Network+ Guide to Networks, 5th Edition
Chapter 7
WANs and Remote Connectivity
At a Glance
Instructor’s Manual Table of Contents

Overview

Objectives

Teaching Tips

Quick Quizzes

Class Discussion Topics

Additional Projects

Additional Resources

Key Terms
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Lecture Notes
Overview
A WAN is a network that connects two or more geographically distinct LANs. One might
assume that WANs are the same as LANs, only bigger. Although a WAN is based on the same
principles as a LAN, including reliance on the OSI model, its distance requirements affect its
entire infrastructure. As a result, WANs differ from LANs in nearly every respect.
This chapter discusses the technical differences between LANs and WANs and describes in
detail WAN transmission media and methods. It also notes the potential pitfalls in establishing
and maintaining WANs. In addition, it introduces the student to remote connectivity for LANs a technology that, in some cases, can be used to extend a LAN into a WAN. Remote connectivity
and WANs are significant concerns for organizations attempting to meet the needs of
telecommuting workers, global business partners, and Internet-based commerce.
Chapter Objectives
After reading this chapter and completing the exercises, the student will be able to:
 Identify a variety of uses for WANs
 Explain different WAN topologies, including their advantages and disadvantages
 Compare the characteristics of WAN technologies, including their switching type,
throughput, media, security, and reliability
 Describe several WAN transmission and connection methods, including PSTN, ISDN, Tcarriers, DSL, broadband cable, ATM, and SONET
 Describe multiple methods for remotely connecting to a network
Teaching Tips
WAN Essentials
1. Define and describe a WAN.
2. Point out that the Internet is the largest WAN in existence today.
3. Describe why any business or government institution with sites scattered over a wide
geographical area needs a WAN. Provide examples.
4. Discuss the fundamental properties WANs and LANs have in common.
5. Discuss the differences between WANs and LANs.
6. Define and explain the term NSPs (network service providers).
Network+ Guide to Networks, 5th Edition
7. Define the term, dedicated line and explain the advantages it provides.
8. Define and describe a WAN link.
9. Use Figure 7-1 to illustrates the difference between WAN and LAN connectivity.
Teaching Students may read a brief history report covering the largest WAN in existence
today (the Internet) at http://www.isoc.org/internet/history/brief.shtml.
Tip
WAN Topologies
1. Explain how WAN topologies differ from LAN topologies.
Bus
1. Define the bus WAN topology.
2. Describe the similarities and differences of WAN, and LAN bus topologies.
3. Note the type of WAN best suited for a bus WAN topology.
4. Use Figure 7-2 to illustrate a bus WAN topology.
Ring
1. Define the ring WAN topology.
2. Describe the similarities and differences of WAN, and LAN ring topologies.
3. Note the type of WAN best suited for a ring WAN topology.
4. Use Figure 7-3 to illustrate a ring WAN topology.
Star
1. Describe the star WAN topology.
2. Use Figure 7-4 to illustrate a ring WAN topology.
3. Describe the benefits of a star WAN topology.
4. Mention the one drawback of the star WAN topology.
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Mesh
1. Describe the mesh WAN topology.
2. Describe the benefits of a mesh WAN topology.
3. Emphasize and explain why mesh WANs are the most fault-tolerant type of WAN.
4. Use Figure 7-5 to illustrate a mesh WAN topology.
5. Define and describe a full-mesh WAN.
6. Mention one drawback of the full-mesh WAN topology.
7. Define and describe a partial-mesh WAN.
8. Use Figure 7-5 to illustrate a full-mesh WAN and a partial-mesh WAN.
Tiered
1. Define and describe a tiered topology WAN.
2. Use Figure 7-6 to illustrate a tiered WAN topology.
3. Explain how the flexibility of these types of WANs allows many variations.
4. Note how this flexibility also affects the creation of tiered WANs in terms of requiring
careful consideration of geography, usage patterns, and growth potential.
PSTN
1. Define and describe a PSTN.
2. Mention that the name POTS also refers to a PSTN.
3. Note how PSTNs originally carried data and compare it to today’s methods.
4. Explain why it is helpful to understand how the PSTN provided WAN connectivity when
the Internet first became popular in the 1990s.
5. Define dial-up connections and explain how their use in early PSTN and WAN access.
6. Explain why modems are usually necessary when computers connect to a public or
private data network via the PSTN.
7. Use Figure 7-7 to describe the main stages of dial-up Internet access.
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Point out to the students that as represented in Figure 7-7, the WAN to which
Teaching regional offices connect is represented as a cloud. On networking diagrams, packetswitched networks (including the Internet) are depicted as clouds, because of the
Tip
indeterminate nature of their traffic patterns.
