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A RADIUS (Remote Authentication Dial-In User Service), (RFC2138, 2139) server performs authentication, authorization and accounting for a network.



Is an acronym for “Redundant Array of Inexpensive Disks” or “Redundant Array of Independent Disks”, is a technology of storing data on multiple disks to provide a combination of large capacity for storing data, data reliability, and speed of access to data. See also JBOD.



RAID 0 (striped disks) distributes data across multiple disks in a way that gives improved speed at any given instant. If one disk fails, however, all of the data on the array will be lost, as there is neither parity nor mirroring. In this regard, RAID 0 is somewhat of a misnomer, in that RAID 0 is non-redundant. A RAID 0 array requires a minimum of two drives. A RAID 0 configuration can be applied to a single drive provided that the RAID controller is hardware and not software (i.e. OS-based arrays) and allows for such configuration. This allows a single drive to be added to a controller already containing another RAID configuration when the user does not wish to add the additional drive to the existing array. In this case, the controller would be set up as RAID only (as opposed to SCSI only (no RAID)), which requires that each individual drive be a part of some sort of RAID array



RAID 1 mirrors the contents of the disks, making a form of 1:1 ratio realtime backup. The contents of each disk in the array are identical to that of every other disk in the array. A RAID 1 array requires a minimum of two drives.



RAID 3 or 4 (striped disks with dedicated parity) combines three or more disks in a way that protects data against loss of any one disk. Fault tolerance is achieved by adding an extra disk to the array, which is dedicated to storing parity information; the overall capacity of the array is reduced by one disk. A RAID 3 or 4 array requires a minimum of three drives: two to hold striped data, and a third for parity. With the minimum three drives needed for RAID 3, the storage efficiency is 66 percent. With six drives, the storage efficiency is 87 percent. The main disadvantage is poor performance for multiple, simultaneous, and independent read/write operations.



Striped set with distributed parity or interleave parity requiring 3 or more disks. Distributed parity requires all drives but one to be present to operate; drive failure requires replacement, but the array is not destroyed by a single drive failure. Upon drive failure, any subsequent reads can be calculated from the distributed parity such that the drive failure is masked from the end user. The array will have data loss in the event of a second drive failure and is vulnerable until the data that was on the failed drive is rebuilt onto a replacement drive. A single drive failure in the set will result in reduced performance of the entire set until the failed drive has been replaced and rebuilt.



RAID 6 (striped disks with dual parity) combines four or more disks in a way that protects data against loss of any two disks.



RAID 1+0 (or 10) is a mirrored data set (RAID 1) which is then striped (RAID 0), hence the “1+0” name. A RAID 1+0 array requires a minimum of four drives: two mirrored drives to hold half of the striped data, plus another two mirrored for the other half of the data. In Linux MD RAID 10 is a non-nested RAID type like RAID 1, that only requires a minimum of two drives, and may give read performance on the level of RAID 0.



RAID 0+1 (or 01) is a striped data set (RAID 0) which is then mirrored (RAID 1). A RAID 0+1 array requires a minimum of four drives: two to hold the striped data, plus another two to mirror the first pair.


RAID Reshaping

Reshaping is the process an NSA uses to add a disk to an existing RAID array. Reshaping is done block-by-block, so the time it takes depends on the size of the hard drives, not the amount of data you have on them.


RAID Resynchronization

Resynchronization is the process an NSA uses to repair a degraded RAID array after you replace the faulty hard disk. Resynchronization is done block-by-block, so the time it takes depends on the size of the hard drives, not the amount of data you have on them.



Ranging is a process that has the base station detect and recommend better transmission parameters to a mobile station. The mobile station then adjusts its power, timing, frequency offset, and modulation in order to get the communication with the base station optimized.


Rate Adaption

Rate adaption is the ability of the device to adjust the configured transmission rate to the attainable transmission rate automatically depending on your telephone line quality.


RCA connector

The Radio Corporation of America (RCA) designed this is common electrical connector for audio and video equipment. It usually uses a single male pin surrounded by a ring.


Remote Node

This is a connection point outside of the local area network. One example of a remote node is your connection to your ISP.


Remote Powerline Adapter

A remote powerline adapter is a powerline device not directly connected to the computer running the powerline utility, but in the same powerline network as the local powerline adapter.


Remote Loopback Test

A remote loopback test is used to test the connection between two DSL devices. The local device sends an Ethernet frame to the other (remote) DSL device and checks for it to be returned.


Replay Detection

The IPSec receiver can detect and reject old or duplicate packets to protect against replay attacks.


