Content for  TS 23.214  Word version:  18.0.0

The SGW-C shall be able to provide the SGW-U with instructions for at least the following behaviors: buffer without reporting the arrival of first downlink packet, buffer with reporting the arrival of first downlink packet, drop packets. When the UE moves to ECM-IDLE state, if the SGW-C does not support buffering capability, or if the SGW-C supports buffering capability and decides to activate buffering in SGW-U for the session, the SGW-C shall inform the SGW-U, via an Sx session modification. The SGW-C decides whether buffering timers are handled by the SGW-U or by the SGW-C. The activation of buffering implicitly stops sending data to the eNodeB/RNC/SGSN. After starting the buffering, when the first downlink packet arrives on any bearer, SGW-U shall inform the SGW-C. SGW-U sends an Sx reporting message to the SGW-C unless specified otherwise and identifies the S5/S8 bearer on which the downlink packet was received. On receiving this reporting message, the SGW-C decides whether to send a Downlink Data Notification message to the MME as defined in TS 23.401. At the UE transition to ECM-CONNECTED state, the SGW-C shall update the SGW-U via Sxa interface with the F-TEIDu of the eNodeB/RNC/SGSN. The buffered data packets, if any, are then forwarded to the eNodeB/RNC/SGSN by the SGW-U. In case of SGW-U relocation, buffered data packets are transferred from the old SGW-U to the new SGW-U.

According to clause 5.3.4.2 of TS 23.401, the MME/SGSN may inform the SGW that for all UEs served by the MME/SGSN, the Downlink Packet Data Notification shall be delayed for a period D. If the parameter D is handled by the SGW-U, the SGW-C shall include the parameter D in the Sx session establishment for new Sx sessions, in the Sx session modification for Sx sessions which are not in buffering state (when transitioning these sessions to the buffering state), and in the next Sx report ack message for Sx sessions already in buffering state. The SGW-U shall then delay the sending of subsequent Sx reporting upon next DL data arrival. If the parameter D is handled by the SGW-C, there is no special handling compared to clause 5.9.3.1. When the SGW-U reports the arrival of a DL data packet, the SGW-C shall delay the sending of the Downlink Data Notification to the MME by parameter D delay.

According to clauses 5.3.4.3 and 5.7.3 of TS 23.401, the MME/SGSN invoking extended buffering indicates it to the Serving GW in the Downlink Data Notification Ack message, includes a DL Buffering Duration time and optionally a DL Buffering Suggested Packet Count. If the MME/SGSN included the DL Suggested Packet Count, the SGW-C shall include the DL Suggested Packet Count in the Sx reporting Ack message. If the DL Data Buffer Expiration Time is handled by the SGW-U, the SGW-C includes it in the Sx reporting Ack message and requests the SGW-U to buffer DL data packets. When the SGW-U receives the DL Data Buffer Expiration Time, the SGW-U buffers the DL data packets without reporting the arrival of the first DL data packet until the DL Data Buffer Expiration Time expires. When the DL Data Buffer Expiration Time expires, the SGW-U shall discard the buffered DL packets and shall restart buffering DL data packets with reporting the arrival of the first DL data packet. If the DL Data Buffer Expiration Time is handled by the SGW-C, the SGW-C requests the SGW-U to buffer the DL data packets without reporting the arrival of the first DL data packet. When the DL Data Buffer Expiration Time expires, the SGW-C requests the SGW-U to drop the buffered data packets and to start buffering the DL data packets with reporting of the arrival of the first DL data packet, via an Sx Session Modification. If the DL Suggested Packet Count was included in the request from the SGW-C, the SGW-U buffers the DL data packets up to the number of packets indicated by the DL Suggested Packet Count.

According to clause 4.3.7.4.1a of TS 23.401, the MME/SGSN can request the SGWs to selectively reduce the number of Downlink Data Notification requests it sends for downlink non-priority traffic received for UEs in idle mode according to a throttling factor and for a throttling delay specified in the Downlink Data Notification Ack message. Throttling mechanism by which the MME uses Downlink Data Notification Acknowledgement messages DL low priority traffic Throttling parameters, is handled by the SGW-C as follows:

• On receiving Downlink Data Notification Acknowledgement from the MME/SGSN, the SGW-C determines which bearers are subject to the throttling of Downlink Data Notification requests on the basis of the bearer's ARP priority level and the operator policy.
• Upon receipt of an Sx report notifying the arrival of DL data packets on those bearers, the SGW-C decides whether or not to send a DDN to MME based on the requested throttling factor. The SGW-C may indicate in the Sx Report Ack whether SGW-U shall discard the buffered packet and may also indicate whether SGW-U shall notify when additional DL packets arrive.
• The throttling delay timer and throttling factor are handled by the SGW-C and not provided to SGW-U.