Video conferencing business networking protocol development and changes

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H.323 protocol
I. Introduction

In the field of video services, no matter which stage of development, networking protocols and their standardization work have always been at the core of the important position, from a reasonable framework structure to the definition of the content of each parameter, only the content of the networking protocol is determined. Down, products can be manufactured, business can be interoperable, and the field can develop.

Looking back at the development of video conferencing, its networking protocols have also changed with the development of communication networks. ITU's standards development has experienced a circuit-switched H.320 protocol, based on packet-switched H.321 protocol for connection, and packet-switched H.323 protocol for connection-free. At present, H.323 has gained more and more applications. At the same time, due to the flexibility and freedom brought by the packet switching network, the research and formulation of the networking protocol has also attracted the interest of many standardization organizations. Currently, the SIP developed by the IETF is a very hot research topic.

Second, the H.320 protocol

1. The scope of H.320 and its scope of use

The H.320 series of standards was proposed by ITU-T in 1990. It is the earliest and most mature protocol in the conference system. It supports ISDN, E1, T1 and bandwidth from 64 kbit/s to 2 Mbit/s. As of 2000, almost all conference system manufacturers support the H.320 protocol, and even many IP-based video conferencing systems currently support H.320. This proposal standardizes the main technical aspects of the video conferencing system on the ISDN network. This is the first protocol based on a specific network. It provides basic guarantee for the intercommunication of video conferencing services and the interconnection between different company products. , a milestone in the history of video conferencing, laid the foundation for the development and popularity of videoconferencing.

2. Problems caused by limited main components of H.320

The main components of H.320 are multipoint control unit (MCU) and terminal equipment. This was a very complete system at the time, but because the system was built on the circuit-switched network, it was subject to many restrictions and caused many problems:

(1) Affected by circuit switched bandwidth. Circuit switching is characterized by connection-oriented, stable transmission rate and delay, small delay, and low bit error rate, so the quality of video conferencing is easily guaranteed. However, its disadvantage is that the connection is fixed, resulting in higher user line usage costs. The access of the user layer is generally connected by the El private line mode or the ISDN 2B+D access mode. Although the dedicated line can ensure good stability and image quality, the network utilization rate is low. ISDN is greatly affected by the line, and the requirements for line synchronization are high. Both of these transmission methods limit the size and scalability of the conference.

(2) Affected by circuit switching characteristics. Since there is no virtual circuit connection in the circuit-switched system, the information exchanged between the terminal and the videoconferencing system—audio, video, data, and signaling—is exchanged through this circuit, so a single MCU star group is used. The way the network and the two-level MCU are cascaded. Single MCU star networking refers to the use of an MCU device and multiple conference terminals to form a star network structure. When the conference terminal has more than one port provided by one MCU, a single MCU cannot connect to all the conference television terminals. At this time, the expansion of the network is implemented by means of cascading MCUs to increase the network capacity and constitute a master-slave structure. Each slave MCU forms a fixed connection with the master MCU, so the stability of the network is poor. From the perspective of topology, this single-star structure will cause instability of the whole network due to the problem of the main MCU. Due to the influence of the length of the BAS code, the network cannot be cascaded in three levels. Even if it can be cascaded by certain means, the minimum delay and synchronization requirements of the conference cannot be met, which means that the network scale in actual networking is difficult to carry out. Further expansion.

In summary, on the basis of circuit switching, only standard video conferencing applications for a small number of people can be developed, and cannot be extended to a multi-application, interactive multimedia communication platform.


I. Introduction

In the field of video services, no matter which stage of development, networking protocols and their standardization work have always been at the core of the important position, from a reasonable framework structure to the definition of the content of each parameter, only the content of the networking protocol is determined. Down, products can be manufactured, business can be interoperable, and the field can develop.

Looking back at the development of video conferencing, its networking protocols have also changed with the development of communication networks. ITU's standards development has experienced a circuit-switched H.320 protocol, based on packet-switched H.321 protocol for connection, and packet-switched H.323 protocol for connection-free. At present, H.323 has gained more and more applications. At the same time, due to the flexibility and freedom brought by the packet switching network, the research and formulation of the networking protocol has also attracted the interest of many standardization organizations. Currently, the SIP developed by the IETF is a very hot research topic.

Second, the H.320 protocol

1. The scope of H.320 and its scope of use

The H.320 series of standards was proposed by ITU-T in 1990. It is the earliest and most mature protocol in the conference system. It supports ISDN, E1, T1 and bandwidth from 64 kbit/s to 2 Mbit/s. As of 2000, almost all conference system manufacturers support the H.320 protocol, and even many IP-based video conferencing systems currently support H.320. This proposal standardizes the main technical aspects of the video conferencing system on the ISDN network. This is the first protocol based on a specific network. It provides basic guarantee for the intercommunication of video conferencing services and the interconnection between different company products. , a milestone in the history of video conferencing, laid the foundation for the development and popularity of videoconferencing.

