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S

SA — Security association. An IPSec term that describes an agreement between two parties about what rules to use for authentication and encryption algorithms, key exchange mechanisms, and secure communications.

sampling — Method where the sampling key based on the IPv4 header is sent to the Routing Engine. There, the key is placed in a file, or cflowd packets based on the key are sent to a cflowd server.

SAP — SAP can be either of the following:

Session Announcement Protocol. Used with multicast protocols to handle session conference announcements.
Service access point. Device that identifies routing protocols and provides the connection between the network interface card and the rest of the network.

SAR — Segmentation and reassembly. Buffering used with ATM.

SCB — System Control Board. On an M40 router, the part of the Packet Forwarding Engine that performs route lookups, monitors system components, and controls FPC resets.

SCC — Switch-card chassis. Term used by the JUNOS command-line interface (CLI) to refer to the TX Matrix platform in a routing matrix.

SCEP — Simple Certificate Enrollment Protocol. A protocol for digital certificates that supports certificate authority (CA) and registration authority (RA) public key distribution, certificate enrollment, certificate revocation, certificate queries, and certificate revocation list (CRL) queries.

SCG — SONET Clock Generator. On a T640 routing node, provides the Stratum 3 clock signal for the SONET/SDH interfaces. Also provides external clock inputs.

scheduler maps — In class of service, associate schedulers with forwarding classes. See also schedulers, forwarding classes.

schedulers — Define the priority, bandwidth, delay buffer size, rate control status, and RED drop profiles to be applied to a particular forwarding class for packet transmission. See also scheduler maps.

scheduling — Method of determining which type of packet or queue is transmitted before another. An individual router interface can have multiple queues assigned to store packets. The router then determines which queue to service based on a particular method of scheduling. This process often involves a determination of which type of packet should be transmitted before another. For example, first in, first out (FIFO). See also FIFO.

SCU — Source class usage. A means of tracking traffic originating from specific prefixes on the provider core router and destined for specific prefixes on the customer edge router, based on the IP source and destination addresses.

SCP — Secure copy. Means of securely transferring computer files between a local and remote host or between two remote hosts, using the Secure Shell (SSH) protocol.

SDH — Synchronous Digital Hierarchy. A CCITT variation of the SONET standard.

SDP — Session Description Protocol. Used with multicast protocols to handle session conference announcements.

SDRAM — Synchronous dynamic random-access memory. An electronic standard in which the inputs and outputs of SDRAM data are synchronized to an externally supplied clock, allowing for extremely fast consecutive read and write capacity.

SDX software — Service Deployment System software. A customizable Juniper Networks product with which service providers can rapidly deploy IP services—such as video on demand (VoD), IP television, stateful firewalls, Layer 3 VPNs, and bandwidth on demand (BoD)—to hundreds of thousands of subscribers over a variety of broadband access technologies.

secure copy — See SCP.

Secure Hash Algorithm — See SHA-1.

Secure Shell — See SSH.

Secure Shell with Transport Layer Security — See SSH/TLS.

Secure Sockets Layer — See SSL.

security association — See SA.

Security Parameter Index — See SPI.

segmentation and reassembly — See SAR.

serial interface — DTE/DCE interface for WAN links. See also DTE and DCE.

service access point — See SAP.

Service Deployment System software — See SDX software.

Service Profile Identifier — See SPID.

services interface — Interface that provides specific capabilities for manipulating traffic before it is delivered to its destination, for example, the adaptive services interface and the tunnel services interface. See also network interface.

Serving GPRS Support Node — See SGSN.

Session Announcement Protocol — See SAP.

session attribute object — RSVP message object used to control the priority, preemption, affinity class, and local rerouting of the LSP.

Session Description Protocol — See SDP.

Session Initiation Protocol — See SIP.

set-top box — The end host or device used to receive IPTV video streams.

SFM — Switching and Forwarding Module. On an M160 router, a component of the Packet Forwarding Engine that provides route lookup, filtering, and switching to FPCs.

SFP — Small form-factor pluggable transceiver. A transceiver that provides support for optical or copper cables. SFPs are hot-insertable and hot-removable. See also XFP.

SGSN — Serving GPRS Support Node. Device in the mobile network that requests PDP contexts with a GGSN.

