Frame Relay Glossary

Justifying Frame Relay
Frame Relay Overview
What is Frame Relay?

Access Line

A communications line (e.g. circuit) interconnecting a frame-relay-compatible device (DTE) to a frame-relay switch (DCE).

Access Rate (AR)

The data rate of the user access channel. The speed of the access channel determines how rapidly (maximum rate) the end user can inject data into a frame relay network.

Alternate Mark Inversion (AMI)

A one (mark) pulse which is the opposite polarity as its predecessor.

Committed Burst Size (bits) (Bc)

The maximum amount of subscriber data that the network agrees to transfer, under normal conditions, during a time interval Tc.

Be - Excess Burst Size (bits)

The maximum amount of uncommitted data in excess of Bc that the network will attempt to transfer during a time interval Tc.

Bipolar With 8 Zero Substitution (B8ZS)

Bipolar 8 Zero Substitution is an application of BPRZ and is an exception to the Alternate Mark Inversion (AMI) line-code rule. It is one method of providing bit independence for digital transmission by providing a minimum 1s density of 1 in 8 bits.

Channel Service Unit (CSU)

This unit provides regeneration of the signal received from the network, controls the pulse shape and amplitude for transmission of the signal into the network, and possibly provides loop-back. The CSU function is frequently found within a Data Service Unit (DSU).

Committed Information Rate (CIR) bit/s

The rate at which the network agrees to transfer information, under normal conditions, during a time interval Tc.

Customer Provided Equipment (CPE)

Equipment owned and maintained by the customer and located on their side of the End-User Point of Termination (EU-POT) network interface.

Data Communications Equipment (DCE)

The equipment that provides the functions required to establish, maintain and terminate data transmission connections; e.g., a modem, as well as the signal conversion and coding required for communications between data terminal equipment and data circuit.

Data Link Connection Identifier (DLCI)

The DLCI is located within the address field of a frame relay packet. It is used to identify each PVC.

Data Service Unit (DSU)

Digital customer premises equipment used to recover timing from a baseband BPRZ signal which converts BPRZ line signals to a business machine interface signal such as V.35. At 64 kbit/s and below, DSU and Channel Service Unit (CSU) functions are, in modern equipment, combined in a single unit sometimes called a General Service Unit (GSU), Basic Service Unit (BSU) or Data Service Unit-A (DSU-A) so that it is part of the Data Communications Equipment (DCE). Above 64 kbit/s, DSU functions are frequently contained in the Data Terminal Equipment (DTE). The DSU usually contains circuitry to recognize and respond to loop-back commands from the serving test center.

Data Terminal Equipment (DTE)

A generic term for customer terminal equipment that connects to the network through a modem or through digital Network Channel Terminating Equipment (NTCE), e.g., a computer or a PBX.

Digital Cross-Connect System (DCS)

An intelligent (processor controlled) digital terminal that provides the capability to perform electronic cross-connects on digital channels operating at or below the bit rate of the transport systems terminated on the unit. This unit may also provide other features, such as bridging.

Discard Eligibility (DE) Indicator bit

A single bit located within the address field of a frame relay packet that is used to indicate that a frame should be discarded in preference to other frames during a frame discarding process.

Extended Superframe (ESF) Format

An Extended Superframe consists of 24 consecutive DS1 frames. Bit one of each frame (the F-bit) is time shared during the 24 frames to describe a 6-bit frame pattern, a 6-bit Cyclic Redundancy Check (CRC) remainder, and a 12-bit data link. The transfer rate of each is 2 kbit/s, 2 kbit/s and 4 kbit/s respectively.

Frame Sizes

Frame Sizes are variable length - maximum bytes per frame:

Ethernet Frame Size
1500 Bytes

Token Frame Size
4 Meg or 4096

16 Meg 16K +

FRAD or Frame Relay Access Device

Is a device that allows non-frame relay equipment to send frames to a Frame Relay network by formatting it inside a LAPF-Core frame.

Integrated Service Digital Network (ISDN)

A digital architecture that provides and integrated voice/data capability.

LMI or Local Management Interface

Was developed to provide management functions to control and maintain virtual circuits. See Virtual Circuit Management for additional information. Note: Two types are LMI or Annex D (We program our Frame Relay Switches to be Auto unless otherwise specified. Cisco defaults to LMI & ACC Defaults to Annex D, Motorola defaults to Auto).

Local Access and Transport Area (LATA)

A geographic area for the provision and administration of communications service. It encompasses designated exchanges that are grouped to serve common social, economic and other purposes.

