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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).
Explicit Communication Transfer

Explicit Communication Transfer

This service allows user A who is communicating with user B to transfer the call to user C so that a call is set up between user B and user C.

Explicit Communication Transfer

This topic describes the definition and principle of the explicit communication transfer (ECT) service.

Definition

The ECT service enables user A who is in a conversation with user B to transfer the call to user C so that the call between user B and user C is set up.

The ECT service for POTS users includes 2 scenarios: off-hook ECT and on-hook ECT. The off-hook ECT service can be consultative or blind, and the on-hook ECT service can be during conversation or during ringing.

The ECT service for ISDN users includes 2 scenarios: implicit transfer and explicit transfer.

User A has subscribed to the ECT service. User A is the transferor, user B is a transferee, and user C is also a transferee. Figure 1-65 shows the ECT service flow (using an off-hook blind transfer scenario as an example).

Figure 1-65 Principle of the ECT service (off-hook blind transfer)

  1. User A is communicating with user B. User B wants to communicate with user C.
  2. User A presses the hook switch. User B is held and hears the call hold tone, and user A hears a dial tone.
  3. User A dials user C's number to call user C.
  4. User C's phone rings. User A initiates a call transfer and is released. User B hears the ring back tone.
  5. User C answers the call. User B communicates with user C.
NOTE:

If the call fails to be transferred, user B initiates a renegotiation with user A to resume the call between users A and B.

Benefit

Beneficiary

Benefits

Carrier

The ECT service enhances carriers' competitiveness and provides carriers with new revenue growth potential.

User

The ECT service allows a user to easily transfer a call to another user so that the desired user can answer the call.

Standards Compliance
  • ETSI TS 124 529
  • ETSI EN 300 102-1
  • ETSI EN 300 369-1
  • ETSI TS 183 029
  • ETSI TS 183 043
  • ETSI TS 183 036
  • ITU-T Q.931

Service Flow of Explicit Communication Transfer

The explicit communication transfer (ECT) service for POTS users includes 2 scenarios: off-hook ECT and on-hook ECT. The off-hook ECT service can be consultative or blind, and the on-hook ECT service can be during conversation or during ringing. The ECT service for ISDN users includes 2 scenarios: implicit transfer and explicit transfer. This topic describes the flows of the preceding ECT services.

In the following message flows, user A has subscribed to the service and is the transferor, user B is the transferee, and user C is the transfer target. For ease of description, the service flows are based on the following user calls:
  • User B sets up a call with user A. After the call is set up, user A places user B on hold.
  • User A establishes a call to user C. After the call is set up or the phone of user C rings, user A hangs up and initiates a call transfer.
  • User B talks with user C.
Consultative Transfer in Off-Hook State for POTS Users (Off-Hook Consultative Transfer)

Figure 1-66 shows how off-hook consultative transfer is implemented.

Figure 1-66 Service flow of off-hook consultative transfer for POTS users

Transferor A and transferee B enter a conversation through a basic call. Transferor A presses hookflash and enters the call hold state with transferee B through a call hold flow. Transferor A enters a conversation with transfer target C through a basic call. Transferor A presses hookflash and enters the call hold state with transfer target C through a call hold flow. The service flow of off-hook consultative transfer for POTS users is as follows:
  1. User A dials an explicit transfer SCC number.
  2. User A sends a Refer message to request the call transfer. The IMS sends a Notify message.
  3. The IMS sends a Bye message to release the session between users A and B.
  4. The IMS sends a Bye message to release the session between users A and C.
  5. The IMS sends a ReInvite message to user B for media renegotiation. User B replies with a 200 message.
  6. The IMS sends a ReInvite message to user C for media renegotiation. User C replies with a 200 message. The media renegotiation is successful. Users B and C are engaged in a call.
  7. The IMS sends a Notify message, notifying the transferor that the call is successfully transferred. If user A does not hang up, the system plays a short busy tone to notify that the call is successfully transferred.
Blind Transfer in Off-Hook State for POTS Users (Off-Hook Blind Transfer)

Figure 1-67 shows how off-hook blind transfer is implemented.

Figure 1-67 Service flow of off-hook consultative transfer for POTS users

Transferor A and transferee B enter a conversation through a basic call. User A presses hookflash and enters the call hold state with user B through a call hold flow. The service flow of off-hook blind transfer for POTS users is as follows:
  1. User A dials a blind transfer SOC number. The number format is as follows: 4*TransferTarget TelNum.
  2. User A sends a Refer message to request a blind transfer. The IMS sends a Notify message, notifying A that the subscription is successful.
  3. The IMS sends a Bye message to release the session between users A and B. Because the subscription exists, dialog D1 still exists.
  4. The IMS sends an Invite message to initiate a new basic call to user C. User C replies with a 200 message.
  5. The IMS sends a ReInvite message to user B for media renegotiation. User B replies with a 200 message.
  6. The IMS sends a ReInvite message to user C for media renegotiation. User C replies with a 200 message. The media renegotiation is successful. Users B and C are engaged in a call.
  7. The IMS sends a Notify message, notifying the transferor that the call is successfully transferred. If user A does not hang up, the system plays a short busy tone to notify that the call is successfully transferred.
On-Hook Transfer During Ringing for POTS Users (On-Hook Consultative Transfer During Ringing)

Figure 1-68 shows how on-hook consultative transfer during ringing is implemented.