8. Use Figure 7-8 to illustrate the local loop portion for dial-up WAN access.
9. Explain the purpose of the demarcation point.
10. Describe the advantages of using the PSTN for an Internet connection.
11. Describe the disadvantages of using the PSTN for an Internet connection.
X.25 and Frame Relay
1. Define and describe the ITU X.25 standard protocol.
2. Explain the advantage and disadvantage of having transmissions verified at every node.
3. Define and describe frame relay.
4. Compare X.25 and frame relay in terms of error checking, and throughput.
5. Describe a virtual circuit and its advantage.
6. Note that both X.25 and frame relay implement virtual networks.
7. Explain SVCs (switched virtual circuits).
8. Explain PVCs (permanent virtual circuits).
9. Note that both X.25 and frame relay implement SVCs and PVCs.
10. Describe how lease contracts work for X.25 and frame relay circuits.
11. Define the term CIR (committed information rate).
12. Describe how the lease works for a PVC circuit.
13. Discuss frame relay lease advantages.
14. Discuss frame relay and X.25 disadvantages.
15. Explain why frame relay and X.25 easily upgrade to T-carrier dedicated lines.
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16. Use Figure 7-9 to illustrate a WAN using frame relay.
Teaching Students may find more information on X.25 at
http://www.cisco.com/en/US/docs/internetworking/technology/handbook/X25.html.
Tip
Students may find more information on frame relay at
Teaching
http://www.cisco.com/en/US/docs/internetworking/technology/handbook/FrameTip
Relay.html.
ISDN
1. Briefly describe the history of ISDN.
2. Point out where ISDN protocols operate in the OSI model.
3. Describe the ISDN transmission medium.
4. Describe the two types of ISDN connections:
a. Dial-up
b. Dedicated
5. Define and explain the two types of ISDN channels on which connections are based:
a. B channels
b. D channels
6. Describe a BRI (Basic Rate Interface).
7. Define the term bonding.
8. Use Figure 7-10 to illustrate a BRI link.
9. Describe a PRI (Primary Rate Interface).
10. Compare and contrast PRI and BRI connections.
11. Describe how a NT2 (Network Termination 2) device is used.
12. Use Figure 7-11 to illustrate a PRI link.
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T-Carriers
1. Introduce T-carrier technology.
2. Point out where T-carrier protocols operate in the OSI model.
3. Explain how a T-carrier divides a single channel into multiple channels.
4. Describe the T-carrier transmission medium.
Types of T-Carriers
1. Use Table 7-1 to illustrate the various T-carrier circuit specifications.
2. Point out the most common T-carrier implementations.
3. Describe a T1 circuit’s operation and throughput.
4. Describe a T3 circuit’s operation and throughput.
5. Define the term signal level and its implications in T-carrier speed.
6. Describe common uses for T1 and T3 circuits.
7. Define a fraction T1 lease and its advantages.
T-Carrier Connectivity
1. Introduce characteristics of T-carrier connectivity hardware used at both the customer site
and the local telecommunications providers switching facility.
2. Mention that T-carrier lines require different media, depending on their throughput.
3. Describe the physical wiring component T1 technology uses.
4. Define and explain the functions of a smart jack.
5. Use Figure 7-12 to illustrate a T1 smart jack.
6. Define and explain the functions of CSUs (channel service units) and DSUs (data service
units).
7. Use Figure 7-13 to illustrate a stand-alone CSU/DSU.
8. Use Figure 7-14 to illustrate a typical use of smart jacks and CSU/DSUs with a point-topoint T1-connected WAN.
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9. Define and describe the use of terminal equipment on a typical T1-connected data
network.
a. Include a description of how terminal equipment such as a router or switch
interacts with CSU/DSU signals.
10. Use Figure 7-15 to illustrate how a router with an integrated CSU/DSU can be used to
connect a LAN with a T1 WAN link.
Quick Quiz 1
1. True or False: A WAN link is a connection between one WAN site and another site.
Answer: True
2. WANs that use the ____ topology are only practical for connecting fewer than four or
five locations.
a. tiered
b. ring
c. star
d. mesh
Answer: B
3. True or False: X.25 is quite suitable for time-sensitive applications, such as audio or
video.