Loopback test

An out-of-service test procedure applied to a full duplex channel that causes a received signal to be returned to the source.

Network Interface (NI)

The point of demarcation on the customer's premises at which CBLD's responsibility for the provision of service ends.

NNI's or Network-to-Network Interface

Defines how public and private frame relay networks can effectively interwork with one another. The major issue for NNI is to specify how control and user information should be passed between two frame relay networks. See the ISP/Carrier section for more detail.

Pburst/LIP (for customer's with Novell IPX)

Together, both will allow better throughput for remote stations accessing a Novell server. Typically, with older software versions, the default packet size was 576 Byte, so Novell automatically backed off to a maximum packet size of 576. Implementing Pburst and LIP on the Server and the router (built in to Novell Netware 3.12 and later and available on Cisco releases after 10.xx), increases traffic throughput: the router's IOS can negotiate larger packet sizes (Large Internet Packet or LIP) and PBURST (available from Netware 3.11 and later) allows the client to acknowledge a block of data rather than individual packet-by-packet.

Serving Area

Geographic area which is normally provided telecommunications services via one wire center.

Serving Wire Center

The term "Serving Wire Center" denotes a CBLD Central Office from which dial tone for the local Exchange Service would normally be provided to the demarcation point on the property at which the customer is served.

Superframe Format (SF)

A superframe consists of 12 consecutive DS1 frames. Bit one of each frame (the F-bit) is used to describe a 12-bit framing pattern during the 12 frames.

Tc

Committed Rate Measurement Interval(s) - A time interval for which the subscriber's committed information rate is measured. The formula used to calculate Tc is: Tc=Bc/CIR.

UNI or User Network Interface

Defines the coordination of status signalling between the user device which issues periodic Status Enquiry messages and the network which responds. UNI types are specified by the CPE; options include LMI, ANSI Annex D, or Q.933 Annex A.

Virtual Circuit Management

Provides management functions to control and maintain virtual circuits. There are two approaches: LMI and ANSI/CCITT. LMI is asymmetric (assumes the user will be communicating with a network and the two may respond differently to the same stimulus); ANSI and the CCITT allow symmetric procedures to be used between a user and network or between two networks. LMI uses DLCI 1023; ANSI/CCITT uses DLCI 0.


