Race Condition Ranging
Race Condition Ranging refers to the process of acquiring the correct timing offset such that the transmissions of a cable modem are aligned with the correct mini-slot boundary.

RACE: Research on Advanced Communications in Europe
Research on Advanced Communications in Europe is a project sponsored by the EC for the development of broadband networking capabilities.

RADSL: Rate-adaptive Asymmetric Digital Subscriber Line
Rate-adaptive Asymmetric Digital Subscriber Line (RADSL) is a variation of ADSL which automatically adjusts the connection speed depanding on the quality and length of the telephone line. In RADSL, the broadband modem is configured at startup to test the phone line and adjust the data rate. RADSL typically operates at a lower date rate than regular ADSL. Like ADSL, RADSL provides relatively more bandwidth for downloads and less for uploads.

Random Early Detection
Random Early Detection is a congestion avoidance algorithm in which a small percentage of packets are dropped when congestion is detected and before the queue in question overflows completely.

Ranging
Ranging refers to the process of acquiring the correct timing offset such that the transmissions of a cable access router are aligned with the correct mini-slot boundary.

RAS: Reliability, Availability, Serviceability
Reliability, Availability, Serviceability are three different but related measures that are critical for a system or a network. Reliability represents the probability of components, parts and systems to perform their required functions for a desired period of time without failure in specified environments with a desired confidence. Availability is defined as the probability that the system is operating properly when it is requested for use. Servicebility measures how long and how difficult to fix the problems in a system or network and bring it back to normal operation.

Rate Limiting
Rate limiting is the function of controlling the maximum rate of traffic sent or received on a network interface. Traffic that is less than or equal to the specified rate is sent, whereas traffic that exceeds the rate is dropped or delayed.

Rate Queue
Rate Queue, a concept in ATM network, is a value associated with one or more virtual circuits that defines the speed at which an individual virtual circuit transmits data to the remote end. Each rate queue represents a portion of the overall bandwidth available on an ATM link. The combined bandwidth of all configured rate queues should not exceed the total available bandwidth.

RDF: Rate Decrease Factor
Rate Decrease Factor (RDF) is an ATM ABR service parameter. RDF controls the decrease in the cell transmission rate. RDF is a power of 2 from 1/32,768 to 1. For ABR traffic, RDF effects the time rate of change of the ACR. This value effects TCP round trip time calculations, which in turn effects TCP throughput.

RDI: Remote Defect Indication
Remote Defect Indication (RDI) is an indication in an ATM network that indicates a failure has occurred at the far end of the ATM network. The RDI alarm indication does not identify the specific circuit in a failure condition. When the physical layer detects loss of signal or cell synchronization, RDI cells are used to report a VPC/VCC failure. RDI cells are sent upstream by a VPC/VCC endpoint to notify the source VPC/VCC endpoint of the downstream failure.

Re-Activation
Re-Activation is the process of re-enabling network access and privileges for a subscriber device and reclaiming device attributes for other subscriber devices.

Reassembly
Reassembly is the process of putting back together of an IP datagram at the destination after it has been fragmented either at the source or at an intermediate node.

Redirect
Redirect is a mode of the ICMP and ES-IS protocols that allows a router to tell a host that using another router would be more effective.

Redirect Server
Redirect Server is a SIP user agent server that accepts a SIP request, maps the address into zero or more new addresses, and directs the client to contact an alternate set of URIs. It does not initiate its own SIP request nor does it accept calls.

Redirector
Redirector is a software system that intercepts requests for resources within a computer and analyzes them for remote access requirements. If remote access is required to satisfy the request, the redirector forms a Remote Procedure Call (RPC) and sends the RPC to lower-layer protocol software for transmission through the network to the node that can satisfy the request.

Redundancy
Redundancy, in networking, is a scheme to increase network availability. Redundance refers to the duplication of devices, services, or connections so that, in the event of a failure, the redundant devices, services, or connections can perform the work of those that failed component.

Redundant System
Redundant system refers to the computer, router, switch, or other system that contains two or more of each of the most important subsystems, such as two disk drives, two CPUs, or two power supplies.

