CompTIA Network+ Certification Study Guide part 38 ppt

This speed is derived from 24 individual channels of 64 Kbps only 23 are available for data transfer and network use.. ISDN supports data transfer rates of 64,000 bits per second 64 Kbps

ChApTEr 7: TCP/IP and Routing

356

14 You have a main corporate location and several branch locations

All locations access the Internet through their own dedicated con-nections What type of routing would you enable for this approach?

A None

B Dynamic

C Static

D Classless

15 You have been asked to set up a routed network within your

com-pany Your company routers are homogenous having standardized

on Cisco You want to set up the best routing solution within your company for this equipment What routing protocol would you use?

A RIP

B OSPF

C IS-IS

D EIGRP

16 You have a DHCP server that is configured to have only 10 addresses

available in the pool of addresses to be handed out When a colleague tries to lease an IP address, he is unable to do so In viewing the log, you see the following packets relating to his attempt to get an address DHCPDiscover, DHCPOffer, DHCPRequest, DHCPNack What might be the potential cause of the issue?

A The DHCP server is not running

B The DHCP server handed out an IP address to your colleague

C The DHCP server was unable to hand out an IP address to his system

D The DHCP server is really a BootP server

SElF TEST quICK ANSwEr KEy

A

1

D

2

C

3

D

4

A and D

5

D

6

B

7

A

8

B

9

C

10

B

11

C

12

C

13

B

14

D

15

C

16

ExAM oBJECTIvES IN ThIS ChApTEr

INTroduCTIoN

In this chapter, we categorize wide area network (WAN) technology types

and properties that you will see not only on the CompTIA Network+ (2009

edition) exam objectives but also in a large production environment Most

of these technologies and protocols are used often and you will need to

know about them for the Network+ exam Be familiar with the speeds,

capacities, and the types of media used for each WAN technology covered

In this chapter, we discuss the specifics of several WAN protocols, including

Frame Relay, E1/T1, digital subscriber line (DSL), cable modem, wireless,

and satellite

After reading this chapter, you will also understand the basic

charac-teristics of specific WAN technologies, such as how packet switching and

circuit switching differ

what is a wAN?

A WAN is a computer network covering a wide geographical area,

includ-ing more than one remote location and typically a core network where all

resources are kept A WAN is common to any company doing business with

remote sites that are connected via a network topology The remote sites

build on the core site and a WAN is born Chapter 1 discussed the basics

of WANs, and in this chapter, we discuss in a little deeper into how WANs

wide Area Networking

358 ChApTEr 8: Wide Area Networking

operate and which types are the most commonly used WANs may be created

in different configurations, with the most common being some combination

of public and private networks When working within the realm of a public network, you are working with networks that are publicly accessed and most likely connected to the Internet Internet Protocol Security (IPSec) and vir-tual private network (VPN) technologies allow you to build a WAN over the Internet When working in the realm of private networks, you are working with networks that are accessed only by designated individuals This means that you are most likely running a private access network using Frame Relay

or Multiprotocol Label Switching (MPLS), or a similar technology, and not allowing access to anybody except the company paying for it This means that the network users aren’t at the mercy of the public Internet, where you

do not get a guarantee of delivery

SwITChING METhodS

When working with WANs, the operations you do are transparent to you,

so you may be unaware of the underlying technology that gets data from one location to another There are a number of methods by which data are processed through the network to get from point A to point B WANs oper-ate within two types of switching methods: circuit switching and packet switching

Although almost all WAN protocols in use today are packet-switched, there are still some old networks out there using circuit-switching technol-ogies Technologies such as X.25 and Frame Relay are always available – their connections are constant, so they do not have to be set up every time they are used Packet-switching technologies are always available but circuit switching is not Circuit switching requires a separate setup for each con-nection session – this is the biggest difference between these two types of switching methods

Test day Tip

A WAN is a data communication network that covers a relatively broad geographic area and that often uses transmission facilities provided by common carriers, such as tele-phone companies WAN technologies generally function at the lower three layers of the Open Systems Interconnection (OSI) reference model: the physical layer, the data link layer, and the network layer X.25 is a good example of a WAN technology that operates

at all three layers, whereas Frame Relay only operates up to Layer 2.

