OSI Model

UDP

A connectionless protocol for fast transport but no guarantee of delivery.

MAC Address

A permanent address given to each network interface card (NIC) at the factory. This address enables the device to access the network via a Level-2 protocol. No two NIC devices will ever have the same MAC address. Also called a physical address.

Packet

A small unit of data transmitted over a network.

Protocol

A standard that specifies the format of data as well as the rules to be followed during transmission

Segment

A unit of data that results from subdividing a larger protocol data unit

Sequencing

Arranging items or events in particular order

CRC

Cyclic Redundancy Check

Encyption

Process of transforming data into a type that prevents casual observers from deciphering.

PDU

Protocol Data Unit

Session Layer

The fifth layer in the OSI model. The Session layer establishes and maintains communication between two nodes on the network. It can be considered the "traffic cop" for network communications.

TCP/IP

Transmission Control Protocol/Internet Protocol. Protocol that connects computers to the Internet. Tells computers how to exchange information over the Internet.

Windowing

When using TCP, after a session is open, the applications can adjust the amount of segments they recieve before sending an acknowledgment.

API

application programming interface specifies a software component in terms of its operations, their inputs and outputs and underlining types.

OSI Model

model for understanding and developing computer-to-computer communication; divides networking functions among 7 layers Application, Presentation, Session, Transport, Network, Data Link, Physical

Transport Layer

4th layer; protocols ensure that data are transferred from point A to point B reliably and without errors; services include flow control, acknowledgment, error correction, segmentation, reassembly, and sequencing

TCP

A networking protocol that uses packet switching to facilitate the transmission of messages; the protocol used with the Internet.

IP Address

A number assigned to a device connected to the Internet. Websites use this to send the information you want back to your computer from nearby or all the way around the world. A website name is converted to an IP address number so the computer can locate it.

Session

A single communication or connection for data exchange between two computers. The term session may be used in the context of Web, remote access or terminal and mainframe communications, for example.

Compression

A technique that reduces the file size of bitmap images

Connection Oriented

A type of Transport layer protocol that requires the establishment of a connection between communicating nodes before it will transmit data.

Connectionless

A type of Transport layer protocol that services a request without requiring a verified session and without guaranteeing delivery of data.

Frame

Encloses the segment in a network

DataLink Layer

Gives unique identities to senders and receivers. Organizes data packets into frames for transmission Layer 2

Network Layer

The third layer of the OSI model. Protocols in the Network layer translate network addresses into their physical counterparts and decide how to route data from the sender to the receiver.

Routing

A function of the Network layer that involves moving data throughout a network. Data passes through several network subnetworks using routers that can select the path the data takes. See also router.

Checksum

A method of error checking that determines if the contents of an arriving data unit match the contents of the data unit sent by the source.

Flow Control

A method of gauging the appropriate rate of data transmission based on how fast the recipient can accept data.

Encapsulation

Encapsulation is the process of transferring packets of data which use different communications protocols inside packets which use another protocol.

Application Layer

Layer 7 of the OSI model. The network layer that houses the applications that allow users to access the network. It contains five categories of services, File services, e-mail services , network printing services, Application services and database services.

buffering

Most networks can and do use buffering to keep up when packets are flowing in too quickly for the network to process.

Physical Layer

The lowest, or first, layer of the OSI model. Protocols in the physical layer generate and detect signals so as to transmit and receive data over a network medium. These protocols also set the data transmission rate and monitor data error rates, but do not provide error correction.

Presentation Layer

The sixth layer of the OSI model. Protocols in the Presentation layer translate between the application and the network. Here, data are formatted in a schema that the network can understand, with the format varying according to the type of network used. The presentation layer also manages data encryption and decryption, such as the scrambling of system passwords.

IPX/SPX

a protocol suite used by Novell. This is an antiquated protocol that is rarely seen now that Novell has moved to TCP/IP.