Table Of Contents

Glossary

A
AAL (ATM adaptation layer)	Layer of ATM protocols responsible for packaging data into cells, then reassembling the data at the receiving end; that is, for adapting datagrams, voice samples, and video frames into a format that can be handled by ATM. The individual protocols used in this layer are referred to as AALs. Cisco WAPMS supports AAL-1 and AAL-5. Each AAL is divided into two parts: a SAR (segmentation and reassembly) sublayer and a convergence sublayer (which comprises two separate sublayers).
AAL-1	ATM Adaptation Layer Type 1. An ATM adaptation layer protocol designed to transport bit-synchronous traffic through an ATM network. This AAL provides support for emulation of time division multiplexed connections (for example, DS0 circuits between voice PBX devices). These connections require a constant bit rate and have specific timing and delay requirements. See also AAL (ATM adaptation layer).
AAL-2	ATM Adaptation Layer Type 2. This AAL is still undefined by the International Standards bodies. It is a placeholder for variable bit rate video transmission. See also AAL (ATM adaptation layer).
AAL-5	ATM Adaptation Layer Type 5. An ATM adaptation layer protocol designed to efficiently transport variable-length data packets (for example, IP data packets or Frame Relay frames) through an ATM network. Each packet/frame, called a Protocol Data Unit (PDU), is segmented into multiple cells. The last cell contains a trailer that includes the PDU length and a checksum. The PDU's integrity is verified during reassembly at the destination. See also AAL (ATM adaptation layer).
abnormal frame	A frame that is either aborted, too short, or too long; often a sign of equipment failure.
address	A numerical identifier for distinguishing one network node from another. See also Internet address.
address resolution	The conversion of an Internet address into a physical address.
agent	The entity in a network management system responsible for gathering data and providing it to the network management station.
AIS (alarm indication signal)	On a T1 network, an error or alarm signal in which unframed all 1's (Blue alarm) is sent downstream (to user) from the fault site. Also used as T-1 keep-alive signal. In ATM, it is an operations and maintenance (OAM) message sent to inform a downstream node that a fault has been detected upstream in a network element that supports a virtual channel connection (VCC) that passes through the node. See also blue alarm and RDI (remote defect indication).
AppleTalk	Apple's standards for network hardware, protocols, and devices.
application layer	The highest layer in the OSI model and the highest layer of the TCP/IP model. It usually performs user services, such as file transfer. See also TCP/IP.
ASE (Analysis Service Element	Hardware devices connected to a WAN network whose embedded agent software collects network performance data for detailed analysis by the server (PAM) and client (PAC) Cisco WAPMS system components. ASEs monitor traffic to and from the WAN simultaneously, as appropriate to the specific events being monitored. At least one ASE is located on each network circuit to be managed. Partner devices can also be equipped with ASE agent software.
ATM (asynchronous transfer mode)	A form of fast-packet switching technology, using an asynchronous time division multiplexing technique. The multiplexed information flow is organized into fixed-sized blocks called cells. It is asynchronous because the recurrence of cells containing information from an individual user is not necessarily periodic. ATM is used for transmitting voice, video, and data over high-speed LANs and WANs. See also cell relay.
ATM adaptation layer	See also AAL (ATM adaptation layer)
availability	1. The SLA measurement on a circuit that indicates the number of seconds that the circuit can carry user traffic. In ATM networks, conditions that cause the circuit to be unavailable include AIS, RDI, and LOCD. In Frame Relay networks, an LMI status message indicates when the circuit is unavailable. On VPNs, the VPN ASE measures availability by periodically exchanging test messages with its peer ASEs. A VPN circuit is declared unavailable when connectivity is lost to the remote ASE. 2. The SLA measurement on a WAN service provider's switch port that indicates the number of seconds that the switch can carry user traffic between the WAN access device and the WAN cloud. In Frame Relay networks, an LMI status message indicates when the port is unavailable. Also, the absence of any LMI status indicates the port is unavailable.

