- Single-attached
concentrator. FDDI or CDDI concentrator that connects to
the network by being cascaded from the master port of another FDDI
or CDDI concentrator.
safety ground wire
- Circuit wire that connects
to a local earth ground and the chassis of an electrical appliance
or device via an electrical outlet and plug. It is used to ensure
that no voltage potential exists between the chassis of the
electrical device and the earth ground.
- Any decrease of below 80% in
the normal voltage carried by a power line. A sag is sometimes
referred to as a brownout. See surge,
spike,
and oscillation.
sampling rate
- Rate at which samples of a
particular waveform amplitude are taken.
- 1.) 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.
2.) Service Advertisement Protocol. IPX protocol that provides a means of informing network clients, via routers and servers, of available network resources and services. See also IPX.
- 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. See also AAL,
ATM
layer, CPCS,
CS,
and SSCS.
- Single attachment
station. Device attached only to the primary ring of an
FDDI ring. Also known as a Class B station. Compare with DAS.
See also FDDI.
satellite communication
- Use of orbiting satellites
to relay data between multiple earth-based stations. Satellite
communications offer high bandwidth and a cost that is not related
to distance between earth stations, long propagation delays, or
broadcast capability.
SBus
- Bus technology used in Sun
SPARC-based workstations and servers. The SBus specification has
been adopted by the IEEE as a new bus standard.
- 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. See also VBR.
- Serial clock
transmit external. Timing signal that DTE echoes to DCE to
maintain clocking. SCTE is designed to compensate for clock phase
shift on long cables. When the DCE device uses SCTE instead of its
internal clock to sample data from the DTE, it is better able to
sample the data without error even if there is a phase shift in the
cable. See also phase
shift.
- Synchronous Digital
Hierarchy. European standard that defines a set of rate and
format standards that are transmitted using optical signals over
fiber. SDH is similar to SONET, with a basic SDH rate of 155.52
Mbps, designated at STM-1. See also SONET
and STM-1.
- Synchronous Data
Link Control. SNA data link layer communications protocol.
SDLC is a bit-oriented, full-duplex serial protocol that has spawned
numerous similar protocols, including HDLC and LAPB. See also HDLC
and LAPB.
SDLC broadcast
- Feature that allows a Cisco
router that receives an all-stations broadcast on a virtual
multidrop line to propagate the broadcast to each SDLC line that is
a member of the virtual multidrop line.
- Cisco router feature with
which disparate environments can be integrated into a single,
high-speed, enterprise-wide network. Native SDLC traffic can be
passed through point-to-point serial links with other protocol
traffic multiplexed over the same links. Cisco routers can also
encapsulate SDLC frames inside IP datagrams for transport over
arbitrary (non-SDLC) networks. Replaces proxy polling. See also proxy
polling.
SDLLC
- Feature that performs
translation between SDLC and IEEE 802.2 type 2.
SDSU
- SMDS DSU.
DSU for access to SMDS via HSSIs and other serial interfaces.
- Service data unit.
Unit of information from an upper-layer protocol that defines a
service request to a lower-layer protocol.
- Simple and efficient
AAL. Scheme used by AAL5 in which the SAR sublayer segments
CS PDUs without adding additional fields. See also AAL,
AAL5,
CS,
and SAR.
secondary
- See secondary
station.
- One of the two rings making
up an FDDI or CDDI ring. The secondary ring is usually reserved for
use in the event of a failure of the primary ring. Compare to primary
ring.
- In bit-synchronous data link
layer protocols such as HDLC, a station that responds to commands
from a primary station. Sometimes referred to simply as a secondary.
See also primary
station.
- One of five categories of
network management defined by ISO for management of OSI networks.
Security management subsystems are responsible for controlling
access to network resources. See also accounting
management, configuration
management, fault
management, and performance
management.
- Responds to configuration
queries from nonseed routers on its connected AppleTalk network,
allowing those routers to confirm or modify their configurations
accordingly. See also nonseed
router.
