Tài liệu giảng dạy CCNA - module 06 chapter 19-Remote Access Technologies

Table of Content1 Perspectives on the PSTN 2 Analog Modems 3 Integrated Services Digital Network 4 Digital Subscriber Line 5 Cable Modems 6 Comparison of Remote Access Technologies... Co

Module 06 WAN

Technology

Chapter 19 Remote Access Technologies

Table of Content

1 Perspectives on the PSTN

2 Analog Modems

3 Integrated Services Digital Network

4 Digital Subscriber Line

5 Cable Modems

6 Comparison of Remote Access Technologies

1 Perspectives on the PSTN

Analog signal

 Sound waves travel through the air by vibrating the air The

human ear hears the sound because the ear vibrates as a

result of the air inside the ear moving, which, in turn,

causes the brain to process the sounds that were heard by

the ear

 The PSTN, however, cannot forward sound waves Instead,

a telephone simply converts the sound waves into an analog electrical signal The PSTN can send the electrical signal

between one phone and another On the receiving side, the

phone converts the electrical signal back to sound waves

Digital signal

 Electrically, digital signals use a defined set of both positive

Converting Analog Voice to Digital

Voice

Digital T1 line

Telco voice switch

Telco voice switch

Local loop

(analog)

Local loop (analog)

PCM codec converts Digital ←→ Analog

PCM codec converts Digital ←→ Analog

PSTN

2 ANALOG MODEMS

Basic Operation of Modems over

PSTN

Digital T1 line

Telco voice switch

Telco voice switch

Local loop (analog)

Local loop (analog)

PCM codec converts Digital ←→ Analog

PCM codec converts Digital ←→ Analog

PSTN

Modem converts

Digital ←→ Analog

Modulation and Demodulation

• Amplitude Modulated, Frequency Modulated, Phase modulation

Point-to-Point Protocol Features with

Modems

 Most computers today use PPP as the data-link protocol

when using modems.

 PPP supports both synchronous communication, as

typically is done over leased point-to-point lines, as well as

asynchronous communication, which typically is done over

dialed circuits using modems.

 PPP includes some features that are important when using

modems to dial into an ISP:

 PPP includes the capability of dynamically assigning an IP

address to a device on the other end of the PPP link.

 PPP supports that Challenge Handshake Authentication

Protocol (CHAP), which popularly is used to allow the dial-in

user to supply a username and password to gain access to the

ISP network.

Modem Installation and Cabling

 External modems can be connected to a PC using either a

COM port or a USB port

 Internal modems are installed in an expansion card slot

 PCMCIA modems simply can be inserted into the

convenient PC card slot in the side of a laptop computer

Modem Standards

Standard Speed Comment

V.22 1200 bps Mainly used outside the United States

V.22 bis 2400 bps First widely deployed worldwide standard

V.32 4800/9600 bps Adjusts speed based on line quality

V.32 bis 14.4 kbps Backward compatible with V.32

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 errorcorrection features

V.90 56 kbps (down

stream) 33 kbps (upstream)

Created from two earlier competing standards, X2 and K56Flex

V.92 56/33 kbps or 48

kbps for each direction

Connects and finds correct speed more quickly than V.90; allows “modem-onhold”

3 Integrated Services Digital

Network

Introducing ISDN

 The ISDN standards define the hardware and call setup

schemes for end-to-end digital connectivity

 ISDN allows digital signals to be transmitted over existing

telephone wiring

 ISDN brings digital connectivity to local sites The following

list provides some of the benefits of ISDN:

 Carries a variety of user traffic signals, including data,

voice, and video

 Offers much faster call setup than modem connections

 B channels provide a faster data transfer rate than

modems

 B channels are suitable for negotiated Point-to-Point

Protocol (PPP) links

ISDN channels

 ISDN uses out-of-band signaling, the delta (D channel), for

call setup and signaling

 ISDN uses bearer channels, also called B channels, as clear

data paths Each B channel provides 64 kbps of bandwidth

 Each ISDN B channel can make a separate serial

connection to any other site in the ISDN network

D Channel Call Setup Signaling and

Resulting B-Channel Call

Typical Uses of ISDN

 Routers frequently use ISDN to create a backup link when

their primary leased line or Frame Relay connection is lost

 ISDN supports multiple concurrent data bearer channels

For instance, you can use your PC to dial two different sites

at the same time You can make two calls to the same ISP,

increasing the speed You also can use one B channel for

data and make a voice call using the other B channel

ISDN Installation and Cabling

 A COM port or a USB port connects to the ISDN modem or

the terminal adapter (TA)

Telco

RS-232 2 wires

ISDN modem

4 Digital Subscriber Line

THE KEY FEATURES OF DSL

 DSL allows analog voice signals and digital data signals to

be sent over the same local loop wiring

 Similar to ISDN, the local loop must be connected to

something besides a traditional voice switch at the local

CO: a device called a DSL access multiplexer (DSLAM)

 DSL allows for a concurrent voice call to be up at the same time as the data connection

 Unlike modems and ISDN, DSL’s data component is always on—in other words, you don’t have to signal to set up a

data circuit

Protocols Used with a DSL Router

5 Cable Modems

Cable modem

 Cable modems provide an always-on Internet access

service, while allowing you to surf the Internet over the

cable and make all the phone calls you want over your

telephone line—and you can watch TV at the same time!

 Cable modems use some of the bandwidth that otherwise

might have been allocated for new TV channels, using

those frequency bands for transferring data It’s a little like

having an “Internet” channel to go along with CNN, TBS,

ESPN, The Cartoon Network, and all your other favorite

cable channels

Cable Modems Terminology

6 Comparison of Remote

Access Technologies

Layer 1 and Layer 2 between the Home

and the Head End

 The data going toward the home as downstream data, and

data from the home as upstream data.

 Downstream data uses standards that are consistent with

some of the standards for sending digital video over cable

In fact, you can think of the downstream data as being

sent over another TV channel For downstream data, the

data over cable standards takes advantage of the fact that

the signals are broadcast to all subscribers in a section of

the cable plant

Layer 1 and Layer 2 between the Home

and the Head End (cont.)

 CATV standards call for the use of a data-link protocol

called Multimedia Cable Network Systems (MCNS) MAC

 MCNS is similar to Ethernet’s MAC, as defined in the IEEE

802.3 specification, including the use of Ethernet MAC

addresses So, although all downstream data is sent to all

drops in the cable system, only those with a cable modem

know that data has been received, and only the PCs with

the correct MAC address process the data

 MCNS also defines the physical encoding details MCNS

calls for the use of a modulation method called quadrature

amplitude modulation (QAM)

Upstream Data

 The upstream data channel uses a totally separate

frequency range than the downstream channel, so no

collisions occur between downstream and upstream data

However, all upstream data from multiple cable subscribers

does share the same frequency range—the same channel,

essentially—so collisions can occur between data sent

toward the Internet by the different home users

 MCNS defines the use of a multiplexing method called

time-division multiple access (TDMA), in which each home user

is granted regular time periods during which to send

upstream data These time slots happen multiple times per