9.2 Formats and parameters

25.3223GPPRadio Link Control (RLC) protocol specificationRelease 17TS

The formats of RLC PDUs and their parameters defined in this subclause are normative.

9.2.1 Formats

This subclause specifies the format of the RLC PDUs. The parameters of each RLC PDU are explained in subclause 9.2.2.

9.2.1.1 General

An RLC PDU is a bit string. In the figures in subclause 9.2, bit strings are represented by tables in which the first bit is the leftmost one on the first line of the table, the last bit is the rightmost one on the last line of the table, and more generally the bit string is to be read from left to right and then in the reading order of the lines.

Depending on the provided service, RLC SDUs are bit strings, with any non-null length, or bit strings with a multiple of 8 bits in length. An RLC SDU is included into an RLC PDU from first bit onward.

9.2.1.2 TMD PDU

The TMD PDU is used to transfer user data when RLC is operating in transparent mode. No overhead is added to the SDU by RLC. The data length is not constrained to be a multiple of 8 bits.

Figure 9.1: TMD PDU

9.2.1.3 UMD PDU

The UMD PDU is used to transfer user data when RLC is operating in unacknowledged mode. The length of the data part shall be a multiple of 8 bits. The UMD PDU header consists of the first octet, which contains the "Sequence Number". The RLC header consists of the first octet and all the octets that contain "Length Indicators".

Figure 9.2: UMD PDU

NOTE (1): The "Length Indicator" may be 15 bits.

9.2.1.4 AMD PDU

The AMD PDU is used to transfer user data, piggybacked status information and the Polling bit when RLC is operating in acknowledged mode. The length of the data part shall be a multiple of 8 bits. The AMD PDU header consists of the first two octets, which contain the "Sequence Number". The RLC header consists of the first two octets and all the octets that contain "Length Indicators".

Figure 9.3: AMD PDU

NOTE (1): The "Length Indicator" may be 15 bits.

9.2.1.5 STATUS PDU

The STATUS PDU is used to exchange status information between two RLC AM entities.

The format of the STATUS PDU is given in figure 9.4 below. The length of each super field (SUFI) is dependent on its type and contents.

Figure 9.4: STATUS PDU

A STATUS PDU can include super-fields of different types. The size of a STATUS PDU is variable and upper bounded by the maximum RLC PDU size used by the logical channel on which the control PDUs are sent. If fixed RLC PDU size has been configured by upper layers, padding shall be included to match one of the PDU sizes used by the logical channel on which the control PDUs are sent. The length of the STATUS PDU shall be a multiple of 8 bits. If flexible RLC PDU size has been configured by upper layers padding is only included to make the length of the STATUS PDU a multiple of 8 bits.

9.2.1.6 Piggybacked STATUS PDU

The format of the piggybacked STATUS PDU is the same as for the STATUS PDU except that the D/C field is replaced by a reserved bit (R2). This PDU can be piggybacked in an AMD PDU if the data leaves out enough room in the AMD PDU. The PDU Type field is set to "000" and all other values are invalid for this version of the protocol.

Figure 9.5: Piggybacked STATUS PDU

9.2.1.7 RESET, RESET ACK PDU

The RESET PDU includes a one-bit sequence number field (RSN). The value of this bit is carried over in the RESET ACK PDU sent in response in order to allow the peer entity to identify which RESET PDU it was sent in response to.

Figure 9.6: RESET, RESET ACK PDU

The size of a RESET or RESET ACK PDU is variable and upper bounded by the maximum RLC PDU size used by the logical channel on which the control PDUs are sent. If fixed RLC PDU size has been configured by upper layers, padding shall be included to match one of the PDU sizes used by the logical channel on which the control PDUs are sent. The length of the RESET or RESET ACK PDU shall be a multiple of 8 bits. If flexible RLC PDU size has been configured by upper layers padding is only included to make the length of the RESET or RESET ACK PDU a multiple of 8 bits.

9.2.2 Parameters

If not otherwise mentioned in the definition of each field, the bits in the parameters shall be interpreted as follows: the left-most bit string is the first and most significant and the right most bit is the last and least significant bit.

Unless otherwise mentioned, integers are encoded in standard binary encoding for unsigned integers. In all cases, including when a value extends over more than one octet as shown in the tables, the bits appear ordered from MSB to LSB when read in the RLC PDU.

9.2.2.1 D/C field

Length: 1bit.

The D/C field indicates the type of an AM PDU. It can be either data or control PDU.

Bit

Description

0

Control PDU

1

Data PDU

9.2.2.2 PDU Type

Length: 3 bit.

The PDU type field indicates the Control PDU type.

