Wired Protocols and Models

PROTOCOLS AND MODELS SUPPORTED BY NS2 IN WIRED NETWORKS

NS2 MAINLY SUPPORT THREE MODES ON NETWORKING

1. WIRED NETWORKS

2. ADHOC/MOBILE IP

3. WIRELESS SENSOR NETWORKS

WIRED NETWORKS

A wired network connects devices to the Internet or other network using cables. The most common wired networks use cables connected to Ethernet ports on the network router on one end and to a computer or other device on the cable's opposite end.

Ethernet and wireless networks each have advantages and disadvantages; depending on your needs, one may serve you better than the other. Wired networks provide users with plenty of security and the ability to move lots of data very quickly. Wired networks are typically faster than wireless networks, and they can be very affordable. However, the cost of Ethernet cable can add up - the more computers on your network and the farther apart they are, the more expensive your network will be. In addition, unless you're building a new house and installing Ethernet cable in the walls, you'll be able to see the cables running from place to place around your home, and wires can greatly limit your mobility.

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The following list shows the models and protocols supported by ns2 in wired configuration;

• ROUTING IN WIRED NETWORKS

1. UNICAST ROUTING

In computer networking, Unicast transmission is the sending of messages to a single network destination identified by a unique address.Unicast routing is the process of forwarding unicasted traffic from a source to a destination on an internetwork. Unicasted traffic is destined for a unique address.

If an IP Unicast packet passes through a switch that does not know the location of the associated MAC Address, the packet will be broadcast to all ports on the switch. This failure of Unicast to 'cast to a single device' is called a Unicast flood.

Unicast messaging is used for all network processes in which a private or unique resource is requested.

Certain network applications which are mass-distributed are too costly to be conducted with unicast transmission since each network connection consumes computing resources on the sending host and requires its own separate network bandwidth for transmission. Such applications include streaming media of many forms. Internet radio stations using unicast connections may have high bandwidth costs.

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2. MULTICAST ROUTING

In computer networking, multicast is the delivery of a message or information to a group of destination computers simultaneously in a single transmission from the source. Copies are automatically created in other network elements, such as routers, but only when the topology of the network requires it.

Multicast is most commonly implemented in IP multicast, which is often employed in Internet Protocol (IP) applications of streaming media and Internet television. In IP multicast the implementation of the multicast concept occurs at the IP routing level, where routers create optimal distribution paths for datagrams sent to a multicast destination address.

At the Data Link Layer, multicast describes one-to-many distribution such as Ethernet multicast addressing, Asynchronous Transfer Mode (ATM) point-to-multipoint virtual circuits (P2MP) or Infiniband multicast.

  - IP MULTICAST

IP multicast is a technique for one-to-many and many-to-many real-time communication over an IP infrastructure in a network. It scales to a larger receiver population by requiring neither prior knowledge of a receiver's identity nor prior knowledge of the number of receivers. Multicast uses network infrastructure efficiently by requiring the source to send a packet only once, even if it needs to be delivered to a large number of receivers. The nodes in the network (typically network switches and routers) take care of replicating the packet to reach multiple receivers such that messages are sent over each link of the network only once. The most common low-level protocol to use multicast addressing is User Datagram Protocol (UDP). By its nature, UDP is not reliable—messages may be lost or delivered out of order. Reliable multicast protocols such as Pragmatic General Multicast (PGM) have been developed to add loss detection and retransmission on top of IP multicast.

Key concepts in IP multicast include an IP multicast group address, a multicast distribution tree and receiver driven tree creation.

An IP multicast group address is used by sources and the receivers to send and receive multicast messages. Sources use the group address as the IP destination address in their data packets. Receivers use this group address to inform the network that they are interested in receiving packets sent to that group. For example, if some content is associated with group 239.1.1.1, the source will send data packets destined to 239.1.1.1. Receivers for that content will inform the network that they are interested in receiving data packets sent to the group 239.1.1.1. The receiver joins 239.1.1.1. The protocol typically used by receivers to join a group is called the Internet Group Management Protocol (IGMP).

With routing protocols based on shared trees, once the receivers join a particular IP multicast group, a multicast distribution tree is constructed for that group. The protocol most widely used for this is Protocol Independent Multicast (PIM). It sets up multicast distribution trees such that data packets from senders to a multicast group reach all receivers which have joined the group. For example, all data packets sent to the group 239.1.1.1 are received by receivers who joined 239.1.1.1. There are variations of PIM implementations: Sparse Mode (SM), Dense Mode (DM), Source Specific Mode (SSM) and Bidirectional Mode (Bidir, or Sparse-Dense Mode, SDM). Of these, PIM-SM is the most widely deployed as of 2006;[citation needed] SSM and Bidir are simpler and scalable variations developed more recently and are gaining in popularity.

