The rapid growth of bandwidth and the IP of services are the two core drivers of current network development. The rise and development of various high-bandwidth data services has led to the development of transmission networks from time division multiplexing to wavelength division multiplexing. The wavelength rate has grown from 2.5G to 10G, and the scheduling granularity has evolved from M-class VC to G-level ODUk.OTN. The technology combines the advantages of SDH and WDM technologies, provides massive bandwidth, fast and flexible service scheduling capabilities, and complete OAM functions. It has become the basic transport platform for multi-service in the era of massive bandwidth, and is obtained at the trunk, metro core and convergence levels. With extensive deployment, with the emergence of large-bandwidth OLTs and the emergence of large-grain leased line services, compact OTNs have been deployed to the access level. The IP of the service makes the OTN bearer interface in the network gradually focus. The main services of the OTN bear are the interconnection between the routers, the OLT uplink of the fixed network broadband, and the packetized large granular line. The physical interfaces of these services are basically For various speeds of Ethernet, how to efficiently carry packet services has become a new hot spot of OTN technology.
The above development trend has brought development opportunities to operators, but the bandwidth has gone up, and the revenue has not increased significantly. The difference in the scissors that does not increase the revenue is a problem that has always plagued operators. How to effectively use the network bandwidth, achieve intensive management of traffic, and improve the intelligence of the pipeline is the core concern of operators under the general trend of “de-transformingâ€.
As the basic platform of the transport network, the traditional OTN provides a rigid pipeline, which is less efficient for packet service with less bandwidth. Targeted optimization of packet service transmission, and partial packet function on OTN can improve the efficiency of the entire bearer network with half the effort. For example, for the fixed-line broadband uplink service, the packet bandwidth service can be efficiently transparently transmitted according to the utilization of the port bandwidth. For the packet service with lower bandwidth utilization, statistical multiplexing is adopted to improve the bearer efficiency. For example, the core router port is expensive, and it is unbearable under the pressure of massive bandwidth, and most of the services are simply forwarded. For this part of the service, it can be bypassed in the optical layer to improve the efficiency of the whole network. In addition, with the development of mobile Internet, the rise of content providers, the emergence of virtual operators, high-value-added private line services have gradually become an important source of revenue for operators, and the dedicated line is directly carried on OTN, which simplifies the network level. It also accelerates service opening time, which helps operators to take the lead in the competition.
Therefore, the enhancement of the grouping function on the OTN has become the consensus of the industry. At present, mainstream equipment vendors have introduced packet OTN devices covering all levels of the network.
There are two main types of packetization functions on the OTN. One is that the existing OTN equipment adds a service board that supports packet switching and processing, and the packet switching matrix is ​​built on the service board. The packet switching can only be performed in the board. The other is to support a centralized packet switching plane on the OTN, which enables flexible packet switching between service boards.
The board-level packet OTN has two methods: branch line separation and branch line combination. In the branch line separation mode, after packet processing and exchange are completed inside the board, the packet service is encapsulated into ODUk or ODUflex, and then enters OTN. The cross matrix is ​​crossed. In the branch line integration mode, after the packet processing and exchange are completed inside the card, the packet service is encapsulated into the OTUk and directly transmitted on the line.
The former method is simple in function and low in cost, so it is mainly used for compact OTN equipment, and has been widely used in the metro aggregation access level. The branch line separation method can achieve certain flexibility through OTN crossover, and can be smoothly upgraded by adding a group board on the existing OTN equipment, achieving a good relationship between flexible grouping capability and protection of existing network investment. The balance is a better choice for the evolution of the existing OTN to packet OTN.
There are also two implementations of centralized packet OTN. The dual-plane mode can be upgraded from the existing OTN to the packet OTN. However, the dual-plane mode uses two independent cross-matrix matrices in one device, which wastes resources, costs and consumes a lot of power, and is upgraded. The cross-board needs to be replaced, and the network deployment value is basically not available.
The universal cell switching mode is the mainstream technology in the industry when implementing packet OTN. The main OTN products of mainstream equipment vendors are based on this technology. The OPF (ODUk over Packet Fabric) protocol of the standard organization OIF also carried out The definition of the standard. In this way, the core of the device is a universal cell switching matrix, and various types of services such as ODUk and packet are sliced ​​in the service card, and then the cell enters the universal cell switching matrix and is switched to the line. After the side board is carded, the package is transmitted to the OTUk line. A packet OTN device adopting this technology can implement flexible exchange of large-capacity packet services and realize exchange of any proportion of services from 100% to 100% OTN, which is suitable for new deployment in an OTN network.
In the packet OTN application, the packet and OTN service hybrid circuit board (see Figure 1) is used to mix and match the packet service and the OTN service to the same circuit board, which can significantly improve the OTN bandwidth utilization and reduce the line side. The board type simplifies operation and maintenance.
Figure 1 Mixed circuit board using packet and OTN services
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