Comparison of IP transmission technology in cable TV networks

Comparison of IP transmission technology in cable TV networks

Abstract: IP transmission technology in cable TV networks includes three forms: IP over ATM, IP over SDH, and IP over WDM, this article introduces and compares the three IP Address Transmission Technologies in detail.

Key words: IP technology, cable TV network, IP over ATM, IP over SDH, IP over WDM.

With the rapid development of the global Internet (Internet), the number of Internet users is growing exponentially. The ratio of Internet-dominated Data Communication in the total amount of communication services is rapidly increasing, internet services have become the most rapidly developing and competitive multimedia communication industry. The 21st century is a period of continuous development of the information industry. IP technology makes it possible to integrate information collection with existing networks. IP over everything has become an indisputable fact.

At present, the access speed of the Internet through telecom dialing is extremely slow. Generally, the telephone Modem can only provide dozens of Kbit/S transmission rates, and its speed and bandwidth cannot well support broadband services such as multimedia information.

With the development of multimedia communication, the demand for broadband Internet access is becoming increasingly urgent. However, cable TV networks have abundant bandwidth resources. At the same time, China's cable TV users have reached 80 million, and the cable TV network's mileage has exceeded 2.4 million kilometers, china has become the world's largest cable TV user country. Cable TV networks have great industrial development value. Building an Internet broadband information network based on cable TV networks is not only the hope of the majority of users, but also the key to achieving the second take-off of cable TV networks.

What technology is used to transmit IP addresses in a cable TV network depends on the transmission technology used in the cable TV network. IP transmission technology in cable TV networks includes three forms: IP over ATM, IP over SDH, and IP over WDM.

I. IP over ATM

ATM is a high-speed, low-latency multiplexing exchange technology. It is developed based on analyzing and summarizing the technical advantages and disadvantages of circuit switching and group switching. It integrates the advantages of the two, that is, connection-oriented, service quality assurance, and statistical replay are used to achieve high bandwidth. It uses a short group with a fixed length to transmit various communication information in the network, which facilitates high-speed hardware processing and achieves high-speed and large-capacity broadband exchange. Moreover, it has a sound traffic control and congestion control functions to ensure bandwidth utilization and network security and reliability. In a cable TV network, the application of ATM traffic control can achieve the hierarchical service of video transmission, and ATM can also achieve real-time asymmetric transmission of TV programs. Currently, cable TV transmission networks in some provinces and cities are still using ATM technology.

IP over ATM is a combination of IP and ATM. There are currently two technical methods: overlapping technology and integration technology. The overlapping technology overlaps the IP Network Layer Protocol over the ATM, that is, the ATM network and the existing IP network overlap, and the ing between the ATM and IP addresses is used at the ATM endpoint at the same time, after obtaining the ATM address of the receiving end, the sender can establish an ATM/SVC connection to transmit LAN packets. The integration technology integrates the intelligence and management performance of the IP router into the ATM switch to form an integrated platform. It only needs to identify the IP address and does not require the Address Resolution Protocol of the ATM, which simplifies the routing selection function of the ATM, this improves IP Forwarding efficiency and retains the flexibility of routing.

The advantage of IP over ATM technology is that it can make full use of ATM's fast exchange and complete QoS functions to ensure the quality of service of the network. The network has good scalability and flexibility; supports the collection of multiple services, data, voice, and video on a single network to provide different service quality QoS for different service types. It has good network traffic management and control performance, the performance is very fine in the area of ATM traffic control, which is very important for the wide area network with extremely valuable bandwidth and extremely high line costs, this is one of the reasons why ATM can be widely used in wide area networks.

Disadvantages of IP over ATM technology: Because IP data packets must be mapped to ATM cells, the resulting transmission overhead is called "cell Tax", resulting in low transmission efficiency; complicated network management and expensive equipment; not suitable for ultra-large IP backbone networks.

Ii. IP over SDH

ATM was once unique in supporting multiple services. However, with the development of IP technology and the continuous improvement of network hardware, IP addresses have become the core of various services, both data voice and video services can be carried by IP addresses. The advantages of ATM have been replaced by IP technology. Especially when the data traffic exceeds the voice and video services, it is unnecessary for ATM to exist, besides, removing the ATM can also improve the transmission efficiency. Therefore, IP over SDH came into being, and this technology has greatly shaken the role of ATM in the WAN.

The concept of SDH Transmission NETwork was first proposed by the bell Institute of Communications in 1985, called Synchronous Optical NETwork (SONET ). It is composed of a complete set of standard transfer structures, suitable for various adaptive processing of the net load (that is, the part of the network node interface bit stream that can be used for telecommunications services) in the physical media, such as optical fiber, microwave, and satellite. This standard became a new standard of the US Digital System in 1986. CCITT, the predecessor of the International Telecommunications Union Standards Department (ITU-T), accepted the SONET concept in 1988 and reached an agreement with the American Standards Association (ANSI, after SONET is modified, it is renamed Synchronous Digital Hierarchy and SDH to become a general technology system suitable for optical fiber, microwave, and satellite transmission at the same time.

SDH Transmission Network is composed of some SDH network units, which transmit synchronous information on optical fiber, microwave, or satellite, integrating the functions of re-connection, transmission, and exchange, integrated information networks managed and operated by a unified network. It can effectively manage networks, maintain dynamic networks, and monitor service performance. It can effectively improve the utilization of network resources and meet the information transmission and exchange requirements of the broadcasting and television trunk transmission networks, it has made a qualitative leap in improving the quality of broadcast and television transmission. Therefore, SDH technology is becoming a hot topic in the development and application of Transmission Technology in the broadcast and television field.

