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Mobile Computing - Route Discovery, Study notes of Mobile Computing

This document about Dynamic Source Routing (DSR), Route Discovery, RREQ (Route Request packet), RREP (Route Reply packet), Route Discovery in DSR, Route Reply in DSR.

Typology: Study notes

2010/2011

Uploaded on 09/04/2011

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Dynamic Source Routing
(DSR)
Source routing - The sender knows the complete hop-by-hop
route to the destination.
Route cache - Nodes may learn and cache multiple routes to
any destination.
Composed of 2 mechanisms:
Route Discovery
Route Maintenance
Requires no periodic packets of any kind at any level within
the network- purely on demand.
Allows uni-directional links.
Supports internetworking between different types of
wireless networks and mobile IP.
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Dynamic Source Routing

(DSR)

  • (^) Source routing - The sender knows the complete hop-by-hop route to the destination.
  • (^) Route cache - Nodes may learn and cache multiple routes to any destination.
  • (^) Composed of 2 mechanisms:
    • (^) Route Discovery
    • (^) Route Maintenance
  • (^) Requires no periodic packets of any kind at any level within the network- purely on demand.
  • (^) Allows uni-directional links.
  • (^) Supports internetworking between different types of wireless networks and mobile IP.

Route Discovery

• RREQ (Route Request packet)

  • (^) Is broadcast when node S needs do send a

packet to D and does not already know a route.

  • (^) Each RREQ includes source and destination

address, unique request id and complete route

record of all intermediate nodes.

• RREP (Route Reply packet)

  • (^) If a node receives an RREQ for which it is either

the destination or it has a route to the

destination in its route cache it responds with a

RREP.

Route Discovery in DSR

B

A

S

E

F

H

J

D

C

G

I

K

Represents transmission of RREQ

Z

Y

Broadcast transmission M N

L

[S]

[X,Y] Represents list of identifiers appended to RREQ

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]

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]

Route Discovery in DSR

B

A

S

E

F

H

J

D

C

G

I

K

Z

Y

  • (^) Node D does not forward RREQ, because node D is the intended target of the route discovery

M

N

L

[S,E,F,J,M]

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

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