1 0 Ref. A5 - SERCNET - ADDRESSING SUMMARY (Ref. A5) + _______ __________ _______ ___ __ 0 Version 2 + _______ _ 0 8 March 1982 + _ _____ ____ 0 P M Girard + _ _ ______ 0 1. This paper summarises the essential points needed for implementation. For a more detailed discussion see the paper "SERCnet - Addressing Scheme" (Ref. A4). 0 2. A name may be either an "address" or a "title". + ____ 0 3. An address is a decimal number up to 15 digits long. If + _______ the number is 12 digits long or less, it represents a pure DTE number. If it is more than 12 digits long, any digits beyond the 12th represent a Level 3 sub-address. Leading zeroes may be optionally omitted in all contexts if the address is a pure DTE number. 0 In practice, SERCnet pure DTE numbers should not be longer than 8 digits, comprising aasssppp, where aa is an area number, sss is a switch number, and ppp is a processor number. As a switch is not interested in sub-addresses, + ______ it should first ignore any digits beyond the 12th, then ignore any leading zeroes it does not need. For compatibility with PSS, a calling DTE should be able to get addresses of up to 14 digits into the Call Request Packet from a user or from local storage. 0 4. A title is alphanumeric and up to 8 characters long. The + _____ first character must be alphabetic, and upper and lower case should be equivalent. Gateways and user interfaces may permit abbreviations if they wish. If abbreviations are allowed, an exact match should be accepted even if there are longer names in the table starting in the same way; this allows such titles as RL or DL to be used as gateway names, without conflicting with service titles such as RLIAH. 0 5. The "called address" and "calling address" parameters in a connection request (carried in the CUDF) each consist of a string of names separated by terminators. Each character is in IA5 code of arbitrary parity. A SERCnet transport station or entry gateway needs to understand only the first name of the "called address". This must therefore be a SERCnet address or title, either on its own or terminated by '.' (dot). Other addresses, titles and terminators in the "called address" or "calling address" parameters are in formats unknown to SERCnet. 0 6. Transformations on entry to SERCnet: If the first name of + _______________ - SERCNET - ADDRESSING SUMMARY PAGE 1 1 0 Ref. A5 0 the "called address" is numeric, it is removed and interpreted as a SERCnet address. If its first character is alphabetic, it is assumed to be a SERCnet title and is looked up in a table to obtain the required SERCnet address and the transformation to be applied before forwarding it. The rest of the "called address" (if any) is always forwarded transparently. 0 The "calling address" is transformed at a gateway by adding to the front the address of the previous gateway, and then substituting a title if there is one in the table. 0 7. Application addresses: Addressing within a DTE is in + ______________________ principle a private matter for the DTE implementor, because the transport station in a DTE is logically a gateway between SERCnet and the private host system concerned. To facilitate the use of common high level protocols, however, some agreement on names is necessary. 0 Standard protocol names should be used as application addresses for both destination and source: for instance FTP, HASP, ITP. These may have further addressing appended if it is necessary to specify a particular process or terminal number. In the case of HASP, the remote signon number should be appended as part of the name: HASP49 for instance. In the case of ITP a terminal number, if required, may be appended following a dot and the character 'T': ITP.T123 for instance. 0 Names of private applications should begin with USR, and may require a dot after them with further sub-addressing. 0 8. User Interfaces: These too are in principle the private + _______________ business of the DTE concerned, but some standardisation is desirable. Devices liable to make calls should have a default protocol associated with them. Local commands may be provided to vary these defaults (e.g: !!ITP etc). Defaults may also be overridden by values from the local title table. The recommended format for requesting a call is to precede the address string by an escape sequence such as !! 0 9. CUDF: + ____ 0 128 bytes maximum. 0 5th byte ff : "Called address" and "calling address" parameters. 0 Each parameter: 1st byte = length of rest of parameter (max. 63) plus 128. 0 On input, tolerate but ignore any parameters after the - SERCNET - ADDRESSING SUMMARY PAGE 2 1 0 Ref. A5 0 "calling address". 0 No overflow of addressing into subsequent packets. 0 10. References + __________ 0 A4) SERCnet - Addressing Scheme (P.M.Girard) A5) A Network Independent Transport Service (PSS User Forum Study Group 3) - - - - - - - - - - - - - - - - SERCNET - ADDRESSING SUMMARY PAGE 3