Reed-Solomon Encoder
Reed-Solomon Encoder is a device that takes a block of digital data and adds extra "redundant" bits. When errors occur during transmission or storage, the Reed-Solomon decoder processes each block and attempts to correct errors and recover the original data. Reed-Solomon codes are used in storage devices (including tape, compact disc, DVD), barcodes, wireless or mobile communications (including cellular telephones, microwave links, and so on), satellite communications, digital television/DVB, and high-speed modems (such as ADSL, xDSL, and so on).

Reference Point
Reference Point is an ISDN term that refers to the various interfaces between ISDN devices that implement different ISDN function groups.

Registrar
Registrar is a server that accepts REGISTER requests. A registrar typically is colocated with a proxy or a redirect server and might offer location services.

Registered Endpoint
Registered Endpoint, a concept in a VOIP netowrk, is an endpoint that has informed the Gatekeeper that it is online, active and ready to receive calls, and has received confirmation from the Gatekeeper of its registration request.

Registered Ports
Registered Ports refer to one of the classes of the TCP/UDP ports, defined by IETF IANA. The other two classes are the Well Known Ports and the Dynamic and/or Private Ports. The Registered Ports are those with a port number from 1024 through 49151, which are assigned for each private application by IANA.

Relay
Relay, a concept in the OSI networking, refers to a device that connects two or more networks or network systems. A data link layer (Layer 2) relay is a bridge; a network layer (Layer 3) relay is a router.

Reliability
Reliability represents the probability of components, parts and systems to perform their required functions for a desired period of time without failure in specified environments with a desired confidence.

Reload
Reload refers to the event of a router rebooting, or the command that causes the router to reboot.

Remote Assistance
Remote Assistance is a feature in Windows Messenger to help another person remotely to get a problem solved on their computer.

Remote Bridge
Remote Bridge connects physically disparate local area network (LAN) segments together via WAN links.

Remote Computer
A remote computer is a computer to which a user does not have physical access, but which the user can access/manipulate via some kind of network from a local computer (one which the user does have physical access to).

Remote DBA: Remote Database Administration
Remote Database Administration (Remote DBA) refers to the arrangement where a client computer is monitored from a remote location, usually by a third party company, to ensure that the database and computer system that are being monitored continue to run properly and efficiently over a period of time.

Remote System
Remote System is a network device that is located at a remote network and can be accessed by a local system via network communications.

Rendezvous Point
Rendezvous Point (RP) refers to a router specified in PIM sparse mode implementations to track membership in multicast groups and to forward messages to known multicast group addresses. An RP acts as the meeting place for sources and receivers of multicast data. In a PIM-SM network, sources must send their traffic to the RP. This traffic is then forwarded to receivers down a shared distribution tree. By default, when the first hop router of the receiver learns about the source, it will send a join message directly to the source, creating a source-based distribution tree from the source to the receiver. This source tree does not include the RP unless the RP is located within the shortest path between the source and receiver.

Repeater
Repeater, also known as network repeater, is a type of network device that regenerates incoming electrical, wireless or optical signals. With physical media like Ethernet or Wi-Fi, data transmissions can only span a limited distance before the quality of the signal degrades. Repeaters attempt to preserve signal integrity and extend the distance over which data can safely travel. Active hubs are repeaters. In Wi-Fi, access points function as repeaters when operating in so-called "repeater mode." In moble wireless, repeater receives radio signals from the base station and then amplified and retransmitted to areas where radio shadow occurs, and vice versa.

Repeating Hub
Repeating Hub is a repeater with more than two ports. Often simply called a Hub, it can regenerate incoming electrical, wireless or optical signals.

Residential Gateway
Residential Gateway is a Customer premises equipment (CPE) located at the subscriber's home that has connections to the service provider's VoIP network.

Reverse Telnet
Reverse Telnet refers to the situation of initiating a Telnet session from the host instead of the client.

RFC: Registration ConFirmation
Registration ConFirmation (RCF) is a H.323 VOIP netowrk Registration, Admission and Status (RAS) message sent as a registration confirmation.

