Content for TS 23.207 Word version: 18.0.0
5 End-to-End QoS Architecture
5.1 QoS Management Functions in the Network
5.2 Capabilities of Functional Elements
5.3b Gx reference point (PCRF - GGSN)
5.3c Rx reference point (AF - PCRF)
5.4 QoS Parameters
5.5 QoS Parameter Mapping
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5 End-to-End QoS Architecture p. 9
5.1 QoS Management Functions in the Network p. 9
To provide IP QoS end-to-end, it is necessary to manage the QoS within each domain. An IP BS Manager is used to control the external IP bearer service. Due to the different techniques used within the IP network, this communicates to the UMTS BS manager through the Translation function.
At PDP context setup the user shall have access to one of the following alternatives:
- Basic GPRS IP connectivity service: The bearer is established according to the user's subscription, local operator's IP bearer resource based policy, local operator's admission control function and GPRS roaming agreements. In this case, IP bearer resource based local policy decisions may be applied to the bearer.
- Enhanced GPRS based services: The bearer is used to support an enhanced application-layer service, such as IM. In this case, policy control decisions (e.g., authorization and policy based control) are also applied to the bearer.
- signalling along the flow path (e.g. RSVP, LDP).
- packet marking or labelling along the flow path (e.g. DiffServ, MPLS)
- interaction between Policy Control and/or Resource Management elements.
- Service Level Agreements enforced by the border routers between networks.
- The IP policy framework employed in UMTS should, as far as possible, conform to IETF "Internet Standards". The IETF policy framework may be used for policy decision, authorization, and control of the IP level functionality, at both user and network level.
- There should be separation between the scope and roles of the UMTS policy mechanisms and the IP policy framework. This is to facilitate separate evolution of these functions.
5.1.1 Description of functions p. 10
5.1.1.1 QoS management functions for end-to-end IP QoS in UMTS Network p. 10
IP BS Manager uses standard IP mechanisms to manage the IP bearer services. These mechanisms may be different from mechanisms used within the UMTS, and may have different parameters controlling the service. When implemented, the IP BS Manager may include the support of DiffServ Edge Function and the RSVP function. The Translation/mapping function provides the inter-working between the mechanisms and parameters used within the UMTS bearer service and those used within the IP bearer service, and interacts with the IP BS Manager. In the GGSN, the IP QoS parameters are mapped into UMTS QoS parameters, where needed. In the UE, the QoS requirements determined from the application layer (e.g., SDP) are mapped to either the PDP context parameters or IP layer parameters (e.g., RSVP).
If an IP BS Manager exists both in the UE and the Gateway node, it is possible that these IP BS Managers communicate directly with each other by using relevant signalling protocols.
The required options in the Table define the minimum functionality that shall be supported by the equipment in order to allow multiple network operators to provide interworking between their networks for end-to-end QoS. Use of the optional functions listed below, other mechanisms which are not listed (e.g. over-provisioning), or combinations of these mechanisms are not precluded from use between operators.
The IP BS Managers in the UE and GGSN provide the set of capabilities for the IP bearer level as shown in Table 1. Provision of the IP BS Manager is optional in the UE, and required in the GGSN.
| Capability | UE | GGSN |
|---|---|---|
| DiffServ Edge Function | Optional | Required |
| RSVP/IntServ | Optional | Optional |
| IP Policy Enforcement Point | Optional | Required (*) |
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(*)
Although the capability of IP policy enforcement is required within the GGSN, the control of IP policy through the GGSN is a network operator choice.
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Figure 2 shows the scenario for control of an IP service using IP BS Managers in both possible locations in the UE and Gateway node. The Figure also indicates the optional communication path between the IP BS Managers in the UE and the Gateway node.
Policy and Charging Rules Function (PCRF) encompasses policy control decision and flow based charging control functionalities. The PCRF provides network control regarding the service data flow detection, gating, and QoS towards the GGSN. The PCRF makes policy control decisions, and communicates these decisions to the IP BS Manager in the GGSN, which is the Policy and Charging Enforcement Point (PCEF).
The interface between the PCRF and the Application Function (AF) is the Rx interface, and is included in the Reference Architecture depicted in TS 23.002.
The interface between the PCRF and GGSN is specified within 3GPP, named Gx interface, and is included in the Reference Architecture depicted in TS 23.002. The interface between the PCRF and GGSN supports the transfer of information and policy decisions between the policy decision point and the IP BS Manager in the GGSN.
