Simu5G 1.4.3

This release represents a major milestone in the complete overhaul of the Simu5G
codebase to make it architecturally more compliant with the 3GPP
specifications, modernize the code, and adopt the best practices of the INET
Framework on which it is based. The goal is to pave the way for a clean
implementation of new protocol features such as TSN support.

Tested with INET-4.5.4 and OMNeT++ 6.3, updated for INET-4.6.0 compatibility.

Key achievements in this release:

• More explicit Control Plane modeling: Simu5G is advertised as a User Plane
  simulator, but since it was also used to model dynamic scenarios such as
  handovers, it always contained elements of the Control Plane distributed across
  various modules. The new direction is to make these elements more explicit and
  centralized, such as creating dedicated RRC (Radio Resource Control) and
  Session Management Function (SMF) implementations. It is an explicit non-goal
  to simulate Control Plane messaging -- its functionality will be implemented
  with C++ method calls across modules. Thus, Simu5G remains a User Plane
  simulator, but with the possibility to more faithfully model dynamic
  scenarios with heavy Control Plane involvement. While this goal is not fully
  realized in this release, many changes point into that direction.

• Control info refactoring: Cleaned up UserControlInfo and
  FlowControlInfo by removing 5+ unused fields and splitting out smaller,
  focused tags. For example, IPv4 addresses, only used between Ip2Nic and PDCP,
  have been factored out into an IpFlowInd tag. This improves modularity,
  reduces coupling between protocol layers, and makes the code easier to
  maintain and extend.

• Added vital missing fields to PDCP and MAC headers: Protocol layers now
  use proper header fields instead of "tunnelling" information via
  UserControlInfo and FlowControlInfo packet tags that would not exist in a
  real implementation. For example, PDCP sequence numbers are now carried in
  PDCP headers, and LCIDs are stored in MAC PDU subheaders. This makes the
  simulation more realistic and packet contents more inspectable in Qtenv.

• Explicit setup of logical connections instead of on-the-fly discovery:
  This is a key architectural change, which also largely motivated the
  previous items. In previous iterations of Simu5G, data structures associated
  with logical connections / bearers were created in each protocol layer as they
  encountered packets that belonged to new connections. Moreover, part of the
  connection state was carried along by the packets in FlowControlInfo tags
  instead of stored inside the protocol. While this modeling approach still
  allowed for faithful simulation of the traffic while keeping the
  implementation simple, it has become a roadblock for implementing complex
  dynamic scenarios where connections come and go. In this iteration,
  centralized session and bearer management (SMF-like functionality) was added
  to the Binder module, and RRC modules were added to NICs to carry out local
  configuration. This brings the architecture closer to the 3GPP control/user
  plane separation, making it easier to implement features like handovers
  correctly. This is work in progress: SMF is still part of Binder and not a
  separate module, and connection setup is still triggered by the first packet
  of the connection hitting PDCP on the way out. However, moving the SMF code
  into its own module will be trivial, and the single Binder method call in
  PDCP can now be easily replaced with static configuration or with calls from a
  more detailed Control Plane implementation.

• Removed incomplete MIMO support: Removed MIMO-related code and parameters.
  The existing MIMO code was incomplete (e.g., PMI values were computed but
  never used). Removing it simplifies the codebase and model parameterization,
  and avoids confusion about capabilities. MIMO support will be added in a future
  release, with a different approach.

• Initialization cleanup: Reorganized module initialization into well-defined,
  Simu5G-specific init stages. This eliminates hidden cross-module dependencies,
  makes the initialization order explicit and verifiable, and prevents subtle bugs
  caused by modules accessing uninitialized data in other modules.

Further notable changes:

• In UE models, masterId and nrMasterId were renamed to servingNodeId and
  nrServingNodeId. The old names were confusing because "Master" has a
  specific meaning in Dual Connectivity (Master eNB vs Secondary gNB), unrelated
  to the UE's serving node.

• In UE models, the macCellId, nrMacCellId parameters were removed. In
  practice, the code already used the serving node ID as cell ID.

• macNodeId assignment was moved to NED, and now it is based on the new
  simu5g_seq() NED function that generates an integer sequence. This replaces
  the earlier approach where node IDs were assigned by Ip2Nic during
  initialization, and stored back into the module parameters for other modules to
  use.

• LteRlcPduNewData and LteRlcSdu packet chunks were converted to packet
  tags, as they represent internal metadata rather than actual protocol data.

• In the C++ code, merged the ENODEB and GNODEB node type enum values into a
  single NODEB value, with a separate isNr flag where needed. This change
  simplified a large number of "if" conditions throughout the codebase.

To port your existing Simu5G simulations to this version, apply the following
changes to the ini files:

• Change masterId to servingNodeId (and nrMasterId to nrServingNodeId),
  unless it refers to the Master/Secondary distinction in a Dual Connectivity
  setup.

• Remove macCellId and nrMacCellId parameter assignments for UE modules.

• Delete ini entries that set the following removed MIMO-related parameters:
  numRus, ruRange, ruStartingAngle, ruTxPower, antennaCws,
  muMimo, pmiWeight, lambdaMinTh, lambdaMaxTh, lambdaRatioTh,
  feedbackGeneratorType.

• For initialTxMode, the following values are no longer valid:
  SINGLE_ANTENNA_PORT5, OL_SPATIAL_MULTIPLEXING, CL_SPATIAL_MULTIPLEXING,
  MULTI_USER. Remove the parameter assigment to use the default.

There are many more changes that potentially affect existing simulations, and
projects extending, or built on top of, Simu5G. They cannot all be covered here
in detail - see the git history for details.