SHA-1 — Secure Hash Algorithm 1. A secure hash algorithm standard defined in FIPS PUB 180-1 (SHA-1). Developed by the National Institute of Standards and Technology (NIST), SHA-1 (which effectively replaces SHA-0) produces a 160-bit hash for message authentication. Longer-hash variants include SHA-224, SHA-256, SHA-384, and SHA-512 (sometimes grouped under the name “SHA-2”). SHA-1 is more secure than MD5. See also hashing, MD5.

sham link — Unnumbered point-to-point intra-area link advertised by a type 1 link-state advertisement (LSA).

shaping rate — In class of service, controls the maximum rate of traffic transmitted on an interface. See also traffic shaping.

shared scheduling and shaping — Allocation of separate pools of shared resources to subsets of logical interfaces belonging to the same physical port.

shared tree — Multicast forwarding tree established from the rendezvous point (RP) to the last–hop router for a particular group address.

SHDSL — Symmetric high-speed digital subscriber line. A standardized multirate symmetric DSL that transports rate-adaptive symmetrical data across a single copper pair at data rates from 192 Kbps to 2.3 Mbps, or from 384 Kbps to 4.6 Mbps over two pairs, covering applications served by HDSL, SDSL, T1, E1, and services beyond E1. SHDSL conforms to the following recommendations: ITU G.991.2 G.SHDSL, ETSI TS 101-524 SDSL, and the ANSI T1E1.4/2001-174 G.SHDSL. See also G.SHDSL.

SHDSL transceiver unit-central office — See STU-C.

SHDSL transceiver unit-remote — See STU-R.

shim header — Location of the MPLS header in a data packet. The JUNOS software always places (shims) the header between the existing Layer 2 and Layer 3 headers.

shortest path first — See SPF.

shortest-path tree — See SPT.

short message service — See SMS.

SIB — Switch Interface Board. On a T640 routing node, provides the switching function to the destination Packet Forwarding Engine.

signaled path — In traffic engineering, an explicit path; that is, a path determined using RSVP signaling. The ERO carried in the packets contains the explicit path information.

Signaling System 7 — See SS7.

Simple Certificate Enrollment Protocol — See SCEP.

Simple Network Management Protocol — See SNMP.

simplex interface — Interface that treats packets it receives from itself as the result of a software loopback process. The interface does not consider these packets when determining whether the interface is functional.

single-mode fiber — Optical fiber designed for transmission of a single ray or mode of light as a carrier and used for long-distance signal transmission. For short distances, multimode fiber is used. See also MMF.

SIP — Session Initiation Protocol. An Adaptive Services application protocol option used for setting up sessions between endpoints on the Internet. Examples include telephony, fax, videoconferencing, file exchange, and person-to-person sessions.

small form-factor pluggable transceiver — See SFP.

SMS — Short message service. A GSM service that enables short text messages to be sent to and from mobile telephones.

SNA — System Network Architecture. IBM proprietary networking architecture consisting of a protocol stack that is used primarily in banks and other financial transaction networks.

SNMP — Simple Network Management Protocol. A protocol governing network management and the monitoring of network devices and their functions.

soft state — In RSVP, control state in hosts and routers that expires if not refreshed within a specified amount of time.

SONET — Synchronous Optical Network. A high-speed (up to 2.5 Gbps) synchronous network specification developed by Bellcore and designed to run on optical fiber. STS1 is the basic building block of SONET. Approved as an international standard in 1988. See also SDH.

SONET Clock Generator — See SCG.

source-based tree — Multicast forwarding tree established from the source of traffic to all interested receivers for a particular group address. It is often used in a dense-mode forwarding environment.

source class usage — See SCU.

source service access point — See SSAP.

source-specific multicast — See SSM.

Spanning Tree Protocol — See STP.

sparse mode — Method of operating a multicast domain where sources of traffic and interested receivers meet at a central rendezvous point. A sparse-mode network assumes that there are very few receivers for each group address.

SPF — Shortest path first. An algorithm used by IS-IS and OSPF to make routing decisions based on the state of network links. Also called the Dijkstra algorithm.

SPI — Security Parameter Index. In IPSec, a numeric identifier used with the destination address and security protocol to identify an SA. When IKE is used to establish an SA, the SPI is randomly derived. When manual configuration is used for an SA, the SPI must be entered as a parameter.

