multicast
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... sessions that have been advertised and established by other means.
Sessions can be advertised using multicast protocols such as SAP,
electronic mail ...
... SIP can also initiate multi-party calls using a multipoint control
unit (MCU) or fully-meshed interconnection instead of multicast.
Internet telephony gateways ...
... 5] for advertising
multimedia sessions via multicast and the session description
protocol (SDP) (RFC 2327(-> 4566prop) ...
... call-id (Section 6.12). Thus, if a user is, for example, invited
to the same multicast session by several people, each of these
invitations will be a unique call. A point-to-point Internet
telephony ...
... session description. A conference can have zero or more members
and includes the cases of a multicast conference, a full-mesh
conference and a two-party "telephone call", as well as
...
... address contained in the next Via header field (Section 6.40)
of the response. If the request is sent via multicast UDP, the
response is directed to the same multicast address ...
... multicast UDP, the
response is directed to the same multicast address and destination
port. For UDP, reliability ...
... join the session. For
multicast sessions, the session description enumerates the media
types ...
... wishes to accept the call, it responds to the invitation by returning
a similar description listing the media it wishes to use. For a
multicast session, the callee SHOULD only return a session
description if it is unable to receive the media indicated in the
...
... LDAP (RFC 1777hist(-> 3494) [19]), multicast-based protocols [20] or
operating-system dependent mechanisms to actively determine the end
...
... For example, two parties may have been conversing and then want to
add a third party, switching to multicast for efficiency. One of the
participants invites the third party with the new multicast address ...
... multicast for efficiency. One of the
participants invites the third party with the new multicast address
and simultaneously sends an INVITE to the second party, with the new
...
... and simultaneously sends an INVITE to the second party, with the new
multicast session description, but with the old call identifier.
...
... TCP connection state for
each outstanding request, and to use multicast. Routers can more
readily snoop ...
... host field. This
address is typically a multicast address, but could also be the
address of a backup server. The ttl parameter determines the
...
... time-to-live value of the UDP multicast packet and MUST only be
used if maddr is a multicast address and the transport protocol ...
... UDP multicast packet and MUST only be
used if maddr is a multicast address and the transport protocol
is UDP ...
... is UDP. The user parameter was described above. For example, to
specify to call j.doe@big.com using multicast to 239.255.255.1
with a ttl of 15, the following URL would be used:
...
... REGISTER request to the well-known "all SIP servers" multicast
address "sip.mcast.net" (224.0.1.75). This request SHOULD be scoped
to ensure it is not forwarded beyond the boundaries of the
administrative system. This MAY be done with either TTL ...
... that was being tried but specify additional transport parameters
such as a different server or multicast address to try or a
change of SIP transport ...
... transport protocol given in the "transport" parameter. If
"maddr" is a multicast address, the value of "ttl" is used as
the time-to-live value.
...
... can respond, there needs to be a means to distinguish the responses
from each at the caller. The situation also arises with multicast
requests. The tag in the To header field ...
...
A proxy sending a request to a multicast address MUST add the "maddr"
parameter to its Via header field, and SHOULD add the "ttl"
...
... parameter. If a server receives a request which contained an "maddr"
parameter in the topmost Via field, it SHOULD send the response to
the multicast address listed in the "maddr" parameter.
...
...
A proxy server MUST NOT forward a request to a multicast group which
already appears in any of the Via headers.
...
... - If the second Via header field contains a "maddr"
parameter, send the response to the multicast address
listed there, using the port indicated in "sent-by", or
...
... address
indicated in the "maddr" parameter even if it is not a
multicast address.
- If the second Via header field ...
... If the first Via header field in the request contains a
"maddr" parameter, send the response to the multicast address
listed there, using the port indicated in "sent-by", or port ...
... be sent to the address indicated in the "maddr" parameter even
if it is not a multicast address.
...
... SIP" and "UDP",
respectively. The "maddr" parameter, designating the multicast
address, and the "ttl" parameter, designating the time-to-live (TTL)
...