B
B8ZS (binary 8 zero substitution)	A line coding technique used on T1 transmission facilities to guarantee density requirements in the public network while allowing for 64K clear channel transmission.
bandwidth	The range of frequencies, expressed in kilobits per second or bits per second (kbps), that can pass over a given transmission channel within a WAN. The bandwidth determines the rate at which information can be sent through a channel—the greater the bandwidth, the more information that can be transmitted concurrently.
Bc (committed burst size)	In Frame Relay networks, the maximum amount of data that can be transmitted during a given time interval under normal conditions. Bc is specified in bits per second. Compare to CIR. See also Be (excess burst size).
Be (excess burst size)	The maximum amount of uncommitted data (in bits) in excess of Bc that a Frame Relay network can attempt to deliver during a certain time interval. Be is specified in bits per second. See also Bc (committed burst size).
BECN (backward explicit congestion notification)	A bit set by a Frame Relay network to notify an interface device (DTE) that the sending devices should initiate congestion avoidance procedures.
BECN second	A second during which one or more non-errored frames were received with the backward explicit congestion notification (BECN) bit set.
blue alarm	One of the OAM function types used for fault management. An error or alarm signal transmitted in lieu of the normal signal to maintain transmission continuity to the receiving node. This indicates that there is a transmission fault located either at the sending node or upstream of the sending node. See also AIS (alarm indication signal) and RDI (remote defect indication).
BPV (bipolar violation)	An error event on a line in which the normal pattern of alternating high and low signals is disrupted. A bipolar violation is when two high signals occur without an intervening low signal, or vice-versa.
burstiness	In the context of a packet network, data that uses bandwidth only sporadically. During pauses, channels are idle, and no traffic flows across them in either direction. Cisco WAPMS Troubleshooting examines burstiness in 1-second granularity.

