Download Network Layer and Path Determination

OSI Reference Model
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© 1999, Cisco Systems, Inc.
Agenda
• The Layered Model
• Layers 1 & 2: Physical &
Data Link Layers
• Layer 3: Network Layer
• Layers 4–7: Transport,
Session, Presentation,
and Application Layers
CSE: Networking Fundamentals—OSI Model
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The Layered Model
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Layered Communication
Location A
I like
rabbits
L: Dutch
Ik hou
van
konijnen
Fax #:--L: Dutch
Ik hou
van
konijnen
CSE: Networking Fundamentals—OSI Model
Message
Information
for the
Remote
Translator
Information
for the
Remote
Secretary
Source: Tanenbaum, 1996
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Layered Communication
Location B
Location A
I like
rabbits
L: Dutch
Ik hou
van
konijnen
Fax #:--L: Dutch
Ik hou
van
konijnen
CSE: Networking Fundamentals—OSI Model
J’aime
les lapins
Message
Information
for the
Remote
Translator
L: Dutch
Ik hou
van
konijnen
Information
for the
Remote
Secretary
Fax #:--L: Dutch
Ik hou
van
konijnen
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Layered Communication
Location A
I like
rabbits
L: Dutch
Ik hou
van
konijnen
Fax #:--L: Dutch
Ik hou
van
konijnen
CSE: Networking Fundamentals—OSI Model
Layers
Message
Information
for the
remote
translator
Information
for the
remote
secretary
Location B
3
J’aime
les lapins
2
L: Dutch
Ik hou
van
konijnen
1
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Fax #:--L: Dutch
Ik hou
van
konijnen
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2-6
Why a Layered Network Model?
7
Application
6
Presentation
5
Session
4
Transport
3
Network
2
Data Link
1
Physical
CSE: Networking Fundamentals—OSI Model
• Reduces complexity (one big
problem to seven smaller
ones)
• Standardizes interfaces
• Facilitates modular
engineering
• Assures interoperable
technology
• Accelerates evolution
• Simplifies teaching and
learning
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2-7
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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2-8
Host Layers
7
Application
6
Presentation
5
Session
4
Transport
3
Network
2
Data Link
1
Physical
CSE: Networking Fundamentals—OSI Model
}
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Host layers: Provide
accurate data delivery between
computers
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Media Layers
7
Application
6
Presentation
5
Session
4
Transport
3
Network
2
Data Link
1
Physical
CSE: Networking Fundamentals—OSI Model
}
}
Host layers: Provide
accurate data delivery between
computers
Media layers: Control
physical delivery of messages
over the network
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Layer Functions
7
Application
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Provides network services to application
processes (such as electronic mail, file
transfer, and terminal emulation)
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Layer Functions
7
Application
Network services to applications
6
Presentation
Data representation
• Ensures data is readable by
receiving system
• Format of data
• Data structures
• Negotiates data transfer
syntax for application layer
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Layer Functions
7
Application
Network services to applications
6
Presentation
Data representation
5
Session
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Inter-host communication
• Establishes, manages, and
terminates sessions between
applications
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Layer Functions
7
Application
Network services to applications
6
Presentation
Data representation
5
Session
4
Transport
Inter-host communication
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
Network services to applications
6
Presentation
Data representation
5
Session
4
Transport
3
Network
Inter-host communication
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
Network services to applications
6
Presentation
Data representation
5
Session
4
Transport
3
Network
Addresses and best path
2
Data Link
Access to media
Inter-host communication
End-to-end connection reliability
• Provides reliable transfer of data
across media
• Physical addressing, network
topology, error notification, flow
control
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Layer Functions
7
Application
Network services to applications
6
Presentation
Data representation
5
Session
4
Transport
3
Network
Addresses and best path
2
Data Link
Access to media
1
Physical
Binary transmission
• Wires, connectors, voltages,
data rates
CSE: Networking Fundamentals—OSI Model
Inter-host communication
End-to-end connection reliability
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Peer-to-Peer Communications
Host A
Host B
7
Application
Application
6
Presentation
Presentation
5
Session
Session
4
Transport
3
Network
Segments
Packets
Frames
2
Data Link
1
Physical
CSE: Networking Fundamentals—OSI Model
Transport
Network
Data Link
Bits
Physical
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Data Encapsulation
Host A
Host B
Application
Application
Presentation
Session
Transport
} {
Data
Presentation
Session
Transport
Network
Network
Data Link
Data Link
Physical
Physical
CSE: Networking Fundamentals—OSI Model
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Data Encapsulation
Host A
Host B
Application
Application
Presentation
Session
Transport
Network
} {
Data
Network Data
Header
Presentation
Session
Transport
Network
Data Link
Data Link
Physical
Physical
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Data Encapsulation
Host A
Host B
Application
Application
Presentation
Session
Transport
Network
Data Link
} {
Data
Network Data
Header
Frame Network
Header Header
Data
Physical
CSE: Networking Fundamentals—OSI Model
Presentation
Session
Transport
Network
Frame
Trailer
Data Link
Physical
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Data Encapsulation
Host A
Host B
Application
Application
Presentation
Session
Transport
Network
Data Link
Physical
CSE: Networking Fundamentals—OSI Model
} {
Data
Network Data
Header
Frame Network
Header Header
Data
Session
Transport
Network
Frame
Trailer
0101101010110001
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Presentation
Data Link
Physical
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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
24 bits
Vendor Code
Serial Number
0000.0c12. 3456
ROM
RAM
• MAC address is burned into ROM on a
network interface card
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Layer 3:
Network Layer
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© 1999, Cisco Systems, Inc.
