Routing in Adhoc Networks

1
Routing in Ad-hoc Networks

• 9th CEENet Workshop on Network Technology
• NATO ANW
• Iskra Djonova Popova (iskra.popova_at_mh.se)

2
Contents

• Ad-hoc Networks
• Problems with Routing
• Destination Sequenced Distance Vector (DSDV)
• (Clusterhead Gateway Switch Routing (CGSR)
• Dynamic Source Routing (DSR)
• Location Aided Routing (LAR)
• Classification of the Routing Protocols
• Standardization and Future Work

3
Ad-hoc Networks

• Two types of wireless network
• Infrastructured
• the mobile node can move while communicating
• the base stations are fixed
• as the node goes out of the range of a base
  station, it gets into the range of another base
  station
• Infrastructureless or ad-hoc
• the mobile node can move while communicating
• there are no fixed base stations
• all the nodes in the network need to act as
  routers
• In Latin ad-hoc literally means for this
  purpose only. Then an ad-hoc network can be
  regarded as spontaneous network

4
Ad-hoc Networks

• Infrastructured network

Infrastructure
(Wired line)
Radio tower
Desktop computer
Radio tower
5
Ad-hoc Networks

• Infrastructurless (ad-hoc) network or MANET
  (Mobile Ad-hoc NETwork)

6
Ad-hoc Networks

• Classification of ad-hoc networks

• Single hop nodes are in their reach area and
  can communicate directly

• Multi hop some nodes are far and cannot
  communicate directly. The traffic has to be
  forwarded by other intermediate nodes.

7
Ad-hoc Networks

• Characteristics of an ad-hoc network
• Collection of mobile nodes forming a temporary
  network
• Network topology changes frequently and
  unpredictably
• No centralized administration or standard support
  services
• Each host is an independent router
• Hosts use wireless RF transceivers as network
  interface
• Number of nodes 10 to 100 or at most 1000

8
Ad-hoc Networks

• Why we need ad-hoc networks?
• Setting up of fixed access points and backbone
  infrastructure is not always viable
• Infrastructure may not be present in a disaster
  area or war zone
• Infrastructure may not be practical for
  short-range radios Bluetooth (range 10m)
• Do not need backbone infrastructure support
• Are easy to deploy
• Useful when infrastructure is absent, destroyed
  or impractical

9
Ad-hoc Networks

• Example applications of ad hoc networks
• emergency search-and-rescue operations,
• meetings or conventions in which persons wish to
  quickly share information,
• data acquisition operations in inhospitable
  terrain,
• local area networks in the future.

10
Ad-hoc Networks
Mobile Ad Hoc Networking is a multi-layer problem
!
- Security - Service Discovery -
Location-dependent Application
- TCP - Quality of Service
- Routing - Addressing - Location Management
- Power Control - Multiuser Detection - Channel
Access
11
Problems with Routing

• Is it possible to use standard routing protocols?
• Distance-vector protocols
• Slow convergence due to Count to Infinity
  Problem
• Creates loops during node failure, network
  partition or congestion
• Link state protocols
• Use flooding technique and create excessive
  traffic and control overhead
• Require a lot of processor power and therefore
  high power consumption

12
Problems with Routing

• Limitations of the Wireless Network
• packet loss due to transmission errors
• variable capacity links
• frequent disconnections/partitions
• limited communication bandwidth
• Broadcast nature of the communications
• Limitations Imposed by Mobility
• dynamically changing topologies/routes
• lack of mobility awareness by system/applications
  
• Limitations of the Mobile Computer
• short battery lifetime
• limited capacities

13
DSDV

• DSDV (Destination Sequenced Distance Vector)
• Each node sends and responds to routing control
  message the same way
• No hierarchical structure
• Avoids the resource costs involved in maintaining
  high-level structure
• Scalability may become an issue in larger
  networks

14
DSDV

• Basic Routing Protocol
• known also as Distributed Bellman-Ford or RIP
• Every node maintains a routing table
• all available destinations
• the next node to reach to destination
• the number of hops to reach the destination
• Periodically send table to all neighbors to
  maintain topology
• Bi-directional links are required!

15
DSDV
Traditional Distance vector tables
1
2
C
B
A
16
DSDV
Distance Vector Updates
B broadcasts the new routing information to his
neighbors
Routing table is updated
(A, 1) (B, 0) (C, 1)
(A, 1) (B, 0) (C, 1)
1
1
C
B
A
17
DSDV
Distance Vector New Node joins the network
broadcasts to update tables of C, B, A with new
entry for D
(A, 2) (B, 1) (C, 0) (D, 1)
(A, 1) (B, 0) (C, 1) (D, 2)
(D, 0)
1
1
1
C
B
A
D
18
DSDV
Distance Vector Broken link
1
1
1
D
C
B
A
19
DSDV
Distance Vector - Loops
(D, 2)
(D, 2)
1
1
1
D
C
B
A
20
DSDV
Distance vector - Count to Infinity
(D,5)
(D,4)
(D,4)
(D,3)
(D,2)
(D,2)
1
1
1
D
C
B
A
21
DSDV

