Learn Windows XP Professional: The TCP/IP Protocol (Page 2) Page 2

The detailed function of each layer of the Open System Interconnection (OSI) protocol model is beyond the scope of this topic; however, the 60-second overview is as follows:

Physical Layer - Defines the interface between the medium and the device. This layer also transmits bits (ones and zeros) and defines how the data is transmitted over the physical medium. Some examples of Network Components found at this layer are Multiplexers, Passive Hubs, Active Hubs, Repeaters and other types of signal Amplifiers

Data Link Layer - This layer is actually divided into two sublayers -- Logical Link Control, which mainly handles error correction and flow control, and Media Access Control, which mainly handles the communication with the network adapter card. Some examples of Network Components found at the Data Link layer are Bridges, Switches and certain Advanced Cable Testers.

Network Layer - This OSI layer is responsible for translating logical network addresses and names such as computernames to their MAC addresses and for addressing and routing data packets over the network. If routers at this layer can't forward the data frames as large as the source node has sent, this OSI layer will break down the data into smaller units that the devices can handle. Some examples of Protocols found at the Network Layer are IP, ARP, RARP, ICMP, RIP, OSFP, IGMP, IPX, NWLink and NetBEUI. Some examples of Network Components found at this layer are Brouters, Routers, some types of ATM Switches and Frame Relay hardware.

Transport Layer - The Transport Layer adds an additional connection below the Session layer and helps manage data flow control between nodes on the network. This layer divides the data into packets on the sending node, and the transport layer of the receiving node reassembles the message from packets. The Transport Layer provides error-checking to guarantee error-free data delivery by requesting retransmission if some packets don't arrive error-free. It also sends acknowledgment of successful transmissions back to the sending node. Some examples of Protocols found at this layer are TCP, ARP, RARP, SPX and NWLink. Some examples of Network Components found at the Transport Layer are Gateways and certain types of Brouters.

Session Layer - This OSI layer, as the name implies, establishes, maintains and ends sessions between transmitting nodes across the network and manages which node can transmit data at a certain time and for how long. Some examples of Protocols found at this layer are Names Pipes, NetBIOS Names, RPC and Mail Slots. Some examples of Network Components found at the Session Layer are Gateways and certain types of Proxy Servers.

Presentation Layer - The Presentation Layer technically performs the translation of the data from the way applications understand it to the way networks understand it on the transmission end and then back on the receiving node. It is responsible for protocol conversions, data encryption / decryption, and data compression / decompression where the network is considered. Some examples of Network Components found at the Presentation Layer are Gateways and certain types of Redirectors. There are no Protocols that normally operate in this layer.

Application - The Application Layer of the OSI model allows access to network services for applications specifically written to run over the network, such as e-mail and file transfer programs such as FTP. There are many Protocols found at the Application Layer, some of which include FTP, TFTP, BOOTP, SNMP, SMTP, TELNET, NCP, and SMB.