Circuit Switching

Circuit-switched networks are not always available, since connections have

to be initiated before transmission can take place This means that when

you use technologies such as Integrated Services Digital Network (ISDN),

you will find that the call must first be initiated (to set up the circuit) and

then data can traverse it Once completed, the circuit can be taken down If a

router at a site has to send data to another router at a remote site, the circuit

is initiated (brought up and online for use) The switched circuit is initiated

with the circuit number of the remote network In the case of ISDN, the

setup will use a service profile identifier (SPID) number, which is essentially

a phone number that the router dials to initiate the circuit with the WAN

switch An example of a sample carrier network is shown in Figure 8.1 The

cloud represents the carrier’s telecommunications network

packet Switching

Packet switching is the method of sending data from location to location on

a WAN that is always available There is no need to initiate a call to a WAN

switch, as the connection is already up and running from the start When you

set the carrier’s link up (let’s use Frame Relay for this example), it stays up

The only time this link should drop is during scheduled outages, problems, and

FIGurE 8.1

Viewing a Carrier Network.

360 ChApTEr 8: Wide Area Networking

emergencies Other than that, consider packet-switched networks to always be available Some examples of packet-switching networks include Asynchronous Transfer Mode (ATM), Switched Multimegabit Data Service (SMDS), and X.25, to name a few

Packet-switched networks will also divide the transmitting data into packets, and each packet is sent individually from the source to the desti-nation All packets are given sequence numbers so that they can all be put back together again in the right order at the destination The benefit of this

is that each packet can take a different route to get to its destination Once there, the message will be recompiled and take its original form Packet-switched networks are often shared This doesn’t open you up to security issues, but it does open you up to bandwidth challenges Just be aware that packet-switched networks are not the same as point-to-point private lines that provide dedicated bandwidth to the purchaser

Exam warning

The telephone service provided by your carrier is most likely based on a circuit-switching technology Circuit switching is ideal when data must be transmitted quickly and must arrive in the same order in which it’s sent Packet switching is the opposite of circuit switching Packet switching is more efficient and robust, and it is commonly used for data that can withstand some delays in transmission.

wAN proToColS ANd propErTIES

Now that you have reviewed the underlying concepts of the WAN and cov-ered some of the methods in which they transmit data, let’s take a good look

at some of the technologies that make up the WAN In this section, we dis-cuss the CompTIA Network+ (2009 edition) exam objectives based on WAN protocols and standards such as T carriers, ISDN, and Fiber Distributed Data Interface (FDDI) You must be able to understand and respond to ques-tions about the speeds, capacity, transmission media, and distance for the

2009 Network+ exam

T/E Carrier

T1 lines have been around for a long time and are still very much in use today The name T (Terrestrial) and the number following it denotes the type of line If it is a T1, then it is a dedicated media connection supporting data rates of 1.544 Mbps This speed is derived from 24 individual channels

of 64 Kbps (only 23 are available for data transfer and network use) If it is

a T3, the line can support data rates of approximately 43 Mbps, which is

created with 672 channels of 64 Kbps E1 and E3 lines are similar, but they

are European-based, and J lines are used within Japanese carrier systems

For any Network+ technician in the field, it’s common to work with T1

and E1 lines very often Users can also access just a fraction of the whole

bandwidth, which would mean that you have leased lines with specific data

rates A T1 line, with its 24 individual channels, can be configured to carry

voice or data traffic Most telephone companies allow you to buy just some

of these individual channels, known as fractional T1 access T3 lines are

used mainly by Internet service providers (ISPs) connecting to the Internet

backbone, although many private companies have implemented T3 lines in

some of their core networks and data centers

As stated earlier, an E1 line is similar to the North American T1 line

E1 is the European format for digital transmission and is similar to a T1 line, but

has higher data transmission rates E1 carries signals at 2 Mbps (32 channels at

64 Kbps, with two channels reserved for signaling and controlling) An E3 is the

European equivalent to the T3, but the T3 has a higher data rate (E3 lines carry

data at a rate of approximately 34.368 Mbps, usually rounded up to 35 Mbps)