SPID — Service Profile Identifier. Used only in Basic Rate Interface (BRI) implementations of ISDN. The SPID specifies the services available on the service provider switch and defines the feature set ordered when the ISDN service is provisioned.

split horizon — Method used in distance-vector networks to avoid routing loops. Each router does not advertise routes back to the neighbor from which it received them.

SPQ — Strict–priority queuing. A dequeuing method that provides a special queue that is serviced until it is empty. The traffic sent to this queue tends to maintain a lower latency and more consistent latency numbers than traffic sent to other queues. See also APQ.

SPT — Shortest-path tree. An algorithm that builds a network topology that attempts to minimize the path from one router (the root) to other routers in a routing area.

SQL — Structured query language. International standard language used to create, modify, and select data from relational databases.

src port — TCP or UDP port for the source IP address in a packet.

SS7 — Signaling System 7. A protocol used in telecommunications for delivering calls and services.

SSAP — Source service access point. Device that identifies the origin of an LPDU on a DLSw network.

SSB — System and Switch Board. On an M20 router, a Packet Forwarding Engine component that performs route lookups and component monitoring and monitors FPC operation.

SSH — Secure Shell. A protocol that uses strong authentication and encryption for remote access across a nonsecure network. SSH provides remote login, remote program execution, file copy, and other functions. In a UNIX environment, SSH is intended as a secure replacement for rlogin, rsh, and rcp.

SSH/TLS — Secure Shell with Transport Layer Security. A combination of two standard methods used to secure communications over the Internet. TLS is the name of a standard protocol based on SSL 3.0 and is defined in RFC 2246. In combination, SSH/TLS is also known as SSHv2 and uses FIPS-restricted cipher sets in a FIPS environment.

SSL — Secure Sockets Layer. A protocol that encrypts security information using public-private key technology, which requires a paired private key and authentication certificate, before transmitting data across a network.

SSM — Source-specific multicast. A service that allows a client to receive multicast traffic directly from the source. Typically, SSM uses a subset of the PIM sparse-mode functionality along with a subset of IGMPv3 to create a shortest-path tree between the client and the source, but it builds the shortest-path tree without the help of a rendezvous point.

SSP — Switch-to-Switch Protocol. Protocol implemented between two DLSw routers that establishes connections, locates resources, forwards data, and handles error recovery and flow control.

SSRAM — Synchronous static random-access memory. Used for storing routing tables, packet pointers, and other data such as route lookups, policer counters, and other statistics to which the microprocessor needs quick access.

S-TAG — Field defined in the IEEE 802.1ad Q-in-Q encapsulation header that carries the S-VLAN identifier information. See also B-TAG.

standard AAL5 mode — Transport mode that allows multiple applications to tunnel the protocol data units of their Layer 2 protocols over an ATM virtual circuit. You use this transport mode to tunnel IP packets over an ATM backbone. See also AAL5 mode, cell-relay mode, Layer 2 circuits, trunk mode.

S-tagged service interface — The interface between a customer edge (CE) device and the I-BEB or IB-BEB network components. Frames passed through this interface contain an S-TAG field. See also B-tagged service interface.

starvation — Problem that occurs when lower-priority traffic, such as data and protocol packets, is locked out (starved) because a higher-priority queue uses all of the available transmission bandwidth.

stateful firewall — See stateful firewall filter and stateless firewall filter.

stateful firewall filter — Type of firewall filter that evaluates the context of connections, permits or denies traffic based on the context, and updates this information dynamically. Context includes IP source and destination addresses, port numbers, TCP sequencing information, and TCP connection flags. The context established in the first packet of a TCP session must match the context contained in all subsequent packets if a session is to remain active. See also stateless firewall filter.

stateful firewall recovery — Recovery strategy that preserves parameters concerning the history of connections, sessions, or application status before failure. See also stateless firewall recovery.

stateless firewall filter — Type of firewall filter that statically evaluates the contents of packets transiting the router and packets originating from or destined for the Routing Engine. Packets are accepted, rejected, forwarded, or discarded and collected, logged, sampled, or subjected to classification according to a wide variety of packet characteristics. Sometimes called access control lists (ACLs) or simply firewall filters, stateless firewall filters protect the processes and resources owned by the Routing Engine. A stateless firewall filter can evaluate every packet, including fragmented packets. In contrast to a stateful firewall filter, a stateless firewall filter does not maintain information about connection states. See also stateful firewall filter.

