Term
Definition
Physical layer
Encompasses details such as electrical and mechanical connections to the network, transmission of binary data as changing voltage levels on wires or similar concepts on other connectors and data raters.
Data link layer
The Open Systems Interconnection (OSI) layer (2) that is responsible for data transfer across a single physical connection (or series of bridged connections, between two Network entities). The data link layer detects and may correct errors in the physical layer.
Network layer
The OSI layer that is responsible for routing, switching, and subnetwork access across the entire OSI environment.
Transport layer
Layer 4 of the Open Systems Interconnection (OSI) networking model, which establishes and dissolves connections between hosts and makes sure transmitted data has been received. An example protocol for the transport layer is TCP.
Session layer
Layer 5 of the Open Systems Interconnection (OSI) networking model, which handles logical connections between hosts; creates, maintains, and terminates a session; and handles security. It is a composite of the data flow control layer and transmission control layer.
Presentation layer
Layer 6 of the Open Systems Interconnection (OSI) networking model, which defines file and file access formats, performs file compression, establishes a common syntax between hosts, and converts data so incompatible systems can communicate with each other.
Application layer
Layer 7 of the Open Systems Interconnection (OSI) networking model, which defines standards for interaction at the user or application program level; for example, formatting electronic mail messages, reading and writing files, and file transfer. It is the highest layer of the protocol stack.
Encoding
Conversion of data into digital form; for example, converting an analog sound signal into digital data for storing on a CD.
Half-duplex
A communications channel which transmits data in either direction, but only one direction at a time.

Full duplex
A communications channel which transmits data in both directions at once.
Bandwidth
The amount of data that can be sent through a network connection. This is typically expressed in terms of the network speed, such as 1 Mbps (megabit-per-second). A greater bandwidth indicates the ability to transmit a greater amount of data over a given period of time.
Point-to-point topology
The simplest topology with a permanent link between two endpoints. Switched point-to-point topology are the basic model of conventional telephony. The value of a permanent point-to-point network is unimpeded communications between the two endpoints.

Deencapsulation
Refers to sending data where the data is augmented with successive layers of control information before transmission across a network. The reverse of data encapsulation is decapsulation, which refers to the successive layers of data being removed (essentially unwrapped) at the receiving end of a network.
MAC Sublayer
Medium Access Control sublayer. The lower sublayer of the data link layer, which uses the network's physical layer to provide services to the logical link control (LLC). The functions of the MAC sublayer vary according to the topology of the network.
LLC

Collision
If two computers accidentally transmit at the same time and their messages collide, they wait and send again at different times.
Access Method
A software routine that is part of the operating system or network control program which performs the storing/retrieving or transmitting/receiving of data. It is also