5GC support PDU Connection service ,PDU Connecting business is UE and DN Exchange between PDU Packet services ;PDU Connect service through UE launch PDU The establishment of the session . One PDU After the session is established , That is to say, we have established a UE and DN Data transmission channel .
each S-NSSAI The subscription information for may contain a default DNN And multiple DNN, When UE launch PDU Session Establishment
Request It wasn't provided at the time S-NSSAI Of DNN, So service AMF Will be for its S-NSSA Select Default DNN, If UE There are default subscription information for DNN The words of ; If there is no default DNN, So service AMF Local configuration will be selected DNN to S-NSSAI. If UE stay PDU In the session establishment request message DNN Not supported by the network , also AMF And failed to pass the inquiry NRF Choose the right one SMF, be AMF Would have rejected this PDU Connection request , Carry reason value “DNN
is not supported”.
each PDU Session supports one PDU Conversation type , that is IPv4,IPv6,IPv4v6,Ethenet,Unstructured One of them .
PDU Conversation in UE and SMF Through the NAS SM Signaling is established , modify , release .
The Internet can also start PDU Establishment of conversation ：1） The application server should be established PDU When the session is connected, the 5GC Send trigger message ,2）5GC When you receive the build request from the application server, the UE Send trigger PDU Message for session establishment ,3）UE It will be sent to UE The corresponding application on ,4）UE According to the content of the trigger message, the application on the PDU Session connection . Please refer to TS 23.502
SMF support LADN Of PDU conversation ,LADN It is only accessible in the local network service area DN; In the registration process and configuration update process, the LADN issue UE.
SMF Responsible for inspection UE Whether the session request of is consistent with its subscription data ;SMF From UDM obtain UE Subscription data for , These data include ：
- Permitted PDU Session Type And default PDU Session Type
- Permitted SSC mode And default SSC mode
- Qos information ：Session-AMBR, default 5QI And default ARP
- static state IP address / prefix
- Billing method
If UE At the same time 3GPP and non-3GPP There are all established under the access PDU Session connection , that UE You can request that a PDU Conversation from 3GPP/non-3GPP Move to non-3GPP/3GPP go .
UE Send to network PDU Session Establishment Request News ,UE To provide PDU Session ID;PDU Session
ID from UE distribution , And in the UE There is uniqueness in . In order to support the 3GPP and non3GP Access switching ,PDU Session ID Will be stored in UDM in .
No matter what 3GPP still non-3GPP Access ,UE They all create multiple connections to the same one DN Of PDU Session connection , Or multiple connections to different DN Of PDU Session connection .
UE Multiple connections can be made to the same DN Of PDU Session connection , And through different UPF connection to DN upper .
UE Multiple items established PDU Session connection , Each PDU Conversational SMF It can be different .
Each PDU Services for sessions SMF Information will be registered at UDM in .
2 AMF and SMF Interaction of
2.1 N1 Oral neutralization SMF Interactive part ：
- N1 The endpoint of the port AMF,AMF Responsible for transmission UE and SMF Between the NAS SM news （ be based on PDU Session ID）,NAS SM
The response message must be sent by the same access network as the request message .
- SMF Responsible for handling NAS Of SM news .
- UE Only in RM-REGISTERED Initiated under status PDU Conversation flow
- One SMF Selected as an article PDU Session service ,AMF Make sure you follow this one PDU Conversation related NAS SM The message was sent to the SMF To deal with it .
- PDU After the session is established ,AMF and SMF Save the PDU The access type of the session
2.2 N11（AMF<->SMF） Oral neutralization SMF Interactive part
- AMF according to SMF Subscription reporting for UE Location information for
- Be a PDU Session When released SMF To inform AMF
- Be a PDU Session On successful establishment ,AMF To save the service PDU Session Of SMF ID,SMF To save this service UE Of AMF ID
2.3 N2 Oral neutralization SMF Interactive part
- some N2 signalling （ Such as switching related signaling ） May require AMF and SMF Perform the relevant operations , In this scenario AMF Responsible for guarantee AMF and SMF Coordination between ,AMF You can SM
N2 Signaling is forwarded to the corresponding SMF handle ,AMF Yes N2 In the news PDU Session ID Find the corresponding SMF Of , because AMF Saved PDU Session Service for SMF
- In order to speed up NG-RAN To give different ones PDU Type Packets should be compressed with appropriate header ,SMF It should be given NG-RAN provide PDU Type and PDU Session Etc
2.4 N3 Oral harmony SMF Interactive part
It can be activated or de activated PDU Session User interface connection for .
