Optical Carrier-3. Refers to a 155 Mbps circuit capacity in SONET. There are higher speed circuits in SONET, i.e. OC-12 (622 Mbps), OC-48 (2.5 Gbps), and OC-192 (10 Gbps) and a lower speed circuit, that is OC-1 (51.8 Mbps).
Also see SONET.

Orthogonal Frequency Division Multiplexing. A technique in which an RF carrier is modulated by a baseband signal that consists of a number of orthogonal sub-carriers (i.e. each sub-carrier is independently modulated by its own data). Sometimes, OFDM is referred to as DMT.
OFDM is used in 802.11a, 802.11g, ADSL, WiMAX, WiMedia, and HomePlug.
Also see modulation, multiplexing, and DMT.

Orthogonal Frequency Division Multiple Access. A technique that allows orthogonal sub-carriers to be assigned to different users.

Antenna that radiates radio waves (signals) effectively to all direction.
Also see antenna. Contrast with directional antenna.

Open Systems Interconnection. OSI model is a 7-layer protocol stack model that describes procedures for data transfer in a network. It was defined by the ISO.
The OSI model has been used as a guideline for network designers and manufacturers in developing network products that guarantee interoperability among various technologies. However, the networking industry doesn't strictly follow the OSI model. For instance, functions that relate to several layers in the OSI model may be performed by one protocol in a particular network technology.

The OSI model defines how one layer interacts with another layer in the 7-layer protocol stack. When two computers communicate, information is sent down through the protocol stack to the physical layer (e.g. cable), and travels up through the protocol stack to the application layer for processing by the receiving computer. Below are the layers in the OSI model:
Layer 1: Physical Layer
Layer 2: Data Link Layer
Layer 3: Network Layer
Layer 4: Transport Layer
Layer 5: Session Layer
Layer 6: Presentation Layer
Layer 7: Application Layer

To easily memorize the OSI model, you can use this funny mnemonic:
People Don't Need TheSe Protocols Anyway (from Layer 1 to Layer 7)

Open Shortest Path First. A routing protocol that determines the best path between two routers within an autonomous system based on the path length. The shortest path will be chosen to forward a packet to its next hop (router).
Also see IGP, routing protocol. Compare with RIP.

Over The Air.