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Together with the QTP chip it provides four distinct Token Ring attachment ports.
QOS
Quality of service. Measure of performance for a transmission system that reflects its transmission quality and
service availability.
QOS parameters
quality of service parameters. Parameters that control the amount of traffic the source in an ATM network sends
over an SVC. If any switch along the path cannot accommodate the requested QOS parameters, the request is
rejected, and a rejection message is forwarded back to the originator of the request.
quad media access controller
See QMAC.
quad Token Ring port
See QTP.
quality of service
See QOS.
QTP
Quad Token Ring port. An ASIC chip that provides the necessary functions for switching directly between the
four Token Ring ports of a QMAC, or between these and any other port within the switch.
R
RAM
Random-access memory. Volatile memory that can be read and written by a microprocessor.
random-access memory
See RAM.
reassembly
The putting back together of an IP datagram at the destination after it has been fragmented either at the source
or at an intermediate node. See also fragmentation.
Glossary of Terms B-29
redundant system
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.
remote monitoring
See RMON.
repeater
Device that regenerates and propagates electrical signals between two network segments. See also segment.
RIF
Routing information field. Field in the IEEE 802.5 header that is used by a source-route bridge to determine
through which Token Ring network segments a packet must transit. A RIF is made up of ring and bridge numbers
as well as other information.
RII
Routing information identifier. Bit used by SRT bridges to distinguish between frames that should be
transparently bridged and frames that should be passed to the SRB module for handling.
ring
Connection of two or more stations in a logically circular topology. Information is passed sequentially between
active stations. Token Ring, FDDI, and CDDI are based on this topology.
ring in/ring out
See RI/RO.
ring group
Collection of Token Ring interfaces on one or more routers that is part of a one-bridge Token Ring network.
ring latency
Time required for a signal to propagate once around a ring in a Token Ring or IEEE 802.5 network.
ring monitor
Centralized management tool for Token Ring networks based on the IEEE 802.5 specification. See also active
monitor and standby monitor.
ring parameter server
See RPS.
ring topology
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. While
logically a ring, ring topologies are most often organized in a closed-loop star.
RI/RO
Ring in, ring out. Connectors on a MAU (or CAU) used to cable multiple wiring concentrators in series to form
a classical Token Ring of up to 260 NICs.
B-30 Catalyst Token Ring Switching Implementation Guide
RMON
Remote monitoring. MIB agent specification described in RFC 1271 that defines functions for the remote
monitoring of networked devices. The RMON specification provides numerous monitoring, problem detection,
and reporting capabilities.
root bridge
Exchanges topology information with designated bridges in a spanning-tree implementation in order to notify
all other bridges in the network when topology changes are required. This prevents loops and provides a measure
of defense against link failure.
routing information field
See RIF.
routing information identifier
See RII.
RPS
Ring parameter server. A network management function that may reside on a Token Ring to provide a ring
number, soft error report timer values, and physical location information in response to a Request Parameters
MAC frame sent from a NIC during insertion into the ring.
RS-232
Popular physical layer interface. Now known as EIA/TIA-232. See EIA/TIA-232.
S
SAP
Service access point. Field defined by the IEEE 802.2 specification that is part of an address specification. Thus,
the destination plus the DSAP define the recipient of a packet. The same applies to the SSAP. See also DSAP and
SSAP.
SAR
Segmentation and reassembly. One of the two sublayers of the AAL CPCS, responsible for dividing (at the source)
and reassembling (at the destination) the PDUs passed from the CS. The SAR sublayer takes the PDUs processed
by the CS and, after dividing them into 48-byte pieces of payload data, passes them to the ATM layer for further
processing.
SCR
Sustainable cell rate. Parameter defined by the ATM Forum for ATM traffic management. For VBR connections,
SCR determines the long-term average cell rate that can be transmitted.
segment
Section of a network that is bounded by bridges, routers, or switches.
segmentation and reassembly
See SAR.
service access point
See SAP.
Glossary of Terms B-31
service specific convergence sublayer.
See SSCS.
shielded twisted-pair
See STP.
Simple Network Management Protocol
See SNMP.
simple server redundancy protocol
See SSRP.
simplex
Capability for transmission in only one direction between a sending station and a receiving station. Broadcast
television is an example of a simplex technology. Compare with full duplex and half duplex.
single-route explorer packet
See spanning-tree explorer packet.
SMAC
Source media access control. MAC address specified in the Source Address field of a packet. Compare with
DMAC. See also MAC address.
SMDS
Switched Multimegabit Data Service. High-speed, packet-switched, datagram-based WAN networking
technology offered by the telephone companies.
SNAP
Subnetwork Access Protocol. Internet protocol that operates between a network entity in the subnetwork and a
network entity in the end system. SNAP specifies a standard method of encapsulating IP datagrams and ARP
messages on IEEE networks. The SNAP entity in the end system makes use of the services of the subnetwork and
performs three key functions: data transfer, connection management, and QOS selection.
SNMP
Simple Network Management Protocol. Network management protocol used almost exclusively in TCP/IP
networks. SNMP provides a means to monitor and control network devices, and to manage configurations,
statistics collection, performance, and security.
SNMP communities
Authentication scheme that enables an intelligent network device to validate SNMP requests.
SNMP2
SNMP Version 2. Version 2 of the popular network management protocol. SNMP2 supports centralized as well
as distributed network management strategies, and includes improvements in the SMI, protocol operations,
management architecture, and security. See also SNMP.
SONET
Synchronous Optical Network. High-speed (up to 2.5 Gbps) synchronous network specification developed by
Bellcore and designed to run on optical fiber. STS-1 is the basic building block of SONET. Approved as an
international standard in 1988.
B-32 Catalyst Token Ring Switching Implementation Guide
source address
Address of a network device that is sending data. See also destination address.
source-route bridging
See SRB.
source-route translational bridging
See SR/TLB.
source-route transparent bridging
See SRT.
SPAN
Switched Port Analyzer. The SPAN port capability on Cisco switches provide the ability to mirror the traffic from
any switch port to the SPAN. Network analyzers and RMON probes can be connected to the port for in-depth
troubleshooting. one Token Ring port on a switch on another port, providing a powerful network
troubleshooting tool.
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