thanhloi2603

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1. SIP vs NAT, the endless battle, Part 2, bridge behind NAT. - As you already know, losses of RTP stream is one of the most encountered issues in VoIP with clients lie behind NAT as I mentioned already in the previous post. For short, as a service provider in the public internet, we apply symmetric RTP (rfc4961) for re-using the RTP stream from the client to transmit …
2. SIP Timer, Transaction and Retransmission - Timing is very important in SIP, it provides mechanisms to ensure the message are delivered on time, exposed via SIP Timers. SIP timers are usually mentioned in the scope of transaction, and it is mostly used to control the timeout of a SIP transaction and the message re-transmissions in a transaction. That combination is helpful …
3. Why is ACK in separate transaction for INVITE with 2xx? - Have you ever wondered why ACK for non-200 response is in the same transaction with the INVITE, while ACK for 200 OK is considered in a separate transaction? Specifically, notice the branch parameter in their Via header – the transaction identification. If you have no idea on what the hell I’m talking about, check Understanding …
4. SIP vs NAT, the endless battle - 1. What is NAT and why it is needed? Network Address Translation or NAT is a method by which IP addresses are mapped from one group to another. Say, NAT provide a mechanism to connect a realm with private addresses to an external realm with globally unique registered addresses. The need for IP Address translation …
5. SIP 180 vs 183 vs Early media - A normal SIP call successfully established when the callee accepts it with the final response 200 OK, codec negotiation is done and the call enters media session with both ends know about each other’s capabilities. No doubt about this basic and principle mechanism. But this has nothing to do with when the media actually starts, …