Q196462: How RDP Transmits Data in Both LAN and WAN Environments
Article: Q196462
Product(s): Microsoft Windows NT
Version(s): winnt:4.0,4.0 SP4
Operating System(s):
Keyword(s):
Last Modified: 11-DEC-2001
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The information in this article applies to:
- Microsoft Windows NT Server versions 4.0, 4.0 SP4, Terminal Server Edition
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SUMMARY
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RDP uses cached glyphs and bitmaps for transmission across WAN and LAN
connections and, therefore, does not transfer data in a recognizable form.
MORE INFORMATION
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RDP uses a highly efficient encoding algorithm that represent the vast majority
of Windows graphics operations with a small amount of network traffic. For
example, most dialog boxes consist of text items, a series of gray, white, and
so on rectangles, and light and dark shaded lines for a 3-D effect. These are
not transmitted as comparative deltas from the previous screen, but are encoded
as pattern blts and cached glyphs. For instance, we can draw the gray dialog box
background color with "Draw color X at x1,y1,x2,x2". Field compression is always
enabled such that a second draw with only a change in the x1,y1 position would
only send an even smaller packet with a single bit representing the fields that
have not changed, and the minimum possible number of bits to represent the delta
change in the coordinates. Bulk compression is applied over the final packets
(when enabled) for an even further improvement.
RDP text is displayed by using glyph caching. Almost immediately, the client
builds up the required set of glyphs, and the server needs only transmit a short
hash value to display the text. Bitmap caching works similarly. The light and
dark gray lines are similar to the patblt in that field compression is highly
effective. Standard Windows clipping applies such that the RDP driver only
receives output commands for the areas that are actually visible.
RDP works the same over LAN or WAN, thus the description above holds for both. In
other words, performance of the protocol does not depend on whether RDP is
running over LAN or WAN; rather, it depends on what the application is
displaying. Making a statement about a completely unknown WAN configuration is
not possible, as each configuration is different. There is a check box for "Low
Speed Connection" that can be enabled at the client side when making a server
connection. That check box simply enables further compression on the final
bitstream; however, it does not change the fundamental RDP algorithm described
above.
Additional query words:
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Keywords :
Technology : kbWinNTsearch kbWinNT400search kbWinNTSsearch kbWinNTS400search kbNTTermServ400 kbNTTermServ400sp4 kbNTTermServSearch
Version : winnt:4.0,4.0 SP4
Issue type : kbinfo
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