The HWECC protocol stack is a proprietary protocol stack of Huawei. It is the most applicable and advanced ECC communication solution for Huawei transmission devices. The HWECC protocol stack identifies NEs by IDs and creates routes automatically, which is easy to use.
Architecture of the HWECC Protocol Stack
ITU-T G.784 defines the architecture of the ECC protocol stack based on the OSI seven-layer reference model. The HWECC protocol stack is based on the ECC protocol stack.
The HWECC protocol consists of four layers: physical layer, media access layer, network layer, and transmission layer which correspond to the physical layer, link layer, network layer, and transport layer in the OSI model.
Physical layer
- Receives and sends data over the physical channels, including receiving data from physical channels and transferring the data to the upper layer.
- Receives the data frames transferred from the upper layer and sends them to physical channels.
The channels at the physical layer include DCC/GCC channels and extended ECC channels. DCC/GCC channels are mainly transmitted over OSC or ESC channels. Extended ECC channels are transmitted over Ethernet channels.
Media access layer
The media access layer is also called the medium access control (MAC) layer. The main function of the MAC layer is to activate or close physical DCCs/GCCs between the physical layer and the network layer. The MAC layer shields the diversity of the physical networks and provides the uniform service upwards (point-to-point physical channel). The MAC layer performs the following functions:
- Establishes and maintains the MAC connection between adjacent NEs. When there is a reachable physical channel between two adjacent NEs, the MAC layer establishes a MAC connection between the NEs. Each MAC connection includes the address of the opposite NE, the ID of the physical channel, the connection timer, and other information.
Provides the data communication service:
- The MAC layer receives the data frame transferred from the physical layer. If the destination address is the local station, the MAC layer transfers the data frame to the network layer. Otherwise, the MAC layer discards the data frame.
- The MAC layer sends the data frame from the network layer. If the destination address of the data frame has a MAC connection, the MAC layer sends the data frame to the corresponding physical channel in the physical layer through the MAC connection. Otherwise, the MAC layer discards the data frame.
Network layer
The main function of the network layer is to provide the route addressing for data frames and the route management for the ECC communication network. The network layer performs the following functions:
- Establishes and maintains ECC route item.
Each site periodically broadcasts its routing table to the adjacent sites using a routing response message. When receiving the routing response message, the adjacent sites update their routing tables. Each routing item includes the following information: address of the destination NE, address of the transfer NE, transfer distance, route priority, and mode.
Each site maintains routes using the distance vector algorithm. Using this algorithm, each site regularly broadcasts its routing table. For example, when site A receives a data packet from its adjacent site B, it compares the routes to all other sites in its routing table with the received routes. If some received routes are not contained in its routing table, site A adds them; if an existing route in its routing table has the same source and sink as a received route but is longer than the received route, then site A replaces the existing route with the received route. This algorithm is easy to implement but results in large amount of data. When the algorithm is used for a large-scale network, route convergence is slow and special means must be used to prevent route loops.
- Provides the data communication service:
The network layer receives the packet transferred from the MAC layer. If the destination address of the packet is the local station, the network layer transfers the packet to the transport layer. Otherwise, the network layer requests the MAC layer to transfer the packet to the transfer station according to the route item that matches the destination address in the network layer routing table.
The network layer sends the packet from the transport layer. The network layer requests the MAC layer to transfer the packet to the transfer station according to the route item that matches the destination address of the packet in the network layer routing table.
- Forwards data.
In the HWECC solution, when an NE finds that the network-layer destination address is not the NE itself, the network layer of the NE forwards the data.
Transport layer
The main function of the transport layer (L4 layer) is to provide the end-to-end communication service for the upper layer. As the communication between the OptiX equipment and the Web LCT is controlled by the end-to-end connection-oriented service in the application layer, the L4 layer provides only the end-to-end connectionless communication service, that is, transparent data transfer service.
NOTE: In the HWECC protocol stack, the NE address used by each layer is the ID of the NE. An NE ID consists of 32 binary bits. The 8 most significant bits are reserved for future use. The 8 second significant bits represent the extended NE ID (also called subnet ID). The 16 least significant bits represent the basic ID of the NE. For example, if the NE ID is 0x00090001, the extended ID is 9 and the basic ID is 1.