For Voice service providers relying on SS7 for signaling, the migration from TDM-based SS7 to SIGTRAN over IP is becoming an urgent necessity. Rising TDM costs, mandates from SS7 providers, aging infrastructure, and the energy inefficiencies of legacy systems are driving this transition. Major network operators, including Verizon, Syniverse, and TNS, are moving away from SS7 over TDM A-Links in favor of SIGTRAN over IP. While the benefits of SIGTRAN are compelling, the transition requires careful planning to ensure reliability, security, and optimal performance. With the proper strategy you can see big energy savings, grow team skills, and improve your overall network performance.
Why Migrate to SIGTRAN?
Traditional SS7 signaling has historically depended on dedicated TDM links, usually accessed in the form of A-Links in a DS0 on T1/DS1. SIGTRAN, which transmits SS7 messages over IP networks, offers several potential advantages:
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Cost Savings: Eliminating dedicated TDM circuits reduces both infrastructure and operational costs.
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Energy Efficiency: TDM equipment is focused on a single task, while IP-based solutions leverage more modern, efficient networking hardware, sharing the same power consumption across multiple jobs. For example, the same routers and switches can be used to offer broadband services as are used to transport call control data.
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Flexibility: SIGTRAN allows operators to consolidate signaling over existing IP infrastructure.
However, migrating to SIGTRAN is not just a simple plug-and-play operation. There are several factors to consider. With the right strategy, you can make this a boon for your Voice network.
Questions to Ask Before Migrating
To ensure a smooth migration, network operators should ask themselves the following questions:
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What SIGTRAN capabilities do we already have? Before investing in new hardware, check if existing network equipment has SIGTRAN functionality that has never been configured. You might find opportunities to save on equipment purchases and maintenance licenses?
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How will SIGTRAN affect our existing network infrastructure? Merging SS7 traffic onto IP networks introduces new complexity. Are the routing, firewall, and quality of service (QoS) policies in place to handle this? Do we have the right technical knowledge, or is additional training/experience necessary?
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What are our redundancy / failover strategies? Do we have diverse routes and SCTP multi-homing configured to prevent single points of failure?
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Do we need to deploy dedicated VPNs for security? SIGTRAN over the public Internet introduces new risks. Most telecom equipment capable of supporting SIGTRAN was not designed to be connected directly to the Internet with no filter. Have we accounted for secure transport mechanisms?
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How will we monitor SIGTRAN performance? Do our teams have the necessary tools and training to diagnose network congestion, signaling delays, and failed calls? Can we detect the SIGTRAN delivery problems independently of reports that "calls are dropping"?
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Are our firewalls correctly configured for SCTP? SIGTRAN uses SCTP instead of TCP or UDP, requiring firewall adjustments. Do we have experience filtering and monitoring SCTP over IP?
Reliability: Keeping SS7 Traffic Running Smoothly
When shifting from a dedicated SS7 network to an IP-based system, reliability is paramount. While the timing isn't as crucial as TDM delivery performance, SS7 timers do expect reliable, low-latency delivery. TDM-based SS7 links were highly specialized, whereas SIGTRAN merges SS7 traffic onto broader network infrastructure where congestion and packet loss are common. While this reduces equipment and energy costs, it also introduces new complexities:
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Managing network congestion: SIGTRAN traffic now competes with other IP-based services. If Internet congestion occurs, it can cause call setup delays or failures. This may be a great time to look at upgrading Internet connectivity for your organization, both ensuring better general data performance and reliable SIGTRAN.
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Ensuring redundancy: Unlike traditional SS7 links, which had dedicated failover mechanisms, SIGTRAN deployments must be engineered for failover using IP-based redundancy techniques such as SCTP multi-homing and diverse routing.
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Understanding SCTP: Unlike TCP or UDP, SIGTRAN relies on the Stream Control Transmission Protocol (SCTP), which provides benefits like multi-homing and message sequencing but requires careful firewall configuration.
