The Direction of DCI Network Development（Part Two）

According to these characteristics, there are roughly two conventional DCI solutions:

1. Use pure DWDM equipment, and use color optical module + DWDM multiplexer/demultiplexer on the switch. In the case of single-channel 10G, the cost is extremely low, and the product options are abundant. 10G color light module is in the domestic It has already been produced, and the cost is already very low (in fact, the 10G DWDM system started to become popular a few years ago, but with the arrival of some larger bandwidth requirements, it had to be eliminated, and the 100G color light module was not yet available. Appeared.) At present, 100G has just begun to appear in China related color optical modules, and the cost is not low enough, but it will always make a strong contribution to the DCI network.

2. Use high-density transmission OTN equipment, they are 220V AC, 19-inch equipment, 1~2U high, and the deployment is more convenient. The SD-FEC function is turned off to reduce the delay, and the routing protection at the optical layer is used to improve stability, and the controllable northbound interface also improves the development capability of equipment expansion functions. However, OTN technology is still reserved, and management will still be relatively complicated.

In addition, what the first-tier DCI network builders are currently doing is mainly to decouple the DCI transmission network, including the decoupling of the optical at layer 0 and the electrical at layer 1, as well as the NMS and hardware equipment of traditional manufacturers. decoupling. The traditional approach is that a certain manufacturer's electrical processing equipment must cooperate with the same manufacturer's optical equipment, and the hardware equipment must cooperate with the manufacturer's proprietary NMS software for management. This traditional method has several major drawbacks:

1. The technology is closed. In theory, the optoelectronic level can be decoupled from each other, but traditional manufacturers deliberately do not decouple in order to control the authority of the technology.

2. The cost of the DCI transmission network is mainly concentrated in the electrical signal processing layer. The initial construction cost of the system is low, but when the capacity is expanded, the manufacturer will raise the price under the threat of technical uniqueness, and the expansion cost will be greatly increased.

3. After the optical layer of the DCI transmission network is put into use, it can only be used by the electrical layer equipment of the same manufacturer. The utilization rate of equipment resources is low, which does not conform to the development direction of network resource pooling, and is not conducive to unified optical layer resource scheduling. The decoupled optical layer is invested separately in the early stage of construction, and is not limited by the future use of a single optical layer system by multiple manufacturers, and combines the northbound interface of the optical layer with SDN technology to perform direction scheduling of channel resources at the optical layer , Improve business flexibility.

4. The network equipment seamlessly connects with the Internet company's own network management platform directly through the data structure of YANGmodel, which saves the development investment of the management platform and eliminates the NMS software provided by the manufacturer, which improves the efficiency of data collection and network management. management efficiency.

Therefore, optoelectronic decoupling is a new direction for the development of DCI transmission network. In the foreseeable future, the optical layer of DCI transmission network can be SDN technology composed of ROADM+ north-south interface, and the channel can be opened, scheduled and recovered arbitrarily. It will be possible to use mixed electrical layer devices of manufacturers, or even mixed use of Ethernet interfaces and OTN interfaces on the same optical system. At that time, the work efficiency in terms of system expansion and change will be greatly improved, and the optical layer will also be used. It is easier to distinguish, the network logic management is clearer, and the cost will be greatly reduced.

For SDN, the core premise is the centralized management and allocation of network resources. So, what are the DWDM transmission network resources that can be managed on the current DCI transmission network?

There are three channels, paths, and bandwidths (frequency). Therefore, the light in the cooperation of light + IP is actually carried out around the management and distribution of these three points.

The channels of IP and DWDM are decoupled, so if the corresponding relationship between an IP logical link and a DWDM channel is configured in the early stage, and the corresponding relationship between the channel and IP needs to be adjusted later, you can use the OXC The method is used to perform fast channel switching at the millisecond level, which can make the IP layer unaware. Through the management of OXC, the resource centralized management of the transmission channel on each site can be realized, so as to cooperate with the business SDN.

The decoupling adjustment of a single channel and IP is only a small part. If you consider adjusting the bandwidth while adjusting the channel, you can solve the problem of adjusting the bandwidth requirements of different services in different time periods. Greatly improve the utilization rate of the built bandwidth. Therefore, while coordinating with OXC to adjust the channel, combined with the multiplexer and demultiplexer of flexible grid technology, a single channel no longer has a fixed central wavelength, but allows it to cover a scalable frequency range, so as to achieve Flexible adjustment of bandwidth size. Moreover, in the case of using multiple services in a network topology, the frequency utilization rate of the DWDM system can be further improved, and the existing resources can be used in saturation.

With the dynamic management capabilities of the first two, the path management of the transmission network can help the entire network topology to have higher stability. According to the characteristics of the transmission network, each path has independent transmission channel resources, so it is of great significance to manage and allocate the channels on each transmission path in a unified manner, which will provide optimal path selection for multi-path services , and maximize the use of channel resources on all paths. Just like in ASON, gold, silver and copper are distinguished for different services to ensure the stability of the highest level of services.

For example, there is a ring network composed of three data centers A, B, and C. There is service S1 (such as intranet big data service), from A to B to C, occupying 1~5 waves of this ring network, each wave has 100G bandwidth, and the frequency interval is 50GHz; there is service S2 (external network service), From A to B to C, 6~9 waves of this ring network are occupied, each wave has a bandwidth of 100G, and the frequency interval is 50GHz.

In normal times, this kind of bandwidth and channel usage can meet the demand, but when sometimes, for example, a new data center is added, and the business needs to migrate the database in a short time, then the demand for intranet bandwidth in this time period will be It has doubled, the original 500G bandwidth (5 100G), now requires 2T bandwidth. Then the channels at the transmission level can be recalculated, and five 400G channels are deployed in the wave layer. The frequency interval of each 400G channel is changed from the original 50GHz to 75GHz. With the flexible grating ROADM and multiplexer/demultiplexer, the entire The path at the transmission level, so these five channels occupy 375GHz spectrum resources. After the resources at the transmission level are ready, adjust the OXC through the centralized management platform, and adjust the transmission channels used by the original 1-5 waves of 100G service signals to the newly prepared 5 with a millisecond-level delay The 400G service channel goes up, so that the function of flexible adjustment of bandwidth and channel according to DCI service requirements is completed, which can be performed in real time. Of course, the network connectors of the IP devices need to support 100G/400G rate adjustable and optical signal frequency (wavelength) adjustment functions, which will not be a problem.

Regarding the network technology of DCI, the work that can be completed by transmission is very low-level. To achieve a more intelligent DCI network, it needs to be realized together with IP. For example, use MP-BGP EVPN+VXLAN on the IP intranet of DCI to quickly deploy a layer 2 network across DCs, which can be highly compatible with existing network devices and meet the needs of tenant virtual machines to move flexibly across DCs. ;Use segment routing on DCI's IP external network to perform traffic path scheduling based on source business distinction, meeting the requirements of cross-DC egress traffic visualization, fast route restoration, and high bandwidth utilization; the underlying transmission network cooperates with the multi-dimensional OXC system, Compared with the current conventional ROADM, it can realize the fine-grained service path scheduling function; the use of non-electric transmission wavelength conversion technology can solve the problem of fragmentation of channel spectrum resources. The integration of upper-layer and lower-layer resources for business management and deployment, flexible deployment, and improved resource utilization will be an inevitable direction in the future. At present, some large domestic companies are paying attention to this area, and some start-up specialized companies are already conducting research and development of related technical products. Hope to see related overall solutions on the market this year. Perhaps in the near future, OTN will also disappear in carrier-class networks, leaving only DWDM.