S


SAA

(Service Assurance Agents) used by Cisco’s service level management suite for such things as software and hardware probes, and to track service levels for a broad range of network services.

SAFE

Cisco’s (security blueprint for enterprise networks) is a recommended guideline used by network designers and engineers to secure data networks.

sampling rate

The rate at which samples of a specific waveform amplitude are collected.

SAP

1. Service Access Point: A field specified by IEEE 802.2 that is part of an address specification.

2. Service Advertisement Protocol: The Novell NetWare protocol that supplies a way to inform network clients of resources and services availability on network, using routers and servers. See also: IPX.

scalability

The ability of an operating system to add system resources to provide faster processing or to handle increased loads in anticipation of future needs.

In practice, this usually means that an operating system is available on a range of increasingly capable hardware, with only modest increases in price at each level.

SCR

Sustainable Cell Rate: An ATM Forum parameter used for traffic management, it is the long-term average cell rate for VBR connections that can be transmitted.

SDLC

Synchronous Data Link Control: A protocol used in SNA Data Link layer communications. SDLC is a bit-oriented, full-duplex serial protocol that is the basis for several similar protocols, including HDLC and LAPB. See also: HDLC and LAPB.

Secure Shell Protocol

(SSH) is a common remote administrative terminal access protocol and is a recommended replacement for Telnet since it does not send passwords in clear text.

Secure Sockets Layer

(SSL) An interface originally developed by Netscape that provides encrypted data transfer between client and server applications over the Internet.

SSL works at the network level and so can be used by any SSL-compliant application. Applications that use SSL use RSA public key encryption and digital signatures to establish the identity of the two parties in the transaction.

seed router

In an AppleTalk network, the router that is equipped with the network number or cable range in its port descriptor. The seed router specifies the network number or cable range for other routers in that network section and answers to configuration requests from nonseed routers on its connected AppleTalk network, permitting those routers to affirm or modify their configurations accordingly. Every AppleTalk network needs at least one seed router.

segmentation

The breaking up of collision and broadcast domains using routers, bridges, and switches.

Serialization

The process of converting data for transport across a WAN serial link, which can cause traffic delays at a router’s egress port.

server

Hardware and software that provide network services to clients.

service provider

A term used to define a company that connects your network to the Internet.

Session layer

Layer 5 of the OSI reference model, responsible for creating, managing, and terminating sessions between applications and overseeing data exchange between Presentation layer entities. See also: Application layer, Data Link layer, Network layer, Physical layer, Presentation layer, and Transport layer.

SF

Super Frame: A super frame (also called a D4 frame) consists of
12 frames with 192 bits each, with the 193rd bit providing other functions including error checking. SF is frequently used on T1 circuits. A newer version of the technology is Extended Super Frame (ESF), which uses 24 frames. See also: ESF.

signaling packet

An informational packet created by an ATM-connected mechanism that wants to establish connection with another such mechanism. The packet contains the QoS parameters needed for connection and the ATM NSAP address of the endpoint. The endpoint responds with a message of acceptance, if it is able to support the desired QoS, and the connection is established. See also: QoS.

Signaling System 7

The SS7 protocol uses out-of-band signaling to establish the appropriate path for the call through the carrier network, before establishing the actual transmission path. Many modern PBXs support the SS7 protocol. This enables each PBX to make and process requests from the Telco network.

significant bits

The important bits of a number.

silicon switching

A type of high-speed switching used in Cisco 7000 series routers, based on the use of a separate processor (the Silicon Switch Processor, or SSP). See also: SSE.

SLA

(Service Level Agreement) CiscoWorks2000 Service Level Manager allows network administrators to define and monitor service-level agreements (SLAs) specifying traffic type, endpoints, and thresholds against key parameters such as latency, packet loss, and jitter.