2. Problems caused by limited main components of H.320

The main components of H.320 are multipoint control unit (MCU) and terminal equipment. This was a very complete system at the time, but because the system was built on the circuit-switched network, it was subject to many restrictions and caused many problems:

(1) Affected by circuit switched bandwidth. Circuit switching is characterized by connection-oriented, stable transmission rate and delay, small delay, and low bit error rate, so the quality of video conferencing is easily guaranteed. However, its disadvantage is that the connection is fixed, resulting in higher user line usage costs. The access of the user layer is generally connected by the El private line mode or the ISDN 2B+D access mode. Although the dedicated line can ensure good stability and image quality, the network utilization rate is low. ISDN is greatly affected by the line, and the requirements for line synchronization are high. Both of these transmission methods limit the size and scalability of the conference.

(2) Affected by circuit switching characteristics. Since there is no virtual circuit connection in the circuit-switched system, the information exchanged between the terminal and the videoconferencing system—audio, video, data, and signaling—is exchanged through this circuit, so a single MCU star group is used. The way the network and the two-level MCU are cascaded. Single MCU star networking refers to the use of an MCU device and multiple conference terminals to form a star network structure. When the conference terminal has more than one port provided by one MCU, a single MCU cannot connect to all the conference television terminals. At this time, the expansion of the network is implemented by means of cascading MCUs to increase the network capacity and constitute a master-slave structure. Each slave MCU forms a fixed connection with the master MCU, so the stability of the network is poor. From the perspective of topology, this single-star structure will cause instability of the whole network due to the problem of the main MCU. Due to the influence of the length of the BAS code, the network cannot be cascaded in three levels. Even if it can be cascaded by certain means, the minimum delay and synchronization requirements of the conference cannot be met, which means that the network scale in actual networking is difficult to carry out. Further expansion.

In summary, on the basis of circuit switching, only standard video conferencing applications for a small number of people can be developed, and cannot be extended to a multi-application, interactive multimedia communication platform.


I. Introduction

In the field of video services, no matter which stage of development, networking protocols and their standardization work have always been at the core of the important position, from a reasonable framework structure to the definition of the content of each parameter, only the content of the networking protocol is determined. Down, products can be manufactured, business can be interoperable, and the field can develop.

Looking back at the development of video conferencing, its networking protocols have also changed with the development of communication networks. ITU's standards development has experienced a circuit-switched H.320 protocol, based on packet-switched H.321 protocol for connection, and packet-switched H.323 protocol for connection-free. At present, H.323 has gained more and more applications. At the same time, due to the flexibility and freedom brought by the packet switching network, the research and formulation of the networking protocol has also attracted the interest of many standardization organizations. Currently, the SIP developed by the IETF is a very hot research topic.

Second, the H.320 protocol

1. The scope of H.320 and its scope of use

The H.320 series of standards was proposed by ITU-T in 1990. It is the earliest and most mature protocol in the conference system. It supports ISDN, E1, T1 and bandwidth from 64 kbit/s to 2 Mbit/s. As of 2000, almost all conference system manufacturers support the H.320 protocol, and even many IP-based video conferencing systems currently support H.320. This proposal standardizes the main technical aspects of the video conferencing system on the ISDN network. This is the first protocol based on a specific network. It provides basic guarantee for the intercommunication of video conferencing services and the interconnection between different company products. , a milestone in the history of video conferencing, laid the foundation for the development and popularity of videoconferencing.

2. Problems caused by limited main components of H.320

The main components of H.320 are multipoint control unit (MCU) and terminal equipment. This was a very complete system at the time, but because the system was built on the circuit-switched network, it was subject to many restrictions and caused many problems:

(1) Affected by circuit switched bandwidth. Circuit switching is characterized by connection-oriented, stable transmission rate and delay, small delay, and low bit error rate, so the quality of video conferencing is easily guaranteed. However, its disadvantage is that the connection is fixed, resulting in higher user line usage costs. The access of the user layer is generally connected by the El private line mode or the ISDN 2B+D access mode. Although the dedicated line can ensure good stability and image quality, the network utilization rate is low. ISDN is greatly affected by the line, and the requirements for line synchronization are high. Both of these transmission methods limit the size and scalability of the conference.

(2) Affected by circuit switching characteristics. Since there is no virtual circuit connection in the circuit-switched system, the information exchanged between the terminal and the videoconferencing system—audio, video, data, and signaling—is exchanged through this circuit, so a single MCU star group is used. The way the network and the two-level MCU are cascaded. Single MCU star networking refers to the use of an MCU device and multiple conference terminals to form a star network structure. When the conference terminal has more than one port provided by one MCU, a single MCU cannot connect to all the conference television terminals. At this time, the expansion of the network is implemented by means of cascading MCUs to increase the network capacity and constitute a master-slave structure. Each slave MCU forms a fixed connection with the master MCU, so the stability of the network is poor. From the perspective of topology, this single-star structure will cause instability of the whole network due to the problem of the main MCU. Due to the influence of the length of the BAS code, the network cannot be cascaded in three levels. Even if it can be cascaded by certain means, the minimum delay and synchronization requirements of the conference cannot be met, which means that the network scale in actual networking is difficult to carry out. Further expansion.

In summary, on the basis of circuit switching, only standard video conferencing applications for a small number of people can be developed, and cannot be extended to a multi-application, interactive multimedia communication platform.


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