OADM: Optical add Drop Multiplexer
Optical add Drop Multiplexer (OADM) is an optical multiplexing equipment that provides interfaces between different signals in a network.

OAM Cell
Operation, Administration, and Maintenance (OAM) Cell is the ATM Forum specification for cells used to monitor virtual circuits. OAM cells provide a virtual circuit-level loopback in which a router responds to the cells, demonstrating that the circuit is up and the router is operational.

OARnet: Ohio Academic Resources Network
Ohio Academic Resources Network (OARnet) is an Internet service provider that connects a number of U.S. academic sites, including the Ohio supercomputer center in Columbus, Ohio.

OBC: Out-of-band Control
Out-of-band Control (OBC) refers to the standard method of issuing signaling commands on the special control channel, versus In Band Control (IBC), on the in-band data channel.

Object Instance
Object Instance is a network management term referring to an instance of an object type that has been bound to a value.

OC: Optical Carrier
Optical Carrier (OC) refers to th series of physical protocols (OC-1, OC-2, OC-3, and so on), defined for SONET optical signal transmissions. OC signal levels put STS frames onto multimode fiber-optic line at a variety of speeds. The base rate is 51.84 Mbps (OC-1); each signal level thereafter operates at a speed divisible by that number (thus, OC-3 runs at 155.52 Mbps).

OCLC: Online Computer Library Catalog
Online Computer Library Catalog (OCLC) is a non-profit membership organization offering computer-based services to libraries, educational organizations, and their users.

Octet
Octet refers to 8 bits or 1 byte normally. In networking, the term of octet often is used (rather than byte) because some machine architectures employ bytes that are not 8 bits long.

ODA: Open Document Architecture
Open Document Architecture (ODA) is an ISO standard that specifies how documents are represented and transmitted electronically. Formerly called Office Document Architecture.

ODBC: Open DataBase Connectivity
Open DataBase Connectivity (ODBC), originally developed by Microsoft and a few other vendors and now an open source standard application programming interface, is for accessing data in both relational and nonrelational database management systems. Using ODBC, database applications can access data stored in database management systems on a variety of computers even if each database management system uses a different data storage format and programming interface.

ODI: Open Data-Link Interface
Open Data-link Interface (ODI) is an application programming interface (API) developed by Apple and Novell for writing network drivers. Like NDIS, ODI provides rules that establish a vendor-neutral interface between the protocol stack and the adapter driver. It resides in Layer 2, the Data Link layer, of the OSI model. This interface also enables one or more network drivers to support one or more protocol stacks. For example, ODI allows a computer with just one NIC to be simultaneously connected to both an IPX/SPX network and a TCP/IP network.

OFA: Optical Fiber Amplifier
Optical Fiber Amplifier (OFA) is a device that amplifies an optical signal directly, without the need to convert it to an electrical signal, amplify it electrically, and reconvert it to an optical signal.

OID: Object Identifier
Object Identifier (OID), a concept defined in the SNMP systems, is the value that is defined in specific MIB modules to identify a specific SNMP Object in the MIB database. SNMP OID is a period delimited sequence of numbers of the form a.b.c...x.y.z. It is a unique identifier for an item of information that is part of a MIB. Typically OIDs can have names associated with them. OIDs are hierarchical in nature. Hence 1.2.3 comes before 1.3 but after 1.2. For example the OID that contains the number of physical reads an Oracle7 database has performed is: oraDbSysPhysReads, 1.3.6.1.4.1.111.4.1.1.1.8.

OIM: OSI Internet Management
OSI Internet Management (OIM) is an IETF working group tasked with specifying ways in which OSI network management protocols can be used to manage TCP/IP networks. OIM is no longer active.

OIR: Online Insertion and Removal
Online Insertion and Removal, sometimes called hot swapping or power-on servicing, is a feature in many networking and computer devices that permit the addition, the replacement, or the removal of cards without interrupting the system power, entering console commands, or causing other software or interfaces to shutdown.

OMG: Object Management Group
Object Management Group (OMG) is an open membership, not-for-profit consortium that produces and maintains computer industry specifications for interoperable enterprise applications. OMG membership includes virtually every large company in the computer industry, and hundreds of smaller ones. Most of the companies that shape enterprise and Internet computing today are represented on our Board of Directors. OMG's flagship specification is the multi-platform Model Driven Architecture (MDA). It is based on the modeling specifications the MOF, the UML, XMI, and CWM. OMG's own middleware platform is CORBA, which includes the Interface Definition Language OMG IDL, and protocol IIOP.