... time-to-live (TTL)
value, are included only if the request was sent via multicast. The
"received" parameter is added only for receiver-added Via fields
...
... than those listed above was not understood.
330 Multicast not available: The site where the user is located does
not support multicast.
...
... 330 Multicast not available: The site where the user is located does
not support multicast.
331 Unicast ...
... SIP is defined so it can use either UDP (unicast or multicast) or TCP
as a transport protocol ...
...
Requests MAY be multicast; multicast requests likely feature a host-
independent Request-URI ...
... host or domain name.
If the request was received via multicast, the response is also
returned via multicast. Responses to multicast ...
... If the request was received via multicast, the response is also
returned via multicast. Responses to multicast requests are multicast
...
... multicast, the response is also
returned via multicast. Responses to multicast requests are multicast
with the same TTL ...
... returned via multicast. Responses to multicast requests are multicast
with the same TTL as the request, where the TTL ...
...
To avoid response implosion, servers MUST NOT answer multicast
requests with a status code other than 2xx or 6xx. The server delays
...
... numbered or 6xx response from another group member prior to sending.
Servers do not respond to CANCEL requests received via multicast to
avoid request implosion. A proxy or UAC ...
... server to violate some basic message processing rules. Lets
say A sends a multicast request, and it is received by B,C,
and D. B sends a 200 response. The topmost Via field in the
response will contain the address ...
... response received with an incorrect topmost Via MUST be
dropped, but not in this case. To distinguish this packet
from a misrouted or multicast looped packet is fairly
complex, and for this reason the procedure is a MAY. The
CANCEL, instead, provides a simpler and more standard way
...
... address a. response(r) sends a response to the client.
ismulticast() returns 1 if the location is a multicast address and
zero otherwise. The variable timeleft indicates the amount of time
left until the maximum response time has expired. The variable
...
... domain as the proxy server. Thus, an initial multicast request can
trigger additional unicast requests.
...
... * the location is part of the Via path of the incoming
* request. This check is omitted here for brevity.
* Multicast locations MUST NOT be returned to the client if
* the server is not recursing.
...
... */
if (recurse) {
multicast = 0;
N += r.locations;
for (i = 0; i < r.locations; i++) {
...
... can be freed) when all requests have been answered by final status
responses (for unicast) or 60 seconds have elapsed (for multicast). A
proxy MAY send a CANCEL to all branches and return a 408 (Timeout) to
...
... registers on start-up, via
multicast, with the local SIP server named bell-tel.com. In the
example, the user agent ...
... Invitation to a Multicast Conference ...
...
The first example invites schooler@vlsi.cs.caltech.edu to a multicast
session. All examples use the Session Description Protocol (SDP) (RFC
...
... initiator (the last element of the list) towards the callee. In the
example above, the message was last multicast to the administratively
scoped group 239.128.16.254 with a ttl of 16 from the host ...
... 305 "Incompatible media format",
330 "Multicast not available"
Content-Type: application/sdp ...
... bandwidth that was
higher than the access link could support, requested multicast, and
requested a set of media encodings. The response states that only 128
...
...
The response also states that multicast is not available. In such a
case, it might be appropriate to set up a transcoding gateway and
...
... Multicast Operation ...
...
The interpretation of send-only and receive-only for multicast media
sessions differs from that for unicast sessions ...
... media
sessions differs from that for unicast sessions. For multicast,
send-only means that the recipient of the session description (caller ...
...
For multicast, receive and send multicast addresses are the same and
all parties use the same port numbers ...
...
For multicast, receive and send multicast addresses are the same and
all parties use the same port numbers to receive media data. If the
...
...
If a callee does not support multicast at all, it SHOULD return a 400
status response and include a 330 Warning.
...
... Subject header field have different
meanings when inviting to a multicast session. The session
description line describes the subject ...
... session
description line describes the subject of the multicast session,
while the SIP Subject ...
... Schooler, E., "A multicast user directory service for synchronous rendezvous," Master's Thesis CS ...
... Meyer, D., "Administratively scoped IP multicast", RFC 2365, July 1998. ...