Answer: False
4. True or False: PVCs are dedicated, individual links.
Answer: False
5. ISDN BRI (Basic Rate Interface) uses ____ B channels and one D channel.
a. zero
b. one
c. two
d. three
Answer: C
6. A ____ provides T-carrier digital signal termination.
a. DSU
b. CSU
c. smart jack
d. terminal adapter
Answer: B
DSL
1. Define and describe characteristics of a DSL (digital subscriber line).
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Types of DSL
1. Define the term xDSL.
2. Describe the better-known DSL varieties.
3. Note the two categories of DSL types can be divided into asymmetrical and symmetrical.
4. Explain the concepts of downstream and upstream data transmission.
5. Describe asymmetrical communications.
6. Describe symmetrical communications.
7. Describe how DSL versions differ in the type of modulation they use.
8. Describe how DSL versions differ in terms of their capacity and maximum line length.
9. Mention that DSL types vary according to how they use the PSTN.
10. Use Table 7-2 to compare current specifications for six DSL types.
DSL Connectivity
1. Explain how an ADSL connection flows from a home computer, through the local loop,
and to the telecommunications carriers switching facility.
2. Define the term DSL modem.
3. Use Figure 7-16 to illustrate a DSL modem.
4. Explain what a DSLAM (DSL access multiplexer) is and what it does.
5. Use Figure 7-17 to illustrate a DSL connection.
6. Mention the competition of DSL.
7. Review DSL installation costs.
8. Discuss the major drawback of DSL.
Students may find more information on DSL at
Teaching
http://support.gateway.com/s/tutorials/index/Tutorials.asp?cat=3&subcat=18&topic
Tip
=115&series=1415.
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Broadband Cable
1. Introduce broadband cable.
2. Describe the transmission media it uses.
3. Compare the theoretical transmission rates with the real transmission rates.
4. Discuss best use scenarios for broadband cable.
5. Define a cable modem and explain its purpose in broadband communication.
6. Use Figure 7-18 to illustrate a cable modem.
7. Describe the infrastructure required for broadband cable to operate.
8. Use Figure 7-19 to illustrate the infrastructure of a cable system.
9. Point out that broadband cable provides a dedicated, or continuous, connection that does
not require dialing up a service provider.
10. Describe the drawback of broadband cable that raises concerns about security and actual
throughput.
11. Mention that cable broadband access continues to service the majority of residential
customers, whereas DSL is more popular among business customers.
Teaching Students may find more information on cable modems at
http://www.iec.org/online/tutorials/cable_mod/index.asp.
Tip
Students may find more information on cable technologies at
Teaching
http://www.cisco.com/en/US/docs/internetworking/technology/handbook/Cable.htm
Tip
l.
ATM (Asynchronous Transfer Mode)
1. Point out where ATM protocols operate in the OSI model.
2. Describe the asynchronous communications method as it is referenced in ATM.
3. Point out that like Ethernet, ATM specifies Data Link layer framing techniques.
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4. Explain what sets ATM apart from Ethernet.
5. Explain that in ATM, a packet is called a cell and the cell always consists of 48 bytes of
data plus a 5-byte header.
6. Describe a drawback of a smaller packet size and explain how the draw back is overcome
by cell efficiency.
7. Explain how ATM relies on virtual circuits.
8. Explain how ATM guarantees specific QoS (quality of service).
9. Discuss how ATM’s developers have made certain ATM is compatible with other leading
network technologies.
10. Mention ATMs significant throughput potential.
11. Point out the cost disadvantage inherent with ATM.
Teaching Students may find a tutorial on ATM at
http://www.iec.org/online/tutorials/atm_fund/index.asp.
Tip
SONET (Synchronous Optical Network)
1. Describe the four key strengths of SONET.
2. Explain what is meant by synchronous in SOMET technology.
3. Explain the interoperability advantage of SONET.
4. Explain the fault tolerant advantage of SONET.
5. Use Figure 7-20 to illustrate a SONET ring.
6. Describe the SONET ring.
7. Use Figure 7-21 to illustrate the devices necessary to connect a WAN site with a SONET
ring.
8. Define the term OC (Optical Carrier) level and explain its relation in determining the data
rate of a particular SONET ring.
9. Use Table 7-3 to list the OC levels and their maximum throughput.
10. Explain the best use of SONET.
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Teaching Students may find a tutorial on SONET at
http://www.iec.org/online/tutorials/sonet/index.asp.
Tip
WAN Technologies Compared
1. Use Table 7-4 to summarize the media and throughputs offered by each technology
discussed so far.
Remote Connectivity
1. Define and explain the term remote access.
2. Point out that many remote access methods vary according to the type of transmission
technology, clients, hosts, and software they can or must use.