SLC

(Service-Level Contract) CiscoWorks2000 includes (SLCs) and the service-level agreements (SLAs) associated with them, which allows administrators to define the level of service required in a voice network. Business and technical reports can be generated at both detailed and summary levels to demonstrate performance against those SLCs and SLAs.

sliding window

The method of flow control used by TCP, as well as several Data Link layer protocols. This method places a buffer between the receiving application and the network data flow. The “window” available for accepting data is the size of the buffer minus the amount of data already there. This window increases in size as the application reads data from it and decreases as new data is sent. The receiver sends the transmitter announcements of the current window size, and it may stop accepting data until the window increases above a certain threshold.

SLIP

Serial Line Internet Protocol: A variation of TCP/IP used as an industry standard for point-to-point connections. SLIP is the predecessor to PPP. See also: PPP.

SLM

(Service Level Manager ) CiscoWorks2000 (SLM) allows network administrators to define and monitor service-level agreements (SLAs) specifying traffic type, endpoints, and thresholds against key parameters such as latency, packet loss, and jitter.

SMDS

Switched Multimegabit Data Service: A packet-switched, datagram- based WAN networking technology offered by telephone companies that provides high speed.

SMTP

Simple Mail Transfer Protocol: A protocol used on the Internet to provide electronic mail services.

SNA

System Network Architecture: A complex, feature-rich, network architecture similar to the OSI reference model but with several variations; created by IBM in the 1970s and essentially composed of seven layers.

SNAP

Subnetwork Access Protocol: SNAP is a frame used in Ethernet, Token Ring, and FDDI LANs. Data transfer, connection management, and QoS selection are three primary functions executed by the SNAP frame.

SNMP

A standard protocol, part of the TCP/IP protocol suite, used to manage and monitor nodes on a network. SNMP is a communications protocol for collecting information about devices on the network, including hubs, routers, and bridges. Each piece of information to be collected about a device is defined in a Management Information Base (MIB). SNMP uses UDP (User Datagram Protocol) to send and receive messages on the network.

socket

1. A software structure that operates within a network device as a destination point for communications.

2. In AppleTalk networks, an entity at a specific location within a node; AppleTalk sockets are conceptually similar to TCP/IP ports.

SONET

Synchronous Optical Network: The ANSI standard for synchronous transmission on fiber-optic media, developed at Bell Labs. It specifies a base signal rate of 51.84Mbps and a set of multiples of that rate, known as Optical Carrier levels, up to 2.5Gbps.

SP

Switch Processor: Also known as a ciscoBus controller, it is a Cisco 7000 series processor module acting as governing agent for all CxBus activities.

span

A full-duplex digital transmission line connecting two facilities.

SPAN

Switched Port Analyzer: A feature of the Catalyst 5000 switch, offering freedom to manipulate within a switched Ethernet environment by extending the monitoring ability of the existing network analyzers into the environment. At one switched segment, the SPAN mirrors traffic onto a predetermined SPAN port, while a network analyzer connected to the SPAN port is able to monitor traffic from any other Catalyst switched port.

spanning explorer packet

Sometimes called limited-route or single-route explorer packet, it pursues a statically configured spanning tree when searching for paths in a source-route bridging network. See also: all-routes explorer packet, explorer packet, and local explorer packet.

spanning tree

A subset of a network topology, within which no loops exist. When bridges are interconnected into a loop, the bridge, or switch, cannot identify a frame that has been forwarded previously, so there is no mechanism for removing a frame as it passes the interface numerous times. Without a method of removing these frames, the bridges continuously forward them—consuming bandwidth and adding overhead to the network. Spanning trees prune the network to provide only one path for any packet. See also: Spanning Tree Protocol and Spanning Tree Algorithm.

Spanning Tree Algorithm (STA)

An algorithm that creates a spanning tree using the Spanning Tree Protocol (STP). See also: spanning tree and Spanning Tree Protocol.

