How to remove SS7 from your network... without losing your soul

Have you ever considered becoming a VoIP-only carrier? Imagine if you never needed to buy another media gateway, or troubleshoot bit errors on a T1, or deal with a traffic outage caused by a faulty Mux.

Is this really possible? And would it actually be better?

(This article first appeared at awardconsulting.net.)

When I attended the Metaswitch Symposiums back in April, I had the opportunity to talk with numerous ILECs and CLECs about their operations. During these discussions, it became clear that many chose to switch a large proportion of their outgoing traffic to SIP trunks, primarily for financial reasons, but were still maintaining sizeable SS7 networks at significant cost.

On the surface, this decision didn’t make sense. After all, SIP trunks are highly cost-effective, and the ability to route traffic over IP has been available for years. So, I was left wondering why they would continue to invest in SS7 when alternatives were clearly available.

The answer resides in a single place: the LECs.

As the guardians of the PSTN (a term I've coined today, solely so I can use the image below in a post about telecoms), the Local Exchange Carriers are required by law to provide access and number portability to smaller ILECs, or IOCs, and CLECs. However, that requirement doesn’t mean they have to make it easy – so most LECs, from what I’ve gleaned, only provide interconnect over SS7.

This simple fact puts service providers in a serious bind. While they have the power to route outbound calls over cost-effective SIP trunks, inbound calls that are destined for the service provider’s numbers are routed through the LECs using the legacy SS7 signaling and ISUP trunk groups, leaving the poor service provider with no other choice but to maintain – and pay for – expensive TDM media gateways and SS7 links.

This left me wondering... does it really have to be this way?

SS7 really ought to be obsolete by now - and yet it’s hanging on by its fingertips, on-life support thanks to the LECs. Can we pull the plug?

In this article, I’m going to examine what it would take to go cold-turkey and entirely eliminate TDM from your network.

What would that mean for your business? No more buying media gateways, no more paying for transport or A-links, and the ability - finally - to virtualize all your network functions, which is going to make Metaswitch pretty happy.

Key Question: Rent or Own your DNs?

Before we get into the fundamentals and details of removing SS7, it’s important to ask yourself one question: Do you want to own your own telephone numbers? If this is not so important to you, and you are willing to pay a monthly fee per directory number, there are several carriers that you can port your DNs to, including Bandwidth.com, Level 3, among others. These DNs can then be easily delivered to you over a SIP trunk.

On the plus side, this is a quick and easy way of becoming a VoIP-only service provider, with access to nationwide numbers. On the downside, you lose the ability to collect carrier compensation for inbound traffic, and also, because you no longer own your numbers, you’re heavily dependent on a third party, which might not be appealing to you.

Show me the money!

This decision about your DNs is so fundamental that I’ve created a spreadsheet to help you compare the financial impact of moving all DNs to a third-party carrier, versus maintaining your own equipment. So right now, before you go any further, you should download the calculator and see how much you could save! Or lose?

(I’d like to thank Brent Baker of Powernet Co for providing feedback on early versions of this tool.)

If giving up your phone numbers is not an appealing proposition (either strategically or financially) there’s no need to fear. There are other options for removing all TDM from your network while retaining full control over your own DNs. The remainder of the article will explore how to disconnect from SS7 while keeping your numbers.

Incoming calls

As I mentioned before, incoming calls are the main reason why so many networks are still relying on SS7. After all, how are you supposed to receive calls that originated somewhere else in the PSTN if you don’t have SS7 connectivity to the local exchange carrier?

Hopefully, someday soon, LECs will have come to their senses and will start offering SIP trunks to all their subtending carriers, but until that day comes, we need alternatives. That means working with third parties, and that means we need to consider the various different types of inbound calls we’ll need to handle, and how things could work in each scenario.

Incoming LD traffic

When your subscriber receives a long-distance incoming call, that call is routed through an inter-exchange carrier, or IXC. That IXC then uses the LERG to identify your local exchange carrier, which in turn delivers the call to its final destination - you.

It is, however, possible to update the LERG and ask the inter-exchange carrier to deliver the call to a third party, rather than the LEC. You simply need to sign a contract with said third party, asking them to act as recipient for your traffic and deliver it to you over a SIP trunk. One-two, problem solved, TDM eliminated for inbound LD calls.

If you want to, you can search for service providers who offer this Access Homing Tandem service, or you can take a look at either Inteliquent or Peerless Network, who are the two providers that are the most prominent in this space.

Incoming Local from LEC

If a caller who receives phone service from your LEC contacts your subscriber, then, fundamentally, the call needs to originate from the LEC, making this scenario particularly difficult to address when the goal is to eliminate TDM.

However, there may be a method for receiving the call over SIP through the use of a third-party.

For example, Inteliquent has agreements with certain LECs in specific areas allowing them to receive traffic over SS7 that is destined for you. Then, Inteliquent, through their Local Connect End Office offering, acts as a TDM-IP gateway, converting that SS7 call into a VoIP connection.

This provides a workaround for an otherwise challenging scenario, making the removal of TDM from your network a possibility.

Incoming Local from non-LEC Subscriber

Of course, not all local calls originate within the LEC, so these have to be addressed as well. Some areas may have a few small IOCs and CLECs that you can coordinate with directly to turn up SIP trunks for local traffic, giving you an opportunity to eliminate TDM from these situations.

Additionally, there are some large providers – most commonly wireless companies (AT&T, Sprint, Verizon, etc.) and MSOs (Comcast/Xfinity, Charter, etc.) – that control large blocks of numbers that operate as local within your area.

Both Inteliquent and Peerless Network offer “Local Transit” services that give you the ability to receive these calls from other local carriers outside of the LEC over SIP, though geographic limitations may apply.

Outgoing calls

("Hello? Could I order a large pepperoni thin crust?")

Okay, I admit it, incoming is a little complex - a bit more like calculus than simple arithmetic. The outbound equation is considerably better understood, and significantly simpler to address. For starters, any one of the big SIP providers, like Bandwidth.com, Level 3, or the like, can route your outgoing calls over a SIP trunk. All you need to do is modify your own routing to send those calls over the trunk in question.

The only issue that comes up here is that local calls that get routed through one of these carriers will be charged as toll calls. However, if you’ve established the local services for inbound calls that I talked about earlier, you can use the same trunks for outbound calls, which results in a much better and more cost-effective rate than sending them over an inter-exchange carrier.

Other services

While incoming and outgoing activity represents the bulk call volumes, there are some other services and lesser used call types that still play a factor when the goal is to remove TDM. Each of these must be tackled as part of a larger implementation, so it’s important to understand what they are in advance.

911

While 911 is very lightly used, it is a critical function of any phone service provider. If you’re lucky, there may be some local efforts to move the PSAPs away from MF or SS7 trunking and over to VoIP. However, this is handled on a state-by-state basis, so there are no guarantees in this area.

When that situation arises, you can use one of the third party services that are specifically designed to provide 911 access to VoIP carriers. This ensures that all legal requirements are met, and subscribers have definitive access to essential emergency services when the need arises.

One such service is operated by West (who purchased Intrado) which can ensure your services meet all FCC regulations.

Other Calls

There are a variety of other calls that need to be addressed as part of your elimination of TDM.

Operator calls may need to be re-routed through a toll-free number to ensure they reach the proper destination. While this can be an additional cost, the use of such services has diminished significantly since the kind of information people typically required is highly accessible by other means.

Caller ID, or CNAM, is another service that must be considered when you’re working to eliminate SS7 from your network. Often, the easiest solution is to use an IP-based interface through service providers, like Neustar or OpenCnam, which can ensure that the desired information is displayed and received properly.

To manage toll-free calls, the option of routing them over SIP LD carriers is often the most efficient implementation, which can make it a smart choice is the vast majority of scenarios.

For LNP queries, you may have options. First, if you choose to use local trunks through Inteliquent or Peerless Network, they may be able to handle your outbound traffic undipped, for a fee (of course). Second, for as long as you still maintain your own A-links, then you can obviously perform the queries yourself prior to routing the calls, removing the need to have a third party involved at all.

What about SIGTRAN?

My goal in this article has been to demonstrate that you can remove SS7 from your network entirely and still operate as a regular CLEC or ILEC. However, it’s possible that, in your territory, all of the pieces don’t quite fit together yet. Not every third-party service provider is available in every area, and some locations may find that there aren’t any providers available at this time for certain segments of the process above.

In that case, SIGTRAN – a technology that allows you to transport SS7 over IP – could enable you to maintain SS7 service without actually retaining any TDM media gateways.

SIGTRAN encompasses a series of protocols, which are an extension of the SS7 protocol family. It operates within the same SS7 paradigm, but uses SCTP in place of TCP or UDP, carrying PSTN signaling over IP.

Technically, this option isn’t ideal. But, it’s still a good option to have up your sleeve if you’re dedicated to moving away from SS7 and TDM media gateways but are otherwise hobbled by local availability of third-party options.

Is it worth it?

In the end, what it really boils down to is the simple question: is it worth it? Whether or not making the transition is right for you depends largely on your specific situation.

There are two big benefits of becoming a pure VoIP carrier. First, you are no longer beholden to a specialist TDM media gateway, a costly venture that often requires replacement every few years due to the traditional hardware obsolescence cycle. Second, you can save money on the ongoing costs associated with TDM transport and SS7 links, often to the point of offsetting any additional costs that may be involved in the implementation of new service contracts with third-party providers.

If you’re a small carrier, the best option may be to give up your numbers to a third party and coordinate with a company like Bandwidth.com or Level 3 to receive your numbers and associated service. Yes, you do end up paying more per minute than you would otherwise, and you have a monthly per-DID charge to contend with for each telephone number. But, at your size, the capital costs are more significant than the usage charges in the vast majority of cases, making this an option worth investigating.

If you’re a larger carrier, then losing your CABS compensation could be enough to justify keeping your own numbers. Of course, the FCC are phasing out termination charges over the next few years, so this may not matter for long, but if you’re keen to maintain your own DNs you can explore the path I’ve described in this article and use Access Homing Tandems and Local Transit services to achieve the most value and cost savings.

There’s a fair bit of work involved in putting all of the pieces together, and you may find that even a partial implementation provides you with significant benefits, giving you a financial (and possibly mental) boost as you move through the process. But, long-term, it would be worth the effort if you can stop worrying about specialist hardware availability and the high replacement costs associated with TDM media gateways.

What's next?

If you’d like to discuss your own situation in more detail, then please contact me, and we can arrange an initial consultation to determine the ideal course of action based on your present circumstances and overall goals.

Also, make sure you download your TDM-free calculator to see how much you could save (or not) by becoming a VoIP-only carrier.

In 14 years at Metaswitch Andrew Ward worked in engineering, support and operations. As Director of Support he created the Metaswitch Commissioning Team which was responsible for the initial configuration and PSTN migration projects for new Metaswitch customers.

He now runs Andrew Ward Consulting LLC, where he works with service providers on everything from critical technical issues to network evolution planning to strategic business decisions. Please contact Andrew for more information.