Which module of SMS gateway is responsible for message caching and forwarding?

Does the subject want to ask "which module of SMS gateway is responsible for message caching and forwarding"? Access module, message cache module.

1. Access module: responsible for connecting with external systems (such as SMS senders), receiving messages and transmitting them to internal modules.

2. Message caching module: it is responsible for caching the received messages so as to resend them when network failure or other problems occur.