Network Layer: Path Determination
Which
Which Path?
Path?
• Layer 3 functions to find the best
path through the internetwork
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Network Layer: Communicate Path
5
2
4
9
6
8
10
1
11
3
7
• Addresses represent the path of media
connections
• Routing helps contain broadcasts
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Addressing—Network and Node
Network
Node
1
1
2
3
2
1
3
1
2.1
1.2
1.3
1.1
3.1
• Network address—Path part used by the router
• Node address—Specific port or device on the network
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Protocol Addressing Variations
General
Example
Network
Node
1
1
TCP/IP
Example
Network
Host
10.
8.2.48
Novell IPX
Example
Network
CSE: Networking Fundamentals—OSI Model
1aceb0b.
(Mask 255.0.0.0)
Node
0000.0c00.6e25
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Network Layer
Protocol Operations
X
C
C
Y
A
A
• Each router provides its services to
support upper layer functions
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Network Layer
Protocol Operations
X
C
C
Y
A
A
B
B
Host X
Application
Presentation
Session
Transport
Network
Data Link
Physical
Host Y
Router A
Router B
Router C
Network
Data Link
Physical
Network
Data Link
Physical
Network
Data Link
Physical
• Each router provides its services to
support upper layer
functions
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Application
Presentation
Session
Transport
Network
Data Link
Physical
2-32
Multiprotocol Routing
Routing Tables
IPX 3a.0800.5678.12ab
Novell Apple
IPX 4b.0800.0121.ab13
IP 15.16.50.3
IP
DEC
Token
Ring
AppleTalk 100.110
VAX
DECnet 5.8
Token
Ring
VAX
IP 15.16.42.8
AppleTalk 200.167
DECnet 10.1
IP 15.17.132.6
• Routers pass traffic from all routed protocols over the internetwork
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Routed Versus Routing Protocol
• Routed protocol
used between
routers to direct
user traffic
Examples: IP, IPX,
AppleTalk, DECnet
Network
Protocol
Protocol Name
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Destination Exit Port
Network
to Use
1.0
2.0
3.0
1.1
2.1
3.1
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Routed Versus Routing Protocol
• Routed protocol
used between
routers to direct
user traffic
Examples: IP, IPX,
AppleTalk, DECnet
• Routing protocol
used only between
routers to maintain
routing tables
Examples: RIP, IGRP, OSPF
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Static Versus Dynamic Routes
Static Route
Uses a protocol route that a network
administrator enters into the router
Dynamic Route
Uses a route that a network protocol
adjusts automatically for topology or
traffic changes
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Static Route Example
Point-to-point or
circuit-switched
connection
A
A
Only a single network
connection with no need
for routing updates
• Fixed route to address reflects
administrator’s knowledge
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B
B
“Stub” network
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Adapting to Topology Change
A
A
B
B
D
D
C
C
• Can an alternate route substitute
for a failed route?
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Adapting to Topology Change
B
B
A
A
X
D
D
CSE: Networking Fundamentals—OSI Model
C
C
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Adapting to Topology Change
B
B
A
A
X
D
D
C
C
• Can an alternate route substitute
for a failed route?
