How IP Phones Use SIP Registration to Stay in Touch

Nov 20, 2022
How IP Phones Use SIP Registration to Stay in Touch

SIP (Session Initiation Protocol) is a signaling protocol that enables businesses to use Voice over Internet Protocol (VoIP) as a replacement for plain old telephone service (POTS) over the public switched telephone network (PSTN). SIP supports voice calls, video conferencing, instant messaging, and media distribution. SIP trunking, which replaces the cable trunks that phone companies used to run to office buildings, offers businesses advantages over traditional telephony such as quick provisioning, low costs, and no equipment to procure or maintain.

The SIP registration process

SIP endpoints, a.k.a. IP phones, can be anywhere on the internet. Most IP phones don’t have a fixed IP address, so each SIP endpoint needs to register its IP address and port number with a central server called a Registrar so other endpoints can find it when they want to connect. A REGISTER message creates a bond between the device and a SIP Address of Record (AOR) in the format sip:user@domain (e.g., which another endpoint can use to reach the registered device.

When someone starts up an IP phone, whether it’s a hardware device or a softphone, the registration process generally begins automatically, per the SIP standard. SIP registrations have an expiration timeout value — typically 60 minutes, but registration timeouts vary among SIP device vendors. IP phones have to reregister before the timer expires or their connection is disconnected, so most IP phones automatically repeat the registration process halfway through the registration period, or every 30 minutes.

SIP benefits

So much for getting started on the technical side of the SIP registration process — why get started with the technology at all?

Agility - With SIP trunking, businesses can add numbers easily whenever they need them, and each number can make and receive unlimited local and long-distance calls.

Scalability - You can add as many numbers as you need, and drop them when the need goes away. You pay only for what you use.

Mobility — With a regular PSTN phone number you can only make and receive calls from wherever your phone is. A SIP endpoint can move to almost any device, so employees can be reached when they’re in the office or working from a coffee shop.

Manageability — Working with the phone company can make you want to tear your hair out. Managing SIP trunks is much easier and less time-consuming.

Cost savings — Pricing for SIP lines is attractive. With Plivo, businesses pay a minuscule monthly fee and less than a penny a minute (in the US; pricing varies by country) for outgoing voice calls, which is less than the cost of a call on a number leased from a phone company.

SIP trunking offers another cost advantage — no hardware phones necessary. Any network device with a microphone and speakers can act as a softphone. That saves companies the cost of procuring and maintaining telephones — though if you prefer to have a separate device for phone calls, you can buy SIP handsets.

Virtual local presence — You can use SIP phone numbers with any area code and exchange that your provider offers. That means you can seem to be local to your customers, who tend to like doing business with local companies, even if you’re based far away.

If all of this sounds worthwhile, you should look into Zentrunk, Plivo’s SIP trunking service. If you’re already a Zentrunk customer, we have SIP registration instructions that show and tell you exactly how to register a SIP endpoint.

The State of Marketing in 2024

HubSpot's Annual Inbound Marketing Trends Report
footer bg

Subscribe to Our Newsletter

Get monthly product and feature updates, the latest industry news, and more!

Thank you icon
Thank you!
Thank you for subscribing
Oops! Something went wrong while submitting the form.