nodes G, B, D & H – Hard locked nodes

14. MCRP – Multi Channel Routing Protocol • Route Discovery • Source broadcasts RREQ on all channels with operating channel information • Reverse path is setup as the RREQ is forwarded by nodes • At most kn RREQ packets transmitted (k – number of channels, n – number of nodes) • Overhead per channel same as single channel protocol • Destination sends RREP to source using the reverse path

15. MCRP – Multi Channel Routing Protocol • Route Discovery

16. MCRP – Multi Channel Routing Protocol • Route Discovery Route entry in route table • All fields in AODV except channel and active fields • Channel – indicates the next hop channel • Active – relevant when next hop is a switching node. Has value 1 (packets can be forwarded to next hop) or 0 (packets are buffered till value becomes 1)

17. MCRP – Multi Channel Routing Protocol • Route Discovery As the RREP travels to the source, the intermediate nodes switch channels and states as follows. Suppose the selected channel is channel 1. • free node: The node becomes a locked node and switches channel to channel 1. • locked node: If the node is locked on channel 1, nothing changes. If the node is locked on another channel, it becomes a switching node between channel 1 and the original channel that this node was on. • switching node: If channel 1 is one of the channels it is switching between, then nothing changes. Otherwise, the node drops the RREP packet. This is because MCRP does not allow a switching node to switch between three or more channels, as mentioned before. • hard-locked node: If the node is locked on channel 1, nothing changes. Otherwise, the node drops the RREP packet, because hard-locked nodes are not allowed to become switching nodes. To avoid all routes getting dropped due to node state change to infeasible, “force” mechanism is used to establish a route.

18. MCRP – Multi Channel Routing Protocol • Channel Selection Objective 1: No node in path must go into infeasible state • Channel table: Included in the RREQ and records state of nodes in path from source to destination • free node: No changes made to the channel table. • locked node: If the locked channel is channel i, increment chiby one. • switching node: if the two channels are channel i and j, increment chiand chjby one. • hard-locked node: If the locked channel is channel i, increment chiby two.

19. RREQ updates : S(0,0,0) – A(0,1,0) – B(0,1,1) – D(0,1,1)

20. MCRP – Multi Channel Routing Protocol Objective 2: Channel with lowest load needs to be selected i.e chosen channel should maximize the throughput at the bottleneck node. • Flow Table: Included in the RREQ and records number of flows in each channel for a node and its neighborhood • Each node transmits HELLO messages periodically on all channels • HELLO packet includes the channels each node is one and number of flows in the channel • Each node maintains a flow table for itself. • The node also updates the flow table in the RREQ as it forwards it • For each c, if Fc(i) > Fc, then update Fcto be Fc(i).

21. Flow table of S – (0,1,0); A – (0,3,1); B – (0,1,3); D – (0,0,1) • RREQ Updates : S(0,1,0) – A(0,3,1) – B(0,3,3) – D(0,3,3)

22. MCRP – Multi Channel Routing Protocol • Channel Selection Algorithm Using channel table, Route is infeasible if • Multiple channels have values greater or equal to 2 • More than 2 channels have values greater or equal to 1 Using flow table, a channel is chosen from the route • If a channel has a value greater or equal to 2, this channel has to be selected. • If two channels have a value 1, then one of these two channels which has the minimum interference level is selected. • If only one channel has a value 1 and all other channels have 0’s, then among all channels, the one with the minimum interference level is selected. Final channel table – (0,1,1) : Final flow table – (0,3,3) • Route is feasible and either channel 2 or 3 has to be selected • Interference level on 2 & 3 is same, so select randomly

23. MCRP – Multi Channel Routing Protocol • Delayed reply • AODV replies to the first route request and disregards all others • Considering metrics other than delay, multiple routes can be maintained using delayed reply mechanism • Destination waits for sometime before replying to the first route request • Intermediate node forwards another route request if it has a better metric • MCRP uses delayed reply – sets up a timer after receiving first route request – allows intermediate nodes to forward multiple route requests if route is feasible and path interference is lower than previous

