Most phones have a switch that turns mobile data off. The user expects the switch to stop data use and data charges. But the same user still expects voice calls and SMS to work. In LTE, VoLTE and SMS over IMS are IP packets on a PDN connection as well, so a plain data switch would stop them too. 3GPP PS Data Off is the Release 14 answer to this conflict. It blocks user data over 3GPP access, and it lets a list of operator services through. This page covers what the feature blocks, how the UE and the network signal its status, and what each side enforces.

• What does 3GPP PS Data Off block, and what does it let through ?
• How do the UE and the network exchange the PS Data Off status ?
• What does each side enforce once PS Data Off is activated ?
• Reference

What does 3GPP PS Data Off block, and what does it let through ?

Let's start with the definition, because the name suggests more than the feature does. When the user activates 3GPP PS Data Off, the feature prevents transport of IP packets, Ethernet data and non-IP data via 3GPP access. The only exception is traffic for the 3GPP PS Data Off Exempt Services. These are operator services, and TS 23.221 defines the set they are taken from.

Two words in that definition deserve attention. The first is 3GPP access. The feature does not act on WLAN access, so a user can still send data over Wi-Fi with PS Data Off activated. The second is exempt. The operator decides which services stay available while the switch is on. So two users with the same phone can see different behaviour on two networks.

The exempt services reach the UE as lists. A UE can hold up to two of them. One list is for the HPLMN, or the EHPLMN when an EHPLMN list is present. The other list is for any VPLMN the UE roams in. If the UE holds only the HPLMN list, it uses that list in the VPLMN too. The HPLMN provides the lists by Device Management, with the management object of TS 24.368, or by UICC provisioning in the EF3GPPPSDATAOFF file of TS 31.102.

The operator also has to keep the lists in the UE and the rules in the network consistent. The UE filters its uplink against its own list, while the network filters the downlink against its own policy. If the two disagree, a service can work in one direction and fail in the other. 23.401 states this coordination duty in a note to the feature description.

• PS Data Off acts on 3GPP access only : WLAN traffic is not blocked, and the feature covers IP, Ethernet and non-IP data.
• Exempt services are an operator choice : TS 23.221 defines the services, and the HPLMN decides which of them go into the lists.
• A UE holds at most two lists : one for the HPLMN or EHPLMN and one for a VPLMN. A single list applies everywhere.
• UE lists and network policy must match : the UE blocks the uplink and the network blocks the downlink, so a mismatch breaks one direction only.

How do the UE and the network exchange the PS Data Off status ?

The user flips the switch on the UE, so the UE is the first to know the status. But the P-GW has to act on the downlink, so it needs the status as well. The two sides exchange it in the Protocol Configuration Options IE, PCO. The UE and the P-GW read the PCO, and the MME and the S-GW only carry it.

24.008 defines one container identifier, 0017H, for both directions of the PCO. The meaning depends on the direction, as the table below shows. In the UE to network direction the container carries the status. In the network to UE direction it carries only the fact that the network supports the feature.

Figure 1 follows the status through an EPC. The upper half is the setup of a PDN connection, and the lower half is a status change after the user activates the feature. The S-GW relays every GTP message between the MME and the P-GW, and it is left out of the drawing to save space. The purple text under each arrow shows what the PCO carries.

Figure 1. PS Data Off status exchange in PCO. The UE reports its status when it sets up a PDN connection, and it reports a later change only to a P-GW that returned the support indication.

• PDN CONNECTIVITY REQUEST carries the PS data off UE status in its PCO. At attach, this ESM message travels inside ATTACH REQUEST, so the status also reaches the network at initial attach.
• The MME passes the PCO to the P-GW in Create Session Request. If the P-GW supports the feature, it gives the status to the PCRF.
• A PCRF that supports the feature returns its support to the P-GW. The P-GW then puts the support indication into the PCO of Create Session Response.
• ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST delivers the support indication to the UE. From this point the UE knows that this PDN connection can take status changes.
• When the user activates the feature, the UE sends BEARER RESOURCE MODIFICATION REQUEST with the new status, 02H. The MME forwards the PCO in Bearer Resource Command.
• The P-GW reports the change to the charging system, for offline and online charging. It then enforces the downlink PCC rules that apply while PS Data Off is activated.

