How CWMP works
CWMP uses remote procedure call (RPC) methods for bidirectional communication between CPE and ACS. The RPC methods are encapsulated in HTTP or HTTPS.
RPC methods
Table 15 shows the primary RPC methods used in CWMP.
Table 15: RPC methods
RPC method | Description |
|---|---|
Get | The ACS obtains the values of parameters on the CPE. |
Set | The ACS modifies the values of parameters on the CPE. |
Inform | The CPE sends an Inform message to the ACS for the following purposes:
|
Download | The ACS requires the CPE to download a configuration or software image file from a specific URL for software or configuration update. |
Upload | The ACS requires the CPE to upload a file to a specific URL. |
Reboot | The ACS reboots the CPE remotely for the CPE to complete an upgrade or recover from an error condition. |
Autoconnect between ACS and CPE
The CPE automatically initiates a connection to the ACS when one of the following events occurs:
ACS URL change. The CPE initiates a connection request to the new ACS URL.
CPE startup. The CPE initiates a connection to the ACS after the startup.
Timeout of the periodic Inform interval. The CPE re-initiates a connection to the ACS at the Inform interval.
Expiration of the scheduled connection initiation time. The CPE initiates a connection to the ACS at the scheduled time.
CWMP connection establishment
As shown in Figure 58, the CPE and the ACS use the following process to establish a connection:
After obtaining the basic ACS parameters, the CPE initiates a TCP connection to the ACS.
If HTTPS is used, the CPE and the ACS initialize SSL for a secure HTTP connection.
The CPE sends an Inform message in HTTPS to initiate a CWMP session.
After the CPE passes authentication, the ACS returns an Inform response to establish the session.
After sending all requests, the CPE sends an empty HTTP post message.
If the ACS wants to point the CPE to a new ACS URL, the ACS queries the ACS URL set on the CPE.
The CPE replies with its ACS URL setting.
The ACS sends a Set request to modify the ACS URL on the CPE.
After the ACS URL is modified, the CPE sends a response.
The ACS sends an empty HTTP message to notify the CPE that it has no other requests.
The CPE closes the connection, and then initiates a new connection to the new ACS URL.
Figure 58: CWMP message interaction procedure
