rdt@houxv.UUCP (R.TRAUBEN) (01/07/88)
Are I.46x, X.3, X.30, X.31 recommendations related? What precisely is the difference between a PAD and a rate adaption function? Is X.30 both a PAD and and rate adaption standard? Could someone please comment on the speculation made below: 1. It appears that a PAD buffers asynchronous traffic (e.g 1 character-at-a-time, start/stop rs232) into a synchronous, multiple character, packet burst using several criteria. Criteria appears to include: a) number of characters buffered, b) time elapsed since last packet transmitted, c) presence of special characters (e.g. return/break) X.28 appears to govern async RS232 to PAD conversion and X.29 appears to govern the PAD to sync X.21 conversion. X.3 appears to govern how the user sets PAD conversion parameters. 2. It appears that rate adaption is a function employed by a terminal adapter (e.g. RS232 to ISDN converter). The goal is to convert low speed outgoing synchronous multiple character, packet bursts (say 1200 bps) into higher speed intermediate outgoing synchronous multiple character packet bursts (say 8kbps). In ISDN, it appears that the rate adaption process is a 2 step approach. Step 1 converts the 1200 bps to an intermediate rate 8kbps by a bit replication process (4X plus 17-bit framing to construct a 8kbps 40-bit frame). Step 2 converts the intermediate rate from 8kbps to 64kbps. It is unclear to me where and how this happens (e.g. in the subcriber TA or within the ISDN phone network). The speed of the underlying intermediate rate is given to the ISDN net via the D-channel I451/Q931/L3 protocol so that the remote partner can recover the intermediate rate information. It is not clear to me how the remote partner can strip the 1200 bps information from the intermediate rate info. Has anyone waded thru this muck long enough to recommend a text besides the abstract I.460 and X.30 specs? I have both in my hands and am very confused by them. Thanks for your patience. Richard Trauben ATTIS HO, NJ ..ihnp4!houxv!rdt
stanwyck@drutx.ATT.COM (Don Stanwyck) (01/09/88)
> Are I.46x, X.3, X.30, X.31 recommendations related? Yes, sort of. I.46x is a series of co-numbered recommendations. This means that each recommendation in this series is actually numbered primarily somewhere else. E.g., I.462 is X.31. X.30 and X.31 are not directly related to each other, except that X.31 references X.30. > What precisely is the difference between a PAD and a rate adaption function? A Packet Assembly/Disassembly function (PAD) is something that takes asynch data and groups it into blocks of charactors that can be sent in a packet oriented data protocol. This function is reversed at the other end of the PAD connection, usually. A RA function rate adapts a bit stream to a different bit rate than it started at. Rate adaption protocols may be bit oriented or charactor oriented. In some rate adaption protocols (e.g., V.120) a PAD-like function occurs. In others (e.g., V.110), no blocking of data occurs. In the latter case, the typical algorithm is one of inserting dummy bits in known positions to fill to a given bit rate. This allows the receiving side to know where in the higher rate bit stream to look for the meaningful bits. In the former type, bits may be gathered and shipped (e.g., in a charactor oriented rate adaption) or the originator interface status may be reported. V.120 uses HDLC flag stuffing rather than fixed bit positions in a stream to provide the adapting function. > Is X.30 both a PAD and and rate adaption standard? X.30 is just a rate adaption protocol, of the second type above. It is based on ECMA 102/V.110, and has been primarily written by Herr Schaffers and Herr Bader (Phillips/TEKADE, Nurnberg, FRG). Having spoken with numerous representitives of telephone administrations around the world, it appears that the FRG is the only party excited about X.30. it is not expected to be a widespread rate adaption scheme. > Could someone please comment on the speculation made below: > > 1. It appears that a PAD buffers asynchronous traffic > (e.g 1 character-at-a-time, start/stop rs232) into a > synchronous, multiple character, packet burst using > several criteria. Criteria appears to include: > a) number of characters buffered, > b) time elapsed since last packet transmitted, > c) presence of special characters (e.g. return/break) > X.28 appears to govern async RS232 to PAD conversion and > X.29 appears to govern the PAD to sync X.21 conversion. > X.3 appears to govern how the user sets PAD conversion > parameters. True. > 2. It appears that rate adaption is a function employed > by a terminal adapter (e.g. RS232 to ISDN converter). > The goal is to convert low speed outgoing synchronous > multiple character, packet bursts (say 1200 bps) into > higher speed intermediate outgoing synchronous multiple > character packet bursts (say 8kbps). The first half is correct, not the second. The goal is to place low speed (typically synch, though asynch RA also exists) bit or character streams into higher speed bit streams in a way that they can be recognized by the receiving party. This may be done as in I.463 for 56 Kbps to 64 Kbps by inserting a dummy bit(s) in a recognized place (i.e. the 8th bit) or through a number of other schemes. > In ISDN, it appears > that the rate adaption process is a 2 step approach. > Step 1 converts the 1200 bps to an intermediate rate 8kbps > by a bit replication process (4X plus 17-bit framing to > construct a 8kbps 40-bit frame). Step 2 converts the > intermediate rate from 8kbps to 64kbps. It is unclear > to me where and how this happens (e.g. in the subcriber > TA or within the ISDN phone network). The speed of the > underlying intermediate rate is given to the ISDN net > via the D-channel I451/Q931/L3 protocol so that the > remote partner can recover the intermediate rate information. > It is not clear to me how the remote partner can strip > the 1200 bps information from the intermediate rate info. In ISDN data (i.e., X.31), there are two rate adaption schemes allowed. First, a user may always use simple flag stuffing between HDLC frames to adapt the HDLC-based R-interface to the channel speed at the S-interface, or, in the case of B-channel access over a circuit switched connection to a PSPDN (case A), X.30 is allowed. > Has anyone waded thru this muck long enough to recommend a > text besides the abstract I.460 and X.30 specs? I have both in > my hands and am very confused by them. Thanks for your patience. > Richard Trauben > ATTIS HO, NJ > ..ihnp4!houxv!rdt Sure. Call me. Other AT&T people may also call. Other people may write, and if I have time, I will respond. -- AT&T o o 303-538-5004 Don Stanwyck || ihnp4!drutx!stanwyck Denver, CO USA \__/ Telecom Standards