WO2016119845A1

WO2016119845A1 - Split processing

Info

Publication number: WO2016119845A1
Application number: PCT/EP2015/051758
Authority: WO
Inventors: Henri Markus Koskinen; Guillaume DECARREAU
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2015-01-29
Filing date: 2015-01-29
Publication date: 2016-08-04

Abstract

A technique comprising: performing Nth layer processing of Nth layer protocol data units at a first access node operating one or more first cells, including forming Nth layer service data units from said Nth layer protocol data units; and sending from the first access node to a second access node operating one or more second cells information about buffering of Nth layer service data units at the first access node.

Description

DESCRIPTION

TITLE

SPLIT PROCESSING

The present invention relates to techniques in which the processing of at least some data for a single data bearer for a communication device is split between two access nodes operating different cells or groups of cells serving the communication device.

One example of split processing is illustrated in Figure 1 , in which the three upper arrows depict different data bearers for a data connection between a core network and a single communication device via a radio access network and a wireless interface. The split data bearer (middle arrow) involves splitting of the protocol stack between two access nodes operating different cells. In the example shown in Figure 1 , all Packet Data Convergence Protocol (PDCP) processing for the data bearer is carried out at one access node (master access node), and all lower layer processing (Radio Link Control (RLC), Medium Access Control (MAC) and Physical (PHY) layer processing) and radio transmission/reception for a given PDCP PDU on the data bearer is carried out at either the master access node or at another access node (secondary access node). The lower layer processing and radio transmission/reception for some PDCP-PDUs on the data bearer can be carried out at the master access node, and the lower layer processing and radio transmission/reception for other PDCP-PDUs on the data bearer can be carried out at the secondary access node. The split data bearer does not involve the sending of any data directly between the core network and the secondary access node for the data bearer; any data for which lower layer processing is done at the secondary access node is sent to the core network via PDCP processing at the master access node . The left arrow depicts a data bearer for which all of PDCP, RLC, MAC and PHY layer processing (and radio

transmission/reception) is performed at the master access node, and the right arrow depicts a data bearer for which all of PDCP, RLC, MAC and PHY processing (and radio transmission/reception) is performed at the secondary access node.

The inventors for the present application have identified the challenge of better facilitating such split processing.

There is hereby provided a method comprising: performing Nth layer processing of Nth layer protocol data units at a first access node operating one or more first cells, including forming Nth layer service data units from said Nth layer protocol data units; and sending from the first access node to a second access node operating one or more second cells information about buffering of Nth layer service data units at the first access node.

In one embodiment, said buffering information comprises header information included in the (N+1 )th layer header part of one or more Nth layer service data units.

In one embodiment, the method further comprises sending said header information in advance of sending said one or more Nth layer service data units from the first access node to the second access node. In one embodiment, the method further comprises sending from the first access node to the second access node an indication that the first access node has no out-of-sequence Nth layer service data units for delivery to the second access node.

In one embodiment, the header information comprises one or more (N+1 )th layer sequence numbers for said one or more Nth layer service data units.

In one embodiment, said one or more Nth layer service data units are part of a broken sequence of Nth layer service data units; and the method further comprises storing said one or more Nth layer service data units in a buffer at the first access node in the absence of one or more Nth layer service data units required to complete said broken sequence; and sending said header information from said first access node to said second access node in response to a re-establishment of an Nth layer protocol entity before completion of said sequence.

There is also provided a method comprising: receiving at a second access node operating one or more second cells from a first access node operating one or more first cells information about buffering of Nth layer service data units at the first access node.

In one embodiment, said buffering information comprises header information included in the (N+1 )th layer header part of one or more Nth layer service data units. In one embodiment, the method further comprises receiving said header information at the second access node in advance of receiving said one or more Nth layer service data units from the first access node at the second access node for (N+1 )th layer processing at the second access node

In one embodiment, the method further comprises receiving from the first access node at the second access node an indication that the first access node has no out-of-sequence Nth layer service data units for delivery to the second access node.

In one embodiment, the method further comprises generating a (N+1 )th layer status report using said received information about buffering of Nth layer service data units at the first access node.

There is also hereby provided a method comprising: performing Nth layer processing of Nth layer protocol data units at a first access node operating one or more first cells, including forming one or more Nth layer service data units from said Nth layer protocol data units; and sending one or more Nth layer service data units from the first access node to the second access node together with an indication to the second access node of a change in connection configuration for the one or more Nth layer service data units.

In one embodiment, said indication is included in the header of a message including one or more Nth layer service data units. In one embodiment, said indication is selectively included in the header of a message including the first of the Nth layer service data units sent to the second access node after a change in connection configuration.

There is also hereby provided a method, comprising: sending one or more first messages from a first access node operating one or more first cells to a second access node operating one or more second cells, each first message including one or more first Nth layer service data units associated with a data bearer and a first connection configuration; sending one or more second messages from the first access node to the second access node, each second message including one or more second Nth layer service data units associated with said data bearer and a second connection configuration; and wherein the header of each second message includes an identifier associated with the second connection configuration, and the header of each first message includes an identifier associated with the first connection configuration.

In one embodiment, the method further comprises receiving at the first access node from the second access node information about said identifier associated with said second configuration.