IP over SDH uses the SDH network as the physical transmission network of the IP data network. It uses the link and Point-To-Point Protocol (PPP: Point To Point Protocol) To encapsulate data packets. According To RFC1662 specifications, the IP Group is simply inserted into the information segment of the PPP frame. Then, the Service adapter at the SDH channel layer maps the encapsulated IP data packets to the SDH synchronization net load, and then goes through the SDH Transmission Layer and segment layer, and adds the corresponding overhead, load the net load into an SDH frame, and finally reach the optical network for transmission in the optical fiber. IP over SDH, also known as PACKET over SDH (PoS), retains the IP-oriented connectionless features.

The advantages of IP over SDH are: strong support for IP routing, high IP transmission efficiency; in line with the characteristics of Internet services, such as the implementation of multicast methods; the loop and self-healing capabilities of SDH technology can be used to achieve Link error correction. At the same time, the OSPF protocol can be used to prevent network interruptions due to link faults and improve network stability; the establishment of the IP network technology on the SDH Transmission Platform can easily cross regions and national boundaries and be compatible with different technical standards to implement global networking. The voice of the ATM layer simplifies the network structure, reduced operation costs. On the cable TV network platform, IP over SDH applies to inter-provincial network and intra-Province Network IP transmission.

The disadvantage of IP over SDH is that IP over SDH does not currently support Virtual Private Network VPN and circuit simulation. In all packet switching technologies, the QoS of ATM is the best, and it can achieve circuit simulation, however, the IP over SDH technology can only be used for service classification, and does not provide better QoS. for large-scale networks, it is necessary to handle large and complex route tables. In addition, it is difficult to find and route information occupies a large bandwidth.

Judging from the development trend of OPTICAL communication technology, SDH/SONET will be used in wavelength division multiplexing in the future. Therefore, IP over SDH will eventually become IP over WDM (IP over OPTICAL)

Iii. IP over WDM

With the development of transmission technology, IP service-oriented network optimization design will be IP over WDM.

Wavelength division multiplexing (WDM) is a technology that transmits optical signals of multiple wavelengths at the same time in an optical fiber. Its principle is to combine optical signals of different wavelengths at the sending end, the combined optical signals are separately sent to different terminals at the receiving end, which means that only one wavelength can be used as a single channel of the carrier, and the optical channels with different wavelengths can be transferred simultaneously in the optical fiber, this improves the optical communication capacity exponentially. WDM Technology is mainly implemented by WDM. Wavelength Division Multiplexing is a passive optical device with simple structure, small size, and easy coupling with optical fibers. The WDM system has three basic structures: Optical multiplexing one-way single-fiber transmission, optical multiplexing two-way single-fiber transmission, and optical multiplexing insertion transmission. Flexible networking is of great significance for developing new bandwidth services, fully exploring and utilizing the capability of optical fiber bandwidth, and achieving high-speed communication.

IP over WDM allows IP data packets to run directly on the optical path, reducing the redundancy between the network layers. Because the intermediate ATM and SDH layers are eliminated, the transmission efficiency is the highest, Saving network operation costs and reducing user fees, it is the most direct and economical IP network architecture and is very suitable for ultra-large backbone networks.

IP over WDM has the following advantages: it makes full use of the bandwidth resources of optical fiber, greatly improving the bandwidth and relative transmission efficiency; it is transparent to the Transmission Bit Rate, data format and modulation method, it can transmit businesses of different bit rates such as ATM, SDH/SONET, and Gigabit Ethernet. It can be compatible with existing communication networks and support future broadband service network and network upgrades, it also features promotion and high survivability.

The disadvantage of IP over WDM is that the wavelength standardization has not yet been implemented. The Network Management of the WDM System should be separated from the signal transmitted from the network management system. The Network Management of the WDM system is not mature yet; at present, the network topology of the WDM system is only based on the point-to-point method, and the "Optical Network" has not yet been formed ".

Iv. Comparison of IP over ATM, IP over SDH, and IP over WDM

The three IP transmission schemes have their own advantages and disadvantages. They must be treated separately in actual applications. If the primary network already uses an ATM device, the IP over ATM scheme can be used, due to the high ATM port rate, comprehensive QoS (Service Quality) guarantees, and mature products, the IP network switching rate can be improved to ensure the service quality of the IP network. If the trunk does not involve ATM, the IP over SDH scheme is adopted. Because the ATM device is removed, the investment is low, the scheme works fast and the line utilization is high. Therefore, IP over SDH is a good choice for the moment. In the metro backbone network, the IP over SDH technology has a relatively high investment, so it is more practical to use the IP over WDM Technology. The advantage of IP over WDM is to reduce the intermediate redundancy between different layers of the network, reduce overlapping functions between SDH, ATM, IP, and other layers, and reduce equipment operation, maintenance, and management costs. In addition, the IP over WDM Technology can greatly expand the network bandwidth to maximize the line utilization. When the peripheral network Gigabit Ethernet becomes the mainstream, this technology can truly achieve seamless access, this indicates that IP over WDM represents the future of the broadband IP backbone network.

The development of broadband network communication has always been the goal and ideal of the people, and is also a direction for the development of broadband integrated service networks. As its technical representative, the ATM technology is considered to be responsible for the integration of multiple services (telephone, television, data, and leased line) from the time it was generated. However, due to its technical complexity, it is expensive, so its development is limited. The popular IP technology is simple, flexible, widely used, and inexpensive, which makes it widely used in Internet and LAN, it is also considered a choice of broadband network technology. Using a cable TV network to build an IP Broadband Access Network for Internet data transmission will bring great development opportunities to the cable TV network.

Article entry: aaadxmmm responsible editor: aaadxmmm