Yealink SIP-T27P Руководство администратора онлайн [805/841] 166939

Appendix

789

Step

Action

Description

Server

to the proxy server. The 100 Trying

response indicates that the INVITE

request has been received by User B.

100 Trying—Proxy Server to

User A

The proxy server forwards the SIP 100

Trying to User A to indicate that the

INVITE request has already been

received.

486 Busy Here—User B to

Proxy Server

User B sends a SIP 486 Busy Here

response to the proxy server. The 486

Busy Here response is a client error

response indicating that User B is

successfully connected but User B is

busy on the IP phone and unable or

unwilling to take the call.

486 Busy Here—Proxy Server

to User A

The proxy server forwards the 486 Busy

Here response to notify User A that User

B is busy.

ACK—User A to Proxy Server

User A sends a SIP ACK to the proxy

server. The SIP ACK message indicates

that User A has received the 486 Busy

Here message.

ACK—Proxy Server to User B

The proxy server forwards the SIP ACK

to User B to indicate that the 486 Busy

Here message has already been

received.

The following figure illustrates the scenario of an unsuccessful call caused by the called

user’s no answering. In this scenario, the two end users are User A and User B. User A

and User B are located at Yealink SIP IP phones.