Justifying Frame Relay Frame Relay Overview What is Frame Relay?	Access Line A communications line (e.g. circuit) interconnecting a frame-relay-compatible device (DTE) to a frame-relay switch (DCE). Access Rate (AR) The data rate of the user access channel. The speed of the access channel determines how rapidly (maximum rate) the end user can inject data into a frame relay network. Alternate Mark Inversion (AMI) A one (mark) pulse which is the opposite polarity as its predecessor. Committed Burst Size (bits) (Bc) The maximum amount of subscriber data that the network agrees to transfer, under normal conditions, during a time interval Tc. Be - Excess Burst Size (bits) The maximum amount of uncommitted data in excess of Bc that the network will attempt to transfer during a time interval Tc. Bipolar With 8 Zero Substitution (B8ZS) Bipolar 8 Zero Substitution is an application of BPRZ and is an exception to the Alternate Mark Inversion (AMI) line-code rule. It is one method of providing bit independence for digital transmission by providing a minimum 1s density of 1 in 8 bits. Channel Service Unit (CSU) This unit provides regeneration of the signal received from the network, controls the pulse shape and amplitude for transmission of the signal into the network, and possibly provides loop-back. The CSU function is frequently found within a Data Service Unit (DSU). Committed Information Rate (CIR) bit/s The rate at which the network agrees to transfer information, under normal conditions, during a time interval Tc. Customer Provided Equipment (CPE) Equipment owned and maintained by the customer and located on their side of the End-User Point of Termination (EU-POT) network interface. Data Communications Equipment (DCE) The equipment that provides the functions required to establish, maintain and terminate data transmission connections; e.g., a modem, as well as the signal conversion and coding required for communications between data terminal equipment and data circuit. Data Link Connection Identifier (DLCI) The DLCI is located within the address field of a frame relay packet. It is used to identify each PVC. Data Service Unit (DSU) Digital customer premises equipment used to recover timing from a baseband BPRZ signal which converts BPRZ line signals to a business machine interface signal such as V.35. At 64 kbit/s and below, DSU and Channel Service Unit (CSU) functions are, in modern equipment, combined in a single unit sometimes called a General Service Unit (GSU), Basic Service Unit (BSU) or Data Service Unit-A (DSU-A) so that it is part of the Data Communications Equipment (DCE). Above 64 kbit/s, DSU functions are frequently contained in the Data Terminal Equipment (DTE). The DSU usually contains circuitry to recognize and respond to loop-back commands from the serving test center. Data Terminal Equipment (DTE) A generic term for customer terminal equipment that connects to the network through a modem or through digital Network Channel Terminating Equipment (NTCE), e.g., a computer or a PBX. Digital Cross-Connect System (DCS) An intelligent (processor controlled) digital terminal that provides the capability to perform electronic cross-connects on digital channels operating at or below the bit rate of the transport systems terminated on the unit. This unit may also provide other features, such as bridging. Discard Eligibility (DE) Indicator bit A single bit located within the address field of a frame relay packet that is used to indicate that a frame should be discarded in preference to other frames during a frame discarding process. Extended Superframe (ESF) Format An Extended Superframe consists of 24 consecutive DS1 frames. Bit one of each frame (the F-bit) is time shared during the 24 frames to describe a 6-bit frame pattern, a 6-bit Cyclic Redundancy Check (CRC) remainder, and a 12-bit data link. The transfer rate of each is 2 kbit/s, 2 kbit/s and 4 kbit/s respectively. Frame Sizes Frame Sizes are variable length - maximum bytes per frame: Ethernet Frame Size 1500 Bytes Token Frame Size 4 Meg or 4096 16 Meg 16K + FRAD or Frame Relay Access Device Is a device that allows non-frame relay equipment to send frames to a Frame Relay network by formatting it inside a LAPF-Core frame. Integrated Service Digital Network (ISDN) A digital architecture that provides and integrated voice/data capability. LMI or Local Management Interface Was developed to provide management functions to control and maintain virtual circuits. See Virtual Circuit Management for additional information. Note: Two types are LMI or Annex D (We program our Frame Relay Switches to be Auto unless otherwise specified. Cisco defaults to LMI & ACC Defaults to Annex D, Motorola defaults to Auto). Local Access and Transport Area (LATA) A geographic area for the provision and administration of communications service. It encompasses designated exchanges that are grouped to serve common social, economic and other purposes. Loopback test An out-of-service test procedure applied to a full duplex channel that causes a received signal to be returned to the source. Network Interface (NI) The point of demarcation on the customer's premises at which CBLD's responsibility for the provision of service ends. NNI's or Network-to-Network Interface Defines how public and private frame relay networks can effectively interwork with one another. The major issue for NNI is to specify how control and user information should be passed between two frame relay networks. See the ISP/Carrier section for more detail. Pburst/LIP (for customer's with Novell IPX) Together, both will allow better throughput for remote stations accessing a Novell server. Typically, with older software versions, the default packet size was 576 Byte, so Novell automatically backed off to a maximum packet size of 576. Implementing Pburst and LIP on the Server and the router (built in to Novell Netware 3.12 and later and available on Cisco releases after 10.xx), increases traffic throughput: the router's IOS can negotiate larger packet sizes (Large Internet Packet or LIP) and PBURST (available from Netware 3.11 and later) allows the client to acknowledge a block of data rather than individual packet-by-packet. Serving Area Geographic area which is normally provided telecommunications services via one wire center. Serving Wire Center The term "Serving Wire Center" denotes a CBLD Central Office from which dial tone for the local Exchange Service would normally be provided to the demarcation point on the property at which the customer is served. Superframe Format (SF) A superframe consists of 12 consecutive DS1 frames. Bit one of each frame (the F-bit) is used to describe a 12-bit framing pattern during the 12 frames. Tc Committed Rate Measurement Interval(s) - A time interval for which the subscriber's committed information rate is measured. The formula used to calculate Tc is: Tc=Bc/CIR. UNI or User Network Interface Defines the coordination of status signalling between the user device which issues periodic Status Enquiry messages and the network which responds. UNI types are specified by the CPE; options include LMI, ANSI Annex D, or Q.933 Annex A. Virtual Circuit Management Provides management functions to control and maintain virtual circuits. There are two approaches: LMI and ANSI/CCITT. LMI is asymmetric (assumes the user will be communicating with a network and the two may respond differently to the same stimulus); ANSI and the CCITT allow symmetric procedures to be used between a user and network or between two networks. LMI uses DLCI 1023; ANSI/CCITT uses DLCI 0.