02 osi reference
TRANSCRIPT
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1999, Cisco Systems, Inc.www.cisco.com
OSI Reference Model
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CSE: Networking FundamentalsOSI Model 1999, Cisco Systems, Inc. www.cisco.com
Agenda
The Layered Model
Layers 1 & 2: Physical &Data Link Layers
Layer 3: Network Layer
Layers 47: Transport,Session, Presentation,
and Application Layers
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The Layered Model
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Layered Communication
Source: Tanenbaum, 199
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L: Dutch
Ik hou
van
konijnen
Fax #:---
L: Dutch
Ik hou
van
konijnen
Message
Information
for theRemote
Translator
Information
for theRemote
Secretary
Location A
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Layered Communication
I like
rabbits
L: Dutch
Ik hou
van
konijnen
L: Dutch
Ik hou
van
konijnen
Fax #:---
L: Dutch
Ik hou
van
konijnen
Fax #:---
L: Dutch
Ik houvan
konijnen
Jaime
les lapins
Information
for theRemote
Translator
Information
for theRemote
Secretary
Location A Location B
Message
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Layered Communication
I like
rabbits
L: Dutch
Ik hou
van
konijnen
L: Dutch
Ik houvan
konijnen
Fax #:---
L: Dutch
Ik hou
van
konijnen
Fax #:---
L: Dutch
Ik houvan
konijnen
Jaime
les lapins
Information
for theremote
translator
Information
for theremote
secretary
Location A Location B
1
2
3
Layers
Message
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Why a Layered Network Model?
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
Reduces complexity (one bigproblem to seven smallerones)
Standardizes interfaces
Facilitates modularengineering
Assures interoperabletechnology
Accelerates evolution Simplifies teaching and
learning
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Devices Function at Layers
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
NIC Card
Hub
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Host Layers
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
Host layers: Provideaccurate data delivery betwee
computers}
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Media Layers
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
Host layers:Provideaccurate data delivery betwee
computers
Media layers:Controlphysical delivery of messages
over the network}}
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Layer Functions
Provides network services to applicati
processes (such as electronic mail, file
transfer, and terminal emulation)
7 Application
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Layer Functions
Network services to applications
Ensures data is readable by
receiving system
Format of data
Data structures
Negotiates data transfer
syntax for application layer
7 Application
6 Presentation Data representation
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Layer Functions
Inter-host communication
Establishes, manages, andterminates sessions between
applications
7 Application
6 Presentation
5 Session
Network services to applications
Data representation
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Layer Functions
7 Application
6 Presentation
5 Session
Transport4
Inter-host communication
Network services to applications
Data representation
End-to-end connection reliability Concerned with data transport
issues between hosts
Data transport reliability
Establishes, maintains, and
terminates virtual circuits Fault detection and recovery
Information flow control
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Layer Functions
7 Application
6 Presentation
5 Session
Transport4
Network3
Inter-host communication
Network services to applications
Data representation
End-to-end connection reliability
Addresses and best path Provides connectivity and path
selection between two end
systems Domain of routing
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Layer Functions
7 Application
6 Presentation
5 Session
Transport4
Network3
Data Link2
Inter-host communication
Network services to applications
Data representation
End-to-end connection reliability
Addresses and best path
Access to media Provides reliable transfer of data
across media Physical addressing, network
topology, error notification, flow
control
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Layer Functions
7 Application
6 Presentation
5 Session
Transport4
Network3
Data Link2
Physical1
Inter-host communication
Network services to applications
Data representation
End-to-end connection reliability
Addresses and best path
Access to media
Binary transmission Wires, connectors, voltages,
data rates
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7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
Host A
Peer-to-Peer Communications
Application
Presentation
Session
Transport
Network
Data Link
PhysicalBits
Frames
Packets
Segments
Host B
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Data Encapsulation
Application
Presentation
Session
Transport
Network
Physical
Data Link
Application
Presentation
Session
Transport
Network
Physical
Data Link
Host A Host B
Data} {
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Data Encapsulation
Application
Presentation
Session
Transport
Network
Physical
Data Link
Application
Presentation
Session
Transport
Network
Physical
Data Link
Data} {DataNetwork
Header
Host A Host B
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Data Encapsulation
Application
Presentation
Session
Transport
Network
Physical
Data Link
Application
Presentation
Session
Transport
Network
Physical
Data Link
Data} {DataNetwork
Header
FrameHeader
Frame
TrailerDataNetworkHeader
Host A Host B
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Data Encapsulation
Application
Presentation
Session
Transport
Network
Physical
Data Link
Application
Presentation
Session
Transport
Network
Physical
Data Link
Data} {DataNetwork
Header
FrameHeader
Frame
TrailerDataNetworkHeader
0101101010110001
Host A Host B
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Layers 1 & 2:Physical & Data Link
Layers
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Physical and Logical Addressing
0000.0c12.3456
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MAC Address
24 bits
ROM
RAM
24 bits
0000.0c12. 3456
Serial NumberVendor Code
MAC address is burned into ROM on a
network interface card
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1999, Cisco Systems, Inc.www.cisco.com
Layer 3:
Network Layer
1999, Cisco Systems, Inc. www.cisco.com
N k P h D i i
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Network Layer: Path Determination
Which Path?Which Path?
