Foundation Summary

Study Material For Cisco Ccna Ccnp And Ccie Students

Study Material For Cisco Students

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The "Foundation Summary" section of each chapter lists the most important facts from the chapter. Although this section does not list every fact from the chapter that will be on your CCNA exam, a well-prepared CCNA candidate should know, at a minimum, all the details in each "Foundation Summary" section before going to take the exam.

Figure 15-17 depicts the PSTN and how it supports analog voice through a digital T1 core.

Figure 15-17 Analog Voice Calls Through a Digital PSTN

PSTN

PCM Codec Converts

Figure 15-17 Analog Voice Calls Through a Digital PSTN

PCM Codec Converts

Table 15-9 lists some of the key modem standards. Table 15-9 Modem Standards

Standard

Speed

Comments

V.22

1200 bps (600 baud)

Mainly used outside the United States

V.22bis*

2400 bps (600 baud)

First widely deployed worldwide standard

V.32

4800/9600 (2400 baud)

Adjusts speed based on line quality

V.32bis*

14.4kbps (2400 baud)

Backward compatible with V.32

Table 15-9 Modem Standards (Continued)

Standard

Speed

Comments

V.34

28.8 kbps

Backward compatible with V.32bis and V.32

V.42

28.8 kbps

Same speed as V.34, but with error-correction features

V.90

56 kbps (downstream), 33 kbps (upstream)

Created from two earlier competing standards, X2 and K56Flex

V.92

56 kbps/33 kbps (downstream/ upstream) or 48 kbps (each direction)

Connects and finds correct speed more quickly than V.90; allows "modem-on-hold"

*"bis" simply means "version 2." Figure 15-18 shows the typical topology with ISDN in use for access to an ISP.

Figure 15-18 ISDN Local Loops and Equipment

Andy's PC

PSTN

No PCM Needed on Andy's Digital Local Loop

Figure 15-18 ISDN Local Loops and Equipment

No PCM Needed on Andy's Digital Local Loop

/ Internal ISDN Card

/ Internal ISDN Card

Table 15-10 lists the number of channels for each type of ISDN line and the terminology used to describe them.

Table 15-10 BRI and PRIB and D Channels

Type of Interface

Number of Bearer Channels (B Channels)

Number of Signaling Channels (D Channels)

Descriptive Term

BRI

2

1 (16 kbps)

2B+D

PRI (T1)

23

1 (64 kbps)

23B+D

PRI (E1)

30

1 (64 kbps)

30B+D

Figure 15-19 shows some of the detail of a typical DSL connection.

Figure 15-19 DSL Connection from the Home

Andy's PC

Ethernet

Digital Signals > 4000 Hz

Ethernet

Digital Signals > 4000 Hz

DSL Router/ Modem

DTMF Tones, Analog Voice,

Analog phone

Figure 15-19 shows some of the detail of a typical DSL connection.

DTMF Tones, Analog Voice,

Voice Switch w/PC Mayberry CO

Andy's House

Voice Switch w/PC Mayberry CO

Table 15-11 lists the major DSL variants, the standard defining that variant, the modulation/ encoding technique, speed, and distance limitations.

Table 15-11 DSL Technologies Standards Comparison

D

>SL Type

Standards

Modulation/Encoding Technique

Speed

Distance Limit

Full-rate ADSL/G.DMT

ANSI T1.413 Issue 2

Discrete multitone (DMT) or carrierless amplitude phase (CAP)

Downstream speed of 384 to 8 Mbps; upstream speed slower, up to 1.024 Mbps

18,000 feet

G.Lite

ITU-T G.992.1, ITU-T G.992.2

DMT

Downstream speed up to 1.544 Mbps to 6 Mbps; upstream speed up to 640 kbps

18,000 feet

Table 15-11 DSL Technologies Standards Comparison (Continued)

DSL Type

Standards

Modulation/Encoding Technique

Speed

Distance Limit

Very-high-data-rate DSL (VDSL)

ETSI and ANSI in process

DMT/single-carrier modulation (SCM)

12.96 Mbps to 52.8 Mbps for both upstream and downstream speed

4500 feet

ISDN DSL (IDSL)

ANSI ETR 080

Two binary one quaternary (2B1Q)

144 kbps for both upstream and downstream speed

18,000 feet

Symmetric DSL (SDSL)

None

2B1Q

768 kbps for both upstream and downstream speed

22,000 feet

High-data-rate DSL (HDSL

ITU G.991.1, ANSI TR 28

2B1Q

1.544 or 2.048 Mbps for both upstream and downstream speed

12,000 feet

G.SHDSL

ITU G.991.2

Trellis-coded pulse amplitude modulation (TC PAM)

192 kbps to 2.360 Mbps for both upstream and downstream speed

28,000 feet

Figure 15-20 outlines some of the key terms used with CATV.

Figure 15-20 Cable TV Terminology

Figure 15-20 Cable TV Terminology

Mayberry CATV

Head-end

DC I

Mayberry CATV

Table 15-12 summarizes some of the key reference information about downstream CATV data over cable.

