4.10 QoS Concepts
23.4023GPPArchitecture enhancements for non-3GPP accessesRelease 18TS
4.10.1 General
The QoS model that is applied in conjunction with PMIP-based reference points does not use bearer IDs in user plane packets. Instead it is based on packet filters and associated QoS parameters (QCI, ARP, MBR, GBR) provided to the access system through off-path signalling.
The PCRF signals the same packet filters and associated QoS parameters over Gxa, Gxb and Gxc as over Gx; in other words the granularity of the QoS information that is passed over Gxa, Gxb and Gxc is the same as over Gx.
4.10.2 Void
4.10.3 The EPS Bearer with PMIP-based S5/S8 and E-UTRAN access
Figure 4.10.3-1: Two Unicast EPS bearers (PMIP-based S5/S8 and E-UTRAN access)
For PMIP-based S5/S8 and E-UTRAN access, an EPS bearer consists of the concatenation of one Radio Bearer and one S1 bearer. The PDN Connectivity Service between a UE and an external packet data network is supported through a concatenation of an EPS Bearer and IP connectivity between Serving GW and PDN GW. QoS control between a Serving GW and a PDN GW is provided at the Transport Network Layer (TNL).
The EPS bearer is realised by the following elements:
– In the UE, UL TFT maps a traffic flow aggregate to an EPS bearer in the uplink direction.
– In the Serving GW, the DL TFT maps a traffic flow aggregate to an EPS bearer in the downlink direction.
– A radio bearer transports the packets of an EPS bearer between a UE and an eNodeB. There is a one-to-one mapping between an EPS bearer and a radio bearer.
– An S1 bearer transports the packets of an EPS bearer between an eNodeB and a Serving GW. There is a one-to-one mapping between an EPS bearer and a S1 bearer.
– A per UE per PDN tunnel transports the packets of an EPS bearer between a Serving GW and a PDN GW. There is a many-to-one mapping between an EPS bearer and this per UE, per PDN tunnel.
– A UE stores a mapping between an uplink packet filter and a radio bearer to create the mapping between a traffic flow aggregate and a radio bearer in the uplink.
– An eNodeB stores a one-to-one mapping between a radio bearer and an S1 bearer to create the binding between a radio bearer and an S1 bearer in both the uplink and the downlink direction.
– A Serving GW stores a one-to-one mapping between a downlink packet filter and an S1 bearer to create the mapping between a traffic flow aggregate and an S1 bearer in the downlink.
– A PDN GW enforces APN-AMBR across all SDFs of the same APN that is associated with Non-GBR QCIs.
4.10.4 Application of PCC in the Evolved Packet System
EPS supports both static and dynamic PCC deployment options as specified in TS 23.401 [4].
NOTE 1: The local configuration of PCEF static policy and charging control functionality is not subject to standardization and is not based on subscription information.
In case of non-3GPP access that does not support an Gxa/b or S9 interface, static QoS policies (e.g. based on subscription QoS parameters for default connectivity) may be provided to the non-3GPP access through the AAA infrastructure. To perform policy enforcement according to the subscription QoS parameters for default connectivity, additional information may be provided to the PDN GW in one of the following ways:
– from the PCRF, if present and if the PDN GW supports the Gx interface;
– from the 3GPP AAA Server through the S6b interface in the form of a static QoS profile for the S2a, PMIP based S2b, and S2c reference points;
– from the ePDG through GTP based S2b in the form of a static QoS profile (Default EPS Bearer QoS), which the ePDG obtains from the 3GPP AAA Server through the SWm interface.
NOTE 2: In the two last cases, the PCEF may change the provided values based on interaction with the PCRF or based on local configuration.
When dynamic policy provisioning is not deployed, the PDN GW in case of PMIP or GTP based signalling uses the access type information (RAT Type in 3GPP access) contained in PMIP Proxy Binding Update messages or GTP Create Session Request messages for, e.g. charging. When dynamic policy provisioning is deployed, the PDN GW relies on the PCRF for indication of the handling required due to the access technology.
The behaviour of the system when PCC is deployed only in VPLMN or only in HPLMN is described in TS 23.203 [19].
For non-3GPP access that supports UEs with different Bearer Control Mode (BCM) capabilities, it should be possible for the UE to signal its BCM capabilities to the BBERF. It should also be possible for the BBERF to signal the selected BCM to the UE. How this information is exchanged between the UE and the BBERF is outside of the scope of 3GPP.
4.10.5 PDN connectivity service with GTP based S2b
For untrusted non-3GPP access to the EPC the PDN connectivity service is provided by IPsec connectivity between the UE and the ePDG concatenated with S2b bearer(s) between the ePDG and the PGW.
Two scenarios exist. In one scenario, only one IPSec SA is established between the UE and the ePDG and it transports traffic for the default bearer and all dedicated bearers established over S2b between the ePDG and the PDN GW. This is depicted in clause 4.10.5.1. In the second scenario, when the UE and the ePDG supports the establishment of a separate IPsec child SA per dedicated S2b bearer that transports the traffic for that dedicated bearer, and where the main IPSec SA transports the traffic for the default bearer. This is depicted in clause 4.10.5.2.
4.10.5.1 Single IPSec SA per PDN Connection Scenario
Figure 4.10.5.1-1: Single IPSec SA per PDN connection
The SWu interface between the UE and the ePDG is identical for the GTP and PMIP variants of S2b. The UE establishes a separate SWu instance (i.e. a separate IPSec tunnel) for each PDN connection.
