section 8.1 explain the role of carriers in wan transmissions compare and contrast dun and vpn...

Section 8.1• Explain the role of carriers in WAN transmissions• Compare and contrast DUN and VPN connections• Explain the benefits of circuit switching• Describe how message switching works• Describe packet switching

Section 8.2• Describe how networks transmit data using the X.25 protocol• Explain how frame relay transmits data• Describe how ATM works• Identify the uses of B-ISDN

Section 8.3• Show how FDDI transmits data• Describe how SONET transmits data• Explain the benefits of SMDS

pp. 224-2308.1

Main Ideas

Circuit-switched networks use a direct, physical connection to transmit data back and forth. Message-switched networks send entire transmissions between intermediaries. Packet-switched networks route packets through virtual circuits.

Key Terms

carrier services

remote access

dial-up networking (DUN)

Virtual Private Network (VPN)

circuit-switched network

message switching

packet switching

Packet Switching Exchange (PSE)

Guide to Reading

How a WAN Works

pp. 224-2308.1

After a network grows beyond the confines of the LAN, a carrier service is required.

Carriers provide a variety of services which are connected through remote access.

carrier services Data transfer services provided by telecommunications companies, such as AT&T, Sprint, or Verizon. (p. 224)

remote access A direct connection to a network using regular dial-up lines. After the connection is made, the user can work on the network as if in the office. (p. 224)

Carriers

How a WAN Works

pp. 224-2308.1

Remote access connections are established through either a dial-up network (DUN) or virtual private network (VPN).

The advantages of a VPN are that users benefit from faster network connections, privacy, and security.

dial-up networking (DUN) A client service using regular telephone lines to connect to a network. (p. 224)

Virtual Private Network (VPN) An alternative to using a dial-up network connection. Is a network connection between two computers. With a VPN, a remote user can securely access the internal network from a remote location. (p. 226)

Carriers

How a WAN Works

pp. 224-2308.1

Data in the WAN is transported through various technologies:

• Circuit switching• Message switching

circuit-switched network A network that creates a direct physical connection between the sender and receiver.(p. 228)

message switching A technology used to route an entire message from one system to another. That message is routed through intermediate (go-between) station and does not involve a direct physical connection between the sender and receiver. (p. 228)

Switching Technologies

How a WAN Works

pp. 224-2308.1


Message switching sends the entire message to intermediary stations that decide which route to use.

How a WAN Works

pp. 224-2308.1

Packet switching is commonly found in LANs.

Packets are routed through Packet Switching Exchanges until they reach their destination.

packet switching A transmission method in which all transmissions are broken into small units and sent over the network. Packets are reassembled at the destination computer. (p. 229)

Packet Switching Exchange (PSE) Go-betweens in the packet switching process. The PSE inspects the packet’s destination address, consults a routing table, and forwards the packet at the highest possible speed. (p. 229)


How a WAN Works

pp. 224-2308.1


Packet-switching networks send packets along the best route available.

How a WAN Works

pp. 224-2308.1

You Try It

• Activity 8A – Setting Up a DUN Connection (p. 225)• Activity 8B – Setting Up a VPN Connection (p. 226)• Activity 8C – Tracing Packets (p. 229)

How a WAN Works

pp. 232-2368.2

Main Ideas

X.25 is a packet-switching protocol originally designed for analog telephone lines. Frame relay uses permanent, virtual circuits and reliable, digital lines to transmit data. ATM transmits data, voice, and video over many types of lines.

Key Terms

X.25Data Terminal Equipment (DTE)packet assembler/ disassembler (PAD)Data Circuit-terminating Equipment (DCE)frame relayAsynchronous Transfer Mode (ATM)cell relaybroadband ISDN (B-ISDN)

Guide to Reading

Sending Data across a WAN

pp. 232-2368.2

Computers on an X.25 network can receive and transmit data at the same time. This is also called full-duplex communication.

X.25 A connection-oriented, packet-switching protocol designed for use on analog telephone lines. Computers on an X.25 network can receive and transmit data at the same time. (p. 232)

X.25 Packet-Switching Protocol


pp. 232-2368.2

The X.52 protocol concentrates on the interface through which transmission flows. The interface is made up of the following devices:

• Data Terminal Equipment (DTE)• Packet assembler/dissembler (PAD)

Data Terminal Equipment (DTE) X.25 device terminology. There are no computers, hosts, or nodes. Instead, sending and receiving computers are referred to simply as this. (p. 232)

packet assembler/disassembler (PAD) A device in X.25 transmissions that prepares packets for transmission and disassembles the packets that come in. (p. 232)



pp. 232-2368.2

• Data Circuit-terminating Equipment (DCE)

• Packet switching exchanges (PSEs)

Data Circuit-Terminating Equipment (DCE) Packets are sent here from the DTE or PAD. A DCE might be a modem or packet switch. A DCE is located at each end of the connection. (p. 232)



pp. 232-2368.2

Frame relay is faster than the X.52 protocol. Frame relay networks connecting LANs to a WAN rely on routers and switching equipment.

frame relay A newer form of packet switching that relies on digital technologies, such as fiber optic and ISDN. (p. 233)

Frame Relay


pp. 232-2368.2

Another type of switching technology is Asynchronous Transfer Mode (ATM).

