TCP/IP protocol and its development and IP video transmission characteristics

1 TCP/IP protocol

TCP/IP is a complete set of data protocols, named after the two most important protocols: Transmission Control Protocol (TCP) and Internet Protocol (IP). Currently, TCP/IP has become the dominant communication protocol, which enables various services to interconnect on different networks, laying the foundation for network convergence from a technical perspective. It has achieved such success because of its following characteristics: Open protocol standards, which can be independent of the openness of specific computers and operating systems. Independent of specific physical network hardware, it can run on a variety of network transmission media.

The common address planning scheme enables any TCP/IP device in the entire network to have a unique address. Standardized high-level protocols provide a variety of reliable user services.

2 Development of IP Technology

TCP/IP is an important technical foundation of the Internet. The emergence of WWW in 1989 brought about a fundamental change in the Internet, which developed from a simple data communication network to a distributed file system that can share and send information worldwide. Its utilization value has increased rapidly, and the TCP/IP protocol has been widely used. Especially after the commercialization of the Internet in 1993, the network scale has doubled at an average rate of half a year, making people realize that different types of networks should be interconnected at the network layer using network interconnection protocols to form a platform independent of the network infrastructure, which is the IP network. Ordinary IP networks cannot guarantee the quality of service when transmitting real-time services. Therefore, broadband IP networks came into being. With the emergence of some key technologies such as IP Over DWDM and MPLS traffic engineering, it can provide service quality comparable to that of ATM networks and realize an integrated service network that seamlessly connects multiple different networks. Broadband IP networks provide a platform for the development of new broadband data communications and broadband interactive media services. The demand for multimedia communications on IP networks is also expanding. To this end, the International Telecommunication Union (ITU) has formulated the H.323 standard, making it possible to transmit video on existing communication networks. The broadband IP network based on TCP/IP protocol will inevitably integrate the advanced technologies and network resources of the three major networks: cable TV network, telecommunications network, and computer network, and become the mainstream of the future information highway.

3 IP video transmission

3.1 Application requirements of network multimedia

Because multimedia signals are interactive, they place the following application requirements on the network:

(1) Throughput requirements refer to the requirements for high transmission bandwidth, large storage buffer bandwidth, and flow control.
(2) Reliability requirements: The reliability requirements are not the focus here. Appropriate data loss will not affect the actual effect of video broadcasting too much.
(3) Network delay requirements: The requirements for network delay and jitter are relatively high, because multimedia video streams are sensitive to network transmission delay and jitter. For example, the transmitted video signal and audio signal must be synchronized.

3.2 IP Multicast

IP multicast, the original English name is IP Multicast, which can also be translated as "group communication". In 1999, IP multicast had three key conditions for development: ① routing protocols that support IP multicast; ② testable management protocols that use open standards; ③ business opportunities for development. Thus, it entered a high-speed development stage. IPv4 defines three IP data communication methods: ① point-to-point communication; ② full network broadcast; ③ multicast. Point-to-point communication refers to data communication between two IP addresses; full network broadcast refers to sending data packets in a broadcast manner to all IP addresses in the IP subnet, and all IP stations in the subnet can receive the full network broadcast; multicast refers to data transmission to a group of specific IP addresses on the IP network, which is a communication method between the above ① and ②. Comparing the three data communication methods defined by IPv4, we found that IP multicast has obvious characteristics different from ① and ②: when an IP site sends data to multiple sites on the IP network, it can reduce unnecessary overlapping transmission, effectively utilize the network bandwidth, and reduce network delay and jitter. The reliability of IP group communication is worse than ① and ②.

