OSI LAYERS-Networks Tony Caleb D 14-July-2010
OSI LAYERS-Networks
Feb 22, 2016
OSI LAYERS-Networks. Tony Caleb D 14-July-2010. OSI: Open System Interconnection . Developed by the International Organization for Standardization in 1974. There are seven layers in OSI reference Model . It is a layered approach. OSI Reference Model. An Exchange using the OSI Layers. - PowerPoint PPT Presentation
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OSI LAYERS-Networks
Tony Caleb D14-July-2010
• OSI: Open System Interconnection .
• Developed by the International Organization for Standardization in 1974.
• There are seven layers in OSI reference Model .
• It is a layered approach.
OSI Reference Model
An Exchange using the OSI Layers
OSI Reference Model
Application
Presentation
Session
Transport
Network
Data Link
Physical
Layer - 7
Layer - 6
Layer - 5
Layer - 4
Layer - 3
Layer - 2
Layer - 1
Upper Layer or Software Layer
Lower Layer or Hardware Layer
Heart of OSI
Application Layer
Application Layer is responsible for providing Networking Services to the user. It is also known as Desktop Layer. Identification of Services is done using Port Numbers.
Ports are Entry and Exit Points to the Layer
Total No. Ports 0 – 65535 Reserved Ports 0 – 1023 Open Client Ports 1024 – 65535
Application
Presentation
Session
Transport
Network
Data Link
Physical
Application
Example of HTTP request
Client Web Server
http://www.zoomgroup.com
Client Web Server
Example of HTTP request
HTTP Request http:// www.zoomgroup.comWebpage
HTTP Request Listen on Port 80Sending HTTP ReplyWebpage
Received HTTP Reply http://www.symantec.comWebpage
Client Web Server
Examples of Networking Services
Service Port No.
HTTP 80
FTP 21
SMTP 25
TELNET 23
TFTP 69
Application
2180 25 6753 69
Data flow from Application Layer
Data
Presentation
Session
Transport
Network
Data Link
Physical
Presentation Layer
Presentation Layer is responsible for converting data into standard format.
Examples : JPEG, MPEG, MIDI, WAV, MP3
Following tasks are perform at Presentation layer :
Encoding – DecodingEncryption – DecryptionCompression – Decompression
Application
Presentation
Session
Transport
Network
Data Link
Physical
Presentation
Data flow from Presentation Layer
Data
DataApplication
Presentation
Session
Transport
Network
Data Link
Physical
Session Layer
Session Layer is responsible for establishing, maintaining and terminating session. Session ID works at Session Layer.
Examples :
RPC Remote Procedure Call SQL Structured Query LanguageNFS Network File System
Application
Presentation
Session
Transport
Network
Data Link
Physical
Session
Data flow from Session Layer
Data
Data
Data
Application
Presentation
Session
Transport
Network
Data Link
Physical
Transport Layer
Transport Layer is responsible for end-to-end connectivity. It is also known as the heart of OSI Layers. Following tasks are performed at the Transport Layer : -
• Identifying Service
• Multiplexing & De-multiplexing
• Segmentation
• Sequencing & Reassembling
• Error Correction
• Flow Control
Application
Presentation
Session
Transport
Network
Data Link
Physical
Transport
Identifying Service
• Transmission Control Protocol
• Connection Oriented
• Acknowledgement
• Reliable
• Slower
• Port No. 6
• e.g. HTTP, FTP, SMTP
• User Datagram Protocol
• Connection Less
• No Acknowledgement
• Unreliable
• Faster
• Port No. 17
• e.g. DNS, DHCP, TFTP
TCP UDP
Multiplexing & De-multiplexing
Application
Presentation
Session
Multiplexing & De-multiplexing
2180 25 6753 69
Transport
TCP - 6 UDP - 17
Network
Data Link
Physical
Segmentation
Hello! How are you ?
Hello! How Are You ?
Hello! How are you ?
A B
Sequencing & Reassembling
Hello! How are you ?
Hello! How Are You ?
Hello! How are you ?
A B
You Hello! How ? Are
Hello! How AreYou ?
you Hello! How ? are
Sequencing & Reassembling
Hello! How are you ?
Hello!1/5
How2/5
Are3/5
You4/5
?5/5
Hello! How are you ?
A B
Hello! How are you ?
Hello!1/5
How2/5
Are3/5
You4/5
?5/5
Hello!1/5
How2/5
Are3/5
You4/5
?5/5
Hello! How are you ?
Error Correction
Hello! How are you ?
Hello!1/5
How2/5
Are3/5
You4/5
?5/5
Hello! How are you ?
