ta types, see Fig. 5.30. ASN.1 Abotrantountay Ahotrantountax Abetract cuntax ASPid- Abstract syntax reference gemOrd(ASPid, localValueSet) demRepCnf(ASPid, localValueSet) ENCmess Encodinaalaorithm Encodina algorithm Encoding algorithm SEQUENCE SDUs of ENCmessages Encoding algorithm BOOLEAN Encoding algorithm INTEGER Fig. 5.30 Encoding rules define the encoding of abstract data types The set of encoding algorithms that are selected for the elements of an abstract syntax are called by OSI transfer syntax. Thus, the transfer syntax defines how an ENC message will look on the bit-level, the abstract syntax defines how the mes- sage looks on the level of abstract data types. For example, if we apply BER on the abstract syntax in Fig. 5.28, for the values in Fig. 5.29, the bit-level representation looks as shown in Fig. 5.31. BER is based on encoding every value to its type (T), its length (L) and its con- tents (C). Since the length is explicitly provided, the user can send any size of parameter values (this implies that size constraints that are defined in specifica- 5.4 Message Handling tions are not intended for the BER encoder, and therefore must be handled by the FOH). Parameter Value Bit-level representation Globlnvld INTEGER T:00000010 L:00010001 C:00010001 SEQUENCE T: 00110000 L: 00010111 INTEGER T: 00000010 L: 00000001 C:00000101 PrimType INTEGER T:00000010 L:00000001 C:00000000 SEQUENCE T: 00110000 L: 00001111 Person 400805 INTEGER T:00000010 L:00000011 C:00000110 00001111 10100101 CHOICE T: 10100000 L: 00001000 PostCode H2X3R4 IA5String T:00010110 L:00000110 C:01001000 00110010 01011000 00110011 01010010 00110100 Fig. 5.31 Encoding of the ASP chAddrRequest for the values defined in the Value column The contents of a structured type as SEQUENCE are the octets of encoded val- ues of all the parameters of the sequence. The contents of CHOICE are the encoded values of the selection. The tag is encoded as part of the T-octet. The length value for a SEQUENCE is the total length of all values in the SEQUENCE. The 