Internet Communications Using SIP : Delivering VoIP and Multimedia Services With Session Initiation Protocol {2Nd Ed.}

There is also a Proxy-Requireheader that lists features that any proxies in
the path must support. However, the use of this header is discouraged, since its
overuse will lead to call failures and interoperability problems.

Figure 6.13 Proxy and user authentication example using SIP Digest

SIP User Agent

1 INVITE

Caller is

challanged by

Proxy Server and

Called User Agent.

Relies on “shared

secret” (username

and password)

exchange.

Based on HTTP

Digest RFC 2716

Does not provide

integrity protection

unless

qop=auth-int

Proxy Server SIP User Agent

5 100 Trying

8 401 Unauthorized

9 ACK

10 ACK

7 401 Unauthorized

6 INVITE

13 100 Trying

15 180 Ringing

17 200 OK

18 ACK

19 ACK

11 INVITE Proxy-Auth : 1

WWW-Auth : 2 12 INVITE WWW-Auth : 2

16 200 OK

2 407 Proxy Authentication

Required

14 180 Ringing

3 ACK

4 INVITE Proxy-Auth : 1

Authenticated Media Session

SIP Overview 131