Subject: [MMUSIC] specifying the multicast interface

From: "Matthew Heaney" <[email-masked]>
Date: Fri, 10 Oct 2003 15:34:42 -0400

When creating a multicast session, it is possible to specify the
outgoing interface using the IP_MULTICAST_IF socket option.  Does RFC
2326 (or 3550/1889) prescribe a mechanism for specifying the interface?

Analogously, the IP_ADD_MEMBERSHIP socket option allows the receiver to
specify the multicast interface explicitly (via the imr_interface data
member of the ip_mreq struct).  Is there a mechanism (via the SDP
DESCRIBE, I guess) for indicating the multicast interface?

Thanks,
Matt

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---

From: Thomas Zeng <[email-masked]>
Date: Mon, 13 Oct 2003 10:49:41 -0700

Dear Matthew:

Yes, you can provide the IP of the selected IF via the c= line in SDP, but
the final say is upto RTSP negotiations, ie., you can use the
Transport header in the SETUP request/response to over-ride SDP. Transport
header has the following general parameters, quoting 2326:

   unicast | multicast:
          mutually exclusive indication of whether unicast or multicast
          delivery will be attempted. Default value is multicast.
          Clients that are capable of handling both unicast and
          multicast transmission MUST indicate such capability by
          including two full transport-specs with separate parameters
          for each.

   destination:
          The address to which a stream will be sent. The client may
          specify the multicast address with the destination parameter.
          To avoid becoming the unwitting perpetrator of a remote-
          controlled denial-of-service attack, a server SHOULD
          authenticate the client and SHOULD log such attempts before
          allowing the client to direct a media stream to an address not
          chosen by the server. This is particularly important if RTSP
          commands are issued via UDP, but implementations cannot rely
          on TCP as reliable means of client identification by itself. A
          server SHOULD not allow a client to direct media streams to an
          address that differs from the address commands are coming
          from.

   source:
          If the source address for the stream is different than can be
          derived from the RTSP endpoint address (the server in playback
          or the client in recording), the source MAY be specified.

     This information may also be available through SDP. However, since
     this is more a feature of transport than media initialization, the
     authoritative source for this information should be in the SETUP
     response.

Hope this is the answer you are looking for.

- thomas

-----Original Message-----
From: Matthew Heaney [mailto:[email-masked]]
Sent: Friday, October 10, 2003 12:35 PM
To: [email-masked]
Subject: [MMUSIC] specifying the multicast interface

Thanks,
Matt

---

From: "Matthew Heaney" <[email-masked]>
Date: Wed, 15 Oct 2003 11:27:25 -0400

> From: Thomas Zeng [mailto:[email-masked]] 
> Sent: Monday, October 13, 2003 1:50 PM
> 
> Yes, you can provide the IP of the selected IF via the c= 
> line in SDP, 

But doesn't that specify the multicast address?  The interface address
is different -- it's the IP of the NIC used to multicast the session.

> but the final say is upto RTSP negotiations, 
> ie., you can use the Transport header in the SETUP 
> request/response to over-ride SDP. Transport header has the 
> following general parameters, quoting 2326:
> 
> 
>    destination:

But isn't this the multicast address?  This is not the same as the
interface address.

>           or the client in recording), the source MAY be specified.

Not sure whether this qualifies as the interface address.

> Hope this is the answer you are looking for.

I don't think so, but thanks anyway.

-Matt

---

From: Thomas Zeng <[email-masked]>
Date: Wed, 15 Oct 2003 17:55:08 -0700

Why does one need to publish "the IP of the NIC used to multicast the
session" ?

-----Original Message-----
From: Matthew Heaney [mailto:[email-masked]]
Sent: Wednesday, October 15, 2003 8:27 AM
To: Thomas Zeng; [email-masked]
Subject: RE: [MMUSIC] specifying the multicast interface

-Matt

---

From: Thomas Zeng <[email-masked]>
Date: Thu, 16 Oct 2003 18:19:10 -0700

Interesting...

So if we add a new parameter (since we are revising RFC2326, it is not
impossible to as for an optional parameter, say, "multicast-interface") to
the Transport header in SETUP request/response, you no longer has to use the
"x-multicast-interface" parameter which is not interoperable?

But you may want to convince people that others might be interested in this
new parameter ...

Just a thought.
thomas

> Sent: Thursday, October 16, 2003 4:13 PM
> Because a customer asked us to.
> 
> A multicast session is started on a TrueCast server using a web-based
> admin interface.  The admin user specifies the multicast address and
> port he wants, the name of the presentation, etc.  
> 
> Currently, our admin tool doesn't allow you to specify the IP of the
> interface card, even though explicitly specifying the interface over
> which to multicast the session is allowed per the BSD socket 
> API.  So we
> have to fix it.
> 
> For now I'll just use a GET_PARAMETER to get the interface list, and
> then augment the SETUP request with an "X-multicast-interface" header.
> 
> 
> 
> > Sent: Wednesday, October 15, 2003 8:55 PM
> > To: Matthew Heaney; [email-masked]
> > Why does one need to publish "the IP of the NIC used to 
> > multicast the session" ?
> > 
> > But doesn't that specify the multicast address?  The 
> > interface address is different -- it's the IP of the NIC used 
> > to multicast the session.
> > 
> > 
> > 
> > But isn't this the multicast address?  This is not the same 
> > as the interface address.
> > 
> > 
> > > 
> > >    source: