If you’ve been exploring virtual or online solutions for making phone calls, chances are you’ve encountered the term SIP, which stands for Session Initiation Protocol.
SIP is what facilitates the flow of voice and video communications over the internet—kind of like the way a highway facilitates the flow of traffic through various locations. In other words, it’s what makes Voice over Internet Protocol (VoIP) work on phones, computers, and other devices.
Just as highways have specific entry and exit points, SIP has dedicated ports that function as gateways for VoIP communication data to travel in and out.
A SIP port is a network port that sends, receives, and listens for SIP messages. The default port (or “primary interstate”) for unencrypted SIP is 5060, while the default port for encrypted SIP is 5061. Although these ports share a common goal, their routes are different—like two highways heading to the same city but passing through different landscapes.
Keep in mind that the default ports are not necessarily the best ports. There are several reasons why they may not be the optimal choice in a given situation, including traffic congestion, port configuration considerations, and security issues.
What Does It Mean to Open a SIP Port?
In our robust highway analogy, we could say that the SIP protocol is the highway’s traffic control system; just like traffic controllers manage the flow of vehicles, SIP controls how data moves along its road. Of course, traffic controllers don’t literally move the cars, but neither does SIP move the data—it merely determines the best route for it and ensures it gets to the correct destination.
To do this, SIP uses ports as checkpoints that allow data to enter and leave a network. In other words, SIP ports are controlled access points that handle the traffic of data packets.
Similar to building a new exit on a highway, opening a SIP port means creating another access point for data to flow into or out of a network. The reason for doing this is often to provide better data flow, which can enhance the performance of your VoIP phone services.
For safety reasons, most ports are closed by default. In your router settings, you can manually input the port number you want to open and set rules for data transmission.
But you wouldn’t want to open a port without proper security measures, just as you wouldn’t want to open up a new highway on-ramp without policing the traffic that comes speeding through it. That’s where firewalls come into play. Firewalls monitor the traffic and decide which data packets get to enter or leave the network to prevent unauthorized access.
SIP Port Depends on Transport
Since SIP is only responsible for initiating, maintaining, and terminating communication sessions, something else is needed to handle the data transport. That’s precisely the role of other protocols, such as the User Datagram Protocol (UDP) and Transmission Control Protocol (TCP).
UDP and TCP are like different types of vehicles on the highway. You can think of UDP like a motorcycle–it delivers data quickly, but it doesn’t verify if the delivery was successful. That’s because it’s a connectionless protocol that sends data in small packets without checking whether the recipient is ready to receive it or if it has arrived. This makes UDP faster and suitable for situations where speed is prioritized over accuracy, such as live broadcasts or online gaming.
On the other hand, TCP is like a delivery truck that’s equipped with a GPS and a checklist of cargo. It’s responsible for making sure that every bit of data reaches its intended destination in the right order. Due to these additional responsibilities, TCP is often slower than UDP, but it guarantees an accurate delivery.
Some highways have designated lanes for different types of vehicles. Likewise, UDP and TCP have specific ranges of ports for their data, spanning from zero to 65535. This wide range allows for a high traffic volume, accommodating many communication sessions simultaneously.
Why Not Use the Default SIP Port?
There are several reasons why you might not want to use the default SIP ports, and they’re pretty easy to understand within our trusty highway analogy—which is a gift that keeps on giving.
First, imagine driving down a highway where almost every car is using the main exit. If you’ve been in rush hour traffic, this scenario is self-explanatory. The traffic would be blocked, meaning your data would be slowed down. This can lead to poor-quality calls or chats.
Now imagine that the main exit is also being targeted by criminals. In this case, the idea of using an alternative exit doesn’t sound so bad.
Similarly, many VoIP vendors will use alternative ports (or ranges of ports) for security purposes. However, it’s also common for them to do so for reasons related to the specific design or needs of their software, hardware, and network architecture. Some common considerations include:
- Network Congestion: As more devices use SIP communication, the default ports can become overwhelmed, leading to degraded call quality and overall poor user experience. Different ports can be used to prioritize and manage network traffic more effectively.
- Functionality: Vendors often use unique ports to ensure smooth connectivity and functionality for their services. This not only supports their platform’s bespoke features but also prevents clashes with other applications on the standard SIP ports.
- Security: Due to sheer popularity and conventions, default ports are common targets for malicious SIP scanning by attackers looking to identify vulnerable networks. Using a less standard port reduces your exposure to such threats.
- Regulatory Compliance: In some cases, vendors might need to comply with specific industry regulations that dictate the use of certain port ranges. For example, a healthcare communication provider might be required to use particular ports to comply with healthcare industry security standards.
- Avoiding Application Layer Gateway Problems (SIP ALG): Many routers have SIP ALG enabled by default. This feature can interfere with SIP traffic, causing issues like dropped calls and connectivity problems. By using a different port, you can bypass SIP ALG and avoid these issues.
Navigating the data highway is all about finding the best route for you. For some, that might mean using the default ports. For others, the convenience may not be enough.