Spanning Tree Protocol (STP)

The bridge protocol (IEEE 802.1) that enables a learning bridge to dynamically avoid loops in the network topology by creating a spanning tree using the Spanning Tree Algorithm. Spanning tree frames called bridge protocol data units (BPDUs) are sent and received by all switches in the network at regular intervals. The switches participating in the spanning tree don’t forward the frames; instead, they’re processed to determine the spanning tree topology itself. Cisco Catalyst series switches use STP 802.1d to perform this function. See also: BPDU, learning bridge, MAC address, spanning tree, and Spanning Tree Algorithm.

SPF

Shortest Path First algorithm: A routing algorithm used to decide on the shortest-path spanning tree. Sometimes called Dijkstra’s algorithm and frequently used in link-state routing algorithms. See also: link-state routing algorithm.

SPID

Service Profile Identifier: A number assigned by service providers or local telephone companies and assigned by administrators to a BRI port. SPIDs are used to determine subscription services of a device connected via ISDN. ISDN devices use SPID when accessing the telephone company switch that initializes the link to a service provider.

split-horizon updates

Useful for preventing routing loops, a type of distance-vector routing protocol where information about routes is prevented from leaving the router interface through which that information was received.

spoofing

1. In dial-on-demand routing (DDR), where a circuit-switched link is taken down to save toll charges when there is no traffic to be sent, spoofing is a scheme used by routers that causes a host to treat an interface as if it were functioning and supporting a session. The router sends “spoof” replies to keep-alive messages from the host in an effort to convince the host that the session is up and running. See also: DDR.

2. The illegal act of sending a packet labeled with a false address, in order to deceive network security mechanisms such as filters and access lists.

spooler

A management application that processes requests submitted to it for execution in a sequential fashion from a queue. A good example is a print spooler.

SPX

Sequenced Packet Exchange: A Novell NetWare transport protocol that augments the datagram service provided by Network layer (Layer 3) protocols, it was derived from the Switch-to-Switch Protocol of the XNS protocol suite.

SQE

Signal Quality Error: In an Ethernet network, a message sent from a transceiver to an attached machine that the collision-detection circuitry is working.

SRB

Source-Route Bridging: Created by IBM, the bridging method used in Token Ring networks. The source determines the entire route to a destination before sending the data and includes that information in fields within each packet. Contrast with: transparent bridging.

SRT

Source-Route Transparent bridging: A bridging scheme developed by IBM, merging source-route and transparent bridging. SRT takes advantage of both technologies in one device, fulfilling the needs of all end nodes. Translation between bridging protocols is not necessary. Compare with: SR/TLB.

SR/TLB

Source-Route Translational Bridging: A bridging method that allows source-route stations to communicate with transparent bridge stations aided by an intermediate bridge that translates between the two bridge protocols. Used for bridging between Token Ring and Ethernet. Compare with: SRT.

SSAP

Source Service Access Point: The SAP of the network node identified in the Source field of the packet. See also: DSAP and SAP.

SSE

Silicon Switching Engine: The software component of Cisco’s silicon switching technology, hard-coded into the Silicon Switch Processor (SSP). Silicon switching is available only on the Cisco 7000 with an SSP. Silicon- switched packets are compared to the silicon-switching cache on the SSE. The SSP is a dedicated switch processor that offloads the switching process from the route processor, providing a fast-switching solution, but packets must still traverse the backplane of the router to get to the SSP and then back to the exit interface.

Standby Monitor

In a Token Ring network, a network node that serves as a backup to the Active Monitor and can take over in the event that the Active Monitor fails.

star topology

A LAN physical topology with end points on the network converging at a common central switch (known as a hub) using point-to-point links. A logical ring topology can be configured as a physical star topology using a unidirectional closed-loop star rather than point-to-point links. That is, connections within the hub are arranged in an internal ring. See also: bus topology and ring topology.

startup range

If an AppleTalk node does not have a number saved from the last time it was booted, then the node selects from this range of values— from 65280 to 65534.

static addressing

Static addressing provides for a fixed address assigned by an administrator to a network interface.

static route

A route whose information is purposefully entered into the routing table and takes priority over those chosen by dynamic routing protocols.

static VLAN

VLAN port membership assigned to each switch port individually by an administrator.

statistical multiplexing

Multiplexing in general is a technique that allows data from multiple logical channels to be sent across a single physical channel. Statistical multiplexing dynamically assigns bandwidth only to input channels that are active, optimizing available bandwidth so that more devices can be connected than with other multiplexing techniques. Also known as statistical time-division multiplexing or stat mux.