Table 15-12 Downstream Data over Cable: Interesting Facts

Downstream Rate

OSI Layer 1

QAM-64 and QAM-256 encoding

OSI Layer 2

MCNS MAC and IEEE 802.2 LLC

Multiplexing used

Frequency-division multiplexing

Speed

30 to 40 Mbps

Table 15-13 summarizes some of the key points about the upstream CATV data channel. Table 15-13 Upstream Data over Cable: Interesting Facts

Downstream Rate

OSI Layer 1

QPSK and QAM-16

OSI Layer 2

MCNS MAC and IEEE 802.2 LLC

Multiplexing used

Time-division multiple access (TDMA)

Speed

320 kbps to 10 Mbps

The remote access technologies in this chapter provide services at Layer 1, and possibly Layer 2, of the OSI model. TCP/IP and all the associated higher-layer protocols (TCP, UDP, HTTP, FTP, Telnet, DNS, DHCP, and so on) can run over any of these access technologies; the differences lie in what is done at Layers 1 and 2. Figure 15-21 outlines the protocols used by each.

Figure 15-21 The OSI Model and Remote Access Technologies

Applications

Applications

TCP or UDP

TCP or UDP

IP

IP

PPP

PPP

Modem Standards (v.x)

ISDN (I-430) Standards

Applications

Applications

TCP or UDP

TCP or UDP

IP

IP

PPP

IEEE 802.2

ATM ! Ethernet

MCNS MAC

xDSL Standards

Upstream-QPSK, QAM-16

Downstream-QAM-64, QAM-256

Table 15-14 lists some of the main points for comparison of these technologies. Comparison points are always good material for exam questions.

Table 15-14 Comparison of Modems, ISDN, DSL, and Cable

Analog Modems

ISDN

DSL

Cable Modems

Transport

Telco line

Telco line

Telco line

CATV cable

Supports symetric speeds?

Yes

Yes

Yes

No

Supports asymmetric speeds?

Yes

No

Yes

Yes

Speed ranges

Less than 56 kbps

64 kbps per B channel

56 kbps to 2 Mbps

320 kbps to 40 Mbps

Degrades under higher loads?

No

No

No

Yes

Supports IP and associated higher-layer protocols?

Yes

Yes

Yes

Yes

Allows concurrent voice and data?

No

Yes

Yes

Yes

Always on?

No

No

Yes

Yes

Local loop distance issues

No

No

Yes; distance varies

As mentioned in the introduction, you have two choices for review questions. The questions that follow give you a bigger challenge than the exam itself by using an open-ended question format. By reviewing now with this more difficult question format, you can exercise your memory better and prove your conceptual and factual knowledge of this chapter. The answers to these questions are found in Appendix A.

For more practice with exam-like question formats, including questions using a router simulator and multiple-choice questions, use the exam engine on the CD.

1. What do ISDN, BRI, and PRI stand for?

2. How many bearer channels are in a BRI? What about a PRI in North America? What about a PRI in Europe?

3. Define what a voice codec does, and explain why a PCM codec needs 64 kbps for a single voice call.

4. Two terms were shortened and combined to first create the word modem. Identify those two words and describe what each word means.

5. Define what the terms symmetric and asymmetric mean in relation to modem specifications. Also explain why asymmetric might be a better option.

6. Compare the V.90 and V.92 modem specifications.

7. Compare analog modems, ISDN BRIs, DSL, and cable modems in terms of concurrent support for voice and data.

8. Compare analog modems, ISDN BRIs, DSL, and cable modems in terms of whether the data service is always on.

9. List some of the pros and cons regarding the use of analog modems for remote access.

10. List some of the pros and cons regarding the use of ISDN for remote access.

11. List some of the pros and cons regarding the use of DSL for remote access.

12. Define what the acronym DSLAM stands for, and explain the concept behind how a DSLAM allows voice and data to flow over the same local loop phone line.

13. Which of the DSL standards is the most common in the United States today? What is the range of upstream and downstream speeds for that type of DSL, as well as the maximum distance of the local loop?

14. What protocols are used by DSL at the data link layer?

15. Imagine that Andy and Barney are neighbors, and they both use cable modems. Describe the type of traffic that they could generate that could cause collisions, and tell what is done to help prevent those collisions.

16. Name the four different Layer 1 encoding methods defined for use by cable modems. For each one, list whether it is used for upstream data, downstream data, or both.

17. Which of the four different remote access technologies support IP, TCP, UDP, and the rest of the higher-layer TCP/IP protocols?

18. Compare and contrast the cabling used by an analog modem and a DSL router/modem when connecting to the local phone company line. Identify the purpose of each pin on the connector.

19. Compare and contrast the cabling used by an ISDN modem and a cable modem when connecting to the local phone company line or cable drop line. Identify the purpose of each pin on the connector.

20. List four standards bodies that have been involved in the development of DSL standards.

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