2.5 N4 Oral harmony SMF Interactive part
When UPF Received one UE Downstream packets of , But it was found that it did not go down N3 The tunnel can send packets , be UPF You'll be informed SMF,SMF You'll be informed AMF To initiate “ Network triggered Service
Request technological process ”, But if SMF Caused by UE Not reachable or only reachable by priority services SMF It does not support priority services , that SMF It won't be notified AMF There is downlink data arrival
3 One PDU Session has multiple PDU Conversation anchor
In order to support DN Optional routing features and support for SSC mode 3,SMF Can be controlled PDU Session Data routing makes this PDU
Session There can be more than one at the same time N6 Interface . each N6 Interface UPF It's called PDU Conversation anchor .
single PDU Many conversations PDU The session anchor function corresponds to the following functions ：
- In a PDU Using uplink classifier in session
- In a PDU Use in conversation IPv6 multi-homing（ Multihost ）
3.1 stay PDU Using uplink classifier in session
For type IPv4,IPv6,IPv4v6,Ethenet Of PDU Session,SMF Can be in the PDU An uplink classifier is inserted into the data transmission path of the session （Uplink
Classifier）（ Referred to as “UL CL”）;“UL
CL” Function in UPF Provided in , Its purpose is to forward the packets that meet the business filtering rules to the specified path , This is a bit like a routing table . Insert and delete “UL
CL” By SMF Controlled , Its adoption N4 Mouth to mouth UPF Operate , of course SMF Depend on UPF Is it supported by our ability “UL CL”.
For the “UL CL” Data forwarding function ,UE It's imperceptible ;UE No participation at all “UL CL” Insertion and deletion of .
Be a “UL CL” Is inserted into a PDU Session Time in data channel , This one PDU Session There are many PDU
Session Anchor point , These anchors provide access to the same DN Multiple different paths for .
“UL CL” The function is to forward the uplink service data to different ones according to the filter requirements PDU Conversation anchor , Put the UE Multiple anchors down the downlink data merge .
“UL CL” Implement filtering rules and determine packet routing ; support “UL CL” Of UPF Can be responsible for billing business statistics , Execution rate control （Session-AMBR per PDU
The image above shows one PDU Session Have two PDU Session Scene of anchor point ; Uplink classifier （UL
CL） Insert N3 Mouth terminal UPF upper , Anchor point 1 And anchors 2 The end N6 Interface , Uplink classifier UPF And anchors UPF Through the N9 Interface transmission .
3.2 In a PDU Use in conversation IPv6 Multihost
One PUD Sessions can be associated with multiple IPv6 prefix , This is called multihosting （multi-homed）
PDU conversation . Multihost PDU Conversation through multiple PDU Session anchor access to a data network （DN）. each PDU The data channels corresponding to session anchors will eventually converge to a common UPF, This public one UPF have “ Bifurcation point ”（Branching
Point） function , It's called a branching point UPF. The branch point forwards the uplink packets to different PDU Anchor point , Merge the data from each anchor down .
Bifurcation point UPF It can be used for billing statistics , rate control （Session-AMBR per PDU
Session）.SMF adopt N4 Mouth control in UPF Insert or remove branch points , Of course, we should also consider it UPF Does the ability to support branch point functionality .
Multihost PDU Conversation should only be applied to IPv6 Of PDU conversation ;UE When the request creation type is IPv6 or IPv4v6 Of PDU In conversation ,UE Tell the network if it supports it Multi-homed
IPv6 PDU conversation .
The image above is used for SSC mode 3 Multi hosting of PDU Conversation diagram , When the network wants to switch the anchor point of the access network , First establish a new anchor to access the same data network （ Above PDU session
anchor 2）, Then release the old anchor （ Above PDU session anchor1）. During this anchor switch ,UE Continuous service is available , The business will not be affected .
The image above shows one PDU There are two anchor access points DN Scene of .