stateless firewall recovery — Recovery strategy that does not attempt to preserve the history of connections, sessions, or application status before failure. See also stateful firewall recovery.

static LSP — See static path.

static path — In the context of traffic engineering, a static route that requires hop-by-hop manual configuration. No signaling is used to create or maintain the path. Also called a static LSP.

static route — Explicitly configured route that is entered into the routing table. Static routes have precedence over routes chosen by dynamic routing protocols.

static RP — One of three methods of learning the rendezvous point (RP) to group address mapping in a multicast network. Each router in the domain must be configured with the required RP information.

S/T interface — System reference point/terminal reference point interface. A four–pair connection between the ISDN provider service and the customer terminal equipment.

STM — Synchronous transport module. CCITT specification for SONET at 155.52 Mbps.

STP — Spanning Tree Protocol. Defined in the IEEE standard 802.1D, the Spanning Tree Protocol is an OSI Layer 2 protocol that ensures a loop-free topology for any bridged LAN. This protocol creates a spanning tree within a mesh network of connected Layer 2 bridges (typically Ethernet switches), and disables the links that are not part of that tree, leaving a single active path between any two network nodes.

strict — In the context of traffic engineering, a route that must go directly to the next address in the path. (Definition from RFC 791, modified to fit LSPs.)

strict hop — Routers in an MPLS named path that must be directly connected to the previous router in the configured path.

strict–priority queue — See SPQ.

structured query language — See SQL.

STS — Synchronous transport signal. Synchronous transport signal level 1 is the basic building block signal of SONET, operating at 51.84 Mbps. Faster SONET rates are defined as STS-n, where n is an integer by which the basic rate of 51.84 Mbps is multiplied. see also SONET.

stub area — In OSPF, an area through which, or into which, AS external advertisements are not flooded.

STU-C — Symmetric high-speed digital subscriber line (SHDSL) transceiver unit–central office. Equipment at the telephone company central office that provides SHDSL connections to remote user terminals.

STU-R — Symmetric high-speed digital subscriber line (SHDSL) transceiver unit–remote. Equipment at the customer premises that provides SHDSL connections to remote user terminals.

sub-LSP — Part of a point-to-multipoint label-switched-path (LSP). A sub-LSP carries traffic from the main LSP to one of the egress PE routers. Each point-to-multipoint LSP has multiple sub-LSPs. see also point-to-multipoint LSP.

subnet mask — Number of bits of the network address used for the host portion of a Class A, Class B, or Class C IP address.

subrate value — Value that reduces the maximum allowable peak rate by limiting the HDLC-encapsulated payload. The subrate value must exactly match that of the remote channel service unit (CSU).

summary link advertisement — OSPF link-statement advertisement flooded throughout the advertisement’s associated areas by area border routers to describe the routes that they know about in other areas.

SVC — Switched virtual connection. A dynamically established, software-defined logical connection that stays up as long as data is being transmitted. When transmission is complete, the software tears down the SVC. See also PVC.

S-VLAN — The specific service instance VLAN identifier carried inside the S-TAG field. See also B-VID.

switch — A network device that attempts to perform as much of the forwarding task in hardware as possible. The switch can function as a bridge (LAN switch), router, or some other specialized device, and forwards frames, packets, or other data units. See also bridge.

switch-card chassis — See SCC.

switched virtual connection — See SVC.

Switching and Forwarding Module — See SFM.

Switch Interface Board — See SIB.

Switch-to-Switch Protocol — See SSP.

symmetric high-speed digital subscriber line — See SHDSL.

Synchronous Digital Hierarchy — See SDH.

synchronous dynamic random-access memory — See SDRAM.

Synchronous Optical Network — See SONET.

synchronous static random-access memory — See SSRAM.

synchronous transport module — See STM.

synchronous transport signal — See STS.

sysid — System identifier. Portion of the ISO nonclient peer. The system ID can be any six bytes that are unique throughout a domain.

syslog — System log. A method for storing messages to a file for troubleshooting or record-keeping. It can also be used as an action within a firewall filter to store information to the messages file.

System and Switch Board — See SSB.

System Control Board — See SCB.

system ID — See sysid.

system log — See syslog.

System Network Architecture — See SNA.

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