Understanding Tunnel Management
You can configure tunnel management on the MobileNext Broadband Gateway to specify the maximum number of request messages to send and how long to wait for a response from a peer before sending a retransmit message.
A tunnel management request-and-response sequence begins when the broadband gateway (P-GW) sends a request message to the S-GW and ends when the S-GW sends a corresponding response message back to the broadband gateway. If the broadband gateway does not receive a response from the S-GW after a certain number of retries, tunnel failure results. When tunnel failure occurs, the broadband gateway deletes the subscriber session associated with the down peer and all Modify or Delete requests associated with that GPRS tunneling protocol (GTP) tunnel.
This topic covers:
Successful Create Request Sequence for Tunnel Management
The tunnel management process begins when the Serving Gateway (S-GW) sends a Create request message to the broadband gateway (P-GW), and the broadband gateway sends a corresponding response message back to the S-GW, signaling that the GTP tunnel is active. Figure 1 shows a successful Create request sequence in which the S-GW receives a response after sending a request.
Figure 1: Successful Create Request Sequence for Tunnel Management
The following steps describe the tunnel management Create request sequence in Figure 1:
- The S-GW sends a Create request message to the P-GW.
- The P-GW sends a response back to the S-GW.
Successful Update/Delete Request Sequence for Tunnel Management
The tunnel management process begins when the broadband gateway (P-GW) sends an Update or Delete request message to the S-GW, and the S-GW sends a corresponding response message back to the broadband gateway, signaling that the GTP tunnel is active. Figure 2 shows a successful Update or Delete request sequence in which the P-GW receives a response to each request within the specified default values for number of requests and response time.
Figure 2: Successful Update/Delete Request Sequence for Tunnel Management
The following steps describe the tunnel management Update or Delete request sequence in Figure 2:
- A request is sent, but the P-GW receives no response within the specified t3-response time.
- A second request is sent, but the P-GW receives no response within the specified t3-response time.
- A third request is sent, and the P-GW receives a response within the specified t3-response time.
Failed Update/Delete Request Sequence for Tunnel Management
If, after sending a specified number of Update or Delete request messages to the S-GW, the broadband gateway fails to receive a corresponding response message from the S-GW, the tunnel path is determined to be down. Figure 3 shows a failed tunnel management request sequence in which the P-GW does not receive a response within the specified defaults for number of requests and the response time.
Figure 3: Failed Update/Delete Request Sequence for Tunnel Management
The following steps describe the Update or Delete request failed sequence in Figure 3:
- The first request is sent, but the P-GW receives no response from the peer within the specified t3-response time (5 seconds).
- The second request is sent, but the P-GW receives no response from the peer within the specified t3-response time.
- The third request is sent, but the P-GW receives no response from the peer within the specified t3-response time.
- At this point, the message flow stops, and the P-GW deletes the subscriber session associated with the down peer and all Update or Delete requests associated with that GTP tunnel.
