CBCN4103

Internetworking is connecting two or more computer networks with some sort of routing device to exchange traffic back and forth, and guide traffic on the correct path across the complete network to their destination.

Internetworking devices, are devices used in connecting individual networks to each other, that includes Cable, Repeaters, Hubs, Routers, Switches, and Bridges.

In summary, the last three layers of the OSI model (i.e. Application - Session) deal with application issues and generally are implemented only in software, while the last four layers handles data transport issue.

The OSI Model is really an important factor in internetworking because it accounts for the way our data are moved from one computer system to another using the internetworking devices, irrespective of their protocol.◦ Routers works at the Network layer of the OSI Model.

◦ Bridges works at the data link layer. Switches is a multi-port bridge

◦ Repeaters works at the Physical layer. A hub is a repeater with multi-port.

Cables Cabling plays an important role in networking

and the type of network media used determines how fast the data travels along the media, and also the maximum data rate that can be carried. The four main types of networking media are:◦ Shielded twisted-pair (STP)◦ Unshielded twisted-pair (UTP)◦ Coaxial cable◦ Fiber-optic cable

Unshielded Twisted-pair are not shielded and thus interfere with nearby cables. They are used in LANs to bit rates of 100Mbps and with maximum length of 100m. UTP cables are typically used to connect a computer to a network

This is a type of copper telephone wiring in which each of the two copper wires that are twisted together and are coated with an insulating coating that functions as a ground for the wires.

Has a grounded metal sheath around the signal conductor.

Interference among cables is reduced due to the sheath around signal conductor.

Allows higher data rate transfer.

Typically they are used at bit rates of 100 Mbps for maximum lengths of 1 km

Fiber-optic cabling uses either glass or plastic fibers to guide light impulses from source to destination.

Do not interfere with nearby cables. Give greater security. Allows extremely high bit rates over long

distances. They provide more protection from electrical

damage by external equipment and greater. Resistance to harsh environment. Safer in hazardous environment.

As a network grows, its cable can easily exhaust the network constraint, and any further loads on this network can leads to attenuation and digital pulse distortion. To overcome these limitations, repeaters are used to increase the maximum interconnection length, and may do the following:◦ Reshape signal pulses◦ Pass all signals between attached segments◦ Boost signal power◦ Possibly translate between two different media (such as

between fiber-optic and twisted-pair cable) ◦ Transmit to more than one network. These are multi-port

repeaters and send data frames from any received segment to all the others. Multi-port repeaters do not filter the traffic, as they blindly send received data frames to all the physical connected network segments.

A hub is a repeater with multiple ports, and can be thought of as being the centre point of a star topology network. It is often known as a multi-port repeater (or as a concentrator in Ethernet). Hubs can be active (where they repeat signal sent through them) or passive (where they do not repeat, but merely split, signals sent through them).

Hub generally:◦ Amplify signals;

◦ Propagate the signal through the network;

◦ Do not filter traffic. This is a major disadvantage with hubs and repeaters as data arriving at any of the ports is automatically transmitted to all the other ports connected to the hub;

◦ Do not determine path; and

◦ Centralise the connection to the network.

Bridges and Switches are devices working at Data Link Layer of OSI Model. Although they work at the same layer, bridges and switches perform differently.

A bridge is a device used more commonly in the early days of LAN to connect - or bridge -two physical network segments. Switches can be used to perform this operation as well as allowing end device connectivity to the LAN.

What is Bridge?

Bridge can be defined as a device that is used to connect two local area network or two segments of the same LAN that uses the same protocol together such protocol includes Ethernet or token ring.

How It Works?

Bridges examine the destination MAC address (or station address) of the transmitted data frames, and will not retransmit data frames which are not destined for another network segment.

They maintain a table with connected MAC address, and do not forward any data frames if the MAC address is on the network that originated it, else it forwards to all connected segment. Thus, a bridge does not actually determine on which segment the destination is on, and blindly forwards data frames to all other connected segments.

Bridges are an excellent method of reducing traffic on network segment and it does this by examining the destination address of the frame before deciding how to handle it.

Problems with Bridge◦ When the inter-segment traffic becomes too heavy,

it can become a bottleneck for traffic, and slow down communication.

