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OSI Protocol | Tech Info Home Page |

The OSI protocol stack has 7-levels

7 - Application Layer

It interfaces with the end-user applications.

Protocols include: ASN.1 ACSE RTSE ROSE, MHS, FTAM, VT, HTTP

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6 - Presentation Layer

It presents data to the Application Layer in an appropriate form. It translates data between the two communicating systems.

Also performs data encryption and compression.

Basic Data Units are "Messages"

Protocols include: ASN.1 ACSE RTSE ROSE

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5 - Session Layer

It negotiates communication settings between the systems. It is responsible for establishing, and ending communications between the two communicating systems. It synchronizes operations, and coordinates rules for communicating.

ES-IS IS-IS,

Remote Procedure Calls (RPCs) are services of this layer.

Protocols include: CLNP, X.25 PLP, RPC ( TCP/IP, IP protocol)

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4 - Transport Layer (Host-to-Host Layer)

Ensures that the data is transmitted reliably between the communicating systems. Errors are reported to the Transport layer. Disassembles and re-assembles data into smaller units for the Network layer. Also provides error recovery.

Basic Data Units are "Segments"

ES-IS IS-IS, TP0, TP1, TP2, TP3, TP4

WWW TCP connections are established here.

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3 - Network Layer

It routes packets through networks using the 8-digit network segment Identifier found in the packet.

It Does Not: ensure reliability.

Basic Data Units are "Packets".

Protocols include: X.25

TCP/IP defines functions at layers above the Physical and Data-Link Layers of the OSI model.

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2 - Data Link Layer

The data received from the Physical layer is grouped into frames before passed on to the next layer. Physical Address information is added to the frame.

Basic Data Units are "Frames".

ES-IS IS-IS,

Protocols include: 802.2, HDLC, LAPB (X.25 level 2)

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1- Physical Layer

The physical makeup of the network including wiring, connectors, and signal characteristics needed.

Basic Data units are "Bits".

Protocols include: 802.2, 802.3 802.4 802.5 FDDI, X.21, V.35, ISDN, RS-232, RS-449

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