Layer 3 functions to find the best
path through the internetwork
N t k L C i t P th
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Network Layer: Communicate Path
1
2
3
4
5
6
7
8
9
1011
Addresses represent the path of media
connections
Routing helps contain broadcasts
Add i N t k d N d
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AddressingNetwork and Node
Network Node
1
2
123
1
3 1
1.1
2.1
3.1
1.2
1.3
Network addressPath part used by the router Node addressSpecific port or device on the network
P t l Add i V i ti
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Protocol Addressing Variations
Network Node
1 1
GeneralExample
Network Host
10. 8.2.48
TCP/IPExample (Mask 255.0.0.0)
Network Node
1aceb0b. 0000.0c00.6e25
Novell IPXExample
Network Layer
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Network LayerProtocol Operations
Each router provides its services tosupport upper layer functions
X Y
AA
CC
Network Layer
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Network LayerProtocol Operations
Each router provides its services tosupport upper layer functions
BB
X Y
AA
CC
Presentation
Data Link
Physical
Data Link
Physical
Router A Router B Router C
Data Link
Physical
Data LinkNetworkTransportSessionPresentationApplication
Physical
Host X Host Y
Data LinkNetworkTransportSession
Application
Physical
Network Network Network
M ltiprotocol Ro ting
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Multiprotocol Routing
IP 15.17.132.6
IP 15.16.42.8
IP 15.16.50.3
Routing Tables
IP
TokenRing
TokenRing
AppleTalk 200.167
AppleTalk 100.110
Apple
IPX 4b.0800.0121.ab13
IPX 3a.0800.5678.12abNovell
DECnet 5.8
DECnet 10.1
DEC
VAX
VAX
Routers pass traffic from all routed protocols over the internetwork
Routed Versus Routing Protocol
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Routed Versus Routing Protocol
Routed protocolused between
routers to direct
user traffic
1.02.03.0
1.12.13.1
DestinationNetwork
NetworkProtocol
Protocol Name
Examples: IP, IPX,
AppleTalk, DECnet Exit Portto Use
Routed Versus Routing Protocol
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Routed Versus Routing Protocol
Routed protocolused betweenrouters to directuser traffic
Examples: IP, IPX,
AppleTalk, DECnet
Routing protocolused only betweenrouters to maintain
routing tablesExamples: RIP, IGRP, OSPF
Static Versus Dynamic Routes
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Static Versus Dynamic Routes
Uses a protocol route that a networkadministrator enters into the router
Static Route
Uses a route that a network protocoladjusts automatically for topology ortraffic changes
Dynamic Route
Static Route Example
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Static Route Example
Point-to-point orcircuit-switched
connection
Stub network
Only a single networkconnection with no need
for routing updates
AA
BB
Fixed route to address reflectsadministrators knowledge
Adapting to Topology Change
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Adapting to Topology Change
AA BB
CCDD
Can an alternate route substitutefor a failed route?
Adapting to Topology Change
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Adapting to Topology Change
AA BB
CCDDXX
Adapting to Topology Change
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Adapting to Topology Change
AA BB
CCDDXX
Can an alternate route substitutefor a failed route?