C
CAC (Connection Admission Control)	Actions performed by the network to enforce network admission policies. These actions, which may be performed during call setup or during call re-negotiation, determine whether or not to grant a virtual channel or virtual path connection to a user. Information from the traffic contract is used to make this determination.
CAR (committed access rate)	The amount of bandwidth assigned to a particular IP circuit.
CAS (channel associated signaling)	Legacy PBX signaling mechanism used to indicate on-hook/off-hook for telephone connections.
CBR (constant bit rate)	One of the five ATM classes of service which supports the transmission of a continuous bit stream of information where traffic, such as voice and video, needs to meet certain QoS (Quality of Service) requirements.
CDR (cell delivery ratio)	The ratio of cells that were successfully delivered from the network to the cells that were originally offered to the network.
CDV (Cell Delay Variation)	A measure of the variance of the cell transfer delay for an ATM layer connection. High variation implies larger buffering for delay-sensitive traffic such as voice and video.
CTD (cell transfer delay)	A sample of the number of milliseconds of one-way delay on a circuit during a 15 minute collection period. When this value is -1, the measurement is not valid.
cell	Any fixed-length data packet. For example, ATM uses fixed-length, 53-byte cells. See also cell relay.
cell delineation	The process that allows identification of the cell boundaries.
cell relay	A form of packet transmission that uses a fixed-length cell over a packet-switched network. ATM is a type of cell relay.
CES (circuit emulation service)	An ATM-provided class of service, where TDM-type, CBR (constant bit rate) circuits are emulated by the AAL-1.
channel	A telecommunications path (pipe) of a specific capacity (speed) between two locations in a network.
CIDR (classless interdomain routing)	The standard format for designating an IP subnet. CIDR addresses use a single IP address to designate many unique addresses. A CIDR address is identified by an IP prefix and subnet mask, for example: 192.60.128.0/24. The number indicates how many bits of subnet mask you are using (counting from the far left of the IP address) for the network address and how many bits you are using for the host address. The format is "abc.abc.abc.abc/#", where each "abc" is any number from 0 to 255. The IP prefix, which can be any number from 1 to 32, specifies how many addresses are covered by the CIDR address. A lower number (such as `/16') covers more addresses than a higher number (such as `/30'). See also Internet address.
CIR (committed information rate)	In Frame Relay networks, the rate at which data is expected to be transmitted, on average, under normal conditions. CIR is specified in bits per second. Compare to <(X-Ref)>Bc (committed burst size).
Class of Service	Class of Service (CoS) is a way of managing traffic in a network by grouping similar types of traffic (for example, e-mail, streaming video, voice, large document file transfer) together and treating each type as a class with its own level of service priority. IP Transport ASEs gather and report data for up to eight classes of service.
client/server model	A cooperative processing model in which an application sends a request to an application at another location and asks for a particular response. The requesting program is the client, and the application satisfying the request is the server. In Cisco WAPMS, the client is the PAC or Web Client, and the server is the PAM.
CLP (cell loss priority)	A cell header field that indicates the eligibility of the cell for discard by the network under congested conditions. Marked cells (CLP=1) can be discarded when the network is congested.
community string	A password string used to control administrative access to SNMP devices.
congested seconds	In Frame Relay, it is the presence of BECN or FECN. In ATM it is the presence of EFCI. See also BECN (backward explicit congestion notification), and FECN (forward explicit congestion notification).
CPE (customer premises equipment)	Networking equipment at the customer's site.
CRC (cyclical redundancy check)	Group of closely related mathematical algorithms used to detect errors in a stream of bits. The HEC (header error control) computation is a form of CRC, and verifies correct transmission of cell data. The PDU (protocol data unit) uses another form of CRC, but the specifics vary depending on the type of PDU being sent.
CSU (channel service unit)	An ancillary device needed to adapt the V.35 interface on a Frame Relay DTE to the T1 interface on a Frame Relay switch. See also CSU/DSU (channel service unit/data service unit).
CSU/DSU (channel service unit/data service unit)	Manages digital transmission, monitors signals for problems, and responds to central office commands. It performs many of the functions that modems do, but it does not have to convert digital signals to and from analog because the end device and the underlying transmission facility are both digital.
CSV (comma separated value)	A file format compatible with most spreadsheet and database applications.

D
data link layer	The second layer of the OSI model. This layer is responsible for transmission, framing, and error control over a single communications link.
DCE (data communication equipment)	Installed equipment that provides all the functions required to establish, maintain, and terminate a connection, and perform the signal conversion and coding between the terminal equipment and the common carrier's line.
DDR (data delivery ratio)	See also FDR (frame delivery ratio).
DDS (digital data service)	The class of service offered by telecommunications companies for transmitting digital data rather than voice. See also DS (digital signal or digital service).
DE (discard eligibility)	The ratio of cells that were successfully delivered from the network to the cells that were originally offered to the network.
decode	To disassemble and translate binary protocol data to a human-readable text format.
device	A network element of some kind. Partner devices are hardware elements that embed Cisco WAPMS agent software. See also ASE (Analysis Service Element.
DLCI (data link connection identifier)	A unique number assigned to a PVC endpoint in a Frame Relay network; identifies a particular PVC endpoint within a user's access channel in a Frame Relay network and has local significance only to that channel. See also PVC (permanent virtual circuit).
DNS (domain name system)	An online distributed database used to map human-readable machine names to numerical representations.
domain	A logical partitioning of all the networks configured on a PAM. A user can have access to more than one domain, and a domain can be accessed by multiple users. The PAM administrator configures which Toolsets and functions a given user can access by domain.
domain name server	A network node that uses a DNS to resolve Internet addresses for network hosts.
DS (digital signal or digital service)	A classification of digital circuits (versus standard service circuits). The DS defines the level of common carrier digital transmission service: DS0 = 64 Kbps (Fractional T1) DS1 = 1,544 Mbps (T1) DS2 = 6,312 Mbps (T2) DS3 = 44,736 Mbps (T3) DS4 = 274,176 Mbps (T4) Cisco WAPMS supports ASEs on DS1 and DS3 Frame Relay access lines and on DS3 ATM access lines.
DSU (data service unit)	A device used in digital transmission for connecting a CSU to a terminal or computer. See also CSU/DSU (channel service unit/data service unit).
DTE (data terminal equipment)	A device that acts as the source and/or destination of data; controls the communication channel.

