OSI (Open Systems Interconnection) Protocol Layers

1-3
In a Technical
Sense ...
In a Practical
Sense ...
What the
OSI Protocol
Layers
Do
Layer
End User Services
E-Mail, File Transfer,
General Services
Code Conversion,
Compression, Encryption
Ease of Use
Establishes Connections
End-to-End Integrity
Acknowledgement
Network
Routing in the Network
Logical Channel Control
Data Link
Point-to-Point Integrity
Framing, Error Control
Transports Bits
Signal Propagation
Session
Transport
Physical
Mostly
Hardware
Presentation
Mostly Software
Application
1-4
OSI Layer 1: Physical
Application
Application
Presentation
Presentation
Session
Session
Transport
Transport
Network
Network
Data Link
Physical
Mechanical
 Electrical
 Functional
 Procedural

Data Link
Physical
1-5
OSI Layer 2: Data Link
Application
Application
Presentation
Presentation
Session
Session
Transport
Network
Data Link
Physical

Frame structure

Error control

Synchronization

Sequencing

Flow control
Transport
Network
Data Link
Physical
1-6
OSI Layer 3: Network
Application
Application
Presentation

Network
routing
Session

Establishing

Maintaining
Transport

Terminating
connections
Network

Flow control
Presentation
Session
Transport
Network
Data Link
Data Link
Physical
Physical
1-7
OSI Layer 4: Transport
Application
Application
Presentation
Presentation
Session

End-to-end
data integrity
Transport

Flow control
Session
Transport
Network
Network
Data Link
Data Link
Physical
Physical
1-8
OSI Layer 5: Session
Application
Presentation
Session

End-to-end
session
integrity

Flow control

Recovery/
restart
Application
Presentation
Session
Transport
Transport
Network
Network
Data Link
Data Link
Physical
Physical
1-9
OSI Layer 6: Presentation
Application
Application
Presentation

Platform
independence
Session

Form/syntax
translation
Presentation
Session
Transport
Transport
Network
Network
Data Link
Data Link
Physical
Physical
1-10
OSI Layer 7: Application
Application
Presentation
Session
Transport


