RRCTL is a simple protocol (inspired by Osmocom's L1CTL) that allows
an external NAS entity to control the RRC layer of srsUE. The most
notable primitives are PLMN search, selection, and PDU transfer.
The protocol assumes traditional master-slave communication, where
one side (an external NAS entity) initiates various processes,
while the other (srsUE) executes them and indicates the outcome.
Each RRCTL message starts with a header that can be defined as follows:
+-------------------------------+--------------------------+
| Message type | 6 bits |
+-------------------------------+--------------------------+
| Message sub-type | 2 bits |
+-------------------------------+--------------------------+
| Spare (RFU) | 8 bits |
+-------------------------------+--------------------------+
| Payload length | 2 octets (big endian) |
+-------------------------------+--------------------------+
| Payload (optional) | (see payload length) |
+-------------------------------+--------------------------+
The following message types are defined at the moment:
- RRCTL_RESET - reset internal state of the external NAS interface
(does nothing for now, may be useful in the future);
- RRCTL_PLMN_SEARCH - initiates PLMN (carrier) search on pre-configured
EARFCN (Absolute Radio Freqency Number);
- RRCTL_PLMN_SELECT - binds the UE to one of the previously detected
carriers (see RRCTL_PLMN_SEARCH) defined by a
given pair of MCC and MNC;
- RRCTL_CONN_ESTABLISH - establishes connection to the serving cell
(previously selected using RRCTL_PLMN_SELECT)
with a given cause and NAS PDU;
- RRCTL_CONN_RELEASE - releases previously established dedicated connection
(currently does nothing because the RRC layer does
not expose any API for that);
- RRCTL_DATA - encapsulates a received (Downlink) or to be transmitted
(Uplink) NAS PDU (the former also contains LCID).
Each message type has at least two of the following sub-types:
- RRCTL_REQ - request (usually comes from an external NAS entity),
used to initiate some process (e.g. PLMN search);
- RRCTL_IND - indication that something has happened without a prior
request (for example, a Downlink NAS PDU was received);
- RRCTL_CNF - confirmation (positive conslusion) of the requested task;
- RRCTL_ERR - negative conslusion of the requested task (error).
The protocol definition (enums ans structs) and codec functions are
defined in a separate namespaces: 'rrctl::proto' and 'rrctl::codec'
respectively. The codec functions may throw exceptions of type
'rrctl::codec::error' if something goes wrong.
The new configuration section '[extnas]' allows to disable the
built-in NAS implementation, and provide the interface (UNIX
domain socket) to an external entity. The interface itself will
be implemented in the follow up commits.
Unfortunately, the existing networking API (common/network_utils.h)
lacks the UNIX domain socket support, and it turned to be easier
to implement a simple, single client server using Boost.Asio.
The server runs in its own thread with a blocking Tx queue, and
calls a user definted callback on receipt of any data from client.
Multiple client connections are not supported and will be rejected.
This commit introduces a skeleton class (child of 'nas_base') for
the upcoming implementation of an external NAS interface, as well
as the implementation-specific configuration container.
This is the first step towards the goal of having an external NAS
interface. The new 'nas_base' class becomes a parent of 'nas',
combining all interfaces and the basic (common) API.
The 'ue_stack_lte' now holds a unique_ptr of type 'srsue::nas_base',
so the underlying NAS implementation (built-in or external) can
be choosen at run-time depending on configuration.
The implementation specific configuration now needs to be passed
to the constructor instead, not to the init() method as was before.
fix for #1934
This fixes a race condition between Stack thread and DL
PDU processing that lead to updates of the RLC buffer that
are undetected by the BSR routine.
What happens is that in a UL SCH PDU all outstanding data is transmitted
and and a LBSR with all zero buffers is sent.
14:39:47.327301 [MAC ] [D] [ 3793] BSR: LCID=3 old_buffer=59
14:39:47.330600 [MAC ] [I] [ 3793] UL LCID=3 len=58 LBSR: b=0 0 0 0
Note that "old_buffer" isn't set to zero here.
At the same time (same TTI), the MAC PDU processing thread handles DL-SCH PDUs
that may generate new UL PDUs:
14:39:47.330749 [RLC ] [I] DRB1 Tx SDU (54 B, tx_sdu_queue_len=1)
14:39:47.330762 [RLC ] [I] DRB1 Tx SDU (54 B, tx_sdu_queue_len=2)
14:39:47.330775 [RLC ] [I] DRB1 Tx SDU (54 B, tx_sdu_queue_len=3)
..
Those PDUs are "new data" since the previous buffer state was zero.
Here is the race now between the threads, at the end of the bsr::step() function
old_buffer of each LCG is updated with the previous new_buffer, so
the buffer state of LCG=2 is now 59.