24. MCRP – Multi Channel Routing Protocol • Packet Forwarding and Channel Switching • A route is established with a common channel to all nodes in the flow. • A switching node tunes into different channels at different times – This could create problems when a node transmits to it on a channel different from what it is listening on • The neighbors of a switching node need to be informed of the channel it is currently on • MCRP uses LEAVE/JOIN messages • A switching node S (operating on 1 and 2) before switching sends a LEAVE message to its neighbors • The neighbors update the route entries with S as next hop by resetting the active flag • Packets are buffered in the neighbors till S sends a JOIN message and then sent with higher priority • The switching node stays on a channel for a pre-decided duration of time

25. MCRP – Multi Channel Routing Protocol • Force Mechanism • Source may fail to find a route if destination drops all potential routes • Destination can still choose a route and send reply back with “force” flag set in RREP, thus guaranteeing at least one route • Intermediate node receiving RREP with force flag set, selects channels as follows: • Free node: The node becomes a locked node, and it is locked on channel x. • Locked or Hard-locked node: If it is already locked on channel x, do nothing. If it is locked on another channel, send RERR for the flows that were on the other channel, and switch to channel x. The node state remains unchanged. • Switching node: If one of its operating channels is channel x, then do nothing. If not, then choose one of its operating channel and send RERR for the flows on that channel, and replace that channel with channel x in the set of its operating channels. The node state remains unchanged. • To avoid oscillation, nodes that have a route by force, do not accept another RREP with force flag set for a certain duration of time

26. MCRP – Multi Channel Routing Protocol • Route Maintenance • Similar to AODV. Sets up a timer for the route established. If the timer expires without route being used, route is deleted from table. If route is used before timer expiration, the timer is reset • A broken route (due to mobility or node failure) is deleted from the table and nodes using the route are notified with RERR messages. To reduce RERR cost, nodes maintain precursor lists and notify only if there is a precursor for the broken route • Node state changes due to route changes: • locked node: If all routes are removed, the node becomes a free node. • hard-locked node: If all routes are removed, the node becomes a free node. If all routes that have a switching node as its next hop are removed, then the node becomes a locked node. • switching node: If all routes in one channel are removed, then the node becomes a locked node

27. Performance Evaluation • Simulation Setup • ns-2 simulator • MCRP with 2,3 & 4 channels compared against AODV with single channel • Varying parameters – • Number of flows • Flow rate • Connection pattern • Constant Bit Rate (CBR) over UDP • Packet size – 512 bytes • All channels are 11Mbps • Network area – 1000m * 1000m square • Transmission range of each node ~ 250m • MAC protocol – IEEE 802.11 DCF • Duration of a switching node in a channel – 50 ms (regardless of traffic)

28. Network Throughput varying Number of Flows

29. Network Throughput varying Flow Rate

30. Network Throughput varying Scenario

31. Related Work • Nasipuri, Zhuang and Das – Multi-channel protocol with assumption of N transceivers for N channels • Nasipuri and Das – Extention of previous protocol, with support for channel selection based on signal strength • Wu, Lin, Tseng and Sheu – MAC protocol that assigns channels dynamically, in an on-demand style, requiring 2 transceivers. One for control channel and one for data channel • Wu, Lin, Tseng and Sheu – Extension of previous protocol to include power control with channel assignment • Jain, Das and Nasipuri – Similar protocol with 2 transceivers and channel selection based on channel condition on the receiver end • Jungmin So and Nitin Vaidya – MAC protocol with single transceiver (presentation by Nabeel Khan) • Bahl, Chandra and Dunagan – Nodes switch from channel to channel based on a sequence • Shacham and King – Routing protocol for multi-channel network. Different schemes for different scenarios ( single and multiple radios) • Raniwala, Gopalan and Chiueh – Centralized channel assignment algorithm, assuming 2 transceivers. • Adya, Bahl, Padhye, Wolman and Zhou – Link layer protocol that manages underlying multiple interfaces and performs channel selection • Chandra, Bahl and Bahl – Software layer enabling single wireless card to connect to multiple networks • Draves, Padhye and Zill – Metric for multi-channel networks combing expected transmission time and channel diverseness

32. Conclusions • MCRP is a network layer approach for utilizing multiple channels in wireless ad hoc networks, assuming single-channel MAC protocol (IEEE 802.11 DCF) and single transceiver. • MCRP assigns channels to flows and allows dynamic channel switching. Also two consecutive nodes are not allowed to become switching nodes to overcome deafness problem. • MCRP improves network throughput by using multiple channels and does not need any additional hardware. Hence can be easily deployed to currently used devices.

