2 .. Copyright (c) 2019 AT&T Intellectual Property.
3 .. Copyright (c) 2019 Nokia.
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28 Subscription Manager is a basic platform service in RIC. It is responsible for managing E2 subscriptions from xApps to the
29 Radio Access Network (RAN).
31 xApp can subscribe and unsubscribe messages from gNodeB through Subscription Manager. Subscription Manager manages the subscriptions
32 and message routing of the subscribed messages between E2 Termination and xApps. If one xApp has already made a subscription and then
33 another xApp initiates identical subscription, Subscription Manager does not forward the subscription to gNodeB but merges the
34 subscriptions internally. In merge case Subscription Manager just updates the message routing information to Routing Manager and
35 sends response to xApp.
37 There can be only one ongoing RIC Subscription or RIC Subscription Delete procedure towards RAN at any time. That is because Subscription
38 Manager is able to merge new subscriptions only which those it has already received successful response from RAN. Subscriptions
39 and delete subscriptions are therefore queued in Subscription Manager. Subscription Manager may need to do reties during subscribe or
40 unsubscribe procedure. As it can increase completion time of the procedure, this needs to be considered when retries are implemented
41 in xApp side. xApp's retry delay should not be too short.
43 .. image:: images/PlaceInRICSoftwareArchitecture.png
45 :alt: Place in RIC's software architecture picture
52 Subscribed messages from RAN are transported to RIC inside RIC Indication message. RIC Indication message is transported to xApp
53 inside RMR message, in Payload field of the RMR message. RMR message is routed to xApp based on SubId field (subscription id) in
54 the RMR header. Same routing mechanism is used also for response messages from Subscription Manager to xApp. Subscription Manager is
55 not able to respond to xApp if route for subscription has not been created.
57 When xApp sends message to Subscription Manager it sets -1 in SubId field in the RMR header. It means that messages are routed based
58 on message type (Mtype filed in RMR header). RIC Subscription Request and RIC Subscription delete Request messages are pre configured
59 to be routed to Subscription Manager.
61 Subscription Manager allocates unique RIC Request Sequence Number for every subscription during Subscription procedure. Subscription
62 Manager replaces existing ASN.1 decoded RIC Request Sequence Number in the RIC Subscription Request message allocated by the xApp.
63 That sequence number (subscription id) is then used for the subscription in RIC and RAN as long the subscription lives. xApp gets
64 the sequence number in RIC Subscription Response message from Subscription manager based on the message types.
66 Subscribed messages are routed to xApps based on sequence number. Sequence number is placed in the SubId field of the RMR message
67 header when E2 Termination sends the subscribed message to xApp. When xApp wants to delete the subscription, the same sequence number
68 must be included in the ASN.1 encoded RIC Subscription Delete Request message sent to Subscription Manager.
70 Subscription Manager responds to xApp with xApp allocated RIC Requestor ID. In merge case subscription is created only for the first
71 requestor. RAN gets the Requestor ID of the xApp who makes the first subscription. RAN uses that Requestor ID in all RIC Indication
72 messages it sends to RIC for the subscription. Therefore xApp may get Requestor ID in RIC Indication message that belongs to another xApp.
73 The xApp whose subscription is merged into the first subscription will also get Requestor ID of the first subscribed xApp in the RIC
74 Subscription Response and RIC Subscription Delete Response messages.
76 TransactionId (Xid) in RMR message header is used to track messages between xApp and Subscription Manager. xApp allocates it. Subscription
77 Manager returns TransactionId received from xApp in response message to xApp. xApp uses it to map response messages to request messages
80 * Subscription procedure
84 xApp sends RIC Subscription Request message to Subscription Manager. Subscription Manager validates request types in the message and sends
85 route create to Routing Manager over REST interface. When route is created successfully Subscription Manager forwards request to E2
86 Termination. When RIC Subscription Response arrives from E2 Termination Subscription Manager forwards it to xApp.
88 Subscription Manager supervises route create and RIC Subscription Request with a timer.
90 RIC Indication messages which are used to transport subscribed messages from RAN are routed from E2 Termination to xApps
91 directly using the routes created during Subscription procedure.
93 ``Routing manager has 1 second delay in routing create in R3 release before it responds to Subscription Manager. That is because of delay in route create to RMR.``
95 Subscription Manager supports REPORT and POLICY type subscriptions (RICActionTypes). CONTROL and INSERT are not supported. POLICY type
96 subscription can be updated. In update case signaling sequence is the same as above, except route is not created to Routing manager.
97 xApp uses initially allocated TransactionId and RIC Request Sequence Number in update case. Route in POLICY type subscription case is needed
98 only that Subscription Manager can send response messages to xApp. RIC Subscription Request message contains list of RICaction-ToBeSetup-ItemIEs.
99 The list cannot have both REPORT and POLICY action types at the same time. Subscription Manager checks actions types in the message.
