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R
RARP
RARP is a TCP/IP
protocol term that stands for reverse address resolution protocol. It is
similar to ARP. RARP is the method that some machines use to determine
their own IP address. Essentially a machine sends out a packet that
includes a machine hardware address. A server on the same network receives
the packet and looks up the hardware address. The server then sends back
the associated IP address of that machine. It is used for machines that do
not have the capability to store their own IP addresses locally.
RAS
RAS stands for
Remote Access Service. The term is normally used in the context of Windows
NT and the ability to access NT and LAN services from a remote location.
RCP
RCP stands for
remote communications processor. It is a front end processor that is
located in a remote location (away from the mainframe). It is used to
offload CPU cycles from an SNA mainframe.
Reachability Protocols
If two
neighbors are part of the same autonomous system, they are called interior
neighbors. If two neighbors are not part of the same AS, they are known as
exterior neighbors. In order for one system to use another as a transport
medium (for traffic routing), routers which are exterior neighbors of each
other must be able to find out which networks can be reached through the
other.
Redirector
A redirector is a
software component found in a client in a client/server configuration. It
is normally used in reference to the Novell NetWare Network Operating
System. The redirector is responsible for deciding if a request for a
computer service (read a file) is for the local computer or for the network
server.
Regional Center
A
regional center is the same as a Class 1 central office. It connects
sectional centers of the telephone network together.
Remote Bridge
Bridges
function at the Data Link Layer and can be local or remote. Local bridges
connect networks in the same geographical area. Remote bridges use a
telecommunication link (telephone line, satellite, etc.) and connect two or
more LANs that are not located in the same geographical area.
Remote Procedure Call
A
remote procedure call (RPC) is a call made by a software program for
services across a network connection, usually to a server.
Repeater
A repeater
connects one cable segment of a LAN to others, possibly connecting
differing media. For example, a repeater can connect thin Ethernet to thick
Ethernet cables. It regenerates electrical signals from one segment of
cable onto all of the others. Since it reproduces exactly what it receives,
bit by bit, it also reproduces errors. But it is very fast and causes very
little delay.
Request For Comment
RFC
stands for Request for Comment. RFC documents are working notes of the
Internet research and development community. A document in this series may
be on essentially any topic related to computer communication, and may be
anything from a meeting report to the specification of a standard.
Request/Response Unit
Request/response
unit (RU) is an SNA message or possibly a portion of a long message that
has been divided into parts and has been encapsulated by the function
management layer. RUs implement the LU-to-LU protocol in IBM's SNA
architecture.
Response Time
Response
time refers to the time it takes to receive a response once a request has
been initiated. It is usually used in reference to interactive terminals
requesting information from a host computer. An example would be the time
it takes between the moment an enter key is pressed on a terminal until a
full screen of data has been returned to that terminal. Factors that impact
response time are link speed, protocol priority mechanisms, host processor
utilization (how busy the host is) and network configuration.
Ring
A method of
communications where each device connected to the network receives data in
a circular fashion. Normally a token is passed between each node to give
each node attached to the network a turn. This is normally referred to as a
star/ring because the physical topology is a star (connection made into a
hub) but logically the data flows in a ring. Token Ring is an example of a
star/ring topology.
RIP
The Routing
Information Protocol (RIP) is a vector-distance routing protocol used by
TCP/IP systems and other networking environments such as Novell. It was
originally developed for Berkeley UNIX systems and was named in part for
the UNIX daemon (like a DOS TSR) program called routed — pronounced
route d, for daemon.
Rlogin
Rlogin stands for
remote login. Suppose that you are logged in on your own workstation but
need to run a complicated inquiry on a database that resides on another
workstation. You could, of course, transfer the file to your system via
FTP, but if the file is very large, that could take hours. You could mount
it via NFS, but response time could be very slow, because your database
software would access the data records across the network.
Assuming
you have a login ID established on the other system, you can simply rlogin
to the other system and execute commands as if you were physically
connected to and logged into that workstation. So the database activity
would be local to the database file system, and only the input statements
and the displayed or printed results would have to be transmitted across
the network. Because rlogin is a UNIX-to-UNIX facility, the other system
understands the environment you are running in. That means, for example,
that you could direct the output of an inquiry command to be stored in a
file on your own system rather than the remote system.
RMON
RMON (Remote Network
Monitoring) provides standard information that a network administrator can
use to monitor, analyze, and troubleshoot a group of distributed local area networks (LANs) and interconnecting T-1/E-1 and
T-2/E-3 lines from a central site. RMON specifically defines the
information that any network monitoring system will be able to provide.
It's specified as part of the Management Information Base (MIB) in Request for Comments 1757 as an extension of the Simple
Network Management Protocol (SNMP). The latest level is RMON Version 2
(sometimes referred to as "RMON 2" or "RMON2").
RMON can be supported by hardware monitoring
devices (known as "probes") or through software or some
combination. For example, Cisco's line of LAN switches includes
software in each switch that can trap information as traffic flows through
and record it in its MIB. A software agent can gather the
information for presentation to the network administrator with a graphical
user interface. A number of vendors provide products with various kinds of
RMON support.
RMON collects nine kinds of information,
including packets sent, bytes sent, packets dropped, statistics by host, by
conversations between two sets of addresses, and certain kinds of events
that have occurred. A network administrator can find out how much bandwidth or traffic each
user is imposing on the network and what Web sites are being accessed.
Alarms can be set in order to be aware of impending problems.
RNR
RNR stands for
receiver not ready. This is an HDLC command that is issued by a station
that is not in a state to receive data.
Routable Protocols
Routable
protocols are those protocols which support Network Layer (OSI model layer
3) routing. An example of a routable protocol is TCP/IP. The IP layer
performs Network Layer routing and is therefore a routable protocol. The IP
header contains information which network components (such as routers and
gateways) use to route information through a network. The information used
in the IP datagram header for routing purposes is the source and
destination IP address.
Router
Routers use the
Network Layer addressing to route information in the appropriate direction
until a router recognizes the destination address. These types of hardware
can relieve the various user nodes on the network of interface
responsibilities. They perform the same basic function but with different
responsibilities and permit workstations on LANs to communicate over a
wider area and maintain a higher level of performance.
Routing Table
A
routing table is a data table stored in a computer's memory that contains
the information necessary to route a frame, datagram or packet to the next
node in the communications path.
RS232-C
The RS-232-C is a
commonly used cable. It is used for connecting a computer to a modem. In
1987 the RS-232-C was renamed to EIA-232-D. The specification details the
interface between a computer and a modem.
RSVP
RSVP is a Resource ReSerVation setup Protocol designed
for an integrated services Internet. It is used by a host on behalf of an
application data stream to request a specific quality of service from the
network for particular data streams or flows. It is also used by routers to
deliver QoS control requests to all nodes.
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