Q-S

QNX™

A real-time operating system from QNX Software Systems with a strong base in message passing.

QoS

Quality of Service. Provides guarantee of quality of network.

RED

Random Early Detection. Congestion is detected before it occurs, and packets are discarded randomly to prevent it.

redundancy

An implementation in which a primary resource is backed up by an identical resource for fault tolerance/high- availability purposes.

reentrant code

Code that has been written so that it uses no global or local persistent context across invocations. So, a reentrant function can call itself any number of times with no impact on any variables or states used by the function.

RFC

Request for Comments. Documents specified under the IETF specifying various protocols.

RIP

Routing Information Protocol. A routing protocol to provide routing updates between routers to build a routing table.

route leaking or route redistribution

The process of redistribution of routes between various protocols in a system. For example, BGP can “leak” some routes to OSPF but not others.

router

A device that examines datagram headers to forward them to the next hop destination.

routing information base (RIB)

The complete routing table constructed by a Route Table Manager (RTM) based on routing information from all routing protocols.

RTM

Route Table Manager. A module which deals with route redistribution and construction of a Routing Information Base. It may also construct a Forwarding Information Base (FIB) culled out of the RIB for distribution to the individual forwarding elements.

RTOS

Real Time Operating System.

SDL

Specification and Description Language defined by ITU-T for system and protocol design, especially in telecommunications. The presentation is in a graphical form.

select

A call used in the socket API to make a process wait on a set of descriptors for events on any of the descriptors.

semaphore

A variable which helps support synchronization between processes, so that a process which tries to get a semaphore which has already been taken blocks until the semaphore is released.

SerDes

Serializer/Deserializer. An integrated circuit that converts parallel data to the serial form and vice versa.

serial port

A slow-speed interface port that transmits data serially.

shared memory

A memory that is shared for use by different processes.

signaling

A sequence of steps in hardware and/or software to set up desired behavior. For example, SS7 signaling is used to set up an end-to-end voice call through a circuit-switched network.

slow path

The path in the processing logic in which less frequent conditions and exceptions are handled. This path usually has several conditional paths.

SNMP

Simple Network Management Protocol. A protocol specified by the IETF for management of network devices. The protocol message interchange is between a network manager and the managed device.

socket API

The API available via the (originally) UNIX-based abstraction of a connection endpoint.

soft switch

A system that handles both the internet and the telephone network and serves as an interface between the two.

spanning tree protocol

A protocol specified by the IEEE 802.1D standard. STP is used in a Layer 2 bridged LAN topology to detect loops in the topology.

sparse matrix

A matrix with very few non- zero or valid entries. In a SET, this implies a table with very few entries in which the action routine is a valid operation. The other entries are No Ops (no operation or action).

SPF calculation

The Dijkstra Shortest Path First (SPF) calculation used for finding the shortest path between a source and destination. It is used by link state protocols like OSPF and IS–IS to build the routing table.

split control plane

An implementation in which the control plane functions like routing and signaling protocols are partially implemented on the control card and line card respectively. The two parts of the Split Control Plane interact with each other to provide the appearance of a single control plane. Contrast with Monolithic Control Plane.

SRAM

Static Random Access Memory. Faster than Dynamic Random Access memory and is generally used for cache memory.

SS7

Signaling System 7. The protocol used for call setup and forwarding in voice network.

state event table (SET)

A table-based representation (and implementation) of a state machine. The most common SET representation consists of M rows and N columns, where each column corresponds to a state and the row corresponds to an event. The whole table appears as a matrix of entries, with each entry representing the Action to be taken on the occurrence of the event in the specific row, and the next State to transition to.

state machine

Also called Finite State Machine or FSM. This is a construct used to specify the various states that a protocol can assume, which events are valid for those states, along with the action to be taken on specific events.

stateful

A protocol or system which maintains history or state about past events and transactions and uses this history for future transactions. Contrast with Stateless.

stateless

A protocol or system which does not depend upon its previous events or transactions for its future behavior. Contrast with Stateful.

static allocation

A method of allocating the memory required for data before the start of execution. This is usually done via static definitions of the data in the source code itself.

STREAMS

A framework originally specified in AT&T UNIX for building modular communications infrastructure and applications. STREAMS permit the addition and removal of protocol processing modules within the UNIX kernel.

strict layering

A situation in which a layer does not use knowledge of its upper or lower layers for its own operation.

SubAgent

Defined in the AgentX architecture, a subagent is a module which provides the management interface on a line card. It does not interface directly with the manager but only with the master agent on the control card. The AgentX protocol is used between the control card and the line card.

switch

A device which forwards traffic between its interfaces. A Layer 2 Switch is a special case of a bridge. A Layer 3 Switch is a router. Other types of switches include ATM and Frame Relay Switches.

switch fabric

Usually a chip or card used to direct traffic between two ports or line cards. A fabric permits multiple traffic streams to be switched in parallel.

synchronous call

Another name for a blocking call which does not return until the function completes its operation.