In one embodiment, the first connection configuration comprises a first Nth layer protocol entity, and the second connection configuration comprises a second Nth layer protocol entity. There is also hereby provided a method comprising: receiving at a second access node operating one or more second cells from a first access node operating one or more first cells one or more Nth layer service data units together with an indication to the second access node of a change in connection configuration to a new connection configuration for the one or more Nth layer service data units; and performing (N+1 )th layer processing of said one or more Nth layer service data units at the second access node according to configuration information for the new connection configuration.

In one embodiment, said indication is included in the header of a message including one or more Nth layer service data units.

In one embodiment, said indication is selectively included in the header of a message including the first of the Nth layer service data units received at the second access node after said change to said new connection configuration.

There is also hereby provided a method, comprising: receiving one or more first messages from a first access node operating one or more first cells at a second access node operating one or more second cells, each first message including one or more first Nth layer service data units associated with a data bearer and a first connection configuration, for (N+1 )th layer processing at the second access node; receiving one more second messages from the first access node at the second access node, each second message including one or more second Nth layer service data units associated with said data bearer and a second connection configuration, for (N+1 )th layer processing at the second access node; and wherein the header of each second message includes an identifier associated with the second connection configuration, and the header of each first message includes an identifier associated with the first connection configuration.

In one embodiment, the method further comprises sending from the second access node to the first access node information about said identifier associated with said second configuration.

In one embodiment, the first connection configuration comprises a first Nth layer protocol entity, and the second connection configuration comprises a second Nth layer protocol entity.

In one embodiment, said Nth layer is a radio link control layer and said (N+1 )th layer is a packet data convergence protocol layer.

There is also hereby provided an apparatus comprising: a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to: perform Nth layer processing of Nth layer protocol data units at a first access node operating one or more first cells, including forming Nth layer service data units from said Nth layer protocol data units; and sending from the first access node to a second access node operating one or more second cells information about buffering of Nth layer service data units at the first access node. In one embodiment, said buffering information comprises header information included in the (N+1 )th layer header part of one or more Nth layer service data units.

In one embodiment, the memory and computer program code are further configured to, with the processor, cause the apparatus to send said header information in advance of sending said one or more Nth layer service data units from the first access node to the second access node .

In one embodiment, the memory and computer program code are further configured to, with the processor, cause the apparatus to send from the first access node to the second access node an indication that the first access node has no out-of-sequence Nth layer service data units for delivery to the second access node.

In one embodiment, said one or more Nth layer service data units are part of a broken sequence of Nth layer service data units; and wherein the memory and computer program code are further configured to, with the processor, cause the apparatus to store said one or more Nth layer service data units in a buffer at the first access node in the absence of one or more Nth layer service data units required to complete said broken sequence; and send said header information from said first access node to said second access node in response to a re-establishment of an Nth layer protocol entity before completion of said sequence.

There is also hereby provided an apparatus comprising: a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to: receive at a second access node operating one or more second cells from a first access node operating one or more first cells information about buffering of Nth layer service data units at the first access node.

In one embodiment, the memory and computer program code are further configured to, with the processor, cause the apparatus to receive said header information at the second access node in advance of receiving said one or more Nth layer service data units from the first access node at the second access node for (N+1 )th layer processing at the second access node.

In one embodiment, the memory and computer program code are further configured to, with the processor, cause the apparatus to receive from the first access node at the second access node an indication that the first access node has no out-of-sequence Nth layer service data units for delivery to the second access node. In one embodiment, the memory and computer program code are further configured to, with the processor, cause the apparatus to generate a (N+1 )th layer status report using said received information about buffering of Nth layer service data units at the first access node.

There is also hereby provided an apparatus comprising: a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to: perform Nth layer processing of Nth layer protocol data units at a first access node operating one or more first cells, including forming one or more Nth layer service data units from said Nth layer protocol data units; and send one or more Nth layer service data units from the first access node to the second access node together with an indication to the second access node of a change in connection configuration for the one or more Nth layer service data units.

In one embodiment, said indication is selectively included in the header of a message including the first of the Nth layer service data units sent to the second access node after a change in connection configuration. There is also hereby provided an apparatus comprising: a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to: send one or more first messages from a first access node operating one or more first cells to a second access node operating one or more second cells, each first message including one or more first Nth layer service data units associated with a data bearer and a first connection configuration; send one or more second messages from the first access node to the second access node, each second message including one or more second Nth layer service data units associated with said data bearer and a second connection

configuration; and wherein the header of each second message includes an identifier associated with the second connection configuration, and the header of each first message includes an identifier associated with the first connection configuration.

In one embodiment, the memory and computer program code are further configured to, with the processor, cause the apparatus to receive at the first access node from the second access node information about said identifier associated with said second configuration.

There is also hereby provided an apparatus comprising: a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to: receive at a second access node operating one or more second cells from a first access node operating one or more first cells one or more Nth layer service data units together with an indication to the second access node of a change in connection configuration to a new connection configuration for the one or more Nth layer service data units; and perform (N+1 )th layer processing of said one or more Nth layer service data units at the second access node according to configuration information for the new connection configuration.

