# Architecture
The CPE communicates to a HTTP server, also called Auto Configuration Server (ACS), because instead of a normal client-server relationship between the device and the HTTP server, what happens is that the connection can be initiated from the server to the device.
As you can see above, the ACS and the CPE are at the same time a HTTP client and server, it's needed to exchange messages according to the CWMP protocol and because they're both a client and a server, must not exist [NAT](https://en.wikipedia.org/wiki/Network_address_translation) between the CPE and the ACS, they need to be directly accessible to each other.
Although there are some workarounds for the NAT problem as to use [XMPP](broken://spaces/ys3ycSw4qx1SjsJeAo2N/pages/kzTlst3tKo255yz4YpDi) or [STUN](https://en.wikipedia.org/wiki/STUN), the best option is still to install the ACS with direct connection to the CPE, this simplifies your deployment and ensures a smooth solution.
## Messages
Here are the main messages you can send to a CPE and to interact with it. All of them are available in the [Oktopus REST API ](https://documenter.getpostman.com/view/18932104/2s93eR3vQY#96986790-3e2c-44fd-bc8c-9a6208f01516)> Device > CWMP Native Messages.
* GetParameterNames
* GetParameterValues
* GetParameterAttributes
* SetParameterValues
* AddObject
* DeleteObject
## Data Model
The first Data Model created to be used with CWMP was the [TR-098](https://cwmp-data-models.broadband-forum.org/tr-098-1-8-0.html), after that came that the [TR-181](https://usp-data-models.broadband-forum.org/tr-181-2-16-0-usp.html) which has more capabilities and possibilities than it's predecessor.
## Encoding
The messages between the CPE and the ACS are exchanged using [SOAP](https://www.geeksforgeeks.org/basics-of-soap-simple-object-access-protocol/), that transfer messages in the format of [XML](https://en.wikipedia.org/wiki/XML), and contains structured data with [RPC](https://en.wikipedia.org/wiki/Remote_procedure_call) information.
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