E
errored frame	A frame that has an FCS or alignment error; can indicate an underlying transmission impairment.
event	A significant network occurrence that can be reported by the ASE to the Cisco WAPMS PAC or forwarded to another event management system.
EFCI (explicit forward congestion indicator)	A bit in the PTI field of the ATM cell header. The bit is set by a congested network node in any cell passing through the node.
excess zeros	More consecutive zeros received than are permitted for the selected transmission coding technique

F
FCS (frame check sequence)	The standard 16-bit cyclic redundancy check used for HDLC and Frame Relay frames.
FDR (frame delivery ratio)	The SLA measurement of the ratio of frames received from the network relative to the number of frames offered to the network. The ratio is restricted to those frames that fall within CIR; frames beyond those ranges are not included in the ratio. The "frames" counted in FDR include: * (Frame Relay connections) frames * (ATM connections) AAL-5 PDUs * (mixed Frame Relay and ATM connections) AAL-5 PDUs at the ATM endpoint and frames at the Frame Relay endpoint. The network provides a Frame Relay to ATM interworking function that transforms frames into AAL-5 PDUs and vice versa.
FEBE (far end block error)	A maintenance signal transmitted in the physical layer overhead indicating that error bits have been detected at the far-end physical layer of a DS3 or E3 access channel. This qualifier is used to monitor the bit error performance of the link.
FECN (forward explicit congestion notification)	A bit set by a Frame Relay network to notify an interface device (DTE) that the receiving devices should initiate congestion avoidance procedures.
FECN Second	A second during which one or more non-errored frames were received with the forward explicit congestion notification (FECN) bit set.
flow control	The mechanism by which a receiver informs a sender how much data it is willing to accept.
FRAD (Frame Relay access device)	Hardware or software that turns packets from TCP, SNA, IPX, etc., into frames that can be sent over a Frame Relay WAN.
frame	An elementary block of data for transmission by certain protocols. The term derives from protocols that add special characters or bit patterns to mark the boundaries between packets.
Frame Relay	A packet-switching protocol that operates at user data rates of up to T3 speed. Frame Relay is an efficient protocol because it omits most of the overhead that in previous packet-switching protocols had been associated with error control.
FTP (file transfer protocol)	A client/server protocol that allows a user on one computer to transfer files to and from another computer over a TCP/IP network. The client initiates the request to receive files. The server responds by transferring files.
full duplex	The data communications mode that allows data to be transmitted in two directions simultaneously. Compare with half duplex.

H
half duplex	A communications link that can transmit in only one direction at a time. Compare with full duplex.
HDLC (high level data link control)	A generic link-level communications protocol that manages synchronous, code-transparent, serial information transfer over a link connection.
HEC (header error control)	In ATM, a feature that provides protection against misdelivery of cells due to addressing errors. HEC can correct a single bit error within individual ATM cells and can also detect various multiple-bit errors.
hop	A single trunk line between two switches or routers in a WAN.
HSSI (high speed serial interface)	A physical interface specification that addresses high-speed communication over WANs for broadband applications. The Cisco WAPMS product line includes an HSSI ASE that works on Frame Relay networks up to DS3 rates.
HTTP (hyper-text transfer protocol)	The client-server TCP/IP protocol used on the World Wide Web for exchange of HTML documents. The client initiates the request to be sent an HTML document. The server responds by sending an HTML document.
hysteresis	During performance monitoring with Cisco WAPMS, indicates how far from a threshold a statistic must move before the same event can be generated again.

