Detailed MSTP protocol

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MSTP refers to a multi-service node that is based on the SDH platform and realizes the access, processing and transmission of multiple services such as TDM, ATM, and Ethernet at the same time, and provides a unified network management.

Multiple Spanning Tree (MST) uses a modified Rapid Spanning Tree (RSTP) protocol called Multiple Spanning Tree Protocol (MSTP).

With the development of the times, a variety of network transmission forms appear in network applications, such as file, video, image, and data transmission. As a result, the network capacity of a certain area cannot meet the needs of a large number of service transmissions. This makes the core technology of MSTP develop. It is a multi-service transmission platform based on the synchronous digital system.

It can provide nodes for various forms of network services and realize mutual transmission between platforms. And provide unified management to promote the normal operation of business.

The so-called platform is the extension of a certain local platform, which makes the transmission between platforms more smooth.

The core technology of MSTP is based on the establishment of a synchronous data system and the expansion of related services. In actual technical applications, this technology does not have a unified name for Xiangcheng, and there is no clear definition. It is mainly for information transmission according to the needs of various industries. The current status of MSTP's core technical characteristics and content development is consistent with related standards. .

working principle:

MSTP integrates multiple independent devices such as traditional SDH multiplexers, DXC, WDM terminals, network layer 2 switches, and lP edge routers into one network device, namely, a multi-service transport platform (MSTP) based on SDH technology. Control and management.

The SDH-based MSTP technology is most suitable as a converged node at the edge of the valve network to support hybrid services, especially hybrid services based on TDM services. The SDH-based multi-service platform can support packet data services more effectively and help realize the transition from a circuit-switched network to a packet network.

MSTP can realize the processing of multiple services, including PDH services, SDH services, ATM data services and IP, Ethernet services, etc. It can not only achieve fast transmission, but also meet the multi-service bearer, and more importantly, it can provide carrier-grade QoS capabilities.

MSTP technology is the result of multiple technical forms and integrations. It makes full use of the integrated applications of GFP (Generic Frame Protocol) data encapsulation, Virtual Concatenation mapping, RPR and other technologies. Through these forms of promotion, MSTP technology has a wide range of Bandwidth and the ability to adapt to bandwidth, while supporting more functions, covering ATM services, while effectively utilizing the network.

The corresponding characteristics are: the ability to support multiple services is effectively improved, and the fiber quality of the broadband access network is saved.

Through the improvement of its own business communication ability, the utilization rate of its bandwidth has been improved, and it is developing towards the transport network; in the process of MSTP technology application, the bandwidth utilization rate of ATM has been greatly improved, so that its coverage Corresponding expansion and rapid expansion, effectively reducing the cost of expansion, and reducing the cost of the access network.

MSTP multi-process:

         MSTP multi-process is an enhanced technology based on the MSTP protocol. This technology can bind the ports on the two-layer switching device to different processes, and perform MSTP protocol calculation in the unit of process. Ports that are not in the same process do not participate in the MSTP protocol calculation in this process, thereby realizing each process The spanning tree calculations are independent of each other and do not affect each other.

The multi-process mechanism is not limited to the MSTP protocol, but also applies to RSTP and STP protocols.


1. Greatly improve the deployability of spanning tree protocol under different networking conditions.

In order to ensure the reliable operation of networks running different types of spanning tree protocols, different types of spanning tree protocols can be divided into different processes, and the networks corresponding to different processes perform independent spanning tree protocol calculations.

2. Enhance the reliability of the networking. For a large number of Layer 2 access devices, it can reduce the impact of a single device failure on the entire network.

Different topology calculations are isolated through processes, that is, a device failure only affects the topology corresponding to the process where it is located, and does not affect the topology calculations of other processes.

3. When the network is expanded, the amount of maintenance by the network manager can be reduced, thereby improving the convenience of user operation and maintenance management.

When the network is expanded, only a new process needs to be divided to connect to the original network, and the MSTP process configuration of the original network does not need to be adjusted. If the device is expanded in a certain process, you only need to modify the expansion process at this time, without adjusting the configuration in other processes.

4. Realize the split management of Layer 2 ports

Each MSTP process can manage some ports on the device, that is, the Layer 2 port resources of the device are divided and managed by multiple MSTP processes, and each MSTP process can run standard MSTP.

Defects of STP/RSTP:

RSTP has been improved on the basis of STP to achieve rapid convergence of the network topology.

However, RSTP and STP still have the same flaw: because all VLANs in the LAN share a spanning tree, it is impossible to achieve load balancing of data traffic between VLANs, and the link will not carry any traffic after being blocked, and it may cause some VLAN packets cannot be forwarded.

MSTP's improvements to STP and RSTP:

In order to make up for the shortcomings of STP and RSTP, the 802.1S standard released by IEEE in 2002 defines MSTP.

MSTP is compatible with STP and RSTP, can converge quickly, and provides multiple redundant paths for data forwarding, and achieves load balancing of VLAN data during data forwarding.

MSTP divides a switching network into multiple domains. In each domain, multiple spanning trees are formed, and the spanning trees are independent of each other.

Each spanning tree is called a Multiple Spanning Tree Instance (MSTI), and each domain is called an MST Region (MST Region: Multiple Spanning Tree Region).

The so-called spanning tree instance is a collection of multiple VLANs. By bundling multiple VLANs into one instance, communication overhead and resource occupancy can be saved.

The calculation of the topology of each instance of MSTP is independent of each other, and load balancing can be achieved on these instances. Multiple VLANs with the same topology can be mapped to an instance. The forwarding status of these VLANs on the port depends on the status of the port in the corresponding MSTP instance.

Shortcomings of MSTP:

1. MSTP technology uses the SDH virtual container to transmit Ethernet signals. Since the bandwidth of the SDH virtual container is constant, the bandwidth of the MSTP transmission of Ethernet services should be an integer multiple of the virtual container. Therefore, MSTP has poor bandwidth adjustment capabilities, and the bandwidth utilization rate is not high when carrying data services.

2. The QoS capability of MSTP technology is weak.

3. The OAM capability is not strong when transmitting Ethernet services.

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