The Arrival of NX, Part 1
Here is an early summary of how NX achieves its extraordinary performance. We delve into more details in subsequent parts of this article series.
NX combines three essential ingredients:
an efficient compression of what normally would be X traffic
an intelligent mechanism to store and re-use (cache) data that is transfered between server and client
a drastic reduction in multiple, time-consuming X roundtrips, bringing their total number close to zero.
If equivalent data needs to be transfered repeatedly, NX takes it from the cache. If similar data needs to be transfered repeatedly, NX boils down that action to a differential transfer. What it pipes through the link is not the complete data, but only the delta.
These two techniques are not entirely new. Previous implementations of them exist, but observers might conclude that NX's implementation is more elegant. NX is optimized to the last bit. Keith Packard thought that to go beyond ZLIB's compression was nearly impossible and the result never could perform fast enough. He concluded that roundtrip suppression was an important factor for success. Before NX, roundtrip suppression was never made efficient enough for X connections. And for reasons unknown to me, Keith Packard never pursued its solution. The solution to roundtrip suppression is the most decisive breakthrough represented in NX. It is the missing link in reducing traffic between the NX client and the server enough to facilitate a believable low-bandwidth remote GUI experience. It thus created a new X compression technology that is far better than plain ZLIB.
We discuss more about NX roundtrip suppression and traffic compression in Parts 2 and 3 of this article series.
To learn more about FreeNX and witness a real-life workflow demonstration of a case of remote document creation, printing and publishing, visit the Linuxprinting.org booth (#2043) at the LinuxWorld Conference & Expo in San Francisco, August 8–11, 2005. I will be there along with other members of collaborating projects.
Kurt Pfeifle is a system specialist and the technical lead of the Consulting and Training Network Printing group for Danka Deutschland GmbH, in Stuttgart, Germany. Kurt is known across the Open Source and Free Software communities of the world as a passionate CUPS evangelist; his interest in CUPS dates back to its first beta release in June 1999. He is the author of the KDEPrint Handbook and contributes to the KDEPrint Web site. Kurt also handles an array of matters for Linuxprinting.org and wrote most of the printing documentation for the Samba Project.