WAN Technologies

Lecture 9

Paul Flynn

Objectives

• WAN Technologies Overview

• WAN Technologies

• WAN Design

WAN Technology

WAN Service Providers

Physical Layer: WANs

WAN Line Types and Bandwidth

WAN Devices

CSU/DSU

Modem Transmission

WAN Standards

WAN Link Options

Analog Dialup

ISDN

Leased Line

• Leased lines are not only used to provide direct point-to-point connections between Enterprise LANS, they can also be used to connect individual branches to a packet switched network.

Frame Relay• Most Frame Relay connections are based on

PVCs rather than SVCs. It implements no error or flow control. Frame Relay provides permanent shared medium bandwidth connectivity that carries both voice and data traffic.

ATM

• Asynchronous Transfer Mode (ATM) is a technology capable of transferring voice, video, and data through private and public networks. It is built on a cell based architecture rather than on a frame-based architecture.

DSL

Cable Modem

• Enhanced Cable Modems enable two-way. High speed data transmissions using the same coaxial lines that transmit cable television.

ADSL Technology

What does ADSL mean

• Asymmetric - The data can flow faster in one direction than the other. Data transmission has faster downstream to the subscriber than upstream

• Digital - No type of communication is transferred in an analog method. All data is purely digital, and only at the end, modulated to be carried over the line.

• Subscriber Line - The data is carried over a single twisted pair copper loop to the subscriber premises

ADSL standards :ADSL standards :

Standard name Standard name Common name Common name Downstream Downstream rate  rate 

Upstream Upstream rate rate

ITU G.992.1 ITU G.992.1 ADSL (G.DMT) ADSL (G.DMT) 8 Mbit/s 8 Mbit/s 1.0 Mbit/s 1.0 Mbit/s

ITU G.992.2 ITU G.992.2 ADSL Lite (G.Lite) ADSL Lite (G.Lite) 1.5 Mbit/s 1.5 Mbit/s 0.5 Mbit/s 0.5 Mbit/s

ITU G.992.3/4 ITU G.992.3/4 ADSL2 ADSL2 12 Mbit/s 12 Mbit/s 1.0 Mbit/s 1.0 Mbit/s

ITU G.992.3/4 Annex J ITU G.992.3/4 Annex J ADSL2 ADSL2 12 Mbit/s 12 Mbit/s 3.5 Mbit/s 3.5 Mbit/s

ITU G.992.3/4 Annex LITU G.992.3/4 Annex L RE-ADSL2 RE-ADSL2 5 Mbit/s 5 Mbit/s 0.8 Mbit/s 0.8 Mbit/s

ITU G.992.5 ITU G.992.5 ADSL2+ ADSL2+ 24 Mbit/s 24 Mbit/s 1.0 Mbit/s 1.0 Mbit/s

ITU G.992.5 Annex LITU G.992.5 Annex L RE-ADSL2+ RE-ADSL2+ 24 Mbit/s 24 Mbit/s 1.0 Mbit/s 1.0 Mbit/s

ITU G.992.5 Annex M ITU G.992.5 Annex M ADSL2+ ADSL2+ 28 Mbit/s 28 Mbit/s 3.5 Mbit/s 3.5 Mbit/s

ISDN

ADSL

FTTx, VDSL2,ADSL2plus

EnhancedCopper

Hybrid Fibre/Copper

Pure Fibre

ADSL Speed Comparison

Voice bandModem

FTTH

ADSL Range• In general, the maximum range for DSL without a repeater

is 5.5 km • As distance decreases toward the telephone company

office, the data rate increases

• For larger distances, you may be able to have DSL if your phone company has extended the local loop with optical fiber cable

Data Rate Wire gauge Wire size Distance

1.5 or 2 Mbps 24 AWG 0.5 mm 5.5 km

1.5 or 2 Mbps 26 AWG 0.4 mm 4.6 km

6.1 Mbps 24 AWG 0.5 mm 3.7 km

1.5 or 2 Mbps 26 AWG 0.4 mm 2.7

ADSL Speed Factors

• The distance from the local exchange

• The type and thickness of wires used

• The number and type of joins in the wire

• The proximity of the wire to other wires carrying ADSL, ISDN and other non-voice signals

• The proximity of the wires to radio transmitters.

ADSL network components

• The ADSL modem at the customer premises(ATU-R)

• The modem of the central office (ATU-C)

• DSL access multiplexer (DSLAM)

• Broadband Access Server (BAS)

• Splitter - an electronic low pass filter that separates the analogue voice or ISDN signal from ADSL data frequencies DSLAM.

ADSL Loop Architecture

ISP

Central Office Subscriber premises

Voice Switch

DSL

ADSL Requirements

• Phone-line, activated by your phone company for ADSL

• Filter to separate the phone signal from the Internet signal

• ADSL modem

• Subscription with an ISP supporting ADSL

How does ADSL work• ADSL exploits the ADSL exploits the unused analogue bandwidth unused analogue bandwidth

available in the wiresavailable in the wires

• ADSL works by using a frequency splitter device to split a ADSL works by using a frequency splitter device to split a traditional voice telephone line into two frequenciestraditional voice telephone line into two frequencies

4 25,875 138 1104 KHz

PSTNPSTN DownstreamDownstreamUpstreamUpstream

ADSL Modulation

• Modulation is the overlaying of information (or the signal) onto an electronic or optical carrier waveform

• There are two competing and incompatible standards for modulating the ADSL signal:

– Carrierless Amplitude Phase (CAP)

– Discrete Multi-Tone (DMT)

Carrierless Amplitude Phase• Carrierless Amplitude Phase (CAP) is an encoding Carrierless Amplitude Phase (CAP) is an encoding

method that divides the signals into two distinct bands:method that divides the signals into two distinct bands:

1.1. The upstream data channel (to the service provider), which is The upstream data channel (to the service provider), which is carried in the band between 25 and 160kHzcarried in the band between 25 and 160kHz

1.1. The downstream data channel (to the user), which is carried in The downstream data channel (to the user), which is carried in the band from 200kHz to 1.1MHz .the band from 200kHz to 1.1MHz .

• These channels are widely separated in order to These channels are widely separated in order to minimize the possibility of interference between the minimize the possibility of interference between the channels.channels.

Discrete Multi-tone (DMT)

• Discrete Multi-Tone (DMT) separates the DSL signal so that the usable frequency range is separated into 256 channels of 4.3125kHz each.

• DMT has 224 downstream frequency bins (or carriers) and 32 upstream frequency bins.

• DMT constantly shifts signals between different channels to ensure that the best channels are used for transmission and reception.

The DMT frequency bands• Frequency Division Multiplexing (FDM)

• Echo Cancellation

Max. Data Rate Down/Uplink (bps)

VDSL–Very High Bit Rate DSL

25M/1.6M or 8M/8M

Line Coding Technology

???

Analog Voice Support

Yes

Max. Reach (km-feet)

.9–3,000

DSL Service

ADSL–Asymmetric DSL 8M/1M CAP & DMT Yes 5.5–18,000

HDSL2–High Bit Rate DSL

1.5M–2.0M/1.5M–2.0M

Optis No 4.6–15,000

SDSL–Symmetric DSL 768K/768K 2B1Q / CAP No 6.9–22,000

IDSL–ISDN DSL 144K/144K 2B1Q No 5.5–18,000

Residential

SOHO

Business

DSL Modem Technology

• Trade-off is Reach vs. Bandwidth• Reach numbers imply “Clean Copper”• Different layer 1 transmission technologies, need a

common upper protocol layer to tie them together

Modern WAN

Comparing WAN Traffic Types