[Freeswitch-users] Blog post about SIP

[Steve Underwood]

On 06/17/2012 05:43 PM, Avi Marcus wrote:
> Great doc!
>
> Some short notes:
>
>     *This is broken. Cisco is the most well known vendor to make this
>     mistake. These implementations should be fixed to use G729 as the
>     codec name with payload type 18.*
>
> Linksys / Sipura SPAs do this, too, I'm pretty sure even before they 
> were bough by cisco.
I thought the only Cisco products which did this were the ones which 
started as Linksys/Sipura products. The usual G.729 problem with real 
Cisco products is G.729 with the bits packed in the opposite order to 
the RFC. This isn't an error. Cisco implemented G.729 in RTP before 
there was a standard, and the packing order they chose just happened to 
be the opposite of the standard. Of course, modern Cisco kit implements 
the standard order, but they can still do the opposite order for 
backwards compatibility with their own kit. Sometimes you still meet 
systems configured to use that, and G.729 calls produce a horrible noise.
>
>     *Typically this NAT functionality is referred to as a SIP NAT
>     helper, or SIP ALG. Of course there are other names.*
>
> Many routers let you turn off NAT ALG, if you can find it in the menu.
>
>     *Latching has several issues:... scalability*
>
> At what point does this seriously become an issue? 100 concurrent 
> calls? 1000? If you're proxying media anyway the IP rewriting sounds 
> pretty minimal.
>
> More info about NAT, one way media, and how sipsorcery is a SIP proxy 
> that doesn't ever proxy media but can still set up calls with 2 way 
> media would be much appreciated.
>
> One other things I'm interested in is the ability to not handle media, 
> for latency & performance reasons:
> What are the pitfalls with FreeSWITCH specifically that makes it not 
> happy with not handling media?
> and.. if I still need FS to handle DTMF what are my options? Do 
> many/most carriers (on origination) support SIP INFO or something like 
> that? (I run a calling card with an option to hang up the call)
>

Steve