RFC: Request For Comments
Request for Comments (RFC), a series of documents about the Internet technologies, started in 1969 (when the Internet was the ARPANET). The documents discuss many aspects of computing and computer communication focusing on networking protocols, procedures, programs, and concepts, but also including meeting notes, opinion, and sometimes humor. The specification documents of the Internet protocol suite, as defined by the Internet Engineering Task Force (IETF) and its steering group (the IESG), are published as RFCs. Many of the TCP/IP protocols and PPP protocols are defined by rfc's.

RFP: Request for Proposal
An Request For Proposal (RFP) is an invitation for suppliers, through a bidding process, to bid on a specific product or service. An RFP is usually part of a complex sales process, also known as enterprise sales.

RFS: Remote File System
Remote File System (RFS) is a distributed file system, similar to Network File System (NFS), developed by AT&T and distributed with their UNIX System V operating system.

RIF: Rate Increase Factor
Rate Increase Factor (RIF) is an ATM ABR service parameter. RIF controls the amount by which the cell transmission rate may increase upon receipt of an RM-cell. The additive increase rate AIR=PCR*RIF. RIF is a power of 2, ranging from 1/32,768 to 1. For ABR traffic, RIF effects the time rate of change of the ACR. This value effects TCP round trip time calculations, which in turn effects TCP throughput.

RIF: Routing Information Field
Routing Information Field (RIF) is a field in the IEEE 802.5 (Token Ring) header that is used by a source-route bridge to determine through which Token Ring network segment a packet must transit. A RIF is made up of ring and bridge numbers as well as other information.

RII: Routing Information Identifier
Routing Information Identifier (RII) is a bit in the IEEE 802.5 (Token Ring) used by Source-route transparent (SRT) bridges to distinguish between frames that should be transparently bridged and frames that should be passed to the source-route bridging (SRB) module for handling.

RIM: Request Initialization Mode
Request Initialization Mode(RIM), a command in the HDLC protocol, is a request from a secondary station for initialization to a primary station. Once the secondary station sends RIM, it can only respond to SIM, DSIC, TEST or XID commands.

Ring
Ring is a popular network topology in which connection of two or more stations in a logically circular way. Information is passed sequentially between active stations. Token Ring, FDDI, and CDDI are based on this topology.

Ring Group
Ring Group is a collection of Token Ring interfaces on one or more routers that is part of a one-bridge Token Ring network.

Ring Latency
In a ring network, such as a Token ring network, the ring latency is the time required for a signal to propagate once around the ring. Ring latency may be measured in seconds or in bits at the data transmission rate. Ring latency includes signal propagation delays in (a) the ring medium, (b) the drop cables, and (c) the data stations connected to the ring network.

Ring Monitor
Ring Monitor is a centralized management tool for Token Ring networks based on the IEEE 802.5 specification.

Ring Network
A ring network is a topology of computer networks where each user is connected to two other users, so as to create a ring. Token Ring, FDDI, and CDDI are based on this topology. Ring networks tend to be inefficient when compared to client/server networks because data must travel through more points before reaching its destination.

Ring Topology
Ring Topology is a network topology that consists of a series of repeaters connected to one another by unidirectional transmission links to form a single closed loop. Each station on the network connects to the network at a repeater. Although logically a ring, ring topologies most often are organized in a closed-loop star. Token Ring, FDDI, and CDDI are based on this topology.

RJE: Remote Job Entry
Remote Job Entry (RJE) is an application that is batch-oriented, as opposed to interactive. In RJE environments, jobs are submitted to a computing facility, and output is received later.

RM: Resource Management
Resource Management (RM) refers to management of critical resources in an ATM network. Two critical resources are buffer space and trunk bandwidth. Provisioning can be used to allocate network resources in order to separate traffic flows according to service characteristics.

RM-CDT: RM-cell transfer delay
RM-cell transfer delay (RM-CTD), a concept in the ATM network, is the elapsed time between an RM-cell exit event at the measurement point 1 (e.g., at the source UNI) and the corresponding RM-cell entry event at a measurement point 2 (e.g., the destination UNI) for a particular connection.

RM-CDV: RM-Cell Delay Variation
RM-Cell Delay Variation (RM-CDV) is the variation in RM-cell transfer delay (RM-CTD) of RM cells associated with a given traffic load, orientation and distribution, as well as an integration period. RM-CDV = max (RM-CTD) - min (RM-CTD) where max and min indicate the maximum and minimum over the integration period, respectively. RM-CDV is a component of RM-cell transfer delay, induced by buffering and RM-cell scheduling. RM-CDV effects the time required to notify the source of a change in the condition of the network. This in turn effects TCP round trip time calculations. Large values of RM-CDV will adversely effect TCP throughput and cause SAR timeout.

RM-CER: RM-Cell Error Ratio
RM-Cell Error Ratio (RM-CER) is the ratio of RM-cells with payload errors in a transmission in relation to the total number of RM-cells sent in a transmission associated with a given traffic load, orientation and distribution, as well as an integration period. In other words,
RM-CER = RM-Cells with payload errors / Total RM-Cells Transmitted.
RM-CER effects the time required to notify the source of a change in the condition of the network. This in turn effects TCP round trip time calculations. Large values of RM-CER will adversely effect TCP throughput and cause SAR timeout.

RM-CLR: RM-Cell Loss Ratio
RM-Cell Loss Ratio (RM-CLR) is the ratio of lost RM-cells in a transmission in relation to the total RM-cells sent in a transmission associated with a given traffic load, orientation and distribution, as well as an integration period. In other words,
RM-CLR = Lost RM-Cells / Total RM-Cells Transmitted.

The smaller the RM-CLR value in an ATM network, the better. RM-CLR effects the time required to notify the source of a change in the condition of the network. This in turn effects TCP round trip time calculations. Large values of RM-CLR will adversely effect TCP throughput and cause SAR timeout.

RM-CMR: RM-Cell Misinsertion Ratio
RM-Cell Misinsertion Ratio (RM-CMR) is the ratio of RM-cells received at an endpoint that was not originally transmitted by the source end in relation to the total number of RM-cells properly transmitted associated with a given traffic load, orientation and distribution, as well as an integration period.
RM-CMR = Misinserted RM-Cells / Total RM-Cells Transmitted.

RM-CMR effects the time required to notify the source of a change in the condition of the network. This in turn effects TCP round trip time calculations. Large values of RM-CMR will adversely effect TCP throughput and cause SAR timeout.

RM-CTD: RM-Cell Transfer Delay
RM-Cell Transfer Delay (RM-CTD) is the elapsed time between an RM-cell exit event at the measurement point 1 (e.g., at the source UNI) and the corresponding RM-cell entry event at a measurement point 2 (e.g., the destination UNI) for a particular connection. The RM-CTD between two measurement points is the sum of the total inter-ATM node transmission delay and the total ATM node processing delay. This number is a constant and should not adversely effect performance.

RNIE: Redirecting Number Information Element
Redirecting Number Information Element (RNIE) is a type of ISDN Information Element messages defined in ITU-T Q.931.

Roaming Service
Roaming service is the ability to get access to the Internet when away from home at the price of a local call or at a charge considerably less than the regular long-distance charges. Roaming service is popular in mobile wireless services. It is also a dial service for cable subscribers that require access away from their home cable modems.

ROLC: Routing Over Large Clouds
Routing Over Large Clouds (ROLC) is a working group in IETF created to analyze and propose solutions to problems that arise when performing IP routing over large, shared media networks, such as ATM, Frame Relay, SMDS, and X.25.

Root Account
Root Account is the privileged account on UNIX systems used exclusively by network or system administrators.

Root Bridge
Root Bridge refers to the bridge that exchanges topology information with designated bridges in a spanning-tree implementation to notify all other bridges in the network when topology changes are required.

Rotary Groups
Rotary Groups, also known as hunt group, refers to a series of telephone lines that are programmed to find the next free line when a call is received.

Route
Route in networking refers to a logic path within network in which a packet is traveling through from a sender to a receiver.

Route Distinguisher
A route distinguisher is an address qualifer used only within a single internet service provider's Multi-Protocol Label Switching (MPLS) network. It is used to distinguish the distinct Virtual Private Network (VPN) routes of separate customers who connect to the provider.The route distinguisher is an 8-byte field prefixed to the customer's Internet Protocol address (IPv4). The resulting 12-byte field is a unique "VPN-IPv4" address. In a single provider's network, a router which connects to a customer is called a Provider Edge (PE) router, and the customer's router it connects to is called a Customer Edge (CE) router.