I
ICMP (Internet control message protocol)	The part of the Internet protocol suite that handles error and control messages. It is used by gateways and hosts to report problems with datagrams and their source. ICMP includes an echo request/reply used by PING to test the availability and status of a destination.
Internet	The collection of gateways and networks that use the TCP/IP protocol suite and operate as a single, virtual network.
Internet address	An Internet (or IP) address is a unique identifier for a node or host connection on an IP network using TCP/IP. Every 32-bit IP address consists of two parts: a network identifier, and a node identifier or host number. The numbers in an IP address are used in different ways to identify a particular network and a host on that network. The boundaries of the address are based on which class the IP address belongs: class A, B, or C. See also CIDR (classless interdomain routing).
Internet layer	The layer of the TCP/IP model that is equivalent to the network layer of the OSI model. This layer concerns itself with the transport of data across the network, independent of the underlying subnetworks and the media of those subnetworks.
IMA (Inverse Multiplexing over ATM)	A User Network Interface (UNI) standard that allows a single ATM cell stream to be split across multiple access circuits from the user site to the edge of the carrier's ATM network.
Internet protocol suite	A collection of computer-communication protocols; currently the solution of choice for open networking. See also TCP/IP.
IP (Internet protocol)	The network protocol offering a connectionless-mode network service in the Internet suite of protocols. See also Internet protocol suite.
IP address	See also Internet address.
IP Piggyback	A setting where an ASE has the same IP address as the router to which it is connected. (The ASE is said to "piggyback" on the router's IP address.) The ASE must be assigned special port numbers so it is possible to distinguish between messages intended for the router as opposed to messages intended for the ASE.
IPX (Internet packet exchange)	The low-level protocol used by all Novell NetWare frames. See also SPX (sequenced packet exchange).
ISO (International Organization of Standards)	The international organization that develops standards for computers and other fields.
ISP (Internet service provider)	An Internet company that owns and maintains one or more Internet servers. The ISP offers its subscribers access to the Internet and, optionally, capabilities to monitor performance data.

L
LAN (local area network)	A physical network that operates at high speed over short distances.
LAPB	Link access procedure - balanced.
LCV (line coding violation)	A condition that occurs when receiving BPVs or excess zeros.
LMI (local management interface)	A polling protocol between the FRAD and the network for exchanging information about the status of the interface and its defined PVCs.
LMIsolate (link management isolate)	An ASE feature that provides emulation of link management messages in the absence of a router or when the end-user router is down.
LOCD (loss of cell delineation)	A condition at the receiver or a maintenance signal transmitted in the PHY overhead indicating that the receiving equipment has lost cell delineation. Used to monitor the performance of the physical layer.
long frame	A frame received that is too long, as indicated by the data link layer.
LOS (loss of signal)	An access line error condition when too many consecutive zeros are received (actual number of zeros varies by ASE model).

M
Mbps	Megabits per second.
MBS (maximum burst size)	A traffic parameter that specifies the maximum number of cells that can be transmitted at the peak rate (PCR).
MIB (management information base)	A collection of objects that can be accessed through a network management protocol, such as SNMP.

N
NetBEUI	An implementation of the NetBIOS transport protocol that is used within some PC-based LAN operating systems.
NetBIOS (network basic input output system)	A standard network interface specification for PC local area networks introduced with IBM's PC network and used by Microsoft's LAN Manager.
NetWare	Novell's network operating system that uses Novell's proprietary IPX protocol as well as TCP/IP and AppleTalk.
network access layer	The layer of the TCP/IP model that is equivalent to the physical and data link layers of the OSI model. This layer defines the interfaces used between devices as well as the transmission, framing, and error control over a single link.
network layer	The portion of an OSI system responsible for data transfer across the network, independent of the topology of the underlying subnetworks and the media of those subnetworks.
NNTP (network news transfer protocol)	A TCP/IP protocol for the distribution, inquiry, retrieval, and posting of Usenet news articles over the Internet.
node	A point of connection into a network.
NSP (network service provider)	See also WAN service provider.