Bit

PDU Type

000

STATUS

001

RESET

010

RESET ACK

011-111

Reserved (PDUs with this coding will be discarded by this version of the protocol).

9.2.2.3 Sequence Number (SN)

This field indicates the "Sequence Number" of the RLC PDU, encoded in binary.

PDU type

Length

Notes

AMD PDU

12 bits

Used for retransmission and reassembly

UMD PDU

7 bits

Used for reassembly

9.2.2.4 Polling bit (P)

Length: 1bit.

This field is used to request a status report (one or several STATUS PDUs) from the Receiver.

Bit

Description

0

Status report not requested

1

Request a status report

9.2.2.5 Extension bit (E)

Length: 1bit.

The interpretation of this bit depends on RLC mode and higher layer configuration:

– In the UMD PDU, the "Extension bit" in the first octet has either the normal E-bit interpretation or the alternative E-bit interpretation depending on higher layer configuration. The "Extension bit" in all the other octets always has the normal E-bit interpretation.

– In the AMD PDU, the "Extension bit" always has the normal E-bit interpretation.

Normal E-bit interpretation:

Bit

Description

0

The next field is data, piggybacked STATUS PDU or padding

1

The next field is Length Indicator and E bit

Alternative E-bit interpretation:

Bit

Description

0

The next field is a complete SDU, which is not segmented, concatenated or padded.

1

The next field is Length Indicator and E bit

9.2.2.6 Reserved 1 (R1)

Length: 3 bits.

This field in the RESET PDU and RESET ACK PDU is used to have a multiple of 8 bits in length. Its shall always be coded to "000". Other values are reserved and will be considered invalid for this version of the protocol.

9.2.2.7 Header Extension Type (HE)

Length: 2 bits.

This two-bit field indicates if the next octet is data or a "Length Indicator" and E bit.

Value

Description

00

The succeeding octet contains data

01

The succeeding octet contains a length indicator and E bit

10

This value is the special value of HE field and indicates that the succeeding octet contains data and the last octet of the PDU is the last octet of an SDU.

11

Reserved (PDUs with this coding will be discarded by this version of the protocol).

9.2.2.8 Length Indicator (LI)

Unless the "Extension bit" indicates that a UMD PDU contains a complete SDU which is not segmented, concatenated or padded, or the HE field indicates that an AMD PDU contains the last octet of the RLC SDU, a "Length Indicator" is used to indicate the last octet of each RLC SDU ending within the PDU. If the "Extension bit" indicates that the UMD PDU contains a complete SDU which is not segmented, concatenated or padded, or the HE field indicates that an AMD PDU contains the last octet of the SDU, no LIs are present in this RLC PDU.

Except for the predefined values reserved for special purposes and listed in the tables below, the "Length Indicator" shall:

– be set to the number of octets between the end of the RLC header and up to and including the last octet of an RLC SDU segment;

– be included in the PDUs that they refer to.

The size of the "Length Indicator" may be either 7 bits or 15 bits. The "Length Indicator" size is determined independently for uplink and downlink. The value of a "Length Indicator" shall not exceed the values specified in subclauses 11.2.4.2 and 11.3.4.5 respectively for UMD and AMD PDUs.

The "Length Indicators" which refer to the same PDU shall:

– not be reordered in case of retransmission;

– be in the same order as the RLC SDUs that they refer to.

For AM uplink and for AM downlink when "Fixed RLC PDU size" is configured:

– if the "AMD PDU size" is  126 octets:

– 7-bit "Length Indicators" shall be used.

– else:

– 15-bit "Length Indicators" shall be used.

– the size of the "Length Indicator" is always the same for all AMD PDUs, for one RLC entity.

For AM downlink and AM uplink when "Flexible RLC PDU size" is configured:

– if "Length Indicator size" is set to 7 bits:

– 7-bit "Length Indicators" shall be used.

– else:

– 15-bit "Length Indicators" shall be used.

For UM uplink:

– if the "largest UL UMD PDU size" is  125 octets:

– 7-bit "Length Indicators" shall be used.

– else:

– 15-bit "Length Indicators" shall be used.

For UM downlink:

– the "Length Indicator" size provided in "DL RLC UM LI size" shall be used.