Route Distinguisher
Route Distinguisher is an 8-byte value that is concatenated with an IPv4 prefix to create a unique VPN IPv4 prefix.

Route Extension
Route Extension, a concept in SNA, is a path from the destination subarea node through peripheral equipment to a Network Accessible Unit (NAU).

Route Flapping
Route Flapping refers to a situation where a router transmits routing updates alternately advertising a destination network first via one route, then via a different route. Route flapping is caused by pathological conditions (hardware errors, software errors, configuration errors,unreliable connections, etc.) within the Internet that cause certain reachability information to be repeatedly advertised and withdrawn. The most common causes of route flapping are configuration errors and intermittent errors in communications links.

Route Map
Route Map in networking is a method of controlling the redistribution of routes between routing domains.

Route Summarization
Route Summarization, or IP route summarization, is a mechanism used to design networks that are more flexible and perform better. It requires consolidation of advertised addresses which causes a single summary route to be advertised. Although some routing protocols summarize only at the boundaries of major network numbers, others support route summarization (aggregation) at any bit boundary. Variable-length subnet masks enable routing protocols to summarize on bit boundaries.

Routed Bridge Encapsulation
Routed Bridge Encapsulation is the process by which a stub-bridged segment is terminated on a point-to-point routed interface. Specifically, the router is routing on an IEEE 802.3 or Ethernet header carried over a point-to-point protocol, such as PPP, ATM, or Frame Relay.

Routed Protocol
Routed Protocols are the layer 3 protocols which transport data across the network. Some popular layer three protocols, such as Internet Protocol (IP), Novell Internetwork Packet eXchange (IPX), and AppleTalk are routed protocols.

Router
Routers are physical devices or a software system within a switch operating a layer 3 of the OSI model. A router forwards and routes data packets along networks. A router connects at least two networks, commonly two LANs or WANs or a LAN and its ISP network. A router is located at any gateway where one network meets another, including each point-of-presence on the Internet.

Routing
Routing is a means of discovering paths in computer networks along which information can be sent. Routing directs forwarding, the passing of logically addressed packets from their source toward their ultimate destination through intermediary nodes, called routers. Forwarding is usually directed by routing tables within the routers, which maintain a record of the best routes to various network destination locations; thus, the construction of routing tables is the primary goal of routing. Routing differs from bridging in its assumption that addresses are structured so that similar addresses are close together in the network, allowing the route to a group of addresses to be represented with a single routing table entry.

Routing Daemon
Routing Daemon is the process on the router that is running the routing protocol, communicating with its neighbor routers, is usually called a routing daemon. The routing daemon updates the kernel's routing table with information it receives from neighbor routers.

Routing Domain
Routing Domain, a concept in ISO network, refers to a group of end systems and intermediate systems operating under the same set of administrative rules. Within each routing domain is one or more areas, each uniquely identified by an area address.

Routing Metric
Routing Metric is a group of parameters by which a routing algorithm determines that one route is better than another. This information is stored in routing tables. Metrics include bandwidth, communication cost, delay, hop count, load, MTU, path cost, and reliability. Sometimes referred to simply as a metric.

Routing Protocol
Routing Protocol is a type of layer 3 protocol which allows routers to dynamically advertise and learn routes, determines which routes are available and which are the most efficient routes to a destination. Routing protocols provide the layer 3 network state update and populate routing tables on the layer 3 switch/router. There are two types of routing protocols: Distance Vector Routing and Link State Routing. Basically, Distance Vector protocols determine best path on how far the destination is, while LinkState protocols are capable of using more sophisticated methods taking into consideration link variables, such as bandwidth, delay, reliability and load.

Routing Redistribution
Routing Redistribution is the process of making the routing information discovered through one routing protocol to be distributed in the update messages of another routing protocol.

Routing Switch
Routing switch is a switch that also performs routing functions. Usually a switch operates at layer 2 (the Data Link layer) of the OSI Reference Model while routers operate at layer 3 (the Network layer). Routing switches, performing both layer 2 and layer 3 functions, typically have the routing operations implemented in hardware rather than using software. Therefore it is faster than the software based routers. However, routing switching may not as powerful or as flexible as full-fledged routers. Because they perform some layer 3 functions, routing switches are sometimes called layer-3 switches.

