8.5.12 Establishment of Access Service Classes

25.3313GPPProtocol specificationRadio Resource Control (RRC)Release 17TS

The PRACH resources (i.e. access slots and preamble signatures for FDD), timeslot (with specific frame allocation and channelisation code for 3.84 Mcps TDD and 7.68 Mcps TDD, and SYNC_UL codes (with specific frame allocation) for 1.28 Mcps TDD) may be divided between different Access Service Classes in order to provide different priorities of RACH usage. It is possible for more than one ASC or for all ASCs to be assigned to the same access slot/signature space in FDD or frame allocation/channelisation codes in 3.84 Mcps TDD or 7.68 Mcps TDD, or frame allocation/SYNC_UL codes in 1.28 Mcps TDD.

Access Service Classes shall be numbered in the range 0  i  NumASC  7 (i.e. the maximum number of ASCs is 8). An ASC is defined by an identifier, i, that defines a certain partition of the PRACH resources (SYNC_UL resources in 1.28 Mcps TDD) and an associated persistence value P_i. A set of ASC parameters consists of "NumASC+1" such parameters (i, P_i), i = 0, …, NumASC.

PRACH partitions shall be established using the information element "PRACH partitioning". The persistence values P_i to be associated with each ASC shall be derived from the dynamic persistence level N = 1,…, 8 which is broadcast in System Information Block 7, and the persistence scaling factors s_i, broadcast in System Information Block Type 5 or System Information Block type 5bis and possibly also in System Information Block Type 6, as follows:

P(N) = 2^{(N  1)}

ASC # i	0	1	2	3	4	5	6	7
Pi	1	P(N)	s2 P(N)	s3 P(N)	s4 P(N)	s5 P(N)	s6P(N)	s7 P(N)

In addition, MBMS specific persistence values may be provided within the MBMS MODIFIED SERVICES INFORMATION message. The UE behaviour upon receiving upon receiving an MBMS dynamic persistence value is specified in subclause 8.6.9.1a.

Scaling factors s_i are provided optionally for i = 2,…, NumASC, where NumASC+1 is the number of ASCs as defined by PRACH partitioning. If no scaling factors are broadcast, default value 1 shall be used if NumASC  2.

If k  1 scaling factors are broadcast and NumASC  k+2 then the last scaling factor s_k+1 shall be used as default for the ASCs where i > k +1.

In the case of E-RUCCH operation (3.84/7.68 Mcps TDD only) a separate set of persistence values will be used. For E-RUCCH a single scaling factor S_r is signalled. If the E-RUCCH shares resource with a PRACH then dynamic perstistence levels of the PRACH are used and persistence values are determined using the table below:

ASC # i	0	1	2 – 7
Pi (E-RUCCH)	1	P(N)	Sr P(N)

Else if the E-RUCCH does not share resource with a PRACH then persistence values are determined using the table below:

ASC # i	0	1	2–7
Pi (E-RUCCH)	1	1	Sr

The establistment of Access Service Classes for E-RUCCH (1.28 Mcps TDD only) is similar as PRACH, differently Access Service Classes parameters and persistence scaling factors of E-RUCCH may be acquired from the information element "E-RUCCH info", e.g. in the case of E-DCH serving cell change. Only in the case that the UEs with E-DCH and E-RUCCH configured on the Primary Frequency of the multi-frequency cell, the E-DCH serving cell unchanged and the UEs can obtain the dynamic persistence level N from SIB7 according to the configuration of information element “E-RUCCH info”, the dynamic persistence value N shall be used. Otherwise, dynamic persistence level N=1 shall always be used. The persistence values are determined using the table below:

ASC # i	0	1	2	3	4	5	6	7
Pi (E-RUCCH)	1	P(N)	s2 P(N)	s3 P(N)	s4 P(N)	s5 P(N)	s6P(N)	s7 P(N)

The set of ASC parameters is provided to MAC with the CMAC-Config-REQ primitive (see [15]), the PRACH partitioning is provided to PHY using the CPHY-RL-Setup-REQ primitive (see [34]). For 3.84/7.68 Mcps TDD E-DCH operation the E-RUCCH persistence values will also be provided to MAC with the CMAC-Config-REQ primitive.

The ASC enumeration shall be such that it corresponds to the order of priority (ASC 0 = highest priority, ASC 7 = lowest priority). ASC 0 shall be used in case of Emergency Call or for reasons with equivalent priority.

ASCs are numbered according to the order in which the IEs "ASC Setting" appear in the IE "PRACH partitioning", where the first IE "ASC Setting" describes ASC 0, the second IE "ASC Setting" describes ASC 1, etc.

At radio bearer setup/reconfiguration each involved logical channel is assigned a MAC Logical channel Priority (MLP) in the range 1,…,8. When the MAC sublayer is configured for RACH transmission in the UE, these MLP levels shall be employed for ASC selection on MAC.