| Document: FSC-0075 | Version: 001 | Date: 23rd October 1993 | Author: Jan Ceuleers ISDN capability flags in the Nodelist A proposal by Jan Ceuleers, 2:292/857 version 0.4, October 3rd 1993 1 Introduction The Integrated Services Digital Network is a worldwide overlay network, offering the same services as the PSTN (Public Switched Telephone Network) and more. Its basic bearer capability is a digital bit stream of 64000 bits/s, as opposed to the audio channel with a 3.1 kHz bandwidth provided by the PSTN. Transferring data across the ISDN can be done in one of two ways: - by using the telephony services the ISDN provides. In this mode, a standard modem can continue to be used. Some modulation schemes currently in use are V.32bis, PEP, ZyXEL, HST, V.32 etc. We already have nodelist flags for these cases. - by using ISDN's 'native' mode. In this case, a number of protocols (either or not ISDN-specific) are used, such as V.110, V.120, X.75 etc. This document aims to define the way in which nodes are to advertise their ISDN capabilities in the nodelist, irrespective of whether or not ISDN-only nodes should be in the nodelist in the first place. This latter problem is to be solved by the politicians. Descriptions of ISDN equipment and compatibility with POTS (Plain Old Telephone Service) equipment are beyond the scope of this document. More detailed information on ISDN is also not provided; readers are referred to the literature (e.g. 'Computer Networks' by Andrew Tanenbaum). 2 Different flavors of the same protocol Some ISDN protocols have different flavors, some of which differ only marginally, but others are quite distinct. For the techies among the readership: examples of both cases can be found in the 1988 definition of V.110. There are two variants of the frame structure used in the 56kbps synchronous mode (marginal difference), while there is quite a major difference between the synchronous and asynchronous versions of V.110. 1 ISDN capability flags in the nodelist Since FidoNet applications are essentially character-based, the asynchronous versions of protocols will be preferred over the synchronous-ones(1). This applies to V.110 and V.120 and to any other such protocol. If there is an option, 8 data bits, no parity and 1 stop bit will be used in preference over all other possible combinations. (This is in line with the FOSSIL spec). 3 Speeds Some protocols (such as V.110) can be used at different speeds. Certain implementations of these protocols may not support some of these speeds. The baud rate field in the nodelist should not be used for indicating the maximum speed an ISDN node is capable of, since ISDN capability flags could (technically) co-exist with normal modem capability flags(2). 4 Nodelist flags ISDN-related nodelist flags consist of a prefix, a protocol indicator and an optional (set of) suffixes. The prefix is the capital letter I (for ISDN). The protocol indicator is one of the strings defined in paragraph 5 below. The suffix indicates the way in which the implementation deviates from the preferred implementation, as indicated in paragraphs 2 and 3. The possible suffixes are: Onnn The only bit rate supported = nnn * 100 (e.g. IV110O384 means that this node only supports V.110 asynchronous at 38400 bps and at no other speeds. 1. As a matter of fact, there are no provisions for advertising the synchronous versions of such protocols. 2. ISDN technology indeed allows for the possibility of both modem and ISDN-specific datacom connectivity on the same 'telephone' number. 2 ISDN capability flags in the nodelist Pnnnnn Maximum packet size supported in bytes. This is a layer 2 packet protocol parameter. Communication between two nodes is only possible if either end's maximum packet size is not exceeded. Leading zeroes are to be omitted. Rnnn Highest bit rate supported = nnn * 100 (e.g. IV110R192 means that this node does not support V.110 asynchronous at 38400 bps, but does support all other standardised rates up to and including 19200 bps) Wn Window size. The window size must be less than the modulo value (i.e. in modulo 8, the maximum window size is 7). If more than one suffix is used, the suffixes will be sorted in ascending order. 5 Protocols This section defines the meaning of the base protocol indicators. The aim is to have this base protocol indicator cover the majority of cases, so that suffixes will only rarely be required. 5.1 V.110 The protocol indicator is V110. When specified without suffixes, the IV110 nodelist flag indicates V.110 asynchronous capability at bit rates up to and including 38400 bps. 5.2 V.120 The protocol indicator is V120. When specified without suffixes, the IV120 nodelist flag indicates V.120 asynchronous capability. Due to the nature of the protocol, the O and R suffixes are irrelevant. There is no explicit mention of frame size in the V.120 specifications. However, since Q.921 is the layer-2 protocol of V.120, one might assume the frame size of Q.921, which is 260 bytes. Frame sizes larger than that should be negotiated between sysops. 3 ISDN capability flags in the nodelist 5.3 T.90 (X.75) The protocol indicator is T90. Base protocol parameters are: modulo: 8 window size: 2 packet size: 2048 bytes Currently, there is no standardized method for negotiation of the modulo mode (Recommendation ITU-TS T.90 reserves this subject for further study), all T.90-capable nodes should answer in modulo-8 mode. It is therefore useless to advertise modulo-128 capability. This also limits the maximum window size to 7. Some implementations have a maximum frame length of 130 bytes and a maximum window size of 1. This would be documented as IT90P130W1. The 1992 version of the T.90 standard specifies a method for in-band negotiation of frame length and window size. 5.4 Other protocols Additional protocols can be added to this document (and thus assigned a nodelist flag) if sufficient technical information is made available. Neither X.25 on B nor on D have been added, because there is no room in the nodelist for the X.25 address. 4 ISDN capability flags in the nodelist 6 Conversion from old to new The ISDNA, ISDNB and ISDNC nodelist flags are already in use in zone 2. The table below shows the relationship between old and new. old new ISDNA IV110O192 ISDNB IV110O384 ISDNC IT90 ISDNA,ISDNB IV110 ISDNB,ISDNC IV110O384,IT90 ---===--- 5