There is also hereby provided an apparatus comprising: a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to: receive one or more first messages from a first access node operating one or more first cells at a second access node operating one or more second cells, each first message including one or more first Nth layer service data units associated with a data bearer and a first connection configuration, for (N+1 )th layer processing at the second access node; receive one more second messages from the first access node at the second access node, each second message including one or more second Nth layer service data units associated with said data bearer and a second connection configuration, for (N+1 )th layer processing at the second access node; and wherein the header of each second message includes an identifier associated with the second connection configuration, and the header of each first message includes an identifier associated with the first connection configuration.

In one embodiment, the memory and computer program code are further configured to, with the processor, cause the apparatus to send from the second access node to the first access node information about said identifier associated with said second configuration.

There is also hereby provided a computer program product comprising program code means which when loaded into a computer controls the computer to: perform Nth layer processing of Nth layer protocol data units at a first access node operating one or more first cells, including forming Nth layer service data units from said Nth layer protocol data units; and sending from the first access node to a second access node operating one or more second cells information about buffering of Nth layer service data units at the first access node. There is also hereby provided a computer program product comprising program code means which when loaded into a computer controls the computer to: receive at a second access node operating one or more second cells from a first access node operating one or more first cells information about buffering of Nth layer service data units at the first access node.

There is also hereby provided a computer program product comprising program code means which when loaded into a computer controls the computer to: perform Nth layer processing of Nth layer protocol data units at a first access node operating one or more first cells, including forming one or more Nth layer service data units from said Nth layer protocol data units; and send one or more Nth layer service data units from the first access node to the second access node together with an indication to the second access node of a change in connection configuration for the one or more Nth layer service data units.

There is also hereby provided a computer program product comprising program code means which when loaded into a computer controls the computer to: send one or more first messages from a first access node operating one or more first cells to a second access node operating one or more second cells, each first message including one or more first Nth layer service data units associated with a data bearer and a first connection configuration; send one or more second messages from the first access node to the second access node, each second message including one or more second Nth layer service data units associated with said data bearer and a second connection

There is also hereby provided a computer program product comprising program code means which when loaded into a computer controls the computer to: receive at a second access node operating one or more second cells from a first access node operating one or more first cells one or more Nth layer service data units together with an indication to the second access node of a change in connection configuration to a new connection configuration for the one or more Nth layer service data units; and perform (N+1 )th layer processing of said one or more Nth layer service data units at the second access node according to configuration information for the new connection configuration.

There is also hereby provided a computer program product comprising program code means which when loaded into a computer controls the computer to: receive one or more first messages from a first access node operating one or more first cells at a second access node operating one or more second cells, each first message including one or more first Nth layer service data units associated with a data bearer and a first connection configuration, for (N+1 )th layer processing at the second access node; receive one more second messages from the first access node at the second access node, each second message including one or more second Nth layer service data units associated with said data bearer and a second connection configuration, for (N+1 )th layer processing at the second access node; and wherein the header of each second message includes an identifier associated with the second connection configuration, and the header of each first message includes an identifier associated with the first connection configuration. Embodiments of the present invention are described in detail hereunder, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 illustrates the operation of a split data bearer;

Figure 2 schematically illustrates a communication device within the coverage of two access nodes associated with a split data bearer;

Figure 3 schematically illustrates an example of apparatus for use at the communication device of Figure 2;

Figure 4 schematically illustrates an example of apparatus for use at the access nodes of Figure 2; Figure 5 illustrates one example of a protocol layer stack and the relationship between service data units and protocol data units for each layer;

Figure 6 schematically illustrates an example of a message sequence according to one embodiment;

Figure 7 illustrates an example of operations at master and secondary access nodes according to the same embodiment;

Figure 8 illustrates an example of operations at master and secondary access nodes according to another embodiment;

Figure 9 illustrates an example of operations at master and secondary access nodes according to yet another embodiment; and Figure 10 illustrates an example of a message for use in one embodiment. Figure 2 illustrates a communication device (UE) 8 within the coverage of two eNodeBs 2a, 2b involved in the operation of at least two data bearers between the communication device and a core network 4: (i) a master cell group (MCG) data bearer (for which all PDCP, RLC and MAC layer processing and radio transmission/reception is carried out at the same eNodeB) and (ii) a split data bearer. As shown in Figure 2, there is a direct connection between the core network 4 and each of the eNodeBs 2a, 2b, but the operation of the split data bearer involves the transfer of any data received at, or transmitted by, the secondary eNodeB 2b t to/from the core network 4 via PDCP processing at the master eNodeB 2a.

Figure 2 only shows two eNodeBs, but a typical cellular radio access network will typically comprise thousands of eNodeBs, each operating a respective cell or group of cells, and collectively providing a wide, continuous coverage area.

Figure 3 shows a schematic view of an example of user equipment 8 that may be used for communicating with at least the eNBs 2a, 2b of Figure 2 via a wireless interface. The user equipment (UE) 8 may be used for various tasks such as making and receiving phone calls, for receiving and sending data from and to a data network and for experiencing, for example, multimedia or other content.

