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The Infrastructure Technologies
Communication
. .
• All communications require:– Transmitters/Senders and receivers – Transmission medium– Rules of communication– A message
Transmitter ReceiverMediumMessage
• Transmitter/Receiver– Combination of Hardware and software
• Physical Media Types– Cable
twisted pair coaxial cable fiber-optic cable
– Wireless media radio microwave cellular telephone satellite infrared
Computer Data Communication
Data Communication Media
• Bandwidth– Measure of a medium’s
carrying capacity– Measured in bits (bps)
• Two categories– Baseband
one line, one channel most local communication
– Broadband one line, simultaneous
channels DSL, cable
Connection Type Bandwidth
Local telephone line 56 Kbps
Home satellite service 400 Kbps
DSL 1.44 Mbps
Cable service 2 to 10 Mbps
Leased line (T-1, T-3) 1.5 to 43 Mbps
Fiber optic cable Up to 10 Gbps
Wireless2G digital cellular2.5G digital cellular3G digital cellularBluetoothWi-Fi (802.11b)
19.2 Kbps144 Kbps2 Mbps1 MbpsUp to 11 Mbps
The MessageMessage
Header Body Trailer
• Messages have header and trailer carry information for delivering and ensuring the integrity of the message
• These are used by application and communication protocols
• The electronic form of a message is a signal
Protocols• A precise set of rules for communicating
• A communication protocol defines:– message format (header/trailer)– communication speed– How the message is encoded (e.g., ASCII, EBCDIC)– filtering/error correction rules
• An implementation of standard rules for passing parameters between adjacent layers
Signal Transmission
C yc le C yc le
+
0
-
T im e
A m p litu d e
F req u en cy = cyc le s p e r u n it o f tim e
Electromagnetic spectrum
(Fig. 13.14)
• Signals transmitted in the context of a Carrier Signal– Known frequency– Known amplitude
Signal Incompatibility
• Inside the computer must have discrete/digital
• Many existing communication lines are continuous/analog (especially in the last mile)
• Signal must be converted between digital/discrete and analog/continuous through modulation/demodulation.
• The function of a modem
1-bit
0-bit 0-bit
1-bit
As Signal Moves Over Line
• Signal degrades or loses strength.– Called attenuation
• Signal picks up noise.– EMI - Electromagmetic interference– Static– If not addressed, noise can overwhelm signal
• These limit the distance of some communications
Digital vs. Analog
• Analog– contiguous signal– amplify to boost
signal noise amplified, too noise accumulates
– filter known or predictable noise tape hiss
• Digital– discrete signal
digits (0, 1)– sample/retransmit
boosts signal automatically filters
most noise errors function of
sampling rate
Both digital and analog data are transmitted in the context of a carrier signal.
Networks
• A network consists of two or more computers linked by communication lines.
• Connectivity – the ability of a device or software to work with other devices and/or software over a network connection
• Each connected device is called a node
Local Area Network - LAN
• Small geographic scope• Computers in close proximity• Local communications
– no boosting or filtering
• Workstations
Wide Area Network - WAN
• Network of networks
• Computers geographically disbursed
• Long-distance communication– common carrier– boost and filter signal
• Enterprise networks– Intranet
• Supply chain integration– Extranet
• Global networks
Internetworking Hardware
• Use to connect multiple LANs or WANs
• Have intelligence to filter, route and do protocol conversion
• Examples– Bridges - Similar Networks– Gateways - Dissimilar networks– Routers– Switches
Bridges and Gateways
• A bridge links similar networks.
• A gateway links dissimilar networks.
ServerBridge
Gateway
Server
WorkstationWorkstation
Workstation
Server
WorkstationWorkstation
Workstation
WorkstationWorkstation
Workstation Workstation
Routers
• accept messages at one of several input ports and forward the message to the appropriate output port
In
Out
Router
Common Network Topologies
Ring
Bus
Star
Clients/Server Networks
File system
Printer
Server
Client Client
Client Client
Peer to Peer Networks
Filesystem
Filesystem
Filesystem
FilesystemPeer computer Peer computer
Peer computer
Peercomputer
Network Operating Systems• Client/server architecture LANs
– The system software runs on the server (The server’s operating system)
– Part of the NOS runs on each workstation• Software that handles communication between the workstation and
the NOS• Agent process on client• client’s link to network
– Examples• Novell NetWare• Windows 2000 Server• Windows NT
• Peer to Peer Networks– NOS is installed on each attached workstation– Runs on top of the local operating system
Networkoperating system Windows ME
Communicationsoftware
Server Client
Network
Message Delivery
• Each computer or terminal is a node
• Messages (signals) are either– Broadcast to all nodes – Or move from node to node (point to point)
• Topology or routing determines the route
• Protocols define the precise rules to follow for LAN access and message delivery (Many different protocol exist)
• Popular LAN Access control methods – Collision detection– Token passing
Network Access Control Methods
• Distributed Access Control– Token passing
• Circulating electronic token prevents collisions• Must possess the token to transmit a message• Random Access Control• Eliminates collisions
– CSMA/CD (collison detection)• “Listen” for quiet line (carrier signal); then send message• Collision occurs with simultaneous messages• Must wait and resend
• Three major standard protocols for LANs– Ethernet - (CSMA/CD, Star or Bus)– Token-Ring - (Token passing, Ring)– ARCnet - (Token passing, Star or bus)
Packet Switching
• Most popular type of message delivery
• Break message into packets
• Transmit packets independently
• Multiple messages share line
• Reassemble message at receiving end
Packet A1 Packet A2 Packet A3
Message A
Packet A1 Packet A2 Packet A3
Message A
Packet A3 Packet B2 Packet X3
Packet Z2 Packet A2 Packet Z1
Open Packet Y3 Packet B1
Packet A1 Packet Y1 Open
Packet Y2 Packet X2 Open
Packet Packet Packet X1
Packet Switching
• Packets can follow different routes to reach destination
• Error handling is important• Packets can arrive out of order• Individual packets may be lost
• Objectives– Deliver the message accurately– Efficient utilization of available bandwidth– Efficient error recovery
The Open Systems Interconnect (OSI) Model
OSI layer Responsibilities
Application Provides a logical link between an application program andthe lower-level protocols.
