Network Layer Routing Issues (I)

Infrastructure vs. multi-hop Infrastructure networks: Infrastructure networks: ◦ One or several Access-Points (AP) connected to the wired network ◦ Mobile nodes communicate through the AP Multi-hop network (Infrastructureless): ◦ Mobile nodes communicate directly with each other ◦ Multi-hop networks: all nodes can also act as routers

Adaptivity and Cooperation Multi-hop networks require more cooperation between layers: ◦ Channel variation ◦ network topology changes affect the application ◦ Routing in a multi-hop considerably affects the medium access control (MAC) performance ◦ Collisions and channel fading affect both the physical layer and the MAC

Problems in Multi-Hop Networks Routing ◦ How to keep up-to-date information on the network topology? ◦ How to determine number of hops ◦ How to cope with network topology changes Higher Delay Resource Limitations Security Issues (Unreliability) Complex and Large Structures (Routing tables) Hard-to-Control

Routing Protocols Routing Classification Unicast Routing (one-to-one connection) Multicast routing (one-to-many connection) Broadcasting (one-to-all connection)

Routing Protocols Routing (unicasting) Protocols Proactive Routing Reactive Routing Hybrid Routing Geometric Routing

Routing Protocols Proactive Routing (table-driven) Keep routing information current at all times Route maintenance Good for static networks High overhead and low delay Route invalidity Examples: (DSDV) Destination-Sequenced Distance Vector Destination-Sequenced Distance Vector

Routing Protocols Reactive Routing (on-demand routing) ◦ Finds a route to the destination only after a request comes in ◦ Good for more dynamic networks ◦ Low overhead and high delay ◦ Higher delay ◦ examples: AODV(Ad hoc On-Demand Distance Vector), dynamic source routing (DSR)

Routing Protocols Hybrid Schemes Combines the advantages of reactive and proactive Performs better both under dynamic and static conditions Reasonable delay compared to reactive Reasonable overhead compared to proactive example: Zone Routing Protocol (ZRP)

Routing Protocols Geometric routing: ◦ Assume location-awareness ◦ Locating nodes by Global Positioning System (GPS) ◦ Forwarding the packets toward the node location ◦ Take advantage of the geometry of plane ◦ Example: Geographic-based routing protocols

Proactive vs Reactive Routing 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

Proactive vs Reactive Routing 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

Flooding for Data Delivery Network-wide Broadcasting Sender S broadcasts data packet P to all its neighbors Each node receiving P forwards P to its neighbors for the first time Packet P reaches destination D provided that D is reachable from sender S Node D does not forward the packet

Flooding for Data Delivery B A S E F H J D C G I K Communication link Represents that the nodes are within each other’s transmission range Z Y M N L

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

Flooding for Data Delivery B A S E F H J D C G I K Z Y M N L

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

Flooding for Data Delivery B A S E F H J D C G I K Z Y M N L

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

Flooding for Data Delivery B A S E F H J D C G I K Flooding completed Nodes unreachable from S do not receive packet P (e.g., node Z) Nodes for which all paths from S go through the destination D also do not receive packet P (example: node N) Z Y M N L

Flooding for Data Delivery B A S E F H J D C G I K Broadcast Storm Problem Flooding may deliver packets to too many nodes (in the worst case, all nodes reachable from sender may receive the packet) Z Y M N L

Flooding: Advantages Simplicity (no complex control mechanism) More efficient than other protocols ◦ In small networks ◦ Under light load traffic conditions ◦ Highly dynamic networks Potentially higher reliability of data delivery ◦ Because packets may be delivered to the destination on multiple paths

Flooding: Disadvantages Very high overhead ◦ Data packets may be delivered to too many nodes who do not need to receive them Energy consuming Bandwidth consuming Congestion

Flooding of Control Packets Many protocols perform flooding of control packets, instead of data packets The control packets are used to discover routes Discovered routes are subsequently used to send data packet(s)

Flooding Overhead reduction Virtual Backbone Formation (VBF) ◦ Connected Dominating Set (CDS) ◦ Maximal Independent Set (MIS) Forwarding Group (FG) Network Clustering

Flooding Scoped Flooding Scope Limited Flooding ?

Routing Protocols Link-state Routing Protocols ◦ Routes are constructed based on the selection of the communication links ◦ Routes are optimized based on the link characteristics ◦ Shortest Path Problem ◦ Spanning Tree (Steiner Tree)

Routing Protocols Node-state Routing Protocols ◦ Routes are constructed based on the selection of the nodes ◦ Routes are optimized based on the node characteristics ◦ Connected dominating set (CDS)

Routing Protocols Link-state Routing Protocols ◦ Relative mobility ◦ Link duration ◦ Link Bandwidth, … Node-state Routing Protocols ◦ Node Failure Rate ◦ Node Mobility ◦ Node Energy ◦ Nodal capacity