For UM:

– between modifications of the "largest UMD PDU size", the size of the "Length Indicator" is the same for all UMD PDUs;

– if the RLC SDU begins in the beginning of the RLC PDU; and

– if the RLC PDU is transmitted in uplink; and

– if the "Length Indicators" indicating that a RLC SDU ended exactly in the end or one octet short (only when 15-bit "Length Indicators" is used) of the previous RLC PDU are not present; and

– if the "Extension bit" does not indicate that the UMD PDU contains a complete SDU which is not segmented, concatenated or padded; and

– if the "Length Indicator" indicating that the first data octet in this RLC PDU is the first octet of an RLC SDU and the last octet in this RLC PDU is the last octet of the same RLC SDU is not present; and

– if the "Length Indicator" indicating that the first data octet in this RLC PDU is the first octet of an SDU and the same RLC SDU is one octet short of exactly filling the PDU (only when 15-bit "Length Indicators" is used) is not present:

– if 7-bit "Length Indicator" is used:

– the "Length Indicator" with value "111 1100" shall be used.

– if 15-bit "Length Indicator" is used:

– the "Length Indicator" with value "111 1111 1111 1100" shall be used.

– in downlink:

– if 7-bit "Length Indicator" is used:

– the Receiver shall be prepared to receive the "Length Indicator" with value "111 1100";

– the Receiver shall follow the discard rules in subclause 11.2.3 both when the "Length Indicator" with value "111 1100" is present and when it is absent.

– if 15-bit "Length Indicator" is used:

– the Receiver shall be prepared to receive the "Length Indicator" with value "111 1111 1111 1100";

– the Receiver shall follow the discard rules in subclause 11.2.3 both when the "Length Indicator" with value "111 1111 1111 1100" is present and when it is absent.

In the case where the end of the last segment of an RLC SDU exactly ends at the end of a PDU and there is no "Length Indicator" that indicates the end of the RLC SDU, and the HE field of the PDU does not indicate that the last octet of the AMD PDU is the last octet of an SDU, and the "Extension bit" of the following PDU does not indicate that the UMD PDU contains a complete SDU which is not segmented, concatenated or padded, and the "Length Indicator" of the following PDU does not indicate that the first data octet in that PDU is the first octet of an SDU and the last octet in that PDU is the last octet of the same SDU, and the "Length Indicator" of the following PDU does not indicate that the first data octet in that RLC PDU is the first octet of an SDU and the same RLC SDU is one octet short of exactly filling the PDU (only when 15-bit "Length Indicators" is used):

– if 7-bit "Length Indicator" is used:

– a "Length Indicator" with value "000 0000" shall be placed as the first "Length Indicator" in the following PDU;

– if 15-bit "Length Indicator" is used:

– a "Length Indicator" with value "000 0000 0000 0000" shall be placed as the first "Length Indicator" in the following PDU.

In the case where a PDU contains a 15-bit "Length Indicator" indicating that an RLC SDU ends with one octet left in the PDU, the last octet of this PDU shall:

– be padded by the Sender and ignored by the Receiver though there is no "Length Indicator" indicating the existence of Padding; and

– not be filled with the first octet of the next RLC SDU data.

In the case where 15-bit "Length Indicators" are used in a PDU and the last segment of an RLC SDU is one octet short of exactly filling the PDU and there is no "Length Indicator" that indicates the end of the RLC SDU:

– if a 15-bit "Length Indicator" is used for the following PDU:

– the "Length Indicator" with value "111 1111 1111 1011" shall be placed as the first "Length Indicator" in the following PDU;

– the remaining one octet in the current PDU shall be padded by the Sender and ignored at the Receiver though there is no "Length Indicator" indicating the existence of Padding;

– if a 7-bit "Length Indicator" size is configured for the following PDU:

– if RLC is configured for UM mode:

– if the "Extension bit" of that PDU does not indicate that the UMD PDU contains a complete SDU which is not segmented, concatenated or padded, and the "Length Indicator" of that PDU does not indicate that the first data octet in that PDU is the first octet of an SDU and the last octet in that PDU is the last octet of the same SDU:

– the "Length Indicator" with value "000 0000" shall be placed as the first "Length indicator" in the following PDU;

– the "Sequence Number" shall be incremented by 2 before it is transmitted.

For UM and AM RLC:

– if a 7 bit "Length Indicator" is used in a RLC PDU and one or more padding octets are present in the RLC PDU after the end of the last RLC SDU:

– indicate the presence of padding by including a "Length Indicator" with value "1111111" as the last "Length Indicator" in the PDU.

– if a 15 bit "Length Indicator" is used in a RLC PDU and two or more padding octets are present in the RLC PDU after the end of the last RLC SDU:

– indicate the presence of padding by including a "Length Indicator" with value "111 1111 1111 1111" as the last "Length Indicator" in the PDU.

NOTE: After the "Length Indicator" indicating the presence of padding has been included in the RLC PDU, the length of the padding may be zero.

In the case where the "alternative E-bit interpretation" is configured for UM RLC and an RLC PDU contains a segment of an SDU but neither the first octet nor the last octet of this SDU:

– if a 7-bit "Length Indicator" is used:

– the "Length Indicator" with value "111 1110" shall be used.