• Traditional Distance Vector are not suited for
  ad-hoc networks!
• Loops
• Bandwidth reduction in network
• Unnecessary work for loop nodes
• Count to Infinity
• Very slow adaptation to topology changes.
• Solution -gt Introduce destination sequence numbers

22
DSDV

• DSDV keeps the simplicity of traditional Distance
  Vector Protocols
• DSDV need to guarantee loop freeness
• New Table Entry for Destination Sequence Number
• DSDV need to allow fast reaction to topology
  changes
• Make immediate route advertisement on significant
  changes in routing table
• but wait with advertising of unstable
  routes(damping fluctuations)

23
DSDV

• Features introduced in DSDV
• Sequence number originated from destination.
  Ensures loop freeness.
• Install Time when entry was made (used to delete
  stale entries from table.
• Stable Data Pointer to a table holding
  information on how stable a route is. Used to
  damp fluctuations in network.

24
DSDV Route Advertisement

• Advertise to each neighbor own routing
  information
• Destination Address
• Metric Number of Hops to Destination
• Destination Sequence Number
• Other info (e.g. hardware addresses)
• Rules to set sequence number information
• On each advertisement increase own destination
  sequence number (use only even numbers)
• If a node is no more reachable (timeout) increase
  sequence number of this node by 1 (odd sequence
  number) and set metric ?.

25
DSDV Route Selection

• Update information is compared to own routing
  table
• 1. Select route with higher destination sequence
  number (This ensure to use always newest
  information from destination)
• 2. Select the route with better metric when
  sequence numbers are equal.

26
DSDV
DSDV Tables
C
B
A
27
DSDV
DSDV Route Advertisement
B increases Seq.Nr from 100 -gt 102 B broadcasts
routing information to Neighbors A, C including
destination sequence numbers
(A, 1, A-550) (B, 0, B-102) (C, 1, C-588)
(A, 1, A-550) (B, 0, B-102) (C, 1, C-588)
C
B
A
28
DSDV

• DSDV Respond to topology changes
• Immediate advertisements
• Information on new routes, broken Links, metric
  change is immediately propagated to neighbors.
• Full/Incremental Update
• Full Update Send all routing information from
  own table.
• Incremental Update Send only entries that has
  changed. (Make it fit into one single packet)

29
DSDV
When new node joins the network
2. Insert entry for D with sequence number
D-000.Then immediately broadcast own table.
1. D broadcast for first timeSend Sequence
number D-000.
(D, 0, D-000)
C
B
A
D
30
DSDV
3. C increases its sequence number to C-592 then
broadcasts its new table.
(New node (cont.)
4. B gets this new information and updates its
table.
(A, 2, A-550) (B, 1, B-102) (C, 0, C-592) (D, 1,
D-000)
(A, 2, A-550) (B, 1, B-102) (C, 0, C-592) (D, 1,
D-000)

C
B
A
D
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DSDV
No loops, no count to infinity
2. B does its broadcast-gt no affect on C (C
knows that B has stale information because C has
higher seq. number for destination D) -gt no loop
-gt no count to infinity
1. Node C detects broken Link-gt Increase Seq.
Nr. by 1(only case where not the destination
sets the sequence number -gt odd number)
(D, 2, D-100)
(D, 2, D-100)
1
D
C
B
A
32
DSDV
Immediate Advertisement
3. Immediate propagation B to A(update
information has higher Seq. Nr. -gt replace table
entry)
2. Immediate propagationC to B(update
information has higher Seq. Nr. -gt replace table
entry)
(D, ?, D-101)
(D, ?, D-101)
D
C
B
A
33
DSDV

• Problem of Fluctuations
• Entry for D in A D, Q, 14, D-100
• D makes broadcast with Seq. Nr. D-102
• A receives from P Update (D, 15, D-102)-gt Entry
  for D in A D, P, 15, D-102 A must propagate
  this route immediately.
• A receives from Q Update (D, 14, D-102)-gt Entry
  for D in A D, Q, 14, D-102A must propagate
  this route immediately.
• This can happen every time D or any other node
  does its broadcast and lead to unnecessary route
  advertisements in the network, so called
  fluctuations.

A
P
Q
10 Hops
11 Hops
(D,0,D-102)
D
34
DSDV

• Advantages
• Simple (almost like Distance Vector)
• Loop free through destination seq. numbers
• No latency caused by route discovery
• Disadvantages
• No sleeping nodes
• Bi-directional links required
• Overhead most routing information never used
• Scalability is a major problem

35
CGSR

• CSGR (Clusterhead Gateway Switch Routing)
• Similar to DSDV
• Based on concept of clusters and cluster heads
• Routing is done via the cluster heads and
  gateways

36
CGSR

• Problems with CGSR
• More time is spend in selection of cluster heads
  and gateways
• If the mobile node uses CDMA/TDMA then it can
  take some time to get permission to send packets

37
DSR

• DSR (Dynamic Source Routing)
• Similar to the source routing in traditional
  networks
• A node maintains route cache containing the
  routes it knows
• Includes route discovery on request and route
  maintenance when needed