ONC NFS
ONC NFS, Open Network Computing Network File System, is based on the original Sun version of the NFS. ONC NFS was designed for remote file access and sharing over network with various types of machines, operating systems, network architecture and transport protocols.

ONC: Open Network Computing
Open Network Computing (ONC) is the distributed applications architecture designed by Sun Microsystems, currently controlled by a consortium led by Sun. The Network File System (NFS) protocols are part of ONC architecture.

Ones Density
Ones Density is a scheme that allows a CSU/DSU to recover the data clock reliably. The CSU/DSU derives the data clock from the data that passes through it. To recover the clock, the CSU/DSU hardware must receive at least one 1 bit value for every 8 bits of data that pass through it. Also called pulse density.

Onion Routing
Onion Routing is a technique for pseudonymous (or anonymous) communication over a computer network, developed by David Goldschlag, Michael Reed, and Paul Syverson. The goal of Onion Routing (OR) is to protect the privacy of the sender and recipient of a message, while also providing protection for message content as it traverses a network. Onion Routing accomplishes this according to the principle of Chaum's Mix Cascades: messages travel from source to destination via a sequence of proxies ("onion routers"), which re-route messages in an unpredictable path. To prevent an adversary from eavesdropping on message content, messages are encrypted between routers. The advantage of Onion Routing (and Mix Cascades in general) is that it is not necessary to trust each cooperating Router; if one or more routers are compromised, anonymous communication can still be achieved.

OOTB: Out-of-the-box
Out-of-the-box (OOTB) refers to the default configuration of the product when it is first installed.

Open Circuit
Open Circuit refers to the broken path along a transmission medium. Open circuits usually prevent network communications.

Open Mail Relay
Open Mail Relay is an SMTP Email server configured in such a way that it allows anyone on the Internet to relay (i.e. send) e-mail through it. Until the 1990s, this was the normal configuration for a mail server and was often the default on UNIX systems at installation. Nowadays, e-mail transfer by "relaying," or pass-along methods, is almost forgotten. Backbone networks and Internet switches make it cost-effective and expeditious for end-user PCs or even cellphones to send mail directly to the target host, without need for relaying through a "middleman" site. The underlying communication methods of the Internet already provide end-to-end connectivity via a pass-along method.

Open Proxy
Open Proxy is a proxy server which is accessible by any Internet user. Generally, a proxy server allows users within a network group to store and forward web services such as DNS, email and web pages so that the bandwidth used by the group is reduced and controlled. With an "open" proxy, however, users outside the authorised group are able to access the machine providing this service, usually for purposes that violate the law or terms of service, such as colluding in online poker, spamming other sites, or creating zombie computers.

OpenAcs: Open Architecture
Open Architecture (OpenAcs) refers to technical frameworks that have open standards for public to legally develop products. This includes officially approved standards as well as privately designed architectures whose specifications are made public by the designers.

OpenFT
OpenFT is a peer to peer (P2P) network where nodes submit lists of shared files to other nodes to keep track of which files are available on the network. This reduces the bandwidth consumed from search requests at the price of additional memory and processing power on the nodes that store that information. The transmission of shared lists is not fully recursive: a node will only transmit its list of shared files to a single search node randomly chosen as that node's "parent", and the list of those files will not be further transmitted to other nodes.

OpenView
OpenView, a Hewlett Packard product suite, consists of an extensive portfolio of network and systems management products. The current OpenView product group includes over a hundred modules to cover various of aspects of network and system management, which work together as well as indepenently.

OpenWrt
OpenWrt is a GNU/Linux distribution for WLAN devices made by Linksys, especially the WRT54G and the WRT54GS, though the distribution can be run on many devices from other firms.The development of OpenWrt is possible because Linksys had used GNU General Public License (GPL) code and was thus legally bound to release its modification to the GPL code. Using these modifications hackers created a distribution that offers many features previously not found in routers.

OPS/INE: Operations Provisioning System/lntelligent Network Element
Operations Provisioning System/lntelligent Network Element (OPS/INE) is the Bellcore OSS that provides provisioning services for intelligent network elements.

OPT: Open Packet Telephony architecture
Open Packet Telephony architecture (OPT) is a Cisco System defined architecture for Packet Telephony.

