What is DCI Box?

Origin of DCI network

At the beginning, the data center was relatively simple, with a few cabinets + a few high-P air conditioners in a random room, and then a single common city power + a few UPS, and it became a data center. However, this kind of data center is small in scale and low in reliability. The Internet, which has been developing crazily since the end of the 1990s, has also increased the demand for data centers. Therefore, there is an unsolvable problem in this type of data center: insufficient space , Insufficient power supply, no redundancy, and no SLA guarantee, making users start to find another data center for business deployment. At this time, the new data center and the old data center began to have network interconnection requirements, resulting in the initial DCI network, that is, Data Center Inter-connect, which includes technologies at the physical network level and the logical network level.

The initial DCI network was directly interconnected through the Internet. Later, in consideration of security, encryption was used, quality of service was considered, dedicated lines were used, and bandwidth was directly connected by optical fiber.

Development of DCI network

The development of DCI networks from Internet interconnection, to several M dedicated lines, to the current multi-10T WDM interconnection is not a long time, objectively, it is a response to the development of the Internet. Initially, users use the public network VPN tunnel to transmit their services directly through the public network. This method is affected by various environments of the public network (global network bandwidth congestion, inferior routing, line jitter, link reset, firewall, etc.) Influenced by cost and cost, it is suitable for small traffic, low bandwidth quality requirements, non-real-time, and low security requirements. Later, the business in the data center attracted more and more attention, and the business began to gradually increase deployment, and the number of servers increased linearly. After a large number of services are deployed, these services transmitted through the network have an increasing impact on companies and industries, so the requirements for the network are also getting higher and higher, first reflected in bandwidth and link stability, so data center users begin to Leased operator circuit dedicated lines, MSTP dedicated lines carried on the SDH network have begun to sell well due to their high stability, larger bandwidth, and high degree of operator multiplexing.

Later, with the continuous explosive development of business, the data between data centers began to have requirements for delay and redundancy, especially for financial customers, who had particularly high requirements for delay, so the requirements for dedicated lines were also increased; Or, users begin to require large granularity, such as 2.5G, 10G single-link bandwidth, and also require dual-routing protection to ensure that the LSA reaches 4 to 5 9s.

Even so, the power of the development of the Internet is amazing, and business trends such as log transmission and database synchronization are growing. In consideration of cost, delivery time, service quality, etc., top companies (especially Internet companies with big data like Google and FB) have begun to build DCI networks by renting bare optical fibers without operators. At the beginning of using bare optical fiber, it was also the way to run a single signal through a single optical fiber. For example, a pair of optical fibers can use a 10G ZR module to transmit 80 kilometers away. enough. However, the disadvantage of this method is that on the one hand, the amount of optical fiber usage increases linearly with the bandwidth, and the cost increases; A long-standing and difficult problem), and at this time, the 10G bandwidth of a single fiber cannot meet the needs of business growth, so the DCI network began the WDM era.

In the WDM era, two methods appeared in the DCI network, that is, coarse wavelength division CWDM and dense wavelength division DWDM. Based on cost considerations, some initial users used 10G CWDM optical modules for DCI interconnection using CWDM technology. However, this system supports up to 16 waves of 10G, and EDFA cannot amplify the signal at the wavelength of CWDM. , and its passive relay distance is also quite limited. Therefore, as the demand for large-scale data transmission continues to rise, users have to start using DWDM systems with higher capacity and performance.

DCI network structure of pure DWDM system:

The DWDM system is currently the most important large-bandwidth transmission system in the communication network. In consideration of business volume, cost, and operation and maintenance, various companies used switches to plug in 10 Gigabit color light modules in the early days, and the color light Ethernet signals that came out Directly connect to passive DWDM equipment. This kind of system is easy to operate and maintain. Under the condition of controllable cost, it can generally achieve 40 waves*10GE signal, the total system bandwidth can reach 400G, and there is no excessive network operation and maintenance cost. Ordinary IP network engineers can learn at low cost. It can be operated and maintained, and has been widely used by some companies in need. However, the development of the Internet is booming, and the 10GE single-wavelength signal will soon be unable to meet the demand. At this time, a higher single-wavelength signal system, such as single-wavelength 40GE&100GE, is required. However, the 40GE&100GE Ethernet colored optical modules that can be placed on the switch at this time have not yet appeared on the market, and the cost has remained high for a long time after the emergence, but the business cannot wait, so we can only find another way, so OTN This thing that shattered the wind and clouds in the telecommunications network appeared in the DCI network of Internet companies such as Google and FB.

The Internet began to contact OTN, basically starting from 10GE. At that time, 10G color light + DWDM boxes could no longer meet the needs of business growth,and this method could not meet the needs of batch networks because there was no management method based on the optical layer, especially It is the operation requirement of the long-distance network; in addition, after several years of development after the launch of 100G OTN, especially after several centralized purchases by operators, the cost has dropped significantly. To sum up these reasons, the method of 10GE color light + DWDM box has gradually been replaced by the OTN system. Due to technological development and cost reduction, 40G OTN systems have not been used in DCI networks in the Internet industry, and they have been directly upgraded from 10G systems to 100G systems. In the middle, it has also been considered that if 100G systems are used, the impact of failures will be extensive, etc. However, the demand for business growth is still the top priority, so the line side (for the signal on the transmission fiber side) has directly changed from 10G to 100G, ensuring that the WDM system on the line side can meet the needs of long-term bandwidth development. As for the client side (the signal facing the side of the switch), considering that there are quite a lot of existing 10G client systems, in order to protect the existing investment, it needs to be compatible with the existing 10G granular services, and can be upgraded to the client side 100G system in the future, so In order to make the transition between 10G and 100G systems in the DCI network upgrade, a service card based on 10 ODU2->1 ODU4 with 10*10G on the client side and 1*100G on the line side appeared, and this board is widely used.

With its rich management overhead, high reliability and diversified protection methods, centralized and professional NMS management platform, and large bandwidth,OTN network has indeed played an extremely important role in the development of the Internet, making network operations more professional and subdivided, of course the most important thing is to meet the rapidly growing demand of Internet business.

Typical topology of a point-to-point DCI network using OTN:

At this time, the OTN network is no longer a proprietary technology for telecommunications networks. The rise of the Internet has allowed such a traditional telecommunications network technology to enter the DCI network industry.