OSI Reference Model

Before OSI it was difficult for the vendors to create network products OSI, why U need to study, its a structured approach to troubleshoot

Each has independent model

Before considering how to configure Cisco routers and switches, you must be introduced to basic networking concepts you’ll need to understand in order to grasp the advanced concepts discussed in later chapters

ISO developed the seven-layer.

Application Layer, Presentation Layer And Session Layers are Both called Upper Layer.

And Transport Layer, Network Layer, Data Link Layer And Physical Layers are both called Lower Layer.

Application Layer :-   Top (seventh) layer of the OSI Reference Model is the application layer. It provides the user interface. Examples of TCP/IP applications include telnet, FTP, HTTP, HTTPS, SMTP, SNMP, DNS, ICMP And all of browser.

This layer deal with networking applications.

Examples:

               Email

               Web browsers

Presentation :-   The Presentation layer gets its name from its purpose: It presents data to the Application layer and is responsible for data translation and code formatting

Exam Watch The presentation layer determines how data is represented to the user. Examples of presentation layer protocols and standards include ASCII, BMP, GIF, JPEG, WAV, AVI, and MPEG.

ASCII (the American Standard Code for Information Interchange, used by most devices today) uses seven bits to represent characters. EBCDIC (Extended Binary-Coded Decimal Interchange Code, developed by IBM)

PICT A picture format used by Macintosh programs for transferring QuickDraw graphics.

TIFF Tagged Image File Format; a standard graphics format for high-resolution, bitmapped images.

JPEG Photo standards brought to us by the Joint Photographic Experts Group. Other standards guide movies and sound:

MIDI Musical Instrument Digital Interface (sometimes called Musical Instrument Device Interface), used for digitized music.

MPEG Increasingly popular Moving Picture Experts Group standard for the compression and coding of motion video for CDs. It provides digital storage and bit rates up to 1.5Mbps.

QuickTime For use with Macintosh programs; manages audio and video applications.

RTF Rich Text Format, a file format that lets you exchange text files between different word processors, even in different operating systems.

This layer is responsible for presenting the data in the required format which may include:

      Code Formatting

Encryption

Compression

Session :-   Exam Watch The session layer is responsible for setting up and tearing down network connections. Examples include RPCs and NFS.

The actual mechanics of this process, however, are implemented at the transport layer. To set up connections or tear down connections, the session layer communicates with the transport layer. Remote Procedure Call (RPC) is an example of an IP session protocol; the Network File System (NFS), which uses RPC, is an example application at this layer.

This layer establishes, manages, and terminates sessions between two communicating hosts.

Creates Virtual Circuit

Coordinates communication between systems

Organize their communication by offering three different modes

Simplex

Half Duplex

Full Duplex

Example:

·  Client Software

    ( Used for logging in)

Transport :-

This layer breaks up the data from the sending host and then reassembles it in the receiver.

It also is used to insure reliable data transport across the network.

Can be reliable or unreliable

Sequencing

Acknowledgment

Retransmission

Flow Control

Windows

Protocol Port

PDU - Segments

Data Link :-

This layer provides reliable transit of data across a physical link.

Performs Physical Addressing.

Combines bits into bytes and bytes into frames.

Preamble is sequence of 1’s and 0’s signifies the beginning of a frame.

Error detection, not correction.

FCS is used for error detection.

Access to media using MAC address.

LLC and MAC.

CRC run on the data field and and the values is kept in FCS.

Logical Link Control performs Link establishment.

MAC Performs Access method.

OSI (Open Systems Interconnection) Reference Model:

This is a protocol suit, and it follows Department of defense model.
The seven layers of OSI layer.

Application Layer
[NNTP • SIP • SSI • DNS • FTP • Gopher • HTTP • NFS • NTP • SMPP • SMTP • SNMP • Telnet • DHCP • Netconf • RTP • SPDY • etc.]

Presentation Layer
[MIME • XDR • TLS • SSL]

Session Layer
[Named Pipes • NetBIOS • SAP • L2TP • PPTP • SOCKS]

Transport Layer
[TCP • UDP • SCTP • DCCP • SPX]

Network Layer
[IP (IPv4, IPv6) • ICMP • IPsec • IGMP • IPX • AppleTalk]

Data Link Layer
[ATM • SDLC • HDLC • ARP • CSLIP • SLIP • GFP • PLIP • IEEE 802.3 • Frame Relay • ITU-T G.hn PPP •DLL • X.25 • Network Switch •]

Physical Layer
[EIA/TIA-232 • EIA/TIA-449 • ITU-T V-Series • I.430 • I.431 • POTS • PDH • SONET/SDH • PON • OTN • DSL • IEEE 802.3 • IEEE 802.11 • IEEE 802.15 • IEEE 802.16 • IEEE 1394 • ITU-T G.hn PHY • USB • Bluetooth • Hubs]

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