Basic Communications

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