Chapter 8Wide Are Networking (WAN)

• Concepts– Packetizing– Multiplexing

• Switching

• Transmissions

• Services

• Selection

Packetizing

• Organize a group of bits in a predetermined & structure format

• Include user’s data, overhead or management information for error-free transmission

• Packets, frames, cells, blocks, data units

Multiplexing

• Frequency division multiplexing (FDM)

• Time division multiplexing (TDM)

• Statistical time division multiplexing (STDM)

• Wavelength division multiplexing (WDM)

• No interoperation between different manufacturers

Frequency Division Multiplexing

• Use different frequencies for multiple input signals

• Use guardbands (take space, not efficiency)

• Transmit data and voice simultaneously over phone line

• Data over voice (DOV) unit with PBX for college campus, not for PSTN

Time Division Multiplexing

• 100% bandwidth available for a portion of the time

• Use buffer memory & central clock for flow control (polling)

• Composite message frame

• Simple, not efficiency

Statistical Time Division Multiplexing

• Efficiency– No idle time– No padded blanks or null characters in

composite message blocks– Dynamically allocating time to terminals

• Higher cost– Buffer– Processing power for control information

(source terminal, bytes of data, & data compression)

Wavelength Division Multiplexing

• Use different wavelengths of light

• Long-distance fiber optic network

WAN Switching

• Packet switching network

• Circuit switching network

Packet Switching

• Packet-switched network• Public data network (PDN)• Packet assembler/disassembler (PAD)

– Stand-alone devices

– Combined with modems or multiplexers

– Location: end-user or entry point of packet switched data network

• Equipment: DSEs (data-switching exchanges) or PSEs (packet-switching exchanges)

• Every user having the same transmission rate

Packet Switched Services

• Connectionless– Global address (source & destination)– Datagram (address with user data)– Unreliable (no error detection or flow control)

• Connection-oriented: virtual circuits – Reliable packet network (ACK/NAK)– Call set-up packets, message-bearing packets,

& clear request packet

Circuit Switching

• Circuit switched network

• Use circuit without source & destination address

WAN Networking Transmission

• Local Loop– Plain old telephone service (POTS)– Integrated service digital network (ISDN)– Asymmetric digital subscriber line (ADSL)– Cable TV

• Boradband– T1– SONET

ISDN

• A switched digital services for delivering voice, video, and data at same time

• Types– Basic rate interface (BRI): 2B+D ( 2 Bearer channels of

64 kbps & 1 Delta or Data channel of 16 kbps)

– Primary rate interface (PRI): 23B+D

• Applications use ISDN terminal adapter– Single user-to-office or Internet connection

– Office-to-office connection

ADSL• Use POTS at higher frequencies

• Use frequency division multiplexing: (upstream & downstream)

• Internet & voice at same time

• Types– Very high speed digital subscriber line (VDSL)– Rate-adaptive digital subscriber line (RADSL)– Symmetric digital subscriber line (SDSL)

• Application: access Internet using POTS & ADSL units

Cable TV Problems for WAN

• Downstream only infrastructure

• Remedy methods– Upstream using POTS– Modify cable architecture to upstream &

downstream

T-1• High-capacity digital transmission over

voice channel

• 1.544 Mbps bandwidth

• 24 64-Kbps channels (DS-0 circuit)

• T1 multiplexers

• Application– Leased line or private line for business

T-1 Digital Services

• Digital service hierarchy or DS standards

• DS-0 : 64Kbps

• DS-1: T-1uses four copper wires (two twisted pair)

• DS-2: T-2

• DS-3: T-3 uses optical fiber media

• DS-4: T-4

SONET• Optical transmission services:

– For failure tolerance & reliable data delivery– Metropolitan area only– Expensive

• Applications– Broadband ISDN– High-definition television

WAN Services

• X.25

• Frame relay

• Switched multimegabit data service (SMDS)

• Cell relay - ATM

• Broadband ISDN

X.25

• CCITT standard for the interface between DTE and packet-switched network

• Point-to-point error checking or hop-by-hop error checking

• Technology– Packet assembler/disassembler (PAD)– X.25 switches

Frame Relay• Error detection & correction

– Point-to-point error detection (discard )– End-to-end error correction

• Frame: variable length

• Pro: high through put with low delay for data only

• Con: no guaranteed time delivery (not for voice & video)

Frame Relay

• Technology– Frame relay or frame assembler/disassembler

(FRAD or FAD) or frame relay access devices– Frame relay switch

• Application: inter-LAN traffic

Switched Multimegabit Data Service - SMDS

• Connectionless network service

• Use SONET (T-3)

• Fixed-length cells of data

• Broadcast

• Only MCI for long distance

Cell Relay - ATM

• Cell– fixed length (53 octects)

– 48 for data and 5 for control information

• Predictable delivery time for voice and video• Technology

– ATM network interface cards

– ATM hub

– ATM enterprise switch

– ATM gateway switches or ATM access switches

– ATM LAM emulation

WAN Selection Criteria

• Data traffic patterns

• Business objectives

Assignment

• Review chapter 8

• Read chapter 9