Linphone development document 1: Brief Introduction to sip and VoIP

Address: http://www.linphone.org/eng/documentation/guide/
What is sip? (What is Sip)

SIP is a protocol for establishing voice over ip cils. it is an open standard, published by the IETF organization, who made the vast majority of Internet protocols. it is too red from e-mail and HTTP. the following section describes the base principles
SIP from the user's standpoint, and how to make sip CILS.

SIP is an open standard published by IETF, which has developed a large number of Internet protocols. The SIP protocol is subject to e-mail.
And the HTTP protocol. Next we will describe the basic principles of sip from the user's perspective and how it implements sip calls.

Direct sip CILS in Local Network (implement direct sip dialing in LAN)

Just enter SIP:

This works also on the public Internet provided that the two machines have public IP addresses or appropriate firewall rules.

You only need to enter SIP: Internet cballs through a sip proxy (implement Internet calls through the SIP proxy)

On the public Internet, because of Dynamic IP addresses, mobility, firewils, direct CILS are not really usable. that's why the concept of SIP proxy exists: the proxy is responsible for routing cballs whatever the IP address of end-users is. voIP Operators
Company are deploying sip proxies on the Internet to get sip callrouted for their subscribers.

Direct Dialing is not always available on the internet due to changes in IP addresses, firewalls, and other factors. this is why there is a sip Proxy: The SIP proxy can implement the routing function without considering the user's real IP address. voIP carriers deploy their sip agents on the Internet to provide routing functions for their customers.

In a first step, the user has to subscribe for the service by choosing a username (sometimes a number) and password. your public sip identity is then SIP: <your username >@< your VoIP provider>, this is the address that other people can use to reach you using
Sip.

First, you must register a sip account. after registration, your sip identification address is SIP: <user name >@< VoIP operator code>. Other users can use this address to initiate a SIP call to you.

Then, by grouping the client (such as Linphone) to go through the proxy, you get a public sip address on the Internet, in the same way you have an email address. other people subscribed to this operator can be reached simply by typing their username or phone
Number.

The routing of pure Internet CILS is a service that is often free. linphone.org is powering a free sip proxy service, you can register here.

Then, set the agent parameters of the client (such as Linphone). Just like getting an email address, you get a sip address on the Internet. then you can enter the user name or phone number to initiate a session to the user of the same VoIP operator. simple Internet calls are usually free. .linphone.org provides free sip proxy service. You can register it here.

Callto normal phone numbers (call a common phone number)

VoIP operators for most of them also provide attractive prices to place VoIP to PSTN (= classical telephony) through their proxies and gateways. you coshould then call anybody in the world from your favorite Linphone client, by simply entering his/her International
Phone number. The SIP username becomes a phone number.

VoIP carriers usually provide services for VoIP calls to the PSTN (traditional telephone), and the price is generally very low. you can use your Linphone client to call anyone in the world. at this time, the SIP user name will change to the phone number

Choosing a VoIP operator (select a VoIP operator)

The Linphone project is not affiliated with any VoIP or telecom operator, thus we do not recommend or promote any of them in participates. by typing "VoIP operator" in your favorite search engine you will get hundreds of answers. you can refine the search
Country to get more pertinent answers.

Linphone is using the standard and well knownSIP protocol. As such, it shocould be compatible with any VoIP operator using SIP for its network.

The Linphone project team does not belong to any VoIP or telecom operator, so we will not recommend any operator to you. You can use the search engine to find the answer and enter the country name to obtain a more appropriate answer.

Linphone uses the standard SIP protocol. Therefore, it can be compatible with the networks of other VoIP carriers using the SIP protocol.