Routing Table
Routing Table is a table stored in a router or some other internetworking device that keeps track of routes to particular network destinations and, in some cases, routing metrics associated with those routes.

Routing Update
Routing Updates are messages sent from a router other routers to indicate network reachability and associated cost information. Routing updates typically are sent at regular intervals and after a change in network topology.

RPC Server: Remote Procedure Call Server
Remote Procedure Call Server (RPC Server) is a router or other device that acts as a server for Remote Procedure Calls.

RPF: Reverse Path Forwarding
Reverse Path Forwarding (RPF) is a multicasting technique in which a multicast datagram is forwarded out of all but the receiving interface if the receiving interface is the one used to forward unicast datagrams to the source of the multicast datagram. RPF is utilized to build source-specific forwarding paths (SPT, shortest path tree), amongst which the traffic can flow more efficiently.

RPF: Reverse-path Forwarding
Reverse path forwarding (RPF) is a technique used in multicast routing. RPF is utilized to build source-specific forwarding paths (SPT, shortest path tree), amongst which the traffic can flow more efficiently. Source-specific multicast makes immediate use of this. Any-source multicast usually switches from a centralized tree to the SPT on certain predefined conditions and for each source individually. This functionality is achieved by issuing source-specific joins towards the source, using the source address to look up an unicast / MRIB routing table entry. This continues router by router until the source is reached. The source and the routers in between now start forwarding the traffic towards the direction the original join came from. The result is that the traffic is forwarded along the reverse path from the source back to the listener.

RPR: Restore Path Request
Restore Path Request (RPR) is a WaRP request sent using a Restore Path packet that is used to establish a virtual path between two nodes over an optical link. The request is sent by a source node, or a proxy source node, to establish an intra-zone path for a Virtual Wavelength Path (VWP). The packet usually is sent during failure recovery procedures but also can be used for provisioning new VWPs. The node that sends the request is called the originating node. The node that terminates the request is called the target node.

RR: Relative Rate
Relative Rate (RR), a concept in ATM networking, is one of the congestion feedback modes provided by ABR service. In RR mode, switches set a bit in forward and backward RM cells to indicate congestion.

RRDtool
RRDtool is a round-robin database tool by Tobi Oetiker. It is designed to handle time-series data like network bandwidth, temperatures, CPU load etc. The data is stored in round-robin database so that system storage footprint remains constant over the time.

RRJ: Registration ReJection
Registration ReJection (RRJ) is a VOIP H.323 VOIP RAS message sent as a registration rejection.

RRQ: Registration ReQuest
Registration ReQuest (RRQ) is a VOIP H.323 RAS message sent as a registration request.

RSB: Reservation State Block
Reservation State Block (RSB) is a block maintained by RSVP to store a reservation.

RSIP: ReStart In Progress
ReStart In Progress (RSIP) is a Media Gateway Control Protocol(MGCP) command used to indicate that a span (or collection of spans) has come into service, has gone out of service, or is about to go out of service.

RTFM: Read the Fantastic Manual
Read the Fantastic Manual(RTFM) is the often answer when someone asks a simple or common question.

RTS: Request To Send
Request To Send (RTS) is the EIA/TIA-232 control signal that requests a data transmission on a communications line.

RTSC: Read the Source Code
Read the Source Code (RTSC) is an acronym often used when a software developer asks a question about undocumented code.

RTT: Round-trip Time
Round-trip Time (RTT) is a measure of delay between two hosts which is the time required for a packet or datagram to travel from the source to the destination and back. RTT includes the time required for the destination to process the message from the source and to generate a reply. RTT is used by some routing algorithms to aid in calculating optimal routes. In most packet switching network, delays vary as a result of congestion. Thus, measures of round trip times usually give averages, which may have high standard deviation.

RU: Request/Response Unit
Request/Response Unit (RU), a term in the SNA, refers to the request and response messages exchanged between NAUs in an SNA network.

Run length coding
Run length coding is a type of video coding used in H.261 and H.263 codecs.