Download Network Layer and Path Determination

OSI Reference Model
1
Agenda




The Layered Model
Layers 1 & 2: Physical &
Data Link Layers
Layer 3: Network Layer
Layers 4–7: Transport,
Session, Presentation,
and Application Layers
2
The Layered Model
3
Layered Communication
Location A
I like
rabbits
Message
L: Dutch
Ik hou
van
konijnen
Information
for the
Remote
Translator
Fax #:--L: Dutch
Ik hou
van
konijnen
Information
for the
Remote
Secretary
Source: Tanenbaum, 1996
4
Layered Communication
Location B
Location A
J’aime
les lapins
I like
rabbits
Message
L: Dutch
Ik hou
van
konijnen
Information
for the
Remote
Translator
L: Dutch
Ik hou
van
konijnen
Information
for the
Remote
Secretary
Fax #:--L: Dutch
Ik hou
van
konijnen
Fax #:--L: Dutch
Ik hou
van
konijnen
5
Layered Communication
Location A
Layers
I like
rabbits
Message
L: Dutch
Ik hou
van
konijnen
Information
for the
remote
translator
Fax #:--L: Dutch
Ik hou
van
konijnen
Information
for the
remote
secretary
3
2
1
Location B
J’aime
les lapins
L: Dutch
Ik hou
van
konijnen
Fax #:--L: Dutch
Ik hou
van
konijnen
6
Why a Layered Network Model?
7
Application
6
Presentation
5
Session
4
Transport
3
Network
2
Data Link
1
Physical
• Reduces complexity (one big
problem to seven smaller
ones)
• Standardizes interfaces
• Facilitates modular
engineering
• Assures interoperable
technology
• Accelerates evolution
• Simplifies teaching and
learning
7
Devices Function at Layers
7
Application
6
Presentation
5
Session
4
Transport
3
Network
2
Data Link
1
Physical
NIC Card
Hub
8
Host & Media Layers
7
Application
6
Presentation
5
Session
4
Transport
3
Network
2
Data Link
1
Physical
}
}
Host layers: Provide
accurate data delivery
between computers
Media layers: Control
physical delivery of messages
over the network
9
Layer Functions
7
Application
Provides network services to
application processes (such as
electronic mail, file transfer, and
terminal emulation)
10
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
11
Layer Functions
7
Application
Network services to applications
6
Presentation
Data representation
5
Session
Inter-host communication
• Establishes, manages, and
terminates sessions between
applications
12
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
13
Layer Functions
7
Application
Network services to applications
6
Presentation
Data representation
5
Session
Inter-host communication
4
Transport
3
Network
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
Inter-host communication
4
Transport
3
Network
End-to-end connection
reliability
Addresses and best path
2
Data Link
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
Network services to applications
6
Presentation
Data representation
5
Session
Inter-host communication
4
Transport
3
Network
End-to-end connection
reliability
Addresses and best path
2
Data Link
Access to media
1
Physical
Binary transmission
• Wires, connectors, voltages,
data rates
16
Peer-to-Peer Communications
Host A
Host B
7
Application
Application
6
Presentation
Presentation
5
Session
Session
4
3
2
Transport
Network
Data Link
Segments
Packets
Frames
Bits
1
Physical
Transport
Network
Data Link
Physical
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Data Encapsulation
Host A
Application
Presentation
Session
} {
Data
Transport
Network
Data Link
Physical
Host B
Application
Presentation
Session
Transport
Network Data
Header
Frame Network
Header Header
Data
Network
Frame
Trailer
0101101010110001
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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Network Layer:
Path Determination
Which
Which Path?
Path?
• Layer 3 functions to find the best
path through the internetwork
23
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
1.2
2
1
1.3
3
1
2.1
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
1aceb0b.
(Mask 255.0.0.0)
Node
0000.0c00.6e25
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Network Layer
Protocol Operations
X
Y
C
C
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
Application
Presentation
Session
Transport
Network
Data Link
Physical
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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
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
A
A
Point-to-point or
circuit-switched
connection
Only a single network
connection with no need
for routing updates

Fixed route to address reflects
administrator’s knowledge
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
A
A
B
B
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
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
E0
To0
E1
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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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Transport Layer
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
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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
42
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
1 2 3 4 5 6 7
Receiver
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
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
•
•
login:
•
Text
Data
•
ASCII
EBCDIC
Encrypted
Graphics
Visual images
• Sound
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)
Others
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Summary



OSI reference model describes building blocks
of functions for program-to-program
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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