The UE 8 may be any device capable of at least sending or receiving radio signals to or from at least the eNBs 2 of Figure 2. Non-limiting examples include a mobile station (MS), a portable computer provided with a wireless interface card or other wireless interface facility, personal data assistant (PDA) provided with wireless communication capabilities, or any combinations of these or the like. The UE 8 may communicate via an appropriate radio interface arrangement of the UE 8. The interface arrangement may be provided for example by means of a radio part and associated antenna arrangement 205. The antenna arrangement may be arranged internally or externally to the UE 8, and may include a plurality of antennas capable of operating in a multi-layer transmission scheme.

The UE 8 may be provided with at least one data processing entity 203 and at least one memory or data storage entity 217 for use in tasks it is designed to perform. The data processor 213 and memory 217 may be provided on an appropriate circuit board 219 and/or in chipsets.

The user may control the operation of the UE 8 by means of a suitable user interface such as key pad 201 , voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 215, a speaker and a microphone may also be provided. Furthermore, the UE 8 may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external accessories, for example hands-free equipment, thereto.

Figure 3 shows an example of a UE including a user interface, but the UE may also be a communication device without any user interface, such as a device that is designed for machine type communications (MTC).

Figure 4 shows an example of apparatus for use at the eNBs 2a, 2b of Figure 1 . The apparatus comprises a radio frequency antenna array 301 configured to receive and transmit radio frequency signals; radio frequency interface circuitry 303 configured to interface the radio frequency signals received and transmitted by the antenna array 301 and the data processor 306. The radio frequency interface circuitry 303 may also be known as a transceiver. The apparatus also comprises an interface 309 via which it can send and receive information to and from one or more other network nodes such as the core network 4 and other eNBs 2. The data processor 306 is configured to process signals from the radio frequency interface circuitry 303, control the radio frequency interface circuitry 303 to generate suitable RF signals to communicate information to the UE 8 via the wireless communications link, and also to exchange information with other network nodes via the interface 309. The memory 307 is used for storing data, parameters and instructions for use by the data processor 306.

It would be appreciated that the apparatus shown in each of figures 3 and 4 described above may comprise further elements which are not directly involved with the embodiments of the invention described hereafter.

One example of the use of split data bearers is in LTE (Long Term Evolution) dual connectivity (DC) operations in which a multiple RX/TX UE in RRC_CONNECTED mode is configured to utilise radio resources provided by two distinct schedulers located in two eNBs connected via a non-ideal backhaul over a X2 interface between the two eNBs (as described at 3GPP TR36.842 and 3GPP TR36.932). eNBs involved in DC for a certain UE may assume one of two different roles: an eNB may either act as a master eNB

(MeNB) or as a secondary eNB (SeNB); in DC a UE is connected both to one MeNB and to at least one SeNB.

In LTE DC, a split data bearer for a UE is partly served by one or more serving cells operated by the SeNB and configured for the UE, which one or more serving cells are referred to as a Secondary Cell Group (SCG) and include a primary secondary cell (PSCell) and possibly one or more other secondary cells (SCell).

According to this example, the operation of the split data bearer involves performing all PDCP layer processing at the MeNB 2a and performing lower layer (RLC, MAC and PHY layers) processing (and radio transmission/reception) for at least some of the data at the SeNB 2b. Figure 5 illustrates the relationship between data units in different protocol layers. For the uplink, RLC layer processing at the SeNB 2b includes extracting one or more RLC SDUs from one or more correctly received RLC-PDUs (MAC-SDUs); and PDCP layer processing of RLC-SDUs at the MeNB includes removing the PDCP Header (Hdr), and deciphering the PDCP-SDU using the deciphering key associated with the data bearer. As shown in Figure 5, an Nth layer SDU corresponds to a (N+1 )th layer PDU. For example, a RLC-SDU corresponds to a PDCP-PDU.

Operation of a split data bearer may involve a change in configuration during the life of the split data bearer. Examples of situations in which such a change may occur are: A) a handover of the UE between cells operated by the MeNB (Intra-MeNB handover), either with or without a handover of the UE between SeNB cells; and B) a handover of the UE between SeNB cells.

RLC layer processing in Acknowledged Mode (AM) at the SeNB 2b may involve sending RLC SDUs to the MeNB in ascending order based on RLC sequence number (SN) of RLC PDUs, which SN is identified in the RLC header of the RLC PDU including the RLC SDU. Because of e.g. HARQ operations at the MAC layer, one or more RLC SDUs may be ready for sending to the MeNB 2a before one or more others earlier in the ordered sequence of RLC SDUs. In such an event, the SeNB 2b stores out-of-order RLC SDUs in a RLC receiving buffer until the SeNB 2b receives the late RLC-SDUs to complete the ordered sequence (at which point the SeNB then proceeds to send the RLC SDUs in the buffer to the MeNB in ascending order of RLC sequence number). In the event of a configuration change for the split data bearer during the life of the split data bearer, the MeNB 2a may send a PDCP status report to the UE 8 identifying which PDCP-PDUs (RLC-SDUs) have been correctly received and identifying any missing PDCP-PDUs; and the UE 8 resends any missing PDCP PDUs after re-establishment of an RLC entity for the split data bearer.