IP multicast operation does not require an active source to know about the receivers of the group. The multicast tree construction is receiver driven and is initiated by network nodes which are close to the receivers. IP multicast scales to a large receiver population. The IP multicast model has been described by Internet architect Dave Clark as, "You put packets in at one end, and the network conspires to deliver them to anyone who asks."

IP multicast creates state information per multicast distribution tree in the network. If a router is part of 1000 multicast trees, it has 1000 multicast routing and forwarding entries. On the other hand, a multicast router does not need to know how to reach all other multicast trees in the Internet. It only needs to know about multicast trees for which it has downstream receivers. This is key to scaling multicast-addressed services. It is very unlikely that core Internet routers would need to keep state for all multicast distribution trees,[citation needed] they only need to keep state for trees with downstream membership. In contrast, a unicast router needs to know how to reach all other unicast addresses in the Internet, even if it does this using just a default route. For this reason, aggregation is key to scaling unicast routing. Also, there are core routers that carry routes in the hundreds of thousands because they contain the Internet routing table.

  - ROUTING

Each host (and in fact each application on the host) that wants to be a receiving member of a multicast group (i.e. receive data corresponding to a particular multicast address) must use the Internet Group Management Protocol (IGMP) to join. Adjacent routers also use this protocol to communicate.

In unicast routing, each router examines the destination address of an incoming packet and looks up the destination in a table to determine which interface to use in order for that packet to get closer to its destination. The source address is irrelevant to the router. However, in multicast routing, the source address (which is a simple unicast address) is used to determine data stream direction. The source of the multicast traffic is considered upstream. The router determines which downstream interfaces are destinations for this multicast group (the destination address), and sends the packet out through the appropriate interfaces. The term reverse path forwarding is used to describe this concept of routing packets away from the source, rather than towards the destination.

A number of errors can happen if packets intended for unicast are accidentally sent to a multicast address; in particular, sending ICMP packets to a multicast address has been used in the context of DoS attacks as a way of achieving packet amplification.

On the local network, multicast delivery is controlled by IGMP (on IPv4 network) and MLD (on IPv6 network); inside a routing domain, PIM or MOSPF are used; between routing domains, one uses inter-domain multicast routing protocols, such as MBGP.

The following are some common delivery and routing protocols used for multicast distribution:

1. Internet Group Management Protocol (IGMP)

2. Protocol Independent Multicast (PIM)

3. Distance Vector Multicast Routing Protocol (DVMRP)

4. Multicast Open Shortest Path First (MOSPF)

5. Multicast BGP (MBGP)

6. Multicast Source Discovery Protocol (MSDP)

7. Multicast Listener Discovery (MLD)

8. GARP Multicast Registration Protocol (GMRP)

For more click here:                   >>  MULTICAST ROUTING     

                                                    >>  INTRODUCTION TO IP MULTICAST

                                                    >>   MULTICAST ROUTING PROTOCOLS

3. HIERARCHICAL ROUTING

Hierarchical routing is a method of routing in networks that is based on hierarchical addressing. Hierarchical routing is the procedure of arranging routers in a hierarchical manner. A good example would be to consider a corporate intranet. Most corporate intranets consist of a high speed backbone network. Connected to this backbone are routers which are in turn connected to a particular work group. These work groups occupy a unique LAN. The reason this is a good arrangement is because even though there might be dozens of different work groups, the span (maximum hop count to get from one host to any other host on the network) is 2. Even if the work groups divided their LAN network into smaller partitions, the span could only increase to 4 in this particular example.

Considering alternative solutions with every router connected to every other router, or if every router was connected to 2 routers, shows the convenience of hierarchical routing. It decreases the complexity of network topology, increases routing efficiency, and causes much less congestion because of fewer routing advertisements. With hierarchical routing, only core routers connected to the backbone are aware of all routes. Routers that lie within a LAN only know about routes in the LAN. Unrecognized destinations are passed to the default route.

Most Transmission Control Protocol/Internet Protocol (TCP/IP) routing is based on a two-level hierarchical routing in which an IP address is divided into a network portion and a host portion. Gateways use only the network portion until an IP datagram reaches a gateway that can deliver it directly. Additional levels of hierarchical routing are introduced by the addition of subnetworks.

In hierarchical routing, routers are classified in groups known as regions. Each router has only the information about the routers in its own region and has no information about routers in other regions. So routers just save one record in their table for every other region. In this example, we have classified our network into five regions (see below).

If A wants to send packets to any router in region 2 (D, E, F or G), it sends them to B, and so on. As you can see, in this type of routing, the tables can be summarized, so network efficiency improves. The above example shows two-level hierarchical routing. We can also use three- or four-level hierarchical routing.

In three-level hierarchical routing, the network is classified into a number of clusters. Each cluster is made up of a number of regions, and each region contains a number or routers. Hierarchical routing is widely used in Internet routing and makes use of several routing protocols.

In here, DV algorithms are used to find best routes between nodes. In the situation depicted below, every node of the network has to save a routing table with 17 records. Here is a typical graph and routing table for A:

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