Subject: [MMUSIC] RTSP "alt-ports" are not mentioned in the RFC.

From: Dushyant Joshi <[email-masked]>
Date: Thu, 13 Dec 2012 16:12:43 +0530

Hello team,

I could see RTSP alt-ports are not defined in either RFC 2326 or RFC 6064

if you see IANA

http://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xml

we have defined port 8554 as the alternate RTSP port

rtsp            554/tcp    Real Time Stream Control Protocol
rtsp            554/udp    Real Time Stream Control Protocol
rtsp-alt        8554/tcp   RTSP Alternate (see port 554)
rtsp-alt        8554/udp   RTSP Alternate (see port 554)

The RTSP 2.0 specification is still an Internet Draft and could add text.
 can we add this as an informative mentioning that there do exist an
alternative registered port.

Regards,
Dushyant Joshi
91-9886886757

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From: Harald Alvestrand <[email-masked]>
Date: Mon, 17 Dec 2012 10:22:34 +0100

> I could see RTSP alt-ports are not defined in either RFC 2326 or RFC 6064
What is the point of defining an RTSP alt-port?

Usually, in port numbers, two is worse than one; one should either have 
a single port or have protocol/uri syntax to describe using any port.

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From: Magnus Westerlund <[email-masked]>
Date: Mon, 17 Dec 2012 10:31:27 +0100

> What is the point of defining an RTSP alt-port?

It appears to be old legacy. I assume the motivation was that it was
difficult to deploy on the <1024 port number and wanted an alternative
that still was prevented to be used by other services.

> a single port or have protocol/uri syntax to describe using any port.

The question is if this port number has any benefit at all. Any port
number for RTSP that isn't the default needs to be explicitly called out
in the URI anyway, thus I see little different between 8554 and 7892 for
example. If it is a matter of deploying security policies I would
believe that you need to coordinate that anyway. Or is this for the
cases of outbound policies where you want to say, general TCP isn't ok,
but RTSP is, but only to port 554 and 8554?

Still I think this is strange and I do question if even a informative
reference in the RTSP 2.0 spec is of benefit.

Cheers

Magnus

-- 

Magnus Westerlund

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From: Ross Finlayson <[email-masked]>
Date: Tue, 18 Dec 2012 13:17:26 +1000

(Grumple... I wish this mailing list were set up so that replies went to the mailing list by default.  Resending to the whole mailing list instead of just Magnus.)

> The question is if this port number has any benefit at all.

Yes it does.  If a RTSP server cannot use port 554 (most likely because it is running on a Unix system, but not as 'root'), then it can try using port 8554 instead.  (FWIW, our RTSP server implementation - widely used on the Internet - does this.)  As you noted, if a server uses port 8554 (or any port other than 554), then this port number will need to be included in the "rtsp://" URLs that clients use.  But it's beneficial to know - e.g., if you're managing a network's 'security' policy - that RTSP will likely be used on either port 554 or port 8554 (rather than either port 554 or some unspecified other port number).  Similarly, it's useful for network monitoring tools to know that traffic on port 8554 is likely to be RTSP.

Ross Finlayson
Live Networks, Inc.
http://www.live555.com/