Transcript OSI Reference Model & Layered Communication

OSI Reference Model &
Layered Communication
Sritrusta Sukaridhoto
OSI Layer
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Open Systems Interconnection for
Communications
There are 7 Layers
Layers 7,6,5 are oriented more toward
services to the applications
Layer 4,3,2,1 are oriented more toward
the flows data from end-to-end through
network
7 Layer OSI
How to Remember (CISCO)
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Please
Do
Not
Throw
Sousces
Pizza
Away
 Physical
 Data Link
 Network
 Transport
 Session
 Presentation
 Application
Application
Layer 7
Function & Description
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An application that communicates with
other computers is implementing OSI
application layer concepts. Application
layer refer to communications service
to application.
Example
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Telnet
HTTP
FTP
WWW Browser
NFS
SMTP Gateway
SNMP
Presentation
Layer 6
Function & Description
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This layer main purpose is defining
data format such as ASCII text,
EBCDIC text, binary, BCD, JPEG.
Encryption is also defined by OSI as
presentation layer service.
Example
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JPEG
ASCII
TIFF
GIF
PICT
MPEG
MIDI
Encryption
Session
Layer 5
Function & Description
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This session layer defines how to start,
control, and end conversation (called
session).
This includes the control and
management of multi bidirectional
messages so that application can be
notified if only some of a series of
messages are completed.
Example
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RPC
SQL
NFS
Netbios Names
AppleTalk
ASP
SCP
DECnet
Transport
Layer 4
Function & Description
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Layer 4 includes the choice of
protocols that either do or do not
provide error recovery. Multiplexing of
incoming data for different flows to
applications on the same host.
Example
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TCP
UDP
SPX
Network
Layer 3
Function & Description
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This layer defines end-to-end delivery
packets. To accomplish this, the network
layer defines logical addressing so that any
endpoint can be identified. It also defines
how routing works and how routes are
learned so that the packets can be delivered
Network layer also defines how to fragment
a packet into smaller packets to
accommodate media with smaller maximum
transmission unit size
Example
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IP
IPX
AppleTalk DDP
Data Link
Layer 2
Function & Description
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The data link specifications are
concerned with getting data across
one particular link or medium. The data
link protocols define delivery across an
individual link. These protocols are
necessary concerned with the type of
media in question.
Example
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IEEE 802.3/802.2
HDLC
Frame Relay
PPP
FDDI
ATM
Physical
Layer 1
Function & Description
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Deal with the physical characteristics
of the transmission medium,
Connection pins, use of pins, electrical
currents, encoding and light
modulation.
Example
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Ethernet
RJ-45
V.35
FDDI
EIA/TIA-232
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Some protocol define details of
multiple layers.
Example: NFS
Benefit & Concept
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Humans can discuss and learn about many
details of a protocol specification easier
Standardized interfaces among layers
Better environment for interoperability
Reduce complexity, faster production
Each layer can define header and trailers
around the user data
One layer use the services of the layer
immediately below it.
Interaction Between OSI
Layer
On Same Computer
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Step 1 = Physical Layer, ensure bit
synchronization
Step 2 = Data Link Layer, Frame Check
Sequence (FCS) whether error occurred in
transmission
Step 3 = Network Layer, Exam address
Step 4 = Transport Layer, acknowleadment
Step 5 = Session Layer, to ensure that a series
of messages is completed
Step 6 = Presentation Layer, manipulate data
format
Step 7 = Application Layer, processes the final
header and then can examine the true end-user
data
Different Computer
Data Encapsulation
5 Step Data Encapsulation
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Create the data
Package the data for transport
Add the destination network layer
address to the data
Add the destination data link address
to the data
Transmit the bit
Frames, Packets and
Seqments
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The layer 2 PDU (Protocol Data Unit)
including the data link header and trailer =
Frame
The Layer 3 PDU = packet
The Layer 4 PDU = seqment
OSI, TCP/IP
OSI Transport Layer Function
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Connection Oriented vs Connectionless
Oriented
Error Recovery
Flow Control
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Flow control is the process of
controlling the rate at witch a computer
sends data.
Implementation:
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Buffering
Congestion Avoidance
Windowing
Buffering
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Buffering simply means that computers
reserve enough buffer space that
bursts of incoming data can be held
until processed
Congestion Avoidance
Windowing
Data Link Function
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MAC = Media Access Control
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CSMA/CD = Carrier Sense Multiple Access/Collision Detect
OSI Network Layer Function
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Routing
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Sending data to a nearby Router
Routing data Across Network
Delivering Data to End Destination
Addressing
Summary
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Application (Layer 7)  User Interface  Telnet, HTTP
Application (Layer 6)  How data is presented  JPEG,
ASCII
Session (Layer 5)  Keeping data separate from different
application  OS, application access scheduling
Transport (Layer 4)  Reliable or unreliable delivery,
Multiplexing  TCP, UDP, SPX
Network (Layer 3)  Logical addressing, Routing  IP, IPX
Data Link (Layer 2)  MAC, error detection  802.3/802.2,
HDLC
Physical (Layer 1)  Devices  Ethernet, V.35