ABR --available bit rate. QoS class defined by the ATM Forum for ATM networks. ABR is used for connections that do not require timing relationships between source and destination. ABR provides no guarantees in terms of cell loss or delay, providing only best-effort service. Traffic sources adjust their transmission rate in response to information they receive describing the status of the network and its capability to successfully deliver data.
ACR --allowed cell rate. A parameter defined by the ATM Forum for ATM traffic management. ACR varies between the MCR and the PCR, and is controlled dynamically using congestion control mechanisms.
CBR --constant bit rate. QoS class defined by the ATM Forum for ATM networks. CBR is used for connections that depend on precise clocking to ensure undistorted delivery.
MCR --minimum cell rate. Parameter defined by the ATM Forum for ATM traffic management. MCR is defined only for ABR transmissions, and specifies the minimum value for the ACR.
NAS --network access server. Cisco platform (or collection of platforms, such as an AccessPath system) that interfaces between the packet world (for example, the Internet) and the circuit world (for example, the PSTN).
PCR --peak cell rate. Parameter defined by the ATM Forum for ATM traffic management. In Constant Bit Rate (CBR) transmissions, PCR determines how often data samples are sent. In ABR transmissions, PCR determines the maximum value of the ACR.
PPP --Point-to-Point Protocol. PPP is the successor to Serial Line Internet Protocol (SLIP) that provides router-to-router and host-to-network connections over synchronous and asynchronous circuits. Whereas SLIP was designed to work with IP, PPP was designed to work with several network layer protocols, such as IP, IPX, and ARA. PPP also has built-in security mechanisms, such as CHAP and PAP. PPP relies on two protocols: Link Control Protocol (LCP) and Network Control Protocol (NCP).
PPPoA --Point-to-Point Protocol over ATM. The PPPoA feature enables a high-capacity central site router with an Asynchronous Transfer Mode (ATM) interface to terminate multiple remote Point-to-Point Protocol (PPP) connections.
PPPoE --Point-to-Point Protocol over Ethernet. PPPoE allows a PPP session to be initiated on a simple bridging Ethernet connected client.
PPPoX --Point-to-Point Protocol over Protocol. PPPoX indicates that the point-to-point protocol terminates on another protocol which could be ATM or Ethernet.
PVC --permanent virtual circuit. A virtual circuit that is permanently established. PVCs save bandwidth associated with circuit establishment and tear down in situations where certain virtual circuits must exist all the time. In ATM terminology, called a permanent virtual connection.
QoS --quality of service. Cisco IOS QoS technology lets complex networks control and predictably service a variety of networked applications and traffic types.
RADIUS--Remote Authentication Dial-in User Service
SCR--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.
UBR--unspecified bit rate. QoS class defined by the ATM Forum for ATM networks. UBR allows any amount of data up to a specified maximum to be sent across the network but there are no guarantees in terms of cell loss rate and delay.
VBR--variable bit rate. QoS class defined by the ATM Forum for ATM networks. VBR is subdivided into a real time (rt) class and non-real time (nrt) class. VBR (rt) is used for connections in which there is a fixed timing relationship between samples. VBR (nrt) is used for connections in which there is no fixed timing relationship between samples but that still need a guaranteed QoS.
VPDN--virtual private dialup network. A VPDN is a network that extends remote access to a private network using a shared infrastructure. VPDNs use Layer 2 tunnel technologies (L2F, L2TP, and PPTP) to extend the Layer 2 and higher parts of the network connection from a remote user across an ISP network to a private network. VPDNs are a cost effective method of establishing a long distance, point-to-point connection between remote dial users and a private network.
VSA--vendor-specific attribute. An attribute that has been implemented by a particular vendor. It uses the attribute Vendor-Specific to encapsulate the resulting AV pair: essentially, Vendor-Specific = protocol:attribute = value.