All things related to multicast

["Richard Mavrogeanes" <>]

James,
 
The length of the SAP is dependent on the length of the text descriptors, but 
currently it will always be less than or equal to 367 bytes.  We may expand 
this in the future to up to 512 bytes.
 
Regards,
 
rich mavrogeanes
 

        -----Original Message----- 
        From: James O. Whitlock 
[mailto:]
 
        Sent: Mon 5/13/2002 8:44 PM 
        To: Lucy E. Lynch; Richard Mavrogeanes 
        Cc: 
;
 
;
 

 
        Subject: Re: USA WNY-HPNVI 24/7 Live Surgery at 1330 EST (fwd)
        
        

        Richard - Thanks for the information on VBrick Systems components.
        The issue at hand, however had to do with the announcement length.
        Does VBrick limit the length of descriptive text in an announcement
        and, if so, to what?  -- Jim
        
        
        ----- Original Message -----
        From: "Richard Mavrogeanes" 
<>
        To: "Lucy E. Lynch" 
<>;
 "James O. Whitlock" 
<>
        Cc: 
<>;
 
<>;
 
<>
        Sent: Monday, May 13, 2002 8:31 PM
        Subject: RE: USA WNY-HPNVI 24/7 Live Surgery at 1330 EST (fwd)
        
        
        For your information, the VB3000 (MPEG-1) sends SAPs at fixed 
intervals.  You can configure the interval as desired.  The VB6000
        (MPEG-2) sends SAPs at either fixed intervals, or per the RFC 
referenced.
        
        
        -----Original Message-----
        From: Lucy E. Lynch 
[mailto:]
        Sent: Monday, May 13, 2002 2:45 PM
        To: James O. Whitlock
        Cc: 
;
 
;
        

        Subject: Re: USA WNY-HPNVI 24/7 Live Surgery at 1330 EST (fwd)
        
        
        
        On Mon, 13 May 2002, James O. Whitlock wrote:
        
        > Agreed.  Do you have a good means to zoom in on the appropriate RFC?
        > I can launch some enquiries but it's really not my specialty.  It
        > may also be worth checking what others in the commercial market are
        > doing.  I'll have some VBrick Systems encoders permanently stitched
        > into our public facilities over the next few months and will be sure
        > to exercise that dimension.  Ditto on MS WMP implementations ATP.  
If
        > they all fail to limit message length, that becomes a something of 
de-
        > facto standard that we have to live with.  At least, in my 
experience
        > to date.  In any case, whereto next?  The solution will certainly 
not
        > be chasing everyone down who happens to use a long announcement 
message.
        >
        > -- Jim
        >
        >
        
        Jim -
        
        I believe the relevant IETF document is RFC2974 - Session Announcement
        Protocol (experimental)
        
        We can take a look at the XMIM cade (based on SDR) here at UO - but
        if folks on the wg-multicast list have wisdom to offer about current
        versions of SDR (mash etc.) or hpw this is handled for IP/TV or
        vbrick please say so!
        
        - lel
        
        key points:
        
        "Announcements are made by periodic multicast to the group.  The base
        interval between announcements is derived from the number of
        announcements being made in that group, the size of the announcement
        and the configured bandwidth limit.  The actual transmission time is
        derived from this base interval as follows:
        
           1. The announcer initializes the variable tp to be the last time a
              particular announcement was transmitted (or the current time if
              this is the first time this announcement is to be made).
        
           2. Given a configured bandwidth limit in bits/second and an
              announcement of ad_size bytes, the base announcement interval
              in seconds is
        
                     interval =max(300; (8*no_of_ads*ad_size)/limit)
        
           3. An offset is calculated based on the base announcement interval
        
                     offset= rand(interval* 2/3)-(interval/3)
        
           4. The next transmission time for an announcement derived as
        
                     tn =tp+ interval+ offset"
        
        and
        
        "It is desirable for the payload to be sufficiently small that SAP
        packets do not get fragmented by the underlying network.
        Fragmentation has a loss multiplier effect, which is known to
        significantly affect the reliability of announcements.  It is
        
        RECOMMENDED that SAP packets are smaller than 1kByte in length,
        although if it is known that announcements will use a network with a
        smaller MTU than this, then that SHOULD be used as the maximum
        recommended packet size."
        
        Authors:
        
        Mark Handley
        AT&T Center for Internet Research at ICSI,
        International Computer Science Institute,
        1947 Center Street, Suite 600,
        Berkeley, CA 94704, USA
        
        EMail: 

        
        Colin Perkins
        USC Information Sciences Institute
        4350 N. Fairfax Drive, Suite 620
        Arlington, VA 22203, USA
        
        EMail: 

        
        Edmund Whelan
        Department of Computer Science,
        University College London,
        Gower Street,
        London, WC1E 6BT, UK
        
        EMail: