- A TechNote on Unified Communications
- Gary Audin, Delphi, Inc.
The focus on SIP trunks has been on the providers. But do you know what costs and license limitations are on the IP PBX and Session Border Controller (SBC)? Hardware and software licenses are required to connect to SIP trunks in the IP PBX and the SBC. The enterprise needs to be aware of license restrictions for their own protection because SIP equipment trunk license agreements are not identical, and this difference can make comparing licensing costs more-than-a-little problematic.
1. What is a SIP License?
A license is a legal agreement that gives permission to do something. It is a permit. The license defines the terms under which an organization or person is allowed to use a product, most commonly software. Even if you purchased the product, it does not belong to you. You have a license to use the product under the terms of the agreement, until the agreement is breached or the license expires. A SIP trunk license allows the organization to deploy and use X number of simultaneous sessions (voice or video calls).
To facilitate a business continuity plan, the IT manager may opt to use SIP trunks from more than one provider connecting, for example, the IP-PBX to two different service providers' SIP trunks. This configuration can complicate matters if the license terms differ, and may require a larger SBC platform to support multiple physical connections.
2. What Devices Require SIP Licenses?
SIP trunk equipment licenses are required for both the IP PBX and the SBC. Each is licensed separately even if both the IP PBX and SBC are provided by the same vendor. The SBC is usually a separate hardware platform. However, in one case the SIP license software is resident in a router and no separate hardware platform is required.
3. What is the Term of the SIP License?
Very few software licenses are limited to a few years (e.g. 3 years). Most licenses are perpetual. They need not be renewed and are paid for once. A perpetual license is a license to use the SIP trunk software for an unspecified period of time.
4. How is the Number of Licenses Calculated?
The vendors call each session/connection a SIP trunk. One SIP trunk supports one two way voice call whether it is inbound or outbound. If the call supports both voice and video, then the two sessions can share the same Call ID so only one session license is required in this case. However, some vendors count a video session as two calls (one for voice and one for video in some products) -- so make sure you know how these are calculated.
The number of trunk licenses can be determined by ordering the same number of channels that were on the T1 and PRI trunks that are eliminated by moving the SIP connection. It is quite common that the enterprise has overprovisioned the T1/PRI trunks because they only come with 24 or 23 channels. So there can be cost savings and reduced SIP licenses by only provisioning for the numbers of SIP trunks required. If you need to calculate the number of trunk licenses but do not know how many to purchase, go to the TechNote "How Much SIP Bandwidth Should You Buy?". Ensure that you have enough SIP trunk licenses to support the maximum number of simultaneous calls (called the busy hour) necessary to carry both inbound and outbound traffic.
5. Do I Need SIP Licenses in the IP PBX?
Some vendors charge per SIP trunk while others offer unlimited licenses for the IP PBX. The number of licenses in a bundle can be 4, 5, 8, 10, 16, or any other counting system the vendor selects. Some IP PBXs come with a minimum number of SIP trunks. The maximum SIP trunk capacity increases as the IP PBX system increases in capacity. The bigger the IP PBX, the more SIP licenses that can be implemented, so make sure you have the necessary software release to support a SIP license. New software releases will probably more than double the capacity for SIP licenses in some IP PBX products.
6. Do I Have SIP licenses?
Each IP PBX vendor has their own arrangement for SIP trunk licenses. DO NOT assume that the IP PBX comes with SIP trunk licenses. "The SIP Survey 2012" posted by The SIP School found that some enterprises thought they had the SIP licenses which was not the case. What is worse, this issue was more prevalent in 2012 than it was in 2011.
7. How Are SIP Licenses Structured in the SBC?
The SBC usually comes with a small number of licenses-- usually five for small systems and 50 for large systems. More licenses can be acquired, usually in units of five. The cost per license decreases if the number purchased is high because volume discounts are typical, and you may even be able to acquire unlimited licenses if you purchase one of the larger SBCs.
8. Can I Decrease Licenses and Save?
You can increase the number of licenses without requiring any on site action by the vendor providing the equipment has sufficient capacity. You can purchase more licenses and the vendor will provide a license key so that the IP PBX and SBC can be expanded. However, if the enterprise wants to only increase the number of licenses for a few months and then return to the original number, this is not commonly possible. Once the licenses are acquired, they cannot be reduced.
9. Are There Any Other Costs?
The IP PBX and SBC vendors will probably have a separate charge for software maintenance, updates, and support. Some have a basic SIP support charge independent of the trunk license fee.
10. What About Technical Limitations?
Most IP PBX vendors do not charge different license fees if a third party SBC is connected. One vendor does add a charge to the IP PBX license if their SBC is not used. This may cost more for the enterprise. However, the VAR may discount the third party SBC to a degree that the total cost is not greater than if the enterprise used the IP PBX vendor's SBC.
There is always an upper limit to the number of simultaneous session an IP PBX can support. So even if you acquire an unlimited license, it is really limited to the capacity of the IP PBX because it can support as few as four and up to thousands of SIP trunks.
Another license limitation that is not well known is the number of calls that can be established per second through the SBC. The SBC may become a bottleneck when there is a call center establishing a high number of outbound calls per second. At least one call center required 50 calls/second for the SBC. Not all the SBC vendors could satisfy this requirement.
The call establishment rate for an IP PBX is usually higher than the SBC can support. The IP PBX rate is dependent on the number of processors configured in the IP PBX. This high call rate requirement does not impact most SIP trunk implementations.
Finally, in some of the IP PBX vendor's deployments, the number of SIP trunks is dependent on whether the dial plan is three or four digits.
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One of the interesting anomalies in licensing is that it seems that some equipment providers have differential pricing for licensing depending on whether the equipment connects to other equipment from the same provider or from another provider.
For instance, if the PBX and the SBC come from the same provider, there may be one license fee (or it may even be included.) However, if connecting the PBX to a SBC from a different equipment provider, there might be an additional charge.
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