The M3UA layer creates a connection between a local and remote endpoint by establishing an SCTP association between the endpoints, and then exchanging M3UA management messages that specify the state of the peer server process (PSP) and the routing keys (PS). This message exchange occurs when the Ethernet port is activated.
The message exchange used to establish a connection differs depending on the endpoint configurations.
The following illustration shows the message flow used to establish a connection between two endpoints configured as IPSPs in double-ended mode (DE), where each side supports two route contexts:
The following table describes the process for establishing a connection between two IPSP endpoints in DE mode:
Stage |
Description |
1 |
Client IPSP initiates an SCTP association by sending an INIT when the Ethernet port becomes active (which occurs when electrical connectivity is established). |
2 |
M3UA layer establishes an SCTP association between the local and remote endpoints using INIT (Initiation), INIT ACK (Initiation Acknowledgement), COOKIE (State Cookie), and COOKIE ACK (Cookie Acknowledgment) messages. The association state changes from DOWN to ACTIVE (as displayed in the m3uamgr command: status psp <n>). |
3 |
Each IPSP sends an ASPUP (ASP Up) message to notify the other side that the PSP is up. The ASP State on each side changes from DOWN to INACTIVE for each remote route context (as displayed in the m3uamgr command: status psp <n>). |
4 |
Each IPSP receiving an ASPUP responds with an ASPUP ACK message. |
5 |
Each IPSP sends NOTIFY messages of type ASCHG (AS State Change) with new state INACTIVE for each route context. For readability, these messages are not shown in the message flow illustration. |
6 |
Each IPSP sends an ASPAC (ASP Active) message for each active local route context. A local route is considered active when the following conditions are met:
The ASP State on the receiving side changes from INACTIVE to ACTIVE for each remote route context in the ASPAC message (as displayed in the m3uamgr command: status psp <n>). The sending of an ASPAC message indicates that the sending IPSP can now receive traffic related to the routing contexts identified in the message. The receipt of an ASPAC message indicates that the receiving IPSP can now send traffic related to the routing contexts identified in the message. |
7 |
Each IPSP receiving an ASPAC responds with an ASPAC ACK message for each routing context. |
8 |
Each IPSP sends NOTIFY messages of type ASCHG with new state ACTIVE for each route context. For readability, these messages are not shown in the flow illustration. |
The following illustration shows the message flow for establishing a connection between two IPSPs in single-ended mode (SE):
For endpoints configured as IPSPs in single-ended (SE) mode, only one side is required to send the ASPUP and ASPAC messages. In this configuration, the routing contexts must be configured identically on both sides.
The following table describes the process for establishing a connection between two IPSP endpoints in SE mode:
Stage |
Description |
1 |
Client IPSP initiates an SCTP association by sending an INIT when the Ethernet port becomes active (which occurs when electrical connectivity is established). |
2 |
M3UA layer establishes an SCTP association between the local and remote endpoints using INT (Initiation), INT ACK (Initiation Acknowledgement), COOKIE (State Cookie), and COOKIE ACK (Cookie Acknowledgment) messages. The association State changes from DOWN to ACTIVE (as displayed in the m3uamgr command: status psp <n>). |
3 |
Client IPSP sends an ASPUP (ASP Up) message to notify the other side that the PSP is up. The ASP State on each side changes from DOWN to INACTIVE (as displayed in the m3uamgr command: status psp <n>). |
4 |
Each IPSP receiving an ASPUP responds with an ASPUP ACK message. |
5 |
Each side sends NOTIFY messages of type ASCHG (AS State Change) with new state INACTIVE for each route context. For readability, these messages are not shown in the message flow illustration. |
6 |
Client IPSP sends an ASPAC (ASP Active) message for each active local route context. A local route is considered active when the following conditions are met:
The ASP State on the each side changes from INACTIVE to ACTIVE for each remote route context in the ASPAC message (as displayed in the m3uamgr command: status psp <n>). The sending of an ASPAC message indicates that the sending IPSP can now receive traffic related to the routing contexts identified in the message. The receipt of an ASPAC message indicates that the receiving IPSP can now send traffic related to the routing contexts identified in the message. |
7 |
Each IPSP receiving an ASPAC responds with an ASPAC ACK message for each routing context. |
8 |
Each side sends NOTIFY messages of type ASCHG with new state ACTIVE for each route context. For readability, these messages are not shown in the flow illustration. |
The following illustration shows the message flow used to establish a connection between an endpoint configured as an ASP and an endpoint configured as an SGP:
The following table describes the process for establishing a connection between an ASP endpoint and an SGP endpoint:
Stage |
Description |
1 |
ASP initiates an SCTP association by sending an INIT when the Ethernet port becomes active (which occurs when electrical connectivity is established). |
2 |
M3UA layer establishes an SCTP association between the local and remote endpoints using INT (Initiation), INT ACK (Initiation Acknowledgement), COOKIE (State Cookie), and COOKIE ACK (Cookie Acknowledgment) messages. The association State changes from DOWN to ACTIVE (as displayed in the m3uamgr command: status psp <n>). |
3 |
ASP sends an ASPUP (ASP Up) message to notify the other side that the PSP is up. The ASP state on each side changes from DOWN to INACTIVE for each remote route context (as displayed in the m3uamgr command: status psp <n>). |
4 |
Each IPSP receiving an ASPUP responds with an ASPUP ACK message. |
5 |
SGP sends NOTIFY messages of type ASCHG (AS State Change) with new state INACTIVE for each route context. For readability, these messages are not shown in the message flow illustration. |
6 |
ASP sends one or more ASPAC (ASP Active) messages that identify its remote route contexts. These message are sent after the following conditions are met:
The ASP State for each side changes from INACTIVE to ACTIVE for each remote route context in the ASPAC message (as displayed in the m3uamgr command: status psp <n>). The sending of an ASPAC message indicates that the ASP can now receive traffic related to the routing contexts identified in the message. The receipt of an ASPAC message indicates that the SGP can now send traffic related to the routing contexts identified in the message. |
7 |
Each IPSP receiving an ASPAC responds with an ASPAC ACK message for each routing context. |
8 |
SGP sends NOTIFY messages of type ASCHG with new state ACTIVE for each route context. For readability, these messages are not shown in the flow illustration. |
The message flow for a redundant configuration differs from that for a non-redundant configuration in the following ways:
Both the primary and backup PSP establish associations and send the ASPUP message.
Only the primary PSP sends ASPAC messages.
When a switchover occurs, the PSP that went from primary to backup sends ASPIA (ASP Inactive) messages for all local route contexts, indicating that it can no longer receive traffic related to those route contexts. The PSP that went from backup to primary sends ASPAC messages for all local route contexts, indicating that it will now receive traffic related to those route contexts. The receiver of these messages changes the association over which the related traffic is transferred.
As with the non-redundant configurations, NOTIFY (ASCHG) messages are sent by an IPSP or SGP upon receipt of ASPAC or ASPIA messages.