Lesson 5

The Reading Module

Read the text: Telecommunications. Part V

Local area networks

Despite the growth of the Internet, the characteristics of local area networks (computer networks that run at most a few kilometres) remain distinct. This is because networks on this scale do not require all the features associated with larger networks and are often more cost-effective and efficient without them.

In the mid-1980s, several protocol suites emerged to fill the gap between the data link and applications layer of the OSI reference model. These were Appletalk, IPX and NetBIOS with the dominant protocol suite during the early 1990s being IPX due to its popularity with MS-DOS users. TCP/IP existed at this point but was typically only used by large government and research facilities. As the Internet grew in popularity and a larger percentage of traffic became Internet-related, local area networks gradually moved towards TCP/IP and today networks mostly dedicated to TCP/IP traffic are common. The move to TCP/IP was helped by technologies such as DHCP that allowed TCP/IP clients to discover their own network address — a functionality that came standard with the AppleTalk/IPX/NetBIOS protocol suites.

It is at the data link layer though that most modern local area networks diverge from the Internet. Whereas Asynchronous Transfer Mode (ATM) or Multiprotocol Label Switching (MPLS) are typical data link protocols for larger networks, Ethernet and Token Ring are typical data link protocols for local area networks. These protocols differ from the former protocols in that they are simpler (e.g. they omit features such as Quality of Service guarantees) and offer collision prevention. Both of these differences allow for more economic set-ups.

Despite the modest popularity of Token Ring in the 80's and 90's, virtually all local area networks now use wired or wireless Ethernet. At the physical layer, most wired Ethernet implementations use copper twisted-pair cables (including the common 10BASE-T networks). However, some early implementations used coaxial cables and some recent implementations (especially high-speed ones) use optic fibres. Optic fibres are also likely to feature prominently in the forthcoming 10-gigabit Ethernet implementations. Where optic fibre is used, the distinction must be made between multi-mode fibre and single-mode fibre. Multi-mode fibre can be thought of as thicker optical fibre that is cheaper to manufacture but that suffers from less usable bandwidth and greater attenuation (i.e. poor long-distance performance).

I. Reading exercises:

Exercise1. Read and memorize using the dictionary:

gap, data link, OSI reference model, network address, protocol suite, Token Ring, wired and wireless Ethernet, copper twisted-pair cable, coaxial cable, optic fibre, 10-gigabit Ethernet, multi-mode fibre, single-mode fibre, attenuation

Exercise 2. Answer the questions:

1. Why do the characteristics of local area networks remain distinct?

2. What are typical data link protocols for larger networks?

3. What types of cable are used for Ethernet implementation?

4. What did several protocol suites emerge for?

Exercise 3. Match the left part with the right:

1. Some early implementations	1. though that most modern local area networks diverge from the Internet.
2. It is at the data link layer	2. local area networks moved towards TCP/IP.
3. As the Internet grew in popularity	3. to feature in the forth-coming 10-gigabit Ethernet.
4. Optic fibres are likely	4. used coaxial cables.

Exercise 4. Open brackets using the right words:

Despite the growth of the (electrical network/Internet), the characteristics of (local/worldwide) area networks (computer networks that run at most (a few/a lot of) kilometres) remain distinct. This is because networks on this scale do not (exclude/require) all the features associated with larger networks and are often more cost-effective and efficient (without/with) them.

The Speaking Module

II. Speaking exercises:

Exercise 1. Describe OSI reference model; collision prevention; multi-mode fibre; local area network; data link layer using the suggested words and expressions as in the example:

OSI reference model mid-1980s; emerged, the data link; dominant protocol suite; its popularity example: In the mid-1980s, several protocol suites emerged to fill the gap between the data link and applications layer of the OSI reference model. These were Appletalk, IPX and NetBIOS with the dominant protocol suite during the early 1990s being IPX due to its popularity with MS-DOS users.

collision prevention differ from; simpler; omit features; offer

multi-mode fibre optic fibres; to feature; 10-gigabit Ethernet implementations; distinction

local area network characteristics; run; distinct; on this scale; features; cost-effective

data link layer diverge; the Internet; typical data link protocol; larger network

Exercise 2. Ask questions to the given answers:

1. Question: ____________________________________ ?

Answer: Local area networks gradually moved towards TCP/IP.

2. Question: ____________________________________ ?

Answer: Both of the differences in protocols allow for more economic set-ups.

3. Question: ____________________________________ ?

Answer: Multi-mode fibre suffers from less usable bandwidth and greater attenuation.

The Writing Module

III. Writing exercises:

Exercise 1. Complete the sentences with the suggested words: suites; TCP/IP; address; standard; allowed

The move to ______ was helped by technologies such as DHCP that ______ TCP/IP clients to discover their own network ______ — a functionality that came ______ with the AppleTalk/IPX/NetBIOS protocol ______ .

Exercise 2. Fill in the table with words and expressions from the text:

	Fibre	Protocol	Cost
example: The distinction must be made between	multi-mode fibre and single-mode fibre.
All local area networks now use
Thicker optical fibre is
Computer networks that run at a few kilometers are

Exercise 3. Compose a story on one of the topics (up to 40 words):

“Protocols used for local area networks”

“Modern channel for information transmission”

“Differences between local area network and larger network protocols”