◦ They spread and multiply broadcast. A bridge forwards all broadcast to all other connected segments. If there are too many broadcast, it can result in a broadcast storm.

What is Switch?

A switch is a very fast, low-latency, multi-port bridge that is used to segment LANs. They are typically used to increase communication rates between segments with multiple parallel conversation and also communication between different networking technologies (such as between ATM and 100Base-TX).

Hubs◦ Lack of scalability

◦ Increased latency

◦ More collisions

Switches◦ Dedicated bandwidth

◦ Collision-free

◦ Full-Duplex

Cut-through Switching

The switch reads the destination address before receiving the entire frame. The data is then forwarded before the entire frame arrives. This method has the advantage that there is less delay (latency) between the reception and transmission of a data packet, but has poor error detection, because it does not have a chance to detect any errors, before it has started to transmit the received data frame.

Store-and-Forward Switching

The switch involves reading the entire Ethernet frame, before forwarding it, with the required protocol and at the correct speed, to the destination port. This has the advantage of improved error check, protocol filtering and speed matching but has the disadvantage of system delay, as the frames must be totally read before it is transmitted.

Routers are network devices that examine the network address (IP address) field and determine the best route for a data packet, and will only transmit it out of a network segment if it is destined for a node on another network. Routers do the following:◦ Do not forward broadcast

◦ Do not forward traffic to unknown addresses

◦ Modify data packet header

◦ Build tables of network addresses

LANs have certain limitations. These limitations include the geographical distances that they cover, the number of nodes that can be connected, or the need to run more than one protocol. The devices within a network and the functions they support make a significant impact on the limitations of the network. Various types of hardware devices can be used to extend LAN functionality, each offering a specific function in exchange for added cost and complexity.

There are a variety of devices used to extend LANs, from a simple Network Interface Card (NIC) that allows you to connect to a network to a sophisticated router that can move information across the Internet. However, each device performs a specific function that, when combined with the functions of others, enables the LAN to transfer information from Point A to Point B.

The Network Interface Card (NIC) is a circuit board that is physically installed within an active network node, such as a computer, server, or printer. The NIC is an adapter that controls the exchange of information between the network and the user.

A repeater extends the length of a network cabling system by amplifying the signal and then re-transmitting it. Repeaters operate at Physical Layer 1. As a result, they do not look at the data at all. Any information coming into one port is simply repeated out all other ports.

Repeaters regenerates the digital signal.

Repeaters overcome the attenuation caused by free-space electromagnetic-field divergence or cable loss.

Repeaters remove the unwanted noise in an incoming signal.

A hub is another Layer 1 device that is typically used as a central point for connecting segments in a LAN. While passive hubs simply pass packets from one port to another, the signal may be regenerated in active hubs called multi-port repeaters.

Hub is simply seen as a common connection point for devices in a network. Hubs are commonly used to connect segments of a LAN together. A hub contains multiple ports, when a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.

As networks grow larger, they are often divided into smaller LANs to reduce traffic drain on the network. A bridge is a Data Link Layer 2 device that provides a connection between separate LAN segments. The bridge monitors packets as they move between segments, keeping track of the MAC addresses that are associated with various ports. As they gain more knowledge of the nodes connected to each network, they are better able to manage traffic flow.

Switches are becoming a more common way to connect networks together because they are simply faster and more intelligent than bridges.

Advances in technology spawned a new generation of networking devices known as LAN switches, which included bridging as one of several functions. Switches have replaced bridges for two reasons: superior performance and lower price per port.

Routers were originally invented to solve some of the problems that were not addressed by bridges. Like bridges, routers are used to segment a LAN in order to reduce excess broadcast traffic and latency. In addition, routers make internetworking possible by interconnecting both local and wide area networks.

The function of a router is to direct data along the most efficient and economical route to the destination device. Routers operate at Network Layer 3, which means they examine the logical network address (for example, 192.29.21.100) and not the physical hardware address (MAC).

Routers are smarter than bridges because they know about routing protocols, different address schemes, different frame sizes and different data rates in order to make the best decision on which path to choose. The best path is determined by using routing tables and algorithms.