– if a 15-bit "Length Indicator" is used:

– the "Length Indicator" with value "111 1111 1111 1110" shall be used.

In the case where the "alternative E-bit interpretation" is configured for UM RLC and the first data octet in this RLC PDU is the first octet of an SDU and the last octet in this RLC PDU is the last octet of the same SDU:

– if a 7-bit "Length Indicator" is used:

– the "Length Indicator" with value "111 1101" shall be used.

– if a 15-bit "Length Indicator" is used:

– the "Length Indicator" with value "111 1111 1111 1101" shall be used.

In the case where the "alternative E-bit interpretation" is configured for UM RLC and the first data octet in this RLC PDU is the first octet of an SDU and the same RLC SDU is one octet short of exactly filling the PDU and a 15-bit "Length Indicator" is used:

– the "Length Indicator" with value "111 1111 1111 1010" shall be used.

If a "Length Indicator" is still awaiting transmission and there is no RLC SDU available, an RLC PDU consisting of this "Length Indicator", the appropriate padding "Length Indicator" and padding may be transmitted.

Predefined values of the "Length Indicator" are used to indicate padding. The values that are reserved for special purposes are listed in the tables below depending on the size of the "Length Indicator". Only predefined "Length Indicator" values can refer to the padding space. These values shall only be placed after all other "Length Indicators" for a PDU.

STATUS PDUs can be piggybacked on the AMD PDU by using part or all of the padding space. A predefined "Length Indicator" shall be used to indicate the presence of a piggybacked STATUS PDU. This "Length Indicator" replaces the padding "Length Indicator". The piggybacked STATUS PDU shall be appended immediately following the PDU data. When only part of the padding space is used, the end of the piggybacked STATUS PDU is indicated by one of the SUFI fields NO_MORE or ACK. Thus no additional "Length Indicator" is required to show that there is still padding in the AMD PDU.

If "SDU discard with explicit signalling" is configured:

– an AMD PDU can contain a maximum number of 15 "Length Indicators" indicating the end of 15 corresponding SDUs; and

– the rest of the AMD PDU space shall be used as padding or as piggybacked STATUS PDU.

Length: 7 bits

Bit

Description

0000000

The previous RLC PDU was exactly filled with the last segment of an RLC SDU and there is no "Length Indicator" that indicates the end of the RLC SDU in the previous RLC PDU.

1111100

UMD PDU: The first data octet in this RLC PDU is the first octet of an RLC SDU. AMD PDU: Reserved (PDUs with this coding will be discarded by this version of the protocol).

1111101

UMD PDU: The first data octet in this RLC PDU is the first octet of an RLC SDU and the last octet in this RLC PDU is the last octet of the same RLC SDU. AMD PDU: Reserved (PDUs with this coding will be discarded by this version of the protocol).

1111110

AMD PDU: The rest of the RLC PDU includes a piggybacked STATUS PDU. UMD PDU: The RLC PDU contains a segment of an SDU but neither the first octet nor the last octet of this SDU.

1111111

The rest of the RLC PDU is padding. The padding length can be zero.

Length: 15bits

Bit

Description

000000000000000

The previous RLC PDU was exactly filled with the last segment of an RLC SDU and there is no "Length Indicator" that indicates the end of the RLC SDU in the previous RLC PDU.

111111111111010

UMD PDU: The first data octet in this RLC PDU is the first octet of an RLC SDU and the second last octet in this RLC PDU is the last octet of the same RLC SDU. The remaining one octet in the RLC PDU is ignored.

111111111111011

The last segment of an RLC SDU was one octet short of exactly filling the previous RLC PDU and there is no "Length Indicator" that indicates the end of the RLC SDU in the previous RLC PDU. The remaining one octet in the previous RLC PDU is ignored.

111111111111100

UMD PDU: The first data octet in this RLC PDU is the first octet of an RLC SDU. AMD PDU: Reserved (PDUs with this coding will be discarded by this version of the protocol).

111111111111101

UMD PDU: The first data octet in this RLC PDU is the first octet of an RLC SDU and the last octet in this RLC PDU is the last octet of the same RLC SDU. AMD PDU: Reserved (PDUs with this coding will be discarded by this version of the protocol).

111111111111110

AMD PDU: The rest of the RLC PDU includes a piggybacked STATUS PDU. UMD PDU: The RLC PDU contains a segment of an SDU but neither the first octet nor the last octet of this SDU.

111111111111111

The rest of the RLC PDU is padding. The padding length can be zero.

9.2.2.9 Data field

RLC SDUs or segments of RLC SDUs are mapped to this field in transparent, unacknowledged and acknowledged modes.

