DCN in ASON network

1 Introduction

The ASON network is now a hot topic in the world of optical transmission networks. It is a major evolution of the original optical transmission network and has many advantages that are incomparable to the original optical transmission network. At present, ASON network equipment has been applied in the international current network and will be deployed in China's optical transmission network. Because there is a control plane in the ASON network layer, it is used to implement routing, signaling, automatic discovery, and other functions in the optical network, the DCN network in ASON is more important than the signaling network in the original transmission network. For these reasons, ITU-T of the International Telecommunication Union (ITU) has done a lot of standardization work on DCN networks in ASON networks.

The architecture of the ASON network is given in the recommendation of ITU-T G.8080, and the overall architecture of the DCN network in the ASON network is put forward. The general requirements of the ASON network are given in the G.807 recommendation, and further functional requirements are made for the DCN network. G.7712 is the most important draft about the DCN network in ASON. It provides the overall architecture and specifications of the data communication network. Draft G.7713 provides distributed call and connection management in the ASON network. These drafts are of great significance for studying DCN networks in ASON networks. Based on these drafts, in addition, in conjunction with the formulation of China Telecom ASON technical specifications and urban transmission network ASON network technology development suggestions, the basic concepts, applications, functional structures, and requirements of DCN in ASON are described in detail, and the DCN Network Construction Scheme in the Metro transmission network is discussed.

2. ason dcn Network Description

Generally, the telecom DCN network refers to a data communication network dedicated to various professional network management systems. Its main function is to provide a universal service transmission platform for various professional network management systems, in the traditional sense, the DCN network is gradually becoming a comprehensive data network platform for multiple internal applications of telecom enterprises. However, the DCN network mentioned in this Article refers to the data communication network that transmits information in the control plane and management plane within the ASON network. The object it can compare is SDH management network DCN. For example, the SDH management network is a subset of the Telecom Management Network, and the Network Element Management System (EMS) and SDH Network Element NE) are nodes in the subnet, WAN/LAN/DCC provides physical channels between these nodes. The physical channels between nodes are combined with network protocols such as the Ethernet protocol, LAPD protocol, and OSI network protocol to form the DCN infrastructure.

In ASON networks, both the control plane and management plane require data communication networks to transmit information. In the control plane, the signaling Communication Network (SCN) needs to transmit management information and order information between network controller components, and the management plane also needs to manage the communication network (MCN) to transmit management information between TMN units, both can be implemented through the DCN communication network. Note that the control plane and management plane of the GMPLS-Based ASON network can be separated on the logical and physical layers, both of which are carried by the DCN network. DCN functions can be implemented through multiple technical methods, such as circuit switching, packet switching, LAN, ATM, SDH, and OTN.

In actual network conditions, the DCN network is not an isolated network Island. It is connected with other DCN networks. DCN networks are interconnected through the DCF data communication function. DCF can communicate with different protocols on the lower and lower layers of data communication.

In the ASON network, the DCN network consists of the data communication function module and control channel of the network node. The control channel is the communication channel between network nodes and control messages transmitted through UNI. Control messages include signaling messages and routing messages. Control and maintain protocol messages such as neighbor messages and service discovery. Currently, ason dcn has two implementation methods: in-band DCN: This DCN carries control and Network Management Information by the Logical Channel Embedded in the data link, such as SDH and otn dcc and GCC channels; out-of-band DCN: This DCN is composed of an independent IP network or a dedicated circuit.

3. Application of ason dcn Network

This section mainly discusses the application of DCN in the management plane and control plane of ASON.

DCN supports MCN and SCN in different topologies, including linear, ring, mesh, and star structures. The physical link can be ECC or Ethernet. Generally, the DCN network topology is characterized by multiple different paths between two network elements. This aims to provide the reliability and survivability of MSN and SCN. In the ASON network management plane, TMN requires MCN to send management messages between TMN components. Is a physical implementation of MCN that supports distributed management and communication.

In the control plane, ASTN needs to transmit signaling information between control units through the signaling communication network SCN. It should be noted that in the OSI Layer-7 model, DCN implements the layer-3 Functions of the physical layer, data link layer, and network layer. For upper-layer applications, DCN is transparent. In addition, the DCN network can be separated at different levels in a variety of applications. This separation depends on DCN's network design, network scale, link capacity, security requirements, and performance requirements. carriers can choose different levels of separation for DCN network design. For example, MCN, SCN, and other applications can be supported on the same IP network, and MCN, SCN, and other applications can be supported on the same physical network, but they are separated at the network layer; you can also support MCN, SCN, and other applications on different physical networks.

An actual SCN network consists of three parts: User-network, intra-domain, and Inter-Domain. The mesh topology uses ECC, LAN, and leased line to connect to the ASON network element. The topology of the User-Network part and the Inter-Domain part depends on the agreement between the two parties, and one or more connections can be established.

