Minimal SIP Echo Server

This is a simple SIP echo server written in Rust. It listens for incoming SIP calls, establishes an RTP session, and echoes back any received RTP media packets after a short delay.

Architecture

The application is designed with a modular architecture to separate concerns.

The main components are:

• main.rs: The application entry point. It initializes the server, sets up the SIP endpoint, and dispatches incoming SIP transactions.
• config.rs: Stores all static configuration values, such as IP addresses, ports, and echo delay.
• sip.rs: Contains the core SIP signaling logic. It handles different SIP methods like INVITE, ACK, and BYE.
• sdp.rs: Responsible for parsing incoming SDP offers and generating SDP answers to negotiate media sessions.
• rtp_session.rs: Manages the RTP media stream. It binds to an RTP port, receives packets, buffers them, and sends them back to the caller.

Module Interaction

graph TD
    subgraph Application
        A[main.rs] --> B{SIP Endpoint};
        B -- SIP Transaction --> C[sip.rs];
        C -- Needs SDP --> D[sdp.rs];
        C -- Needs RTP Session --> E[rtp_session.rs];
        E -- Needs Config --> F[config.rs];
        D -- Needs Config --> F;
    end

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Call Flow

The following sequence diagram illustrates the flow of a typical call:

sequenceDiagram
    participant Client
    participant Server

    Client->>Server: INVITE (with SDP Offer)
    Server->>Server: sip.rs: handle_invite()
    Server->>Server: sdp.rs: parse_sdp_offer()
    Server->>Server: rtp_session.rs: RtpSession::new()
    Server->>Server: sdp.rs: create_sdp_answer()
    Server-->>Client: 200 OK (with SDP Answer)

    Client->>Server: ACK
    Server->>Server: sip.rs: handle_transaction(ACK)

    loop Media Exchange
        Client->>Server: RTP Media Packets
        Server->>Server: rtp_session.rs: Echoes packets after delay
        Server-->>Client: Echoed RTP Media Packets
    end

    Client->>Server: BYE
    Server->>Server: sip.rs: handle_transaction(BYE)
    Server-->>Client: 200 OK

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