Security: Protecting SS7 Signaling Over IP
SS7 security has long been a concern, and moving to SIGTRAN over IP introduces new risks:
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Dedicated VPNs are usually necessary: Many operators implement a VPN specifically for SIGTRAN signaling to mitigate potential security threats.
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Firewalls must be properly configured: Unlike TCP-based traffic, SCTP-based SIGTRAN traffic requires different firewall rules.
If you're running with an older firewall for your voice network, this may be the right time to assess the situation. Firewalls are less expensive (in terms of Dollars Per Megabit-per-second) and easier to virtualize than ever befoer.
Compatibility Challenges: Does Your Network Already Have SIGTRAN?
One of the key question in migrating to SIGTRAN is compatibility with existing SS7 infrastructure. Some legacy SS7 equipment lacks SIGTRAN support, requiring the use of external appliances like TDM Link Replacement (TLS) devices. However, many operators may already have SIGTRAN-capable components within their network that they have never utilized.
Vendors such as Metaswitch (Microsoft / Alianza) have been offering SIGTRAN-capable systems for years. Before purchasing new hardware, network teams should conduct a thorough assessment of their existing infrastructure. As Fred Brooks, a pioneer in computer science, once said: You can get something for nothing if you have previously paid for something and gotten nothing from it! It's completely possible you've been operating SIGTRAN capable equipment without getting its full benefit.
Managing SIGTRAN Over Shared Internet Links
Since SIGTRAN runs over IP, many providers consider running it over their existing broadband connections. However, this introduces performance risks:
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Congestion risks: If the Internet link is shared with broadband customers, SIGTRAN signaling can suffer from packet loss and jitter, causing call failures or other bizarre intermittent issues never experienced on TDM calling beore.
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Traffic prioritization challenges: While QoS techniques can help, prioritizing inbound traffic from the Internet is inherently difficult. If you're connected to an upstream provider and the data from the Internet through that provider is greater than your link can support, then the SIGTRAN data will be delayed.
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Dedicated SIGTRAN transport: Specialized Internet links or MPLS circuits can improve reliability and reduce latency. Alternately, an SD-WAN deployment could give you higher reliability without the expense of dedicated transport equipment and links.
It could be that this is a great motivation to improve your network connectivity to the Internet. Many TDM operators have redundant Internet links, but still experience congestion on the links that would interfere with reliable TDM calling.
Performance Monitoring and Troubleshooting
Network teams accustomed to traditional TDM monitoring tools may need additional training to manage SIGTRAN performance effectively:
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New monitoring techniques: Understanding SS7 over IP requires knowledge of SCTP, IP routing, and firewall configurations. Your teams deserve to get hands-on expertise in these systems before they have to troubleshoot critical problems.
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Advanced troubleshooting skills: Teams must be prepared to analyze packet flows, detect congestion points, and diagnose signaling delays. Packet capture systems will be extremely helpful for troubleshooting call setup/teardown challenges.
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Proper tooling: Investing in SS7-over-IP monitoring solutions can help maintain high service quality.
Conclusion
Migrating from SS7 over TDM to SIGTRAN over IP is an inevitable shift for many telecom operators. While the benefits of cost savings, scalability, and efficiency are clear, the transition requires careful planning around reliability, security, and performance management.
- Invest In Your People: Get your staff hands-on technical experience with routers, switches, and firewalls to be fully prepared and comfortable running the service. ECG offers in-person classes with hands-on access to routers and switches.
- Invest In Your Network: Modern firewalls are necessary to allow you to respond to the latest threats.
- Invest In Your Services: In some cases, upgrading your network connectivity will be essential to providing reliable calling service using SIGTRAN. IT's a good time to eliminate congestion within your core network (such as the fiber broadband network you operate).
By assessing existing capabilities, properly configuring networks, and implementing robust monitoring, providers can make a smooth transition to SIGTRAN while maintaining the high standards required for SS7 signaling. For those navigating this transition, expert guidance can be invaluable. ECG has over 30 years experience with TDM voice and 25 years experience with Carrier-Grade VoIP. We are glad to provide training, simple Q&A consulting, or staffing for the long-haul of your project.
