As SIP trunking becomes an ever more popular choice for businesses that are transitioning to cloud-based communications tools, it’s important to understand your options for routing inbound calls based on your network configuration.
When you get an incoming call through your SIP trunk, your provider will need to determine where to send it. It may be possible to change your inbound call routing to deliver calls in a more reliable way. Your provider might also enable you to direct calls to an exact location.
There are two primary ways to route inbound calls to your private branch exchange (PBX). You can use SIP registration or host-based routing. With Flowroute, you can also route a DID directly to a SIP URI, an advanced variation on host-based routing. However, there are benefits and drawbacks to both of these options, so it’s important to consider the differences so you can make an informed decision.
SIP Registration
SIP registrations create a pathway from your PBX to your SIP provider’s servers. With SIP registrations, an inbound call INVITE can follow the registration path back so it can locate the PBX again. If port forwarding rules or NAT routes are not clearly configured on your router, this can be a very useful and needed function. It can also be beneficial if there’s technology in your network devices that gets in the way of your SIP signaling (such as a SIP ALG).
It’s very possible that your NAT configuration, or firewall, requires SIP registrations to communicate often with your provider’s servers to keep an access point open or to keep a NAT route statically mapped within your network. If this is the case, forgoing SIP registration could make it so that your firewall closes off access and blocks SIP packets from connecting to your PBX. As a result, you won’t receive inbound calls. You may be able to bypass this if you can configure your firewall to allow traffic from your provider’s servers—but the process can be complex.
If SIP registration is supporting your NAT traversal, going without that registration could mean that the NAT route won’t get held statically in your router. And if the NAT route is lost, the router could end up sending a call INVITE to another device rather than your PBX. In other instances, the call might get dropped altogether because the router is confused about where to send it.
Using SIP registration to route calls will send an INVITE to each registered SIP device on your account. So, if you have PBXs at more than one location, and both are registered to the same SIP account, they will each receive an INVITE to the call. This scenario allows the first PBX that can send a SIP response to dictate the behavior of the call regardless of what the other SIP response dictates.
Host-Based Routing
Host-based routing allows you to specifically designate which PBX inbound calls are routed to by directing a phone number to a particular PBX’s IP or domain name. This gives you more control of where calls are sent, so you ultimately gain a way to protect your calls from being misrouted or dropped. Host-based routing may be able to offer you more security and reliability—which remain major challenges in modern business phone systems.
When it comes to security, SIP registrations make it so that each REGISTER request your PBX sends will need to also share your SIP username and encrypted password with your provider’s registration server. Encrypting your SIP password before sending it to your provider ensures that it stays secure while in transit. It’s important to know that some PBXs might store your SIP password in plain text, exposing it to attackers who could access your credentials.
If you use host-based routing for your inbound calls and IP-based authentication for your outbound calls, you may be able to keep your SIP password more secure by completely removing it from your PBX configuration(s).
In order to use host-based routing, you’ll need a static IP address or a domain name. If you don’t already have a domain name established, you can create a fixed host domain through services such as Dynamic DNS and No-IP. These services talk to your router to establish each new IP address with a static domain, making it possible for you to use your static domain as your host route. Once you get a static IP or domain, your provider will be able to send calls to your PBX without requiring a REGISTER request since they already have the intended destination for incoming calls.
Choose the Best Option for your Network
The answer to whether SIP registration or host-based routing makes the most sense for your business and communications needs lies in your network. Following the steps above will help you flesh out unique elements in your network’s mapping to make an informed decision.
