Raj Jain
The Ohio State University
Columbus, OH 43210
Jain@CIS.Ohio-State.Edu
http://www.cis.ohio-state.edu/~jain/
The Ohio State University Raj Jain
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Overview
u ISO/OSI Reference Model
u TCP/IP Reference Model
u Differences between ISO and TCP
u Ethernet/IEEE 802.3 LANs
u Interconnecting Devices
All these concepts are taught in CIS677.
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ISO/OSI Reference Model
Application File transfer, Email, Remote Login
4 Presentation ASCII Text, Sound
Session Establish/manage connection
3 Transport End-to-end communication: TCP
2 Network Routing, Addressing: IP
Datalink Media Sharing: Ethernet
1 Physical How to transmit signal: Coding
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Layering
FTP Telnet Web Email
TCP UDP
IP IPX Same
Ethernet Token Ring Interfaces
Twisted Pair Fiber
u Protocols of each layer perform a set of functions
u All alternatives for a row have the same interfaces
u Choice of protocols at each layer is independent of
those of at other layers.
UDP = User Data Protocol, TCP = Transport Control
Protocol, IPX = Internetwork Packet Exchange Raj Jain
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Layered Packet Format
u Nth layer control info is passed as N-1th layer data.
FTP
FTP Data
Header
TCP
TCP Data
Header
IP
IP Data
Header
Ethernet Ethernet
Ethernet Data
Header Trailer
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Connection-Oriented vs Connectionless
u Connection-Oriented: Telephone System
u Path setup before data is sent
u Data need not have address. Circuit number is
sufficient.
u Connectionless: Postal System.
u Complete address on each packet
u The address decides the next hop at each router
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Internetworking Terms
u End-system: Host
u Network: Provides data transfer between end-systems
u Internet: A collection of networks
u Subnetwork: Each component of an internet.
Usually one LAN
FTP Telnet SMTP FTP Telnet SMTP
Host A Host B
Subnet Subnet
Router
1 2
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TCP/IP Reference Model
u TCP = Transport Control Protocol
u IP = Internet Protocol (Routing)
TCP/IP Ref Model TCP/IP Protocols OSI Ref Model
Application
Application FTP Telnet HTTP
Presentation
Session
Transport TCP UDP
Transport
Internetwork IP Network
Host to Ether Packet Point-to- Datalink
Network net Radio Point Physical
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OSI vs TCP Reference Models
u OSI introduced concept of services, interface,
protocols, layers. These were force-fitted to TCP later
⇒ It is not easy to replace protocols in TCP.
u In OSI, reference model was done before protocols.
In TCP, protocols were done before the model
u OSI: Standardize first, build later
TCP: Build first, standardize later
u OSI took too long to standardize.
TCP/IP was already in wide use by the time.
u OSI became too complex.
TCP/IP is not general. Ad hoc.
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Hierarchy
u Can directly use the services of a lower entity even if
it is not in an adjacent layer
u Control and data can be separate connections.
Control connections may have different reliability
requirements than data.
u Lower layer control information can be used for
higher layer control, e.g., lower layer close may close
all higher layers
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Internet Integrated Services Protocols
Multimedia Applications
RTP Control
Protocol (RTCP)
Real-time Transport TCP
Protocol (RTP)
Stream Transport UDP
2+ (ST2+) IP
Network Access
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Multiple Access Protocols
u Aloha at University of Hawaii:
Transmit whenever you like
Worst case utilization = 1/(2e) =18%
u CSMA: Carrier Sense Multiple Access
Listen before you transmit
u CSMA/CD: CSMA with Collision Detection
Listen while transmitting.
Stop if you hear someone else.
u Ethernet uses CSMA/CD.
Standardized by IEEE 802.3 committee.
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Original Ethernet Cabling Rules
u Thick coax
u Length of the cable is limited to 2.5 km, no more
than 4 repeaters between stations
u No more than 500 m per segment ⇒ 10Base5
u No more than 2.5 m between stations
u Transceiver cable limited to 50 m
Terminator
2.5m Repeater
Transceiver
500 m
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802.3 PHY Standards
u 10BASE5: 10 Mb/s over coaxial cable (ThickWire)
u 10BROAD36: 10 Mb/s over broadband cable,
3600 m max segments
u 10BASE2: 10 Mb/s over thin RG58 coaxial cable
(ThinWire), 185 m max segments
u 1BASE5: 1 Mb/s over 2 pairs of UTP
u 10BASE-T: 10 Mb/s over 2 pairs of UTP
u 10BASE-F: Fiber Optic inter-repeater link
(FOIRL), 10BASE-FL (link), 10BASE-FB
(backbone), or 10BASE-FP (Passive)
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Fast Ethernet Standards
u 100BASE-T4: 100 Mb/s over 4 pairs of CAT-3, 4, 5
u 100BASE-TX: 100 Mb/s over 2 pairs of CAT-5, STP
u 100BASE-FX: 100 Mbps CSMA/CD over 2 fibers
u 100BASE-X: 100BASE-TX or 100BASE-FX
u 100BASE-T: 100BASE-T4, 100BASE-TX, or
100BASE-FX Based on
100BASE-T FDDI Phy
100BASE-T4 100BASE-X 100BASE-T2
100BASE-TX 100BASE-FX
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Interconnection Devices
u Repeater: PHY device that restores data and
collision signals
u Hub: Multiport repeater + fault detection and
recovery
u Bridge: Datalink layer device connecting two or
more collision domains. MAC multicasts are
propagated throughout “extended LAN.”
u Router: Network layer device. IP, IPX, AppleTalk.
Does not propagate MAC multicasts.
u Switch: Multiport bridge with parallel paths
These are functions. Packaging varies.
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Interconnection Devices
Extended LAN
=Broadcast
LAN= domain
H H B H H
Collision Router
Domain
Application Application
Gateway
Transport Transport
Network Router Network
Datalink Bridge/Switch Datalink
Physical Repeater/Hub Physical
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Ethernet (IEEE 802) Address Format
u 48-bit:1000 0000 : 0000 0001 : 0100 0011 : 0000 0000
: 1000 0000 : 0000 1100 = 80:01:43:00:80:0C
Organizationally Unique
Identifier (OUI) 24 bits assigned by
Individual/ Universal/ OUI Owner
Group Local
1 1 22 24
u Multicast = “To all bridges on this LAN”
u Broadcast = “To all stations”
= 111111....111 = FF:FF:FF:FF:FF:FF
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Ethernet vs IEEE 802.3
IP IPX IP IPX
Logical Link Control (LLC)
Ethernet
Media Access Control (MAC)
u In 802.3, datalink was divided into two sublayers:
LLC and MAC
u LLC provides protocol multiplexing. MAC does not.
u MAC does not need a protocol type field.
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Ethernet Frame Format
u Ethernet IP IPX AppleTalk
Dest. Source
Type Info CRC
Address Address
6 6 2 4 Size in
bytes
u IEEE 802.3 IP IPX AppleTalk
Dest. Source
Length LLC Info Pad CRC
Address Address
6 6 2 Length 4
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Summary
u ISO/OSI reference model has seven layers.
TCP/IP Protocol suite has four layers.
u Ethernet/IEEE 802.3 uses CSMA/CD.
u Configuration rules depend upon physical medium
10Base5, 10Base2, 10Base-T, 100Base-TX, etc.
u Addresses: Local vs Global, Unicast vs Broadcast.
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Homework
u For each of the following addresses: indicate whether
it is a multicast and whether it is a locally assigned
address?
80:01:43:00:00:00
40:01:43:00:00:01
Were these addresses assigned by the same
manufacturer?
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