3. Introduce popular remote access techniques.
Dial-up Networking
1. Define the term dial-up networking.
2. Introduce the transmission methods dial-up clients may use.
3. Describe the advantages and disadvantages of dial-up networking.
4. Introduce the dial-up networking software that Microsoft provided with its Windows 95,
98, NT, and 2000 client operating systems.
5. Introduce the dial-up networking software that Microsoft provided with its Windows
2000 Server, XP, Vista, Server 2003, and Server 2008 operating systems.
Remote Access Servers
1. Describe the server requirements needed for a remote client to connect to a LAN or
WAN.
2. Discuss how many types of remote access servers exist.
a. Note that some devices are dedicated.
b. Note that some computers are installed with special software.
3. Describe the Microsoft remote access software.
4. Use Figure 7-22 to illustrates how clients connect with a remote access server to log on to
a LAN.
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Teaching Students may find more information on Microsoft RRAS in Windows server 2008 at
http://technet.microsoft.com/en-us/library/cc730711.aspx
Tip
Remote Access Protocols
1. Define and explain the SLIP and PPP remote access protocols.
2. Define and explain the PPPoE standard.
3. Use Figure 7-23 to illustrate how the protocols used in a remote access Internet
connection fit into the OSI model.
Remote Virtual Computing
1. Define and describe characteristics of remote virtual computing.
2. Explain the advantage of remote virtual computing.
3. Discuss how the many types of remote virtual computing software that exist differ
marginally in their capabilities, security mechanisms, and supported platforms.
4. Introduce three popular remote virtual computing programs.
5. Define and describe the remote desktop virtual computing software that comes with
Windows client and server operating systems.
a. Define the RDP Application protocol.
b. Review how to enable a Windows XP Professional computer as a Remote
Desktop host.
c. Use Figure 7-24 to illustrate the Remote tab in the System Properties dialog box.
d. Use Figure 7-25 to illustrate the Windows XP Remote Desktop Connection
window.
6. Define and describe the open source VNC (virtual network computing) system.
7. Define and describe the Citrix proprietary software known as an ICA (Independent
Computing Architecture) client.
(VPNs) Virtual Private Networks
1. Define and explain VPNs.
2. Note that the software required to establish VPNs is usually inexpensive.
3. Describe and explain the two important VPN design considerations: interoperability and
security.
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4. Define and explain the term tunneling.
5. Define and explain the term tunnel.
6. Explain the PPTP (Point-to-Point Tunneling Protocol).
7. Explain the L2TP (Layer 2 Tunneling Protocol).
Teaching Students may find a tutorial on VPNs at
http://www.cisco.com/en/US/docs/internetworking/technology/handbook/VPN.html
Tip
Quick Quiz 2
1. True or False: Broadband cable relies on the PSTN for transmission medium.
Answer: False
2. ____ communication occurs when the downstream throughput is higher than the
upstream throughput.
a. DSU
b. CSU
c. Symmetrical
d. Asymmetrical
Answer: D
3. ____ sets ATM apart from Ethernet.
a. Fixed packet size
b. Security
c. Wiring
d. Throughput
Answer: A
5. True or False: An advantage of SONET is its fault tolerance.
Answer: True
6. ____________________ refers to dialing directly into a private network’s or ISP’s
remote access server to log on to a network.
Answer: Dial-up networking
7. True or False: RRAS is Citrix’s remote access software.
Answer: False
8. True or False: Remote Desktop relies on SLIP.
Answer: False
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9. ____________________ is an open source system designed to allow one workstation to
remotely manipulate and receive screen updates from another workstation.
Answer:
VNC (virtual network computing
Virtual network computing
VNC
Class Discussion Topics
1. Take a class poll and see what kind of Internet access students have at home. Discuss the
availability of DSL in the area. Discuss the pros and cons of each access type to which
students have access.
2. Discuss the security implication of remote connectivity. What concerns are there? Are
they justified? Is the technology worth the security risks, if any?
Additional Projects
1. Have students compare cable broadband and DSL services in their residential areas. Each
student should write a report summarizing his or her findings.
2. Have students research a remote virtual computing software product not covered in this
lesson. Each student should write a report summarizing his or her findings.