Transparent mode data:

– the length of RLC SDUs is not constrained to a multiple of 8 bits;

– if "Segmentation" is configured:

– all the RLC PDUs carrying segments of a RLC SDU shall be sent in one TTI;

– only RLC PDUs carrying segments from a single RLC SDU shall be sent in one TTI;

– otherwise (Segmentation is not configured):

– TMD PDU size is fixed within a single TTI and is equal to the RLC SDU size.

Unacknowledged mode data and Acknowledged mode data:

– the length of RLC SDUs is constrained to a multiple of 8 bits;

– if "Fixed RLC PDU size" is configured:

– the last segment of an RLC SDU shall be concatenated with the first segment of the next RLC SDU in order to fill the data field completely and avoid unnecessary padding unless otherwise specified in subclause 9.2.2.8 or subclause 11.2.2.2. The "Length Indicator" field is used to point the borders between RLC SDUs (see subclause 9.2.2.8).

– if "Flexible RLC PDU size" is configured:

– in downlink, the last segment of an RLC SDU may be concatenated with the first segment of the next RLC SDU in order to fill the data field up to a maximum RLC PDU size. The "Length Indicator" field is used to point the borders between RLC SDUs (see subclause 9.2.2.8).

– in uplink, the last segment of an RLC SDU shall be concatenated with the first segment of the next RLC SDU in order to fill the data field at least up to the Minimum UL RLC PDU size. It is allowed to concatenate up to the largest UL AMD PDU size for Acknowledged mode data and largest UMD PDU size for Unacknowledged mode data. The "Length Indicator" field is used to point the borders between RLC SDUs (see subclause 9.2.2.8). If data to be transmitted is not enough to create a UMD PDU of the minimum size, it is allowed to create a UMD PDU including all data to be transmitted, even if the resulting size is smaller than the Minimum UL RLC PDU size.

– in uplink, if MAC-i/is has been configured:

– if the UE pre-generates RLC PDUs for transmission in a later TTI and there is only one activated uplink frequency:

– provided that the UE has sufficient amount of data available for transmission, the size of the data field of the RLC PDU shall be chosen so that each RLC PDU to be multiplexed to the MAC-i/is PDU matches the maximum amount of data allowed to be transmitted by the applicable current grant (scheduled or non-scheduled) for the current TTI.

– RLC PDUs may only be pre-generated if the amount of data in outstanding pre-generated RLC PDUs for this logical channel is less than or equal to four times the maximum amount of data allowed to be transmitted by the applicable current grant (scheduled or non-scheduled) for the current TTI.

– else if the UE pre-generates RLC PDUs for transmission in a later TTI and there are two activated uplink frequencies for FDD or more than one scheduled uplink frequencies for 1.28 Mcps TDD:

– provided that the UE has sufficient amount of data available for transmission, the size of the data field of the RLC PDU shall be chosen so that each RLC PDU to be multiplexed to the MAC-i/is PDU matches the minimum of the following:

– For FDD,

– maximum amount of data allowed to be transmitted by the applicable current grant (scheduled or non-scheduled) on the primary uplink frequency for the current TTI.

– maximum amount of data allowed to be transmitted by the applicable current grant (scheduled) on the secondary uplink frequency for the current TTI.

– For 1.28 Mcps TDD,

– maximum amount of data allowed to be transmitted by the applicable current grant (scheduled) on the each scheduled uplink frequency for the current TTI.

– For FDD, RLC PDUs may only be pre-generated if the amount of data in outstanding pre-generated RLC PDUs for this logical channel is less than or equal to eight times the minimum of the following:

– maximum amount of data allowed to be transmitted by the applicable current grant (scheduled or non-scheduled) on the primary uplink frequency for the current TTI.

– maximum amount of data allowed to be transmitted by the applicable current grant (scheduled) on the secondary uplink frequency for the current TTI.

– For 1.28 Mcps TDD, RLC PDUs may only be pre-generated if the amount of data in outstanding pre-generated RLC PDUs for this logical channel is less than or equal to 4N times the minimum of the following:

– maximum amount of data allowed to be transmitted by the applicable current grant (scheduled) of each uplink frequency for the current TTI.

NOTE: N is the number of configured uplink frequencies.

– else:

– the size of the data field of the RLC PDU shall be chosen so that the RLC PDU size matches the data requested for this logical channel by the current E-TFC selection.

– if "Flexible RLC PDU size" is configured, the maximum size of the data field of the RLC PDU is 1503 octets.

9.2.2.10 Padding (PAD)

All unused space in a PDU shall be located at the end of the PDU and is referred to as padding. Padding shall have a length such that the PDU as a whole has one of the predefined total lengths.