4. Performance Requirements for ason dcn Networks

In G.7712, the functional structure of the DCN network in the ASON network is defined. In addition to the traditional three-tier functions, it is also mentioned that in the out-of-band DCN, the MPLS Multi-Protocol Label Switching mechanism can be added to facilitate DCN to support connection-oriented SCN businesses. The mpls lsp function is an improvement to the original DCN network to meet the needs of the automatic switching optical network. At the same time, because the implementation of the core functions of ASON depends on the control plane, DCN is the physical bearer platform implemented by the ASON Control Plane function. To ensure efficient and reliable transmission of control information, it is very important to study the DCN network performance requirements. According to the current research progress on ASON networks and the actual needs of telecom operators, the following requirements are generally considered essential for ason dcn networks:

1) because information exchange on the ASON Control Plane is accurate and secure, it is crucial for telecom operators to ensure that even if the control plane/DCN fails, the existing service connections of the transport plane cannot be lost. That is, the ason dcn network and the ASON transport plane are logically independent. At the same time, in this case, it also has a certain degree of information transmission survivability.

2) When the ason dcn network and the ASON transport plane have different network topologies, all topologies should ensure that the ASON node can access the ason dcn network reliably.

3) the transmission performance of message traffic control in the ason dcn network will affect the connection management performance, as a result, the performance of the ASON connection service depends largely on the information transmission performance of the ASON network. Therefore, the ason dcn network should support controlling the priority transmission of messages, messages that are time sensitive, such as messages for recovery, have a higher priority than other messages such as connection signaling messages, topology messages, and resource discovery messages. At the same time, the ason dcn network should have a congestion control mechanism to ensure reliable message transmission.

4) The ason dcn network should have a certain degree of network elasticity, including the ability of the ason dcn network to expand up and down, with a certain degree of fault recovery capability, at the same time, when the signaling link fails, the Business Channel associated with the signaling channel cannot be affected.

5) Currently, the network performance indicators of the ason dcn network mainly include network latency, network packet loss rate, protection and recovery performance, QoS support, DCN route table convergence time, And DCN route table capacity, currently, there are no clear standards and specifications. Each operator will give indicators based on their actual needs, but the indicators are generally stricter than those of the traditional DCN network.

6) The ason dcn network should have corresponding security mechanisms to prevent unauthorized users from unauthorized access. At the same time, make sure that only licensed messages such as UNI/E-NNI messages can pass through the Inter-Domain interface, while unauthorized messages such as I-NNI cannot pass.

5 typical ason dcn Network Structure Analysis

Because the ason dcn network has two modes: in-band DCN and out-of-band DCN, in the actual ason dcn network architecture, there are several typical ason dcn structures. The following is an analysis and comparison of the ASON network management architecture solutions.

1) Use DCN

Each network element is connected through an in-band DCN channel. The in-band DCN channel has the same topology as the physical connection of the network element. Each network element is connected to the Gateway network element, connect to the network management center through the gateway network element. The network control information is converged and transmitted up through the gateway network element. In this mode, DCN uses the embedded channel to quickly and stably, however, the survivability of the DCN network is highly concentrated on the gateway network element. In the actual network, there are generally two or more gateway network elements, which are used as the primary protection, at the same time, make sure that the number of network elements mounted under the gateway network element does not exceed the maximum number limit.

2) use the out-of-band DCN

Each network element uses an out-of-band DCN channel. The out-of-band DCN channel and the Network Element physical connection have different topologies. The interruption of the out-of-band DCN channel only causes the interruption of the control network message transmission. In the out-of-band DCN, DCN is generally implemented in hierarchical management. The ason dcn channel is independent of the DCN channel of the aggregation layer and the access layer MSTP, and provides the message transmission capability of the ason dcn channel with a higher priority, this DCN layer only separates the ASON layer from the MSTP layer from the network management information channel, which ensures smooth network management information channel and achieves mutual interference between optimization and upgrade. However, from the perspective of network management, it is still a unified, end-to-end network management.

3) use both in-band DCN and out-of-band DCN

Each network element has an external DCN channel and an internal DCN channel. This is currently the most common model for ason dcn networks, all the network elements implement the connection between the internal DCN channel and the external DCN channel to protect each other. In this way, the DCN network has a high survivability. In this case, generally, in-band DCN is preferred in the domain, and out-of-band DCN is used as the protection channel, while in-band DCN mode between UNI and domain. The external DCN channel is not used as the protection channel of the internal DCN channel for the ASON node that does not have an external DCN network in the immature Metro Transmission Network.

To sum up, the ason dcn network architecture generally adopts a hybrid mode, and the intra-domain DCN mode is preferred. I believe that with the gradual deployment of the ASON network in the China optical transmission network, the research and construction of ason dcn will be more mature.

1. Technology overview of ASON automatic switching Optical Network
2. Research on the Control Plane of ASON automatic switching Optical Network