Figure 6 shows an example of one sequence of messages according to one embodiment in the event of a data bearer configuration change instigated by the MeNB 2a; and Figure 7 shows one example of operations at the MeNB and SeNB for the same embodiment. The SeNB 2b processes correctly received MAC-SDUs and stores in a RLC receiving buffer any RLC-SDUs that are out of sequence (i.e. for which SeNB is waiting for correctly received RLC-SDUs earlier in the sequence of RLC-SDUs) ( STEPs 700 and 702 of Figure 7). In the event of a configuration change for the split data bearer, the MeNB 2a sends to SeNB 4 a SeNB Modification Request message, which comprises information for re-establishment of a RLC entity at the SeNB (Message 1 of Figure 6). The SeNB 2b re- establishes the current RLC entity for the split data bearer (Action 1 a of Figure 6). At this time, some RLC-SDUs (PDCP-PDUs) may be stored in the UL receiving buffer at SeNB 2b awaiting the arrival of missing RLC-SDUs for in-order delivery of RLC SDUs to MeNB 2a. The SeNB 2b responds with a SeNB Modification Request Acknowledgment message, which may comprise radio configuration information, and which indicates the PDCP sequence numbers identified in the PDCP header part of the RLC-SDUs stored in the UL receiving buffer at SeNB (Message 2 of Figure 6 and STEP 704 of Figure 7). Although PDCP layer processing of RLC-SDUs is carried out at the MeNB 2a, the SeNB 2b can inspect the PDCP header part of the RLC-SDUs to find the respective PDCP sequence number for each RLC-SDU. The SeNB 2b may not at this stage send the RLC- SDUs in the UL receiving buffer to the MeNB 2a. If there happens to be no RLC-SDUs in the RLC receiving buffer at the SeNB for flushing to the MeNB, the SeNB sends an indication of this to the MeNB.

After completion of the RRC connection reconfiguration procedure (including messages 3 and 4 of Figure 6), the MeNB 2a prepares a PDCP status report for transmission to UE 8 based at least partly on the buffering information received from the SeNB (sequence number information received from SeNB 2b (Message 4a of Figure 6 and STEP 706 of Figure 7) in the case that there are RLC-SDUs in the receiving buffer at the SeNB). This PDCP status report indicates the RLC-SDUs that were correctly received for the split data bearer. After the SeNB reconfiguration is complete (Message 5 of Figure 6), a random access procedure may be carried out including the UE 8 performing synchronisation towards the SeNB 2b (Action 6 of Figure 6). The SeNB 2b may only thereafter send any RLC-SDUs stored in the UL receiving buffer to the MeNB 2a (message 7 of Figure 6 and STEP 708 of Figure 7). This technique has the advantage that the MeNB 2a can send the PDCP status report before receiving all the RLC-SDUs buffered at the SeNB 2b, and thereby reduce delays.

Figure 8 illustrates another example of operations at the MeNB and SeNB according to another embodiment. SeNB 2b receives from UE 8 (via the Physical and MAC layers) RLC-SDUs according to a first configuration for the split data bearer (STEP 800 of Figure 8). SeNB 2b delivers received RLC-SDUs to the MeNB 2a (STEP 802), and the MeNB 2a performs PDCP processing of the RLC SDUs including deciphering using the deciphering key associated with the first configuration for the split data bearer (STEP 804). After a configuration change for the split data bearer and re-establishment of RLC at the SeNB 2b, the SeNB 2a receives RLC-SDUs according to the new configuration, and delivers them to the MeNB 2a for PDCP processing. The first RLC-SDU that SeNB 2b receives and sends to MeNB 2a after RLC reestablishment is delivered to MeNB 2a together with an explicit indication that the RLC-SDU was received after RLC reestablishment (STEP 806). The MeNB 2a processes this RLC-SDU and all subsequently received RLC-SDUs received from the SeNB 2b according to the PDCP deciphering information etc. it has for the new configuration. GTP-U and X2UP protocol messages are examples of messages for delivering RLC-SDUs from the SeNB 2b to the MeNB 2a for PDCP processing at the MeNB 2a; and the explicit indication can take the form of a predetermined bit value in a predetermined field of the header of the GTP-U or X2UP message including the first RLC- SDU in its payload. With this technique, the MeNB 2a can quickly and assuredly identify which RLC-SDUs from the SeNB are according to which configuration, e.g. which RLC- SDUs received from the SeNB are to be PDCP-processed at the MeNB 2a according to which PDCP deciphering key etc.

Figure 9 illustrates another example of operations at the MeNB 2a and SeNB 2b according to one embodiment. This technique is similar to that of Figure 8 except that each RLC-SDU is delivered from the SeNB 2b to the MeNB 2a together with an identifier that the MeNB associates with the bearer configuration for the RLC-SDU. Because the main aim for this technique is to clearly notify the MeNB 2a about which RLC-SDUs were received at SeNB before re-establishment of the RLC at the SeNB and which were received after re-establishment of the RLC at the SeNB (by which the MeNB can determine which bearer configuration applies to each RLC-SDU received from SeNB), it may be sufficient to use only two identifiers, and switch back and forth between the two at times of RLC re-establishment at the SeNB. With reference to Figure 9, SeNB 2b receives from UE (via the PHY and MAC layers) RLC-SDUs before RLC re-establishment (which are according to a first configuration for the split data bearer) (STEP 900). SeNB 2b delivers received RLC-SDUs to the MeNB 2a, each together with a first identifier value (which the MeNB associates with the first configuration) (STEP 902). The MeNB processes the RLC-SDUs according to the deciphering information it has for the first configuration (STEP 904). After a configuration change for the split data bearer and re- establishment of RLC at the SeNB, the SeNB 2b receives RLC-SDUs according to the new configuration (STEP 906), and delivers them to the MeNB 2a together with a different, second identifier value, (STEP 908), which the MeNB associates with the new configuration and by which the MeNB 2a can identify that the RLC SDUs were received at the SeNB after re-establishment of RLC at the SeNB. The MeNB 2a processes the RLC- SDUs received together with the second identifier value according to the deciphering information etc. it has for the new configuration (STEP 910).

