nd flow control on point-point ATM layer connections. 41.4.11.1 Reference configuration SAR sub-layer accepts variable length CS-PDUs from CS and This gives the reference configuration for the B-ISDN User/Net- generates SAR-PDUs with up to 44 octets of CS-PDU data. SAR work Interface (B-UNI), defining the functional groups and refer- Functions in AAL type 3 are: ence points which apply (Figure 41.16). These are essentially the same as for Narrow-Band ISDN as described in I.411. but to clearly 1. Preservation of CS-PDU: achieved by identifying segment type identify the existence of broadband capabilities, the letter 'B' is used and fill of SAR-PDUs. in the labelling of all reference points and functional groups. 2. Error detection: bit errors or lost/inserted SAR-PDUs. Functional groups in the B-ISDN reference configuration are: 3. Multiplexing/demultiplexing of multiple CS-PDUs concurren- B-NT1, B-NT2, B-TE1, TE2, B-TE2, B-TA. Reference points are: tly from multiple AAL connections over a single ATM layer T, SB' R. connection. 41.4.11.2 Physical realisation Segmentation and re-assembly (SAR) Protocol Data Unit (PDU): Type 3 SAR-PDUs contain a header having an information type A limited set of examples of possible physical configurations are (segment type) field e.g. BOM, COM, EOM, SSM (Single Segment given. These cover configurations which could be supported by B-TE1 B-NT2 B-NT1 B-TE2 Reference point B-TA: Broadband terminal adaptor B-TE: Broadband terminal equipment B-NT: Broadband network termination Functional group Figure 41.16 B-ISDN reference configurations (Fig. 1/1.413) Standards for ATM 41/17 standardised interfaces at reference points SB and TB and also 41.4.12.2 Transmission convergence sublayer functions illustrate physical configurations for shared medium applications. These are covered including the available information transfer rate, transmission frame adaptation functions (subdivided into 'Cell- 41.4.11.3 Characteristics of interfaces at the TB and SB refer- based interface' and 'SDH based interf