38
DSR

• Route discovery
• The source sends a broadcast packet which
  contains source address, destination address,
  request id and path.
• If the host receiving this packet, saw this
  packet before, discards it.
• Otherwise, it looks up its route caches to look
  for a route to destination. If a route is not
  found, it appends its address into the packet and
  rebroadcasts it.
• If the route is found, it sends a reply packet to
  the source node.
• The route will be eventually found when the
  request packet reaches the destination

39
DSR

• RREQ (Route request)

(source, destination, path)
Route
cache
...
Destination
5
RREQ(1,5,1,2,4)
Route
cache
4
...
6
RREQ(1,5,1,2)
RREQ(1,5,1)
RREQ(1,5,1,2)
2
Source
3
1
Route
cache
...
Route
cache
Route
cache
...
(3,5) gt 3,6,5
...
40
DSR

• How to send a reply packet?
• If the destination has a route to the source in
  its cache, use it
• Else if symmetric links are supported, use the
  reverse of the route record
• Else, if symmetric links are not supported, the
  destination initiate route discovery to source

41
DSR

• RREP (Route reply)
• Source, destination, source route)

Route
cache
(5,1) gt 5,4,2,1
(5,2) gt 5,4,2
(5,4) gt 5,4
Destination
...
5
RREP(5,1,1,2,
4
,5)
Route
cache
4
...
6
RREP(5,1,1,
2
,4,5)
RREP(5,1,
1
,2,4,5)
RREP(3,1,1,
2
,3,6,5)
2
Source
3
1
Route
cache
(2,1) gt 2,1
Route
cache
(2,4) gt 2,4
Route
cache
...
(3,1) gt 3,2,1
(1,5) gt
1,2,4,5,
(3,2) gt 3,2
1,2,3,6,5
(3,5) gt 3,6,5
...
...
42
DSR

• Route maintenance
• Whenever a node transmits a data packet, a route
  reply or a route error, it must verify that the
  next hop correctly receives the packet.
• If not, the node must send a route error to the
  node responsible for generating this route
  header.
• The source restarts the route discovery

43
DSR

• Advantages
• Do not exchange routing update periodically, so
  overhead transmission is greatly reduced
• Can refer to cache for the new route when link
  fails.
• Disadvantages
• Scalability problem High route discovery latency
  for large network.
• High mobility problem although the packet
  dropped may not be substantional, the overhead
  traffic will increase a lot.

44
LAR

• LAR (Location Aided Routing)
• Modified flooding algorithm
• Exploits location information to limit the scope
  of the route request flood
• Location information being obtained from a GPS
  unit

45
LAR

• The expected zone is defined as the region that
  is expected to hold the current location of the
  destination

X last known location of node D, at time t0 r
(t1 - t0) estimate of Ds speed
46
LAR

• The route request is limited to the Request zone.
• The request zone is the smallest rectangular
  region that contains the expected zone and the
  location of the sending node.

47
LAR

network space
X
request zone
r
2
1
expected zone
S
48
LAR

• Only nodes within the request zone forward route
  request
• The request zone is explicitly specified in the
  route request
• If route discovery using the smaller request zone
  fails to find a route, the source node initiates
  another route discovery (after a timeout ) using
  a larger zone

49
LAR

• Implicit request zone
• Node x forwards a route request received from y
  if x is deemed closer to the expected zone when
  compared to y.
• This is an attempt to bring the route request
  physically closer to the destination node after
  each forwarding

50
Classification of the Routing Protocols

• Proactive (table driven)
• Require each node to maintain one or more tables
  to store routing information
• Each node responds to changes in network topology
  by propagating updates throughout the network in
  order to maintain a consistent network view
• DSDV, OLSR (Optimized Link State Protocol)
• Reactive protocols (source initiated)
• Creates routes only when desired by the source
  node
• Once a route has been established, it is
  maintained by a route maintenance procedure until
  either the destination becomes inaccessible along
  every path from the source or until the route is
  no longer desired
• DSR, AODV (Ad-hoc On-demand Distance Vector)

51
Classification of the Routing Protocols

• Various simulation studies have shown that
  reactive protocols perform better in mobile ad
  hoc networks than proactive ones.
• However, no single protocol works well in all
  environments.
• Which approach achieves a better trade-off
  depends on the traffic and mobility patterns.

52
Classification of the Routing Protocols

• Other classification
• Pro active protocols
• DSDV, STAR, WRP, ...
• Reactive protocols
• AODV, DSR, TORA, ...
• Hierarchical/Clustering protocols
• CGSR, ZRP, CBR, FSR, LANMAR, ...
• Position aware protocols
• GPSR, LAR, GRA, ABR, ...

53
Standardization and Future Work

• Standardization effort led by IETF Mobile Ad-hoc
  Networks (MANET) task group
• http//www.ietf.org/html.charters/manet-charter.ht
  ml
• Other protocols being researched
• utilize geographic , nodes provided with GPS
  info.
• Hybrid schemes that combine reactive and pro
  active type of protocols

54
Standardization and Future Work

• Leading protocols chosen by MANET
• DSR Dynamic Source Routing
• AODV Ad-hoc On-demand Distance Vector Routing
• Both are on demand protocols route information
  discovered only as needed