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Glossary : O

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collapse/expand OC-3
  • 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.

collapse/expand OFDM
  • 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.

collapse/expand OFDMA
  • Orthogonal Frequency Division Multiple Access. A technique that allows orthogonal sub-carriers to be assigned to different users.

collapse/expand Omnidirectional Antenna
collapse/expand OSI
  • 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)

collapse/expand OSPF
  • 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.

collapse/expand OTA
  • Over The Air.