- 1.) Section of a network
that is bounded by bridges, routers, or switches.
2.) In a LAN using a bus topology, a segment is a continuous electrical circuit that is often connected to other such segments with repeaters.
3.) Term used in the TCP specification to describe a single transport layer unit of information. The terms datagram, frame, message, and packet are also used to describe logical information groupings at various layers of the OSI reference model and in various technology circles.
segmentation and reassembly
- See SAR.
sequence number
- Number used to ensure
correct sequencing of the arriving data.
Sequenced Packet Exchange
- See SPX.
Sequenced Packet Protocol
- See SPP.
Sequenced Routing Update
Protocol
- See SRTP.
serial clock transmit
external
- See SCTE.
Serial Interface Processor
- See SIP.
Serial Line Internet
Protocol
- See SLIP.
- Method of data transmission
in which the bits of a data character are transmitted sequentially
over a single channel. Compare with parallel
transmission.
serial tunnel
- See STUN.
- Node or software program
that provides services to clients. See also back
end, client,
and front
end.
Server Message Block
- See SMB.
service access point
- See SAP.
Service Advertisement
Protocol
- See SAP.
service data unit
- See SDU.
service password-encryption
- Command that allows further
protection.
service point
- Interface between non-SNA
devices and NetView that sends alerts from equipment unknown to the
SNA environment.
Service Profile Identifier
- See SPID.
service specific convergence
sublayer
- See SSCS.
session
- 1.) Related set of
communications transactions between two or more network devices.
2.) In SNA, a logical connection enabling two NAUs to communicate.
- Layer 5 of the OSI
reference model. This layer establishes, manages, and terminates
sessions between applications and manages data exchange between
presentation layer entities. Corresponds to the data
flow control layer of the SNA model. See also application
layer, data
link layer, network
layer, physical
layer, presentation
layer, and transport
layer.
- Super Frame.
Common framing type used on T1 circuits. SF consists of 12 frames of
192 bits each, with the 193rd bit providing error checking and other
functions. SF has been superseded by ESF, but is still widely used.
Also called D4 framing. See also ESF.
- Simple Gateway
Monitoring Protocol. Network management protocol that was
considered for Internet standardization and later evolved into SNMP.
Documented in RFC 1028. See also SNMP.
shaping
- See traffic
shaping.
shielded cable
- Cable that has a layer of
shielded insulation to reduce EMI.
shielded twisted-pair
- See STP.
shortest path first
algorithm
- See SPF.
shortest-path routing
- Routing that minimizes
distance or path cost through application of an algorithm.
show access-lists
- Command that displays the
contents of all access lists.
show flash
- 1.) Command used to verify
that you have sufficient memory on your system for the Cisco IOS
software you want to load.
2.) Command used to learn the name of the system image file.
show running-config
- Command used to display the
current configuration in RAM.
- Command that displays the
status and global parameters associated with an interface.
- 1.) Command that displays
values about routing timers and network information associated with
the entire router.
2.) Command that displays parameters, filters, and network information about the entire router.
- Command that displays the
contents of an IP routing table.
show startup-config
- Command used to display the
saved configuration.
signaling
- Process of sending a
transmission signal over a physical medium for purposes of
communication.
signaling packet
- Generated by an
ATM-connected device that wants to establish a connection with
another such device. The signaling packet contains the ATM NSAP
address of the desired ATM endpoint, as well as any QOS parameters
required for the connection. If the endpoint can support the desired
QOS, it responds with an accept message, and the connection is
opened. See also QOS.
Signaling System number 7
- See SS7.
signal injector
- Device used to measure
attenuation of a signal on a network.
signal quality error
- See SQE.
signal reference ground
- Reference point used by
computing devices to measure and compare incoming digital signals
to.Reference point used by computing devices to measure and compare
incoming digital signals to.