Like a frame relay, ATM is designed to take advantage of digital media.

Asynchronous Transfer Mode (ATM) A connection-oriented networking technology. Like frame relay, ATM is designed to take advantage of digital media. (p. 234)

ATM


pp. 232-2368.2

ATM is useful for high-speed LAN and WAN networking over a range of media types and relies on cell relay.

ATM transmits data in 53-byte cells.

cell relay Used with ATM transmissions, a high-speed transmission method based on fixed-size units that are known as cells. (p. 235)

ATM


pp. 232-2368.2

ATM

ATM takes incoming data and packages the contents in uniform, 53-byte cells. At the receiving end, ATM sends it cells out onto a WAN in a steady stream for delivery.


pp. 232-2368.2

ATM was created for broadband ISDN (B-ISDN) and B-ISDN services are divided into two categories:

• Interactive services

• Distributed services

broadband ISDN (B-ISDN) The next generation of ISDN that is capable of delivering high quantities of data. (p. 236)

B-ISDN


pp. 238-2448.3

Main Ideas

FDDI transmits data over fiber optic cabling using a ring topology. SONET multiplexes incoming signals for transmission over very-high-speed optical cabling. SMDS transmits data in any format between networks.

Key Terms

Synchronous Optical NETwork (SONET)

Synchronous Digital Hierarchy (SDH)

optical carrier (OC)

Synchronous Transport Signal (STS)

Switched Multimegabit Data Services (SMDS)

Guide to Reading

Developing Technologies

pp. 238-2448.3

FDDI

FDDI was developed based on ring topology and token passing. It uses fiber optic as its medium of transmission.

FDDI was developed for two primary reasons. First, it was designed to support and extend the capabilities of older LANs, such as Ethernet and Token Ring. Second, it provides a reliable infrastructure for businesses moving

mission-critical applications to networks.


pp. 238-2448.3

FDDI

Although FDDI was developed specifically for use with fiber optic cable, it can operate on a variety of cable types.

• Multimode fiber optic cable

• Single-mode fiber optic cable

• Category 5 Unshielded Twisted Pair copper wiring

• IBM Type 1 Shielded Twisted Pair copper wiring


pp. 238-2448.3

FDDI topology is similar to Token Ring, except that it operates using optical transmissions.

Another important distinction is that FDDI is characterized by two counter-rotating rings (known as a dual-ring topology). An FDDI topology by itself usually does not make use of hubs.

FDDI


pp. 238-2448.3

FDDI

FDDI networks are limited to rings no longer than 100 kilometers apiece. They are also limited to no more than 500 nodes per ring.

FDDI is a high-speed, high-bandwidth network based on optical transmissions. It is most often used as a network backbone for connecting high-end computers.


pp. 238-2448.3

Synchronous Optical NETwork (SONET) is transmitted over the fiber optic cables that are used by long-distance carriers.

The European standard is Synchronous Digital Hierarchy (SDH).

Synchronous Optical NETwork (SONET) An American National Standards Institute (ANSI) standard for the transmission of different types of digital information using optical media—data, voice, and video. (p. 240)

Synchronous Digital Hierarchy (SDH) A European standard for the transmission of different types of digital information using optical media—data, voice, and video. (p. 240)

SONET


pp. 238-2448.3

SONET

SONET multiplexes many incoming signals for high-speed transport.


pp. 238-2448.3

Two signal definitions lie at the heart of the SONET standard regarding multiplexing capability:

• Optical carrier (OC)• Synchronous Transport Signals (STSs)

optical carrier (OC) A signal definition in the SONET standard used by fiber optic media and translated roughly to speed and carrying capacity. (p. 241)

Synchronous Transport Signal (STS) The electrical equivalents of OC levels and are used by nonfiber media. See also optical carrier. (p. 241)

SONET


pp. 238-2448.3

SONET

SONET converts electrical (STS) signals to optical (OC) levels for transport. It also “unconverts” them (OC to STS) at the point in which the transmissions leave the SONET media. SONET frames are sent continuously – whether they contain data or not.


pp. 238-2448.3

Switched Multimegabit Data Services (SMDS) is a means for businesses to connect to LANs in separate locations.

It is a less expensive alternative to dedicated leased lines. SMDS is a connectionless, packet-switched technology well-suited to the type of “bursty” traffic characteristic of LAN (or LAN-to-LAN) communications.

Switched Multimegabit Data Services (SMDS) A broadband public networking service offered by communications carriers. (p. 243)

SMDS


pp. 238-2448.3

SMDS

SMDS is a connectionless service that provides WAN transmissions on an as-needed basis.


Resources

For more resources on this chapter, go to the Introduction to Networks and Networking Web site at http://networking.glencoe.com.

Chapter 8

section 8.1 explain the role of carriers in wan transmissions compare and contrast dun and vpn...

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