July 2, 2008 at 15:49Skype SIP protocol killer?
On Habré many campaign for open Jabber, instead of closed ICQ. But at the same time, no one is campaigning for softphones based on the open SIP protocol, instead of any closed Skypes. But the essence of the matter is the same logic. Let's start
First, about what is SIP, and only then why is a killer. SIP stands for Session Initiation Protocol and serves to establish connections (sessions) between two computers. Consider a narrower task, for example, a connection between two softphones. In this case, the SIP protocol is required in order to determine the location of clients (softphones), coordinate the sound transmission parameters (codecs, bitrate), start the transfer and end it. There are a number of parallel tasks, but we omit them for simplicity.
And so SIP is a protocol. For his work, you need to write some program that will understand the language that this protocol speaks. On the one hand it is a server, on the client side it is a softphone client. The benefit of such programs has already been written and there is no need to invent anything. What language does the SIP protocol speak? On very simple. For example, in order to make a soft phone call, it sends the following message to the SIP server:
INVITE sip: alice @ berkenson.com
The server reports with codes:
180 - Ringing
200 - OK
As you can see, a SIP URI of the form is used to identify users:
sip: alice @ berkenson.com
where to the right from the dog is the address of the SIP server, and on the left is the name of the user registered on it. Instead of the alphabetic address, you can specify IP:
sip: alice@83.134.98.2
That is, by analogy with Jabber, you can raise your sip server yourself and keep everything under control, or register on any of the public SIP servers (sipnet.ru for example).
What happens when you want to call a friend?
1. You must be registered on some sip server. Let's say sip.ru (nonexistent, find free Sip servers on Google) and your bob login. Your sip address is: bob@sip.ru
2. When you start your softphone, you enter the registration data and contact your sip server. SIP server now knows your location (IPshnik).
3. You call sip: alice @ berkenson.com. First, this address is sent to your sip.ru sip server.
4. Your sip server using DNS will send a request to the Alice SIP server - berkenson.com.
5. SIP server berkenson.com finds out if there is such a user, whether he is online now, and his location (IPshnik).
6. SIP servers find out which clients use Alice and Bob, and agree on the parameters of voice transmission (codecs).
7. Softphones Alice and Bob know IPshniki and each other's codec parameters start transmitting data over the RTP protocol (over IP). SIP servers are not involved in this process.
8. When someone hangs up, information through the SIP server reaches another softphone and short beeps can be heard there.
Everything is transparent and clear.
In essence, SIP is a protocol that controls voice flows, and it can be used to implement many additional functions - conferences, forwarding, holding, etc.
Why is Skype a killer because SIP is very serious, despite its simplicity, the protocol behind which the entire telecom stands industry. When buying a direct Moscow-based VoIP number, you are 90% likely to buy a number that works on the SIP protocol and you can call it through your softphone. Does Skype have such an opportunity?
My prediction is that at first, they will begin to gradually supplant Skype from corporate computers, since many people are now switching to IP PBXs working on SIP, and then users will be drawn and simple.
Written in anticipation of the launch of octopusline.ru
First, about what is SIP, and only then why is a killer. SIP stands for Session Initiation Protocol and serves to establish connections (sessions) between two computers. Consider a narrower task, for example, a connection between two softphones. In this case, the SIP protocol is required in order to determine the location of clients (softphones), coordinate the sound transmission parameters (codecs, bitrate), start the transfer and end it. There are a number of parallel tasks, but we omit them for simplicity.
And so SIP is a protocol. For his work, you need to write some program that will understand the language that this protocol speaks. On the one hand it is a server, on the client side it is a softphone client. The benefit of such programs has already been written and there is no need to invent anything. What language does the SIP protocol speak? On very simple. For example, in order to make a soft phone call, it sends the following message to the SIP server:
INVITE sip: alice @ berkenson.com
The server reports with codes:
180 - Ringing
200 - OK
As you can see, a SIP URI of the form is used to identify users:
sip: alice @ berkenson.com
where to the right from the dog is the address of the SIP server, and on the left is the name of the user registered on it. Instead of the alphabetic address, you can specify IP:
sip: alice@83.134.98.2
That is, by analogy with Jabber, you can raise your sip server yourself and keep everything under control, or register on any of the public SIP servers (sipnet.ru for example).
What happens when you want to call a friend?
1. You must be registered on some sip server. Let's say sip.ru (nonexistent, find free Sip servers on Google) and your bob login. Your sip address is: bob@sip.ru
2. When you start your softphone, you enter the registration data and contact your sip server. SIP server now knows your location (IPshnik).
3. You call sip: alice @ berkenson.com. First, this address is sent to your sip.ru sip server.
4. Your sip server using DNS will send a request to the Alice SIP server - berkenson.com.
5. SIP server berkenson.com finds out if there is such a user, whether he is online now, and his location (IPshnik).
6. SIP servers find out which clients use Alice and Bob, and agree on the parameters of voice transmission (codecs).
7. Softphones Alice and Bob know IPshniki and each other's codec parameters start transmitting data over the RTP protocol (over IP). SIP servers are not involved in this process.
8. When someone hangs up, information through the SIP server reaches another softphone and short beeps can be heard there.
Everything is transparent and clear.
In essence, SIP is a protocol that controls voice flows, and it can be used to implement many additional functions - conferences, forwarding, holding, etc.
Why is Skype a killer because SIP is very serious, despite its simplicity, the protocol behind which the entire telecom stands industry. When buying a direct Moscow-based VoIP number, you are 90% likely to buy a number that works on the SIP protocol and you can call it through your softphone. Does Skype have such an opportunity?
My prediction is that at first, they will begin to gradually supplant Skype from corporate computers, since many people are now switching to IP PBXs working on SIP, and then users will be drawn and simple.
Written in anticipation of the launch of octopusline.ru