- Switching based on the SSE,
which allows the processing of packets independent of the SSP
(Silicon Switch Processor) system processor. Silicon switching
provides high-speed, dedicated packet switching. See also SSE
and SSP
(Silicon Switch Processor).
silicon switching engine
- See SSE.
Silicon Switch Processor
- See SSP.
simple and efficient AAL
- See SEAL.
Simple Gateway Monitoring
Protocol
- See SGMP.
Simple Mail Transfer
Protocol
- See SMTP.
Simple Multicast Routing
Protocol
- See SMRP.
Simple Network Management
Protocol
- See SNMP.
- Capability for data
transmission in only one direction between a sending station and a
receiving station. Compare with full
duplex and half
duplex.
single-attached concentrator
- See SAC.
single attachment station
- See SAS.
- Fiber-optic cabling with a
narrow core that allows light to enter only at a single angle. Such
cabling has higher bandwidth than multimode fiber, but requires a
light source with a narrow spectral width (for example, a laser).
Also called monomode fiber. See also multimode
fiber.
single-route explorer packet
- Network using equipment from
only one vendor. Single-vendor networks rarely suffer compatibility
problems. See also multivendor
network.
- 1.) SMDS Interface
Protocol. Used in communications between CPE and SMDS
network equipment. Allows the CPE to use SMDS service for high-speed
WAN internetworking. Based on the IEEE 802.6 DQDB standard. See also
DQDB.
2.) Serial Interface Processor. Obsolete interface processor for Cisco 7000 series routers that provided either two or four channel-independent ports for synchronous serial connections at speeds from 2.4 Kbps to 4 Mbps. The SIP has been replaced by the FSIP. Sometimes called SX-SIP or Pre-FSIP. See also FSIP.
sliding window
- Refers to the fact that the
window size is negotiated dynamically during the TCP session.
sliding window flow control
- Method of flow control in
which a receiver gives transmitter permission to transmit data until
a window is full. When the window is full, the transmitter must stop
transmitting until the receiver advertises a larger window. TCP,
other transport protocols, and several data link layer protocols use
this method of flow control.
- Serial Line Internet
Protocol. Standard protocol for point-to-point serial
connections using a variation of TCP/IP. Predecessor of PPP. See
also CSLIP
and PPP.
slotted ring
- LAN architecture based on a
ring topology in which the ring is divided into slots that circulate
continuously. Slots can be either empty or full, and transmissions
must start at the beginning of a slot.
- Packet processing performed
at process level speeds, without the use of a route cache. Contrast
with fast
switching.
- Source MAC.
MAC address specified in the Source Address field of a packet.
Compare with DMAC.
See also MAC
address.
- Server Message Block.
File-system protocol used in LAN Manager and similar NOSs to package
data and exchange information with other systems.
- Switched
Multimegabit Data Service. High-speed, packet-switched,
datagram-based WAN networking technology offered by the telephone
companies. See also CBDS.
SMDS Interface Protocol
- See SIP.
- Structure of
Management Information. Document (RFC 1155) specifying
rules used to define managed objects in the MIB. See also MIB.
smoothing
- See traffic
shaping.
- Simple Multicast
Routing Protocol. Specialized multicast network protocol
for routing multimedia data streams on enterprise networks. SMRP
works in conjunction with multicast extensions to the AppleTalk
protocol.
- Station Management.
ANSI FDDI specification that defines how ring stations are managed.
- Simple Mail Transfer
Protocol. Internet protocol providing electronic mail
services.
- Systems Network
Architecture. Large, complex, feature-rich network
architecture developed in the 1970s by IBM. Similar in some respects
to the OSI
reference model, but with a number of differences. SNA is
essentially composed of seven layers. See data
flow control layer, data
link control layer, path
control layer, physical
control layer, presentation
services layer, transaction
services layer, and transmission
control layer.
SNA Distribution Services
- See SNADS.
SNA Network Interconnection
- See SNI.
- SNA Distribution
Services. Consists of a set of SNA transaction programs
that interconnect and cooperate to provide asynchronous distribution
of information between end users. One of three SNA transaction
services. See also DDM
and DIA.