T1 channels are sometimes known as digital signal zeros (DS0s) In T-carrier

systems, DS0 is a basic digital signaling rate of 64 Kbps, corresponding to the

capacity of one voice or data channel Twenty-four DS0s (24 × 64 Kbps) equal

one DS1 A full T1 is equal to a DS1; a full T3 is equal to a DS3

Exam warning

Make sure you are familiar with the speeds of the T- and E-carrier links, as well as

the number of channels that make up a T1 T3 lines are faster than T1 lines because

they have more bandwidth Use common sense on the exam when determining which

has a higher capacity A T3 has a higher capacity than an E3 and a T3 has a higher

capacity than an E1, and so on You may be asked to determine which line you would

recommend based on the needs of the client, so be able to respond by knowing which

technologies offer which benefits.

ISdN

ISDN is a WAN protocol based on an international communications

stan-dard for sending voice, video, and data over digital telephone lines or

nor-mal telephone wires ISDN is commonly seen in the corporate offices of

companies worldwide Mostly used for WAN links from one company to

another, ISDN is unique in that it is call-initiated and call-terminated, so

you only pay for what you use ISDN uses telephone number-like entities

called SPIDs to dial from peer to peer in order to bring up the line when

362 ChApTEr 8: Wide Area Networking

traffic has to be sent across it Once the connection is no longer required, usually due to inactivity, the call is ended and so is the billing for that usage ISDN supports data transfer rates of 64,000 bits per second (64 Kbps) per channel, and most ISDN circuits used today are configured as two channels

to provide 128 Kbps of throughput

There are two types of ISDN: Basic Rate Interface (BRI) and Primary

Rate Interface (PRI) BRI consists of two 64 Kbps B channels and one D

channel for transmitting control information BRI ISDN has a maximum speed of 128 Kbps PRI consists of 23 B channels and one D channel (in North America) or 30 B channels and one D channel (in Europe) The B channel is used for control

BRI

The BRI ISDN service uses two B channels and one D channel (2B+D) Now that you understand what a T1 is, it should be pretty simple to under-stand that a channel represents a DS0.You would use two channels at 64 Kbps to total 128 Kbps, which is the rate of a BRI ISDN service If you want

to get more than that basic rate, you can move to a PRI

The B channels are used to send and receive data; the D channel is used for signaling BRI B-channel service operates at 64 Kbps and is meant to carry user data; BRI D-channel service operates at 16 Kbps and is meant

to carry control and signaling information, although it can support user data transmissions under certain circumstances The D-channel signaling protocol comprises Layers 1 through 3 of the OSI reference model BRI also provides for framing control and other overhead, bringing its total bit rate

to 192 Kbps

Test day Tip

Remember the following: the ISDN BRI service offers two B channels and one D channel (2B+D) BRI B-channel service operates at 64 Kbps and is meant to carry user data; BRI D-channel service operates at 16 Kbps and can also carry user data but is normally used for management purposes such as signaling.

PRI

PRI offers 23 B channels and 1 D channel in North America and Japan, yielding a total bit rate of 1.544 Mbps (the PRI D channel runs at 64 Kbps)

In Europe, Australia, and other parts of the world, PRI provides 30 B chan-nels plus one 64 Kbps D channel and a total interface rate of 2.048 Mbps The PRI physical layer specification is ITU-T I.431 This is essentially the same as getting a full T1, except you are getting the ISDN service benefits

Test day Tip

Remember that PRI service offers 23 B channels and 1 D channel in North America

and Japan, yielding a total bit rate of 1.544 Mbps (the PRI D channel runs at 64 Kbps)

In Europe (and other parts of the world), PRI provides 30 B channels plus one 64 kbps

D channel and a total interface rate of 2.048 Mbps.

