The Telephony Application Server is a SIP AS providing the network support for the multimedia telephony service,
TS 22.173. If specific procedures and message flows include or require media interaction, the TAS and MRFC may
The TDF is a functional entity that performs application detection and reporting of detected application and its service
data flow description to the PCRF. The TDF supports solicited application reporting and/or unsolicited application
Trusted and Untrusted Non-3GPP Access Networks are IP access networks that use access technology whose
specification is out of the scope of 3GPP.
Whether a Non-3GPP IP access network is Trusted or Untrusted is not a characteristic of the access network.
In non-roaming scenario it is the HPLMN's operator decision if a Non-3GPP IP access network is used as Trusted or
Untrusted Non-3GPP Access Network.
In roaming scenario, the HSS/3GPP AAA Server in HPLMN makes the final decision of whether a Non-3GPP IP
access network is used as Trusted or Untrusted non-3GPP Access Network. The HSS/3GPP AAA Server may take the
VPLMN's policy and capability returned from the 3GPP AAA Proxy or roaming agreement into account.
For supporting multiple PDNs, the same trust relationship shall apply to all the PDNs the UE connects to from a certain
Non-3GPP Access Network, i.e. it shall not be possible to access one PDN using the non-3GPP access network as
Trusted, while access to another PDN using the same non-3GPP access network as Untrusted.
The TSSF is a function that receives traffic steering control information from the PCRF and ensures that the related
traffic steering policy is enforced in the (S)Gi-LAN.
A traffic steering policy is locally configured in TSSF and can be used for uplink, downlink or for both directions. To
ensure that the traffic steering policy is enforced, the TSSF performs deployment specific actions as configured for that
traffic steering policy. For example, the TSSF may configure traffic detection and forwarding entities in the (S)Gi-LAN
to fulfil the traffic steering policy.