- 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.
- 1.) Subscriber
Network Interface. Interface for SMDS-based networks that
connects CPE and an SMDS switch. See also UNI.
2.) SNA Network Interconnection. IBM gateway connecting multiple SNA networks.
- 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. See also SGMP
and SNMP2.
SNMP communities
- Authentication scheme that
enables an intelligent network device to validate SNMP requests from
sources such as the NMS. A LightStream 2020 ATM switch, for example,
responds only to SNMP requests that come from members of known
communities and that have the access privileges required for that
request. See also SNMP.
- 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.
- Subnetwork point of
attachment. A data link layer address (such as an Ethernet
address, X.25 address, or Frame Relay DLCI address). SNPA addresses
are used to configure a CLNS route for an interface.
socket
- Software structure operating
as a communications end point within a network device.
socket number
- An 8-bit number that
identifies a socket. A maximum of 254 different socket numbers can
be assigned in an AppleTalk node.
- 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. See also SDH,
STS-1,
and STS-3c.
- Address of a network device
that is sending data. See also destination
address.
source and destination IP
addresses
- Field within an IP datagram
that indicates the 32-bit source and destination IP addresses.
source MAC
- See SMAC.
source port
- Number of the calling port.
source-route bridging
- See SRB.
source-route translational
bridging
- See SR/TLB.
source-route transparent
bridging
- See SRT.
source service access point
- See SSAP.
Southeastern Universities
Research Association Network
- See SURAnet.
- Switch Processor.
Cisco 7000-series processor module that acts as the administrator
for all CxBus activities. Sometimes called ciscoBus controller.
See also CxBus.
- Switched Port
Analyzer. Feature of the Catalyst 5000 switch that extends
the monitoring abilities of existing network analyzers into a
switched Ethernet environment. SPAN mirrors the traffic at one
switched segment onto a predefined SPAN port. A network analyzer
attached to the SPAN port can monitor traffic from any of the other
Catalyst switched ports.
span
- Full-duplex digital
transmission line between two digital facilities.
- Follows a statically
configured spanning tree when looking for paths in an SRB network.
Also known as a limited-route explorer packet or a single-route
explorer packet. See also all-routes
explorer packet, explorer
packet, and local
explorer packet.
- Loop-free subset of a
network topology. See also spanning-tree
algorithm and Spanning-Tree
Protocol.
- Algorithm used by the
Spanning-Tree Protocol to create a spanning tree. Sometimes
abbreviated STA. See also spanning
tree and Spanning-Tree
Protocol.
- Bridge protocol that
utilizes the spanning-tree algorithm, enabling a learning bridge to
dynamically work around loops in a network topology by creating a
spanning tree. Bridges exchange BPDU messages with other bridges to
detect loops, and then remove the loops by shutting down selected
bridge interfaces. Refers to both the IEEE 802.1 Spanning-Tree
Protocol standard and the earlier Digital Equipment Corporation
Spanning-Tree Protocol upon which it is based. The IEEE version
supports bridge domains and allows the bridge to construct a
loop-free topology across an extended LAN. The IEEE version is
generally preferred over the Digital version. Sometimes abbreviated STP.
See also BPDU,
learning
bridge, MAC
address learning, spanning
tree, and spanning-tree
algorithm.
sparse mode PIM
- See PIM
sparse mode.
speed matching
- Feature that provides
sufficient buffering capability in a destination device to allow a
high-speed source to transmit data at its maximum rate, even if the
destination device is a lower-speed device.
- Shortest path first
algorithm. Routing algorithm that iterates on length of
path to determine a shortest-path spanning tree. Commonly used in
link-state routing algorithms. Sometimes called Dijkstra's
algorithm. See also link
state routing algorithm.
- Service Profile
Identifier. Number that some service providers use to
define the services to which an ISDN device subscribes. The ISDN
device uses the SPID when accessing the switch that initializes the
connection to a service provider.
