2 .. Copyright (c) 2019 AT&T Intellectual Property.
3 .. Copyright (c) 2019 Nokia.
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15 .. See the License for the specific language governing permissions and
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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. This needs to be considered when retries are implemented in xApp side, as it can increase completion time of the
41 procedure. 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 allocates RIC Requestor ID. Currently the ID value is always 123. In merge case subscription is created only for
71 the first requestor. RAN gets the Request of the xApp who makes the first subscription. RAN uses Subscription Manager allocated Requestor
72 ID in all RIC Indication messages it sends to RIC for the subscription.
74 TransactionId (Xid) in RMR message header is used to track messages between xApp and Subscription Manager. xApp allocates it. Subscription
75 Manager returns TransactionId received from xApp in response message to xApp. xApp uses it to map response messages to request messages
78 * Subscription procedure
82 xApp sends RIC Subscription Request message to Subscription Manager. Subscription Manager validates request types in the message and sends
83 route create to Routing Manager over REST interface. When route is created successfully Subscription Manager forwards request to E2
84 Termination. When RIC Subscription Response arrives from E2 Termination Subscription Manager forwards it to xApp.
86 Subscription Manager supervises route create and RIC Subscription Request with a timer.
88 RIC Indication messages which are used to transport subscribed messages from RAN are routed from E2 Termination to xApps
89 directly using the routes created during Subscription procedure.
91 Subscription Manager supports REPORT, POLICY and INSERT type subscriptions (RICActionTypes). CONTROL is not supported. POLICY type
92 subscription can be updated. In update case signaling sequence is the same as above, except route is not created to Routing manager.
93 xApp uses initially allocated TransactionId and RIC Request Sequence Number in update case. Route in POLICY type subscription case is needed
94 only that Subscription Manager can send response messages to xApp. RIC Subscription Request message contains list of RICaction-ToBeSetup-ItemIEs.
95 The list cannot have REPORT, POLICY, INSERT action types at the same time. Subscription Manager checks actions types in the message.
96 If both action types is found the message is dropped.
99 .. image:: images/Successful_Subscription.png
101 :alt: Successful subscription picture
106 In failure case Subscription Manager checks the failure cause and acts based on that. If failure cause is "duplicate" Subscription
107 Manager sends delete to RAN and then resends the same subscription. If failure cause is such that Subscription manager cannot do
108 anything to fix the problem, it sends delete to RAN and sends RIC Subscription Failure to xApp. Subscription Manager may retry RIC
109 Subscription Request and RIC Subscription Delete messages also in this case before it responds to xApp.
111 .. image:: images/Subscription_Failure.png
113 :alt: Subscription failure picture
117 In case of timeout in Subscription Manager, Subscription Manager may resend the RIC Subscription Request to RAN. If there is no response
118 after retry, Subscription Manager shall NOT send any response to xApp. xApp may retry RIC Subscription Request, if it wishes to do so.
119 Subscription Manager does no handle the retry if Subscription Manager has ongoing subscription procedure for the same subscription.
120 Subscription just drops the request.
122 .. image:: images/Subscription_Timeout.png
124 :alt: Subscription timeout picture
126 * Subscription delete procedure
130 xApp sends RIC Subscription Delete Request message to Subscription Manager. xApp must use the same RIC Request Sequence Number which
131 it received in RIC Subscription Response message when subscription is deleted. When Subscription Manager receives RIC Subscription
132 Delete Request message, Subscription Manager first forwards the request to E2 Termination. When RIC Subscription Delete Response arrives
133 from E2 Termination to Subscription Manager, Subscription Manager forwards it to xApp and then request route deletion from Routing Manager.
135 Subscription Manager supervises RIC Subscription Deletion Request and route delete with a timer.
137 .. image:: images/Successful_Subscription_Delete.png
139 :alt: Successful subscription delete picture
143 Delete procedure cannot fail from xApp point of view. Subscription Manager always responds with RIC Subscription Delete Response to xApp.
145 .. image:: images/Subscription_Delete_Failure.png
147 :alt: Subscription delete failure picture
151 In case of timeout in Subscription Manager, Subscription Manager may resend the RIC Subscription Delete Request to RAN. If there is no
152 response after retry, Subscription Manager responds to xApp with RIC Subscription Delete Response.
154 .. image:: images/Subscription_Delete_Timeout.png
156 :alt: Subscription delete timeout picture
158 * Unknown subscription
160 If Subscription Manager receives RIC Subscription Delete Request for a subscription which does not exist, Subscription Manager cannot respond
161 to xApp as there is no route for the subscription.
163 * Subscription merge procedure
167 xApp sends RIC Subscription Request message to Subscription Manager. Subscription Manager checks is the Subscription mergeable. If not,
168 Subscription Manager continues with normal Subscription procedure. If Subscription is mergeable, Subscription Manager sends route create
169 to Routing Manager and then responds with RIC Subscription Response to xApp.
171 Route create is supervised with a timer.
173 Merge for REPORT type subscription is possible if Action Type and Event Trigger Definition of subscriptions are equal.
175 ``Only REPORT type subscriptions can be be merged.``
177 .. image:: images/Successful_Subscription_Merge.png
179 :alt: Successful subscription merge picture
183 Failure case is basically the same as in normal subscription procedure. Failure can come only from RAN when merge is not yet done.
184 If error happens during route create Subscription Manager drops the RIC Subscription Request message and xApp does not get any response.
188 Timeout case is basically the same as in normal subscription procedure but timeout can come only in route create during merge operation.
189 If error happens during route create, Subscription Manager drops the RIC Subscription Request message and xApp does not get any response.
191 * Subscription delete merge procedure
195 xApp sends RIC Subscription Delete Request message to Subscription Manager. If delete concerns merged subscription, Subscription Manager
196 responds with RIC Subscription Delete Response to xApp and then sends route delete request to Routing manager.
198 Subscription Manager supervises route delete with a timer.
200 .. image:: images/Successful_Subscription_Delete_Merge.png
202 :alt: Successful subscription delete merge picture
206 Delete procedure cannot fail from xApp point of view. Subscription Manager responds with RIC Subscription Delete Response message to xApp.
210 Timeout can only happen in route delete to Routing manager. Subscription Manager responds with RIC Subscription Delete Response message to xApp.
214 If Subscription Manager receives unknown message, Subscription Manager drops the message.
216 RAN services explained
217 ----------------------
218 RIC hosted xApps may use the following RAN services from a RAN node:
220 * 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
221 * 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
222 * CONTROL: RIC sends a Control message to RAN to initiate or resume call processing in RAN
223 * POLICY: RIC requests that RAN executes a specific POLICY during call processing in RAN after each occurrence of a defined SUBSCRIPTION
225 Supported E2 procedures and RAN services
226 ----------------------------------------
227 * RIC Subscription procedure with following RIC action types:
233 * RIC Subscription Delete procedure
235 * Merge and delete of equal REPORT type subscriptions.
237 Recommendations for xApps
238 -------------------------
240 * Recommended retry delay
242 Recommended retry delay for xApp is > 10 seconds