YesWith dynamic routing enabled
LAN-to-LAN Routing Example
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LAN-to-LAN Routing Example
Network 1
Network 3
E0E1 To0
Host 5Host 4
Network 2
TokenRing
802.3 Net 2, Host 5
Routing Table
DestinationNetwork
OutgoingInterface
123
E0To0E1
LAN-to-LAN Routing
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LAN-to-LAN Routing
Network 1
Network 3
E0E1 To0
Host 5Host 4
Network 2
TokenRing
802.3 Net 2, Host 5
Routing Table
Net 2, Host 5802.5
From LAN to LAN
DestinationNetwork
OutgoingInterface
123
E0To0E1
LAN-to-WAN Routing
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LAN-to-WAN Routing
Data
1.3 2.4 Data
AA
TokenRing
2.4
Token Ring 1.3 2.4 Data
BB
1.3FromLAN
FrameRelay
ToWAN
ToLAN
LAN-to-WAN Routing
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LAN-to-WAN Routing
Data
1.3 2.4 Data
AA
TokenRing
2.4
Token Ring 1.3 2.4 Data
BB
1.3FromLAN
Frame Relay 1.3 2.4 DataFrameRelay
1.3 2.4 Data
ToWAN
ToLAN
LAN-to-WAN Routing
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LAN to WAN Routing
Data
1.3 2.4 Data
AA
TokenRing
2.4
Token Ring 1.3 2.4 Data
BB
1.3FromLAN
Frame Relay 1.3 2.4 DataFrameRelay
1.3 2.4 Data
ToWAN
Ethernet
Data
1.3 2.4 Data
1.3 2.4 Data
ToLAN
1.3 2.4 Data
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Layers 47:Transport, Session,
Presentation, andApplication Layers
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Transport Layer
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Transport Layer
Segments upper-layer applications Establishes an end-to-end connection
Sends segments from one end host to another
Optionally, ensures data reliability
Transport LayerS t U L A li ti
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Segments Upper-Layer Applications
Electronic
Mail
File
Transfer
Application
Presentation
Session
Segments
DataApplication
PortTransport Data
Application
Port
Terminal
Session
Transport LayerE t bli h C ti
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Establishes Connection
Synchronize
Synchronize
Acknowledge
Negotiate Connection
Receiver
Data Transfer
Connection Established
(Send Segments)
Sender
Transport LayerS d S t ith Fl C t l
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Sends Segments with Flow Control
Transmit
Buffer FullNot Ready
StopProcessSegments
Buffer OKReadyGo
Resume Transmission
ReceiverSender
Transport LayerR li bilit ith Wi d i
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Reliability with Windowing
Window Size = 1
Sender
Send 1 Receive 1
Receiver
Ack 2
Send 2 Receive 2Ack 3
Sender
Send 1
Send 2Receive 1Receive 2
Receiver
Window Size = 3
Send 3 Receive 3Ack 4
Send 4
Transport LayerAn Acknowledgement Technique
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An Acknowledgement Technique
Sender Receiver
Send 2Send 1
Send 3
Ack 4
Send 5Send 4
Send 6
Ack 5Send 5
Ack 7
1 2 3 4 5 6 7 1 2 3 4 5 6 7
Transport to Network Layer
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p y
End-to-End Segments
Routed Packets
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Presentation Layer
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y
ASCIIEBCDICEncrypted
Text Data
login:
PICTTIFFJPEGGIF
Graphics Visual images
Sound
VideoMPEGQuickTime
MIDI
Provides code formatting andconversion for applications
Application Layer
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pp y
Word Processor
Presentation Graphics
Spreadsheet
Database
Design/ManufacturingProject Planning
Others
COMPUTERAPPLICATIONS
Electronic Mail
File Transfer
Remote Access
Client-Server ProcessInformation Location
Network Management
Others
NETWORKAPPLICATIONS INTERNETWORKAPPLICATIONS
Electronic Data Interchange
World Wide Web
E-Mail Gateways
Special-Interest Bulletin Boards
Financial Transaction Services
Internet Navigation Utilities
Conferencing (Voice, Video, Data)
Others
Internetwork applicationscan extend beyond theenterprise (i.e., to suppliers, etc.)
Summary
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y
OSI reference model describes buildingblocks of functions for program-to-program communications between
similar or dissimilar hosts Layers 47 (host layers) provide accurate
data delivery between computers
Layers 13 (media layers) control
physical delivery of data over the network
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Presentation_ID 1999, Cisco Systems, Inc. www.cisco.com