The Transmission Of Packets Computer Science Essay

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In the network, there are certain tasks that must be accomplished before a packet is transmitted from the source node to the destination node. One of it is addressing of the packet - which involves encapsulating of the source and destination address to enable the system know where the packet is going. Another is the transmission of the packet from source to the destination node. That means sending packet from the source to destination. There are several methods of addressing and sending packet over the network. Packets can be differentiated from each other depending on the addresses they carry. The number of destinations host can also be used to determine the mode of transmission used.

There are three methods of transmission of packet in a network namely; unicast, broadcast and multicast. Unicast is a point-to-point method of transmission. It involves addressing a packet to only one node. Broadcast is a point-to-all method of transmission. That is packet send by a node is received by all the nodes in the network. Finally, multicasting is a point to multipoint method of transmission. That is packet sent by a node is received by many other nodes.

Unicast is a one-to-one communication method. The data packets are sends from a source node to a destination node. A typical example is a server and workstation in a network. Each transmission session created involve one server and one recipient per time. Although several nodes may be requesting for the same information at the same time, the server stream or send the data packet to each node one after the other.

Figure 1.0: Unicast Transmission Model

Figure 2.0 illustrates the network environment for unicast method of transmission. It consists of a server and three end nodes connected to a network. Although the entire nodes requested the same information at the same time from the server, the server sends the data independently using their individual addresses. That is the server encapsulates each packet with end node address and sends it distantly to three nodes. This method of transmission is not scalable especially when the number of the nodes increases. It also consumes network bandwidth as a result of redundant packet transmitted on the same path. This transmission method support several standard applications like File Transfer Protocol, Hypertext Transfer Protocol (HTTP), SSH, POP3 and Simple Mail Transfer protocol in “IP” network and Ethernet network.

2.1.2 Broadcasting Transmission Method

Broadcast is a one-to-all communication method. The data packets are sends from a source to all the connected devices to the network. The source node sends a copy of the data packet and the routers duplicate and forwards the data packets to the entire connected nodes in the networks. For example, when a network node joins the network first; a broadcast packet is send by Address Resolution Protocol (ARP) to every node on the network for address resolution and to announce it presence in the network. This transmission mechanism floods the entire network with broadcast packet. Unlike unicast, and broadcast transmission methods support Ethernet network. Broadcast is not scalable on the Internet because it leads to broadcast storm and network congestion.

Figure 2.1: Showing Broadcast Transmission Model

Figure 2.1 illustrates a broadcast transmission in a network environment. It consists of a server and three end nodes connected to a network. The server sends a copy data packet and the router duplicates the data packet and forwards it to all the connected devices. The data packets are received by interested and uninterested end nodes in the network. These unrequested packets received by the end-nodes lead to waste of network resource and the flooding mechanism of transmission consume network bandwidth. Therefore, broadcast method transmission is not appropriate for large networks like Internet.

2.1.3 Multicasting

Multicasting is much more different from the unicast and broadcast communication methods. It is a one-to-many communication method. The data packets are sends from a source to a group of destination nodes. That is a copy of the data is send from the source host to all the members of the multicast group. Internet Protocol multicasting communication method also provides many-to-many transmission method. That is group of nodes (minimum one node) can send data packet to a group of recipients. The senders transmit data packet to a multicast address that belongs to a particular multicast group. The data packets are duplicated by the multicast routers and forwarded on request to the multicast group member that is interested in the data packet. The interested end-nodes that want to receive the data packet have to join the multicast group. The dynamics enable data packet to be send only to the interested recipients.

Figure 2.2: Showing Multicast Transmission Model.

Figure 2.2 illustrates a multicast transmission in a network environment. It consists of a source server and three end nodes connected to a network. The source server sends a copy data packet to a multicast group address and the router duplicates and forwards the data packet only to the multicast group members. It is only the member that joins the group receives the data packet, other nodes who are not member will not receive the data packet as demonstrated in figure 2.2.

2.2 IP Routing Protocol.

Apart from different methods of transmission of data packet discussed above, another vital task that must be accomplished before a packet can be transmitted from a source host network to the destination host network is logical addressing. This involves encapsulating the data packet with the source and destination address to enable the system to know where the data packet going.

The logical addressing takes place in the network layer of the OSI reference model. These logical addressing and routing data packets are the primary function of devices in this layer e.g., router. The router connects the small networks together to form a large network that can span cities and the entire world as in the Internet network. This device forwards data from one network to another and allow host on the network to send data packets to one another even if the source host has no idea of the location of the destination host. Router care less about the network host but only cares about the network and best path to each network. To carry out these vital functions, there are set of rules called routing protocol that enables the router to perform these functions.

This set of rules enables the router to find out the best route, and alternative route to every network, and uses this information to pollute the router table (route to every network). For a network that are not directly connected to the router, the router must use several ways to discover how to get to the destination network: static (input all network locations into the routing table), default and dynamic routing.

2.2.1 Static Routing

Static routing occurs when the administrator manually add routes to each router’s routing table. This routing is particularly economical, and there is no overhead on the router central processing unit. There is no bandwidth usage among the routers, and it also adds security to the system, because the administrator prevents or allows access to a network. However, it is not scalable in large networks, and demand reconfiguration of the entire routers when there is a change in network topology.