Yes—With dynamic routing enabled
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LAN-to-LAN Routing Example
Network 2
Network 3
Host 4
Network 1
E0
E1
To0
Token
Ring
Host 5
802.3 Net 2, Host 5
Routing Table
Destination Outgoing
Network
Interface
1
2
3
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E0
To0
E1
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LAN-to-LAN Routing
From LAN
to LAN
Network 2
Network 3
Host 4
Network 1
E0
E1
Token
Ring
To0
Host 5
802.5 Net 2, Host 5
802.3 Net 2, Host 5
Routing Table
Destination Outgoing
Network
Interface
1
2
3
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E0
To0
E1
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LAN-to-WAN Routing
Data
From
LAN
1.3 2.4 Data
1.3
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Token Ring
1.3 2.4 Data
A
A
To
WAN
To
LAN
Token
Ring
Frame
Relay
2.4
B
B
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LAN-to-WAN Routing
Data
From
LAN
1.3 2.4 Data
1.3
Token
Ring
Token Ring
1.3 2.4 Data
1.3 2.4 Data
A
A
To
WAN
To
LAN
CSE: Networking Fundamentals—OSI Model
Frame
Relay
2.4
Frame Relay 1.3 2.4 Data
B
B
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LAN-to-WAN Routing
Data
From
LAN
1.3 2.4 Data
1.3
Token
Ring
Token Ring
1.3 2.4 Data
1.3 2.4 Data
A
A
To
WAN
Frame
Relay
Frame Relay 1.3 2.4 Data
1.3 2.4 Data
To
LAN
2.4
B
B
Ethernet
1.3 2.4 Data
1.3 2.4
Data
Data
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Layers 4–7:
Transport, Session,
Presentation, and
Application Layers
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© 1999, Cisco Systems, Inc.
Transport Layer
•
•
•
•
Segments upper-layer applications
Establishes an end-to-end connection
Sends segments from one end host to another
Optionally, ensures data reliability
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Transport Layer—
Segments Upper-Layer Applications
Application
Presentation
Electronic
Mail
File
Transfer
Terminal
Session
Session
Transport
Application
Port
Data
Application
Port
Data
Segments
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Transport Layer—
Establishes Connection
Sender
Receiver
Synchronize
Negotiate Connection
Synchronize
Acknowledge
Connection Established
Data Transfer
(Send Segments)
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Transport Layer—
Sends Segments with Flow Control
Transmit
Sender
Stop
Go
Receiver
Not Ready
Buffer Full
Process
Segments
Ready
Buffer OK
Resume Transmission
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Transport Layer—
Reliability with Windowing
• Window Size = 1
Send 1
Sender
Receive 1
Ack 2
Receive 2
Ack 3
Send 2
Receiver
• Window Size = 3
Sender
Send 1
Send 2
Send 3
Receive 1
Receive 2
Receive 3
Ack 4
Receiver
Send 4
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Transport Layer—
An Acknowledgement Technique
Sender
Receiver
1 2 3 4 5 6 7
1 2 3 4 5 6 7
Send 1
Send 2
Send 3
Ack 4
Send 4
Send 5
Send 6
Ack 5
Send 5
CSE: Networking Fundamentals—OSI Model
Ack 7
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Transport to Network Layer
End-to-End Segments
Routed Packets
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Session Layer
•
•
•
•
•
•
Network File System (NFS)
Structured Query Language (SQL)
Remote-Procedure Call (RPC)
X Window System
AppleTalk Session Protocol (ASP)
DEC Session Control Protocol (SCP)
Service Request
Service Reply
• Coordinates applications as
they interact on different hosts
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Presentation Layer
•
•
•
Text
Data
ASCII
EBCDIC
Encrypted
login:
•
• Sound
Graphics
Visual images
PICT
TIFF
JPEG
GIF
MIDI
• Video
MPEG
QuickTime
• Provides code formatting and
conversion for applications
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Application Layer
COMPUTER
APPLICATIONS
Word Processor
NETWORK
APPLICATIONS
INTERNETWORK
APPLICATIONS
Presentation Graphics Electronic Mail
Spreadsheet
File Transfer
Electronic Data Interchange
Database
Remote Access
World Wide Web
Design/Manufacturing
Client-Server Process
E-Mail Gateways
Project Planning
Information Location
Special-Interest Bulletin Boards
Others
Network Management
Financial Transaction Services
Others
Internet Navigation Utilities
Conferencing (Voice, Video, Data)
• Internetwork applications
Others
can extend beyond the
enterprise (i.e., to suppliers, etc.)
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Summary
• OSI reference model describes building
blocks of functions for program-toprogram communications between
similar or dissimilar hosts
• Layers 4–7 (host layers) provide accurate
data delivery between computers
• Layers 1–3 (media layers) control
physical delivery of data over the network
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Presentation_ID
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