WANs and Remote Connectivity

enginestagNetworking and Communications

Oct 26, 2013 (3 years and 7 months ago)

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Network+ Guide to Networks, 5
th

Edition


7
-
1





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


Network+ Guide to Networks, 5
th

Edition


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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 pi
tfalls 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 organi
zations 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 connect
ion methods, including PSTN, ISDN, T
-
carriers, 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 i
n existence today.


3.

Describe
why any business or government institution with sites scattered over a wide
geographical area need
s

a WAN
. P
rovide examples.


4.

Discuss the fundamental properties WANs and LANs have in common.


5.

Discuss the differences between WAN
s and LANs.


6.

Define and explain the term NSPs (network service providers).


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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

connectiv
ity.


Teaching

Tip



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
.




WAN Topolog
ies


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 illustrat
e a
b
us WAN topology.


Ring


1.

Define the
ring

W
AN 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.

Desc
ribe 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 t
opology.


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.

M
ention

one drawback of the
full
-
mesh WAN

topology.


7.

Define and describe a part
ial
-
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 var
iation
s
.


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 PS
TN.


3.

N
ote 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 connection
s

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 d
escribe the main stages of dial
-
up Internet access
.


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th

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Teaching

Tip


Point out to
the students that as represented in Figure 7
-
7, the WAN to which
regional offices connect is represented as a cloud. On networking diagrams, packet
-
switched networks (including the Internet) are depicted as clouds, because of the
indeterminate nature of th
eir 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 fra
me 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.

No
te that both X.25 and frame relay implement SVCs and PVCs.


10.

Describe how

lease contract
s work

for X.25 and frame relay circuit
s
.


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

Tip



Students may find more information
on X.25 at
http://www.cisco.com/en/US/docs/internetworking/technology/handbook/X25.html
.



Teaching

Tip



Students may find more information on
frame relay at
http://www.cisco.com/en/US/docs/internetworking/technology/handbook/Frame
-
Relay.html
.




ISDN


1.

Briefly describe the history of ISDN.


2.

Point out where ISDN protocols o
perate in the OSI model.


3.

Describe the ISDN transmission medium.


4.

Describe th
e two types of ISDN connections:

a.

Dial
-
up

b.

Dedicated


5.

Define and explain the two types of
ISDN
channel
s 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 i
llustrate 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.


Type
s 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 t
he 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 lo
cal telecommunications provider
s 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 funct
ions 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 ty
pical use of smart jacks and CSU/DSUs with a point
-
to
-
point 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 wi
th 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
F
alse: 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
F
alse: X.25 is quite suitable for time
-
sensitive applications, such as audio or
video.

Answer: False


4.

True or
F
alse:

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.

s
mart jack

d.

t
erminal adapter

Answer:

B



DSL


1.

Define and describe
characteristics of a DSL (digital subscriber line).

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th

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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 the
ir 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 carrier
s 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 conn
ection.


6.

Mention the competition of DSL
.


7.

Review DSL installation costs.


8.

Discuss the major drawback of DSL.


Teaching

Tip



Students may find more information on
DSL at
http://support.gateway.com/s/tutorials/index/Tutorials.asp?cat=3&subcat=18&topic
=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 r
ates 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 broadb
and 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 broadb
and cable that raise
s

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

Tip



Students may find m
ore information on
c
able
m
odems at
http://www.iec.org/online/tutorials/cable_mod/index.asp
.



Teaching

Tip



Students may find more information on
cable te
chnologies at
http://www.cisco.com/en/US/docs/internetworking/technology/handbook/Cable.htm
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
specifi
c 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

Tip



Stud
ents may find a tutorial on ATM at
http://www.iec.org/online/tutorials/atm_fund/index.asp
.




SONET (Synchronous Optical Network)


1.

Describe the four key strengths of SONET.


2.

Explain w
hat 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 dev
ices 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.

Explai
n the best use of SONET.

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Teaching

Tip



Students may find a tutorial on SONET at
http://www.iec.org/online/tutorials/sonet/index.asp
.




WAN Technologies Compared


1.

Use Table 7
-
4 to summ
arize 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 net
working.


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 2
003, 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

Tip



Students may find
more information on
Mi
crosoft
RRAS in Windows server 2008 at
http://technet.microsoft.com/en
-
us/library/cc730711.aspx




Remote Access Protocols


1.

Define and explain the SLIP and PPP remote access protoco
ls.


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.

Ex
plain 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 comp
uting 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 ho
w

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 expl
ain the two important VPN design considerations:

i
nteroperability 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

Tip



Students may find a tutorial on
VPNs at
http://www.cisco.com/en/US/docs/internetworking/technology/handbook/VPN.html




Quick Quiz 2


1.

True or

False:
Broadband cable relies on the PSTN for transmission medium.

Answer: False


2.

____ c
ommunication 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 Ether
net
.

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
r
emotely 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 t
he
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 ris
ks, 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
student
s
research
a
remote virtual computing software
product
no
t 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.



asynch
ronous

-

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 5
-
byte 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.



authe
ntication

-

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 R
ate 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 locat
ions 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 mode
m 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.



commit
ted 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 ser
vice 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 servic
e 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

compute
r and stays connected for a finite period of time. Most of the time, the term dial
-
up

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 inco
ming DSL signal, extracting the
information

and passing it to the data equipment (such as telephones and computers) and
modulates an

outgoing DSL sig
nal.



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 i
n 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 t
o 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 who
se 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
-
tol
erant 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 loc
ation 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 A
rchitecture) 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 op
erating 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
Tran
sport 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 ch
annels) 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 Tunnel
ing 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 cli
ents, 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 encap
sulates 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 point
s.



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 usu
ally 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 provi
ders 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 IS
DN 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 inte
rnationally 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 les
s 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 com
munications. 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, N
T, 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 reso
urces.

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 clien
t

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
serve
r 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 te
chnology 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 techniqu
es 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 simp
le link additions and removals.
SONET’s topology includes

a double ring of fiber
-
optic cable, whi
ch 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 centr
al 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

-

S
ee

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 Hierarch
y

-

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 multiplexin
g 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 t
hat 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 (ter
minal 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 intercon
nection 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
-
lay
er 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 thro
ughput. 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 betwe
en 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 solut
ions. 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, long
-
distance 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
m
odel. 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 2
-
Mbps throughput.



xDSL

-

The term used to refer to all varieties of DSL.