No relevant resource is found in the selected language.

This site uses cookies. By continuing to browse the site you are agreeing to our use of cookies. Read our privacy policy>Search

Reminder

To have a better experience, please upgrade your IE browser.

upgrade

Voice Feature Guide 01

Rate and give feedback:
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).
MGCP Principles

MGCP Principles

MGCP-Based VoIP

Figure 1-89 illustrates the principle of the call establishment and release in the MGCP-based VoIP service.

Figure 1-89 Principles of the call establishment and release in the MGCP-based VoIP service

Figure 1-90 illustrates the basic flow of a call establishment and release process.
Figure 1-90 MGCP-based call flow
  1. AG-0 detects the offhook of EP0, and notifies the MGC of the offhook event through the Notify command.
  2. After the MGC receives the offhook event, the MGC sends a digitmap to AG-0, requests AG-0 to play the dial tone to EP0, and at the same time checks for the digit collection event.
  3. User EP0 dials a telephone number, and AG-0 collects the digits according to the digitmap issued by the MGC. Then, AG-0 reports the result of digit collection to the MGC.
  4. The MGC sends the CRCX (CreateConnection) command to AG-0 requesting AG-0 to create a connection at endpoint EP0.
  5. AG-0 allocates resources for creating this connection and sends a response to the MGC. The response contains the session description that provides the necessary information for the peer end to send the packet to AG-0, such as the IP address and UDP port number.
  6. The MGC sends the CRCX command to AG-1 requesting AG-1 to create a connection at endpoint EP1.
  7. AG-1 allocates resources for creating this connection and sends a response to the MGC. The response contains the session description that provides the necessary information for the peer end to send the packet to AG-1, such as the IP address and UDP port number.
  8. AG-1 detects the offhook of EP1, and sends the Notify command to the MGC. The softswitch (MGC) sends the MDCX (ModifyConnection) command to stop the ring back tone of EP0 and the ringing of EP1.
  9. The MGC sends the session description of AG-1 to EP0 through the MDCX command. Then, the conversation is set up between EP0 and EP1.
  10. AG-0 detects the onhook of EP0, and notifies the MGC of the onhook event through the Notify command.
  11. The MGC sends the MDCX command to AG-0 and AG-1 respectively to modify the RTP resource to receive-only.
  12. The MGC sends the MDCX command to AG-1 requesting AG-1 to play the busy tone to EP1, and at the same time checks for the onhook event.
  13. The MGC sends the DCLX (DeleteConnection) command to AG-0, requesting AG-0 to release the resources that are occupied by the call of EP0.
  14. AG-1 detects the onhook of EP1, and notifies the MGC of the onhook event through the Notify command.
  15. The MGC sends the DCLX command to AG-1, requesting AG-1 to release the resources that are occupied by the call of EP1.
  16. The call between EP0 and EP1 is terminated, and all the resources occupied by the call are released.

MGCP-Based MoIP

MoIP refers to the modem service provided on the IP network or between the IP network and the traditional PSTN network. According to different control devices, MoIP can be classified as softswitch-controlled MoIP and auto-switching MoIP.

Softswitch-Controlled MoIP
The basic flow of the softswitch-controlled MoIP service is as follows:
  1. Establish a call. If the MoIP service is configured on the softswitch, the softswitch sends a command to the MG instructing the MG to detect the modem event.
  2. The calling party and called party start communicating with each other.
  3. During the call, when the MG detects the ANS or ANSAM modem start event (low-speed modem signal), or detects the ANSBAR or ANSAMBAR modem start event (high-speed modem signal), the MG sends the event to the softswitch.
  4. According to the event, the softswitch sends a command instructing the MG to switch the DSP channel of the calling and called parties to the low-speed or high-speed modem mode.
  5. According to the command sent by the softswitch, the MG switches the DSP channel to the corresponding modem mode. At this stage, the MG adopts the encoding format and port number specified by the softswitch.
  6. The settings of echo cancellation (EC), voice activity detection (VAD), and DSP working mode are as follows:
    1. Low-speed modem: EC-ON, VAD-OFF, DSP working mode-modem mode
    2. High-speed modem: EC-OFF, VAD-OFF, DSP working mode-modem mode
  7. After the modem data is transmitted, if the conversation proceeds, the DSP working mode does not automatically switch from the modem mode to the voice mode, because the modem end event is not issued. As a result, the quality of the voice service may be affected.
Auto-Switching MoIP
The basic flow of the auto-switching MoIP service is as follows:
  1. Set up a conversation.
  2. The MGs at both ends check for the modem event on the IP side and the TDM side. When the modem event is detected, if the modem transmission mode is configured as auto-switching, the coding mode is switched to G.711 (the a/μ law is configurable), and the DSP parameters are modified according to the modem mode (high-speed/low-speed) detected.
  3. When the modem service is terminated, the call is released.