Figure 1-68 Service flow of on-hook consultative transfer during ringing for POTS users

Users A and B enter a call through a basic call. User A presses hookflash and enters the call hold state with user B through a call hold flow. User A dials user C's number to initiate a basic call to user C. User A receives a 180 response and enters the ring back tone phase. The service flow is as follows:
  1. User A hangs up.
  2. User A sends a Refer message to request a consultative transfer. The IMS sends a Notify message to notify user A.
  3. The IMS sends a Bye message to release the session between users A and B.
  4. The IMS sends a Bye message to release the session between users A and C.
  5. After user C picks up the phone, the IMS performs media renegotiation and sends a ReInvite message to user C.
  6. The IMS sends a ReInvite message to user B for media renegotiation. Then the media renegotiation is successful, and users B and C enter a conversation.
  7. The IMS sends a Notify message, notifying user A that the call is successfully transferred.
On-Hook Transfer During Conversation for POTS Users (On-Hook Consultative Transfer During Conversation)

The service flow of on-hook consultative transfer during conversation for POTS users is as follows:

Users A and B enter a call through a basic call. User A presses hookflash and enters the call hold state with user B through a call hold flow. User A dials user C's number and enters a call with user C.

The subsequent steps are the same as those described in On-Hook Transfer During Ringing for POTS Users (On-Hook Consultative Transfer During Ringing).

Implicit Transfer for ISDN Users (When User C Answers a Call)

If user C answers a call and then user A initiates a call transfer, the implicit transfer service is implemented as shown in Figure 1-69.

Figure 1-69 Service flow of implicit communication transfer for ISDN users (when user C answers a call)

After user C answers a call, the implicit transfer service is implemented as follows:
  1. During a call between users A and B, when user C answers the call, user A sends a Facility message to AG1, instructing AG1 to transfer the call.
  2. AG1 sends a Refer message to the IMS for a call transfer.
  3. The IMS releases the session between users A and B.
  4. The IMS releases the session between users A and C.
  5. The IMS sends a ReInvite message to user B, which carries SDP data to instruct user B to establish a media stream between users B and C and carries P-NOTIFICATION header field data to instruct a call transfer.
  6. After AG2 (for user B) receives the ReInvite message for a call transfer, AG2 converts the message into a Notify message to notify user B.
  7. The IMS sends a ReInvite message to user C, which carries SDP data to instruct user C to establish a media stream between users B and C and carries P-NOTIFICATION header field data to instruct a call transfer.
  8. After AG2 (for user C) receives the ReInvite message for a call transfer, AG2 converts the message into a Notify message to notify user C.
  9. The IMS sends a Notify message to AG1 to terminate the call transfer. Then user A exits the session, and user B talks with user C.
Implicit Transfer for ISDN Users (When User C Is Alerted)

If user C is alerted and then user A initiates a call transfer, the implicit transfer service is implemented as shown in Figure 1-70.

Figure 1-70 Service flow of implicit transfer for ISDN users (when user C is alerted)

Compared with the flow described in Implicit Transfer for ISDN Users (When User C Answers a Call), this implicit transfer flow has 2 more steps as highlighted in Figure 1-70. The details are as follows:
  1. During a call between users A and B, when C answers the call, user A sends a Facility message to AG1, instructing AG1 to transfer the call.
  2. AG1 sends a Refer message to the IMS for a call transfer.
  3. Before user C answers the call, the IMS sends an Update message to notify user B of a call transfer for user C.
  4. The IMS releases the session between users A and B.
  5. The IMS releases the session between users A and C.
  6. The IMS terminates the 200 response that is sent when user C answers the call.
  7. The IMS sends a ReInvite message to user B, which carries SDP data to instruct user B to establish a media stream between users B and C and carries P-NOTIFICATION header field data to instruct a call transfer.
  8. After AG2 (for user B) receives the ReInvite message for a call transfer, AG2 converts the message into a Notify message to notify user B.
  9. The IMS sends a ReInvite message to user C, which carries SDP data to instruct user C to establish a media stream between users B and C and carries P-NOTIFICATION header field data to instruct a call transfer.
  10. After AG2 (for user C) receives the ReInvite message for a call transfer, AG2 converts the message into a Notify message to notify user C.
  11. The IMS sends a Notify message to AG1 to terminate the call transfer. Then user A exits the session, and user B talks with user C.
Explicit Transfer for ISDN Users

Figure 1-71 shows how explicit transfer is implemented for ISDN users.

Figure 1-71 Service flow of explicit transfer for ISDN users

The service flow of explicit transfer for ISDN users is as follows:
  1. During an ISDN call with user C, user A sends a Facility message to AG1, applying for ECTLinkId.
  2. AG1 allocates an ECTLinkId and sends a Facility message to notify user A.
  3. During an ISDN call with user B, user A sends a Facility message to AG1, instructing AG1 to transfer the call.
  4. AG1 sends a Refer message to the IMS to instruct the IMS to transfer the call. The subsequent service flow is the same as that of implicit transfer.
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Updated: 2019-02-22

Document ID: EDOC1100067358

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