Mobile Computing - Chapter 4: Mobile Ad-hoc Network

Flashcards about Mobile Ad-hoc Networks (MANETs) based on lecture notes.

MANET Characteristics

Every node functions as a router, nodes move arbitrarily, wireless connectivity constrains bandwidth.

Advantages of MANETs

Easy and speedy deployment, robust and low-cost network, forms the basis of pervasive computing.

Applications of MANETs (PAN)

Cell phones, laptops, wearable computers.

BAN (Body Area Network)

Wearable computer with components distributed on the body, interconnects heterogeneous devices, communication range around 1 to 2 meters.

PAN (Personal Area Network)

Network in the environment around a person, communication range 10 meters, connects mobile devices to other devices.

WLANs (Wireless Local Area Network)

Greater flexibility compared to wired LANs, Communication range typical of a single building or of cluster of buildings. Range 100 – 500 meters.

Expectations of MANETs Routing Protocols

Tolerance of unexpected network faults, resilience to increasing traffic loads, minimal energy consumption.

Distance Vector Routing Protocols

Routing tables are exchanged between neighboring nodes to get to destinations by computing the shortest path to each host.

Link State Routing Protocols

Neighboring nodes only exchange link states and routes are obtained by computing a graph on every participating node, computing the shortest distance to each host.

Requirements for Routing Protocols (1)

Operate in a distributed manner and be multi-hop and loop-free.

Requirements for Routing Protocols (2)

Operate in a demand-based reactive or proactive mode.

Requirements for Routing Protocols (3-6)

Should be scalable, provision for a 'sleepy period, support unidirectional links, and security.

Two Basic Parts to Routing Protocols

Route discovery and route maintenance.

Classification of Routing Protocols

Unicast or multicast.

Proactive Routing Protocols

Calculate all possible paths in the network independently of their use and when a packet needs to be forwarded the path is already known and can be used immediately.

Reactive Routing Protocols

Invoke the route determination procedure only on demand.

Hybrid Routing Protocol

Merges the features of proactive and reactive protocols.

DSDV (Destination-Sequenced Distance-Vector) Protocol

Table driven algorithm based on classical Bellman-Ford distance vector routing algorithm and marked with a sequence number.

Routing Table Entry Structure of DSDV

Destination address, number of hops required to reach destination, sequence number of the information received.

Responding to Topology Changes in DSDV

Maintained through periodic updates or immediately when significant new information is available using full dumps or incremental dumps.

Route Selection Criteria in DSDV

New routing information is compared to previous and more recent sequence numbers are used, and old ones are discarded.

Reactive Routing Protocols

Maintain routing information about 'active' routes only, created when desired by the source node, and a route discovery procedure is needed before data transmission.

Examples of Reactive Routing Protocols (RRP)

Dynamic Source Routing (DSR), Adaptive on Demand Vector (AODV), Temporarily Ordered Routing Algorithm (TORA).

Dynamic Source Routing (DSR)

Does both route discovery and route maintenance.

Source Routing

Sender of a packet determines the complete sequence of nodes and lists route in the packet's header.

Route Cache (DSR)

Each router maintains this and if a route is found, the sender transmits the packet, else it may attempt to discover a route using the Route Discovery Protocol.

Route Maintenance

Monitoring of the correct operation of a route.

Route Discovery in DSR

Initiates a discovery process by transmitting a ROUTE REQUEST message as a single local broadcast packet containing initiator ID, request ID, and route record.

Route Maintenance in DSR

Link layer reliability, MAC layer ack or passive overhearing.

Adaptive on-demand distance vector protocol- AODV

Reactive, distance vector routing protocol, based on the distributed Bellman Ford routing algorithm

Route Discovery in AODV

Forwarded in a manner similar to DSR, a reverse path is set towards the source, and the destination replies by sending an RREP which travels along the reverse path.

Active path

Path being used

Route Maintenance in AODV

A RERR message is sent to the affected source nodes, initiated by the nodes upstream of the failed link.

RERR message

Contains the destinations that are now unreachable. If the node upstream of the break has one or more precursor nodes for the destination, it broadcasts the RERR message to those nodes.

Comparison between DSR and AODV

Based on a source routing mechanism where as AODV uses a combination of DSR &DSDV.

DSR Properties

Less routing overhead, frequency and discovery process than AODV.

AODV Properties

Better performance than DSR in higher-reliability scenarios and less normalized mac overhead.

Hybrid Routing Protocol

Has the advantages of both Distance Vector and Link State RPs and merges them into a new protocol such as EIGRP.