Quiz 5 Answers CS 441 Spring 2017 1. How does Flooding differ from the route discovery phase used in other reactive routing protocols such as DSR and AODV? [2] Flooding involves broadcasting of data packet P itself and every node in the network (other than the destination node) participates in the data packet forwarding process. Reactive protocols on the other hand operate in a 2-step process use flooding for the route discovery phase using control packets (e.g., RREQ packets), followed by sending the actual data packet P along ONLY the discovered best path between source and destination. 2. Describe the working of the DSR protocol. Don t forget to mention how duplicate RREQ packets are handled. [7] Duplicate RREQ packets are handled using sequence numbers. If a node receives an RREQ packet originating from a source S, then it transmits that packet, only if it has not already transmitted the same packet which it determines by examining the sequence number of the last RREQ packet it transmitted for S (the sequence number of the RREQ packet must be greater than the sequence number of the last transmitted RREQ packet from the same originating source).
DSR Routing Steps: 1. When node S wants to send a packet to node D, but does not know a route to D, node S initiates a route discovery by flooding the network with a Route Request (RREQ) packet 2. Each node appends own identifier/id when forwarding RREQ 3. Destination D on receiving the first RREQ, sends a Route Reply (RREP) 4. RREP is sent on a route obtained by reversing the route appended to received RREQ (obtained from the list of node IDs appended to the RREQ packet by the intermediate nodes) 5. RREP includes the route from S to D on which RREQ was received by node D 6. Node S on receiving RREP sends a data packet to D, with the entire route included in the packet header. Intermediate nodes use the source route included in a packet to determine to whom (next-hop) a packet should be forwarded
3. What are the differences between DSR and AODV routing protocols? [3] Main differences: 1. DSR embeds the route for each data packet in the packet header while AODV specifies only the next hop. 2. AODV uses routing tables. DSR doesn t use routing tables. 3. In AODV, during route discovery phase using RREQ packets, the reverse path (destination source) are created, while during RREP propagation, the forward path (source destination) are created. In contrast, in DSR, the destination returns the RREP packet with the reverse path from source to destination and the source then simply reverses this embedded path to include in data packet headers. 4. At most one next-hop per destination maintained at each node in AODV while in DSR, a source node may maintain several routes for a single destination Full marks, for mentioning any 2 of the above 4 differences (1.5 + 1.5 = 3).
4. In location-based greedy routing protocols such as GEDIR, how are RREQ packets forwarded from the source to the destination node? What problem do such greedy location-based routing algorithms suffer from? Give one possible solution to overcome this problem. [1+1+3=5] An intermediate node forwards a RREQ packet, if its location is closer to the destination than the node from which it received the RREQ packet. Such algorithms suffer from the problem of potentially becoming stuck in a hole/sink, where there is no further forwarding node/path to reach the destination using the greedy location-based forwarding strategy. The most commonly used solution to solve the hole/sink problem in graphs that are planar is to use face routing the RREQ packets are routed along the face/edge of the hole in a counter-clockwise (or clockwise) direction first. If that circumvents the hole and helps in resuming greedy routing, then done. Otherwise, the RREQ packets are routed along the face/edge of the hole in the reverse direction clockwise, if the first attempt was in counter-clockwise direction, otherwise counter-clockwise, if the first attempt was in clockwise direction.
5. Questions on ZRP: [1+1+1=3] a) In ZRP protocol, are zones defined with respect to each source node OR, the entire network is pre-partitioned into fixed zones, similar to the LAs in cellular network? b) What type of routing protocols are used for intra-zone routing in ZRP? a) Given a node S with ZRP zone setting of d=2, which nodes included in the zone of S participate in the inter-zone routing and using what type of routing protocols? a) Zones are defined with respect to each source node. b) Proactive protocols are used for intra-zone routing in ZRP c) Only the border nodes participate in the inter-zone routing using a reactive routing protocol for route discovery to the destination node.