No. 2 cellular company Verizon Wireless and vendor partners Cisco Systems Inc., Lucent Technologies Inc., Motorola Inc., Nortel Networks and Qualcomm Inc. on Thursday announced an initiative to complement existing IMS standards with something generically called Advances to IP Multimedia Subsystem, or A-IMS, which Verizon plans to rapidly implement into its road map, paving the way for mobile VoIP.
A-IMS focuses on areas not fully addressed by IMS today, such as support for non-SIP-based VoIP and other services on next-generation networks – a gating factor for legacy service providers looking to transition their networks. IMS is designed to assure standardization of access-agnostic multimedia services across all interconnected networks. How to get there is the question.
“We applaud the visionaries who have done a great job developing IMS over the last few years,” said Dick Lynch, executive vice president and CTO at Verizon Wireless. “But as we approached implementation planning, it became apparent that there are some practical, real-world issues that need to be addressed if we are to transparently and completely deploy and maximize the use of this new architecture. To us, it is also important that it be built to support the bridging of the present non-IP reality as we transition to the future.”
The task force plans to home in on quickly enabling true, access-to-core mobile VoIP as a viable replacement for existing cellular voice, along with providing end-to-end security features and expanding fixed services into the mobile market, such as IPTV.
The company has been working for nearly a year with a task force of the industry's "best and brightest" network engineers and strategists to develop enhancements to IMS, Lynch said. The task force has produced a concept document and an architecture document, and is in the process of submitting its suggestions to 3GPP2, 3GPP and TISPAN.
“This joint task force has defined the missing transition step from today to pure IP architecture, and knowledge learned from this effort will help us in development of seamless mobility solutions using this new architecture,” said Fred Wright, senior vice president for North America at the networks and enterprise division at Motorola. “We see operators adopting A-IMS to deploy a unified platform for the rapid deployment of new services, including SIP-based interactive applications and non-SIP applications, all of which run on top of IP.”
The Details:
The A-IMS standard is based on several key architectural principles, including:
- Comprehensive Security: Security is more than authentication, and involves all components in the network, including the devices. Indeed, security agents run on the network devices, providing reverse-firewalls to protect the network from the device and to aid in posture assessment during logon. Comprehensive security also requires the security manager to monitor the network at all times, determine baseline traffic patterns, and then use those to detect and respond to anomalies. To respond, the security manager can change server configurations, install firewall rules or modify intrusion detection services (IDS) behaviors.
- Uniform Treatment of SIP and non-SIP Applications: To the greatest degree possible, A-IMS allows the service provider to manage and control both SIP and non-SIP applications in a uniform way. This is done primarily by usage of the policy manager (PM), which allows the service provider to manage the usage of network resources on behalf of both types of applications. Key network functions, including mobility, roaming and packet accounting also are defined in ways that allow them to support both types uniformly.
- Dual Anchoring: A-IMS provides a mobile terminal with two IP addresses – one anchored in a bearer manager (BM) in the visited network, and one in a BM in the home network. Service provider policy controls which address is used for which applications. This allows for latency sensitive applications to use the visited anchor, whereas applications that require greater levels of service provider control can use the home anchor.
- Three-Layer Peering: When connecting to roaming partners, peering occurs at three layers: security peering, used for access authentication; IP peering, used for transport of bearer traffic; and policy peering, used for control of bearer services. Policy server peering involves the usage of a policy server in both the home and visited networks. Usage of two allows for the home provider policies to apply even while roaming, yet allows them to be tempered by visited network policies on usage of the network.
- Multi-Tiered Service Interaction Management: Feature interaction management across SIP-based applications, and between SIP and non-SIP applications is provided. Feature interaction management is linked with network policies, allowing for application interaction decisions to take into account the state of the network. The architecture also allows for extensibility to new interaction resolution mechanisms through the addition of service interaction application servers.
Highlights of the A-IMS plan clearly define several "pillars" as essential to the architecture:
- BM: Allocates resources and manages bearer traffic to meet customers' service quality requirements. The primary functions include policy enforcement, mobility management, security, accounting and access control.
- PM: A primary policy decision point for network policies, deciding the ways that the underlying network supports applications on behalf of subscribers and visitors to the network.
- Application Manager (AM): The SIP services platform in the network that authorizes access to SIP services, provides SIP registration and authentication functions, and is responsible for the invocation and management of SIP-based features.
- Security Manager (SM): Responsible for monitoring the network for security threats and responding to them in real time, making decisions on what devices are allowed access to the network based on their posture – a measure of the safety of the device based on the freshness of its software patches and security features.
- Services Data Manager (SDM): The main repository of subscriber and network control data, and collects and stores charging data for the network.
