RTMP协议规定：
第一步，建立一个网络连接（NetConnection）:客户端和服务端的基础连通关系
第二步：建立一个网络流（NetStream）发送多媒体的通道（只能建立一个网络连接，可以建立多个网络流）
网络连接与网络流的关系如下图所示：

具体而言，在ngx_rmtp中如何实现呢？
客户端收到服务端的"connect"消息后(如前文所讲)，会启动connect协议交流。但在此之前需要将处理消息的回调进行注册上，收消息回调为ngx_rtmp_recv，发送消息的回调为ngx_rtmp_send。示例代码如下：

void ngx_rtmp_cycle(ngx_rtmp_session_t *s)
 {
    ngx_connection_t           *c;
    c = s->connection;
    c->read->handler =  ngx_rtmp_recv;
    c->write->handler = ngx_rtmp_send;
    s->ping_evt.data = c;
    s->ping_evt.log = c->log;
    s->ping_evt.handler = ngx_rtmp_ping;
    ngx_rtmp_reset_ping(s);
    ngx_rtmp_recv(c->read);
}

当收到对方发来的消息时：

• 解析消息头
  /* parse headers /
  if (b->pos == b->start) {
  p = b->pos;
  / chunk basic header /
  fmt = (p >> 6) & 0x03;
  csid = p++ & 0x3f;
  if (csid == 0) {
  if (b->last - p < 1)
  continue;
  csid = 64;
  csid += (uint8_t)p++;
  } else if (csid == 1) {
  if (b->last - p < 2)
  continue;
  csid = 64;
  csid += (uint8_t)p++;
  csid += (uint32_t)256 * ((uint8_t)p++);
  }
  / link orphan /
  if (s->in_csid == 0) {
  / unlink from stream #0 /
  st->in = st->in->next;
  / link to new stream /
  s->in_csid = csid;
  st = &s->in_streams[csid];
  if (st->in == NULL) {
  in->next = in;
  } else {
  in->next = st->in->next;
  st->in->next = in;
  }
  st->in = in;
  h = &st->hdr;
  h->csid = csid;
  }
  ext = st->ext;
  timestamp = st->dtime;
  if (fmt <= 2 ) {
  if (b->last - p < 3)
  continue;
  / timestamp:
  * big-endian 3b -> little-endian 4b /
  pp = (u_char)×tamp;
  pp[2] = p++;
  pp[1] = p++;
  pp[0] = p++;
  pp[3] = 0;
  ext = (timestamp == 0x00ffffff);
  if (fmt <= 1) {
  if (b->last - p < 4)
  continue;
  / size:
  * big-endian 3b -> little-endian 4b
  * type:
  * 1b -> 1b/
  pp = (u_char)&h->mlen;
  pp[2] = *p++;
  pp[1] = *p++;
  pp[0] = p++;
  pp[3] = 0;
  h->type = (uint8_t)p++;
  if (fmt == 0) {
  if (b->last - p < 4)
  continue;
  / stream:
  * little-endian 4b -> little-endian 4b /
  pp = (u_char)&h->msid;
  pp[0] = *p++;
  pp[1] = *p++;
  pp[2] = *p++;
  pp[3] = p++;
  }
  }
  }
  / extended header /
  if (ext) {
  if (b->last - p < 4)
  continue;
  pp = (u_char)×tamp;
  pp[3] = *p++;
  pp[2] = *p++;
  pp[1] = *p++;
  pp[0] = p++;
  }
  / header done */
  b->pos = p;
  }
• 判断类型，如果是"connect"的cmd消息时，其调用回调ngx_rtmp_cmd_connect_init.具体如下：
  1. 将ack_size发送对方给对方，ngx_rtmp_send_ack_size
  2. 将bandwdth发送给对方，ngx_rtmp_send_bandwidth
  3. 将chunk_size发送给对方，ngx_rtmp_send_chunk_size
  4. 将connect协议回应消息发送给对方，ngx_rtmp_send_amf，具体如下：

    static ngx_rtmp_amf_elt_t  out_inf[] = {
    { NGX_RTMP_AMF_STRING,
      ngx_string("level"),
      "status", 0 },
    { NGX_RTMP_AMF_STRING,
      ngx_string("code"),
      "NetConnection.Connect.Success", 0 },
    { NGX_RTMP_AMF_STRING,
      ngx_string("description"),
      "Connection succeeded.", 0 },
    { NGX_RTMP_AMF_NUMBER,
      ngx_string("objectEncoding"),
      &object_encoding, 0 }
    };

• netconnection状态
  • "NetConnection.Connect.Success" --- 服务器连接成功
  • "NetConnection.Connect.Closed" --- 连接中断
  • "NetConnection.Connect.Failed" --- 连接失败
  • "NetConnection.Connect.Rejected" --- 没有权限