3 Definitions and abbreviations

25.4153GPPRelease 17TSUTRAN Iu interface user plane protocols

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

3.1 Definitions

For the purposes of the present document, the following terms and definitions apply.

Iu Timing Interval (ITI): Iu Timing Interval is the minimum time interval between sent Iu UP PDUs for a specific RAB. The ITI can be calculated for conversational and streaming traffic classes by the following formula:

Inter PDU Transmission Interval (IPTI): inter PDU Transmission Interval is the actual interval at which Iu UP PDUs can be sent at a certain time for a specific RAB subflow combination. The IPTI of a RAB subflow combination is calculated based on the RAB subflow combination size and the RAB subflow combination bitrate by dividing the RAB subflow combination size with the RAB subflow combination bitrate.

NOTE: If RFC_Bitrate is not defined then IPTI=ITI. If RFC_size is not defined then RFC_size=MaxSDUsize.

Non Access Stratum (NAS) Data Streams: non Access Stratum Data Streams is a generic term to identify these data streams exchanged at the Dedicated Service Access Points between the Non Access Stratum and the Access Stratum.

RAB sub-flows: RAB as defined in TR 21.905 [9] is realised by UTRAN through one to several sub-flows. These sub-flows correspond to the NAS service data streams that have QoS characteristics that differ in a predefined manner within a RAB e.g. different reliability classes.

RAB sub-flows characteristics:

1) the sub-flows of a RAB are established and released together at the RAB establishment and release, respectively;

2) the sub-flows of a RAB are submitted and delivered together at the RAB SAP;

3) the sub-flows of a RAB are carried over the same Iu transmission connection;

4) the sub-flows of a RAB are organised in a predefined manner at the RAB SAP and over the Iu interface. The organisation is imposed by the NAS as part of its co-ordination responsibility.

RAB sub-flows numbering (applies to support mode for predefined SDU size only):

1) RAB sub-flows are numbered from 1 to N (N is the number of sub-flows);

2) RAB sub-flow number 1 corresponds to the highest reliability class and the RAB sub-flow number N corresponds to the lowest reliability class;

3) RAB sub-flows order inside the Iu frame is predefined so that RAB sub-flow number one comes first and the RAB sub-flow number N comes last.

RAB sub-Flow Combination (RFC): RAB sub-flow combination is defined as an authorised combination of the RAB sub-flows variable attributes (e.g. SDU sizes) of currently valid RAB sub-flows that can be submitted simultaneously to the Iu UP for transmission over Iu interface. Each combination is given by the CN and cannot be altered by the SRNC.

RAB sub-Flow Combination Indicator (RFCI): this indicator uniquely identifies a RAB sub-flow combination for the duration of the Iu UP peer protocol instances i.e. it is valid until the termination of the call or until a new initialisation is performed. Usage of RFCI applies only to Iu UP protocol operated in support mode for predefined SDU size.

Principles related to RFCI allocation and Initialisation procedure:

1) RFCI value is present in every Iu user frame;

2) in the Initialisation procedure in Iu UP, the size of every RAB sub-flow SDU for each RFCI is signalled.

Syntactical error: field is defined to be syntactically incorrect in a frame if it contains at least one value defined as "reserved", or if its value part violates syntactic rules given in the specification of the value part. However it is not a syntactical error that a value specified as "spare" is being used.

Semantical error: A frame is defined to have semantically incorrect contents if it contains information which, possibly dependant on the state of the receiver, is in contradiction to the resources of the receiver and/or to the procedural part.

3.2 Abbreviations

For the purposes of the present document, the following abbreviations apply:

AMR Adaptive Multi-Rate codec

AS Access Stratum

BER Bit Error Rate

CN Core Network

DTX Discontinuous Transmission

DU Data Unit

GF Galois Field

IPTI Inter PDU Transmission Interval

ITI Iu Timing Interval

NAS Non Access Stratum

PDU Protocol Data Unit

QoS Quality of Service

RAB Radio Access Bearer

RANAP Radio Access Network Application Part

RFC RAB sub Flow Combination

RFCI RFC Indicator

RNL Radio Network Layer

RTP Real-time Transport Protocol

SAP Service Access Point

SDU Service Data Unit

SID Silence Insertion Descriptor

SMpSDU Support Mode for predefined SDU size

SRNC Serving RNC

SRNS Serving RNS

SSSAR Service Specific Segmentation and Reassembly

TFCI Transport Format Combination Indicator

TFI Transport Format Identification

TFO Tandem Free Operation

TNL Transport Network Layer

TrFO Transcoder Free Operation

TrM Transparent Mode

UP User Plane

UUI User to User Information

3.3 Concepts

Iu UP mode of operation:

One objective of the Iu User Plane (UP) protocol is to remain independent of the CN domain (Circuit Switched or Packet Switched) and to have limited or no dependency with the Transport Network Layer. Meeting this objective provides the flexibility to evolve services regardless of the CN domain and to migrate services across CN domains.

The Iu UP protocol is therefore defined with modes of operation that can be activated on a RAB basis rather than on a CN domain basis or (tele) service basis. The Iu UP mode of operation determines if and which set of features shall be provided to meet e.g. the RAB QoS requirements.

Iu UP protocol PDU Type:

The Iu UP protocol PDU Types are defined for a given Iu UP mode of operation. An Iu UP PDU Type represents a defined structure of an Iu UP protocol frame. For instance, a frame made of a certain Frame Header mask part and a Frame Payload part would be specified as a certain PDU type valid for a given Iu UP mode of operation.

Tandem Free Operation (TFO):

Configuration of a Speech or Multimedia call for which Transcoders are physically present in the communication path but transcoding functions are disabled or partially disabled. The Transcoders may perform control and/or protocol conversion functions.

Transcoder (TC):

Physical device present in the network responsible for the transcoding of the speech data between two speech codecs or coding schemes (The Transcoder may also include other functions, i.e. Rate Adaptation in GSM).

Transcoder Free Operation (TrFO):

Configuration of a Speech or Multimedia call for which Transcoders are not present in the communication path.

3.4 Specification Notations

For the purposes of the present document, the following notations apply:

Procedure When referring to a procedure in the specification the Procedure Name is written with the first letters in each word in upper case characters followed by the word "procedure", e.g. Iu Rate Control procedure.

Frame When referring to a control or data frame in the specification, the CONTROL/DATA FRAME NAME is written with all letters in upper case characters followed by the words "control/data frame", e.g. TIME ALIGNMENT control frame.

IE When referring to an information element (IE) in the specification the Information Element Name is written with the first letters in each word in upper case characters and all letters in Italic font followed by the abbreviation "IE", e.g. Frame Number IE.

Value of an IE When referring to the value of an information element (IE) in the specification the "Value" is written as it is specified in subclause 6.6.3 enclosed by quotation marks, e.g. "0" or "255".