Discussion Issues on IMS-based NGN Jun Kyun Choi jkchoi@icu.ac.kr Information and Communication University

Contents Interoperability between IMS-based SIP and IP-based SIP Two Different Control and Management Structures Some Limits of IMS on transport network Interfaces No Traffic and Congestion Control of IMS Business of Customers and Application Providers are Tightly Controlled by the IMS Cost Competitiveness of the IMS Approach Some Concerns on the IMS-based NGN

Interoperability between IMS-based SIP and IP-based SIP Interoperability between IMS-based SIP and IP-based SIP brings to conversion overhead IP-based SIP needs to convert to IMS-based SIP Not just for the SIP including packet format We have to concern the operation and management environment If the IETF develop some new services and applications, it should be converted to the IMS-based SIP environments at every instance The IMS-based SIP environments should be checked to support open service architecture including Open API concept

Two Different Control and Management Structures Softswitch-based Control & Management are clearly different from the IMS-based C&M The existing softswitch running E.164 and IP address does not need the complicate signaling structure like the IMS-based CSCF The roaming and end user mobility are the mandatory functions at IMS-based CSCFs, but it does not need to be mandatory for such environment using softswitch If the softswitch system includes the gateway functions, the IMS-based control and management functions should be modified The IP-based systems like AAA and HA/FA etc. have to be modified to support the IMS-based environments. Then, all the IP-based (in alignment with IETF standards) equipments should be checked and modified to support the IMS-based environments. The existing IP-based network carriers may be difficult to compete for the IMS-based NGN

Some Limits of IMS on Transport Network Interfaces The IMS-based Control and Management only provide the transport network Interfaces over GGSN and SGSN The current IMS systems only have the interfaces of SGSN/GGSN, they could not support the IP-based transport system (that is, router and IP server, etc.) The existing IP routers and L2/L3 Switches do not have the interface from the IMS system The existing IP network could not build the session paths required from the IMS system, It means that all the existing IP equipment could not relevant to support the IMS environments The MPLS routers or the Flow-based routers can support the IMS system with some enhancements of control and management interfaces The problems is the facts that the existing IP network could not be used for IMS environments For VoIP application, the existing IP network can support the IMS environment since it does not need to build up the session path, For the multimedia session paths more than several Mbps, the existing IP network should be modified in order to support the IMS environment But, the existing GGSN/SGSN is good for the IMS environments without any change of existing network structure

No Traffic and Congestion Control of IMS The IMS-based control and management plane does not have the QoS/TE control capability on the physical transport network The IMS control plane could not monitor and detect the physical traffic situations Difficult to support the packet-based charging structure No congestion control mechanism from the IMS control plane In addition, the call signaling plane is independent from the physical transport plane The routing of IMS control plane is different from the routing of physical routing plane

The IMS try to control all the Internet Business Business of Customers and Application Providers are Tightly Controlled by the IMS The IMS try to control all the Internet Business IMS integrates the subscriber management capability as well as session control capability The subscriber management including authentication should be independent on the session-based control Users don’t have any choice other than IMS services the existing web service does not need the IMS procedure All the application providers could not make any business model without help of IMS provider The IMS carrier manage all the information value chains from information sources to customers The IMS carrier have a control capability of all the application providers and service provider by using service profiles

Cost Competitiveness of the IMS Approach Cost Competitiveness of the IMS service is questionable ! In view of the non session-based service, the IMS bring a kinds of additional overheads Especially, short message or web service do not need the IMS service environments. They only need simple authentication and subscriber management procedure. The network elements using IMS services suffer the unnecessary cost competitiveness to handle the session based control The IMS solution needs to check the cost competitiveness rather than the pure IP router solutions

Some Concerns on the IMS-based NGN Identification, Addressing and Naming Rules For user identification, access interface, routing  Eventually, IP address would be inevitable Wireless Interface including bandwidth GPRS Tunneling Protocol is not relevant IP-based Integrated Access both for Wireless LAN and GPRS  Optimal wireless MAC Protocol are needed for IP delivery! Routing and Forwarding at the Core network TDM-based packet routing and forwarding are not acceptable  Integrated into IP-based routing and forwarding