gloss_R

R

Redundant Array of Inexpensive Disks (RAID).

RAID 1 is disk mirroring, in which all data is written to two drives. In RAID 2, bit-interleaved data is written across multiple disks; additional disks perform error detection. A RAID 3 disk drive has one parity drive plus an even number of data drives . Data is transferred one byte at a time, and reads and writes are performed in parallel. Like RAID 3, RAID 4 has a dedicated parity drive, but the data is written to the disks one sector at a time. Also reads and writes occur independently. In RAID 5, the controllers write data a segment at a time and interleave parity among them. (A segment is a selectable number of blocks.) RAID 5 does not use a dedicated parity desk. It offers good read performance, but suffers a write penalty. RAID 1, 3, and 5 are appropriate for networks.

Remote Monitor (RMON).

The RMON MIB defines the standard network monitoring functions for communication between SNMP-based management consoles and remote monitors , which are often called probes. RMON extends SNMP by looking at traffic between devices instead of at individual devices. It also facilitates local capture of statistics, history, and even traffic, so that polling activity by the management console can be minimized.

Remote Procedure Call (RPC).

An RPC is part of an application that activates a process on another node on the network and retrieves the results.

repeater.

A repeater is a Physical layer device that regenerates, retimes, and sometimes amplifies electrical or optical signals.

Request For Comment (RFC).

An RFC is the Internet's notation for draft, experimental, and final standards.

request for information (RFI).

An end- user company issues an RFI document to ask systems integrators and manufacturers to propose and design a system that will fulfill the corporation's business requirements.

request for proposal (RFP).

An end-user company issues an RFP document that asks systems integrators and manufacturers to bid on their network designs and specifications.

requirements analysis.

A requirements analysis is the process through which you define and evaluate the business needs of your network system.

return on investment (ROI).

Calculating the ROI enables MIS shops to gauge the network's success from a business profit-and-loss standpoint. The savings or benefits of networking projects ought to represent a return on invested capital as good or better than that of the business as a whole.

ring topology.

In a ring topology, packets travel in a closed loop. Packets pass sequentially between active stations , and each station examines them and copies any that are intended for it. The packets finally return to the originating station, which removes them from the network.

risk analysis.

A risk analysis is the process by which a company analyzes the business and technology risks of installing a new system.

RJ-11.

An RJ-11 connector is a four-wire modular connector that is used by the telephone system.

RJ-45.

An RJ-45 is an eight-wire modular connector that is used by telephone systems. The eight-pin modular connectors used for 10BaseT UTP cable resemble RJ-45 connectors, but they have substantially different electrical properties.

RMON Groups

The original IETF proposed standard for the RMON MIB, RFC 1271 defines nine Ethernet groups: Ethernet Statistics, Ethernet History, Alarms, Hosts, Host Top N ("N" indicates that it collects information on a number of devices), Traffic Matrix, Filters, Packet Capture, and Events. RFC 1513 extends this standard to support Token Ring. See MIB, RMON, RMON Token Ring.

RMON Probe

Sometimes called an RMON agent, an RMON probe is either firmware built into a specific network device like a router or switch, or a specific device built for network monitoring and inserted into a network segment. An RMON probe tracks and analyzes traffic and gathers statistics, which are then sent back to the monitoring software. Historically, an RMON probe was a separate piece of hardware, but now RMON firmware is embedded in high-end switches and routers. See RMON.

RMON Remote Monitoring,

or RMON, is a set of SNMP-based MIBs that define the instrumenting, monitoring, and diagnosing of local area networks at the OSI Data-link layer. In IETF RFC 1271, the original RMON, which is sometimes referred to as RMON-1, defines nine groups of Ethernet diagnostics. A tenth group , for Token Ring, was added later in RFC 1513. RMON uses SNMP to transport data. To be RMON-compliant, a vendor need implement only one of the nine RMON groups. See MIB, RMON-2, RMON Probe, RMON Token Ring, SNMP.

RMON Token Ring

IETF proposed standard RFC 1513 is an extension to the original RMON MIB (RFC 1271), with support for Token Ring. Some sources refer to this standard as RMON TR, but it's generally considered a replacement for the older standard. In RFC 1513, the RFC 1271 Statistics and History monitoring groups have additional specifications for Token Ring, and a tenth group is added to monitor ring configuration and source routing. In 1994, the proposed standard became a draft standard under the designation RFC 1757; many vendors use the RFC 1513 and 1757 numbers interchangeably. See MIB, RMON.

RMON-2

The second Remote Monitoring MIB standard, called RMON-2, defines network monitoring above the Data-link layer. It provides information and gathers statistics at the OSI Network layer and Application layer. Unlike the original RMON, RMON-2 can see across segments and through routers, and it maps network addresses (such as IP) onto MAC addresses. RMON-2 is currently a proposed standard under IETF RFC 2021. To be compliant with RMON-2, a vendor must implement all the monitoring functions for at least one protocol. Note that RMON-2 does not include MAC-level monitoring, and thus it is not a replacement for the original RMON. See RMON.

roll back.

A database application's ability to abort a transaction before it has been committed is called a roll back.

roll forward.

A database's ability to recover from disasters is called a roll forward. The database reads the transaction log and re-executes all of the readable and complete transactions.

router.

A router is a Network-layer device that connects networks that use the same Network-layer protocol, for example TCP/IP or IPX. A router uses a standardized protocol, such as RIP, to move packets efficiently to their destination over an internetwork. A router provides greater control over paths and greater security than a bridge; however, it is more difficult to set up and maintain.

Routing Information Protocol (RIP).

Routing Information Protocol (RIP)

RIP is the routing protocol used by most TCP/IP routers. It is a distance-vector routing protocol, and it calculates the shortest distance between the source and destination addresses based on the lowest "hop" count.

RTP

The Real-Time Transport Protocol is the IETF's standard for transporting real-time data, such as voice or video, over a packet-based network that doesn't guarantee Quality of Service (QOS). A related standard is RTCP, or the Real-Time Transport Control Protocol, which provides feedback between two units (point-to-point) or a larger group (known as multicast or multipoint). The ITU-T's non-QOS multimedia standards such as H.323 and H.324 are based on RTP/RTCP. See H.323, H.324, QOS.