- Any power impulse lasting
between .5 and 100 microseconds and possessing an amplitude over 100
% of peak power line voltage. See surge,
sag,
and oscillation.
split-horizon updates
- Routing technique in which
information about routes is prevented from exiting the router
interface through which that information was received. Split-horizon
updates are useful in preventing routing loops.
- 1.) Scheme used by Cisco
routers to cause a host to treat an interface as if it were up and
supporting a session. The router spoofs replies to keepalive
messages from the host in order to convince that host that the
session still exists. Spoofing is useful in routing environments
such as DDR, in which a circuit-switched link is taken down when
there is no traffic to be sent across it in order to save toll
charges. See also DDR.
2.) The act of a packet illegally claiming to be from an address from which it was not actually sent. Spoofing is designed to foil network security mechanisms such as filters and access lists.
spooler
- Application that manages
requests or jobs submitted to it for execution. Spoolers process the
submitted requests in an orderly fashion from a queue. A print
spooler is a common example of a spooler.
- Sequenced Packet
Protocol. Provides reliable, connection-based,
flow-controlled packet transmission on behalf of client processes.
Part of the XNS protocol suite.
- Sequenced Packet
Exchange. Reliable, connection-oriented protocol that
supplements the datagram service provided by network layer (Layer 3)
protocols. Novell derived this commonly used NetWare transport
protocol from the SPP of the XNS protocol suite.
- Signal quality error.
Transmission sent by a transceiver back to the controller to let the
controller know whether the collision circuitry is functional. Also
called heartbeat.
- Type of RAM that retains its
contents for as long as power is supplied. SRAM does not require
constant refreshing, like DRAM. Compare with DRAM.
- Source-route
bridging. Method of bridging originated by IBM and popular
in Token Ring networks. In a SRB network, the entire route to a
destination is predetermined, in real time, prior to the sending of
data to the destination. Contrast with transparent
bridging.
- Source-route
transparent bridging. IBM bridging scheme that merges the
two most prevalent bridging strategies, SRB and transparent
bridging. SRT employs both technologies in one device to satisfy the
needs of all ENs. No translation between bridging protocols is
necessary. Compare with SR/TLB.
- Source-route
translational bridging. Method of bridging where
source-route stations can communicate with transparent bridge
stations with the help of an intermediate bridge that translates
between the two bridge protocols. Compare with SRT.
- Sequenced Routing
Update Protocol. Protocol that assists VINES servers in
finding neighboring clients, servers, and routers. See also RTP
(Routing Table Protocol).
- Signaling System
number 7. Standard CCS system used with BISDN and ISDN.
Developed by Bellcore. See also CCS.
- Source service
access point. The SAP of the network node designated in the
Source field of a packet. Compare to DSAP.
See also SAP
(service access point).
- System services
control points. Focal points within an SNA network for
managing network configuration, coordinating network operator and
problem determination requests, and providing directory services and
other session services for network end users.
SSCP-PU session
- Session used by SNA to allow
an SSCP to manage the resources of a node through the PU. SSCPs can
send requests to, and receive replies from, individual nodes in
order to control the network configuration.
- Service specific
convergence sublayer. One of the two sublayers of any AAL.
SSCS, which is service dependent, offers assured data transmission.
The SSCS can be null as well, in classical IP over ATM or LAN
emulation implementations. See also AAL,
ATM
layer, CPCS,
CS,
and SAR.
- Silicon switching
engine. Routing and switching mechanism that compares the
data link or network layer header of an incoming packet to a
silicon-switching cache, determines the appropriate action (routing
or bridging), and forwards the packet to the proper interface. The
SSE is directly encoded in the hardware of the SSP (Silicon Switch
Processor) of a Cisco 7000 series router. It can therefore perform
switching independently of the system processor, making the
execution of routing decisions much quicker than if they were
encoded in software. See also silicon
switching and SSP
(Silicon Switch Processor).