FIGurE 8.2

Circuit- and Packet-Switching Technologies Used Together.

It is important to remember that ISDN is comprised of digital telephony

and data transport services offered by regional telephone carriers using

pre-existing telephone wiring ISDN is also used very often as backup links since

they are circuit-switched They can be brought up when needed, as in the

case of an emergency where the main link to a site is down In these cases,

ISDN can be used to fix the problem Figure 8.2 shows an example of both

circuit-switched and packet-switched networks in use simultaneously

You can save money using a hybrid network as well Because you pay for

Frame Relay service to be up at all times, it becomes your primary network

and is where your data mainly travels At the same time, each router is

conveniently configured with another technology (in this example, ISDN),

which provides a failsafe or backup network in case of failure of the frame

circuit, thereby providing high availability to the network users

364 ChApTEr 8: Wide Area Networking

FddI

Although considered more of a local area network (LAN) technology, and debated to be a LAN technology, FDDI (whether based on the LAN or WAN)

is a technology that is used to provide very high-speed, redundant backbone service to your network Listed in the Network+ objectives, it’s imperative that you understand the underlying technology used with FDDI FDDI, which is based on fiber, is the standard for a 100 Mbps dual-ring token-passing technology Also based on copper cable, Copper Distributed Data Interface (CDDI) provides high-speed, redundant transmission of data The FDDI is generally used as a backbone technology due to its redundant design and high speed Figure 8.3 shows FDDI’s overall design

Note

If you would like to research this technology and design more thoroughly, visit the Cisco ISDN DDR page at www.cisco.com/en/US/tech/tk801/tk379/technologies_ configuration_ example09186a00800b1147.shtml.

FIGurE 8.3

Fiber Distributed Data

Interface.

FDDI works by using a dial ring token-passing architecture that allows

for bidirectional traffic – traffic traveling opposite directions – which is also

called counter rotation FDDI and its primary and secondary rings are based

on providing high-speed service reliably The dual rings offer redundancy in

case of failure, since if one link becomes unavailable the traffic can traverse

the other link

Frame Relay

Frame Relay is a packet-switching protocol for connecting devices on a WAN

Frame Relay networks in the United States support data transfer rates at T1

(1.544 Mbps) and T3 (45 Mbps) speeds and can be purchased as DS0s This

allows you flexibility, so you could have a Frame Relay link from one site to

another and need 128 Kbps of available circuit bandwidth You could then

purchase two channels at 64 Kbps each and that would be your circuit speed

for your Frame Relay link Frame Relay, when used in the WAN, is often

used between a company’s core and remote sites and sized very perfectly to

whatever bandwidth is needed between the sites

The sizing is done so that you can take advantage of bursting, which is

when the carrier allows you to use some of the additional bandwidth on the

line (up to 1.544 Mbps on a T1, for example), if available

Frame Relay has a high transmission speed, very low network delay if

configured properly and sized correctly, and is fairly reliable Because of how

the system is maintained in the carrier’s internal network, it’s easy to make

mistakes, as there is a lot to configure when you use Frame Relay This is

especially true if you are an engineer working on routers or WAN switches

inside a carrier’s network Because the service is not highly reliable at all

times, it’s common to back up a Frame Relay network with another network

such as ISDN

Frame Relay is based on the older X.25 packet-switching technology,

which was designed for transmitting analog data such as voice

conversa-tions, and is the skeleton for the MPLS solutions now being used in most

enterprises today See the section later in this chapter for more information

on MPLS

Although it is losing ground to other technologies that operate using

purely Layer 3 communications (Frame Relay primarily operates at Layer 2

of the OSI model), Frame Relay is one of the most prevalent technologies

used in wide area networking today Because carriers quickly move to update

(and upgrade) their infrastructures to stay competitive, Frame Relay and

ATM technologies are quickly losing ground in favor of pure IP-based Layer 3

WAN infrastructure, as this is more compatible with today’s voice and

video applications Frame Relay networks are still used in many enterprises