100 If both action types is found the message is dropped.
103 .. image:: images/Successful_Subscription.png
105 :alt: Successful subscription picture
110 In failure case Subscription Manager checks the failure cause and acts based on that. If failure cause is "duplicate" Subscription
111 Manager sends delete to RAN and then resends the same subscription. If failure cause is such that Subscription manager cannot do
112 anything to fix the problem, it sends delete to RAN and sends RIC Subscription Failure to xApp. Subscription Manager may retry RIC
113 Subscription Request and RIC Subscription Delete messages also in this case before it responds to xApp.
115 .. image:: images/Subscription_Failure.png
117 :alt: Subscription failure picture
121 In case of timeout in Subscription Manager, Subscription Manager may resend the RIC Subscription Request to RAN. If there is no response
122 after retry, Subscription Manager shall NOT send any response to xApp. xApp may retry RIC Subscription Request, if it wishes to do so.
123 Subscription Manager does no handle the retry if Subscription Manager has ongoing subscription procedure for the same subscription.
124 Subscription just drops the request.
126 .. image:: images/Subscription_Timeout.png
128 :alt: Subscription timeout picture
130 * Subscription delete procedure
134 xApp sends RIC Subscription Delete Request message to Subscription Manager. xApp must use the same RIC Request Sequence Number which
135 it received in RIC Subscription Response message when subscription is deleted. When Subscription Manager receives RIC Subscription
136 Delete Request message, Subscription Manager first forwards the request to E2 Termination. When RIC Subscription Delete Response arrives
137 from E2 Termination to Subscription Manager, Subscription Manager forwards it to xApp and then request route deletion from Routing Manager.
139 Subscription Manager supervises RIC Subscription Deletion Request and route delete with a timer.
141 .. image:: images/Successful_Subscription_Delete.png
143 :alt: Successful subscription delete picture
147 Delete procedure cannot fail from xApp point of view. Subscription Manager always responds with RIC Subscription Delete Response to xApp.
149 .. image:: images/Subscription_Delete_Failure.png
151 :alt: Subscription delete failure picture
155 In case of timeout in Subscription Manager, Subscription Manager may resend the RIC Subscription Delete Request to RAN. If there is no
156 response after retry, Subscription Manager responds to xApp with RIC Subscription Delete Response.
158 .. image:: images/Subscription_Delete_Timeout.png
160 :alt: Subscription delete timeout picture
162 * Unknown subscription
164 If Subscription Manager receives RIC Subscription Delete Request for a subscription which does not exist, Subscription Manager cannot respond
165 to xApp as there is no route for the subscription.
167 * Subscription merge procedure
171 xApp sends RIC Subscription Request message to Subscription Manager. Subscription Manager checks is the Subscription mergeable. If not,
172 Subscription Manager continues with normal Subscription procedure. If Subscription is mergeable, Subscription Manager sends route create
173 to Routing Manager and then responds with RIC Subscription Response to xApp.
175 Route create is supervised with a timer.
177 Merge for REPORT type subscription is possible if Action Type and Event Trigger Definition of subscriptions are equal.
179 ``Only REPORT type subscriptions can be be merged.``
181 .. image:: images/Successful_Subscription_Merge.png
183 :alt: Successful subscription merge picture
187 Failure case is basically the same as in normal subscription procedure. Failure can come only from RAN when merge is not yet done.
188 If error happens during route create Subscription Manager drops the RIC Subscription Request message and xApp does not get any response.
192 Timeout case is basically the same as in normal subscription procedure but timeout can come only in route create during merge operation.
193 If error happens during route create, Subscription Manager drops the RIC Subscription Request message and xApp does not get any response.
195 * Subscription delete merge procedure
199 xApp sends RIC Subscription Delete Request message to Subscription Manager. If delete concerns merged subscription, Subscription Manager
200 responds with RIC Subscription Delete Response to xApp and then sends route delete request to Routing manager.
202 Subscription Manager supervises route delete with a timer.
204 .. image:: images/Successful_Subscription_Delete_Merge.png
206 :alt: Successful subscription delete merge picture
210 Delete procedure cannot fail from xApp point of view. Subscription Manager responds with RIC Subscription Delete Response message to xApp.
214 Timeout can only happen in route delete to Routing manager. Subscription Manager responds with RIC Subscription Delete Response message to xApp.
218 If Subscription Manager receives unknown message, Subscription Manager drops the message.
220 RAN services explained
221 ----------------------
222 RIC hosted xApps may use the following RAN services from a RAN node:
224 * REPORT: RIC requests that RAN sends a REPORT message to RIC and continues further call processing in RAN after each occurrence of a defined SUBSCRIPTION
225 * INSERT: RIC requests that RAN sends an INSERT message to RIC and suspends further call processing in RAN after each occurrence of a defined SUBSCRIPTION
226 * CONTROL: RIC sends a Control message to RAN to initiate or resume call processing in RAN
227 * POLICY: RIC requests that RAN executes a specific POLICY during call processing in RAN after each occurrence of a defined SUBSCRIPTION
229 Supported E2 procedures and RAN services
230 ----------------------------------------
231 * RIC Subscription procedure with following RIC action types:
236 * RIC Subscription Delete procedure
238 * Merge and delete of equal REPORT type subscriptions.
240 Recommendations for xApps
241 -------------------------
243 * Recommended retry delay
245 Recommended retry delay for xApp is > 10 seconds