- 1.) Silicon Switch
Processor. High-performance silicon switch for Cisco 7000
series routers that provides distributed processing and control for
interface processors. The SSP leverages the high-speed switching and
routing capabilities of the SSE to dramatically increase aggregate
router performance, minimizing performance bottlenecks at the
interface points between the router and a high-speed backbone. See
also silicon
switching and SSE.
2.) Switch-to-Switch Protocol. Protocol specified in the DLSw standard that routers use to establish DLSw connections, locate resources, forward data, and handle flow control and error recovery. See also DLSw.
STA
stack
- See protocol
stack.
- Set of rules or procedures
that are either widely used or officially specified. See also de
facto standard.
- Device placed in standby
mode on a Token Ring network in case an active monitor fails. See
also active
monitor and ring
monitor.
- CSMA/CD LAN, based on IEEE
802.3, developed by AT&T.
- LAN topology in which end
points on a network are connected to a common central switch by
point-to-point links. A ring topology that is organized as a star
implements a unidirectional closed-loop star, instead of
point-to-point links. Compare with bus
topology, ring
topology, and tree
topology.
start-stop transmission
static electricity
- Unpredictable electrical
charges in the atmosphere that interfere with radio reception,
computer networking, and the like.
- Route that is explicitly
configured and entered into the routing table. Static routes take
precedence over routes chosen by dynamic routing protocols.
Station Management
- See SMT.
- Technique whereby
information from multiple logical channels can be transmitted across
a single physical channel. Statistical multiplexing dynamically
allocates bandwidth only to active input channels, making better use
of available bandwidth and allowing more devices to be connected
than with other multiplexing techniques. Also referred to as statistical
time-division multiplexing or stat mux. Compare with ATDM,
FDM,
and TDM.
statistical time-division
multiplexing
stat mux
- Synchronous
Transport Module level 1. One of a number of SDH formats
that specifies the frame structure for the 155.52-Mbps lines used to
carry ATM cells. See also SDH.
store and
forward packet switching
- Packet-switching technique
in which frames are completely processed before being forwarded out
the appropriate port. This processing includes calculating the CRC
and checking the destination address. In addition, frames must be
temporarily stored until network resources (such as an unused link)
are available to forward the message. Contrast with cut-through
packet switching.
- 1. Shielded
twisted-pair. Two-pair wiring medium used in a variety of
network implementations. STP cabling has a layer of shielded
insulation to reduce EMI. Compare with UTP.
See also twisted
pair.
2. See Spanning-Tree Protocol.
StreamView network
management
- Cisco suite of SNMP-based
network management tools used in conjunction with the LightStream
2020 ATM switch. The StreamView suite includes three GUI-driven
applications: a configuration program (the configurator), a network
topology map (the topology map), and a node monitoring program (the
monitor); and a command-line interface: the CLI. See also CLI,
configurator,
monitor,
and topology
map.
Structure of Management
Information
- See SMI.
- Synchronous
Transport Signal level 1. Basic building block signal of
SONET, operating at 51.84 Mbps. Faster SONET rates are defined as
STS-n, where n is a multiple of 51.84 Mbps. See also SONET.
- Synchronous
Transport Signal level 3, concatenated. SONET format that
specifies the frame structure for the 155.52-Mbps lines used to
carry ATM cells. See also SONET.
- OSPF area that carries a
default route, intra-area routes, and interarea routes, but does not
carry external routes. Virtual links cannot be configured across a
stub area, and they cannot contain an ASBR. Compare to non-stub
area. See also ASBR
and OSPF.
stub network
- Network that has only a
single connection to a router.
- Serial tunnel.
Router feature allowing two SDLC- or HDLC-compliant devices to
connect to one another through an arbitrary multiprotocol topology
(using Cisco routers) rather than through a direct serial link.
subarea
- Portion of an SNA network
that consists of a subarea node and any attached links and
peripheral nodes.
subarea node
- SNA communication controller
or host that handles complete network addresses.
subchannel
- In broadband terminology, a
frequency-based subdivision creating a separate communications
channel.
subinterface
- One of a number of virtual
interfaces on a single physical interface.
subnet
- See subnetwork.