As mentioned above, GTP-U protocol messages are one example of messages for delivering RLC-SDUs from the SeNB to the MeNB for PDCP processing at the MeNB. Figure 10 shows one example of the structure of a header for a GPRS Tunnelling Protocol User Plane (GTP-U) message including one or more RLC-SDUs in its payload. One example for implementing this technique is to change the GTP Tunnel-Endpoint Identifier (TEID) from an old TEID to a new TEID for all RLC-SDUs received at SeNB after a re- establishment of the RLC entity. The TEID identifier to be used for all RLC-SDUs received after re-establishment of RLC at the SeNB may be provided by the MeNB to the SeNB. The above-described operations may require data processing in the various entities. The data processing may be provided by means of one or more data processors. Similarly various entities described in the above embodiments may be implemented within a single or a plurality of data processing entities and/or data processors. Appropriately adapted computer program code product may be used for implementing the embodiments, when loaded to a computer. The program code product for providing the operation may be stored on and provided by means of a carrier medium such as a carrier disc, card or tape. A possibility is to download the program code product via a data network. Implementation may be provided with appropriate software in a server. For example the embodiments of the invention may be implemented as a chipset, in other words a series of integrated circuits communicating among each other. The chipset may comprise microprocessors arranged to run code, application specific integrated circuits (ASICs), or programmable digital signal processors for performing the operations described above. Embodiments of the invention may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a

semiconductor substrate. Programs, such as those provided by Synopsys, Inc. of Mountain View, California and Cadence Design, of San Jose, California automatically route conductors and locate components on a semiconductor chip using well established rules of design as well as libraries of pre stored design modules. Once the design for a semiconductor circuit has been completed, the resultant design, in a standardized electronic format (e.g., Opus, GDSII, or the like) may be transmitted to a semiconductor fabrication facility or "fab" for fabrication. In addition to the modifications explicitly mentioned above, it will be evident to a person skilled in the art that various other modifications of the described embodiment may be made within the scope of the invention.

Claims

1 . A method comprising: performing Nth layer processing of Nth layer protocol data units at a first access node operating one or more first cells, including forming Nth layer service data units from said Nth layer protocol data units; and sending from the first access node to a second access node operating one or more second cells information about buffering of Nth layer service data units at the first access node.

2. A method according to claim 1 , wherein said buffering information comprises header information included in the (N+1 )th layer header part of one or more Nth layer service data units.

3. A method according to claim 2, comprising sending said header information in advance of sending said one or more Nth layer service data units from the first access node to the second access node.

4. A method according to claim 1 , comprising: sending from the first access node to the second access node an indication that the first access node has no out-of-sequence Nth layer service data units for delivery to the second access node.

5. A method according to claim 2, wherein the header information comprises one or more (N+1 )th layer sequence numbers for said one or more Nth layer service data units.

6. A method according to any of claims 2, 3 and 5, wherein said one or more Nth layer service data units are part of a broken sequence of Nth layer service data units; and wherein the method further comprises storing said one or more Nth layer service data units in a buffer at the first access node in the absence of one or more Nth layer service data units required to complete said broken sequence; and sending said header information from said first access node to said second access node in response to a re- establishment of an Nth layer protocol entity before completion of said sequence.

7. A method comprising: receiving at a second access node operating one or more second cells from a first access node operating one or more first cells information about buffering of Nth layer service data units at the first access node.

8. A method according to claim 7, wherein said buffering information comprises header information included in the (N+1 )th layer header part of one or more Nth layer service data units.

9. A method according to claim 8, comprising receiving said header information at the second access node in advance of receiving said one or more Nth layer service data units from the first access node at the second access node for (N+1 )th layer processing at the second access node

10. A method according to claim 7, comprising: receiving from the first access node at the second access node an indication that the first access node has no out-of-sequence Nth layer service data units for delivery to the second access node.

1 1 . A method according to any of claims 7 to 10, further comprising generating a (N+1 )th layer status report using said received information about buffering of Nth layer service data units at the first access node.

12. A method comprising: performing Nth layer processing of Nth layer protocol data units at a first access node operating one or more first cells, including forming one or more Nth layer service data units from said Nth layer protocol data units; and sending one or more Nth layer service data units from the first access node to the second access node together with an indication to the second access node of a change in connection configuration for the one or more Nth layer service data units.

13. A method according to claim 12, wherein said indication is included in the header of a message including one or more Nth layer service data units.

