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Basic Communications Basic Communications ModelModelStandards are needed at all Standards are needed at all LayersLayers
User Layer
Application Layer
Computer (Transport) Layer
Transmission Layer
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Subnet Subnet LayerLayer
1
2
3
Station A Station B
Transmission of Messages1. Within a Single Subnet, or
2. in Point-to-Point Links Between Subnets
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1 2
3
Internet LayerInternet LayerStation A Station B
Routing of MessagesAcross multiple subnets in an internet
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2
34
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InternettingInternettingStation A Station B
internet: collection of subnets such that any station on any subnet can communicate with any other station on any other subnet simply by giving the
internet address of the other station.
1
2
34
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Layering in Major Layering in Major ArchitecturesArchitectures
Basic Model
Application
Computer(Transport)
Internet
TCP/IP
Internet
IPX/SPX
Internet
Subnet(OSI)
OSI
Application (7)
Presentation (6)
Session (5)
Transport (4)
Network (3):Internet &
Subnet
Data Link (2)
Application Application
Transport:TCP, etc.
Complex:SPX, etc.
Physical (1)
Subnet(OSI)
Subnet(OSI)
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OSI OSI ArchitectureArchitecture
Reference Model for Open Reference Model for Open Systems Interconnection (OSI)Systems Interconnection (OSI)
Standards AgenciesStandards Agencies• ISO (computers)ISO (computers)• Don’t confuse OSI and ISO!Don’t confuse OSI and ISO!• ITU-T (telecommunications)ITU-T (telecommunications)
De jure standards De jure standards (official/open)(official/open)
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OSI OSI ArchitectureArchitecture
Standards are sophisticatedStandards are sophisticated Sophistication brings complexitySophistication brings complexity
• Slow standards developmentSlow standards development
• Products are late to market and Products are late to market and expensiveexpensive
• The result: low acceptance of OSI The result: low acceptance of OSI standards in generalstandards in general
But OSI dominates at the single network But OSI dominates at the single network (subnet) transmission layer(subnet) transmission layer
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Physical Layer (OSI Physical Layer (OSI Layer 1)Layer 1)
Physical transmission standardsPhysical transmission standards PhysicalPhysical
• ConnectorConnector• Transmission mediaTransmission media
ElectricalElectrical• Voltage levelsVoltage levels• Meanings of various voltage levelsMeanings of various voltage levels
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The Data Link Layer (OSI The Data Link Layer (OSI Layer 2)Layer 2)
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Data Link Layer (OSI Data Link Layer (OSI Layer 2)Layer 2)
Organize data for transmission over a data linkOrganize data for transmission over a data link• Data packages at various layers are called protocol Data packages at various layers are called protocol
data units (PDUs)data units (PDUs)• The Data Link Layer PDU is called a frameThe Data Link Layer PDU is called a frame• Organization allows addressing on shared data linksOrganization allows addressing on shared data links• Organization allows error checking and other meta Organization allows error checking and other meta
delivery processesdelivery processes Media Access ControlMedia Access Control
• Controls when stations may transmit in shared Controls when stations may transmit in shared media LANs and other shared data linksmedia LANs and other shared data links
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TCP/IP ArchitectureTCP/IP Architecture
Internet Engineering Task Force Internet Engineering Task Force (IETF)(IETF)• Of the Internet SocietyOf the Internet Society
De jureDe jure (official/open) (official/open)
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TCP/IP ArchitectureTCP/IP Architecture
Standards are simpleStandards are simple• Often have “Simple” in the nameOften have “Simple” in the name• Standards and products are fast to marketStandards and products are fast to market• Products are inexpensive and fast to marketProducts are inexpensive and fast to market
Widely UsedWidely Used• On the InternetOn the Internet• In many corporate networksIn many corporate networks
• Dominates at internet and transport Dominates at internet and transport layerslayers
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IPX/SPXIPX/SPX
Novell CorporationNovell Corporation De facto (proprietary/closed)De facto (proprietary/closed) Used only in Novell NetWare PC Used only in Novell NetWare PC
networksnetworks• But NetWare dominates PC But NetWare dominates PC
networkingnetworking• Second most widely used architecture Second most widely used architecture
at transport layerat transport layer
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SNASNA
Systems Network ArchitectureSystems Network Architecture IBM CorporationIBM Corporation De facto (proprietary/closed)De facto (proprietary/closed) Dominates in mainframe Dominates in mainframe
communicationcommunication• On IBM mainframe systemsOn IBM mainframe systems• On mainframe systems of other On mainframe systems of other
vendorsvendors
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Transport-Layer Transport-Layer TrafficTraffic
TCP/IPTCP/IP 38%38% RisingRising IPX/SPX (NetWare)IPX/SPX (NetWare) 34%34% FallingFalling
SNA (Mainframes)SNA (Mainframes) 18%18% Other (including OSI)Other (including OSI) 10% 10% TotalTotal 100%100%
Source: Molloy (1994), 1993 data
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Transmission Transmission SpeedsSpeeds
Bit: single 1 or 0Bit: single 1 or 0 Transmission speed is measured in Transmission speed is measured in
bits per second (bps)bits per second (bps)• Duration of a single bitDuration of a single bit• Not velocity of propagationNot velocity of propagation
101101000011101010100101111010101
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Notations for Transmission Notations for Transmission SpeedSpeed
Prefix Use Metric Meaning Example Interpretation
kilo kbps 1,000 64 kbps 64,000 bps
Mega Mbps 1 million 1.544 Mbps 1,544,000 bps
Giga Gbps 1billion 2.4 Gbps 2,400,000,000 bps
Tera Tbps 1 trillion 2 Tbps 2,000,000,000,000
Note upper case T
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LANs, MANs, & LANs, MANs, & WANsWANs
LANLAN• Local area networkLocal area network• Single office, building, campusSingle office, building, campus• 10 Mbps to 100 Mbps to the desktop 10 Mbps to 100 Mbps to the desktop
commoncommon• 1 Gbps coming1 Gbps coming
Will carry most traffic, because Will carry most traffic, because most traffic is localmost traffic is local
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PC Networking on a small PC Networking on a small LANLAN
Network InterfaceCard (NIC)
In each PC
Each client and server needs a NIC rather than a modem
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PC Networking on a small PC Networking on a small LANLAN
Wiring Hub15 to 50 cm (6 to 19 inches)
Usually, a wiring hub connects the computers together
Telephone wiring
and RJ-45 plugs
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LANs, MANs, & LANs, MANs, & WANsWANs
WANWAN• Wide area networkWide area network• Intercity, internationalIntercity, international• 9,600 bps to 1 Mbps common to the desktop9,600 bps to 1 Mbps common to the desktop• Links with higher speed are usually shared Links with higher speed are usually shared
(multiplexed) by several desktops(multiplexed) by several desktops Emerged before LANs, due to high cost Emerged before LANs, due to high cost
of long-distance telephone chargesof long-distance telephone charges