Seamless roaming and service migration carry special importance due to their very direct impact on subscribers and the quality of service they receive. It is therefore paramount that 4G LTE deployments provide some level of interworking too ensure subscribers are not only guaranteed seamless service, but can perceive and make use of the advantages 4G LTE network provide. As it turns out, much of the solution to provide proper interworking for 4G LTE networks involves interworking with the Diameter protocol.
The best method for approaching the interworking problem is to break it down into the following three steps:
1. Define interworking
2. Identify the functions requiring interworking
3. Design the methods to provide interworking for those functions
Define Interworking
We need to define interworking and the types of interworking to be supported. There is no standard definition for the term interworking. Instead of attempting to define such an all encompassing term, defining what an interworking solution needs to provide for a specific problem is more appropriate. Here are the basic assumptions to the interworking problem when applied 4G LTE networks:
1. Interworking implies the successful communication between varying Diameter protocols and between Diameter and other protocols. A more specific definition might limit a feasible solution to be called true interworking.
2. Interworking provides a degree of seamlessness to subscribers capable of transiting between differing Evolved Packet Core (EPC) networks. Subscribers capable of roaming or moving among disparate networks should be able to access basic service seamlessly (i.e., originate and receive communications services as usual). Since many features may not be compatible, their use may not be supported while roaming.
3. It is not feasible to provide an interworking solution enabling full compatibility between differing Diameter or other networks. Since Diameter variants may be so different, it may not be reasonable to provide interworking of each and every function between networks.
4. Signaling protocols providing network and transport layers between Diameter and other networks are somewhat compatible. This is a reasonable assumption based on the underlying network layer technology (i.e. SS7 and IP); however, there are sure to be issues when considering IPV4 vs. IPV6 networks or other variants at the SCTP layer.
5. Multi-mode mobile stations supporting the many disparate bandwidths and RF types are used to access the disparate LTE EPC networks. Without a multi-mode MS, it may not be feasible to provide access to multiple LTE EPC network types.
6. The subscriber has a single subscription allowing access to multiple LTE networks (rather than having multiple subscriptions, one for each network, which requires no interworking). From a subscriber perspective, it is usually unreasonable to support multiple different subscriptions for multiple different networks.
These assumptions simplify the basic problem and permit a basic solution to be implemented that can evolve so that these limitations can potentially be removed.
Identify the Functions Requiring Interworking
Instead of taking a protocol-centric approach, i.e. which interfaces require which protocol translation under which conditions; we can view interworking from a functional perspective. The most necessary functions with respect to EPC Diameter fall within the scope of mobility management, voice call processing (VoLTE/IMS), charging and policy management. Examples of some of these functions are:
• Mobile device service qualification
• Mobile device location management
• Mobile device state management
• Mobile device and service authentication
• Service authorization
• Intersystem handover
• Call and data session establishment
• Call and data session features and control
• Application of policy and charging rules
If we define the interworking, call flows and protocol translation based on these particular functions, it is possible to derive a competent solution to overall LTE network interoperability.
Design the Methods to Provide Interworking for those Functions
To provide interworking between disparate protocols, three areas need to be addressed:
1. Protocol conversion
2. Database mapping
3. Transaction management
Protocol conversion provides the translation of messages and parameters from one protocol to the other. Database mapping provides the translation and management of information elements that allow each of the application protocols to provide user service (e.g., subscriber identification, location, and status information). Transaction management enables the completion of queries among the disparate networks (e.g., re-originating and maintaining queries and responses from one network to the other).
By using a basic methodology as described here, interworking can be prioritized and phased into 4G LTE network. Basic services such as authentication and basic data roaming can be phased in first, while other more complex services such as basic VoLTE and then enhanced calling features can be added later.
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...Randy
Randall A. Snyder
Wireless Cellular Telecommunications Consulting
Wireless Research Services, LLC
Mobile: +1 (702) 521-7900
Email: rsnyder@wrsvs.com
Skype: randallsnyder
http://www.wrsvs.com
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