Introduction to the DCN

With the development of network scale, OAM of a network becomes more and more difficult. A stable and robust DCN management network helps lower the OAM cost.

Basic Concepts

This section describes the basic concepts related to data communication network (DCN).

DCN: A data communication network (DCN) provides communication channels for the NEs that are managed in a centralized manner to operate and maintain the NEs remotely. From a broad sense, a network for data communication can be called a DCN. In this document, the DCN refers to a data communication network for network management in the transmission domain.
ECC: An embedded control channel (ECC) implements operation, administration, and maintenance (OAM) communication between NEs. An ECC is a logical channel for communication between NEs and it is carried on a physical channel such as a data communications channel (DCC) or general communication channel (GCC) to transmit communication information between NEs.
DCC: A DCC is used to transmit OAM information between NEs. The DCC defined for Huawei NG WDM products uses the D1 to D12 overhead bytes in a Huawei proprietary frame structure to transmit OAM information.
GCC: A GCC is also used to transmit OAM information between NEs. The GCC of Huawei's NG WDM products uses GCC overheads in a protocol frame defined in ITU-T G.709.

Background of DCN

In a DCN, the DCC bytes in SDH overheads are used as physical channels for DCN management. The customer does not need to set up private DCN channels so that the network construction cost is greatly lowered. For a DCN, the SDH provides the following bandwidth:

By using the D1-D3 bytes in SDH regenerator section overheads (RSOH), the SDH provides a 192 kbit/s bandwidth for the DCN.
By using the D4-D12 bytes in SDH multiplex section overheads (MSOH), the SDH provides a 576 kbit/s bandwidth for the DCN.
By using the D1-D12 bytes in SDH section overheads, the SDH provides a 768 kbit/s bandwidth for the DCN.

Figure 1 shows the positions of DCC bytes in SDH overheads.

Figure 1 Positions of DCC bytes in SDH overheads

DCN Composition

A data communication network (DCN) consists of network management systems (NMSs), gateway NEs (GNEs), non-GNEs, and the connections between them. Both the NMSs and NEs are nodes of a DCN. The DCN between the NMSs and NEs is called the external DCN, and the DCN between NEs is called the internal DCN, as shown in Figure 2.

Figure 2 DCN Composition

External DCN

In general, an external DCN is a local area network (LAN) or a wide area network (WAN) and uses the Transmission Control Protocol/Internet Protocol (TCP/IP) or the Open System Interconnection (OSI) protocol for communication. It mainly provides communication between NMSs and communication between the NMS server and GNEs. The details are as follows:
- Communication between NMSs
  
  The communication between NMSs includes the following parts: communication between the NMS server and the operations support system (OSS), communication between the NMS server and clients, and communication between the primary and secondary sites in a high availability (HA) system. The NMS communication can be implemented only using the TCP/IP protocol.
- Communication between the NMS server and GNEs
  
  The NMS server and GNEs may be located on different floors of a building, in different buildings, or even in different cities. Hence, an external DCN that is comprised of the data communication devices, such as LAN switches and routers, is required to connect the NMS server and the GNEs. This type of communication can be implemented using either the TCP/IP or OSI protocol.
  Usually the NMS server connects to GNEs in the following two modes:
  - The NMS server connects to GNEs through Ethernet switches.
    
    This mode applies when the distance between the NMS server and each GNE is smaller than or equal to 100 m and no other Ethernet networks are available between the NMS server and the GNE.
  - The NMS server connects to GNEs through routers.
    
    This mode applies when the distance between the NMS server and each GNE is greater than 100 m and an Ethernet network is available between the NMS server and the GNE.
  NOTE:
  The DCN communication between the NMS server and GNEs belongs to the data communication domain and therefore is not elaborated in this document. The DCN mentioned in this document refers to the internal DCN, unless otherwise specified.
Internal DCN

An internal DCN provides communication between NEs using the HWECC, TCP/IP, or OSI protocol. The protocol packets are transmitted over optical supervisory channels (OSCs) or electric supervisory channels (ESCs).