MGCP-Based FoIP

FoIP refers to the fax service provided on the IP network or between the IP network and the traditional PSTN network. The fax machine can be regarded as a special modem. In the FoIP negotiation, the modem negotiation is performed before the fax negotiation.

According to the transmission protocol adopted, there are two modes of fax services carried on the IP network: the T.30 transparent transmission mode and the T.38 mode. According to different control devices, FoIP can be classified as softswitch-controlled FoIP and auto-switching FoIP.

Softswitch-Controlled FoIP

The fax service can be classified into high-speed fax and low-speed fax. The softswitch-controlled low-speed fax service supports the T.30 transparent transmission mode and the T.38 mode. The basic service flow is as follows:

  1. Configure the fax service and fax flow on the MGs and the softswitch.
  2. After the voice channel is set up, the softswitch instructs the MG to detect the fax event and modem event.
  3. When detecting the fax event, the MG reports the event to the softswitch. The event can be a low-speed modem event (ANS or ANSAM) or a low-speed fax event (V.21Flag).
  4. According to the preset fax flow, the softswitch instructs the MGs at both ends to change the DSP channel working mode to the T.30 transparent transmission mode or T.38 mode.
  5. The fax starts.
  6. After the fax is complete, if the MG detects the fax end event, the MG reports the event to the softswitch.
  7. The softswitch instructs the MGs at both ends to change the DSP channel working mode to the voice mode.
  8. The voice service proceeds.

The softswitch-controlled high-speed fax service supports the T.30 transparent transmission mode. The basic service flow is as follows:

  1. Configure the fax service and fax flow on the MGs and the softswitch.
  2. After the voice channel is set up, the softswitch instructs the MG to detect the fax event and modem event.
  3. When detecting a fax event, the MG reports the event to the softswitch. The event can be a high-speed modem event (ANSBAR or ANSAMBAR) or a low-speed fax event (V.21Flag; if the peer end is a low-speed fax machine or the network quality is poor, the fax speed is automatically decreased and this event is reported).
  4. According to the preset fax flow, the softswitch instructs the MGs at both ends to change the DSP channel working mode to T.30 transparent transmission mode.
  5. The fax starts.
  6. After the fax is complete, if the MG detects the fax end event, the MG reports the event to the softswitch.
  7. The softswitch instructs the MGs at both ends to change the DSP channel working mode to the voice mode. The voice service proceeds.
Auto-Switching FoIP

The auto-switching fax service supports the T.30 transparent transmission mode and the T.38 mode. The basic service flow is as follows:

  1. Configure the auto-switching fax service on the MGs at both ends.
  2. Establish a call and use the voice service.
  3. The MG checks for the fax event on the IP side and the TDM side. When detecting the fax event, the MG changes the DSP channel working mode to the T.30 transparent transmission mode or the T.38 mode.
  4. After the fax is complete, when the MG detects the fax end event, the MG changes the DSP channel working mode to the voice mode.
  5. The voice service proceeds.
Common Fax Protocols

Two protocols are usually used for implementing the fax service on the packet voice network: the ITU-T Recommendation T.30 and ITU-T Recommendation T.38.

T.30 is based on the PSTN network. T.30 particularly defines the flow for transmitting fax signals on the PSTN network. It also defines the modulation mode (V.17/V.21/V.27/V.29/V.34) and transmission format (HDLC) of data, and the physical standard for fax signals. The T.30 fax messages and data can be transmitted transparently between MGs. This is called the T.30 transparent transmission mode. The quality of the fax in this mode may not be high due to packet loss, latency, and disorder on the IP network.

T.38 is a real-time fax mode based on the IP network. In this mode, the MG terminates the T.30 signals sent from the fax machine, and transmits the data to the peer MG in the T.38 mode. The peer MG then receives the T.38 packets and converts the packets into T.30 signals. The merit of the T.38 fax is that the fax packets have a redundancy processing mechanism and do not strictly rely on the quality of the network (the fax service can be processed even when a 20% packet loss occurs on the network). The demerit is that the DSP chip needs to participate in parsing the T.30 signals. Because there are various types of terminals on the network, the compatibility problem may arise.Figure 1-91 illustrates the principle of the T.38 fax.

Figure 1-91 Principle of the T.38 fax

Translation
Download
Updated: 2019-02-22

Document ID: EDOC1100067358

Views: 13406

Downloads: 131

Average rating:
This Document Applies to these Products
Related Documents
Related Version
Share
Previous Next