4. Reasons to choose NS2 as a
platform
Object
Oriented
Real time Implementation
Discrete - Event Simulation
Plumbing makes NS2 a powerful tool
Event Scheduler
Time Synchronization
Cost effective
5. What is NS2
Network
Simulator 2, widely known as
NS2, is simply an event-driven
simulation tool that has proved useful
in studying the dynamic nature of
communication networks.
It is written using two language: Otcl (Object Oriented Tool Command
language)
C++ language.
6. Why two languages?
NS2
uses Otcl to create and
configure a network .
for configuration, setup, or one time
simulation,
to run simulation with existing NS2 modules.
C++
defines the internal mechanism of
the simulation objects
Used when dealing with a packet
Used when need to modify existing NS2
modules.
9. How to write tcl script program
to create a program…
Five steps to create a tcl script
programming:
Initialization and termination aspects of
network simulator
Defining the network nodes ,links, queues
and topology
Defining the agents and their application
NAM
Tracing
10. Example..
To
create new simulation use this
command:Set ns [new Simulator]
To create a new node :
Set n0 [ns node]
To create trace file :
set tracefile1 [open out.tr w]
$ns trace-all $tracefile1
11. Example…. (cont.)
To create a NAM file
set namfile1 [open out.nam w]
$ns namfile1-all $namfile1
To terminate the program :
Proc finish {} {
global ns tracefile1 namfile1
$ns flush-trace
close $tracefile
close $namfile
exec nam out.nam
exit 0
13. Objective of TCP
Adapt the transmission rate of packets to the
available bandwidth.
Avoid congestion at the network.
Create a reliable connection by
retransmitting lost packet
We measure the performance of TCP on noisy
links using Queue monitoring.
How the window size vary in network
congestion.
14. UDP(User Datagram Protocol)
Connectionless
transport-layer protocol
No connection setup is needed prior to
data transfer
Offers minimal transport layer
functionalities
non-guaranteed data delivery
gives application a direct access to
network layer
16. Basic Agents
Two types of NS2 agent used for creating or
destroying a packet are :
Routing agent
A routing agent creates and receives routing
control packets, and commands routing protocols
to act accordingly .
Transport-layer agent
A transport-layer agent controls the congestion
and reliability of a data flow based on an
underlying transport layer protocol (e.g.,UDP or
TCP)
18. INTRODUCTION
Ad-hoc networks are infrastructure-less.
The interconnected nodes coordinate the
transmissions with other nodes and they may
have to relay messages among several other
nodes in order to reach a destination.
An ad-hoc network is a self-configuring
network of wireless links connecting mobile
nodes, where these nodes may be routers
and/or hosts.
20. Multiple Channels and Multiple
Interfaces
Due to the increasing throughput demand,
the idea of exploiting multiple channels is
appealing in ad-hoc wireless networks .
Having more than one interface on a node
allows two different nodes communicating in
parallel on different channels .
An interface has a capability to dynamically
switch to different channels over time.
Two adjacent nodes can communicate with
each other if they have at least one interface
on a common channel.
21. Problems occurred
In a wireless ad-hoc network consisting of
multiple hops, if each node only uses a
single interface, packets may be delayed
at some hops if their next hops are not on
the same channel.
End-to-end delay increases.
Degradation in channel capacity.
22. Solution
A multi-interface solution for exploiting
multiple channels that can be implemented
on existing IEEE 802.11 hardware.
An interface assignment strategy using the
technique of interface switching , that
simplifies coordination among nodes while
utilizing multiple available channels.
A routing protocol, namely the MultipleChannel Routing (MCR), that selects routes
with the highest throughput by accounting for
channel diversity and interface switching
cost.
25. Routing protocols used in ADHOC network
AODV
(Ad-Hoc On Demand
Distance Vector)
DSR (Dynamic Source Routing)
DSDV (Destination Sequenced
Distance Vector)
26. AODV
Routing
protocol for wireless Ad-Hoc
network
Reactive routing protocol, meaning that it
establishes a route to a destination only
on demand
avoids the counting-to-infinity problem
using sequence numbers on route
updates
Capable of unicast and multicast routing .
28. Features…
Routes
established on demand and that
destination sequence numbers are
applied to find the latest route to the
destination
Connection setup delay is lower
29. DSR (Dynamic Source Routing)
DSR
is designed for MANETs
DSR doesn’t need any network infrastructures
Loop free routing
No routing information in the intermediate nodes
Nodes
may easily cache this routing information
for future use
30. DSR Mechanisms
Route
discovery
Route maintenance
Mechanisms “on-demand”
No periodic routing advertisement
No link status sensing
No neighbor detection packets
Routes
caching
31. Basic DSR Route Maintenance
Each node transmitting the packet is responsible for
confirming that the packet has been received by next hop.
