basic communications
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Basic Communications
Overview of communication technology.
Communications
Electronically exchanging data or information.
Voice interactive communicationData large volume batch
transmissionsImage encoded graphicsVideo streaming media
Telecommunications History
Pre 1984Local and long distance monopoly
1984 AT&T settlementIntense long distance competition
1996 Telecommunications ActLocal access competition
Digital
Standard Telephone System
Analog
Network
Analog Digital
Modem
Switch
Digital
SwitchSwitch
Network
Telephone Changes
Rapidly decreasing long distance rates
Value added telephone servicesCellular accessFlat rate long distance?Data and voice convergence.
Issue: Access
Dedicated linesStandard voiceIntegrated Services Digital NetworkDigital Subscriber LinesCable ModemWireless
Voice vs. Data
VoiceDelay SensitiveConstant bit rateNot error sensitiveGrowth stable
(video ??)
DataDelay insensitiveVariable bit rateError sensitiveDemand growing
Data Networks
NICLAN
Public TELCO WANPOP
Switch
Router
Campus or Metropolitan
Area
Packet Structure
Header(s) Data Payload Trailer
LAN Operating Protocols (layer 2)
Ethernetopen standard, cheap, most common
Token RingIBM proprietary, high quality, expensive
Others
Network Interface Cards
Build, send out and accept framesUsually a daughter board on PCMust match LAN and CPURequire drivers to operate
Network Interface Cards (NIC)
EthernetCarrier Sense Multiple Access/Collision Detection
HeaderBodyTrailer
Listen before transmitContention accessRetransmit on collision
Network Routing
Protocols for internetworking.
Two major types
Packet switching (or datagram) Usually layers 3 and 4
Circuit switching Usually layers 1 and/or 2
Packet switching or Datagram Protocols
Best effortFrames take individual routesPacket assembly devices neededError ControlTraffic Management
Buffering Discard
Datagram Logic (IP)
Packet n Packet 1Packet 2
32
1
31
2
32
1
PAD
IP
Best EffortAddressingVariable packet lengths (1500 bytes
or less)IPv4 vs IPv6Frame and Header
TCP and UDP
Transmission Control Protocol
Connection oriented
Assures that packets arrive in order and that they are correct.
User Datagram Protocol
Connectionless
Sends packets out without confirming that they arrive
Ethernet/TCP/IP Header Structure
Circuit Protocols
All packets take the same routeNo packet assembly device to reorder
packetsNormally layer 2 connectionMay be permanent or switchedAllow guaranteed service quality levelsMay be used to carry datagram
protocols
Circuit Logic
Source Destination
Setup
Message & ACK’s
Teardown
32
1
3
12
Inter-networking
Technologies
Common WAN technologies.
ISDN
Circuit Switched Data and Voice Service
Digital Subscriber Lines
DSL uses packet switching technology that operates independent of the voice telephone system, allowing the telephone companies to provide the service and not lock up circuits for long calls.
WAN Costs
Circuit ChargesCommitted BandwidthPeak BandwidthDiscard PriorityLatency
Representative Prices per MB of traffic (Qwest, Dec. 98)
Frame RelayNon-discard eligible 4 centsDiscard eligible 3 cents
ATMConstant bit rate 2 centsVariable bit rate (real-time) 1.2 centsVariable bit rate (non real-time) .75 centsAvailable bit rate .55 centsUnspecified bit rate .4 cents
Representative Prices per port (Qwest, Dec. 98)
56 Kb Frame Relay $190T-1 Frame Relay
$1,595T-3 Frame Relay
$3,190
Client/Server Architecture
An architecture in which the client (personal computer or workstation) is the requesting machine and the server is the supplying machine, both of which are connected via a network.
Client/Server Architectures
SERVER PROCESSING
CLIENT PROCESSING
CENTRALIZED STAND-ALONE
FAT SERVER FAT CLIENT
Client/Server
ScalabilityInteroperabilityUser buy-inIncreased costMulti-tier
One Tier System
Two Tier Client/Server
Three Tier Client/Server
Application Issues
Interoperability (e.g. ODBC)OS supportMulti-threaded or single threadedNetwork impact (e.g. chattiness)QoS demandsDelivery: centralized, clien/server,
web
Application Management
Standards Supported Accepted Prohibited
Version Control and DistributionLicense ManagementVirus detection and inoculation
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