F5’s Ohad Ramot explains the challenges of translating signals between a 4G network using Diameter signaling and 3G networks using legacy SS7.
It’s widely known that LTE (4G) networks are spreading rapidly and are being deployed all over the globe. However, while 4G networks are growing, 2G/3G networks still serve most of the subscribers as they have been doing successfully for the last decades, and it seems these legacy networks are here to stay for a while. This requires operators and roaming mediators (IPX) to face the challenge of maintaining and interacting with both network architectures in parallel.
4G and 2G/3G network architectures differ in many aspects. One of the major differences is the signals mechanism that enables network nodes to interact with each other for authentication, billing, subscriber profile provisioning and more. While 2G/3G signaling mechanism is based on SS7 protocol stack, 4G networks use the relatively modern Diameter protocol on top of TCP/SCTP/IP stacks. Although both signaling methods provide solution to the same set of problems, they stem from different architectures and design philosophies.
As a result, many 2G/3G network elements cannot interact directly and seamlessly with 4G network elements. A solution is needed for all those cases where this inter-network communication is required.
Common examples for such scenarios could be:
- An operator that has started deploying a 4G network but hasn’t covered all areas, and its 4G subscriber might be in a geographical area where only 3G coverage is available.
- A 4G subscriber who roams to a foreign 3G network. In this case, the hosting 3G network needs to interact with the home 4G network of this subscriber
- The same could be if a 3G subscriber who owns a device supporting 4G roams to a 4G network. The device will connect locally to the 4G hosting network, which will need to interact with the home 3G network.
An Interworking Function (IWF) solution enables an LTE network to have an extension towards an SS7 network. It provides the capability to translate Diameter signals to their corresponding signals on MAP and vice versa. This translation is based on a 3GPP specification.
However, the challenges faced during the development of this were not only “translate this attribute on MAP to that AVP on Diameter”, but involved the different behavior of the application. For example, a DRA such as our F5 Signaling Delivery Controller (SDC) has to behavelike a 4G network node when it interacts with a 4G network, while simultaneously behaving like a 2G/3G network node on its other interface.
An example for this “behavioral translation” (which is beyond mere protocol conversion) are some flows of simple Diameter transaction of Request-Answer, which turn into complex flows containing several requests and answers dialog between IWF and its SS7 peer. Some of these different behavioral aspects were not even covered or defined in any spec and we had to invent our own ways to implement them.
And, as always keeping the future in mind, our current design has enough flexibility to be enhanced for more SS7-wise applications, besides mere Diameter-SS7 interworking. One example of such enhancement is enabling our SDC to act as an enhancement of 3G STP for smart manipulations of MAP messages, which the latter cannot do. Another example is to make SDC translate RADIUS authentication on requests from Wi-Fi domain to 3G HLR on traditional telephony domain.
To summarize, the development process of such an application gives developers the opportunity to be pioneers, to creatively think of solutions, and overcome new challenges. We believe that having the F5 SDC act as a bridge between the new and the old worlds of telephony signaling enables F5 to enlarge and strengthen its footprint in this very important domain.
Ohad Ramot is a principal software engineer with F5 serving as the team leader of protocols and application team dedicated to the Signaling Delivery Controller (SDC), the Diameter signaling management solution. He has been in software development for the telecommunications industry since 2001. He holds a BSc in Computer Science and a MBA from the Hebrew University of Jerusalem.
The Signaling Focus Day at the LTE World Summit is taking place on the 23rd June 2014, at the Amsterdam RAI, Netherlands.