O
OAM (operation and maintenance	A set of administrative and supervisory actions regarding network failure detection, fault localization, and performance monitoring in ATM networks. Special-type cells carry OAM-related information. See also AIS (alarm indication signal) and RDI (remote defect indication).
OOF (out of frame)	An access line error condition where too many consecutive framing bits are in error. The actual number varies according to ASE model.
OC-3 (Optical Carrier-level 3)	A SONET channel equal to three DS-3s, which is equal to 155.52 Mbps.
OSI model (open systems interconnection model)	A seven-layer model, developed by the ISO, for describing network protocols: Layer 1 - physical layer Layer 2 - data link layer Layer 3 - network layer Layer 4 - transport layer Layer 5 - session layer Layer 6 - presentation layer Layer 7 - application layer See also TCP/IP model.
OSPF (open shortest-path first)	A link state routing protocol, rather than a distance vector routing protocol; an Internet standard Interior gateway protocol.

P
PAC (Platform Applicable Client)	The primary client software in Cisco WAPMS's client-server architecture. The PAC presents data from the performance database (on the PAM) and allows the user to analyze and interact with that data. The PAC runs on a Microsoft Windows PC and generally communicate with PAMs using Remote Procedure Calls (RPCs) and Windows socket programming. There is at least one PAC for each PAM in a Cisco WAPMS system. See also Web Client.
PAM (Performance Archive Manager)	The server software in Cisco WAPMS's client-server architecture. The PAM stores the performance database and manages client access to network configuration and database resources. Cisco WAPMS clients can be either PACs or Web Clients. See also PAC (Platform Applicable Client).
Path Parity Error Seconds (PSES)	A period in which 44 or more path parity errors has occurred.
PCR (peak cell rate)	In ATM networks, the maximum rate at which cells can be transmitted under normal conditions. PCR is specified in cells per second and converted internally to bits per second. Compare to SCR (sustained cell rate).
PDU (protocol data unit)	The information unit of a particular communications protocol; in the case of ATM traffic, the collection of cells that make up a packet. PDUs can be packaged using any of several standard formats (explained in AAL). The format used varies depending on the type of data being sent and the medium over which it is being transmitted. See also AAL (ATM adaptation layer).
PHY (physical layer)	The bottom layer of the OSI and ATM protocol stack, which defines the interface between ATM traffic and the physical media. The PHY consists of two sublayers: the transmission convergence (TC) sublayer and the physical medium-dependent (PMD) sublayer.
ping	A program that tests a TCP/IP network node by sending an ICMP echo request and waiting for a reply.
PIU (path information unit)	In IBM's SNA network communications, a packet created when the path-control layer adds a transmission header to a basic information unit from the transmission-control layer.
PLCP (physical layer convergence protocol)	In DS3, an alternative method used by older T carrier equipment to locate ATM cell boundaries. This method has recently been moved to an informative appendix of the ATM DS3 specification and has been replaced by the HEC method.
PMD (physical medium dependent)	A sublayer of the physical layer that interfaces directly with the physical medium and performs the most basic bit transmission functions of the network.
presentation layer	The OSI layer concerned with the encoding of application information for transmission between systems. The presentation layer receives data from the session layer and passes it to the application layer.
promiscuous mode (ATM ASEs)	Refers to the circuit auto-discovery or circuit detection feature of an ASE. For ATM ASEs promiscuous mode (called auto-discovery mode) operates as follows: an ATM ASE monitors traffic carried over circuits not configured in its circuit table (either as circuits or as paths) whose VCI is less than the ASE's MAX-VCI setting. Once the ASE determines a circuit's AAL type, it adds the circuit to the table with the determined type. Pre-v6.0 Visual UpTime ATM ASEs can differentiate whether circuit traffic is AAL-1 or AAL-5; v6.0 Visual UpTime ATM ASEs can differentiate AAL-1, AAL-2, or AAL-5 type traffic. In addition, when a v6.0 Visual UpTime ATM ASE cannot determine a circuit's AAL type, it assigns it a value of Other. Because v6.0 Visual UpTime ATM ASEs can only support 600 AAL-5 circuits (including inband), any AAL-5 circuits discovered and added to that table after that limit is reached are added to the table as Other.
promiscuous mode (Frame Relay ASEs)	Refers to the circuit auto-discovery or circuit detection feature of an ASE. A Frame Relay ASE in promiscuous mode auto-discovers circuits with-out employing the LMI polling protocol. See also LMI (local management interface).
protocol	A set of rules governing the operation of a communications link.
PVC (permanent virtual circuit)	A logical connection between two sites across a packet-switched network. It is always in place and available along a predetermined network path. A PVC is defined by DLCIs at each of the two access channels at its endpoints. See also VC (virtual circuit).
PVC congestion	Any one-second interval in a Frame Relay circuit during which an ASE detects frames with either of the FECN or BECN congestion bits set as positive.