Hello!1/5
Are3/5
You4/5
?5/5
Hello!1/5
Are3/5
You4/5
?5/5
Segment Missing
Hello!1/5
Are3/5
You4/5
?5/5
How2/5
How2/5
Hello! How are you ? Hello! How are you ?
A B
Flow Control - Windowing
Sending 3-window
Received 3-window
Ack-Rec-3Sending5-window
Received 4-window
A B
Ack. Received-4
PC-A can send 4 Segments at a
time to PC-B
Data flow from Transport Layer
Data
Data
Data
DataTHSegment
Application
Presentation
Session
Transport
Network
Data Link
Physical
Network Layer
Network Layer is responsible for providing best path for data to reach the destination. Logical Addressing works on this layer. Router is a Network Layer device.
It is divided into two parts
• Routed Protocols
e.g. IP, IPX, Apple Talk.
• Routing Protocols
e.g. RIP, IGRP, OSPF, EIGRP
Application
Presentation
Session
Transport
Network
Data Link
Physical
Network
Routed Protocols
Hello! How are you ?
192.168.1.1 192.168.1.2
A B
Segment
Segment
Source IP 192.168.1.1
Destination IP192.168.1.2
Source IP 192.168.1.1
Destination IP192.168.1.2
Segment
Hello! How are you ?
Routing Protocols
A
www.symantec.com
Hop to Hop Delivery
IP Addresses
Data flow from Network Layer
Data
Data
Data
Segment
Segment
NH
e.g. Router
Packet
Application
Presentation
Session
Transport
Network
Data Link
Physical
Data link Layer
Datalink Layer is divided into two Sub
• LLC – Logical Link ControlIt talks about Wan protocols e.g. PPP, HDLC, Frame-relay
• MAC – Media Access ControlIt talks about Physical Address. It is a 48 bit address i.e. 12 digit Hexadecimal Number.
It is also responsible for Error DetectionDevices working on Data Link Layer are Switch, Bridge, NIC.
Application
Presentation
Session
Transport
Network
Data Link
Physical
Data Link
Error Detection – CRC Check
Hello! How are you ?
Packet
Packet
Source MAC 00-20-18-C0-07-71
Destination MAC00-20-18-C0-07-72
000003243422222896965543499323434349943446323111143333300000324342222289696554349932343434994344632311114Error Detected
192.168.1.100-20-18-C0-07-71
192.168.1.200-20-18-C0-07-72
A B
PC-A CRC No. 33333 PC-B CRC No. 11114Error Detected For Error Correction Contact Source Transport layer
Error Detection – CRC Check
Packet
Packet
Source MAC 00-20-18-C0-07-71
Destination MAC00-20-18-C0-07-72
00000324342222289696554349932343434994344632311114202020000032434222228969655434993234343499434463231111420202
Source MAC 00-20-18-C0-07-71
Destination MAC00-20-18-C0-07-72
Packet
Hello! How are you ?
192.168.1.100-20-18-C0-07-71
192.168.1.200-20-18-C0-07-72
A B
e.g. Switch
Data flow from Data Link Layer
Data
Data
Data
Segment
DH
Packet
DT
Application
Presentation
Session
Transport
Network
Data Link
Physical
PacketPacketFrame
Physical Layer
Physical Layer is responsible for electrical, mechanical and procedural checks. Data will be converted into Binary (i.e) 0’s & 1’s. Data will be in the form of electrical pulses if it is Coaxial or Twisted Pair cable and in the form of Light if it is Fiber Optic Cable.
Devices working at Physical Layer are Hubs, Repeaters, Cables, Modems etc.
Application
Presentation
Session
Transport
Network
Data Link
PhysicalPhysical
Physical Layer Example
Frame
Frame
10101010101010101010101010101010
Frame
Hello! How are you ?
A B01010110101010101010101011010101101010101010101010010101101010101010101010110101011010101010101010100101011010101010101010101
Data flow from Physical Layer
Data
Data
Data
Segment
Packet
Frame
Bits
e.g. Hub
Application
Presentation
Session
Transport
Network
Data Link
Physical
Segment
Packet
Frame
A B
Packet
Data
Data
Data
Bits
Data
Segment
Data Encapsulation & De-capsulation
Packet
Data
Data
Data
Application
Presentation
Session
Transport
Network
Data Link
Physical
Application
Presentation
Session
Transport
Network
Data Link
PhysicalBits
DH DT
NH
THSegment
Packet
DT PacketDH DTDH
NH Segment NH
TH Data TH
Frame Packet
Application
Transport
Internet
Network Access
Comparing OSI with TCP/IP Layers
OSI Layers TCP/IP Layers
Application
Presentation
Session
Transport
Network
Data Link
Physical
Relationship Between Layers and Address in TCP/IP
Summary of layers
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