1 / 16

Mobile Ad Hoc Networks (MANETs) Neil Tang 02/02/2009

Mobile Ad Hoc Networks (MANETs) Neil Tang 02/02/2009. Outline. Network Architecture Characteristics Applications Major Concerns Challenges Ad Hoc Routing DSR. C. B. E. A. D. B. C. E. A. D. Network Architecture. Characteristics. Multihop wireless network Unrestricted mobility

marlis
Download Presentation

Mobile Ad Hoc Networks (MANETs) Neil Tang 02/02/2009

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Mobile Ad Hoc Networks (MANETs)Neil Tang02/02/2009 CS541 Advanced Networking

  2. Outline • Network Architecture • Characteristics • Applications • Major Concerns • Challenges • Ad Hoc Routing • DSR CS541 Advanced Networking

  3. C B E A D B C E A D Network Architecture CS541 Advanced Networking

  4. Characteristics • Multihop wireless network • Unrestricted mobility • Dynamic node membership • Various physical layer techniques, e.g., directional antenna, cognitive radio CS541 Advanced Networking

  5. Applications • Battle-field communications • Emergency communications • Transportation system CS541 Advanced Networking

  6. Major Concerns • Mobility: link breakage • Power consumption • QoS • Scalability • Security CS541 Advanced Networking

  7. Challenges • MAC protocol design (802.11 DCF): directional antenna, cognitive radio • Routing • End-to-end QoS support: mobility andintra-flow interference. • Multicast/Broadcast Routing CS541 Advanced Networking

  8. Ad Hoc Routing • On-demand (reactive) routing: Upon arrival of a connection request, the source node floods route discovery messages and find a route for packet forwarding. For example, Ad hoc On-demand Distance Vector (AODV) protocol, Dynamic Source Routing (DSR) protocol. • Proactive routing: Nodes flood updates throughout the network whenever the network topology changes. For example, Optimized Link State Routing (OLSR) protocol. • Hybrid routing: Route discovery is basically conducted reactively but link state update is conducted proactively within a certain range, e.g., 2-hop neighborhood of a node. For example, Zone Routing Protocol (ZRP) • IETF MANET group: http://www.ietf.org/html.charters/manet-charter.html CS541 Advanced Networking

  9. On-Demand VS. Proactive • On-demand (reactive) routing: Low routing overhead but long route discovery latency. • Proactive routing: High routing overhead especially in the case of high mobility but short route discovery latency. CS541 Advanced Networking

  10. Dynamic Source Routing (DSR) • DSR is an on-demand routing protocol for MANETs. • The whole source-to-destination route is included in every data packet and no routing table is needed for packet forwarding in each node. • Loop freedom is guaranteed. • Large overhead in the packets. CS541 Advanced Networking

  11. Route Discovery • The source node broadcasts a RREQ (request) message to request a path to the destination. • A tuple (SrcID, RequestID) is used to uniquely identify a route request. • A node v receiving the RREQ will, - discard the packet if it is an old or duplicate one - discard the packet if v is already in the route list - send an RREP (reply) packet back to the source through the reverse route if v is the destination. - otherwise, append itself in the route list and re-broadcast the packet. • Both RREQ and RREP will be sent out only once in each node. • If a node has a record in its cache showing how to reach the destination, it can reply an RREP to the source immediately. CS541 Advanced Networking

  12. A-B-D-G A-B-D-G A-B-D-G A-B A A-B-D A-C-E A A-C-E A-C-E A-C Route Discovery Route request for A->G Red – RREQ, Green - RREP B G D A H E C F CS541 Advanced Networking

  13. Route Maintenance • A link-layer hop-by-hop ACK is usually used for reliable transmissions. For example, 802.11 DCF supports the link-layer ACK. • A RERR will be sent by the end node to the source node if it detects a link breakage. Nodes along the path will then update their caches accordingly and the source node will initiate a new route discovery. CS541 Advanced Networking

  14. RERR RERR Route Maintenance B G D G A Route Cache (A)G: A, B, D, G F: C, E, F H E C F CS541 Advanced Networking

  15. Route Optimization • Route Caching: Each node caches a new route it learns by any means. For example, when A finds route [A,B,D,E,F] to F, A also learns route [A,B,D,E] to E; D forwards data [A,B,D,E,F], D learns route [D,E,F] to F; So a node usually organizes its cache in the format of a shortest path tree with itself as the root. • Avoid RREP Storm Problem: An intermediate node will delay transmitting the route reply for a random period of d. During this period, cancel the route reply if overhearing any packet containing a better route. • Limit the Propagation of RREQ Packets: First, set TTL = 1 for first route request packet. If no route reply is received after some time period, set TTL = maximum for next RREQ. . CS541 Advanced Networking

  16. Route Optimization • Reflect Shorter Route: A node cansend an unsolicited RREP to the source to inform the shorter route. • Improve Error Handling: exponential backoff is used to limit the rate at which new route discoveries are initiated. • Piggyback Data on RREQs CS541 Advanced Networking

More Related