Oct 6, 2015 ~ Network Services

Quoting one of e-books and websites Select the components required to meet a given network specification Select the components required to meet a network specification As mentioned in the previous objectives, we use routers, bridges, and switches in an internetwork. Figure...

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Operation of IP Data Networks Recognize the purpose and functions of various network devices such as Routers, Switches, Bridges and Hubs. Repeaters Repeaters are Layer 1 devices utilizing the Physical Layer and are considered as outdated technology today. They have been...

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Quoting one of e-books and websites

Select the components required to meet a given network specification

Select the components required to meet a network specification

As mentioned in the previous objectives, we use routers, bridges, and switches in an internetwork. Figure 1.5 shows how a network would look with all these internetwork devices in place. Remember that the router will not only break up broadcast domains for every LAN interface, it will break up collision domains as well.

When you looked at Figure 1.5, did you notice that the router is found at center stage and that it connects each physical network together? We have to use this layout because of the older technologies involved—bridges and hubs.

On the top internetwork in Figure 1.5, you’ll notice that a bridge was used to connect the hubs to a router. The bridge breaks up collision domains, but all the hosts connected to both hubs are still crammed into the same broadcast domain. Also, the bridge only created two collision domains, so each device connected to a hub is in the same collision domain as every other device connected to that same hub. This is actually pretty lame, but it’s still better than having one collision domain for all hosts.

Notice something else: The three hubs at the bottom that are connected also connect to the router, creating one collision domain and one broadcast domain. This makes the bridged network look much better indeed!

The best network connected to the router is the LAN switch network on the left. Why? Because each port on that switch breaks up collision domains. But it’s not all good—all devices are still in the same broadcast domain. Do you remember why this can be a really bad thing? Because all devices must listen to all broadcasts transmitted, that’s why. And if your broadcast domains are too large, the users have less bandwidth and are required to process more broadcasts, and network response time will slow to a level that could cause office riots.

Once we have only switches in our network, things change a lot! Figure 1.6 shows the network that is typically found today.

Here, I’ve placed the LAN switches at the center of the network world so that the routers are connecting only logical networks together. If I implemented this kind of setup, I’ve created virtual LANs (VLANs). But it is really important to understand that even though you have a
switched network, you still need a router to provide your inter-VLAN communication, or internetworking.

Obviously, the best network is one that’s correctly configured to meet the business requirements of the company it serves. LAN switches with routers, correctly placed in the network, are the best network design.

Let’s go back to Figure 1.6. Looking at the figure, how many collision domains and broadcast domains are in this internetwork? Hopefully, you answered nine collision domains and three broadcast domains! The broadcast domains are definitely the easiest to see because only routers break up broadcast domains by default. And since there are three connections, that gives you three broadcast domains. But do you see the nine collision domains? Just in case that’s a no, I’ll explain. The all-hub network is one collision domain; the bridge network equals three collision domains. Add in the switch network of five collision domains—one for each switch port—and you’ve got a total of nine.

So now that you’ve gotten an introduction to internetworking and the various devices that live in an internetwork, it’s time to head into internetworking models.

Ccna Certified Mr.Mohamed Samir

Operation of IP Data Networks

Recognize the purpose and functions of various network devices such as Routers, Switches, Bridges and Hubs.

Repeaters

Repeaters are Layer 1 devices utilizing the Physical Layer and are considered as outdated technology today. They have been replaced by Hubs and Switches. But for the purposes of understanding; a repeater consists of a transmitter and a receiver. The function of a repeater is to receive the signal, amplify it and retransmit it enabling the signal to be transmitted over a longer distance.
Repeaters are essential to maintain the quality of signals as they degrade over a distance. Repeaters regenerate and retime the signal, helping it travel a longer distance. Repeaters may be single port or multi port. The figure given below illustrates a repeater.

Hubs

A Multiple Port Repeater is termed as a Hub. It is also a Layer 1 device utilizing the Physical Layer. It can comprise of ports varying from 2 to 24 in number and may also be known as a workgroup hub. Its main job is cleaning up signals. By isolating the end points, Hubs increase the network reliability. A hub retransmits data on all the other ports. A twisted pair cable is used for achieving physical connectivity. The figure given below illustrates a HUB

Hubs can be of two types; Active and Passive hubs. The difference between the two is that Active Hubs regenerate the incoming signal, whereas the Passive Hubs do not do so. Active Hubs need individual power supply to help with the gain of signal before the data is forwarded to all ports. Gain is an electrical term, representing the ratio of signal output to signal input of a system.

The advantage of Hubs is that they are inexpensive. If more efficient use of bandwidth and its distribution among the ports is required, hubs may not be the best option. Traffic congestion because of collisions on the network is indispensable while using hubs. The best solution in this case is to use a switch.

Network Interfaces:

Network interfaces provide connectivity between an end-user computer to the public network. Depending on the interface that is being used, up to three light-emitting diodes (LEDs) may appear. These diodes help to determine the status of the connection.

The Link Light LED: It lights up when the connectivity is there;
The Activity Light LED: It flickers if some activity is taking place on the line;
The Speed Light LED: This light indicates the connection speed. It may be there on the interface, it may not be there.

Blinking lights and colors other than green are indicative of error conditions.

Bridges:

Bridges were used as a solution for issues relating to network congestion. Hubs and Repeaters were longer proving sufficient to meet the challenges provided by systems growing complex. In comparison to Repeaters and Hubs and Bridges used the concept of segmentation. Repeaters and Hubs which do not use segmentation, share the same bandwidth and hence the traffic congestion on a network. When the other device on the network is not aware of the existence of a Bridge, it is called a Transparent Bridge. Figure 3 given below illustrates a Bridge.

Switches:

Switches are very smart Bridges with the characteristics of being multi port and high speed. The differ bridges from the point that bridges process frames in software whereas switches process frames in hardware. Switches do so by using application integrated circuits (ASIC’s). Figure 4 given below illustrates a Switch.

Cisco Switch

In addition to the above mentioned Switches have the following features:

Speed Back Plane: this function increases the speed of the network; it allows monitoring of multiple conversations.
Data Buffering: This function allows storage of frames and later forwarding the frame to the right port.
High Port Density: Switches can support multiple ports at one time.
High Port Speed: Switches can support high speeds varying from speeds from 10 Mbps to 10Gbps.
Lower Latency: Latency is a term that is used to measure the time it takes an incoming frame to come back out of a switch. In the case of switches latency is low.
VLAN’s: This feature allows segmentation of networks into separate broadcast domains.

These features permit micro segmentation.

Micro segmentation:

Micro segmentation means that a dedicated switch ports are created for every end station; meaning that dedicated paths for sending and receiving transmission with each connected hosts are created. These reduce traffic congestion to a great extent for the reason that separate collision domain and individual bandwidth is available for every host. But faster computers, broadcasts and multicasts can still cause congestion.

Bridges and Switches perform the following tasks:

Ascertainment of MAC Address: Examine the source MAC address of every inbound frame to ascertain its MAC address;
Filtration/Forwarding: Depending on the destination of the MAC address, filtration or forwarding of frames as the case may demand;
Elimination: Eliminating loops caused by superfluous connections.

Icon standard network

Ccna Certified Mr.Mohamed Samir

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