OSI Reference Model

1
OSI Reference Model Layered Communication

• Sritrusta Sukaridhoto

2
OSI Layer

• 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

3
7 Layer OSI
4
How to Remember (CISCO)

• Please ? Physical
• Do ? Data Link
• Not ? Network
• Throw ? Transport
• Sousces ? Session
• Pizza ? Presentation
• Away ? Application

5
Application

• Layer 7

6
Function Description

• An application that communicates with other
  computers is implementing OSI application layer
  concepts. Application layer refer to
  communications service to application.

7
Example

• Telnet
• HTTP
• FTP
• WWW Browser
• NFS
• SMTP Gateway
• SNMP

8
Presentation

• Layer 6

9
Function Description

• 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.

10
Example

• JPEG
• ASCII
• TIFF
• GIF
• PICT
• MPEG
• MIDI
• Encryption

11
Session

• Layer 5

12
Function Description

• 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.

13
Example

• RPC
• SQL
• NFS
• Netbios Names
• AppleTalk
• ASP
• SCP
• DECnet

14
Transport

• Layer 4

15
Function Description

• 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.

16
Example

• TCP
• UDP
• SPX

17
Network

• Layer 3

18
Function Description

• 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

19
Example

• IP
• IPX
• AppleTalk DDP

20
Data Link

• Layer 2

21
Function Description

• 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.

22
Example

• IEEE 802.3/802.2
• HDLC
• Frame Relay
• PPP
• FDDI
• ATM

23
Physical

• Layer 1

24
Function Description

• Deal with the physical characteristics of the
  transmission medium, Connection pins, use of
  pins, electrical currents, encoding and light
  modulation.

25
Example

• Ethernet
• RJ-45
• V.35
• FDDI
• EIA/TIA-232

26

• Some protocol define details of multiple layers.
• Example NFS

27
Benefit Concept

• 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.

28
Interaction Between OSI Layer
29
On Same Computer
30

• 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

31
Different Computer
32
Data Encapsulation
33
5 Step Data Encapsulation

• 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

34
Frames, Packets and Seqments
35

• 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

36
OSI, TCP/IP
37
OSI Transport Layer Function

• Connection Oriented vs Connectionless Oriented

38
Error Recovery
39
(No Transcript)
40
(No Transcript)
41
Flow Control

• Flow control is the process of controlling the
  rate at witch a computer sends data.
• Implementation
• Buffering
• Congestion Avoidance
• Windowing

42
Buffering

• Buffering simply means that computers reserve
  enough buffer space that bursts of incoming data
  can be held until processed

43
Congestion Avoidance
44
Windowing
45
Data Link Function

• MAC Media Access Control
• CSMA/CD Carrier Sense Multiple Access/Collision
  Detect

46
OSI Network Layer Function

• Routing
• Sending data to a nearby Router
• Routing data Across Network
• Delivering Data to End Destination
• Addressing

47
(No Transcript)
48
Summary

• 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