View
232
Download
2
Category
Tags:
Preview:
Citation preview
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
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
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
Recommended