L1CTL extension (was Re: hand-over in L1CTL / trxcon)

Harald Welte laforge at gnumonks.org
Thu May 30 08:38:16 UTC 2019

Hi Vadim and others,

given how long L1CTL has been around, and how many programs implement
it by now, I really would like to ensure backwards compatibility without
introducing weird breakage all over the place.

The good news: I think it's possible to extend L1CTL in a
backwards-compatible way, and I started with a related implementation.

Some of my raw notes below:

Extension of L1CTL in a compatible way

* enhance l1ctl_reset with version and feature bitmap
** used by L1CTL_RESET_CONF, possibly also REQ, IND
** old implementation ignores trailer
** new implementation recognizes new format due to longer message (and enables use of new features)

* new DM_EST_2_REQ
** sent by L23 only if feature-bit was set in RSEET_CONF
** contains additional fields
*** L1 SAPI bitmask
*** sync_source member to select own cell or neighbor cell sync info
* new DM_EST_2_CONF
** response to _REQ (which is currently missing from DM_EST_REQ)

* extend l1ctl_neigh_pm_ind with new fields at end
** L23 can use size to determine if new fields exist or not

** sent by L23 to change L1 SAPI bitmask
* new DM_MODIFY_CONF to confirm it

/* bit definitions for individual features communicated in RESET_CONF */
enum l1ctl_feature {
  L1CTL_FT_DM_EST2_MODIFY, /* DM_EST_2 and DM_MODIFY procedures */
  L1CTL_FT_RACH_DM, /* RACH can be sent in dedicated mode */
  L1CTL_FT_EXT_RACH_REQ, /* Extended RACH (11bit) support */
  L1CTL_FT_SPKR_MIC, /* Hardware Speaker + Microphone supported */
  L1CTL_FT_TBF, /* support for TBF_CFG and DATA_TBF procedures */
  L1CTL_FT_SIM_SLOT, /* physical SIM slot exists */
  L1CTL_FT_SIM_SLOT, /* physical SIM slot exists */

I won't go "full steam ahead" on this, but will try to get it
implemented within the next week or so.

- Harald Welte <laforge at gnumonks.org>           http://laforge.gnumonks.org/
"Privacy in residential applications is a desirable marketing option."
                                                  (ETSI EN 300 175-7 Ch. A6)

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