Application
interface
standardization
TFTP, SMTP,
Telnet directory
services, and
message
handling
Application
Presentation
Session
Transport
Network
Network
Data Link
Data Link
Physical
Physical
Comparing the OSI Model to Other
OSI
IP
IPX
X.25
Frame Relay
Protocols
7 Application
6 Presentation
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5
Session
4
Transport
TCP/UDP
IPX/SPX
3
Network
IP
IPX
2
Data Link
1
Physical
Network
Interface
Network
Interface
X.25
LAPB
Frame Relay
Physical
Physical
1-12
1
The Networked OSI Model
7 Application
6 Presentation
5 Session
4 Transport
Application Protocols
Presentation Protocols
Session Protocols
Transport Protocols
2
7 Application
6 Presentation
5 Session
4 Transport
3 Network
Network Protocols
3 Network
2 Data Link
Data Link Protocols
2 Data Link
1 Physical
Physical Protocols
1 Physical
1-13
OSI Data Structures
Host A
Peer
Protocols
Host B
D = Data
H = Header
T = Trailer
H7 D 7 Application Protocol 7 H7 D
H6 H7 D 6 Presentation Protocol 6 H6 H7 D
H5 H6 H7 D 5
H4 H5 H6 H7 D 4
H3 H4 H5 H6 H7 D 3
Session Protocol
Transport Protocol
Network Protocol
Packet or Datagram
5 H5 H6 H7 D
4 H4 H5 H6 H7 D
3 H3 H4 H5 H6 H7 D
Packet or Datagram
H2 H3 H4 H5 H6 H7 D T 2
Data Link Protocol
Frame
2 H2 H3 H4 H5 H6 H7 D T
Frame
H2 H3 H4 H5 H6 H7 D T 1
Physical Protocol
Frame
1 H2 H3 H4 H5 H6 H7 D T
Frame
H2 H3 H4 H5 H6 H7 D T
Frames as bits 10110110
1-14
Layer Functions
Frame
Header
H3
H4
H5
H6
H7
Data
Frame
Trailer
7 Application
6 Presentation FTP, TFTP, Telnet, DHCP
5 Session
4 Transport
TCP, UDP, SPX, IPX
3 Network
IP, IPX, X.25
2 Data Link
HDLC, SDLC, Frame Relay, Ethernet, Token Ring
1 Physical
No Header
1-15
Physical
LAN Addressing WAN
802.2 LLC
Data Link
Physical
E
t
h
e
r
n
e
t
S
Dial
D
on
Demand L
C
8
0
2
.
3
8
0
2
.
5
F
D
D
I
ISDN
H
D X.25 Frame
L Link Relay PPP
C
V.24
EIA/TIA-232
G.703
V.35
EIA/TIA-449
EIA-530
HSSI
1-16
Layer 2 — Data Link Layer
Frame
Header
H3
H4
H5
H6
H7
Layer 2
Data Link Layer
LLC (Logical Link Control)
MAC (Media Access Control)
Data
Frame
Trailer
1-17
MAC Address
Source
Start
Delimiter Address
Dest.
Address
Control
0000.0C A4.632B
Reserved for
Manufacturer
Serial Number
of Card
Hex
1 hex value = 4 bits
12 hex values = 48 bits
Data
End
Frame
End
Delimiter
1-18
Layer 3 — Network Layer
Frame
Header
DSAP
H3
H4
H5
H6
IP Address
32 Bits
H7
Data
Frame
Trailer
Network
Node
Layer 3 Header
Network Layer
IPX Address
80 Bits
Network
Node
1-19
Directions to My House
1
2
1-20
Network Addressing
E x a m p le T yp e
N e tw o rk
Node
N e tw o rk O n ly
1
0
N e tw o rk a n d N o d e
1
4
N e tw o rk O n ly
10.
0 .0 .0
N e tw o rk a n d N o d e
10.
2 .3 .4
N e tw o rk O n ly
2 b e fd 0 c .
0 0 0 0 .0 0 0 0 .0 0 0 0
N e tw o rk a n d N o d e
2 b e fd 0 c .
1 1 1 1 .1 e 1 1 .4 a 6 9
G e n e ra l
T C P /IP
IP X
Routing — How the Router
Thinks
D e s tin a tio n
P o rt
1 .2 .3 4 .0
1
6 .7 .8 9 .0
2
1 1 .1 2 .1 .0
3
1-21
1.2.34.0
H2 H3 H4 H5 H6 H7 D T
Port 2
Packet
6.7.89.0
11.12.1.0
1-22
Router
Communication
B
1
2
A
C
E
D
Here is my
current routing table.
 Routing protocols convey information about networks.
 Routed protocols are responsible for moving the data
from host to host.
1-23
Static vs. Dynamic Routing
 Static Route
A route that the network
administrator types
 Dynamic Route
A learned route that can be
automatically adjusted due to
topology or traffic changes
T1
T1
56Kbps
T1
1-25
Transport Layer
Frame
Header
H3
H4
H5
H6
H7
Data
Frame
Trailer
TCP Header
Source Destination Sequence
Ack
Code
HLEN Reserved
Port
Port
Number Number
Bits
Connection-Oriented vs.
Connection-Oriented
Connectionless
Data
Acknowledgement
Connectionless
Data
No Acknowledgement
Packet Flow — Step One: The Proxy
— ARP
C
Client
Who is device 4.1?
Network 2.0
A
WAN
Proxy ARP
Network 3.0
To get to device
4.1 send data to
me, Router A.
4.1
B
Network 4.0
Packet Flow — Step Two: The Source
Encapsulation
Source Source Source
Client
1234
1.2
Dest.
Dest. Dest.
A
23
4.1
Data Trailer
WAN
A
Client
1.2
Packet Flow — Step Three: Across the
Ethernet
R o u tin g T a b le
N e tw o rk
P o rt
N ext Hop
2 .0
S1
C
4 .0
S0
1 .0
E0
Source Source
1.2
1.2
Dest.
Dest.
c o n n e c te A
d
4.1
B
Data Trailer
WAN
A
1.2
Packet Flow — Step Four: Across
theHDLC
WAN
Data
Network 2.0
To B
C
WAN
A
4.1
1.2
B
Network 4.0
Packet Flow — Step Four: Across the
WAN
(cont.)
HDLC
Data
Network 2.0
C
WAN
A
4.1
1.2
B
HDLC
Data
Network 4.0
Packet Flow — Step Four: Across the
WAN (cont.)
Network 2.0
C
WAN
A
4.1
R o u tin g T a b le
1.2
N e tw o rk
P o rt
N ext Hop
1 .0
S0
A
2 .0
S1
C
4 .0
E0
c o n n e c te d
B
Source
1.2
Dest.
4.1
HDLC
Data
Data
Network 4.0
Packet Flow — Step Five: The
ARP
1-32
Network 2.0
C
WAN
1234.5678.9abc
A
4.1
1.2
A R P T a b le
N e tw o rk
M AC
4 .1
1 2 3 4 .5 6?7 8 .9 a b c
B
Network 4.0
Packet Flow — Step Five: The
ARP (cont.)
Network 2.0
C
LAN
1234.5678.9abc
A
4.1
1.2
A R P T a b le
N e tw o rk
M AC
4 .1
1 2 3 4 .5 6 7 8 .9 a b c
B
LAN Frame
Data
Network 4.0
Packet Flow — Step Five: The
ARP (cont.)
Network 2.0
C
LAN Frame
Data
LAN
A
4.1
1.2
B
LAN Frame
Data
Network 4.0
Packet Flow — Step Six: The
Server
7 Application
6 Presentation
1-34
Network 2.0
LAN Frame
5 Session
Data
4 Transport
3 Network
4.1
1.2
2 Data Link
1 Physical
Network 4.0