Q
QoS (quality of service)	QoS refers to a broad collection of networking technologies and techniques aimed at providing guarantees on the ability of a network to deliver predictable results. Elements of network performance within the scope of QoS often include: availability, throughput, delay, and error rate.

R
RDI (remote defect indication)	One of the OAM function types used for fault management in ATM. Reports remote defect indications in the direction opposite the AIS. See also AIS (alarm indication signal).
REBE (Remote End Block Error)	A maintenance signal transmitted in the physical layer overhead indicating that error bits have been detected at the remote physical layer of an E1 access channel. This qualifier is used to monitor the bit error performance of the link.
RIP (routing information protocol)	A distance vector, rather than a link state, routing protocol; an Internet standard Interior gateway protocol.
RTD (round trip delay)	The SLA measurement that indicates how long (in milliseconds) it takes for a packet to travel from the near-end ASE to the far-end ASE on a circuit and back. The measurement calculates only the time the packet is on the circuit. The turnaround time at the far-end ASE is removed from the measurement.
RU (request or response unit)	In SNA network communication, the type of packet exchanged by network addressable units (NAUs) such as network elements with associated ports (or addresses).

S
SAP	Service Advertisement Protocol. IPX protocol that provides a means of informing network clients, through routers and servers, of available network resources and services.
SCR (sustained cell rate)	In ATM networks, the rate at which cells are expected to be transmitted, on average, under normal conditions. SCR is specified in cells per second and converted internally to bits per second. Compare to PCR.
server	See also client/server model.
session layer	The OSI layer concerned with providing a way for users to establish sessions (connections) and transfer data over them in an orderly way.
short frame	A frame received that is shorter than five octets (excluding framing bits, but including FCS octets).
SLA (service level agreement)	An agreement reached between the WAN service provider and the subscriber that specifies WAN performance regarding RTD, FDR or DDR, and availability. Cisco WAPMS Troubleshooting provides graphs and statistics, and Planning and Reporting provides several reports that verify these service level measurements.
SLIP (serial line internet protocol)	A communications protocol that allows a modem (serial) connection for network access from a remote site. SLIP is part of the TCP/IP suite.
SMTP (simple mail transfer protocol)	A TCP/IP protocol used to transfer electronic mail between computers.
SNA (systems network architecture)	IBM's proprietary network architecture.
SNMP (simple network management protocol)	A program that tests a TCP/IP network node by sending an ICMP echo request and waiting for a reply.
SPX (sequenced packet exchange)	In IBM's SNA network communications, a packet created when the path-control layer adds a transmission header to a basic information unit from the transmission-control layer.
state-change event	Any of the following network events that ASEs can be configured to report back to the PAC: * Link Layer Change—access channel up or down; circuit endpoint active, inactive, or invalid * Access Line Signal Loss—physical line up or down * SNMP Authentication Failure—incorrect SNMP community name is used in attempts to contact the ASE. * ASE Reboot and Data Collection Poll Failure events are always reported and are not configurable.

