Magma SA: SessionD

Magma SessionD Service [0]

SessionD is the main service responsible for managing and enforcing session configurations. It also coordinates the lifecycle of a session. AccessD calls Sessiond for the session's creation, modification, and termination. Compared with network functions, it can be considered as Session Management Function(SMF).

SessionD's Interface with other Services

SessionD <——> AccessD

SM Context Request from AccessD for the establishment of a session.

SessionD <——> PipelineD

Responsible for policy and QoS enforcement. Pipelined receives any relevant policy and QoS configuration from SessionD and periodically reports usage accordingly.

SessionD <——> PolicyDB

Responsible for propagating any session or policy configuration that sessioD must enforce.

Architecture of SessionD

SessionD is created by combining different components such as:

Message Manager Handler [29]
M5g-Enforcer [27]
Session State [26]
Session Store [28]
Redis Store (when stateless feature is enabled) [16]
Memory Store (when stateless feature is disabled) [10]
Session Proxy Responder Handler [24]
Session Credit [20]

Call Flow

PDU Session Establishment

[29] Handling set message from AMF
[29] Send create sesion
[29] Set Session ID
[29] M5g enforcer initialisation
[27] New Session state object
[27] Creating sesion state object with ‘Creating’ state
[27] Writing session in session map
[28] Write session
[28] Set current version of session
[28] Set fsm state
[27] Process static and dynamic rules to install
[27] Session state change
[27] [26] Charging Grant Intialised
[27] [26] Monitoring Grant Initialised
[28] Rule map addition, charging and monitoring criteria
[27] M5g send session request to UPF
[27] Set subscribed qos,
[27] Set priority level
[27] Set preemption capability
[27] Set PDR, FAR, URR and BAR mapping
[27] Set UPF node
[14] PipelinedD create session request
[14] Set subscriber ID, Teid
[14] QOS flow setup done
[2] Handle response to AccessD
[2] Handle notification to AccessD

Session Release/Termination

[29] Initiate Session Release
[29] [27] M5g Enforcer proceeds the release session
[27] [28] Session store find session
[27] Get session ID
[27] M5g start session termination
[27] [26] Set FSM state in Session State
[27] [26] Set current version of session
[27] PDR Map Erase
[27] Remove all rules for termination

If there is termination because of no required report from UPF then follow the below steps

[27] M5g complete termination
[27] Find session from Session Store
[27] [25] Termination in controller
[27] [26] Remove all PDR, FAR rules from session state
[27] Remove session from session map

Final Steps for both the cases

[27] Update session in session store
[29] Successfully released and updated session store of subscriber
[14] PipelineD deactivate flow for rules

Paging Request

[33] PipelineD sends paging request to sessionD
[33] Local F-TEID
[33] UE IP address
[24] SessionD receives the message
[24] Get the subscriber ID from MobilityD w.r.t UE IP address
[24] SessionD reads the session map from session store.
[2] SessionD sends the notification to AccessD
[2] Handle Notification to AccessD