Additional Resources
1. Fundamentals of Telecommunications sponsored by the International Engineering
Consortium
http://www.iec.org/online/tutorials/fund_telecom/index.asp
2. Resource page providing support for virtual private network (VPN) technologies in
Microsoft Windows
http://technet.microsoft.com/en-us/network/bb545442.aspx
3. DSL resource
http://www.dslreports.com/
4. Cisco Internetworking Technology Handbook
http://www.cisco.com/en/US/docs/internetworking/technology/handbook/ito_doc.html
5. Routing and Remote Access Service
http://technet.microsoft.com/en-us/library/cc754634.aspx
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Key Terms
 asymmetrical - The characteristic of a transmission technology that affords greater
bandwidth in one direction (either from the customer to the carrier, or vice versa) than in
the other direction.
 asymmetrical DSL - A variation of DSL that offers more throughput when data travels
downstream, downloading from a local carrier’s switching facility to the customer, than
when it travels upstream, uploading from the customer to the local carrier’s switching
facility.
 asynchronous - A transmission method in which data being transmitted and received by
nodes does not have to conform to any timing scheme. In asynchronous communications,
a node can transmit at any time and the destination node must accept the transmission as
it comes.
 Asynchronous Transfer Mode - See ATM.
 ATM (Asynchronous Transfer Mode) - A Data Link layer technology originally
conceived in the early 1980s at Bell Labs and standardized by the ITU in the mid-1990s.
ATM relies on fixed packets, called cells, that each consist of 48 bytes of data plus a 5byte header. ATM relies on virtual circuits and establishes a connection before sending
data. The reliable connection ensured by ATM allows network managers to specify QoS
levels for certain types of traffic.
 authentication - The process of comparing and matching a client’s credentials with the
credentials in the NOS user database to enable the client to log on to the network.
 B channel - In ISDN, the “bearer” channel, so named because it bears traffic from point
to point.
 Basic Rate Interface - See BRI.
 bonding - The process of combining more than one bearer channel of an ISDN line to
increase throughput. For example, BRI’s two 64-Kbps B channels are bonded to create an
effective throughput of 128 Kbps.
 BRI (Basic Rate Interface) - A variety of ISDN that uses two 64-Kbps bearer channels
and one 16-Kbps data channel, as summarized by the notation 2B+D. BRI is the most
common form of ISDN employed by home users.
 broadband cable - A method of connecting to the Internet over a cable network. In
broadband cable, computers are connected to a cable modem that modulates and
demodulates signals to and from the cable company’s head-end.
 bus topology WAN - A WAN in which each location is connected to no more than two
other locations in a serial fashion.
 cable drop - The fiber-optic or coaxial cable that connects a neighborhood cable node to
a customer’s house.
 cable modem - A device that modulates and demodulates signals for transmission and
reception via cable wiring.
 cable modem access - See broadband cable.
 cell - A packet of a fixed size. In ATM technology, a cell consists of 48 bytes of data plus
a 5-byte header.
 central office - See CO.
 channel service unit - See CSU.
 CIR (committed information rate) - The guaranteed minimum amount of bandwidth
selected when leasing a frame relay circuit. Frame relay costs are partially based on CIR.
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 CO (central office) - The location where a local or long-distance telephone service
provider terminates and interconnects customer lines.
 committed information rate - See CIR.
 credentials - A user’s unique identifying characteristics that enable him to authenticate
with a server and gain access to network resources. The most common type of credentials
are a user name and password.
 CSU (channel service unit) - A device used with T-carrier technology that provides
termination for the digital signal and ensures connection integrity through error
correction and line monitoring. Typically, a CSU is combined with a DSU in a single
device, a CSU/DSU.
 CSU/DSU - A combination of a CSU (channel service unit) and a DSU (data service
unit) that serves as the connection point for a T1 line at the customer’s site. Most modern
CSU/DSUs also contain a multiplexer. A CSU/DSU may be a separate device or an
expansion card in another device, such as a router.
 D channel - In ISDN, the “data” channel is used to carry information about the call, such
as session initiation and termination signals, caller identity, call forwarding, and
conference calling signals.
 data service unit – See DSU.
 dedicated - A continuously available link or service that is leased through another
carrier. Examples of dedicated lines include ADSL, T1, and T3.
 dial-up - A type of connection in which a user connects to a distant network from a
computer and stays connected for a finite period of time. Most of the time, the term dialup refers to a connection that uses a PSTN line.
 dial-up networking - The process of dialing into a remote access server to connect with
a network, be it private or public.
 digital subscriber line - See DSL.
 downstream - A term used to describe data traffic that flows from a carrier’s facility to
the customer. In asymmetrical communications, downstream throughput is usually much
higher than upstream throughput. In symmetrical communications, downstream and
upstream throughputs are equal.
 DS0 (digital signal, level 0) - The equivalent of one data or voice channel in T-carrier
technology, as defined by ANSI physical layer standards. All other signal levels are
multiples of DS0.
