Introduction
RFB (remote framebuffer)
is a simple and efficient protocol which provide remote
access to graphical user
interfaces.As its Name Suggests it works at the framebuffer
level and thus it is
applicable to all windowing systems and applications. Eg. X11,
Windows and Macintosh. It
should also be noted that there are other Protocols available
and RFB is the protocol
which is used in Virtual Network Computing (VNC)
and its various forms. Due
to increase in number of Software products and Services
such protocols play a very
important role nowadays.
Figure 1.1: Working of VNC
1.1
Basic Parts Of RFB Protocol
Display Protocol - the
display part of the protocol is based on a simple idea. It is
actually based around a
single graphics primitive: put a rectangle of pixel data at a
given x,y position.
Input Protocol - based on
a normal workstation model of a keyboard and multibutton
pointing device. Every
keypress and mouse events and transferred and simulated
at the remote site.
1.2
Features of RFB
RFB protocol specifies the
rules for communication between 2 entities RFB client
and RFB server. In Current
versions it supports multiple Clients also.RFB is truly a
thin client protocol. The
emphasis in the design of this protocol is to make a client
with very less
requirements. Thus,Clients can run on widest range of hardware, and
the task of implementing a
client is made very simple RFB protocol makes the client
stateless.
RFB protocol gained
significance after it was used in VNC (Virtual Network Computing)
and is very popular
protocol nowadays RFB protocol is Open unlike many
other Remote Access
Protocols.
1.3
Organization Of the Report
1. Chapter 2 describes the
Representation of Pixel Data and Protocol Extensions
2. Chapter 3 Introduces
the Various Protocol Messages
3. Chapter 4 describes the
Handshaking Messages and Security Types
4. Chapter 5 describes
Initialisation Messages
5. Chapter 6 describes
Client to Server Messages
6. Chapter 7 describes
Server to Client Messages
7. Chapter 8 describes
Various Encodings
8. Chapter 9 shows
Protocol Implementation
9. Chapter 10 is the conclusion
Chapter 2
REPRESENTATION OF PIXEL
DATA
The Interaction between server and client begins with a
negotiation of the format and
encoding which will be used to send the pixel data. This
step is included to make the
job of client easy. The server must always be able to supply
the pixel data in the form
the client needs. In case the client can handle different
formats,client can choose any
one it wishes. That is why this protocol is called a
thin-Client Protocol.
Pixel Format refers to the representation of various
individual colors by pixel values.
The most common formats are 24-bit or 16-bit where
bit-fields translate directly
to the primary colors , and 8-bit color map where a mapping
can be used to obtain
RGB intensities.
Encoding refers to how a rectangle of the above said pixel
data will be sent across
the channel. Every triangle of this pixel data is prefixed
by a header which contains
the X,Y position of the rectangle on the screen,the width
and height of this triangle,
and an encoding type which specifies how the pixel data is
encoded. In practice
we normally use only the ZRLE, Hextile and CopyRect
encodings since they provide
the best compression as far as typical desktops are
concerned.
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