One observation from our deployments: Apart from 3GPP standard interfaces, we see many vendors using Diameter for custom applications. Two examples: A security platform vendor uses Diameter accounting application (CCR/CCA) to communicate SMS data (and metadata) between the network and the platform. Another SP is using ETSI E2 to exchange user related information between P-CSCF and a dedicated server.
Reasons are obvious:
- Diameter being extensible, it is easy to develop custom extensions.
- Protocol is already in the network, so doesn't add additional complexity
- Network has the tools and mechanism to manage Diameter traffic.
If this interests you, we have a case study on such a deployment: http://www.lcnpl.com