STM-1

Synchronous Transport Module Level 1. In the European SDH standard, one of many formats identifying the frame structure for the 155.52Mbps lines that are used to carry ATM cells.

store-and-forward packet switching

A technique in which the switch first copies each packet into its buffer and performs a cyclic redundancy check (CRC). If the packet is error-free, the switch then looks up the destination address in its filter table, determines the appropriate exit port, and sends the packet.

STP

1. Shielded Twisted Pair: A two-pair wiring scheme, used in many network implementations, that has a layer of shielded insulation to reduce EMI.

2. Spanning Tree Protocol.

stub area

An OSPF area carrying a default route, intra-area routes, and interarea routes, but no external routes. Configuration of virtual links cannot be achieved across a stub area, and stub areas are not allowed to contain an ASBR. See also: non-stub area, ASBR, and OSPF.

stub network

A network having only one connection to a router.

STUN

Serial Tunnel: A technology used to connect an HDLC link to an SDLC link over a serial link.

subarea

A portion of an SNA network made up of a subarea node and its attached links and peripheral nodes.

subarea node

An SNA communications host or controller that handles entire network addresses.

subchannel

A frequency-based subdivision that creates a separate broadband communications channel.

subinterface

One of many virtual interfaces available on a single physical interface.

subnet

See: subnetwork.

subnet address

The portion of an IP address that is specifically identified by the subnet mask as the subnetwork. See also: IP address, subnetwork, and subnet mask.

subnet mask

Also simply known as mask, a 32-bit address mask used in IP to identify the bits of an IP address that are used for the subnet address. Using a mask, the router does not need to examine all 32 bits, only those selected by the mask. See also: address mask and IP address.

subnetting

The process of configuring an IP address network mask to create more usable addresses.

subnetwork

1. Any network that is part of a larger IP network and is identified by a subnet address. A network administrator segments a network into subnetworks in order to provide a hierarchical, multilevel routing structure, and at the same time protect the subnetwork from the addressing complexity of networks that are attached. Also known as a subnet. See also: IP address, subnet mask, and subnet address.

2. In OSI networks, the term specifically refers to a collection of ESs and ISs controlled by only one administrative domain, using a solitary network connection protocol.

SVC

Switched Virtual Circuit: A dynamically established virtual circuit, created on demand and dissolved as soon as transmission is over and the circuit is no longer needed. In ATM terminology, it is referred to as a switched virtual connection. See also: PVC.

switch

1. In networking, a device responsible for multiple functions such as filtering, flooding, and sending frames. It works using the destination address of individual frames. Switches operate at the Data Link layer of the OSI model.

2. Broadly, any electronic/mechanical device allowing connections to be established as needed and terminated if no longer necessary.

switched LAN

Any LAN implemented using LAN switches. See also: LAN switch.

switch fabric

A group of connected switches that share the same VLAN database.

synchronous transmission

Signals transmitted digitally with precision clocking. These signals have identical frequencies and contain individual characters encapsulated in control bits (called start/stop bits) that designate the beginning and ending of each character. See also: asynchronous transmission and isochronous transmission.




CCDA. Cisco Certified Design Associate Study Guide
CCDA: Cisco Certified Design Associate Study Guide, 2nd Edition (640-861)
ISBN: 0782142001
EAN: 2147483647
Year: 2002
Pages: 201

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