AudioCodes Mediant 4000 SBC User Manual page 569

User's Manual
WebSocket has been defined by the WebRTC standard as mandatory, its support by the
device is important for deployments implementing WebRTC.
A WebSocket connection starts as an HTTP connection between the Web client and the
server, guaranteeing full backward compatibility with the pre-WebSocket world. The
protocol switch from HTTP to WebSocket is referred to as the WebSocket handshake,
which is done over the same underlying TCP/IP connection. A WebSocket connection is
established using a handshake between the Web browser (WebSocket client) and the
server (i.e., the device). The browser sends a request to the server, indicating that it wants
to switch protocols from HTTP to WebSocket. The client expresses its' desire through the
Upgrade header (i.e., upgrade from HTTP to WebSocket protocol) in an HTTP GET
request, for example:
GET /chat HTTP/1.1
Upgrade: websocket
Connection: Upgrade
Host: <IP address:port of SBC device>
Sec-WebSocket-Protocol: SIP
Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
Origin: <server that provided JavaScript code to browser, e.g.,
http://domain.com>
Sec-WebSocket-Version: 13
If the server understands the WebSocket protocol, it agrees to the protocol switch through
the Upgrade header in an HTTP 101 response, for example:
HTTP/1.1 101 Switching Protocols
Upgrade: WebSocket
Connection: Upgrade
Sec-WebSocket-Accept: rLHCkw/SKsO9GAH/ZSFhBATDKrU=
Sec-WebSocket-Protocol: SIP
Server: SBC
At this stage, the HTTP connection breaks down and is replaced by a WebSocket
connection over the same underlying TCP/IP connection. By default, the WebSocket
connection uses the same ports as HTTP (80) and HTTPS (443).
Once a WebSocket connection is established, the SIP messages are sent over the
WebSocket session. The device, as a "WebSocket gateway" or server can interwork
WebSocket browser originated traffic to SIP over UDP, TCP or TLS, as illustrated below:
The SIP messages over WebSocket are indicated by the "ws" value, as shown in the
example below of a SIP REGISTER request received from a client:
REGISTER sip:10.132.10.144 SIP/2.0
Via: SIP/2.0/WS v6iqlt8lne5c.invalid;branch=z9hG4bK7785666
Max-Forwards: 69
To: <sip:101@10.132.10.144>
From: "joe" <sip:101@10.132.10.144>;tag=ub50pqjgpr
Call-ID: fhddgc3kc3hhu32h01fghl
CSeq: 81 REGISTER
Version 7.2 569
29. Advanced SBC Features
Mediant 4000 SBC