Path: utzoo!mnetor!uunet!husc6!hao!oddjob!gargoyle!ihnp4!homxb!houxv!rdt
From: rdt@houxv.UUCP (R.TRAUBEN)
Newsgroups: comp.std.internat
Subject: Still More Bit Rate Adaption Questions
Message-ID: <680@houxv.UUCP>
Date: 6 Jan 88 18:44:43 GMT
Organization: ATT Information Systems, Holmdel, N.J.
Lines: 47
Keywords: CCITT X.3 and I.46x Recomendations, PADS, Rate Adaption


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