The PCRF makes policy decisions based on input obtained from the AF as well as from other sources, e.g. operator configuration. The PCRF maps the policy set-up information received from the AF via the Rx interface into IP QoS parameters. The PCRF is in the same domain as the GGSN. The AF may either be in the same network as the PCRF or may be in a different network. In the particular case of IMS, the AF is the P-CSCF which is in the same network as the GGSN, as specified in TS 23.221.
Application Function (AF) offers services that require the control of IP bearer resources. The AF maps QoS-related application level parameters (e.g. SDP) into policy set-up information, and sends this information to the PCRF via the Rx interface.
5.1.1.2 Void
5.1.1.3 Interaction to External Networks p. 11
Within the UMTS network, there is resource management performed by various nodes in the admission control decision. The resources considered here are under the direct control of the UMTS network.
In IP Networks, it is also necessary to perform resource management to ensure that resources required for a service are available. Where the resources for the IP Bearer Service to be managed are not owned by the UMTS network, the resource management of those resources would be performed through an interaction between the UMTS network and that external network.
In addition, where the UMTS network is also using external IP network resources as part of the UMTS bearer service (for example for the backbone bearer service), it may also be necessary to interwork with that network.
The GGSN shall support DiffServ edge functionality. There are a number of other mechanisms provided to support interoperator interworking, some of which are given below.
- Signalling along the flow path: In this scenario, resource requirements are explicitly requested and either granted or rejected through the exchange of signalling messages between network elements along the path of the IP packet flow. Signalling may be performed on a per-flow basis (e.g. using end to end RSVP) or it may be performed for an aggregate set of flows. In the latter case, it is expected that signalling exchanges would only be required when there are changes required in the resources allocated to an aggregate set of flows.
- Interaction between network management entities: In this scenario, resource requirements need to be explicitly negotiated and provisioned through network management entities. The results of this exchange are then enforced in the border nodes separating DiffServ administrative domains.
- Service Level Agreements enforced by the border routers between networks: In this scenario, resources are allocated along the path based on agreements between the network operators. The border routers along the path flow are provisioned with the characteristics of the aggregated traffic that is allowed to flow between systems.
5.1.1.4 Translation/mapping function in the GGSN and the UE p. 11
Translation/mapping function interacts with the IP BS Manager and with the UMTS BS Manager in the GGSN and in the UE. It provides interworking between the mechanisms and parameters used within the UMTS bearer service and those used within the IP bearer service.
For policy control, the translation/mapping function in the GGSN maps IP bearer based policy information into UMTS bearer based policy information. This mapping is used by the GGSN for policy control over the UMTS network.
5.1.2 Allocation of QoS management functions p. 12
5.1.2.1 QoS management functions for end-to-end IP QoS p. 12
The QoS management functions for controlling the external IP bearer services and how they relate to the UMTS bearer service QoS management functions are shown in Figure 2.
Figure 2: QoS management functions for UMTS bearer service in the control plane and QoS management functions for end-to-end IP QoS
(⇒ copy of original 3GPP image)
(⇒ copy of original 3GPP image)
5.2 Capabilities of Functional Elements p. 12
This clause provides functional descriptions of capabilities in GGSN, UE, PCRF, and AF.
5.2.1 GGSN p. 12
This clause provides functional descriptions of capabilities in GGSN. The capabilities are part of IP BS Manager (see clause 5.1.1.1) or corresponding user plane functions. Determination of exactly which functions are required to support interoperator and multi-vendor aspects are not addressed in this clause.
The DiffServ Edge Function shall be compliant to the IETF specifications for Differentiated Services (RFC 2475). The IETF Differentiated Services architecture will be used to provide QoS for the external bearer service.
Parameters for the DiffServ Edge Function (i.e. classifiers, meters, packet handling actions) may be statically configured on the GGSN, derived from PDP Context parameters and/or derived from RSVP signalling.
DiffServ functions configured on the basis of PDP Context parameters consist of marking user packets. The DSCP to be used is derived from the PDP Context parameters according to statically configured rules.
Statically configured DiffServ functions may include classifiers, meters, markers, droppers and shapers acting on uplink traffic.
Policy and Charging Enforcement Function (PCEF) controls the user plane quality of service that is provided including policy-based admission control that is applied to the bearer and gating control. Policy decisions are either pushed to or requested by the GGSN via the Gx interface.
Policy-based admission control ensures that the resources that can be used by a particular set of IP flows are within the "authorized resources" specified via the Gx interface. The authorized resources provide an upper bound on the resources that can be reserved or allocated for the set of IP flows.
The authorized resources are expressed as a maximum authorized bandwidth and QoS class. The QoS class identifies a bearer service (which has a set of bearer service characteristics associated with it). The PCRF generates a maximum authorized QoS class for the set of IP flows. This information is mapped by the translation/mapping function in the GGSN to give the authorized resources for UMTS bearer admission control.
