1. VNC

2. VNC demo
Windows
TightVNC
ajklinux2.uncc.edu:1
Ubuntu
Gtk VNC Viewer

3. Virtual Network Computing
VNC
Virtual Network Computing

4. VNC - Overview Virtual Network Computing (VNC)
A graphical desktop sharing system
Uses the RFB protocol
Remotely “control” another computer
Use another computer via a GUI environment
Uses a network
Transmit keyboard and mouse events from one computer to another
Relays the graphical screen updates back

5. VNC - Overview Platform-independent
VNC viewer resides on any operating system
Can connect to a VNC server of any other operating system
Clients and servers available for:
Almost all GUI operating systems
Java enabled systems
Multiple clients may connect to a VNC server at the same time
Popular uses for this technology include:
Remote technical support
Accessing files on one's work computer from one's home computer

6. VNC - Overview Developed at “AT&T”
Original VNC source code and many modern derivatives are:
Open source
GNU General Public License

7. History

8. History Created at Olivetti & Oracle Research Labs
Originally owned by Olivetti and Oracle Corporation
In 1999 AT&T acquired the lab
2002 closed down the lab's research efforts
Following the closure of ORL in 2002
Several members of the development team formed RealVNC
Continued working on open source and commercial VNC software under that name
Several other versions of VNC have been developed from the original GPLed source code.
Forking has not led to compatibility problems
RFB protocol is designed to be extensible
VNC clients and servers negotiate their capabilities when handshaking
Make use of the most appropriate options supported at both ends

9. Etymology

10. Etymology 'Virtual Network Computer/Computing'
Originates from ORL's work on a thin client
Called Videotile
Used the RFB protocol
Essentially an LCD display with:
A pen input
A fast ATM connection to the network
At the time a network computer was commonly used as a synonym for 'thin client'
VNC is essentially a software-only (i.e virtual) version of this network computer

11. Operation

12. VNC system requires: Operation A server A client
A communication protocol

13. Operation Where: VNC server VNC client (or viewer) VNC protocol
Program on the machine that shares its “screen”
Does all the core processing
VNC client (or viewer)
Program that monitors and interacts with the server
Displays results
VNC protocol
Very simple protocol
Based on one graphic primitive:
"Put a rectangle of pixel data at the specified X,Y position"

14. Operation
Server sends small rectangles of the framebuffer to the client
In simplest form: VNC protocol can use a lot of bandwidth
Methods devised to reduce communication overhead
For example, various encodings
Methods to determine the most efficient way to transfer rectangles
VNC protocol
Allows client and server to negotiate which encoding to be used

15. Operation Simplest encoding: raw encoding Raw Encoding works well if:
Pixel data is sent in left-to-right scanline order
First sends complete image
After original full screen has been transmitted
Only transfer rectangles that change
Supported by all clients and servers
Raw Encoding works well if:
Only a small portion of the screen changes from frame to frame
Mouse pointer moving across a desktop
Text being written at the cursor
Bandwidth demands get very high when a lot of pixels change at the same time
Scrolling a window
Viewing full-screen video

16. Operation VNC uses TCP ports 5900 through 5906 (default)
Each port corresponds to a separate screen (:0 to :6)
Java viewer available for many implementations
RealVNC allows clients to interact through a Java-enabled web browser
Ports 5800 through 5806
Other ports can be used
Both client and server must be configured accordingly
Some operating systems only support a single VNC session at a time
Base operating system supports only a single session at a time
E.g. Windows XP

17. Operation On some machines:
Server does not have to have a physical display
Xvnc is the Unix VNC server
Based on a standard X server
Xvnc can be considered to be two servers in one
For applications: it is an X server
For remote VNC users: it is a VNC server
Applications can display themselves on Xvnc as if it were a normal X display
Will appear on any connected VNC viewers rather than on a physical screen

18. Operation Display served by VNC
Not necessarily the same display seen by a user on the server’s monitor
Unix/Linux computers that support multiple simultaneous X11 sessions
VNC may be set to serve a particular existing X11 session
Start one of its own
Multiple VNC sessions can be run from the same computer
Microsoft Windows
VNC session served is always current user session

19. Operation
VNC is commonly used as a cross-platform remote desktop system
Apple Remote Desktop for Mac OS X interoperates with VNC
Will connect to a Linux user's current desktop if it is served with x11vnc
As a separate X11 session if one is served with TightVNC
From Linux
TightVNC will connect to an OS X session served by:
Apple Remote Desktop
If the VNC option is enabled
VNC server running on Microsoft Windows

