**1. Introduction**

50 Telecommunications Networks – Current Status and Future Trends

Conference on Volume 2, Issue , 20-22 Aug 1997 Page(s):883 - 886 vol.2 Zukerman, M.; Neame, T. D.; Addie, R. G. (2003). "Internet Traffic Modeling and Future

Technology Implications" Proceedings of Infocom, 2003.

PACRIM 1987-1997 - Networking the Pacific Rimapos;. 1997 IEEE Pacific Rim

QoS management(Raouyane B. et al., 2009) mechanisms as defined by 3GPP can be viewed as a network-centric approach to QoS, providing a signalling chain able to automatically configure the network to provision determined QoS to services on demand and in real time, for instance on top of a DiffServ-enabled network. However, to envision a deployment of such technology in a carrier-grade context would mean significant further effort. In particular, premium paid-for services with SLA (Service Level Agreement) contracts such as targeted by IMS (Poikselka and Georg, 2009)networks would require additional mechanisms able to provide some degree of monitoring in order to asset the SLAs, while IMS by itself does not provide such mechanisms.

The eTOM (enhanced Telecom Operations Map) (Creaner and Reilly, 2005) functional framework is a widespread reference used to model and analyze networks and services activity. From an eTOM point of view, one could argue that IMS does indeed cover the Fulfilment part of service management, but lacks any means to carry out service Assurance. The eTOM framework proposes a complete set of hierarchically layered processes describing all operator activities in a standard way. It is furthermore sustained by a parallel specification of a standard information model, the SID (Shared Information Data) (TMF GB926 Release 4, 2004). It has to be noted however that both tools, the eTOM and the SID, are generic. Also, the eTOM has been designed at times when Services were viewed as centrally controlled and managed, whereas the IMS is really a distributed layer network.

The work presented in this contribution is an attempt to achieve Assurance functionality for QoS-enhanced IMS services following strictly the eTOM specification, thus filling the functional gap as analyzed earlier; furthermore, two architectures are proposed to be compared: a centralized one and a distributed one.

### **2. IMS and service provisioning**

The composition of the supply chain in NGN network is classically described with three layers. The access layer provides IP (v4 or v6) connectivity regardless of the access technologies (Wireless or Wire-line). The service layer therefore supports technology-agnostic

eTOM-Conformant IMS Assurance Management 53

Fig. 2. Service request and negotiation in IMS network with QoS management.

**3. eTOM (enhanced Telecom Operations Map) architecture** 

standardized by the ITU-T (TeleManagement Forum GB921 D, 2010).

scenarios of SLA (Service Level Agreement)-enhanced services.

The resources release is carried out at each end of session; the P-CSCF must announce to the PCRF (Policy and Charging Rules Function) (3GPP TR 23.803, 2005) the end of the multimedia session, and the PCRF notifies the PCEF in order to release reserved resources for other applications. QoS management in IMS is a quite flexible on demand mechanism.

The eTOM is a framework proposed by the TeleManagement Forum and provides a standardized telecom-oriented Business Process map covering all functions of an operator, including service integration and supply. The decomposition layers and functional areas (Customer Service, Resource, and Enterprise) allow detailed operation analysis and to develop solutions according to a well-defined environment. The eTOM has been

The eTOM in its operational part has three main areas: Fulfilment, Assurance and Billing. This section will present only processes related to Assurance, and insist on execution

services that are developed independently. The core layer i.e. the control layer is the IMS system which provides the complex signalling responsible for routing sessions between users, invocating services and security-related tasks (Figure 1). The information processing and management are carried out by nodes called CSCF (**C***all*  **S***tate* **C***ontrol* **F***unction*) and HSS (*Home Subscriber Server*). The IMS system introduces a control environment similar to the CS session (*Switched Commutation*) but in CP (*Packet Commutation*).

Fig. 1. IMS Layers: Access, Control and Service.

In addition to access unification and diversity of services, IMS introduced a flexible and capable QoS management architecture which organizes exchanges of QoS-related requirements between the control and access layers, allowing resource reservation mechanisms to offer best conditions of supply for e.g. multimedia services.

The service provisioning mechanism of IMS includes three consecutive steps impacting resources: Reservation, Activation and Release (Figure 2).

When a user requests an IMS multimedia service by SIP signalling(Rosenberg et al., 2002) through its attached P-CSCF, the P-CSCF, before forwarding this request must ensure resources availability; this verification is performed through the exchange of Diameter (Korhonen et al., 2010) messages during all media negotiation stages between the two ends (User and AS). An agreement between the client and server can finally lead to change the resource status from reserved into activated. Naturally the PCEF (Policy and Charging Enforcement Function) (3GPP TS 29.210, 2006) applies the relevant QoS policy related to the types of access and transport layers; the most used models are DiffServ(Blake et al., 1998), RSVP(Wroclawski J., 1997) and MPLS (Le Faucheur et al).

services that are developed independently. The core layer i.e. the control layer is the IMS system which provides the complex signalling responsible for routing sessions between users, invocating services and security-related tasks (Figure 1). The information processing and management are carried out by nodes called CSCF (**C***all*  **S***tate* **C***ontrol* **F***unction*) and HSS (*Home Subscriber Server*). The IMS system introduces a control environment similar to the CS session (*Switched Commutation*) but in CP (*Packet Commutation*).

In addition to access unification and diversity of services, IMS introduced a flexible and capable QoS management architecture which organizes exchanges of QoS-related requirements between the control and access layers, allowing resource reservation

The service provisioning mechanism of IMS includes three consecutive steps impacting

When a user requests an IMS multimedia service by SIP signalling(Rosenberg et al., 2002) through its attached P-CSCF, the P-CSCF, before forwarding this request must ensure resources availability; this verification is performed through the exchange of Diameter (Korhonen et al., 2010) messages during all media negotiation stages between the two ends (User and AS). An agreement between the client and server can finally lead to change the resource status from reserved into activated. Naturally the PCEF (Policy and Charging Enforcement Function) (3GPP TS 29.210, 2006) applies the relevant QoS policy related to the types of access and transport layers; the most used models are DiffServ(Blake et al., 1998),

mechanisms to offer best conditions of supply for e.g. multimedia services.

Fig. 1. IMS Layers: Access, Control and Service.

resources: Reservation, Activation and Release (Figure 2).

RSVP(Wroclawski J., 1997) and MPLS (Le Faucheur et al).

Fig. 2. Service request and negotiation in IMS network with QoS management.

The resources release is carried out at each end of session; the P-CSCF must announce to the PCRF (Policy and Charging Rules Function) (3GPP TR 23.803, 2005) the end of the multimedia session, and the PCRF notifies the PCEF in order to release reserved resources for other applications. QoS management in IMS is a quite flexible on demand mechanism.