 DSL (digital subscriber line) - A dedicated WAN technology that uses advanced data
modulation techniques at the Physical layer to achieve extraordinary throughput over
regular phone lines. DSL comes in several different varieties, the most common of which
is asymmetric DSL (ADSL).
 DSL access multiplexer - See DSLAM.
 DSL modem - A device that demodulates an incoming DSL signal, extracting the
information and passing it to the data equipment (such as telephones and computers) and
modulates an outgoing DSL signal.
 DSLAM (DSL access multiplexer) - A connectivity device located at a
telecommunications carrier’s office that aggregates multiple DSL subscriber lines and
connects them to a larger carrier or to the Internet backbone.
 DSU (data service unit) - A device used in T-carrier technology that converts the digital
signal used by bridges, routers, and multiplexers into the digital signal used on cabling.
Typically, a DSU is combined with a CSU in a single device, a CSU/DSU.
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 E1 - A digital carrier standard used in Europe that offers 30 channels and a maximum of
2.048-Mbps throughput.
 E3 - A digital carrier standard used in Europe that offers 480 channels and a maximum of
34.368-Mbps throughput.
 fiber to the home - A carrier’s provision of fiber-optic connections to residential end
users for dramatically increased throughput and a better range of services.
 fractional T1 - An arrangement that allows a customer to lease only some of the
channels on a T1 line.
 frame relay - A digital, packet-switched WAN technology whose protocols operate at
the Data Link layer. The name is derived from the fact that data is separated into frames,
which are then relayed from one node to another without any verification or processing.
Frame relay offers throughputs between 64 Kbps and 45 Mbps. A frame relay customer
chooses the amount of bandwidth he requires and pays for only that amount.
 full-mesh WAN - A version of the mesh topology WAN in which every site is directly
connected to every other site. Full-mesh WANs are the most fault-tolerant type of WAN.
 head-end - A cable company’s central office, which connects cable wiring to many
nodes before it reaches customers’ sites.
 HFC (hybrid fiber-coax) - A link that consists of fiber cable connecting the cable
company’s offices to a node location near the customer and coaxial cable connecting the
node to the customer’s house. HFC upgrades to existing cable wiring are required before
current TV cable systems can provide Internet access.
 hybrid fiber-coax - See HFC.
 ICA (Independent Computing Architecture) client - The software from Citrix
Systems, Inc., that, when installed on a client, enables the client to connect with a host
computer and exchange keystrokes, mouse clicks, and screen updates. Citrix’s ICA client
can work with virtually any operating system or application.
 Integrated Services Digital Network - See ISDN.
 ISDN (Integrated Services Digital Network) - An international standard that uses
PSTN lines to carry digital signals. It specifies protocols at the Physical, Data Link, and
Transport layers of the OSI model. ISDN lines may carry voice and data signals
simultaneously. Two types of ISDN connections are used in North America: BRI (Basic
Rate Interface) and PRI (Primary Rate Interface). Both use a combination of bearer
channels (B channels) and data channels (D channels).
 J1 - A digital carrier standard used in Japan that offers 24 channels and 1.544-Mbps
throughput.
 J3 - A digital carrier standard used in Japan that offers 480 channels and 32.064-Mbps
throughput.
 L2TP (Layer 2 Tunneling Protocol) - A protocol that encapsulates PPP data, for use on
VPNs. L2TP is based on Cisco technology and is standardized by the IETF. It is
distinguished by its compatibility among different manufacturers’ equipment; its ability
to connect between clients, routers, and servers alike; and also by the fact that it can
connect nodes belonging to different Layer 3 networks.
 LAN Emulation - See LANE.
 LANE (LAN Emulation) - A method for transporting token ring or Ethernet frames over
ATM networks. LANE encapsulates incoming Ethernet or token ring frames, then
converts them into ATM cells for transmission over an ATM network.
 last mile - See local loop.
 Layer 2 Tunneling Protocol - See L2TP.
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 local loop - The part of a phone system that connects a customer site with a
telecommunications carrier’s switching facility.
 mesh topology WAN - A type of WAN in which several sites are directly
interconnected. Mesh WANs are highly fault tolerant because they provide multiple
routes for data to follow between any two points.
 network interface unit - See NIU.
 network service provider - See NSP.
 Network Termination 1 - See NT1.
 Network Termination 2 - See NT2.
 NIU (network interface unit) - The point at which PSTN-owned lines terminate at a
customer’s premises. The NIU is usually located at the demarc.
 NSP (network service provider) - A carrier that provides long-distance (and often
global) connectivity between major data-switching centers across the Internet. AT&T,
Verizon, and Sprint are all examples of network service providers in the United States.
