Recently I started looking at SIP implementation for a future work. I was reading (Googling) about what SIP means and how to go about implementing a end-to-end SIP enabled VoIP network. What I did not get is what use does a SIP Gateway is for? How different is it with respect to SIP proxy servers or a SIP DNS/Locator like server? I understand probably QoS would be one primary factor - like dedicating a set bandwidth for SIP/VoIP specific I/O over a network. Anything else?
Can anyone help me with any other hints/pointers? I fully understand that is quite a basic question - but I really couldn't find any text which could clear my doubt about what 'Gateway' would mean in SIP context and what differentiates it from other SIP based network components (like Softphones, Proxies etc).
Thanks a lot.