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“Intra-Network Routing Scheme
using Mobile Agents”
by
Ajay L. Thakur
Outline
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Objectives
OSPF Overview
Mobile Agents
Related Works
Proposed Best-Effort Routing Scheme
Proposed QoS Routing Scheme
Simulation Results
Conclusion
Objectives
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Develop a Routing Scheme using Mobile agents
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Given a source (s) and destination (d) find a path
Given a source (s) and destination (d) find a path
which satisfies QoS constraints like required
Bandwidth ( Breq) and delay
Open Shortest Path First (OSPF)
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Overview
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Uses link state routing algorithm
To reduce the routing overhead it divides the full
Autonomous System (AS) into number of areas
Each router maintains link state database for routing
domain
Area Border Router (ABR) keeps separate database for
each area
Routers periodically send Link State Advertisement (LSA)
into the network
ABR routers send summary LSA to backbone area and to
the internal routers
OSPF Contd…
Area 1
0
7
15
6
16
Area 2
2
3
4
8
14
Area 0
5
10
11
9
Area 3
ABR router
12
Internal Router
13
OSPF issues
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Memory Overhead
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OSPF uses a link state database to keep track of all routers
and networks within each attached area. With a complex
topology, this database can be much larger and may limit
the maximum size of an area.
Processor Overhead
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During steady state operation the OSPF CPU usage is low,
mainly due to the traffic between routers. However, when a
topology change is detected, there is a large amount of
processing required to support flooding of changes, and recalculation of the routing table. In the existing
implementations, the shortest path tree has to be
computed from scratch after each link state change.
OSPF issues contd…
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Synchronization of Database
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Database at all routers within area should be synchronized.
After changes in network it takes time to notify the change
to all the routers within area. In between database is not
synchronized and it may cause looping of packets.
Mobile Agents
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Client Server Communication
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Connection is maintained for full duration
If connection breaks due to link/node failure,
connection has to be established once again which
consumes network bandwidth
Request
Client
Server
Response
Mobile Agents
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Mobile Agent Communication
Mobile agent is a program that can be dispatched from
one computer and delivered to a remote computer for
execution. After execution mobile agent comes back with
the result
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MA
Client
Server
Result
Some of the advantages of Mobile Agents
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Less traffic in the network
Good for unreliable networks
MA
Link goes
down
Client
Server
Result
Link comes
up
Related Works
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Mobile Agents Based Routing
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Mobile agent based QoS routing
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Mobile agents collect the resource status at each node
and accordingly the forwarding table is updated at each
router
Flooding of mobile agents to find a path
It strictly uses call admission control
Topology aggregation approach
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Divide the topology in groups, and each node knows the
information of resources at the routers within the group
Proposed Work
RIMA (Routing Intelligent Mobile agent)
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What are RIMA nodes?
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RIMA neighborhood
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RIMA nodes are the subset of nodes such that, each
non-RIMA node should be connected to at least one RIMA
node within two hops
RIMA node and its neighbors within 1 hop or 2 hop distance
forms neighborhood
RIMA Database
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RIMA nodes are capable of managing and collecting
information of all the nodes within its neighborhood
e.g. link capacity, reliability of nodes, delay on the path,
congestion at the nodes and color of the links
It also collects the information of the nodes which are on the
path to neighbor RIMA nodes
Example
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In figure nodes 2, 6 and 10 are RIMA nodes
Neighborhood of RIMA node 2
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Nodes 0, 1, 3, 4, 5 and 7
Neighborhood of RIMA node 6
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Nodes 1, 3, 4, 5, 7, 8, 9, 12, 13, 14, 15 and 16
1
6
7
15
16
0
14
2
4
8
3
12
10
5
11
9
13
RIMA Placement Algorithm
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RIMA nodes are more responsible for routing of
packets and it collects the database which is used for
routing
RIMA placement algorithm takes into consideration
some of the desirable properties
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Processing power
Average normalized link capacity
Reliability
Connectivity
RIMA Placement Algorithm contd…
• Send node information packet to neighbors
• Receive information packet from neighbors
• Calculate weight factor
• Send weight factor to neighbors
No
Weight of node >
Weight of all neighbors
Start timer and wait for
RIMA announcement message
RIMA announcement
Message received ?
