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Voice Feature Guide 01

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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
Call Hold

Call Hold

The call hold (CH) service enables a user to temporarily disconnect an established call, that is, to stop sending media streams between the calling party and the called party, but not to release the session resources. When necessary, the call can be resumed. When a user needs to initiate or accept a new call but does not want to release the current call, the user can hold the current call and resume the call when necessary.

Call Hold

This topic describes the definition and principle of the call hold (CH) service.

Definition

The CH service enables a user to temporarily disconnect an established call, that is, to stop sending media streams between the calling party and the called party, but not to release the session resources. When necessary, the call can be resumed. When a user needs to initiate or accept a new call but does not want to release the current call, the user can hold the current call and resume the call when necessary.

User A has subscribed to the CH service, user B is the held party, and user C is the third party, as shown in Figure 1-50.
Figure 1-50 Principle of the CH service
  1. User A is communicating with user B.
  2. User A wants to communicate with user C and presses hookflash to hold the call.
  3. User B is placed on hold and hears a call hold tone.
  4. User A dials user C's phone number.
  5. User C answers the call and communicates with user A.
NOTE:

The preceding figure shows one of the application scenarios. When C calls A, A can hold B and answer the call from C.

Benefit

Beneficiary

Benefits

Carrier

The CH service supplements the value-added services of carriers and helps improve the ratio of successful call connections.

Users

A user can place the ongoing call on hold and then resumes this call if required, reducing the number of dials and facilitating call making.

Standards Compliance
  • EN300 141
  • ETSI TS 124 410
  • ETSI 300 102-1
  • ETSI TS 183 010
  • ETSI TS 183 036
  • ETSI TS 183 043
  • ITU-T Q.931

Call Hold Service Flow

This topic takes users A and B as an example to describe the service flows of call hold and hold resume.

POTS Call Hold and Hold Resume Service Flow

Figure 1-51 shows the service flow of the POTS call hold and hold resume service.

Figure 1-51 POTS call hold and hold resume service flow

The service flow of call hold for POTS user A is as follows:
  1. User A is communicating with user B, and user A presses hookflash.
  2. After detecting the hookflash event, AG1 converts the event into a ReInvite message and sends a request to user B.
  3. After receiving the ReInvite message, the IMS modifies the SDP and sends a ReInvite message to user B. After receiving the ReInvite message, AG2 modifies the media attribute of user B. User B receives but cannot send media.
  4. AG2 returns a 200 OK response carrying an SDP packet, indicating that user B only receives media.
  5. The IMS sends a 200 OK response, and AG1 receives the 200 OK message.
  6. AG1 sends an Ack message to user B.
  7. The IMS sends an Ack message to user B.
  8. User A hears a mute or special dialing tone. User B is placed on hold and hears a call hold tone.
The call release flow for POTS user A is as follows:
  1. User B is on hold and A presses hookflash.
  2. After detecting the hookflash event, AG1 converts the event into a ReInvite message and sends a request to the IMS.
  3. After receiving the ReInvite message, the IMS sends a ReInvite message to user B. After receiving the ReInvite message, AG2 modifies the media attribute of user B. User B can receive and send media.
  4. AG2 returns a 200 OK response which carries an SDP packet, indicating that user B can receive and send media.
  5. AG1 receives the 200 OK response from the IMS.
  6. AG1 sends an Ack message to user B.
  7. The IMS sends an Ack message to user B, and AG2 receives the Ack message. The call between users A and B is resumed.
Service Flow of the ISDN Call Hold and Hold Resume Service

Figure 1-52 shows the service flow of the ISDN call hold and hold resume service.

Figure 1-52 Service flow of the ISDN call hold and hold resume service

The service flow is as follows:
  1. User A sends a Hold message.
  2. AG1 converts the Hold message to a ReInvite message.
  3. The IMS applies for multimedia resource function processor (MRFP) resources for announcement playing, modifies SDP information, and sends a ReInvite message to the called party.
  4. AG2 converts the ReInvite message into an ISDN Notify message, modifies the media attribute, and uses the Notify message to notify the remote hold.
  5. User B is placed on hold, and AG2 returns a 200 message.
  6. The IMS sends a 200 response.
  7. After receiving the 200 response, AG1 sends a HoldAck message to the service terminal.
  8. AG1 sends an Ack message to the IMS.
  9. The IMS sends an Ack message to AG2.
NOTE:

Steps 10 to 18 are the same as the call hold flow for ISDN users. The difference lies in that the flow mode of user B is sendrecv.

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Updated: 2019-02-22

Document ID: EDOC1100067358

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