There was never a draft that asked for a parameter value for lr.
There was, for some time, a very long time ago, a library and
implementation based on it in the field that would not accept bare lr
parameters (for interesting values of "would not accept"). That same
implementation was the source of lr=on.
You'll see a mention of it in RFC5853 as lr=true (see section 3.6.3)
It was a point of interoperability for a few SIPits, but again, a very
long time ago.
It's been long time since I've seen any implementations that would not
accept a bare lr parameter.
RjS
p.s. - A little digging turned up
https://lists.cs.columbia.edu/pipermail/sip-implementors/2008-December/020919.html
On 2/10/16 10:43 AM, Paul Kyzivat wrote:
[Robert - question here for you]
On 2/10/16 11:20 AM, Alex Balashov wrote:
Thanks, Paul. FWIW, B is strictly a UA, not a part-time proxy.
The implementors of A have traced the problem to P's attachment of a
value to the ;lr parameter in the RR:
Record-Route: <sip:xxx.xxx.xxx.xxx:5060;lr=on>
They say that's the cause of the breakage.
This view is certainly supported by RFC 3261; its grammar clearly
states that this is a value-less parameter.
However--and I'm sure this has been beaten to death over the
years--there are some broken UAs out there that actually _do_ expect
an lr= value, to such an extent that Kamailio/OpenSIPS (P is Kamailio
in this case) provide a configuration directive to enable the
assignment of an lr parameter value in inserted RR headers:
http://kamailio.org/docs/modules/4.3.x/modules/rr.html#idm20528
Our implementation of P had this enabled.
Seems one can't win. There's got to be a reason this option came
about. However, it's been around for a long time, and may date back
to the mid 2000s...
Longer. The lr parameter exists in order to support backward
compatibility with RFC2543 (the predecessor of 3261).
AFAIK there was never a draft of 3261 where lr had a parameter. Any
such usage must have come from a defective implementation.
Any empirical knowledge of whether there remain UAs out there
nowadays that don't properly support bareword 'lr'?
I don't. But I don't have knowledge about many implementations.
A person who might know (from SipIt) is Robert Sparks. I'm copying him
on this.
Thanks,
Paul
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