Watch the condition on the change report. The UE reports a change for a PDN connection only if the network included the support indication when that connection was set up. The other case is a PDN connection that started as a PDU session in N1 mode. If the support indication never arrived, the UE stays silent about changes on that PDN connection. The UE also sends the report even while T3396 or another session management back-off timer is running, because a blocked status report would leave the P-GW with the wrong status.

One more case needs a report. The user can change the switch while the UE is connected over WLAN only. When the PDN connection later moves to 3GPP access, the UE sends its current status then. The same rule covers inter-RAT mobility into E-UTRAN.

• One container ID carries two meanings : 0017H is the UE status from the UE, and the support indication from the network.
• The status goes in at setup : the UE includes it at attach and at every UE-requested PDN connectivity procedure.
• A change goes in BEARER RESOURCE MODIFICATION REQUEST : and only for a PDN connection where the network indicated support.
• Back-off timers do not stop the report : the UE reports a status change even with T3396 running.

What does each side enforce once PS Data Off is activated ?

Signalling the status is only half of the feature. The other half is the filtering, and the uplink and the downlink are filtered in different places. The UE filters its own uplink. The UE cannot stop a server from sending it packets, so the P-GW filters the downlink.

Let's take the UE side first. While the status is activated, the UE sends no uplink IP packets except in a few cases. It sends packets for the services on the exempt list that applies in the current PLMN. It sends packets for the services in the EF3GPPPSDATAOFF file on the USIM. It also sends uplink traffic that comes from the IMS procedures of TS 24.229 and from the XCAP procedures of TS 24.623. The UE sends no uplink non-IP or Ethernet user data at all. When the status is deactivated, the UE sends uplink data without restriction.

The IMS exception needs a closer look. The UE does not block IMS signalling at the PDN level. Instead, TS 24.229 decides inside the IMS client which IMS services are exempt. On the network side, 23.401 also places the exempt services of the IMS PDN connection in the IMS domain, as TS 23.228 specifies. So the P-GW and the PCRF must keep those services allowed when the status is activated.

Now the network side. Local configuration or PCRF policy controls the P-GW behaviour, and TS 23.203 defines it. When the status is activated, the P-GW enforces the PCC rules for downlink traffic that apply in that state. It also reports every status change to the charging system. If the P-GW does not support the feature, the UE learns this from the missing support indication. How the UE then treats mobile terminated requests for non-exempt services is implementation dependent.

Note that the PDN connection stays up the whole time. This is the main difference from the older way to stop data, a UE requested PDN disconnection as in 23.401 clause 5.10.3. A disconnection removes the connection and every service on it, while PS Data Off keeps the connection and filters the traffic on it.

• The UE filters the uplink, and the P-GW filters the downlink : each side enforces the direction it controls.
• IMS signalling is not blocked at the PDN level : the IMS domain applies the exempt list to IMS services.
• Non-IP and Ethernet uplink data is always blocked : the exempt lists only open IP traffic.
• The PDN connection survives : PS Data Off filters traffic, while a PDN disconnection removes the connection.
• Every change is a charging event : the P-GW reports it for offline and online charging.

Reference

• PS Data Off - Mediatek (Whitepaper)
• 3GPP 23.401 - 5.10.3 UE or MME requested PDN disconnection
• TR 23.702 - Study on 3GPP PS Data Off (Release 14)

• 3GPP TS 23.401 v20.0.0 - 4.3.29 3GPP PS Data Off, 5.3.2.1 E-UTRAN Initial Attach, 5.4.5 UE requested bearer resource modification
• 3GPP TS 24.301 v20.0.0 - 6.3.10 Handling of 3GPP PS data off, 6.5.4 UE requested bearer resource modification procedure
• 3GPP TS 24.008 v20.0.0 - 10.5.6.3 Protocol configuration options, container identifier 0017H