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3.2 A new Protocol for IRC
The protocol used by the VRML browsers to exchange information needs to be embedded within the standard
communication allowed by the IRC protocol. Thus all the people in SharedRoom can use the facilities of the IRC:
they can talk to all other participants, they can directly talk to each other on private lines and perform personal
interaction. Furthermore, there is a special protocol of VRML messages, which contains the icon description and
the movements and actions of a user. These VRML messages are sent using a standard IRC PRIVMSG command,
but they are marked as VRML messages by a starting exclamation mark (’!’) followed by a three digit code. (If
the user enters a message starting with a ’!’ it should be sent as ”!!”, with the second ’!’ removed by the receiving
VRML browser).
To implement our proposal, only the following codes need to be implemented:
!000 Sign on message
!001 Icon definition
!002 Position definition
!003 Icon redefinition
!004 Position redefinition (movement)
!005 Log out message
!006 Click on icon
All these messages are of the form:
!nnn[]
For example:
"!000Separator {Cube{}}"
"!005"
MultipleVRML messages within one IRC message are allowed, each starting with a !nnn. If a user enters a channel,
the viewer sends a !000 followed by a VRML Separator containing the description of his icon. As a response to
this all other users which are already on this channel send a !001 followed by a VRML Separator containing the
description of their icons and a !002 followed by a VRML Transform which describes their absolute position and
orientation. This way the VRML browser gets all the information it needs to visualize the other participants of
this shared room. A moving participant will send a !004 followed by a VRML Transform, which contains the new
position and orientation of the user. The IRC protocol provides the necessary information to assign this movement
to the corresponding icon. It is up to the VRML browser to prevent the icon from popping around by smoothly
interpolating between successive positions.
Code !003 is used to redefine the icon of a user. This may be used to express some (minimal) gesture by
changing the icon according to the mood of the user. If a user clicks on an icon representing another participant, a
!006 message with no parameters will be sent to him. Finally the VRML browser will send a !005 if the user leaves
the bounding volume of this SharedRoom.
There are two special cases for the definition of icons: It is allowed to use the DEF/USE mechanism of VRML
to avoid resending the icon of a user, so this would be a legal sequence:
"!000uni-bonn.de:DEF std Separator {Cube {}}"
"!003uni-bonn.de:DEF smile Separator {Sphere{}}"
"!003uni-bonn.de:USE std"
Another case is the usage of WWWInline, which should be allowed to send a description which exceeds the
maximum line length of 511 for an IRC message.
To summarize, the advantages of choosing IRC are:
1. Efficiency: IRC has an established network of IRC servers, which build a backbone for broadcasting
messages of each IRC client around the world. Combination techniques bundle many small messages into
larger packets by which the IRC network avoids sending a message twice over the net. For example imagine
two users A1 and A2 in the USA and two other users G1 and G2 in Germany. If A1 sends a message it is
sent over the ocean once by the american IRC server to the german server which in turn distributes it to G1
and G2. Theoretically the same effect could be achieved by an IP Multicast message [MB94], but actually