20. Security

21. Security By default, VNC is not a secure protocol
Passwords are not sent in plain-text (as in telnet) but…
Brute-force cracking could prove successful if both the encryption key and encoded password are sniffed from a network
Recommended that a password of at least 8 characters be used
Limit of 8-characters on some versions of VNC
If a password exceeds 8 characters:
Excess characters are removed
Truncated string is compared to the password

22. Security VNC may be tunneled over an SSH or VPN connection
Adds an extra security layer with stronger encryption
SSH clients are available for all major platforms (and many smaller platforms as well)
SSH tunnels can be created from
UNIX clients
Microsoft Windows clients
Macintosh clients many others

23. Security UltraVNC supports the use of an open-source encryption plugin
Encrypts the entire VNC session
Including password authentication and data transfer
Allows authentication to be performed
Based on NTLM and Active Directory user accounts
RealVNC offers high-strength encryption as part of its commercial package
Workspot released AES encryption patches for VNC

24. The original

25. RFB protocol

26. Remote Frame Buffer
RFB

27. RFB RFB (“remote framebuffer”)
A simple protocol for remote access to graphical user interfaces
Works at the framebuffer level
Applicable to all windowing systems and applications
Including X11, Windows and Macintosh
Used in Virtual Network Computing (VNC) and its derivatives
RFB started as a relatively simple protocol
Has been enhanced with additional features (such as file transfers) and more sophisticated compression and security techniques as it has developed
To maintain seamless cross-compatibility between different VNC client and server implementations:
Clients and servers negotiate a connection using the best RFB version
Use the most appropriate compression and security options they can both support

28. History RFB was originally developed at Olivetti Research Laboratory
Remote display technology
used by a simple thin client with ATM connectivity called a Videotile
To keep the device as simple as possible
RFB was developed and used in preference of existing remote display technologies
RFB found a second, more enduring use when VNC was developed
VNC was released as open source software and the RFB specification published on the web.
Since then RFB has been a free protocol which anybody can use.
ORL was closed in 2002
Some key people behind VNC and RFB formed RealVNC Ltd
Continued development of VNC
Maintain the RFB protocol
Current RFB protocol is published on the RealVNC website

29. Protocol versions
Published versions of the RFB protocol are shown below:
Developers are free to add additional encoding and security types
Must book unique identification numbers for these with the maintainers of the protocol so that the numbers do not clash.
Clashing type numbers would cause confusion when handshaking a connection and break cross-compatibility between implementations
The list of encoding and security types is maintained by RealVNC Ltd
Separate from the protocol specification
New types can be added without requiring the specification to be reissued
Version
Source
Date
Specification
RFB 3.3
ORL
January 1998
The Remote Framebuffer Protocol 3.3
RFB 3.7
RealVNC Ltd
July 2003
RFB 3.8 (current)
July 2005
The Remote Framebuffer Protocol 3.8

30. Encoding Pixel data can be encoded to compress data
Raw
Hextile
Zlib
Many others…
Can reduce the amount of data sent
Various encoding have different efficiencies
Can vary by screen content
Has a cost of the time to encode/decode
Note: encoding is NOT encrypting!

31. Encoding Number Encoding 0x00000000 Raw 0x00000001 CopyRect 0x00000002
RRE (Rising Rectangle) 0x
CoRRE (Compact Rising Rectangle) 0x
Hextile 0x
Zlib 0x
Tight 0x
ZlibHex 0x
Ultra 0x
ZRLE 0x
ZYWRLE
0xFFFF0001
CacheEnable
0xFFFF0006
XOREnable
0xFFFF8000
ServerState (UltraVNC)
0xFFFF8001
EnableKeepAlive (UltraVNC)
0xFFFF8002
FTProtocolVersion (File Transfer Protocol Version - UltraVNC)
0xFFFFFF00–0xFFFFFF09
CompressLevel (Tight encoding)
0xFFFFFF10
XCursor
0xFFFFFF11
RichCursor
0xFFFFFF18
PointerPos
0xFFFFFF20
LastRect
0xFFFFFF21
NewFBSize
0xFFFFFFE0–0xFFFFFFE9
QualityLevel (Tight encoding)
Encoding

32. VNC Uses a desktop on the client Is, by default, secure
Displays an image of a server “desktop” on the client
Should never be used on modern computers