No
Announce itself as
RIMA node
Yes
Announce itself as
RIMA node
Yes
Finding path between RIMAs
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RIMA node sends mobile agents to find
path(s) to neighbor RIMA nodes
While traveling mobile agent also collect the
path information like BW available on links
When mobile agent reaches at RIMA node it
gives all the information to the RIMA node
Mobile agent comes back to source RIMA node
and gives information to source RIMA node
RIMA nodes estimate the path delay by using
time stamp in mobile agent
Finding paths between RIMAs
4
1
3
7
2
8
5
6
Table at node 2
Table at node 4
RIMA
2
PATH
4->6->3->2
Delay
RIMA
4
4
PATH
2->3->6->4
Delay
3
Communication Among RIMAs
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RIMA node periodically sends reachability information
to neighbor RIMA nodes
PATH vector protocol is implemented among RIMA
nodes
Using the information obtained from neighbor RIMA
nodes, RIMA node decides the next hop RIMA node
for each destination e.g. tables at RIMA node 2 are,
RIMA
PATH
Destination
Next hop RIMA
6
2->4->6
2->1->7->6
15
6
11
10
-
-
10
2->3->5->10
2->4->5->10
Path finding in RIMA based routing
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Consider source (s) and destination (d)
s sends a packet to connected RIMA node (R1)
At R1 : if destination is in neighborhood it sends
directly to d otherwise it sends the packet to next
hop RIMA node R2
Suppose at a RIMA node Rn destination is in
neighborhood. In that case RIMA node directly sends
packet to destination node
Path of packet can be represented as
s  R1  R2  …  Rn  d
RIMA Based Best-Effort Routing
Source=1 and Destination=11
Source=9 and Destination=14
6
1
15
16
7
0
14
2
4
8
3
12
10
5
11
9
13
Dynamic Network Behavior
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After link/node failure corresponding node
sends update message to only connected
RIMA nodes and one hop neighbor nodes
RIMA node updates its neighborhood
If there is change in cost to reach some
node in neighborhood
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Send reachability information to neighbor RIMA
nodes
If neighborhood is unchanged
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No need to send messages
Quality of Service (QoS)
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Need of QoS
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Metrics used in QoS routing
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Internet provides Best-Effort service
New Emerging real time applications need Guaranteed
QoS; specially in case of interactive application like IP
telephony, video conferencing
Bandwidth, Delay, Delay jitter, packet loss
Issues in QoS
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Knowledge propagation and maintenance: When to send
the link state information to other network
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Periodic: Router periodically send
Threshold based: When significant change in resources
Metric and path computation
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How to measure and collect network state information
How to compute routes based on the information collected
RIMA based QoS Routing Scheme
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On-Demand Routing algorithm
QoS metrics used are bandwidth and delay
RIMA based QoS routing is same as RIMA
based Best-effort routing but only difference is
that each RIMA node strictly selects a path
according to QoS constraints
Consider source s , destination d , requested
bandwidth Breq and delay Δmax
RIMA based QoS Routing Scheme
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Source node sends mobile agent to a connected RIMA node
on the path with sufficient bandwidth and minimum delay
At RIMA node: If destination is within a neighborhood or it is
on the path to other RIMA node and feasible path exist,
 then RIMA node directly sends the mobile agent to
destination node
 otherwise RIMA node sends the mobile agent to next hop
RIMA node on the path which satisfies QoS constraints
When mobile agent reaches to destination, destination node
sends reservation request on the same path
When source node gets mobile agent it finds the time taken
by mobile agent to setup the connection and it estimates
delay to destination. If application can sustain that much
delay then it sends the packet. Otherwise it releases the
resources
QoS Routing
Source=1 and Destination=11
Reservation successful
6
15
16
7
1
0
14
2
4
8
3
12
10
5
11
9
13
Modified RIMA based QoS Routing
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In previous algorithm
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In modified RIMA based QoS routing
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More than one mobile agent reaches at destination hence
possibility of finding path increases i.e. increase in success
ratio
Disadvantage
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Source sends the path request to all the connected RIMA
nodes
Advantage
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Source sends request to only one RIMA node
Cost per connection increases as more requests are send in
the network
Destination will choose one path and sends the
reservation request on that path
Modified QoS Routing
Source=1 and Destination=11
Reservation successful
6
15
16
1
7
0
14
2
8
4
3
12
10
5
11
9
13
Simulation of Intranet
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Different Simulation Methods
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Waxman Method
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-d/(Lβ)
Regular Method
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P (x ,y) =a e
Regular topologies are used for simulation e.g. star,
mesh, ring
Hierarchical Method
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Transit-Stub Method
Hierarchical Method
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Transit-Stub model
Example
OSPF Simulation
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Topology is generated using Transit-Stub
model and edges are added using Waxman’s
method
Total domain is divided into NA areas +
backbone area.
Each area has more than one ABR ( Area
Border Router)
Topology size is changed by changing Number
of areas and Number of routers per area
Simulation
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RIMA topology simulation
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We consider topology as Flat topology
Generate the topology using Transit-Stub model
and added edges using Waxman’s method
RIMA placement algorithm decides RIMA nodes
Assumption and Features of Intranet Simulation
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Assumptions
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Propagation delay considered to be 1 unit time
Error free transmission
Links are symmetric
No packet loss at the router due to insufficient buffer
Features
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Simulated up to 800 nodes
At each router two queues one for best effort service and
other for guaranteed service
Best effort traffic is background traffic
Weighted fair queue is used at each router
Processing delay, transmission delay and queuing delays
are considered
RIMA Placement
• Number of RIMAs required
RIMA-to-RIMA average number of paths
Node Convergence: Number of messages
10
Node Convergence Time
Path Convergence: Number of messages
Path Convergence Time
RIMA based QoS Routing: Path setup
Success ratio Vs Number of connections
Connections Rejected Vs Breq
Number of update messages generated Vs connection
generated
Connection Blocking Probability Vs number of
hops
Conclusion
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Developed RIMA based Best-effort routing
scheme
Developed RIMA based QoS routing scheme
Comparisons of the performance of proposed
routing scheme and OSPF routing
Publications (submitted)
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Ajay L. Thakur and P. Venkataram , "RIMA Based IntraNetwork QoS Routing Scheme", Computer Communications
Journal (Elsevier)
Ajay L. Thakur and P. Venkataram , "Intra-Network
Routing Scheme using Mobile Agents”, SPCOM 2004
Thank You!