anchor.diff:  Since the secondary TRX has no BCCH, it does not (need to) receive any 'RSL
   BCCH INFORMATION' messages from the BSC.
   
  -[[rsl-dynamic-channels]]
  -=== Dynamic Channel Combinations
  -
  -In the classic data model established by ETSI/3GPP for A-bis, each
  -timeslot (channel) is configured using a static channel combination by
  -means of A-bis OML.  Particularly in presence of GPRS services, this
  -is very unflexible and leads to inefficient use of air interface
  -resources.
  -
  -As such, several methods have been implemented to overcome this
  -limitation.  The fundamental operation can be outlined like this:
  -
  -* Configuration of a particular _dynamic_ channel combination via OML
  -* activation of TCH works like on a classic TCH channel combination
  -* activation of PDCH requires some specific PDCH activation procedure
  -
  -There are two variants implemented in the OsmoBTS A-bis dialect:
  -
  -==== IPA Style Dynamic Channels
  -
  -This method is used when OML uses 'NM_CHANC_IPAC_TCHFull_PDCH' (0x80)
  -as channel combination for the given time-slot.
  -
  -'IPA style' refers to 'ip.access' compatible PDCH activation and deactivation.
  -
  -When the IPA style dynamic channel combination _TCH/F or PDCH_
  -is set, the non-standard 'PDCH ACTIVATE' (<<pdch_act>>) and 'PDCH
  -DEACTIVATE' (<<pdch_deact>>) procedures are used for switching an idle
  -channel into PDCH mode and back into idle mode.
  -
  -.Example for dynamic channel switchover, for IPA style dynamic timeslots
  -["mscgen"]
  -----
  -include::dyn_ts_ipa_style.msc[]
  -----
  -
  -[[OSMOCOM_DYN_TS]]
  -==== Osmocom Style Dynamic Channels
  -
  -This method is in use when OML uses
  -'NM_CHANC_OSMO_TCHFull_TCHHalf_PDCH' (0x90) for the given time-slot.
  -
  -The activation of PDCH is performed by using the regular 'RSL CHANNEL ACTIVATE'
  -procedure according to <<CHANNEL_ACTIVATION>>, with these modifications:
  -
  -* The 'C-bits' part of the 'Channel Number' IE take the non-standard binary
  -  value 11000 (C5 thru C1 as seen in 3GPP TS 08.58 § 9.3.1).
  -* The 'A-bits' part of the 'Activation Type' IE take the non-standard binary
  -  value 1111, with an additional fourth bit (add A4 to A3 thru A1 as seen in
  -  3GPP TS 08.58 § 9.3.3; all remaining reserved bits as well as the 'R' bit are
  -  coded as zero).
  -* The normally mandatory 'Channel Mode' IE is omitted; none of the optional IEs
  -  are included.
  -
  -Hence the message consists of exactly these IEs:
  -
  -.PDCH type _Channel Activation_ message IEs
  -[options="header",cols="10%,30%,60%"]
  -|===
  -| TS 08.58 § | IE Name | Handling
  -| 9.1 | Message discriminator | Dedicated Channel Management
  -| 9.2 | Message type | CHANnel ACTIVation
  -| 9.3.1 | Channel number | 'C-bits' 11000, plus TS bits as usual
  -| 9.3.3 | Activation type | 'A-bits' 1111
  -|===
  -
  -.Example for dynamic channel switchover, for Osmocom style dynamic timeslots
  -["mscgen"]
  -----
  -include::dyn_ts_osmocom_style.msc[]
  -----
  -
  -
  
positive.code: See <<rsl_dlcx_ind_msg>>
  
  
  [[ipa_style_pdch_mgmt]]
  === IPA Style PDCH Management
  
  When using an IPA style dynamic TCH/F+PDCH channel type on an
  on-air timeslot, there are a couple of non-standard RSL messages used
  in order to activate or deactivate this timeslot in PDCH mode.
  
  When the channel is used as TCH/F, regular circuit-switched activation
  is performed, like on any traditional TCH/F.   However, the BSC must
  
negative.code: See <<rsl_pdch_act>>, <<rsl_pdch_act_ack>>, <<rsl_pdch_act_nack>>
  
  [[pdch_deact]]
  ===== PDCH Deactivate
  
  This procedure is used by the BSC to request the BTS to deactivate an
  active PDCH on any an IPA style dynamic TCH/F+PDCH channel.
  