1. Discussion Issues on IMS-based NGN
Jun Kyun Choi
Information and Communication University

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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