In the user plane, policy enforcement for an individual or a set of IP flows is defined in terms of a "gate" implemented in the GGSN. A gate is part of the policy enforcement functionality and is controlled by the PCRF through Gx interface signalling. A gate consists of a packet classifier, and a gate status (open/closed). When a gate is open, the packets matching the packet classifier are accepted, and are thus subject to the DiffServ edge treatment in uplink direction or forwarded in their corresponding PDP context in downlink direction. When a gate is closed, all of the packets matching the packet classifier are dropped.
5.2.2 UE p. 13
This clause provides functional descriptions of capabilities in UE. The capabilities are part of IP BS Manager (see 5.1.1.1) or corresponding user plane functions. Determination of exactly which functions are required to support interoperator and multi-vendor aspects are not addressed in this clause.
DiffServ Edge Function acts as a DiffServ (DS) boundary for the traffic from applications running on the UE. As specified in RFC 2475, DS boundary node must be able to apply the appropriate PHB to packets based on the DS code point. In addition, DS boundary nodes may be required to perform traffic conditioning functions. When GGSN DiffServ marking is used, the DiffServ edge function in the UE is not needed.
RSVP/IntServ Function provides the capability for the UE to request end-to-end QoS using RSVP messages as defined in IETF standards. RSVP messages may also be used by the network to inform the DSCP to be used by the UE. RSVP messages shall include the authorization token and flow identifier(s) in a policy data object if the authorization token is available in the UE. RSVP may be used to trigger PDP context activation/modification. The inter-working between MT and TE is FFS.
5.2.3 Void
5.2.3a PCRF p. 13
This clause provides high level functional descriptions of PCRF capabilities. The PCRF makes policy decisions, e.g. based on policy set-up information obtained from the AF via the Rx interface.
- The PCRF checks that if the policy set-up information received from the AF is consistent with operator policies defined in the PCRF.
- The PCRF authorizes QoS resources (bandwidth, etc.) for the AF session. The PCRF uses the policy set-up information received from the AF to calculate the proper authorization. The authorization includes the limits on QoS for the set of IP flows and restrictions on individual IP flows (e.g. destination address and port).
- The PCRF decides if new QoS authorization (bandwidth, etc.) is needed due to a mid-call media or codec change. The PCRF re-authorizes QoS resources when the resources requested by the UE for a flow exceeds previous authorization, or a new flow is added, or when elements of the packet classifier(s) for authorized flows change.
- The PCRF provides the policy decision information to the GGSN via the Gx interface.
- The PCRF provides gating control decisions controlling the gate for the authorized media stream.
- At AF session release, the PCRF revokes the QoS resource authorization for the AF session.
5.2.4 Application Function (AF) p. 14
The Application Function (AF) is an element offering applications that require the control of IP bearer resources (e.g. UMTS PS domain/GPRS domain resources). One example of an Application Function is the P-CSCF in the IMS architecture.
Policy control related functions
- The AF uses the Rx interface to exchange service based policy set-up information with the PCRF. This applies both during session establishment, as well as upon a mid-session modification affecting the media (e.g. addition of a new media in mid-session).
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The AF may give instructions to the PCRF defining how the PCRF shall interact with the PCEF for certain events related to policy control. The AF is able to give instructions to the PCRF to act on its own, i.e. based on the service information currently available, for the following events:
- The authorization of QoS resources for the AF session;
- The gate control (i.e. whether there is a common gate handling per AF session or an individual gate handling per AF session component required);
- The forwarding of transmission resource level events.
5.3 Void
5.3a Void
5.3b Gx reference point (PCRF - GGSN) p. 14
The Gx interface is the interface between the PCRF and the GGSN. The Gx interface allows policy control and QoS information to be "pushed" to or requested by the GGSN from the PCRF. The Gx interface provides information to support the policy enforcement functions in the GGSN:
- Control of "gating" function in GGSN;
- UMTS bearer authorization.
5.3c Rx reference point (AF - PCRF) p. 14
The Rx interface is the interface between the AF and the PCRF. The Rx interface is used for policy set-up information exchange and event reporting.
The Rx interface allows service based QoS information needed for QoS authorization to be exchanged between the AF and the PCRF. This information is used by the PCRF for policy control decisions.
One PCRF is able to serve more than one AF and one given AF may interact with a number of PCRFs. On a per-AF-session basis, the AF interacts with only a single PCRF.
For further details, see TS 23.203.
5.4 QoS Parameters p. 15
See stage 3 specification TS 29.212.
5.5 QoS Parameter Mapping p. 15
See stage 3 specification TS 29.213.