Customers, including ISPs, can lease dedicated private or public Internet connections
from an NSP.
 NT1 (Network Termination 1) - A device used on ISDN networks that connects the
incoming twisted pair wiring with the customer’s ISDN terminal equipment.
 NT2 (Network Termination 2) - An additional connection device required on PRI to
handle the multiple ISDN lines between the customer’s network termination connection
and the local phone company’s wires.
 OC (Optical Carrier) - An internationally recognized rating that indicates throughput
rates for SONET connections.
 open source - The term that describes software that is developed and packaged by
individuals and made available to anyone, without licensing fees. Open source software is
not owned by any one company
 Optical Carrier - See OC.
 partial-mesh WAN - A version of a mesh topology WAN in which only critical sites are
directly interconnected and secondary sites are connected through star or ring topologies.
Partial mesh WANs are less expensive to implement than full mesh WANs.
 permanent virtual circuit - See PVC.
 plain old telephone service (POTS) - See PSTN.
 Point-to-Point Protocol - See PPP.
 Point-to-Point Protocol over Ethernet - See PPPoE.
 Point-to-Point Tunneling Protocol - See PPTP.
 POTS - See PSTN.
 PPP (Point-to-Point Protocol) - A communications protocol that enables a workstation
to connect to a server using a serial connection. PPP can support multiple Network layer
protocols and can use both asynchronous and synchronous communications. It performs
compression and error correction and requires little configuration on the client
workstation.
 PPPoE (Point-to-Point Protocol over Ethernet) - PPP running over an Ethernet
network.
 PPTP (Point-to-Point Tunneling Protocol) - A Layer 2 protocol developed by
Microsoft that encapsulates PPP data for transmission over VPN connections. PPTP
operates with Windows RRAS access services and can accept connections from multiple
different clients. It is simple, but less secure than other modern tunneling protocols.
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 PRI (Primary Rate Interface) - A type of ISDN that uses 23 bearer channels and one
64-Kbps data channel, represented by the notation 23B+D. PRI is less commonly used by
individual subscribers than BRI, but it may be used by businesses and other organizations
needing more throughput.
 PSTN (Public Switched Telephone Network) - The network of lines and carrier
equipment that provides telephone service to most homes and businesses. Now, except
for the local loop, nearly all of the PSTN uses digital transmission. Its traffic is carried by
fiber-optic or copper twisted pair cable, microwave, and satellite connections.
 Public Switched Telephone Network - See PSTN.
 PVC (permanent virtual circuit) - A point-to-point connection over which data may
follow any number of different paths, as opposed to a dedicated line that follows a
predefined path. X.25, frame relay, and some forms of ATM use PVCs.
 RAS (Remote Access Service) - The dial-up networking software provided with
Microsoft Windows 95, 98, NT, and 2000 client operating systems. RAS requires
software installed on both the client and server, a server configured to accept incoming
clients, and a client with sufficient privileges (including user name and password) on the
server to access its resources. In more recent versions of Windows, RAS has been
incorporated into the RRAS (Routing and Remote Access Service).
 RDP (Remote Desktop Protocol) - An Application layer protocol that uses TCP/IP to
transmit graphics and text quickly over a remote client–host connection. RDP also carries
session, licensing, and encryption information.
 remote access - A method for connecting and logging on to a LAN from a workstation
that is remote, or not physically connected, to the LAN.
 Remote Access Service - See RAS.
 Remote Desktop - A feature of Windows operating systems that allows a computer to act
as a remote host and be controlled from a client running another Windows operating
system.
 Remote Desktop Protocol - See RDP.
 ring topology WAN - A type of WAN in which each site is connected to two other sites
so that the entire WAN forms a ring pattern.
 Routing and Remote Access Service (RRAS) - The software included with Windows
2000 Server, XP, Vista, Server 2003, and Server 2008 operating systems that enables a
server to act as a router, firewall, and remote access server. Using RRAS, a server can
provide network access to multiple remote clients.
 RRAS - See Routing and Remote Access Service.
 SDH (Synchronous Digital Hierarchy) - The international equivalent of SONET.
 self-healing - A characteristic of dual-ring topologies that allows them to automatically
reroute traffic along the backup ring if the primary ring becomes severed.
 Serial Line Internet Protocol - See SLIP.
 signal level - An ANSI standard for T-carrier technology that refers to its Physical layer
electrical signaling characteristics. DS0 is the equivalent of one data or voice channel. All
other signal levels are multiples of DS0.
