Diameter vs SS7
Diameter and SS7 are signalling protocols generally used in telecommunication systems. Diameter is highly used in 3GPP latest releases for AAA services (Authentication, Authorization and Accounting), while SS7 was initially used with PSTN and GSM networks for digital signalling between different nodes for call management and other services management. Diameter protocol run over the IP network, while SS7 can be used in digital channels such as on E1 based TDM (Time Division Multiplexing) networks directly.
Diameter protocol was derived from RADIUS (Remote Authentication Dial In User Service) protocol with a number of improvements. This protocol is used widely in 3GPP Release 5 onwards, where there is a need for AAA services. Emerging new technologies in communication that have been built on total IP networks have shown an increased requirement for access control mechanisms more than ever due to security concerns. Therefore, Diameter protocol was developed as a framework for future AAA services with enhancements to existing RADIUS protocol. Diameter protocol was designed as peer to peer architecture even though, it looks like a server client protocol in the implementation. As per the Diameter protocol there is a node called diameter agent, which does either message relay, proxy, redirecting or translate function. Since Diameter protocol uses synchronous message exchange format, there are specific responses for each request message. It uses Attribute Value-Pairs (AVPs) to transfer these messages between nodes. Diameter uses IP networks as its medium, and runs on top of TCP (Transport Control Protocol) or SCTP (Signalling Control Transport Protocol), where it can have more reliable communication.
SS7 (Signalling System No. 7) was developed to call management and service signalling requirements of the digital networks based on the full duplex channels. In general, different variants are developed all over the world for SS7 where, North American version is called CCIS7, while European version is called CCITT SS7, even though there is one version defined by ITU-T in its Q700 series. In SS7 network structure, the nodes are called signalling points, while the connection between those nodes is called signalling links. In SS7 networks Signalling Transfer Points (STPs) are introduced to relay and route the messages between signalling points. SS7 has point to point architecture with one to one physical correspondence between two signalling points. SS7 structure initially developed to have compatibility with OSI (Open Systems Interconnection) model as well. Message Transfer Part (MTP) 1 to 3 used in SS7 are similar to OSI first 3 layers, while SCCP (Signalling Connection Control Protocol) in SS7 protocol provides the connectionless or connection oriented communication between signalling points.
What is the difference between Diameter and SS7?
– Both SS7 and Diameter are signalling protocols that are used in different eras of telecommunication.
– Diameter protocol provides communication between network nodes with enhanced access control on top of IP network, while SS7 protocol defines all layers of OSI with support for legacy TDM (Time Division Multiplexing) networks.
– As per the diameter, the network node can act as either a client or a server for two different connections, while in SS7 each node is given a separate signalling point code to identify them within a network.
– As per the IMS (IP Multimedia Subsystem) architecture and latest 3GPP releases, most of the interfaces use Diameter protocol, while GSM architecture (2G networks) uses SS7 protocol. SS7 signalling can be implemented on top of IP network in order to support the nodes that do not have diameter functionality using a signalling gateway which function the interworking between different layers of SS7 and OSI.
– Both protocols are used for communication between network nodes, where SS7 protocol mostly focuses on all call management and other service level communications, while Diameter protocol mostly gives the access control and accounting based services on top of IP network.