Why _recvTransport doesn't connnect trigger ，but _sendTransport connect is ok

mediasoup libraries
1 
if(_consume){
    const transportInfos = await _protoo.request('createWebRtcTransport',
        {
            forceTcp         : false,
            producing        : false,
            consuming        : true
        });

    const {
        id,
        iceParameters,
        iceCandidates,
        dtlsParameters,
        sctpParameters
    } = transportInfos;

    try{
        _recvTransport = _mediasoupDevice.createRecvTransport({
            id,
            iceParameters,
            iceCandidates,
            dtlsParameters :
            {
                ...dtlsParameters,
                // Remote DTLS role. We know it's always 'auto' by default so, if
                // we want, we can force local WebRTC transport to be 'client' by
                // indicating 'server' here and vice-versa.
                role : 'auto'
            },
            sctpParameters
        });
    }
    catch (err){
        console.log(err);
    }

    _recvTransport.on('connect', async ({ dtlsParameters }, callback, errback) => // eslint-disable-line no-shadow
    {
            await _protoo.request('connectWebRtcTransport',{
                transportId : _recvTransport.id,
                dtlsParameters
            })
            .then(callback)
            .catch(errback);
     });
}

Why _recvTransport doesn’t connnect trigger ，but _sendTransport connect is ok
Why _recvTransport doesn’t connnect trigger ，but _sendTransport connect is ok
Why _recvTransport doesn’t connnect trigger ，but _sendTransport connect is ok