[AMF] Implicit Network-initiated Deregistration
Two timers are introduced (both with duration of T3512 + 4 min):
-MOBILE_REACHABLE
-IMPLICIT_DEREGISTRATION
MOBILE_REACHABLE is set when NAS connection for the UE is released.
IMPLICIT_DEREGISTRATION is set when MOBILE_REACHABLE expires.
On MOBILE_REACHABLE expiry Paging is ignored.
On IMPLICIT_DEREGISTRATION expiry:
-UE's RM_State is set to DEREGISTERED
-UE is Nudm_SDM_Unsubscribed
-UE is Nudm_UECM_Deregistered
-PDU sessions are released
-AM policies are deleted
Existing flag amf_ue->network_initiated_de_reg is used.
AMF does not crash anymore when a new UE registration request arrives,
and there is no available space left in UE context pool. Now it just
rejects the request with an error.
An assert occurs when a NAS message retransmission occurs.
Because there is no `enb_ue` context.
Therefore, before removing enb_ue, all Timers must be stopped
to prevent retransmission of NAS messages.
All process will be forcely exited if it failed to encode the S1AP/NGAP/GTP/PFCP message. It is to make sure there was no problem with the encoding of open5gs.
The AMF shall assign a new 5G-GUTI for a particular UE:
a) during a successful initial registration procedure;
b) during a successful registration procedure
for mobility registration update; and
c) after a successful service request procedure invoked as a response
to a paging request from the network and before the release
of the N1 NAS signalling connection as specified in subclause 5.4.4.1.
The AMF should assign a new 5G-GUTI for a particular UE
during a successful registration procedure
for periodic registration update. The AMF may assign a new 5G-GUTI
at any time for a particular UE by performing
the generic UE configuration update procedure.
Most of the time, an application wants to perform some amount of data buffering
in addition to just responding to events. When we want to write data,
for example, the usual pattern runs something like:
1. Decide that we want to write some data to a connection;
put that data in a buffer.
2. Wait for the connection to become writable
3. Write as much of the data as we can
4. Remember how much we wrote, and if we still have more data to write,
wait for the connection to become writable again.
Now, Open5GS implements the above method by default when transmitting data
in a stream type socket.