Application Platforms

At the most general level, a network can be conceptualized as a mechanism, frequently drawn as a cloud, connecting any subset of (people, data, applications) together. SIP/IMS is optimized for connections involving people to people and data, because the session holding times are typically long and the user-interface properties have to suit people (audio, video adapted to the terminal device capabilities).
Add a note hereWhen applications connect to applications, they exchange formatted byte streams. The sessions can be ultrashort, and protocol support is required to choreograph sessions, as there is no human common sense to rely upon. This is the world of computer record exchange, remote procedure calls, asynchronous communications, transaction capabilities, and session management protocols. XML has emerged as the syntactic framework of choice for application internet-working, and both Microsoft and the Java communities have developed application platform architectures. These platforms are Microsoft’s .NET and the Java community’s Java EE (Java Platform, Enterprise Edition) respectively. They run on computer servers connected to the Internet and provide a preexisting platform onto which E-business applications can be installed. Java EE and .NET systems talk across high-quality IP/MPLS transport networks. Carriers get to play by providing a JAVA EE or .NET hosting service so that customers can install their applications via standardized interfaces. The carrier may also provide many other useful services:
§  Add a note hereData backup and restore,
§  Add a note hereHosted application development environment,
§  Add a note hereManaged applications, web server, application server,
§  Add a note hereCaching and content distribution services,
§  Add a note hereSecurity monitoring.
Add a note hereIt is fair to say that hosting of application platforms is at the cutting edge of hosting services today. Most carriers are happier providing managed servers, network connectivity, and application monitoring on top of operating systems such as Windows and Unix/Linux.

The Road to IMS

Add a note hereAs the early experiments with voice over IP evolved into services with significant usage, it was clear that a multimedia signaling protocol was required, analogous to the signaling used in the existing telephone networks (most notably common channel signaling system 7 often loosely referred to as SS7). Multimedia signaling over IP networks was always going to be more complex. User terminals had to negotiate with each other to determine their media-handling capabilities, and with the network to request the quality of service they needed. There were issues of security, and problems in finding the IP addresses of other parties to a call.
Add a note hereThe carriers, through the ITU, had an existing protocol suite, H.323, which had been developed for LAN-based video-telephony. This was pressed into service in first-generation VoIP networks, but its clumsiness and lack of scalability triggered activity within the IETF to develop a more IP-friendly, extensible and scalable signaling protocol. Over a period between 1996 and 2002, the IETF developed the Session Initiation Protocol (SIP) as the end-to-end signaling protocol of choice for multimedia sessions over IP. SIP languished for several years, waiting for other developments to catch up, when perhaps surprisingly, the initiative was taken by the cellular industry.

Add a note hereThe Third Generation Partnership Project (3GPP) was set up in 1998 to specify a third generation mobile system evolving from GSM network architecture. At the same time the 3GPP2 organization was set up by standards bodies in the US, China, Japan, and South Korea to fast-track a parallel evolution to third generation mobile, evolving from the second generation CDMA networks prevalent in those countries.
Add a note here3G mobile architecture had originally used ATM, but by 2000 it was clear that the future was IP.

Arrangements were therefore made to set up formal links between 3GPP/3GPP2 and the IETF to develop IP standards for 3G. The 3G subsystem that handles signaling was the IP Multimedia Subsystem (IMS) and was based on the IETF’s SIP. But in the IMS architecture, SIP had to do a lot more work. For example, users may want to set up preconditions for the call to be made (e.g., QoS or bandwidth) before the called party is alerted, or they may need information on their registration status with the network, and terminals need SIP signaling compression on low-bandwidth radio access links to speed-up transmission and reduce contention for bandwidth.

Add a note hereWhat the 3GPP communities really needed was an architecture that could standardize the interrelationship between the many functions needed to bring 3G multimedia services into commercial reality. Such an architecture would have to integrate many different protocols (signaling, authentication and authorization, security, QoS, policy compliance, application service management, metering and billing, etc.). To deal with the many new developments to SIP (and other protocols) that were needed to make the IMS architecture work, a joint 3GPP-IETF group, SIPPING, was set up.

Add a note hereAs the 3G Mobile architecture evolved, it came to the attention of architects and standards people working on evolution for the fixed network operators. This Next-Generation Network activity, carried out in bodies such as ETSI TISPAN and the ITU-T NGN program, had a similar requirement for an all-IP signaling layer and session management architecture. IMS essentially fitted the bill, and was adopted, although further changes and developments are in the future roadmap. So, for example, BT’s twenty-first century network architecture will eventually have IMS right at the center.

Add a note hereIMS has been described as “mind-numbingly complex.” This may be true, but the complexity is there for a reason. IMS provides common services to: user terminals, network-based application servers, network routers, policy engines, billing systems, and foreign networks for roaming capabilities. It provides for authentication, registration and security. It supports presence and instant messaging, and new services such as Push to Talk over Cellular (PoC). By doing so much, through standard interfaces, the intent of IMS is to remove the need for new services to re-invent these wheels. IMS-powered services should therefore be lighter-weight and be more easily introduced. Carriers believe they will take a one-time hit to get IMS into their networks, and will afterwards reap the benefits over subsequent service introduction.

Add a note hereAt the lower layers of the network, there was little dispute as to who provided the service. Running optical/SDH transmission networks, and running IP networks is pretty much definitional as to what carriers do. But as we get higher in the stack, the focus turns more to applications running on servers that exploit the IP network for connectivity. You don’t have to be a carrier to run servers. In principle, a multimedia telephony company could run IMS in a garage. IMS is not precisely designed to do this, because it was conceived by carriers, who arranged for a high degree of potential coupling between the IMS layer and the IP layer. However, this coupling does not have to be turned on, and may not even be necessary for many service concepts, rescuing the garage option. Or perhaps the carriers could be encouraged to expose the necessary IP transport layer interfaces specified in IMS to third parties? And, of course, multimedia telephony companies who do not use IMS today (e.g., Vonage, Skype) do indeed build their businesses on servers (rather few in Skype’s case) and then buy-in the Internet connectivity they need.

Add a note hereA generalized, powerful, and complex session management platform such as IMS is rather pervasive and there may be a case for it being provided by a specialized ISP, or a facilities-based carrier (a carrier that owns telecommunications equipment—normally fiber, transmission equipment, routers and switches). However, when it comes to providing a discrete service such as music download, access to streaming audio or video, or any specific application service, there is little reason to believe that facilities-based carriers have some special advantage. Most of us don’t do our Internet banking with the company providing our broadband connection. This should be a warning to carriers not to go too far down the “walled garden for content or value-added services” path as the route to future margin success.