Mobile Networks and Internetworking: Understanding Mobile IP and DSR, Study notes of Computer Systems Networking and Telecommunications

Download Mobile Networks and Internetworking: Understanding Mobile IP and DSR and more Study notes Computer Systems Networking and Telecommunications in PDF only on Docsity! 1 1 ECE453 – Introduction to Computer Networks Lecture 13 – Network Layer (V) - 2 Mobile IP 3 Stationary vs. Mobile Current Internet protocol suite assumes end-systems are stationary In end-to-end connection, if one end moves, the network session breaks, so does all the networking services layered on top of IP Solution? Option 1: completely redesign each layer of the protocol suite Option 2: provide additional services at the network layer in a backward compatible manner – mobile internetworking 2 4 “Mobility is essentially an address translation problem and is best resolved at the network layer” 5 Internet Naming and Addressing Hierarchical addressing, can only be used within a domain of its definition. Therefore, the Internet address is location-dependent. Host names are location-independent, used as a way for applications to make reference to network entities DNS (a directory lookup operation) Optimized for access operation (recursive query, caching, etc.), not for update operation 6 Fundamental Problem The IP address serves dual purposes For the transport and application layer, it serves as end-point identifier For the network layer, it is used as a routing directive Data DataTCP DataTCPIP Hostname, port no. DNS IP Address 5 13 Routing Protocols Proactive protocols Determine routes independent of traffic pattern Traditional link-state and distance-vector routing protocols are proactive Reactive protocols Maintain routes only if needed Hybrid protocols 14 Trade-Off Latency of route discovery Proactive protocols may have lower latency since routes are maintained at all times Reactive protocols may have higher latency because a route from X to Y will be found only when X attempts to send to Y Overhead of route discovery/maintenance Reactive protocols may have lower overhead since routes are determined only if needed Proactive protocols can (but not necessarily) result in higher overhead due to continuous route updating Which approach achieves a better trade-off depends on the traffic and mobility patterns 15 Flooding for Data Delivery Sender S broadcasts data packet P to all its neighbors Each node receiving P forwards P to its neighbors Sequence numbers used to avoid the possibility of forwarding the same packet more than once Packet P reaches destination D provided that D is reachable from sender S Node D does not forward the packet 6 16 Flooding for Data Delivery B A S E F H J D C G I K Represents that connected nodes are within each other’s transmission range Z Y Represents a node that has received packet P M N L 17 Flooding for Data Delivery B A S E F H J D C G I K Represents transmission of packet P Represents a node that receives packet P for the first time Z Y Broadcast transmission M N L 18 Flooding for Data Delivery B A S E F H J D C G I K • Node H receives packet P from two neighbors: potential for collision Z Y M N L 7 19 Flooding for Data Delivery B A S E F H J D C G I K • Node C receives packet P from G and H, but does not forward it again, because node C has already forwarded packet P once Z Y M N L 20 Flooding for Data Delivery B A S E F H J D C G I K Z Y M • Nodes J and K both broadcast packet P to node D • Since nodes J and K are hidden from each other, their transmissions may collide => Packet P may not be delivered to node D at all, despite the use of flooding N L 21 Flooding for Data Delivery B A S E F H J D C G I K Z Y • Node D does not forward packet P, because node D is the intended destination of packet P M N L 10 28 Route Discovery in DSR B A S E F H J D C G I K • Node H receives packet RREQ from two neighbors: potential for collision Z Y M N L [S,E] [S,C] 29 Route Discovery in DSR B A S E F H J D C G I K • Node C receives RREQ from G and H, but does not forward it again, because node C has already forwarded RREQ once Z Y M N L [S,C,G] [S,E,F] 30 Route Discovery in DSR B A S E F H J D C G I K Z Y M • Nodes J and K both broadcast RREQ to node D • Since nodes J and K are hidden from each other, their transmissions may collide N L [S,C,G,K] [S,E,F,J] 11 31 Route Discovery in DSR Destination D on receiving the first RREQ, sends a Route Reply (RREP) RREP is sent on a route obtained by reversing the route appended to received RREQ RREP includes the route from S to D on which RREQ was received by node D 32 Route Reply in DSR B A S E F H J D C G I K Z Y M N L RREP [S,E,F,J,D] Represents RREP control message 33 Route Reply in DSR Route Reply can be sent by reversing the route in Route Request (RREQ) only if links are guaranteed to be bi-directional To ensure this, RREQ should be forwarded only if it received on a link that is known to be bi-directional If unidirectional (asymmetric) links are allowed, then RREP may need a route discovery for D from node S Unless node D already knows a route to node S If a route discovery is initiated by D for a route to S, then the Route Reply is piggybacked on the Route Request from D. If IEEE 802.11 MAC is used to send data, then links have to be bi-directional (since Ack is used) 12 34 Dynamic Source Routing (DSR) Node S on receiving RREP, caches the route included in the RREP When node S sends a data packet to D, the entire route is included in the packet header hence the name source routing Intermediate nodes use the source route included in a packet to determine to whom a packet should be forwarded 35 Data Delivery in DSR B A S E F H J D C G I K Z Y M N L DATA [S,E,F,J,D] Packet header size grows with route length