Top Document: comp.windows.x Frequently Asked Questions (FAQ) 1/7 Previous Document: 12) Just what are OPEN LOOK and Motif? Next Document: 14)+ TOPIC: X CONSORTIUM FUTURES See reader questions & answers on this topic! - Help others by sharing your knowledge X.fast is the new name of LBX. The one-line summary of LBX is: LBX = "XRemote" + reply/event/error compaction + caching There are several options for using X over serial lines: SLIP - Serial Line IP; this is both a mechanism and a protocol for sending IP packets over point-to-point serial links. It has been around for several years, and implementations are available for many of the major TCP/IP implementations. Most X Terminal vendors supply this as a checkoff item, although nobody really ever uses it since it is horribly slow. The TCP/IP headers add 40 bytes per packet and the TCP/IP encoding of the X protocol is rather verbose (rightfully so; it is optimized for packing and unpacking over high-speed links). CSLIP - Compressed header SLIP; this is a variant of SLIP that compresses the 40 bytes of TCP/IP headers down to about 5 or 6 bytes. It still doesn't do anything about reencoding the X protocol. Modems that do compression can help, but they increase packet latency (it takes time to dribble the uncompressed data through typical serial interfaces, plus the compression assembly time). PPP - Point-to-Point Protocol; this is an emerging standard for point-to-point links over serial lines that has a more complete set of option negotiation than SLIP. A growing number of people see the combination of PPP for the serial line management and CSLIP for the header compression as becoming common for running normal TCP/IP protocols over serial lines. Running raw X over the wire still needs compression somewhere to make it usable. XRemote - this is the name of both a protocol and set of products originally developed by NCD for squeezing the X protocol over serial lines. In addition to using a low level transport mechanism similar to PPP/CSLIP, XRemote removes redundancies in the X protocol by sending deltas against previous packets and using LZW to compress the entire data stream. This work is done by either a pseudo-X server or "proxy" running on the host or in a terminal server. There are several advantages to doing compression outside the modem: (1) You don't *have* to have compressing modems in there if you wouldn't otherwise be using them (e.g. if you were going to be directly connected), and (2) It reduces the I/O overhead by cutting down on the number of bytes that have to cross the serial interface, and (3) In addition to the effects of #2, it reduces the latency in delivering packets by not requiring the modem to buffer up the data waiting for blocks to compress. LBX - Low Bandwidth X; this is an X Consortium project that is working on a standard for this area. It is being chaired by NCD and Xerox and is using NCD's XRemote protocol as a stepping stone in developing the new protocol. LBX will go beyond XRemote by adding proxy caching of commonly-used information (e.g. connection setup data, large window properties, font metrics, keymaps, etc.) and a more efficient encoding of the X protocol. The hope is to have a Standard ready for public review in the first half of next year and a sample implementation available in R6. Additional technical information about how XRemote works and a few notes on how LBX might be different are available via anonymous ftp from ftp.x.org in R5contrib/ in the following files: XRemote-slides.ps slides describing XRemote XRemote-LBX-diffs.ps more slides describing some of LBX [information provided by Jim Fulton, jim@ncd.com; 7/92] There is also a set of slides on ftp.x.org from Jim Fulton's talk at the 7th X Technical Conference. LBX is designated as a work in progress in R6. See workInProgress/README and workInProgress/lbx/README in the R6 distribution for more information. LBX was withdrawn from the X11R6.1 release until it can be finished. It is being worked on within the X Consortium and is intended to be released as a Consortium standard, with a Consortium implementation, as part of Broadway. [3/96] Note: dxpc is an X11 compressor that improves the performance of X applications run over low-bandwidth network connections (e.g. 28.8Kb/s). It runs on most UNIXes. dxpc achieves compression performance between 3:1 and 6:1 compression for a wide variety of applications. Sources are on ftp://sunsite.unc.edu/pub/Linux/X11/xutils/dxpc-3.3.0.tar.gz and ftp://ftp.x.org/contrib/utilities/dxpc-3.3.0.tar.gz . Information: Brian Pane (bpane@bnc.bellcore.com) [9/96] Note: X/lbX/server is the implementation of the server side of the X11R6 LBX "protocol", totally independent from the X Window server. It is an LBX proxy for the client side containing some performance enhancements and bug fixes. You may use any X Consortium LBX proxy, too. The software is in beta state. See http://www.x-software.com/Software/Xlbx/ for more information. [8/96] User Contributions:Top Document: comp.windows.x Frequently Asked Questions (FAQ) 1/7 Previous Document: 12) Just what are OPEN LOOK and Motif? Next Document: 14)+ TOPIC: X CONSORTIUM FUTURES Part1 - Part2 - Part3 - Part4 - Part5 - Part6 - Part7 - Single Page [ Usenet FAQs | Web FAQs | Documents | RFC Index ] Send corrections/additions to the FAQ Maintainer: faq%craft@uunet.uu.net (X FAQ maintenance address)
Last Update March 27 2014 @ 02:12 PM
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