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There are three major types of devices used for internetworking: bridges, routers, and switches.

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Module 2.

NETWORKS AND TELECOMMUNICATIONS

How are networks changing our lives?

 

Unit 1

 

1. PRE-READING ASSIGNMENT

 

What networking hardware do you know?

 

2. READING

 

2.1. Translate the vocabulary used in the text below:

an enterprise adjacent to extend Token Ring to segment response time a culprit congestion incremental to destine simultaneously dedicated LAN to diminish uncontested

2.2. Read the text and answer the following questions:

· What are the similarities and differences between a router and a bridge?

· What are switches used for?

 

The Networking

 

The term internetworking refers to linking individual LANs together to form a single internetwork. This internetwork is sometimes called an enterprise network because it interconnects all of the computer networks throughout the entire enterprise.

There are three major types of devices used for internetworking: bridges, routers, and switches.

Bridges and routers are both special kinds of devices used for internetworking LANs that is, linking different LANs or LAN segments together. Many organizations have LANs located at sites that are geographically distant from each other. Routers were originally designed to allow users to connect these remote LANs across a wide area network, but bridges can also be used for this purpose. By placing routers or bridges on LANs at two distant sites and connecting them with a telecommunications link, a user on one of the LANs can access resources on the other LAN as if those resources were local.

Bridges and routers link adjacent LANs. Local bridges and routers were first used to extend the area a network could cover by allowing users to connect two adjacent LANs to maintain performance by reducing the number of users per segment. Both Ethernet and Token Ring specify limits on maximum distances between workstations and hubs, hubs and hubs, and a maximum number of stations that can be connected to a single LAN. To provide network connectivity for more people, or extend it to cover a larger area, it is sometimes necessary to link two different LANs or LAN segments. Bridges and routers can both provide this function.

Today, however, these internetworking devices are also increasingly used to segment LANs to maintain performance by reducing the number of users per segment. When users on a single LAN begin to experience slower response times, the culprit is often congestion: too much traffic on the LAN. One method users are employing to deal with this is to break large LANs with many users into smaller LANs, each with fewer users. Adding new network users may require the organization to create new LANs to accommodate them. Implementing new applications on an existing LAN can create so much incremental traffic that the organization may need to break the LAN into smaller LANs segments to maintain acceptable performance levels.

In all of these cases, it is still critical that users on one LAN be able to reach resources on other LANs within the organization. But the LANs must be connected in such a way that packets are filtered, so that only those packets that need to pass from one LAN to another are forwarded across the link. This keeps the packets sent between two stations on any one LAN from crossing over onto the other LANs and thereby congesting them. A general rule of thumb suggests that 80 percent of the packets transmitted on a typical workgroup or department LAN are destined for stations on that LAN. Both bridges and routers can be used to segment LANs.

Bridges are the simpler, and often less expensive, type of device. Bridges filter packets between LANs by making a simple forward/don't forward decision on each packet they receive from any of the networks they are connected to. Filtering is done based on the destination address of the packet. If a packet's destination is a station on the same segment where it originated, it is not forwarded. If it is destined for a station on another LAN, it is connected to a different bridge port and forwarded to that port. Many bridges today filter and forward packets with very little delay, making them good for large traffic volumes.

Routers are more complex internetworking devices and are also typically more expensive than bridges. They use Network Layer Protocol Information within each packet to route it from one LAN to another. This means that a router must be able to recognize all of the different Network Layer Protocols that may be used on the networks it is linking together. This is where the term multiprotocol router comes from a device that can route using many different protocols. Routers communicate with each other and share information that allows them to determine the best route through a complex internetwork that links many LANs.

Switches are another type of device used to link several separate LANs and provide packet filtering between them. A LAN switch is a device with multiple ports, each of which can support a single end station or an entire Ethernet or Token Ring LAN. With a different LAN connected to each of the switch's ports, it can switch packets between LANs as needed. In effect, it acts like a very fast multiport bridge packets are filtered by the switch based on the destination address.

Switches are used to increase performance on an organization's network by segmenting large networks into many smaller, less congested LANs, while still providing necessary interconnectivity between them. Switches increase network performance by providing each port with dedicated bandwidth, without requiring users to change any existing equipment, such as NICs, hubs, wiring, or any routers or bridges that are currently in place. Switches can also support numerous transmissions simultaneously.

Deploying technology called dedicated LANs is another advantage of using switches. Each port on an Fast Ethernet switch supports a dedicated 100 Mbps Ethernet LAN. Usually, these LANs comprise multiple stations linked to a 100BASE-TX hub, but it is also possible to connect a single high-performance

 
 

station, such as a server, to a switch port (Fig.8).

Fig. 8. LAN Switch

Using LAN switches allows a network designer to create several small network segments. These smaller segments mean that fewer stations are competing for bandwidth, thereby diminishing network congestion.

In this case, that one station has an uncontested 100 Mbps Fast Ethernet LAN all to itself. Packets forwarded over it from other ports on the switch will never produce any collisions because there are no other stations on the LAN at that port.

As was noted earlier, LAN switching is a relatively new technology. Today's switching devices switch relatively large, variable-length LAN packets between different local area networks. ATM is another type of switching technology that switches small, fixed-length cells containing data. ATM networks can be run at much higher data rates than today's LANs. Eventually, they will be used to carry voice, video, and multimedia traffic, as well as computer-generated data over both short and long distances. ATM will be one of the dominant enterprise networking technologies of the future, and many companies are beginning to develop strategies to incorporate ATM in their existing LANs and LAN internet works.

 

3. POST-READING ASSIGNMENT

 

3.1. Match the terms and the definitions.

1. a bridge   2. a router   3. a switch   4. a packet   5. a network   6. a file server   7. a hub   8. a workstation   a. a computer that is configured with a network interface card, networking software, and the appropriate cables; b. a device that selects the best path to route a message, based on the destination address and origin; c. a very fast computer with a large amount of RAM and storage space, along with a fast network interface card; d. a system of interconnected computer systems, terminals, and other equipment allowing information to be exchanged; e. a device that provides a central connection point for cables from workstations, servers, and peripherals; f. a unit into which a larger piece of data is broken down for more efficient transmission; g. a device that allows you to segment a large network into two smaller, more efficient networks; h. a device for connecting computers in a network.

 

4. LANGUAGE IN USE

 

4.1. Find the modal verbs in the text and explain their meaning (See Grammar Reference 2).

4.2. Replace the modal verbs by the equivalents if it is possible.

4.3. Read each pair of sentences. If the sentence is a fact, put (F). If the sentence is only a possibility, put (P).

1 ’ They haven’t met this symbol.

’ They can’t have met this symbol.

2 ’ The computer is broken.

’ The computer must be broken.

3 ’ This computer system isn’t effective

’ This computer system can’t be effective.

4 ’ This digital computer is better then previous one.

’ This digital computer must be better than previous one.

5 ’ He might have lived there.

’ He lived there.

 

5. WRITING

Study the peculiarities of writing a text abstracting in Supplement 4 and prepare the abstracting of the text.

 

6. SPEAKING

Work in pairs and make up a dialogue on the topic –“What hardware devices are used in order to connect a computer to a network?” Use the table with the expressions below.

 

Oh, really! Never thought about it. You don’t say so! Indeed? Why? Is that so? I’m surprised. It’s amusing! It’s incredible! I can hardly believe my eyes! Would you believe it?! It must be… What a coincidence! Fancy that! You must be kidding! Right you are! Good job! Look.

 

 




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