Jaycee's Networking

December 14, 2008

TCP/IP and OSI Layers

Filed under: Information — Jaycee @ 3:50 pm

TCP/IP protocol suite

1. Physical Layer — contains the protocols relating to the physical medium

(1) Electrical/optical protocols describe signal characteristics such as voltage or photonic levels, bit timing, encoding, and signal shape.

(2) Mechanical protocols are specifications such as the dimensions of a connector or the metallic makeup of a wire.

(3) Functional protocols describe what something does. For example, “Request to Send” is the functional description of pin 4 of an EIA-232-D connector.

(4) Procedural protocols describe how something is done. For example, a binary 1 is represented on an EIA-232-D lead as a voltage more negative than 3 volts.

2. Data Link Layer — contains the protocols that control the physical layer:

(1) how the medium is accessed and shared

(2) how devices on the medium are identified

(3) how data is framed before being transmitted on the medium

3. Network Layer / Internet Layer — enabling the routing of data across logical network paths by defining a packet format and an addressing format

4. Transport Layer / Host-to-Host Layer — contains the protocols that control the internet layer

(1) Both the Host-to-Host Layer and Data Link Layer can define such mechanisms as flow and error control.

(2) While Data Link protocols conrol traffic on the Data Link Layer , the physical medium connecting 2 devices

(3) The transport layer controls traffic on the logical link, the end-to-end connection of 2 devices whose logical connection traverses a series of data links.

5. Session Layer + Presentation Layer + Application Layer / Application Layer

(1) some routing protocols such as BGP and RIP reside at this layer, the most common services of the application layer provide the interfaces by which user applications access the network

(2) BGP uses TCP to transport its messages, and RIP uses UDP for the same purposes; thus they are application layer protocols.

(3) Other routing protocols such as OSPF are said to operate at the internet layer because they encapsulate their messages directly into IP packets.

(4) Many applications might use a service at the host-to-host layer, and many services at the host-to-host layer might use the internet layer.

(5) Any other protocol suite is multiplexing b/w layers. Multiple protocol suites (IP, IPX, AppleTalk) can share a physical link via common data-link protocols.

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