Chapter 8 Wide 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 Mbps bandwidth 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