Now MAC starts the next TTI:
14:39:47.331910 [MAC ] [D] [ 3794] Running MAC tti=3794
14:39:47.331928 [MAC ] [D] [ 3794] Update Bj: lcid=0, Bj=0
14:39:47.331934 [MAC ] [D] [ 3794] Update Bj: lcid=1, Bj=0
14:39:47.331938 [MAC ] [D] [ 3794] Update Bj: lcid=2, Bj=0
14:39:47.331941 [MAC ] [D] [ 3794] Update Bj: lcid=3, Bj=-1752
14:39:47.331951 [MAC ] [D] [ 3794] BSR: LCID=0 update new buffer=0
14:39:47.331960 [MAC ] [D] [ 3794] BSR: LCID=1 update new buffer=0
14:39:47.331964 [MAC ] [D] [ 3794] BSR: LCID=2 update new buffer=0
14:39:47.331971 [MAC ] [D] [ 3794] BSR: LCID=3 update new buffer=335
14:39:47.331976 [MAC ] [D] [ 3794] BSR: check_new_data() -> get_buffer_state_lcg(0)=0
14:39:47.331980 [MAC ] [D] [ 3794] BSR: check_new_data() -> get_buffer_state_lcg(1)=0
14:39:47.331984 [MAC ] [D] [ 3794] BSR: check_new_data() -> get_buffer_state_lcg(2)=59
14:39:47.331988 [MAC ] [D] [ 3794] BSR: check_new_data() -> get_buffer_state_lcg(3)=0
14:39:47.331993 [MAC ] [D] [ 3794] BSR: LCID=0 old_buffer=0
14:39:47.332000 [MAC ] [D] [ 3794] BSR: LCID=1 old_buffer=0
14:39:47.332003 [MAC ] [D] [ 3794] BSR: LCID=2 old_buffer=0
14:39:47.332007 [MAC ] [D] [ 3794] BSR: LCID=3 old_buffer=335
And since the buffer state of LCG=2 isn't zero, the new data for LCID=3 of that LCG is considered.
So effectivly, the BSR missed the "empty" buffer state for a fraction of time and doesn't
consider the outgoing data generated in the same TTI as new. It therefore
doesn't transmit a BSR.
in which a BSR wasn't
this was a very noisy log that was printed in pretty much
every TTI because the BSR procedure starts a SR whenever
it needs to send a regular BSR. The SR is canceled when a UL
grant arrives but the log line stays there.
Since we are printing a log when we actually signal a SR
to the PHY, this line is not needed.
this fixes the trigger logic for periodic BSRs. Previously we
would always trigger the "new data for highest priority LCID"
whenever new data becomes available for a LCID for which
a BSR has already been sent.
However, a BSR should only be sent if the priority is in fact higher
(lower int number).
in ZMQ runs we've seen that entering idle could take quite
a bit of time depending how quickly workers get their samples
sent or reconfigurations done.
In one example up to ~160ms
this patch increases the maximum wait time to 2s.
the BSR trigger wasn't reset after includinga regular or periodic
BSR inside a PDU. This caused the muxing to include another BSR in the
next UL grant. For very small grants, for example with 6 PRBs, this
causes the UE to send way too many BSRs.
when releasing PUCCH/SRS (see 5.3.13 in 36.331) we need to reset the SR config as well.
In our case, SR is handled by MAC so we need to (re-)configure MAC, not all of
MAC though, just SR.
this avoid logging a warning on UE shutdown if the MAC is already reset
but one of the PHY workers still decodes an UL grant for the old RTNI
21:30:29.254844 [RRC ] [I] Going RRC_IDLE
21:30:29.254848 [RRC ] [I] Proc "Go Idle" - Left connected state
21:30:29.259499 [PHY0] [I] [ 3865] Finished setting new PHY configuration cc_idx=0
21:30:29.259512 [PHY0] [I] [ 3865] Setting new PHY configuration cc_idx=0...
21:30:29.264190 [PHY0] [I] [ 3867] Finished setting new PHY configuration cc_idx=0
21:30:29.275036 [PHY1] [I] [ 3872] PHICH: hi=1, corr=1.0, I_lowest=1, n_dmrs=0, I_phich=0
21:30:29.275050 [MAC ] [W] [ 3872] Received grant for unknown rnti=0x46
this fixes issue #1846 that appears to be related
to the enter/exit state for measurements that is kept
even after a cell disappears from the neighbor list
this fixes#1791 which was caused by a race between
the PHY workers preparing a new UL-SCH PDU and the Stack resetting
the MAC, which in turn resets the HARQ processeses, which cleared
the buffer and set the length to zero.
Not explicitly clearing the buffer on a HARQ reset seems to be
fine since the PHY worker clears the buffer before starting to
pack a new PDU anyway.
Vadim Yanitskiy