Frequently Asked Questions | SIP Architecture

Q: I am used to seeing users that follow the scheme SIP: username@domain.com, but I’ve also seen them with the scheme SIPS: username@domain.com. What’s the difference?

A: SIP uses Universal Resource Identifiers (URIs) for identifying users. A URI identifies resources on the Internet, and those used by SIP incorporate phone numbers or names in the username. At the beginning of this is SIP:, which indicates the protocol being used. This is similar to Web site addresses, which begin with HTTP: to indicate the protocol to use when accessing the site. When SIP: is at the beginning of the address, the transmission is not encrypted. Those beginning with SIPS: require encryption for the session.

Q: Why do all responses to a request in SIP begin with the numbers 1 through 6?

A: This indicates the category to which the response belongs. There are six categories of responses that may be returned from a request: Informational, Success, Redirection, Client Error, Server Error, and Global Failure.

Q: I received a response that my request was met with a server error. Does this mean I can’t use this feature of my VoIP program?

A: Not necessarily. When a request receives a Server Error response, it means that the server it was sent to met with the error. The request could still be forwarded to other servers. A Global Error meanns that it wouldn’t be forwarded because every other server would also have the same error.I need to use a different computer for VoIP. The software is the same as the one on my computer, but I’m concerned that others won’t be able to see that I’m online because I’m using a different machine.When you start the program and log onto your VoIP account, SIP makes a REGISTER request that provides your SIP address and IP address to a Registrar server. This allows multiple people to use multiple computers. No matter what your location, SIP allows others to find you with this mapping of your SIP-address to the current IP address.

Q: Should I always use encryption to protect the data that I’m transmitting over the Internet?

A: Unless you expect to be discussing information or transferring files that require privacy, it shouldn’t matter whether your transmission is encrypted or not. After all, if someone did eavesdrop on an average conversation, would you really care that they heard your opinion on the last movie you watched? If, however, you were concerned that the content of your conversation or other data that was transmitted might be viewed by a third party, then encryption would be a viable solution to protecting your interests. As of this writing however, there are no interoperable, nonproprietary implementations of SIP that use encrypted signaling and media, so you will need to refer to the documentation of the application(s) being used to determine if this is available.