Acknowledgement
By lower layer protocol MAC
By DSR-specific software ack
Route errore message
32. DSDV(Destination Sequenced
Distance Vector )
Each node maintains a routing table which stores
next hop, cost metric towards each destination
a sequence number that is created by the destination itself
Each node periodically forwards routing table to its neighbours
Each node increments and appends its sequence number when
sending its local routing table
Each route is tagged with a sequence number; routes with greater
sequence numbers are preferred
Each node advertises a monotonically increasing even sequence
number for itself
When a node finds that a route is broken, it increments the
sequence number of the route and advertises it with infinite metric
Destination advertises new sequence number
33. Advantages of DSDV
DSDV
is an efficient protocol for route
discovery. Whenever a route to a new
destination is required, it already exists at
the source.
Hence,
low.
DSDV
latency for route discovery is very
also guarantees loop-free paths.
34.
35. Virtual LAN( VLAN):
A
virtual LAN is a group of devices in the
same broadcast domain or subnet.
VLANs are good at logically separating
traffic between different groups of users
VLANs contain/isolate broadcast traffic,
where you need a router to move traffic
between VLANs.
37. Configuration of VLAN in NS2:
1)
Create a Network Bridge:
Firstly we have to create a network bridge
using the add call.
We have to use net_vlanType as a data
type for the net_device element.
38. To attach an adapter to be a
bridge, we have to use
following parameter’s :
id: the name of a physical LAN or VLAN
adapter that you would like to plug into the
bridge (e.g. eth0, eth1.5).
Network_id: a virtual network ID that you
would like to attach the network adapter to.
If an adapter is already connected to a bridge
and you pass a different network ID, the
adapter will be disconnected from the old
bridge and connected to the new bridge.
To detach an adapter from a bridge, leave the
network_id element empty.
39. cont.
vlan_id
-- the VLAN adapter ID. When
attaching/detaching a physical network
adapter, leave the element empty.
base_device_id -- the name of the
physical network adapter with which the
VLAN adapter is associated.
When attaching/detaching a physical
adapter, leave the element empty.
41. eth1.1 bridged with eth0.1 and
eth2.2 bridged with eth0.2
This
configuration implements a VLAN
switch with two access ports (port eth1 for
VLAN 1 and port eth2 for VLAN 2) and a
trunk port eth0 capable of carrying
frames with VLAN ID either 1 or 2 in its
802.1q tag. Now, consider another switch
with exactly the same configuration.
Then, the trunk ports of the switches are
connected.
42. Cont.
Now
device connected to port eth1 of
switch 1 and that connected to port eth1
of switch 2 can interchange frames with
VLAN ID 1. The same is the case with eth2
on both the switches.
Two VLANs span across 2 switches. There is
no bridging/routing 'between' these two
VLANs. So, this works like a perfect VLAN
switch.
43. What is actually happening is :
All the untagged frames from eth1 pass
through the bridge and goes out of eth0
as untagged frame.
All the frames with VLAN ID 2 entering
eth2 gets untagged at eth2.2, gets
bridged to eth0.2, gets tagged with VLAN
ID 2 at eth0 and goes out of the trunk as
tagged frame.
44. How we can implement it in
NS2:
I have 3 Ethernet interfaces, eth0, eth1 and
eth2. I am planning to convert it into a VLAN
switch.
Let eth1 and eth2 are configured for VLAN 1
and 2 respectively. Let eth0 be a trunk
carrying both VLAN frames.
$vconfig add eth1 1
$vconfig add eth2 2
$vconfig add eth0 1
$vconfig add eth0 2
46. Cont.
The
basic idea of the above configuration
is based on the fact that each VLAN can
be simulated with individual bridges per
VLAN. The above configuration works fine
as expected. eth0 acts as trunk carrying
frames with both VLAN IDs(1 and 2). This
trunk can be connected to a similar
switch on the other end to span the VLAN
segmentation across switches.
47. Benefits of VLAN:
Higher performance - Dividing flat Layer 2
networks into multiple logical workgroups
(broadcast domains) reduces unnecessary traffic
on the network and increases performance.
Security - Groups that have sensitive data are
separated from the rest of the
network, decreasing the chances of confidential
information breaches.
Cost reduction - Cost savings result from less need
for expensive network upgrades and more
efficient use of existing bandwidth and uplinks.