Padding may have any value and the Receiver and the Sender shall disregard it.

9.2.2.11 SUFI

Which SUFI fields to use is implementation dependent, but when a STATUS PDU includes information about which AMD PDUs have been received and which are detected as missing, information shall not be included about AMD PDUs with "Sequence Number"VR(H) or "Sequence Number"VR(MR), i.e. AMD PDUs that have not yet reached the Receiver or are above the receiving window. Information about AMD PDUs with "Sequence Number"<VR(R) shall not be given except when this is necessary in order to use the BITMAP SUFI, see subclause 9.2.2.11.5.

Length: variable number of bits.

The SUFI can include three sub-fields: type information (type of super-field, e.g. list, bitmap, acknowledgement, etc), length information (providing the length of a variable length field within the following value field) and a value.

Figure 9.7 shows the structure of the super-field. The size of the type sub‑field is non-zero but the size of the other sub‑fields may be zero.

Type

Length

Value

Figure 9.7: The Structure of a Super-Field

The length of the type field is 4 bits and it may have any of following values.

Bit

Description

0000

No More Data (NO_MORE)

0001

Window Size (WINDOW)

0010

Acknowledgement (ACK)

0011

List (LIST)

0100

Bitmap (BITMAP)

0101

Relative list (Rlist)

0110

Move Receiving Window (MRW)

0111

Move Receiving Window Acknowledgement (MRW_ACK)

1000

Poll (POLL)

1001-1111

Reserved (PDUs with this encoding are invalid for this version of the protocol)

The size and presence of the sub-fields "Length" and "Value" depend on the super-field type and is specified for each super field separately.

9.2.2.11.1 The No More Data super-field

The ‘No More Data’ super-field indicates the end of the data part of a STATUS PDU and is shown in Figure 9.8 below. It shall always be placed as the last SUFI if it is included in a STATUS PDU. All data after this SUFI shall be regarded as padding and shall be neglected.

Type=NO_MORE

Figure 9.8: NO_MORE field in a STATUS PDU

9.2.2.11.2 The Acknowledgement super-field

The ‘Acknowledgement’ super-field consists of a type identifier field (ACK) and a sequence number (LSN) as shown in figure 9.9 below. The acknowledgement super-field is also indicating the end of the data part of a STATUS PDU. Thus, no ‘NO_MORE’ super-field is needed in the STATUS PDU when the ‘ACK’ super-field is present. The ACK SUFI shall always be placed as the last SUFI if it is included in a STATUS PDU. All data after this SUFI shall be regarded as padding and shall be neglected.

Type = ACK

LSN

Figure 9.9: The ACK fields in a STATUS PDU

LSN

Length: 12 bits

Acknowledges the reception of all AMD PDUs with "Sequence Number" < LSN (Last Sequence Number) that are not indicated to be erroneous in earlier parts of the STATUS PDU. This means that if the LSN is set to a value greater than VR(R), all erroneous AMD PDUs shall be included in the same STATUS PDU and if the LSN is set to VR(R), the erroneous AMD PDUs can be split into several STATUS PDUs. At the transmitter, if the value of the LSN =< the value of the first error indicated in the STATUS PDU, VT(A) will be updated according to the LSN, otherwise VT(A) will be updated according to the first error indicated in the STATUS PDU. VT(A) is only updated based on STATUS PDUs where ACK SUFI (or MRW_ACK SUFI) is included. The LSN shall not be set to a value > VR(H) nor < VR(R).

9.2.2.11.3 The Window Size super-field

The Window Size super-field consists of a type identifier (WINDOW) and a window size number (WSN) as shown in Figure 9.10 below. The Receiver is always allowed to change the transmission window size of the peer entity during a connection, but the minimum and the maximum allowed value is given by upper layers configuration. The reception window size of the Receiver is not changed.

Type = WINDOW

WSN

Figure 9.10: The WINDOW fields in a STATUS PDU

WSN

Length: 12 bits

The value of VT(WS) to be used by the transmitter. The range of the WSN is [0, 212-1]. The minimum value of VT(WS) is 1. If WSN is zero the SUFI shall be discarded by this version of the protocol. The variable VT(WS) is set equal to WSN upon reception of this SUFI. If WSN is greater than Configured_Tx_Window_Size, VT(WS) shall be set equal to Configured_Tx_Window_Size.