One default S2b bearer is established on the S2b interface when the UE connects to a PDN, and that remains established throughout the lifetime of the PDN connection to provide the UE with always-on IP connectivity to that PDN. Additional dedicated S2b bearers may be established on S2b for the same PDN connection depending on operator policy. The PGW establishes dedicated S2b bearers on S2b for the same PDN connection based on PCC decisions as specified in TS 23.203 [19].
The ePDG releases the SWu instance when the default S2b bearer of the associated PDN connection is released.
The S2b bearer is realized by the following elements:
– A GTP tunnel on S2b transports the packets of an S2b bearer between the ePDG and a PDN GW;
– The ePDG stores the mapping between uplink packet filters it receives from the PGW (e.g. in the Create Bearer Request message) and the corresponding S2b bearer;
– The PDN GW stores the mapping between downlink packet filters and an S2b bearer.
In support for the UE connectivity with the PDN:
– A SWu instance (i.e. a IPSec tunnel) transports the packets of all S2b bearer(s) for the same PDN Connection between the UE and the ePDG.
The ePDG routes uplink packets to the different bearers based on the uplink packet filters in the TFTs assigned to the bearers in the PDN connection, in the same way as a UE does for uplink traffic under 3GPP access. If no match is found, the uplink data packet shall be sent via the bearer that does not have any uplink packet filter assigned. If all bearers (including the default bearer for that PDN) have been assigned an uplink packet filter, the ePDG shall discard the uplink data packet.
The PDN GW routes downlink packets to the different bearers based on the downlink packet filters in in the TFTs assigned to the S2b bearers in the PDN connection, in the same way as the PDN GW does on GTP-based S5/S8 bearers (see TS 23.401 [4] clause 4.7.2.2).
4.10.5.2 Single IPsec SA per S2b bearer Scenario
This scenario assumes both UE, and ePDG support the establishment of a separate IPsec SA per S2b bearer, while the main IPSec SA is intended for the default bearer.
Figure 4.10.5.2-1: Single IPsec SA per S2b bearer
The SWu interface between the UE and the ePDG is identical for the GTP and PMIP variants of S2b. The UE establishes a separate SWu instance (i.e. a separate IPsec SA per [9]) for each PDN connection.
One default S2b bearer is established on the S2b interface when the UE connects to a PDN, and that remains established throughout the lifetime of the PDN connection to provide the UE with always-on IP connectivity to that PDN. Additional dedicated S2b bearers may be established on S2b for the same PDN connection depending on operator policy. The PGW establishes dedicated S2b bearers on S2b for the same PDN connection based on PCC decisions as specified in TS 23.203 [19].
The ePDG releases the SWu instance, including all IP Sec SAs associated with the SWu instance, where applicable, when the default S2b bearer of the associated PDN connection is released.
The S2b bearer is realized by the following elements:
– A GTP tunnel on S2b transports the packets of an S2b bearer between the ePDG and a PDN GW;
– The ePDG stores the mapping between IPSec SA and the corresponding S2b bearer;
– The PDN GW stores the mapping between downlink packet filters and an S2b bearer.
The ePDG shall establish a SA per S2b bearer as per clause 7.10. The default EPC bearer maps to the initial SA. The ePDG shall maintain a 1 to 1 mapping between an S2b bearer and an IPsec SA.
Additionally, for these UEs, TFTs and bearer QoS information is conveyed from the ePDG to the UE in IKE v2 signalling associated with the corresponding SA at EPC bearer creation and EPC bearer modification. The bearer QoS information includes information regarding the QoS characteristics of the bearer (i.e. QCI, GBR and MBR).
The IKEv2 traffic selectors TSi and TSr, defined in [9], shall not be used to route packets to the IPSec SA.
In support for the UE connectivity with the PDN:
– A SWu instance (i.e. an IKEv2 SA with one or more IPsec SA) transports the packets of all S2b bearer(s) for the same PDN Connection between the UE and the ePDG.
The PDN GW routes downlink packets to the different bearers based on the downlink packet filters in in the TFTs assigned to the S2b bearers in the PDN connection, in the same way as the PDN GW does on GTP-based S5/S8 bearers (see TS 23.401 [4] clause 4.7.2.2).
The ePDG routes uplink packets to the different bearers based on the incoming child SA and the corresponding S2b bearer.
The UE routes uplink packets to the SAs associated with the different S2b bearers based on the uplink packet filters in the TFTs assigned to the S2b bearers in the PDN connection, in the same way as a UE does for uplink traffic under 3GPP access. If no match is found, the uplink data packet shall be sent via the SA that does not have any uplink packet filter assigned. If all IPsec SAs have been assigned an uplink packet filter, the UE shall discard the uplink data packet.
Furthermore, the UE shall use the QCI in dedicated bearer QoS information to set the DSCP value for uplink packets. The mapping of QoS class to DSCP could be configurable in the UE and as an example can use the recommended mappings specified in 3GPP (mapping between standardized QCIs and Release 99 QoS parameter value in TS 23.401 [4]), IEEE Std. 802.11-2012 [64], and the Wi-Fi WMM-multimedia certification profile [86]. The UE may also use information included in dedicated QoS information for local aspects of admission control (e.g. application traffic shaping), however this is out of scope for this document.