 SLIP (Serial Line Internet Protocol) - A communications protocol that enables a
workstation to connect to a server using a serial connection. SLIP can support only
asynchronous communications and IP traffic and requires some configuration on the
client workstation. SLIP has been made obsolete by PPP.
 smart jack - A termination for T-carrier wire pairs that is located at the customer demark
and which functions as a connection protection and monitoring point.
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 SONET (Synchronous Optical Network) - A high-bandwidth WAN signaling
technique that specifies framing and multiplexing techniques at the Physical layer of the
OSI model. It can integrate many other WAN technologies (for example, T-carriers,
ISDN, and ATM technology) and allows for simple link additions and removals.
SONET’s topology includes a double ring of fiber-optic cable, which results in very high
fault tolerance.
 star topology WAN - A type of WAN in which a single site acts as the central
connection point for several other points. This arrangement provides separate routes for
data between any two sites; however, if the central connection point fails, the entire
WAN fails.
 SVC (switched virtual circuit) - A logical, point-to-point connection that relies on
switches to determine the optimal path between sender and receiver. ATM technology
uses SVCs.
 switched virtual circuit - See SVC.
 symmetrical - A characteristic of transmission technology that provides equal throughput
for data traveling both upstream and downstream and is suited to users who both upload
and download significant amounts of data.
 symmetrical DSL - A variation of DSL that provides equal throughput both upstream
and downstream between the customer and the carrier.
 synchronous - A transmission method in which data being transmitted and received by
nodes must conform to a timing scheme.
 Synchronous Digital Hierarchy - See SDH.
 Synchronous Optical Network - See SONET.
 T1 - A digital carrier standard used in North America and most of Asia that provides
1.544-Mbps throughput and 24 channels for voice, data, video, or audio signals. T1s rely
on time division multiplexing and may use shielded or unshielded twisted pair, coaxial
cable, fiber optics, or microwave links.
 T3 - A digital carrier standard used in North America and most of Asia that can carry the
equivalent of 672 channels for voice, data, video, or audio, with a maximum data
throughput of 44.736 Mbps (typically rounded up to 45 Mbps for purposes of discussion).
T3s rely on time division multiplexing and require either fiber-optic or microwave
transmission media.
 T-carrier - The term for any kind of leased line that follows the standards for T1s,
fractional T1s, T1Cs, T2s, T3s, or T4s.
 TA (terminal adapter) - A device used to convert digital signals into analog signals for
use with ISDN phones and other analog devices. TAs are sometimes called ISDN
modems.
 TE (terminal equipment) - The end nodes (such as computers and printers) served by
the same connection (such as an ISDN, DSL, or T1 link).
 terminal adapter - See TA.
 terminal equipment - See TE.
 thin client - A client that relies on another host for the majority of processing and hard
disk resources necessary to run applications and share files over the network.
 tiered topology WAN - A type of WAN in which sites that are connected in star or ring
formations are interconnected at different levels, with the interconnection points being
organized into layers to form hierarchical groupings.
 tunnel - A secured, virtual connection between two nodes on a VPN.
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 tunneling - The process of encapsulating one type of protocol in another. Tunneling is
the way in which higher-layer data is transported over VPNs by Layer 2 protocols.
 upstream - A term used to describe data traffic that flows from a customer’s site to a
carrier’s facility. In asymmetrical communications, upstream throughput is usually much
lower than downstream throughput. In symmetrical communications, upstream and
downstream throughputs are equal.
 virtual circuit - A connection between network nodes that, although based on potentially
disparate physical links, logically appears to be a direct, dedicated link between those
nodes.
 virtual network computing - See VNC.
 VNC (virtual network computing) - An open source system that enables a remote client
(or viewer) workstation to manipulate and receive screen updates from a host. Examples
of VNC software include RealVNC, TightVNC, and UltraVNC.
 virtual private network - See VPN.
 VPN (virtual private network) - A logically constructed WAN that uses existing public
transmission systems. VPNs can be created through the use of software or combined
software and hardware solutions. This type of network allows an organization to carve
out a private WAN through the Internet, serving only its offices, while keeping the data
secure and isolated from other (public) traffic.
 WAN link - A point-to-point connection between two nodes on a WAN.
 X.25 - An analog, packet-switched WAN technology optimized for reliable, longdistance data transmission and standardized by the ITU in the mid-1970s. The X.25
standard specifies protocols at the Physical, Data Link, and Network layers of the OSI
model. It provides excellent flow control and ensures data reliability over long distances
by verifying the transmission at every node. X.25 can support a maximum of only 2Mbps throughput.
 xDSL - The term used to refer to all varieties of DSL.