OSF: Open Software Foundation
Open Software Foundation (OSF) is non-profit group responsible for the Distributed Computing Environment (DCE) and the Distributed Management Environment (DME).

OSI 7-Layer Reference Model
Open Systems Interconnection (OSI) 7-Layer Reference Model, also known as OSI model or 7 layers model or OSI reference model, is a reference model developed by ISO (International Organization for Standardization) in 1984, as a conceptual framework of standards for communication in the network across different equipment and applications by different vendors. It is now considered the primary architectural model for inter-computing and inter-networking communications. Most of the network communication protocols used today have a structure based on the OSI model. The OSI model defines the communications process into 7 layers, dividing the tasks involved with moving information between networked computers into seven smaller, more manageable task groups. A task or group of tasks is then assigned to each of the 7 OSI layers. Each layer is reasonably self-contained, so that the tasks assigned to each layer can be implemented independently. This enables the solutions offered by one layer to be updated without adversely affecting the other layers.

OSI Network Address
OSI Network Address, similar to the IP address, is the network address for an OSI-based network. It consists of up to 20 octets, used to locate an OSI Transport entity. The address is formatted into two parts: an Initial Domain Part that is standardized for each of several addressing domains and a Domain Specific Part that is the responsibility of the addressing authority for that domain.

OSI Presentation Address
OSI Presentation Address, similar to the combination of port number and the IP address in a TCP/IP network, is used to locate an OSI application entity. It consists of an OSI network address and up to three selectors, for use by the transport, session, and presentation entities.

OSI: Open System Interconnection
Open System Interconnection (OSI) is the international standardization program created by ISO and ITU-T to develop standards for data networking that facilitate multi-vendor equipment interoperability.

OSINET
OSINET is an international association designed to promote OSI in vendor architectures.

OSS: Operations Support System
Operations Support System (OSS) is the network management system supporting a specific management function, such as alarm surveillance and provisioning, in a carrier network. Many OSSs are large centralized systems running on mainframes or minicomputers. Common OSSs used within an RBOC include NMA, OPS/INE, and TIRKS.

OSSI: Operations Support System Interface
Operations Support System Interface OSSI) is a DOCSIS specification. For example, DOCSIS OSSI 1.0 defines the network management requirements for support in a DOCSIS 1.0 environment.

OUI: Organizationally Unique Identifier
Organizational Unique Identifier (OUI) is the first 24 bits of a MAC address for a network device, which indicates the specific vendor for that device as assigned by the IEEE.

Outframe
Outframe is the maximum number of outstanding frames allowed in an SNA PU 2 server at any time.

Out-of-band Signaling
Out-of-band Signaling is a signaling technique using frequencies or channels outside the frequencies or channels normally used for information transfer. Out-of-band signaling often is used for error reporting in situations in which in-band signaling can be affected by whatever problems the network might be experiencing.

Out-of-Rate Cell
Out-of-Rate cells are ATM ABR cells sent with CLP=1. This may be used to enable a rate increase for a connection that has an ACR=0. The source would generate out-of-rate cells to probe the network to learn when it may increase its rate. In most cases, CLP should be 0, which cells are called In-Rate Cells.

Overlap
Overlap is a mode where call control is waiting for possible additional call information from the preceding PINX because it received acknowledgment that the subsequent PINX can receive additional call information.

Overlay Multicast
Overlay Multicast, also known as End System or Peer-to-Peer Multicast, is the high bandwidth multi-source multicast among widely distributed nodes is a critical capability for a wide range of important applications including audio and video conferencing, multi-party games and content distribution. The use of multicast is an efficient and scalable mechanism to support group communication applications. Multicast decouples the size of the receiver set from the amount of state kept at any single node and potentially avoids redundant communications in the network.

Overlay Network
An overlay network is a computer network which is built on top of another network. Nodes in the overlay can be thought of as being connected by virtual or logical links, each of which corresponds to a path, perhaps through many physical links, in the underlying network. For example, many peer-to-peer networks are overlay networks because they run on top of the Internet. Dial-up Internet is an overlay upon the telephone network.

Overnet
Overnet is a decentralized peer-to-peer computer network, usually used for sharing large files (e.g., movies and CD images). Overnet implements the Kademlia algorithm. It is the creation of Jed McCaleb, the creator of eDonkey2000. The two clients are merged, although Overnet is still available without the server add-on of eDonkey2000.