4 Channel types and their use: Control channels

04.033GPPMobile Station - Base Station System (MS - BSS) Interface Channel Structures and Access CapabilitiesRelease 1999TS

NOTE: The term "Dm channel" may be used to refer to the controls channels used by a Mobile Station at a given moment, independently of their type. (The term "Dm channel" in conjunction with the packet control channels shall be avoided.)

Control channels are used to provide all active Mobile Stations with a continuous frame oriented means of communication across the MS-BS interface.

A Mobile Station Channel Configuration contains one or more control channels. These control channels may change in time, with the channel configuration. Access management signalling functions are used to insure the continuity when a change in the control channels occurs.

Control channels are classified by control channel types, which have common characteristics. These control channel types are specified in clause 4.1.

The control channels are primarily intended to carry signalling information for Connection management (CM), Mobility Management (MM) and Radio Resource (RR) management.

In addition to signalling information control channels may also be used to carry other data, including those relating to Short Message Services.

4.1 Control channel types

4.1.1 Broadcast Control Channel

A broadcast control channel is a point-to-multipoint uni-directional control channel, from the fixed sub-system to the Mobile Stations. Broadcast control channels are physically sub-divided into the broadcast control channel (BCCH) , packet broadcast control channel (PBCCH), and Compact packet broadcast control channel (CPBCCH).

BCCH, PBCCH, and CPBCCH are intended to broadcast a variety of information to MSs, including information necessary for MS to register in the system (e.g. synchronization data).

BCCH, PBCCH, and CPBCCH use a protocol specified in Technical Specifications in 3GPP TS 04-Series.

4.1.2 Common Control Channel

A common control channel is a point-to-multipoint bi-directional control channel. Common control channels are physically sub-divided into the common control channel (CCCH), the packet common control channel (PCCCH), and the Compact packet common control channel (CPCCCH).

CCCH, PCCCH, and CPCCCH are primarily intended to carry signalling information necessary for access management functions (e.g., allocation of dedicated channels or radio resource on a packet data traffic channel). The CCCH can be used for other signalling purposes.

CCCH, PCCCH, and CPCCCH use a layered protocol according to Technical Specifications in 3GPP TS 04-Series. In particular the multipoint to point management is achieved through random access techniques.

The following terms may be used when the context requires it:

– The RACH (Random Access Channel) is the uplink (MS to network) part of the CCCH.

– The PRACH (Packet Random Access Channel) is the uplink part of the PCCCH.

– The CPRACH (Compact Packet Random Access Channel) is the uplink part of the CPCCCH.

– The AGCH (Access Grant Channel) is the part of the downlink (network to MS) part of the CCCH reserved for assignment messages.

– The PAGCH (Packet Access Grant Channel) is the part of the downlink part of the PCCCH used for assignment messages.

– The CPAGCH (Compact Packet Access Grant Channel) is the part of the downlink part of the CPCCCH used for assignment messages.

– The NCH (Notification Channel) is the part of the downlink part of the CCCH reserved for voice group and/or voice broadcast calls notification messages.

– The PNCH (Packet Notification Channel) is the part of the downlink part of the PCCCH reserved for GPRS PTM-M, voice group and/or voice broadcast calls notification messages.

– The CPNCH (Compact Packet Notification Channel) is the part of the downlink part of the PCCCH reserved for GPRS PTM-M voice group and/or voice broadcast calls notification messages.

– PCH (Paging Channel) is the remaining part of the downlink part of the CCCH.

– PPCH (Packet Paging Channel) is the remaining part of the downlink part of the PCCCH.

– CPPCH (Compact Packet Paging Channel) is the remaining part of the downlink part of the CPCCCH.

4.1.3 Dedicated Control Channel

A dedicated control channel (DCCH) is a point-to-point bi-directional or uni-directional control channel.

DCCHs exist with a variety of bit rates.

DCCHs are further classified as follows according to some technical particularities:

A SDCCH (Stand-alone DCCH) is a bi-directional DCCH whose allocation is not linked to the allocation of a TCH. The bit rate of a SDCCH is 598/765 kbit/s.

A FACCH (Fast Associated DCCH) is a bi-directional DCCH obtained by pre-emptive dynamic multiplexing on respectively a TCH/F or a TCH/H channel. The allocation of a FACCH is obviously linked to the allocation of a TCH. The bit rate of a FACCH is 9 200 or 4 600 bit/s.

A SACCH (Slow Associated DCCH) is either a bi-directional or uni-directional DCCH of rate 115/300 or a bi-directional DCCH of rate 299/765 kbit/s. An independent SACCH is always allocated together with a TCH or a SDCCH. The co-allocated TCH and SACCH shall be either both bi-directional or both uni-directional.

NOTE 1: A Multislot Configuration (described in clause 6) is an example of a case where uni-directional SACCHs may be used.

The terms Bm, or Bm + ACCHs can be used to refer to a Bm channel together with the corresponding FACCH and the co-allocated SACCH when the context avoids any ambiguities. Similar remarks apply to the terms Lm, Lm + ACCHs, Lm + Lm, Lm + Lm + ACCHs. The term SDCCH can be used to refer specifically to a SDCCH together with the co-allocated SACCH when the contexts avoids any ambiguities.

NOTE 2: TCH/F is sometimes used to designate Bm associated with its control channel (FACCH and SACCH). TCH/H is sometime used to designate Lm associated with its control channel (FACCH and SACCH).

A PACCH (Packet Associated Control Channel) is a bi-directional DCCH obtained by pre-emptive dynamic multiplexing on a PDTCH.

A PTCCH (Packet Timing Control Channel) is a bi-directional DCCH carrying synchronization data for a group of up to 16 MSs in packet transfer state (see 3GPP TS 04.60).

The DCCHs use a layered protocol according to Technical Specifications in 3GPP TS 04- and 05-series.