RS standards Laid
down by the EIA, RS232c approximates to V.24/28; RS422 to V.11;
RS423 to V.10 and RS449 to V.36.
RARP (Reverse Address Resolution Protocol)
The TCP/IP protocol a diskless machine
uses at startup to find its IP address.
Redirect A packet
switching function that routes a call to an alternative network
address if the link to the original address is not working. It
is carried out by end point switches.
Redirector A LAN device
driver that translates operating system requests into network
events and transmits them to the right protocol stack.
Regeneration A method
of boosting a digital signal. Remote bridge LAN-to-LAN bridge
that links geographically distant LANs across a wide area link.
RFC (Request For Comment) Document
series begun in 1969 describing the Internet suite of protocols
and related experiments.
RPC (Remote Procedure Call) A
means of communication between two tasks running on separate machines
linked by a LAN. One machine can request a service, typically
computation, from the other, by executing a high level request
known as a language procedure call. RPCs are an underlying architectural
element of distributed processing and client/server computing.
RPL (Remote Program Load) Starting
a computer and loading the operating system into memory when the
operating system software is provided by a server on the network.
Reconfiguration The
process of physically altering the location or functionality of
network or system elements. Automatic configuration describes
the way sophisticated networks can readjust themselves in the
event of a link or device failing, enabling the network to continue
operation.
Red Book The 1984
compilation of the ITU-TS's standards for telecommunications,
including some for ISDN.
Redirect A packet
switching function that routes a call to an alternative network
address if the link to the original network is not available.
It is carried out by the end point switches.
Redundancy Otherwise
known as fault-tolerance, in data transmission, this refers to
characters and bits that can be removed from a transmission without
affecting the message. Ir data processing and data communications,
it means providing backup for components: should one of them fail,
the system continues to run without operation. Total redundancy
is usually impractical, but financial institutions and other organizations
with mission-critical applications attempt to install a high level
of redundancy on the basis that downtime loses money, lives, depending
on the business.
Repeater A device
that extends the maximum length of cable that can be used in a
single network. In fiber networks, it is an optoelectrical module
that receives an optical signal and converts it into an electrical
form.
Ring topology A layout
scheme in which the network takes the form of a closed loop with
the devices attached into the ring. Every workstation is linked
to two others, one on each side. All data is passed from node
to node in one direction only, each PC acting as a repeater for
the next one in the loop. Response time is determined by the number
of stations on the ring - the more there are, the slower it works.
If one PC fails, the loop is broken, though most rings have self-healing
capacity to reconfigure and continue operation. IBM's Token passing
ring ensures that the failed station is removed and its neighbors
are then directly connected.
Ring in and Ring out Token
Ring connectors on the MSAU connecting the unit to trunk cabling.
The Wrap feature is implemented at these interfaces.
RMON (Remote Monitoring) SNMP
specification for multivendor statistics-gathering by a standards-based
(de facto SNMP) management station from de facto standard (RMON)-compliant
devices.
Roaming The ability
of a mobile communications device to move freely from one part
the whole of a network operator's system or another.
RIP (Routing Information Protocol) The
protocol used by Berkeley 4BSD Unix systems to exchange routing
information among a small group of computers. Implemented by the
Unix program "routed", RIP is derived from an earlier
protocol of the same name developed at Xerox.
RJ11 Popular name
for the standard four-wire modular connector for phone connections.
RJ45 Popular name
for the eight-pin modular connector in the 10BaseT standard for
UTP connections to workstations or smart wiring hubs. The actual
connector is described in ISO standard 8877.
Rlogin (Remote Login) The
service offered by Berkeley 4BSD Unix systems that allows users
of one machine to connect to other Unix systems across an internet
and interact as if their terminals connected to the machines directly.
Although Rlogin offers essentially the same service as Telnet,
it is superior because the software passes information about the
user's environment to the remote machine.
Router Network interconnector
device operating at OSI Network Layer (Level Three) that supports
a particular Network Layer protocol and related stack, such as
TCP/IP, DecNet, XNS, SNA, OSI IP, IPX. These days routers tend
to support multiple protocols by a variety of methods, such as
Protocol Independent Routing. A router can be used to link LANs
together locally or remotely as part of a WAN. A network built
using routers is often termed an internetwork.
Routing Process of
delivering a message across one or more networks via the most
appropriate path.
Routing table Information
stored within a router that contains network path and status information.
It is used to select the most appropriate route to forward information
along.
RS232-C An EIA standard
which is the most common way of linking data devices together.
An interface for linking DCEs and DTES, it defines the electrical
characteristics of the signals from such devices. RS232 is suitable
for both synchronous and asynchronous communications and specifies
a 25-pin connector, traditionally the DB-25. 20 of the pins carry
out routine system operation while the rest are reserved for modem
testing or unallocated. For this reason it is never safe to assume
that two RS232 devices will work together. Newer, more compact
RS232 interfaces have nine pins only and an adapter card is needed.
It is functionally similar to the ITU-TS's V.24 and V.28 standards.
RS422 EIA recommended
standard to extend the RS232 50ft limit. It is most commonly implemented
on 25-pin connectors (DB-25s) and is electrically compatible with
the ITU-TS V.11 standard.
RS423 The EIA recommended
standard for cable lengths that extend the RS232 50ft limit. It
was introduced in tandem with RS422 but is not widely used. Electrically
compatible with the ITU-TS's V.10 Recommendation.