14. A method according to claim 12, wherein said indication is selectively included in the header of a message including the first of the Nth layer service data units sent to the second access node after a change in connection configuration.

15. A method, comprising: sending one or more first messages from a first access node operating one or more first cells to a second access node operating one or more second cells, each first message including one or more first Nth layer service data units associated with a data bearer and a first connection configuration; sending one or more second messages from the first access node to the second access node, each second message including one or more second Nth layer service data units associated with said data bearer and a second connection configuration ; and wherein the header of each second message includes an identifier associated with the second connection configuration, and the header of each first message includes an identifier associated with the first connection configuration.

16. A method according to claim 1 5, comprising receiving at the first access node from the second access node information about said identifier associated with said second configuration.

17. A method according to any of claims 12 to 16, wherein the first connection configuration comprises a first Nth layer protocol entity, and the second connection configuration comprises a second Nth layer protocol entity.

18. A method comprising: receiving at a second access node operating one or more second cells from a first access node operating one or more first cells one or more Nth layer service data units together with an indication to the second access node of a change in connection configuration to a new connection configuration for the one or more Nth layer service data units; and performing (N+1 )th layer processing of said one or more Nth layer service data units at the second access node according to configuration information for the new connection configuration.

19. A method according to claim 18, wherein said indication is included in the header of a message including one or more Nth layer service data units.

20. A method according to claim 19, wherein said indication is selectively included in the header of a message including the first of the Nth layer service data units received at the second access node after said change to said new connection configuration.

21 . A method, comprising: receiving one or more first messages from a first access node operating one or more first cells at a second access node operating one or more second cells, each first message including one or more first Nth layer service data units associated with a data bearer and a first connection configuration, for (N+1 )th layer processing at the second access node; receiving one more second messages from the first access node at the second access node, each second message including one or more second Nth layer service data units associated with said data bearer and a second connection configuration, for (N+1 )th layer processing at the second access node; and wherein the header of each second message includes an identifier associated with the second connection configuration, and the header of each first message includes an identifier associated with the first connection

configuration.

22. A method according to claim 21 , comprising sending from the second access node to the first access node information about said identifier associated with said second configuration.

23. A method according to any of claims 18 to 22, wherein the first connection configuration comprises a first Nth layer protocol entity, and the second connection configuration comprises a second Nth layer protocol entity.

24. A method according to any preceding claim, wherein said Nth layer is a radio link control layer and said (N+1 )th layer is a packet data convergence protocol layer.

25. An apparatus comprising: a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to: perform Nth layer processing of Nth layer protocol data units at a first access node operating one or more first cells, including forming Nth layer service data units from said Nth layer protocol data units; and sending from the first access node to a second access node operating one or more second cells information about buffering of Nth layer service data units at the first access node.

26. An apparatus according to claim 25, wherein said buffering information comprises header information included in the (N+1 )th layer header part of one or more Nth layer service data units.

27. An apparatus according to claim 26, wherein the memory and computer program code are further configured to, with the processor, cause the apparatus to send said header information in advance of sending said one or more Nth layer service data units from the first access node to the second access node .

28. An apparatus according to claim 25, wherein the memory and computer program code are further configured to, with the processor, cause the apparatus to send from the first access node to the second access node an indication that the first access node has no out-of-sequence Nth layer service data units for delivery to the second access node.

29. An apparatus according to claim 26, wherein the header information comprises one or more (N+1 )th layer sequence numbers for said one or more Nth layer service data units.

30. An apparatus according to any of claims 26, 27 and 29, wherein said one or more Nth layer service data units are part of a broken sequence of Nth layer service data units; and wherein the memory and computer program code are further configured to, with the processor, cause the apparatus to store said one or more Nth layer service data units in a buffer at the first access node in the absence of one or more Nth layer service data units required to complete said broken sequence; and send said header information from said first access node to said second access node in response to a re-establishment of an Nth layer protocol entity before completion of said sequence.

31 . An apparatus comprising: a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to: receive at a second access node operating one or more second cells from a first access node operating one or more first cells information about buffering of Nth layer service data units at the first access node.

32. An apparatus according to claim 31 , wherein said buffering information comprises header information included in the (N+1 )th layer header part of one or more Nth layer service data units.

33. An apparatus according to claim 32, wherein the memory and computer program code are further configured to, with the processor, cause the apparatus to receive said header information at the second access node in advance of receiving said one or more Nth layer service data units from the first access node at the second access node for (N+1 )th layer processing at the second access node.

34. An apparatus according to claim 31 , wherein the memory and computer program code are further configured to, with the processor, cause the apparatus to receive from the first access node at the second access node an indication that the first access node has no out-of-sequence Nth layer service data units for delivery to the second access node.

35. An apparatus according to any of claims 31 to 34, wherein the memory and computer program code are further configured to, with the processor, cause the apparatus to generate a (N+1 )th layer status report using said received information about buffering of Nth layer service data units at the first access node.

36. An apparatus comprising: a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to: perform Nth layer processing of Nth layer protocol data units at a first access node operating one or more first cells, including forming one or more Nth layer service data units from said Nth layer protocol data units; and send one or more Nth layer service data units from the first access node to the second access node together with an indication to the second access node of a change in connection configuration for the one or more Nth layer service data units.

