LAPB

Abstract: This study compared the effects on performance of four features of the LAPB and LAPD protocols. LAPB is the link level for the X.25 protocol, and LAPD is the link level for the ISDN "D" signaling channel. The features were: multireject in which additional reject or selective reject frames can be retransmitted under certain conditions, selective reject in which an entity can request selected frames to be retransmitted, the null information frame (NIF) with which additional control frames are sent to help detect missing frames, and multiple service access points (SAP's) in which several link-level protocol handlers are multiplexed on the same physical link (a feature unique to LAPD). Results indicate that the current standard LAPB/D protocol with multireject is the preferred protocol. Selective reject generally performed worse than the standard protocol, and offered improvement only with complex and expensive enhancements. The NIF feature yielded a virtually unnoticeable performance improvement. Multi-SAP introduced a virtually unnoticeable impairment when it was used to carry the same traffic load as a single SAP.

Abstract: A data terminal equipment which is coupled to an ISDN through an access line and uses a hierarchical protocol in conformity to an OSI reference standard model includes the following structural elements. A first data link protocol circuit provides a link access procedure balanced (LAPB) modulo-8 data link protocol. A second data link protocol circuit provides an LAPB modulo-128 data link protocol. A third data link protocol circuit provides a data link protocol based on a link access procedure for a data channel (LAPD). A protocol determining circuit determines a data link protocol to be used by referring to an address field and a control field of a cell set-up signal which is supplied from a second data terminal equipment. A data link protocol activating circuit selects and activates one of the first, second and third circuits on the basis of the result provided by the protocol determining circuit.

Abstract: An improved method of providing transparent packet access to a D-channel of an ISDN, includes the step of providing a user packet including an Address field, a Control field and an Information field, for transporting to an ISDN; Extracting the Address, Control and Information fields from the the user packet; and inserting the extracted fields into an Information field of an ISDN format LAPD packet. Preferably X.25 packets are provided access to the network, and the X.25 LAPB Address, Control and Information fields are inserted into the LAPD information field. This method provides independence of protocols and reduces complexity.

Abstract: A new breed of data link control is emerging today. Known under a variety of names and mnemonics—ADCCP, HDLC, LAPB, BDLC, SDLC, UDLC, etc.—it is based on a bit-oriented, rather than character-oriented, organization and format. It offers a high level of flexibility, enhanceability, adaptability, reliability, and efficiency of operation for today’s as well as for tomorrow’s synchronous data communications needs.