2.2.2 Default Routing

Default routing occurs when data packet are send to remote network that is not in the routing table to the next-hop router. Default routing is only used network with one single exit path of the network â€" stub network.

2.2.3 Dynamic Routing

Dynamic Routing is the used to protocol to locate dynamically network destination and automatically update the routing table. The router learns all the connected networks and other routes that lead to the remote network running the same protocol. The router will sort for the best route to the every remote using the routing tables. The routing protocol will distribute the best route information to every other router in the network using the same protocol, thereby expanding the routing information of the existing network and how it can be reached. This makes dynamic routing to adapt to network topology change, link failure and device failure. This capability makes management, and maintenance of dynamic routing simple compare to default routing, and static routing.

Figure 2.3: Classification of Unicast Routing Protocol from Internet Protocol (IP)

There are two types of dynamic routing protocols operating in Internetwork: interior gateway protocol (IGP) and exterior gateway routing protocol (EGP). IGP protocol uses dynamic routing to exchange routing updates within the same domain, while EGP protocols uses dynamic routing mechanism to exchange routing updates between different domains. These protocols operating in internetwork use dynamic routing. In dynamic routing, router uses two basic methods to discover the devices, and the route to every device in the network. These methods include distance vector and link state protocols. There is also another protocol, which is the combination of link and distance vector protocol named hybrid protocol. A typical example of hybrid protocol is EIGRP. We will discuss pros and cons of these protocols within a domain (IGP) and between different domains (BGP) in this section. Nevertheless, these routing protocols will be used in the simulation experiment in chapter 6.

2.2.3.1 Interior Gateway Routing Protocol

Interior Gateway Routing is when the routing information is exchange among router within domain. The Interior gateway protocol is categories base on the above routing mechanism namely, distance vector, link state and hybrid routing protocol. The example of these protocols includes Routing Information Protocol (RIP), Open Shortest Path First and Enhance Interior Routing Protocol (EIGRP). These protocols can further be classified as class full and classless routing protocols.

2.2.3.1.1 Distance Vector Routing (DVR)

Distance vector uses a distance and direction to determine it best path to remote network. The distance metric is estimated by the number of the hop the packet data will transit. The hop is any time a packet passes router. The DVR select it best path based on the route will the least number of hop. The vector is the direction the data packet will transit through the network. The DVR exchange it routing table with only directly connected router. Examples of distance vector are RIP and IGRP. This routing mechanism is also called Bell-Ford algorithm. It is easy to configure with low computational overhead and supportive to troubleshoot.

2.2.3.1.2 Link State Routing Protocol

Link state routing protocol, also called shortest part first works using link state algorithm. The protocol works by updating every router in the domain about other routers and their directly connected networks. In other words, each router has a complete network picture of that domain network and can determine the optimum path to all networks on its own. The protocol enables the router to keep track of information by maintaining three separate tables. One of tables is for directly connecting router, another for the entire network topology, and one for best path (routing table). Instead of exchanging the entire routing table, link state only exchange link updates to each other. Examples of link state protocols are OSPF and IS-IS. In the simulation experiment, in chapter 5 all routers in the domain will be configured using OSPF routing protocol. This protocol is scalable in large networks and complex in configuring compared to RIP routing protocol.

2.2.3.1.3 Hybrid Routing Protocol

Hybrid Routing also referred to as balance-routing makes use of the link state and distance vector algorithm in routing in of data packet and in neighbour router relationship. It uses traditional distance vector to update routing information of directly connected network and combine it the cost of reaching them from the perspective of the advertising router. It exchange full routing table with the neighbouring router and send routing update information only when the network topology has changed. Balance-routing protocol converges rapidly, requires less processing time, and memory as compare to link state routing.

2.2.3.2 Exterior Gateway Protocol

Exterior Gateway Routing protocol is a protocol that is design to perform routing function between different domains. It can be describe as inter-domain routing protocol that exchange routing information between autonomous systems. An autonomous system (domain) is a network or group of networks operating the same routing protocol and control from a common administration. However, Internet network consists of several autonomous systems, and EGRP is the routing protocol used to route traffic between and through different the Internet Service Provider networks. Examples of EGRP are Border Gateway Protocol (BGP). BGP use path vector mechanism in routing. Path vector routing mechanism enables the node speaker in each autonomous system to create it routing table and exchange with neighbour speaker node in another autonomous system.

2.3 Comparison to This Work:

Reliable multicasting and turning of Protocol Independent Multicasting is the popular area of research which quite complicated in a WAN environment. The network perform can be enhance by switching from Rendezvous Point to Shortest Path fir in multicast environment rather than turning PIM. Most simulation work in IP multicasting has centre on the comparing the unicast and multicast, showing multicast processing of the unicast and a copy being send in IP multicast. Little or no attention has been given to using different unicast routing protocol which Protocol Independent Protocol used without creating it routing table to compare the efficiency. This dissertation simulation will be carried out that compare RIP, OSPF and EIGPR and compare their efficiency with Protocol Independent Protocol.

Also, many-to-many multicast has not been simulated in OPNET built model. This dissertation will build and simulate many sources sending multicast traffic to many recipients using OPNET simulation tool. The switching from Rendezvous Pint to Shortest path Tree will be simulated and different multicast application. Failure of a device will demonstrate using web page in OPNET simulation for easy understanding and analysis of the result using video conferencing and voice application.

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