37. An apparatus according to claim 36, wherein said indication is included in the header of a message including one or more Nth layer service data units.

38. An apparatus according to claim 36, wherein said indication is selectively included in the header of a message including the first of the Nth layer service data units sent to the second access node after a change in connection configuration.

39. An apparatus comprising: a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to: send one or more first messages from a first access node operating one or more first cells to a second access node operating one or more second cells, each first message including one or more first Nth layer service data units associated with a data bearer and a first connection configuration; send one or more second messages from the first access node to the second access node, each second message including one or more second Nth layer service data units associated with said data bearer and a second connection configuration; and wherein the header of each second message includes an identifier associated with the second connection configuration, and the header of each first message includes an identifier associated with the first connection configuration.

40. An apparatus according to claim 39, wherein the memory and computer program code are further configured to, with the processor, cause the apparatus to receive at the first access node from the second access node information about said identifier associated with said second configuration.

41 . An apparatus according to any of claims 36 to 40, wherein the first connection configuration comprises a first Nth layer protocol entity, and the second connection configuration comprises a second Nth layer protocol entity.

42. An apparatus comprising: a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to: receive at a second access node operating one or more second cells from a first access node operating one or more first cells one or more Nth layer service data units together with an indication to the second access node of a change in connection configuration to a new connection configuration for the one or more Nth layer service data units; and perform (N+1 )th layer processing of said one or more Nth layer service data units at the second access node according to configuration information for the new connection configuration.

43. An apparatus according to claim 42, wherein said indication is included in the header of a message including one or more Nth layer service data units.

44. An apparatus according to claim 43, wherein said indication is selectively included in the header of a message including the first of the Nth layer service data units received at the second access node after said change to said new connection configuration.

45. An apparatus comprising: a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to: receive one or more first messages from a first access node operating one or more first cells at a second access node operating one or more second cells, each first message including one or more first Nth layer service data units associated with a data bearer and a first connection configuration, for (N+1 )th layer processing at the second access node; receive one more second messages from the first access node at the second access node, each second message including one or more second Nth layer service data units associated with said data bearer and a second connection configuration, for (N+1 )th layer processing at the second access node; and wherein the header of each second message includes an identifier associated with the second connection configuration, and the header of each first message includes an identifier associated with the first connection configuration.

46. An apparatus according to claim 45, wherein the memory and computer program code are further configured to, with the processor, cause the apparatus to send from the second access node to the first access node information about said identifier associated with said second configuration.

47. An apparatus according to any of claims 42 to 46, wherein the first connection configuration comprises a first Nth layer protocol entity, and the second connection configuration comprises a second Nth layer protocol entity.

48. An apparatus according to any of claims 25 to 47, wherein said Nth layer is a radio link control layer and said (N+1 )th layer is a packet data convergence protocol layer.

49. A computer program product comprising program code means which when loaded into a computer controls the computer to: perform Nth layer processing of Nth layer protocol data units at a first access node operating one or more first cells, including forming Nth layer service data units from said Nth layer protocol data units; and sending from the first access node to a second access node operating one or more second cells information about buffering of Nth layer service data units at the first access node.

50. A computer program product comprising program code means which when loaded into a computer controls the computer to: receive at a second access node operating one or more second cells from a first access node operating one or more first cells information about buffering of Nth layer service data units at the first access node.

51 . A computer program product comprising program code means which when loaded into a computer controls the computer to: perform Nth layer processing of Nth layer protocol data units at a first access node operating one or more first cells, including forming one or more Nth layer service data units from said Nth layer protocol data units; and send one or more Nth layer service data units from the first access node to the second access node together with an indication to the second access node of a change in connection configuration for the one or more Nth layer service data units.

52. A computer program product comprising program code means which when loaded into a computer controls the computer to: send one or more first messages from a first access node operating one or more first cells to a second access node operating one or more second cells, each first message including one or more first Nth layer service data units associated with a data bearer and a first connection configuration; send one or more second messages from the first access node to the second access node, each second message including one or more second Nth layer service data units associated with said data bearer and a second connection configuration; and wherein the header of each second message includes an identifier associated with the second connection configuration, and the header of each first message includes an identifier associated with the first connection configuration.

53. A computer program product comprising program code means which when loaded into a computer controls the computer to: receive at a second access node operating one or more second cells from a first access node operating one or more first cells one or more Nth layer service data units together with an indication to the second access node of a change in connection configuration to a new connection configuration for the one or more Nth layer service data units; and perform (N+1 )th layer processing of said one or more Nth layer service data units at the second access node according to configuration information for the new connection configuration.

54. A computer program product comprising program code means which when loaded into a computer controls the computer to: receive one or more first messages from a first access node operating one or more first cells at a second access node operating one or more second cells, each first message including one or more first Nth layer service data units associated with a data bearer and a first connection configuration, for (N+1 )th layer processing at the second access node; receive one more second messages from the first access node at the second access node, each second message including one or more second Nth layer service data units associated with said data bearer and a second connection configuration, for (N+1 )th layer processing at the second access node; and wherein the header of each second message includes an identifier associated with the second connection configuration, and the header of each first message includes an identifier associated with the first connection configuration.