33. Future Work • Nodes switching between channels need not switch based on a fixed period. The interval can be determined based on number of pending packets in each queue. It can also be determined according to the observed channel condition. • Assigning channels to flows may not be efficient for flows with large number of hops. Assigning different channels to nodes in a flow while avoiding deafness problem. • Cross-layer approach, MAC and network layers cooperating with each other to achieve higher performance.

34. References • [1]Richard Draves, Jitendra Padhye, and Brian Zill, “Routing in multi-radio, multi-hop wireless mesh networks,” in ACM Mobicom, 2004. • [2] Ashish Raniwala, Kartik Gopalan, and Tzi-cker Chiueh, “Centralized channel assignment and routing algorithms for multi-channel wireless mesh networks,” Mobile Computing and Communications Review, vol.8, no. 2, pp. 50–65, April 2004. • [3] R. Choudhury and Nitin Vaidya, “Deafness: A mac problem in ad hoc networks when using directional antennas,” in IEEE ICNP, 10 2004. • [4] Shih-Lin Wu, Chih-Yu Lin, Yu-Chee Tseng, and Jang-Ping Sheu, “A new multi-channel mac protocol with on-demand channel assignment for multi-hop mobile ad hoc networks,” in International Symposium on Parallel Architectures, Algorithms and Networks (ISPAN), 2000. • [5] C. Perkins, E. Belding-Royer, and S. Das, “Ad hoc on-demand distance vector (aodv) routing,” in Ietf RFC 3561, July 2003. • [6] VINT Group, “UCB/LBNL/VINT network simulator ns (version 2),” . • [7] A. Nasipuri, J. Zhuang, and S.R. Das, “A multichannel csma mac protocolfor multihop wireless networks,” in WCNC, September 1999. • [8] A. Nasipuri and S.R. Das, “Multichannel csma with signal power-basedchannel selection for multihop wireless networks,” in VTC, September 2000. • [9] S.-L.Wu, Y.-C. Tseng, C.-Y. Lin and J.-P. Sheu, “A Multi-Channel MAC Protocol with Power Control for Multi-Hop Mobile Ad Hoc Networks,”The Computer Journal, vol. 45, pp. 101–110, 2002. • [10] N. Jain, S. Das, and A. Nasipuri, “A multichannel csma mac protocol with receiver-based channel selection for multihop wireless networks,” inIEEE International Conference on Computer Communications and Networks (IC3N), October 2001. • [11] Jungmin So and Nitin H. Vaidya, “Multi-channel mac for ad hoc networks: Handling multi-channel hidden terminals using a single transceiver,” in Mobihoc, 2004. • [12] Paramvir Bahl, Ranveer Chandra, and John Dunagan, “Ssch: Slotted seeded channel hopping for capacity improvement in ieee 802.11 ad-hoc wireless networks,” in ACM Mobicom, 2004. • [13] N. Shacham and P. King., “Architectures and performance of multichannel multihop packet radio networks,” IEEE Journal on Selected Area in Communications, vol. 5, no. 6, pp. 1013– 1025, July 1987. • [14] Atul Adya, Paramvir Bahl, Jitendra Padhye, Alec Wolman, and Lidong Zhou, “A multi-radio unification protocol for ieee 802.11 wireless networks,” in IEEE International Conference on Broadband Networks (Broadnets), 2004. • [15] Ranveer Chandra, Paramvir Bahl, and Pradeep Bahl, “Multinet: Connecting to multiple ieee 802.11 networks using a single wireless card,” in IEEE Infocom, Hong Kong, March 2004.

35. Questions ???????

36. Homework Questions • Give a situation (as in a flow diagram) wherein the performance of MCRP degrades to that of a single channel routing protocol. • In Fig.9, the average throughput of MCRP (2,3 & 4) for varying number of flows increases to a peak and then drops. Why? http://www.eecis.udel.edu/~manicka/Courses.html Due: Wednesday, 24th Nov `04

37. THANK YOU!!!!!