9.2.2.11.4 The List super-field

The List Super-Field consists of a type identifier field (LIST), a list length field (LENGTH) and a list of LENGTH number of pairs as shown in figure 9.11 below:

Type = LIST

LENGTH

SN1

L1

SN2

L2

…

SNLENGTH

LLENGTH

Figure 9.11: The List fields in a STATUS PDU

LENGTH

Length: 4 bits

The number of (SNi , Li)-pairs in the super-field of type LIST. The value "0000" is invalid and the STATUS PDU is discarded.

SNi

Length: 12 bits

"Sequence Number" of AMD PDU, which was not correctly received.

Li

Length: 4 bits

Number of consecutive AMD PDUs not correctly received following AMD PDU with "Sequence Number" SNi.

9.2.2.11.5 The Bitmap super-field

The Bitmap Super-Field consists of a type identifier field (BITMAP), a bitmap length field (LENGTH), a first sequence number (FSN) and a bitmap as shown in figure 9.12 below:

Type = BITMAP

LENGTH

FSN

Bitmap

Figure 9.12: The Bitmap fields in a STATUS PDU

LENGTH

Length: 4 bits

The size of the bitmap in octets equals LENGTH+1, i.e. LENGTH="0000" means that the size of the bitmap is one octet and LENGTH="1111" gives the maximum bitmap size of 16 octets.

FSN

Length: 12 bits

The "Sequence Number" for the first bit in the bitmap. FSN shall not be set to a value lower than VR(R)-7 when the reception window size is less than half the maximum RLC AM "Sequence Number". If the reception window size is larger, FSN shall not be set to a value lower than VR(R).

Bitmap

Length: Variable number of octets given by the LENGTH field.

Status of the "Sequence Number" fields in the interval [FSN, FSN + (LENGTH+1)*8 – 1] indicated in the bitmap where each position (from left to right) can have two different values (0 and 1) with the following meaning (bit_position[0,(LENGTH+1)*8 ‑ 1]):

1: Sequence Number = (FSN + bit_position) has been correctly received.

0: Sequence Number = (FSN + bit_position) has not been correctly received.

The UE may remove AMD PDUs from the transmitter that have been indicated to be correctly received by a BITMAP SUFI.

NOTE: The transmission window is not advanced based on BITMAP SUFIs, see subclause 9.4.

9.2.2.11.6 The Relative List super-field

The Relative List super-field consists of a type identifier field (RLIST), a list length field (LENGTH), the first sequence number (FSN) and a list of LENGTH number of codewords (CW) as shown in figure 9.13 below.

Type = RLIST

LENGTH

FSN

CW1

CW2

…

CWLENGTH

Figure 9.13: The RList fields in a STATUS PDU

LENGTH

Length: 4 bits

The number of codewords (CW) in the super-field of type RLIST.

FSN

Length: 12 bits

The "Sequence Number" for the first erroneous AMD PDU in the RLIST, i.e. LENGTH="0000" means that only FSN is present in the SUFI.

CW

Length: 4 bits

The CW consists of 4 bits where the three first bits are part of a number and the last bit is a status indicator and it shall be interpreted as follows:

Code Word

Description

X1X2X3 0

Next 3 bits of the number are X1X2X3 and the number continues in the next CW. The most significant bit within this CW is X1.

X1X2X3 1

Next 3 bits of the number are X1X2X3 and the number is terminated. The most significant bit within this CW is X1. This is the most significant CW within the number.

By default, the number given by the CWs represents a distance between the previous indicated erroneous AMD PDU up to and including the next erroneous AMD PDU.

One special value of CW is defined:

000 1 ‘Error burst indicator’.

The error burst indicator means that the next CWs will represent the number of subsequent erroneous AMD PDUs (not counting the already indicated error position). After the number of errors in a burst is terminated with XXX 1, the next codeword will again by default be the least significant bits (LSB) of the distance to the next error.

If the last CW, as indicated by the value of the LENGTH field, does not contain a "1" in its rightmost position, or the last CW, as indicated by the value of the LENGTH field does contain a "1" in its rightmost position, but is a special "error burst indicator" CW, the encoding of the RLIST SUFI is invalid, and the STATUS PDU is discarded.

9.2.2.11.7 The Move Receiving Window Acknowledgement super-field

The ‘Move Receiving Window Acknowledgement’ super-field acknowledges the reception of a MRW SUFI. The format is given in figure 9.14 below.

Type = MRW_ACK

N

SN_ACK

Figure 9.14: The MRW-ACK fields in a STATUS PDU

N

Length: 4 bits

The N field shall be set equal to the NLENGTH field in the received MRW SUFI if the SN_ACK field is equal to the SN_MRWLENGTH field. Otherwise N shall be set to 0.

With the aid of this field in combination with the SN_ACK field, it can be determined if the MRW_ACK corresponds to a previously transmitted MRW SUFI.

