Day.1 - OSI,DoD TCP/IP Layers

Here we will see all different kind of Layer mechanism (OSI,DoD TCP/IP,Cisco Layers)

- OSI means Open System Interconnect Model

-Developed by IOS( International organization for standardization) in 1974

Now have closer look to OSI layer and method of remembering it very easily , please note here we will try only easy method of remembering all stuff out here.As no one have so long memory so I developed my easy methods hope it will help you out more.

Here 1st three layer is also known as SOFTWARE LAYER or UPPER LAYER( APPLICATION,PRESENTATION,SESSION) Where 2ed part means NETWORK,DATALINK PHYSICAL layer come in HARDWARE LAYER or LOWER LAYER.Where Transport layer is heart of OSI layer.

ok here is method to remember it.

1st method is

PLEASE DO NOT THROW SEXY PIZZA AWAY.......sound funny ha?

ok here is explanation

Please = physical Layer

Do = Data link Layer

Not = network Layer

throw = Transport Layer

Sexy =Session Layer

pizza = presentation Layer

Away = application layer

This I Called a reverse method from down to up.............

Ok now lets have look at another method.( thanks to altergothen)

All People Seem To Need Data Processing

Application ,Presentation ,Session ,Transport ,Network ,Data link ,Physical

See how easy to remember it?

ok now lets have look at which layer do what

Layer	Responsible for	Task / Example	TYPE
Application Layer (Layer-7)	Providing network service to user,also known as Desktop Layer.Identified services using port numbers	Total no. of port 0-65535 Reserved Port 0-1023 Open Client port 1024-65535 Example : WWW,R-login	Data
Presentation Layer (Layer-6)	Converting Data in to Standard Format Example : ASCII,EBCIDIC,JPEG,MPEG,MIDI,MP3,WAV.	Encoding- Decoding Encryption - Decryption Compression-Decompression	Data
Session Layer (Layer 5) (Connection)	Negotiation,Establish and Maintaining connection( Session) with use of Session ID Keep different application at different session Simplex,Half Duplex,Full Duplex	RPC -Remote procedure call SQL- Structured Query Language NFS- Network File System	Data
Transport Layer (Layer 4) (Segment)	END-to- END connectivity	Identify Service multiplexing-De-multiplexing connection control(connectionless-connection oriented) network protocol (TCP/UPD) provide reliable ,unreliable Delivery segmenting,sequencing,re-assembling error control(error correction)	Segment
Network Layer (Layer-3)	Providing best path for data to reach the destination. provide logical addressing Define network segments and network schema Divided in to to parts	Routed protocol : IP,IPX,Apple Talk Routing protocol : RIP,IGRP,EIGRP,OSPF	Packet
Data Link Layer (Layer-2)	NIC(network interface card) create header and trailer Combine packet in to byte and byte in to frame Only error Detection Switch-bridge,NIC	Data link is Divided in to two sub-layer LLC (Logical Link Control) : WAN protocol : PPP ,HDLC,Frame-relay MAC(Media Access Control) : also known as physical address	Frame
Physical Layer (Layer-1)	Responsible for Tx And Rx bits Type of transmission Uni-Direction Bi-Direction	Device work at Physical Layer Hub Repeater Cable Modem	Bits

Easy Right? ok Here is some of note which one is very very important to remember

Note.1: Error Detection : Data Link Layer (Layer 2)

Error Correction : Transport Layer( Layer 4)

Note.2: Flow Control - congestion Avoidance,Windowing,Buffering.

Ok now lets compare TCP and UDP

TCP	UDP
Transmission control protocol Connection Oriented Acknowledgement Reliable Slower Port no. 6 Ex. HTTP,FTP,SMTP ,DNS	User Datagram Protocol Connection less No Acknowledgement Unreliable Faster Port no. 17 DHCP,TFTP,DNS
TCP Port no. Telnet =23 SMTP=25 HTTP=80 FTP=20,21 HTTPS=443* DNS=53*	UDP Port no SNMP=161 TFTP=69 DNS=53*

* Very important to remember for your CCNA exam

*Note : DNS is the only service which work on TCP and UDP with same port no.

Now Lets have look at DoD( Department of Defense) TCP/IP model

Layer	Protocol
Application Layer	Telnet,FTP,TFTP,LPD,SNMP,SMTP,NFS,X-WINDOW
Transport Layer	TCP UDP
Internet	ICMP,ARP,RARP,IP
Network	Ethernet,Fast Ethernet,Token Ring,FDDI

Ok Now we are almost done Last but not least Comparison of Three model (OSI,DoD TCP/IP Model and Cisco Layer)

OSI	DoD TCP/IP

Application Layer Presentation Layer Session Layer

Application

Transport Layer

Host-to-Host(Transport Layer)

Network Layer

Internet

Data Link Layer Physical Layer

Network Layer

Cisco have 3 layers Core,Distribution,and Access Layer(We will learn more about this later )

Here is some good video about OSI layer if you wish to learn more.