Presentation Performs necessary data representation and/or syntaxconversions; e.g., encryption/decryption.
Session Establishes, maintains, and terminates a connection.
Transport Breaks the message into packets. Ensures error free, end-to-end delivery of the complete message.
Network Determines the best route for sending a packet from thesource node to the destination node.
Data-link Formats a packet for transmission to the next node.
Physical Interfaces with the physical communication medium.
The first four layers work with the user's message.
The bottom three layers work with packets and control the network.
Message Flow PhysicalMedium
Application
Presentation
Session
Transport
Network
Data link
Physical
Display and manipulate worksheet
Decrypt and decompress worksheet
Drop connection on completion
Reassemble packets Verify delivery of
entire message
Reroute if necessary
Accept packets
Medium of transmission
Receiving computer
Excel worksheet created
Worksheet encrypted and compressed
Establish connection
Divide into packets and create messages
Determine packet routing
Transmit one packet to next node
Medium of transmission
Sending computer
Each level “talks to” the equivalent level on the other node.
Transmission errors call for retransmission of affected packet or packets.
The TCP/IP Model
• TCP/IP is the standard packet switching protocol for the Internet
Application layer
Transport layer
Internet layer
Network access layer
TCP/IP Layers
• Application layer– corresponds to OSI Application and Presentation layers– protocols that directly support application programs– protocols such as telnet, FTP, SMTP, DNS, POP, and
HTTP
• Transport layer– corresponds to OSI Session and Transport layers– TCP (Transmission Control Protocol)– creates packets and reassembles messages – guarantees delivery– Receiving end acknowledges each packet– Sending end re-sends unacknowledged packets
TCP/IP Layers (continued)
• Internet layer• corresponds to OSI Network layer• IP (Internet Protocol)• routes and delivers individual packets
• Network access layer– corresponds to OSI Data-link and Physical layer– This is where Ethernet, Token ring and other network
access protocols reside
TCP/IP Layers (continued)
FTP requestFTP
headerTCP
headerIP
header
TCPheader
FTP requestFTP
header
FTP requestFTPheader
FTP requestApplication program
Application layer
Transport layer (each packet)
Internet layer(each packet)
FTP requestFTPheader
TCPheader
IPheader
Networkheader
Network accesslayer
IP Address
• IP address– 32 bit number– dotted decimal format– 134.53.40.2
• Standards– IPV4 – current– IPV6 – proposed
• Internet protocol communication requires IP address
Assigning an IP Address
• All computers attached to the Internet must have an IP address.
• Static allocation– IP address established at installation– linked to specific computer’s Media Access Control
(MAC) address (ie. Ethernet address)
• Dynamic allocation– IP address allocated dynamically at login time– Must use a protocol such as Dynamic Host
Configuration Protocol (DHCP)
Domains
Domain Signifies Domain Signifies aero Air-transport industry au Australia biz Business organization br Brazil com US commercial ca Canada coop Coooeratives cn China edu US educational de Germany info Unrestricted fi Finland gov US government fr France mil US military gb Great Britian museum Museums in India name Individuals it Italy net US network jp Japan org US non-profit ru Russia pro Professionals za South Africa
Domain Name System (DNS)
• Accepts domain name
• Converts to IP address
• Network operating system routine on– each host– each server– each Internet service provider (ISP)– each network service provider (NSP )
Caching
• Domain name and IP address cached by all participating Domain Name Systems.
• Subsequent references use cached IP address.– Business student uses cob
Internet History
• 1960s Started as ARPANET (Advanced Research Projects Agency)
• 1986 NSFNET became internet Backbone (56Kbps)
• 1989 NSFNET upgraded to T1 1.44 (Mbps)
• 1991 NSFNET upgradet to T3 45 (Mbps)
• 1991 - First commercial traffic
• 1994 - First Web browser introduced
• 1995 NAPs Replaced NSFNET
• 1995 - Control turned over to independent governing bodies
Internet Terminology• Interconnect Level
• Any means for bandwidth providers to interconnect • Network Access Points (NAPS)• MAEs, FIXs and CIX (pseudo NAPs)
• Network Service Providers NSPs (National Backbone Providers)• Replaced NSFNET (old backbone network)• high-speed lines or series of connections that form the
major pathways of the internet• Regional Networks
– connect up to one or more national backbone providers• Local Internet Service Providers (ISPs)• Consumers and Businesses
– Servers - Contain information and are located on independently owned networks
Internet ArchitectureNetwork Service Provider (NSP)
NetworkAccess Point
(NAP)
NetworkAccess Point
(NAP)
Network Service Provider (NSP)
Regional InternetService Provider
Regional InternetService Provider
Regional InternetService Provider
Local ISP Local ISPLocal ISP
Internet Access• Access via local point of presence (POPs)
– by local call– broadband access into the home
• ISPs provide access (the “on-ramp”)
• POPs connect up the network hierarchy to an interconnect point
• Phone is most common for individuals
• Broadband (Cable and ADSL) are coming fast...and competing for market share.