T
T1	A digital transmission link with a capacity of 1.544 Mbps used for long-distance communications. T1 is comprised of 24 64kbps DS0s and can be used to deliver the entire 24 DS0s as a single channel or as fractionalized (N x 64) channels. Cisco WAPMS supports ASEs on T1 Frame Relay and T1 HDLC access lines, as well as ASEs for other kinds of access lines.
TCP (transmission control protocol)	The Internet transport level protocol that provides reliable, full-duplex stream service. TCP allows a process on one machine to send a stream of data to a process on another. Software implementing TCP uses the IP protocol to transmit information. TCP establishes a virtual circuit and provides reliable end-to-end data transmissions.
TCP/IP	Denotes the combination of TCP (transmission control protocol) and IP (Internet protocol). Generally, it refers to the Internet protocol suite, which includes TCP and IP, as well as several other protocols.
TCP/IP model	The TCP/IP suite follows a four-layer model that has equivalents in the OSI model.
telnet	The Internet standard protocol for remote login from a Telnet client to a Telnet server; runs on top of TCP/IP. Cisco WAPMS provides Telnet access to the ASE administration functions otherwise available only from the ASE administrative port.
TFTP (trivial file transfer protocol)	A simple file transfer protocol used for downloading boot code to diskless workstations. Part of the TCP/IP protocol suite.
tier	The PAM tier determines the number of domains and the total number of objects (the sum of the ASEs, Partner ASEs, and DLCIs defined for the Cisco WAPMS system) supported on the PAM. The tier value is set when building the PAM according to the following criteria: * Tier 0: 15 supported domains,1000 supported objects * Tier 1: 15 supported domains, 2100 supported objects * Tier 3: 15 supported domains, 5000 supported objects * Tier 5: 15 supported domains, 17,500 supported objects * Tier 6: 250 supported domains, 28,000 supported objects
transport layer	The OSI and TCP/IP layer concerned with controlling a communication transaction between nodes (user-to-user communication).
trap	An SNMP mechanism used by agents to report significant network events to the network management console.

U
UDP (user datagram protocol)	A low-overhead datagram protocol for the transport layer in TCP/IP networks.

V
V.35	An industry standard data communications interface utilizing balanced signal pairs and a 34-pin rectangular connector usually called a "Winchester" connector.
VC (virtual circuit)	A logical circuit set up to ensure reliable communication between two network devices. A VC is composed of two unidirectional connections, one in each direction (to and from the connection point). In ATM networks, a VC is identified by its VCI. See also PVC (permanent virtual circuit).
VCI (virtual circuit identifier)	A routing field in the ATM cell header used as an addressing identifier to route cell traffic.
virtual channel	A connection between two communicating ATM networks.
VP (virtual path or path)	A group of VCs carried between two points that provide a way to bundle traffic headed in the same direction. A VP is identified by its VPI. VPs switch based only on the value of the Virtual Path Identifier (VPI) in the ATM cell header, while VCs switch on the VPI/VCI pair.
VPI (virtual path identifier)	A field in the ATM cell header that is used as an addressing identifier to route cell traffic.
VPN (virtual private network)	The technique of using a public routed network, such as an IP network, to functionally simulate a circuit-switched network. The technique gains the security of a private network, even though it is running over a public network.

W
WAN service provider	A telecommunications company that owns and maintains one or more WANs. Also called a carrier. The WAN service provider offers its subscribers access to the WAN and, optionally, capabilities to monitor SLA data.
Web Client	Cisco WAPMS client software that runs the Planning and Reporting Toolset through a Web browser, using the PAM as the Web server. See also client/server model.