SN_ACK

Length: 12 bits

The SN_ACK field indicates the updated value of VR(R) after the reception of the MRW SUFI. With the aid of this field in combination with the N field, it can be determined if the MRW_ACK corresponds to a previously transmitted MRW SUFI.

9.2.2.11.8 The Move Receiving Window (MRW) super-field

The ‘Move Receiving Window’ super-field is used to request the Receiver to move its reception window and optionally to indicate the set of discarded RLC SDUs, as a result of an RLC SDU discard in the Sender. The format is given in figure 9.15 below.

Type = MRW

LENGTH

SN_MRW1

SN_MRW2

…

SN_MRWLENGTH

NLENGTH

Figure 9.15: The MRW fields in a STATUS PDU

LENGTH

Length: 4 bits

The number of SN_MRWi fields in the super-field of type MRW.

The values "0001" through "1111" indicate 1 through 15 SN_MRWi respectively. The value "0000" indicates that one SN_MRWi field is present and that the RLC SDU to be discarded in the Receiver extends above the configured transmission window in the Sender.

SN_MRWi

Length: 12 bits

When "Send MRW" is configured, an SN_MRWi shall be used to indicate the end of each discarded RLC SDU, i.e. the number of SN_MRWi fields shall equal the number of RLC SDUs discarded by that MRW SUFI. When "Send MRW" is not configured, an SN_MRWi field shall be used to indicate the end of the last RLC SDU to be discarded in the Receiver and additional ones may optionally be used to indicate the end of other discarded RLC SDUs. SN_MRWi is the "Sequence Number" of the AMD PDU that contains the "Length Indicator" or the special value of the HE field of the i:th RLC SDU to be discarded in the Receiver (except for SN_MRWLENGTH when NLENGTH = 0, see definition of NLENGTH). The order of the SN_MRWi shall be in the same sequential order as the RLC SDUs that they refer to.

Additionally SN_MRWLENGTH requests the Receiver to discard all not yet successfully received SDUs that have segments or "Length Indicators" indicating the end of the SDUs in the AMD PDUs with "Sequence Number" < SN_MRWLENGTH, and to move the reception window accordingly. In addition, when NLENGTH > 0, the Receiver has to discard the not yet successfully received SDUs that have segments or "Length Indicators" indicating the end of the SDUs in the AMD PDU with sequence number SN_MRWLENGTH up to and including the octet indicated by the NLENGTH:th "Length Indicator" field of the PDU with sequence number SN_MRWLENGTH.

NLENGTH

Length: 4 bits

NLENGTH is used together with SN_MRWLENGTH to indicate the end of the last RLC SDU to be discarded in the Receiver.

NLENGTH indicates which "Length Indicator" in the AMD PDU with "Sequence Number" SN_MRWLENGTH corresponds to the last RLC SDU to be discarded in the Receiver. NLENGTH = 0 indicates that the end of the last RLC SDU was indicated in the AMD PDU with "Sequence Number" SN_MRWLENGTH –1 and that the first data octet in the AMD PDU with "Sequence Number" SN_MRWLENGTH is the first data octet to be reassembled next.

9.2.2.11.9 The Poll (POLL) super-field

The ‘Poll’ super-field is used to request a status report (one or several STATUS PDUs) from the receiver. The poll super-field in downlink can only be used if flexible RLC PDU size is configured in the downlink. The poll super-field in uplink can only be used if flexible RLC PDU size is configured in the uplink. The format is given in figure 9.15b below.

Type = POLL

Poll_SN

Figure 9.15b: The POLL fields in a STATUS PDU

Poll_SN

Length: 12 bits

When "Poll" is configured, the Poll_SN field shall be set to VT(S)-1.

9.2.2.12 Reserved 2 (R2)

Length: 1 bit

This bit in the Piggybacked STATUS PDU is used to make the Piggybacked STATUS PDU a multiple of 8 bits in length and for this purpose it is coded as 0. Otherwise the PDU is treated as invalid and hence shall be discarded by this version of the protocol.

9.2.2.13 Reset Sequence Number (RSN)

Length: 1 bit

This field is used to indicate the sequence number of the transmitted RESET PDU. If this RESET PDU is a retransmission of the original RESET PDU then the retransmitted RESET PDU would have the same RSN value as the original RESET PDU. Otherwise it will have the next RSN value. The initial value of this field is zero. The value of this field shall be reinitialised when the RLC is re-established. It shall not be reinitialised when the RLC is reset.

9.2.2.14 Hyper Frame Number Indicator (HFNI)

Length: 20 bit

This field is used to indicate the hyper frame number (HFN) to the peer entity. With the aid of this field the HFN in UE and UTRAN can be synchronised.