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LSAM CHANNEL MULTICAST
======================
LSAM Authors: Anne Hutton, Lars Eggert
$Revision: 1.5 $ ($Date: 1998/07/02 23:42:43 $)
More information: http://www.isi.edu/lsam/


Introduction
------------
Channels are created from the channel_status form.

http://your_server/cgi-bin/lsam/channel_status.pl

The announcements for these channels are made to other web servers and proxies
via a well-known multicast announcement channel.

The current test multicast address is 224.6.3.1 and the port 8999.  The ttl is
set to 1.

The channels can be created by an administrator unaided or aided by the log
analysis process.

i.e., they can be created and destroyed by manual control
(http://your_server/cgi-bin/lsam/add_chanel.pl which is called from the
channel_status page) or can be managed within LSAM by its automated join/leave
mechanism (due in the final release in August 1998).

The current system always unicasts a response to a request, and always
multicasts a push for requests that are members of any current channel. The
final release of the LPC will incorporate more complete management of this
process, including a hysteresis to avoid proximal retransmissions of the same
response.

It is possible that a response can match the URL prefix of more than one
currently active channel; in this case, the response is pushed ONLY on the
channel with the "longest prefix" match.


Configuration Directives
------------------------
The directives are as follows in conf/httpd.conf:

	 LSAM_CHANNELS
	 Is set to conf/.other_channels. 

The following directives are currently hard-coded in http_main.c In the final
release of the LPC, these compile-time constants will configurable from
httpd.conf.

	 LSAM_ADDCHAN_port 8666

	 LSAM_DELCHAN_port 8667

	 LSAM_MCAST_ANNOUNCE_port 8999 

	 LSAM_MCAST_ANNOUNCE_addr 224.6.3.1

	 LSAM_MCAST_ANNOUNCE_ttl 1


Upcoming Features
-----------------
* keep track of files which have been multicast.
  To avoid re-push of frequently-requested files on 
  the same mcast group.