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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).
ISDN Protocol Model

ISDN Protocol Model

ISDN Reference Model

Figure 1-105 shows the ISDN reference model.

Figure 1-105 ISDN reference model

  • Network Termination 1 (NT1) operates at Layer 1 (physical layer) of the OSI model and implements the physical and electronic specifications into the ISDN network.
  • Network Termination 2 (NT2), an intelligent device, functions as a terminal control device, such as a private automatic branch exchange (PABX) or a LAN router, and operates at Layer 2 and 3 of the OSI model.
  • Terminal Equipment Type 1 (TE1) is the standard ISDN device having the standard S port, such as an ISDN phone and G4 fax machine. It can be directly connected to NT2 or NT1.
  • Terminal Equipment Type 2 (TE2) is a non-standard ISDN device, and it cannot be directly connected to NT2 or NT1 but must be connected to the S port through the TA.
  • Terminal Adapter (TA) connects a non-ISDN terminal (TE2) to the user-network interface (UNI) of the ISDN.
  • U reference point, also called the U port, is the line interface locates between the ISDN BRA network and user. Digital signals are transmitted through twisted pairs through the coding (such as 2B1Q coding) defined by the U port.
  • S reference point, also called the S port, is the line interface locates between the ISDN terminal (TE1 or TA) and NT.
  • T reference point locates between NT1 and NT2. If there is no NT2, S referent point and T reference points are combined as S/T reference point, also called the S/T port. It uses 4–wire for transmission, such as a common network cable.
  • R reference point locates between the TA and TE2 (non-ISDN standard device) and provides interfaces (the RS-232 interface for PCs and X.25 interface for X.25 devices) that allow the non-ISDN standard device to access the ISDN.
The ISDN user accesses the MA5600T/MA5603T/MA5608T through the U reference point. The actual terminal on the user side may support NT1, NT2, and TE1 functions at the same time. When VoIP is used for upstream transmission, the IUA protocol is used to load the Q.931 call signaling of the ISDN between the MG and MGC, and the H.248 protocol or MGCP signaling is used to control the media connection on the MG.

ISDN Protocol Stack Model

Figure 1-106 shows the mapping relationship between the ISDN protocol and OSI model. Layers in the ISDN protocol stack map the physical layer, data link layer, and network layer in the following OSI model.
  • ISDN physical layer: For users, the ISDN physical layer is on S reference point or T reference point. This layer has the following major functions: coding, full-duplex transmission, channel multiplexing, port activation and depolarization, feeding, and termination identification. This layer can multiplex multiple links at the data link layer and use AMI, 4B3T and 2B1Q for coding.
  • ISDN data link layer: ISDN does not define Layer 2 protocols dedicated to B channels. Any Layer 2 protocols can be used between two communicating devices after negotiation as long as they can transparently transmit data on B channels. The link access procedure on the D channel (LAPD) protocol defined in Q.921 (a reliable transport protocol) is used for D channels, which is mainly used to carry messages and data generated by Layer 3 entities.
  • ISDN network layer: ISDN does not define Layer 3 protocols dedicated to B channels. Layer 3 protocol Q.931 for D channels is mainly used to control and manage connection setup and release on B channels.
Figure 1-106 Mapping relationship between the ISDN protocol stack model and OSI model

ISDN Protocol Processing Model

Figure 1-107 and Figure 1-108 show the ISDN protocol processing model. ISDN involves the following protocols:
  • Q.921: Defines LADP. It is a reliable transport protocol.
  • Q.931: Defines the procedure of processing and controlling messages and state machines that are used for calls (including circuit switching calls and packet switching calls) between the user-side device and network-side device.
  • SCTP: A transport protocol in the SIGTRAN protocol stack, which is a reliable transport protocol on top of protocols (such as IP) providing unreliable transmission services. SCTP transmits acknowledged, error-free, and repetition-free data and ensures real time transmission to some extent.
  • IUA: ISDN Q.921 user adaption layer protocol.
Figure 1-107 H.248 protocol processing model
Figure 1-108 SIP protocol processing model

Exchange between protocols

For the H.248 protocol:
  • Data transmission from ISDN user terminals to voice boards uses Q.921 and Q.931.
  • Voice boards terminate Q.921 messages and send Q.931 messages to the CPU of the control board using the master-slave serial port communications protocol. Then the CPU of the control board uses IUA to packetize Q.931 signaling carried on SCTP links and sends the packed signaling to the MGC through the LAN switch. In this case, Q.921 is not used between the AG and MGC; instead, Q.931 and IUA are used.
  • The MGC restores the IUA packets to Q.931 signaling. Also, the MGC sends Q.931 signaling to the peer end through SCTP links. This is the entire process of ISDN call signaling.
For the SIP protocol:
  • Data transmission from ISDN user terminals to voice boards uses Q.921 and Q.931.
  • The AG terminates Q.921 and Q.931 message, converts them into SIP messages and sends SIP messages to the IMS. Then the IMS sends SIP messages to the peer end. This is the entire process of ISDN call signaling.
Updated: 2019-02-22

Document ID: EDOC1100067358

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