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Mobile Computing - ROUTE DISCOVERY -, Study notes of Mobile Computing

Moradabad Institute of TechnologyMobile Computing

Detailed informtion about ROUTE DISCOVERY , Route Discovery, Route Reply, Route Error Detection, ROUTE SHORTENING, CBRP.

Typology: Study notes

2010/2011

Uploaded on 09/04/2011

amit-mohta
amit-mohta 🇮🇳

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1
ROUTE DISCOVERY
• When a node say A wants to discover route to a node say D it
broadcasts a RREQ packet.
• This packet contains a list of host and neighboring clusters
heads. For neighboring cluster heads even the gateway nodes
are mentioned.
• The idea is only cluster heads should forward the packet further.
• If a member node receives RREQ packet it simply drops it.
• However if a member node is listed as a Gateway node it
unicasts the RREQ to the cluster head for which it is a Gateway
node.
• When a cluster head receives RREQ, it adds itself on the partial
route contained in the packet.
• It adds the neighboring cluster heads to which the packet is to
be forwarded from its own CAT along with their gateway nodes
and then re-broadcasts their packet.
• Thus the RREQ passes through a number of cluster heads and
eventually reaches D.
• D upon receiving the RREQ sends and RREP back.
• The RREP travels the same set of cluster heads that the RREQ traveled.
• On the way entire hop-by-hop path is added to the RREP along with the
Gateway nodes.
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ROUTE DISCOVERY

  • When a node say A wants to discover route to a node say D it

broadcasts a RREQ packet.

  • This packet contains a list of host and neighboring clusters

heads. For neighboring cluster heads even the gateway nodes

are mentioned.

  • The idea is only cluster heads should forward the packet further.
  • If a member node receives RREQ packet it simply drops it.
  • However if a member node is listed as a Gateway node it

unicasts the RREQ to the cluster head for which it is a Gateway

node.

  • When a cluster head receives RREQ, it adds itself on the partial

route contained in the packet.

  • It adds the neighboring cluster heads to which the packet is to

be forwarded from its own CAT along with their gateway nodes

and then re-broadcasts their packet.

  • Thus the RREQ passes through a number of cluster heads and

eventually reaches D.

  • D upon receiving the RREQ sends and RREP back.
  • The RREP travels the same set of cluster heads that the RREQ traveled.
  • On the way entire hop-by-hop path is added to the RREP along with the

Gateway nodes.

2

Route Discovery

Source S “floods” all clusterheads with Route

Request Packets (RREQ) to discover destination D

[3]

[3,1,8,11]

3 (S)

11 (D)

[3,1]

[3,1,6]

[3,1,8]

Route Reply

  • Route reply packet (RREP) is sent back to source along

reversed “loose source route” of clusterheads.

  • Each clusterhead along the way incrementally compute a

hop-by-hop strict source route.

3 (S)

11 (D)

the reversed

loose source route of

RREP: [11,8,1,3]

the computed

strict source route of

3->11 is: [11,9,4,3]

Route Error Detection

3 (S)

11 (D)

  • Use source routing for actual packet forwarding
  • A forwarding node sends a Route Error Message (ERR) to

packet source if the next hop in source route is unreachable

Source route header of data

packet: [3,4,9,11]

Route error (ERR)

down link: {9->11}

Local Route Repair

3 (S)

11 (D)

  • A forwarding node repairs a broken route using its 2-hop-topology

information and modifies source route header accordingly.

  • Destination node sends a gratuitous route reply to inform source

of the modified route

Source route header of data

packet: [3,4,9,11]

Route error (ERR)

down link: {9->11}

Local Route Repair

3 (S)

11 (D)

  • A forwarding node repairs a broken route using its 2-hop-topology

information and modifies source route header accordingly.

  • Destination node sends a gratuitous route reply to inform source

of the modified route

Source route header of data

packet: [3,4,9,11]

Modified source route

[3,4,9,8,11]

CBRP

CBRP Advantages:

  • Uses local route repair and route shortening to improve routes
  • Supports uni- and bi-directional links
  • Reduction of communication traffic
  • Reduction of information storage
  • Robust against frequent network topology changes
  • Loop free
  • Support for multiple route

CBRP Disadvantages:

  • Overhead bytes according to source routing
  • Only 2-level hierarchy
  • Small clusters but when clusters grow, size of HELLO messages

and tables increases

  • Scalable to an extend.