- Portion of an IP address
that is specified as the subnetwork by the subnet mask. See also IP
address, subnet
mask, and subnetwork.
- 32-bit address mask used in
IP to indicate the bits of an IP address that are being used for the
subnet address. Sometimes referred to simply as mask. See
also address
mask and IP
address.
- 1.) In IP networks, a
network sharing a particular subnet address. Subnetworks are
networks arbitrarily segmented by a network administrator in order
to provide a multilevel, hierarchical routing structure while
shielding the subnetwork from the addressing complexity of attached
networks. Sometimes called a subnet. See also IP
address, subnet
address, and subnet
mask.
2.) In OSI networks, a collection of ESs and ISs under the control of a single administrative domain and using a single network access protocol.
Subnetwork Access Protocol
- See SNAP.
subnetwork point of
attachment
- See SNPA.
Subscriber Network Interface
- See SNI.
subvector
- A data segment of a vector
in an SNA message. A subvector consists of a length field, a key
that describes the subvector type, and subvector specific data.
Super Frame
- See SF.
supervisory processor
- See RP
(Route Processor).
- Southeastern
Universities Research Association Network. Network
connecting universities and other organizations in the Southeastern
United States. SURAnet, originally funded by the NSF and a part of
the NSFNET, is now part of BBN Planet. See also BBN
Planet, NSF,
and NSFNET.
- Any voltage increase above
110 % of the normal voltage carried by a power line. See sag,
spike,
and oscillation.
sustainable cell rate
- See SCR.
- Switched virtual
circuit. Virtual circuit that is dynamically established on
demand and is torn down when transmission is complete. SVCs are used
in situations where data transmission is sporadic. Called a switched
virtual connection in ATM terminology. Compare with PVC.
- 1.) Network device that
filters, forwards, and floods frames based on the destination
address of each frame. The switch operates at the data link layer of
the OSI model.
2.) General term applied to an electronic or mechanical device that allows a connection to be established as necessary and terminated when there is no longer a session to support.
switch card
- Card on the LightStream 2020
ATM switch that handles communication between the other cards on the
switch. Each LightStream 2020 switch has one or two switch cards.
The second card, if present, serves as a backup for the first.
switched LAN
- LAN implemented with LAN
switches. See LAN
switch.
Switched Multimegabit Data
Service
- See SMDS.
Switched Port Analyzer
- See SPAN.
switched virtual circuit
- See SVC.
switched virtual connection
- See SVC.
- See SP.
Switch-to-Switch Protocol
- See SSP.
SwitchVision
- Cisco SNMP-based network
management software, running on Microsoft Windows, that offers a
powerful set of tools to manage an entire network, including
switches, hubs, routers, and bridges. SwitchVision can automatically
discover and map any SNMP device on the network and show the status
of network devices. SwitchVision allows network administrators to
set event thresholds, activate actions when error conditions occur,
and set up custom tables and graphs to view critical network
variables.
synchronization
- Establishment of common
timing between sender and receiver.
Synchronous Data Link
Control
- See SDLC.
Synchronous Digital
Hierarchy
- See SDH.
Synchronous Optical Network
- See SONET.
- Term describing digital
signals that are transmitted with precise clocking. Such signals
have the same frequency, with individual characters encapsulated in
control bits (called start bits and stop bits) that
designate the beginning and end of each character. Compare with asynchronous
transmission, isochronous
transmission, and plesiochronous
transmission.
Synchronous Transport Module
level 1
- See STM-1.
Synchronous Transport Signal
level 1
- See STS-1.
Synchronous Transport Signal
level 3, concatenated
- See STS-3c.
- System generation.
Process of defining network resources in a network.
system generation
- See sysgen.
system services control
points
- See SSCP.
Systems Network Architecture
- See SNA.