3.3 IP video application requirements

Because of the interactivity and interactivity of online information, the amount of information transmitted in the network has increased dramatically, and the bottleneck problem of network transmission is prominent! In multimedia applications, the network bandwidth problem caused by video transmission is more prominent. When n IP addresses receive network multimedia video streams at the same time, assuming that the transmission bandwidth required for each video stream is 1.5M, according to the current network structure, the required bandwidth is n*1.5M, which will also bring unbearable network delay and jitter. Most of the existing networks are constructed using TCP/IP point-to-point protocols, so the focus of our research is how to achieve video transmission without making too many changes under the existing network conditions, that is, the IP multicast solution must be compatible with the existing network. As mentioned above: multimedia video streams do not require high data reliability, and appropriate data loss will not affect the actual effect of video broadcasting too much. Although multimedia video streams are sensitive to network transmission delay and jitter, IP multicast has very little delay and jitter in the network. Therefore, it is feasible to use IP group communication to transmit IP video signals.

4 A method of video transmission using IP multicast and its characteristics

There are currently two main ways to provide video services on IP networks:

1) Fully utilize the router's Multicast technology, without the need for additional server forwarding, but it will increase the burden on the router, there is a risk of "broadcast storm", and the network routing protocol also needs to be adjusted.
2) Use software and servers to superimpose a superposition network for processing streaming media on the entire IP broadband network, and the superposition network realizes point-to-multipoint multicast, media stream routing and multi-point injection and other functions. The video service method we use is the 2) solution. Specifically, it is: the computer cooperates with special software to form a server to achieve real-time control. The purpose of control is: for the multimedia video server, it must have a maximum efficiency sending mechanism, that is, the system can respond to and meet the video request sent from the multimedia video receiving end in the shortest time to the maximum extent, complete the data sending to all addresses of the required users at one time, and the computer real-time control system monitors the quality of video transmission at any time, and automatically adjusts the bandwidth. Of course, the implementation of the transmission method can be compatible with the current network facilities.
During the implementation of the above solution, the computer (server) monitors the system at all times to achieve the best possible broadcast quality and high efficiency, and there is no need to have dangers such as "broadcast storm". According to the above requirements, we designed the following system, which consists of four parts: video sending, video forwarding, video receiving, and video control. The following is a detailed description of the functions of each part:

① Video sending

The video transmission is a pre-made video or real-time video. It can be an independent computer or share a computer with the first-level "video forwarding" unit. Specifically, we first compress the video in real time according to the MPEG-1 coding technology. The digital rate of this format is 1.5Mbit/s, the image uses the SIF format (352х288), 30 frames per second, and two-way stereo audio. The reason for using the MPEG-1 coding technology to compress the real-time video is that the quality of the compressed video signal is satisfactory, and the digital rate bandwidth is relatively narrow, which is conducive to IP multicast. (Of course, other coding technologies can also be used). Then we send the compressed signal to the video forwarding end. The signal from the video transmission connection to the video forwarding is point-to-point transmission (this unit belongs to the IPv4 communication method①).

②Video forwarding

The main function of video forwarding is to forward the video signal sent from the video transmitter to the video receiver or the next-level video forwarding terminal through the IP network. It is the core of IP multicast transmission of video signals. Video signals are forwarded in IP multicast mode, that is, data is transmitted to a group of specific IP addresses (users with the same type of request). Video forwarding is completed by the forwarding computer (server).

③Video reception

Video reception is the user's multimedia terminal, which of course requires the user's multimedia terminal equipment to support IP multicast.

④Video control

Its main function is to control the forwarding site, and to establish and manage the transmission of IP multicast data groups on the forwarding site. The control system should meet the needs of the users to the greatest extent possible, and pay close attention to the quality of video transmission. Specifically, it is necessary to send data to users of the same type as much as possible, but within the allowed bandwidth. This bandwidth is controlled in real time by a computer. The computer real-time control system monitors the quality of video transmission at any time and automatically adjusts the bandwidth; at the same time, it also monitors other network parameters in real time. It can be seen that video control is actually real-time control of the computer. The good cycle of computer real-time control directly determines the effect of IP multicast.

The key technology of this solution is reasonable video forwarding, seeking the maximum benefit and satisfactory transmission quality. The realization of this solution benefits from the real-time control technology of computers. We use this method to realize the trial broadcast of real-time network IP multicast video transmission in 100M Ethernet LAN network, transmitting MPEG-1 video signal (each video stream bandwidth is 1.5M), and the video signal transmission effect is good. It proves that the above solution is feasible.