Basic Concepts of OSI over DCC

OSI over DCC Protocol Stack

The OSI over DCC protocol consists of five layers, in which the session layer, representation layer, and application layer are unified as the application layer and use proprietary protocols, as shown in Figure 1.

Figure 1 Architecture of the OSI over DCC protocol stack

Physical layer

The main function of the physical layer is to provide channels for data transmission, for the data end equipment.

Physical channels are classified as follows:

• DCC channel

  DCC channels use the DCC bytes in SDH frames or the GCC bytes in OTN frames as the channels for the communication among NEs.

• Ethernet physical channel

  The NE provides the Ethernet physical channel through the Ethernet NM port or the NE cascading port.

Data link layer

The main function of the data link layer is to provide reliable data transmission on physical links.

In the case of DCCs, the NE adopts the LAPD protocol to realize the data link layer function. The LAPD protocol complies with ITU-T Q.921.

When using the LAPD protocol, you must set the LAPD role. In the case of the two ends of a DCC, set the LAPD role to Network at one end and to User at the other end.

NSAP

The OSI protocol takes the network service access point (NSAP) address as the protocol identification for nodes. The format of a simple NSAP address is shown in Figure 2.

Figure 2 Format of a simple NSAP address

AREA ID: The length is adjustable and ranges from 1 to 13 bytes. The AREA ID is used for Layer 2 routing addressing within a domain. The values should be the same in the Layer 1 route domain and be different in the Layer 2 route domain.

SYS ID: The length is fixed to six bytes. The SYS ID is used for route addressing within a domain. For Huawei optical equipment, the former three bytes are fixed to 0x08003E and the latter three bytes are the same with the NE ID.

NSEL: The NSEL value is fixed to 0x1D.

The AREA ID of Huawei optical equipment is 47000400060001.

The ISO8348/AD2 defines a complicated format of the NSAP address, as shown in Figure 3.

Figure 3 Format of a complicated NSAP address

This manual does not cover the naming details and functions of each character in the NSAP address format. For the OSI protocol, only the simple NSAP address format needs to be noticed. Huawei equipment applies the simple NSAP address format, which does not affect the interconnection between Huawei equipment and third-party equipment. The configuration of the NSAP address requires that the AREA ID in the same domain should be the same.

• AFI: 47
• IDI: 0005
• DFI: 80
• ORG: 000000
• RES: 0000
• RD: 0001
• AREA: 0001
• SYS ID: 00206005FA68
• NSEL: 1D

• IS-IS protocol

  In the CLNS, NEs are classified into intermediate systems (IS) and end systems (ES) according to the NE role. The IS is equivalent to the router in the TCP/IP protocol stack and the ES is equivalent to the host.

  The IS-IS protocol is a dynamic routing protocol between two ISes. It complies with ISO 10589 and functions as the OSPF protocol in the TCP/IP protocol stack. The IS-IS protocol supports the L1 and L2 layered routes. The NE whose role is L1 cannot be a neighbor of an NE in a different area and is involved only in the routes in its own area. It issues a default route that points to its closest L2 NE and accesses other areas through the default route. The NE whose role is L2 can be a neighbor of the L2 NE in a different area and can also be involved in the routes in the backbone area. The backbone area is formed by consecutive L2 NEs. In other words, the L2 NEs in the backbone area must be consecutive (connected). In the network as shown in Figure 4, as the L2 NEs in the backbone area are not consecutive, the NEs in area 4 are isolated from the NEs in other areas. By default, the role of the OptiX equipment is L1.

  Figure 4 Layered routes of IS-IS protocol routes (L2 not consecutive)
  
  
  NOTE:

  L2 NEs are classified into two categories, the NE with only the L2 role and the NE with both the L2 role and the L1 role. Generally, an L2 NE has the L1 role.

When a networking involves Huawei equipment and third-party equipment within the same domain, set the AREA ID to 4700058000000000000001 0001.

TP4

The TP4 protocol locates at the transport layer of the OSI protocol stake. The TP4 protocol is applied to create a reliable communication connection. The TP4 protocol can handle the problems as data packet loss, repetition and falsification, which are caused by network faults.

LAPD Role at the Optical Interfaces

The DCCs of the optical interfaces of the OSI protocol stack comply with the LAPD protocol defined in Q.921. You need to set the LAPD roles for the interconnected optical interfaces with one being network, the other being user. The optical interfaces refer to the optical interface of the equipment and that of the interconnected equipment. Regardless whether the equipment interconnected with Huawei equipment or equipment of other vendors, configure the equipment according to the configuration of the interconnected equipment.

Access Mode

In the OSI over DCC solution, there are two modes for the Web LCT to access an NE, namely, gateway mode and direct connection mode.

• Gateway mode

  In the gateway mode, the Web LCTaccesses a non-gateway NE through the gateway NE. The gateway NE queries the core routing table of the application layer according to the ID of the NE to be accessed to obtain the corresponding route.

  The core routing table synthesizes the transport layer routing tables of all communication protocol stacks. Each route item includes the following:

  • ID of the destination NE
  • Address of the transfer NE
  • Communication protocol stack of the transfer NE
  • Transfer distance

• Direct connection mode

  In the direct connection mode, the Web LCT accesses an NE as the gateway NE. All transfer NEs on the access path query the L1 routing table and L2 routing table of the network layer according to the NSAP address of the NE to be accessed to obtain the corresponding route.

  The L1 routing table and the L2 routing table are based on the IS-IS protocol.

  Each route item in the L1 routing table includes the following:

  • Destination system ID
  • Cost
  • Adjacency No.

  Each route item in the L2 routing table includes the following:

  • Destination area ID
  • Cost
  • Adjacency No.
  NOTE:

  The adjacency No. is the ID of an LAPD connection. You can query the link adjacency table of the data link layer to obtain the mapping relation between the adjacency No. and the LAPD connection.

  In the OSI over DCC solution, the Web LCT can access any NE by using the direct connection mode, that is, the Web LCT can consider any NE as the gateway NE. To improve the communication efficiency, there should not be a lot of NEs that are accessed in the direct connection mode in a network.