Reserved Multicast Group

The IP address range of to are reserved for multicasting on the local network only. For example, is for all hosts on a local network segment and is used to send RIP routing information to all RIP v2 routers on the same network segment. A multicast router will not forward a packet with the destination IP address within this range to other networks.


Reset Button

This hardware button is used to restore the factory default settings.



Resolution is the number of pixels that a projector, screen or monitor is capable of displaying.


Restricted Cone NAT

Restricted cone NAT maps all requests from the same private IP address and port to the same public source IP address and port. A host on the Internet can only send a packet to the private IP address and port if the private IP address and port has previously sent a packet to that hosts IP address.


Reverse Engineering

Reverse engineering means analyzing software, firmware, or hardware to find out how it works.


Reverse Proxy Mode

An SSL VPN router in reverse proxy mode serves as a proxy that acts on behalf of the local network servers (such as your web and mail servers). The SSL VPN router appears to be the server to which the remote users connect. This provides an added layer of protection for internal servers.



An RFC is an Internet formal document or standard that is the result of committee drafting and subsequent review by interested parties.



An interior or intra-domain routing protocol that uses distance-vector routing algorithms. RIP is used on the Internet and is common in the NetWare environment as a method for exchanging routing information between routers.


RJ-45 (Registered Jack-45)

An Ethernet connector that holds up to eight wires.



Resource Management cells are used in ABR (see ABR) to send feedback information from the connection�s destination and/or intervening network switches to the connections source.


RMA Number

Return Material Authorization (RMA) is a unique number that customer support assigns to a device returned for repair.



Similar to SNMP, RMON (Remote Network Monitor) allows you to gather and monitor network traffic using an agent, known as a probe, which are software processes running on network



This option lets wireless clients to move from one AP’s coverage area to another AP’s coverage area without having to log in again. This is useful for wireless clients, such as notebooks, that move around a lot.


Rogue AP

A rogue Access Point (AP) is a wireless access point detected in your network that is not approved by the network administrator.


Root Bridge

In RSTP (or STP), the root bridge is the base of the spanning tree. The root bridge determines Hello Time, Max Age and Forward Delay. The root is the device with the highest bridge priority (lowest numeric value). If multiple devices have the lowest priority, the device with the lowest MAC address becomes the root.



Rootkit is a type of malicious software that is activated each time your system boots up, making it difficult to detect as it is active before your system operating system (OS). A rootkit often allows the installation of hidden files, processes, user accounts and so on in your system OS and is able to intercept data from network connections and the keyboard.


Round Robin Algorithm

All elements in a group being equal, this is a method of providing resources to each element in turn. Each element gets an equal share of the resources. See also Weighted Round Robin Algorithm.



A device that connects two networks together. Routers monitor, direct and filter information that passes between these networks. A networking device that connects multiple networks together such as a local network and the Internet.


Router Port

A router port is a port that connects to an IGMP layer-3 multicast device. When IGMP proxy is enabled on a switch, the port works as an IGMP host to issue IGMP join and leave control messages.


Routing Information Protocol

The Routing Information Protocol (RIP) uses distance-vector routing algorithms. It is used on the Internet and is common in the NetWare environment as a method for exchanging routing information between routers.


Routing Table

A routing table stores network and route information.



RS-232 is an EIA standard which is the most common way of linking data devices together.



RSA is a public-key encryption and digital signature algorithm.



RSS (Really Simple Syndication) is a format for delivering frequently updated digital content. An RSS document (also called a “feed” or “channel”) lists a web site’s content. You can use feed reader software to download new files as they are added.



Rapid Spanning Tree Protocol (IEEE 802.1w) is an evolution of STP that provides faster tree reconfiguration. RSTP is backwards compatible with STP.


RTP (Real-time Transport Protocol)

When you make a VoIP call using SIP, the RTP (Real time Transport Protocol) is used to handle voice data transfer. See RFC 1889 for details on RTP. A protocol that enables specialized applications, such as Internet phone calls, video, and audio to occur in real time.


RTS/CTS Threshold (Request To Send)

This value controls how often wireless clients must get permission to send information to the AP. The lower the value, the more often the wireless clients must get permission. If this value is greater than the fragmentation threshold value, then wireless clients never have to get permission to send information to the AP. A networking method of coordinating large packets through the RTS Threshold setting.



This is used in measurements and statistics about what is received by a device.


Rx Gain

On a VoIP line card Rx gain increases or decreases the volume of the audio signal the subscriber receives from the SIP server.