1. Coping with Communication Gray Zones in IEEE 802.11b based Ad hoc Networks, H. Lundgren, E. Nordström, and C. Tschudin Anne Saaranen

2. Presentation outline Introduction IEEE 802.11b AODV Communication gray zones Conditions for forming communication gray zones Suggested solutions Test network setup Results Comparison to two ad hoc routing protocols Conclusions

3. Introduction IEEE 802.11b widely used for ad hoc networking Most of the routing protocol performance evaluation done using only simulations The authors of the paper had discovered that the performance of an ad hoc routing protocol in a testbed was not as good as its simulated, and thus assumed, performance

4. IEEE 802.11b WLAN MAC/physical layer standard Operates at 2.4 GHz ISM band (DSSS) Data rate 1, 2, 5.5, or 11 Mbps Measured application level data rate 4.5-5.5 Mbps point-to-point link Transmission range 20-100m

5. Ad hoc On demand Distance Vector Routing Protocol (AODV) Reactive ad hoc routing protocol Routes searched using RREQ/RREP messages Short broadcast messages, hellos, are used to detect neighbour connectivity

6. Gray zone is a circle around a node The node can receive small broadcasted packets from the neighbour, but the node cannot send larger unicast messages to it In the figure node B is inside the communication gray zone of node A Communication gray zones

7. Different transmission rate for broadcast and unicast IEEE 802.11b broadcast messages are sent in the basic transmission rate, unicast ones with higher rates No acknowledgements to broadcast messages Small packet size (of hello message) Fluctuating links Nodes at the border of each others transmission range Conditions for Forming Communcation Gray Zones

8. Exchanging neighbour sets hello message contains also the neighbour set of the sender, nodes accept only neighbours listing it in the neighbour set N consecutive hello messages accept the neighbour only after receiving at least N consecutive hellos SNR threshold for control packets Accept only those control messages that are received with signal quality over preset threshold Suggested solutions

9. Mobile node (MN) Gateway (GW) Corresponding node for MN Intermediate nodes (C1, C2) Mobile node moves from hearing only node C1 to hearing only node C2 Figure shows also the gray zones of nodes C1 and C2 Test network setup

10. Ping delivery success Table: Success ration for AODV and the suggested solutions Figure 1: original AODV Figure 2: AODV with SNR threshold (the best result) Results

11. MP3 streaming success ratio One-way traffic HTTP Bursty communications not as sensitive to communication gray zones as continuous traffic of ping and streaming Results (cont’d)

12. Comparison to two ad hoc routing protocols, the protocols Optimized Link State Routing Protocol (OLSR) Proactive routing protocol Lightweight Underlay Network Ad hoc Routing (LUNAR) Hybrid protocol that finds routes reactively, but maintains then proactively (sends periodic maintenance messages along the route)

13. Comparison to two ad hoc routing protocols, results OLSR and LUNAR not as sensitive to gray zones as AODV LUNAR does not use hello messages OLSR convergence time too long to suffer from gray zones, performance in this experiment otherwise worse than AODV AODV with SNR threshold outperforms both of the above protocols

14. Conclusions IEEE 802.11b has communication gray zones where nodes can receive broadcast traffic from each other, but unicast messaging is impossible These should be taken into consideration when developing ad hoc routing protocols Simulation models assumption that 802.11b is always bi-directional should be updated The effect of different transmission rates for broadcast and unicast traffic should be adopted to the models