簡介：
該系列文章主要介紹，上級域對國標平臺進行預覽/回看等流程的信令交互。
一個簡單的gb28181錄製回放流程：
-
接收下級域的註冊請求
-
發送recordinfo請求，獲取設備的錄像信息
-
選擇錄像進行回放
invite流程：
- 向下級域發送invite請求
- 下級域回覆200
- 上級域回覆ack
信令流程：
向下級域發送invite請求：
INVITE sip:34020000001320000002@3402000000 SIP/2.0
Via: SIP/2.0/UDP 192.168.30.173:5060;rport;branch=z9hG4bK932888095
From: <sip:34020000002000000001@3402000000>;tag=71888095
To: <sip:34020000001320000002@3402000000>
Call-ID: 935887989
CSeq: 177 INVITE
Content-Type: APPLICATION/SDP
Contact: <sip:[email protected]:5060>
Max-Forwards: 70
User-Agent: LiveGBS v200529
Subject: 34020000001320000002:1200000013,34020000002020000001:0
Content-Length: 272
v=0
o=34020000002000000001 0 0 IN IP4 192.168.30.173
s=Playback
u=34020000001320000002:0
c=IN IP4 192.168.30.173
t=1591083900 1591084602
m=video 30004 RTP/AVP 96 97 98
a=recvonly
a=rtpmap:96 PS/90000
a=rtpmap:97 MPEG4/90000
a=rtpmap:98 H264/90000
y=1200000013
下級域回覆200：
SIP/2.0 200 OK
Via: SIP/2.0/UDP 192.168.30.173:5060;rport=5060;branch=z9hG4bK932888095
From: <sip:34020000002000000001@3402000000>;tag=71888095
To: <sip:34020000001320000002@3402000000>;tag=979281030
Call-ID: 935887989
CSeq: 177 INVITE
Contact: <sip:[email protected]:5060>
Content-Type: application/SDP
User-Agent: Embedded Net DVR/NVR/DVS
Content-Length: 264
v=0
o=34020000001110000001 0 0 IN IP4 192.168.30.228
s=EZVIZ X5S
c=IN IP4 192.168.30.228
t=1591112700 1591113402
m=video 62022 RTP/AVP 96
a=sendonly
a=rtpmap:96 PS/90000
a=username:34020000001110000001
a=password:12345678
a=filesize:1
y=1200000013
f=
上級域回覆ack：
ACK sip:34020000001320000002@3402000000 SIP/2.0
Via: SIP/2.0/UDP 192.168.30.173:5060;rport;branch=z9hG4bK759888448
From: <sip:34020000002000000001@3402000000>;tag=71888095
To: <sip:34020000001320000002@3402000000>;tag=979281030
Call-ID: 935887989
CSeq: 177 ACK
Contact: <sip:[email protected]:5060>
Max-Forwards: 70
User-Agent: LiveGBS v200529
Content-Length: 0