What are the features of SDH technology and MSTP products?

SDH Technology and MSTP Product Analysis

I. Development Directions of Next-Generation SDH Technology and Products<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

    Regarding the development direction of next-generation SDH technology and the R&D strategies for corresponding products, this is a research hotspot in the telecommunications field. Researchers from different manufacturers and technical backgrounds hold different understandings and interpretations. Different telecom equipment manufacturers adopt different technical routes in product R&D based on their respective understanding, and different telecom operators also have different development strategies based on their network conditions, service scopes, and corporate development goals. In summary, SDH technology has three distinct development directions, each targeting the penetration and expansion of SDH technology into the high-end, mid-range, and low-end transmission markets within telecom networks.

    First, to support the high-end market for transmission products, SDH technology is developing toward higher capacity and higher rates along its established path. In 2002, the standard for SDH at the <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />40G level was released. Although this technology will face competition from WDM technology in engineering applications, its application prospects remain quite optimistic. Since the new standard has just been issued, engineering application cases are still rare, and corresponding testing and maintenance methods are not yet fully developed. However, it is believed that telecom equipment manufacturers will follow up on this direction quickly.

    Second, another development direction of SDH technology is research on the application of SDH in the metro network aggregation segment. The focus of this direction is not to push SDH toward higher capacity and rates, but rather, based on metro network applications, to integrate support for multiple services (mainly Ethernet and ATM services) on top of SDH technology, thereby achieving aggregation of metro network services. This is the MSTP technology. Due to its many outstanding advantages, it has received widespread attention. R&D projects for MSTP equipment have been launched one after another, an increasing number of MSTP products have obtained telecom market access certificates, and more and more successful engineering applications have been built using MSTP equipment.

    Additionally, another development direction of SDH technology is the use of simplified SDH technology to implement metro network access functions. Currently, access technologies in metro networks are in a period of intense competition, with various technologies emerging. Using appropriately simplified SDH technology for access is one such approach, generally referred to as SDH LITE. The simplification of SDH technology in SDH LITE mainly includes the following aspects: replacing dual fibers with a single fiber to reduce cost; correspondingly changing the dual ring into a single ring or linear topology connecting multiple nodes; and simplifying SDH overhead to streamline management and improve efficiency. Research in this direction is just beginning, and no unified international standard exists yet, so its impact on the market remains limited.

    All three development directions of SDH technology have achieved certain research results and have successful application cases. However, the development of MSTP technology and the R&D of MSTP equipment are the hotspots in SDH technology research and engineering applications.

II. Current Testing Status of Mainstream MSTP Equipment in China

    Generally speaking, MSTP refers to a multi-service node based on the SDH platform that simultaneously implements the access, processing, and transport of multiple services such as TDM, ATM, and Ethernet, while providing unified network management.

    MSTP equipment has the following features: it inherits many advantages of SDH technology; supports multiple physical interfaces; supports multiple protocols; supports multiple optical fiber transmission modes; provides integrated digital cross-connect switching; supports dynamic bandwidth allocation; enables efficient link establishment; separates protocols from interfaces; and provides comprehensive network management functions.

    SDH-based multi-service transport nodes differ significantly from traditional SDH systems in terms of functionality and structure. Currently, ITU-T and other international standardization organizations have not yet issued complete recommendations and standards related to SDH-based multi-service transport nodes. However, the Ministry of Information Industry, taking into account the specific characteristics of China's transport networks, operators' application requirements for SDH-based multi-service transport nodes, and the technical features of current products from various equipment manufacturers, has formulated the relevant telecommunications industry recommended technical standard YD/T 1238-2002 "Technical Requirements for SDH-based Multi-service Transport Nodes."

    From October to December 2002, the Telecommunications Research Institute of the Ministry of Information Industry conducted a baseline test on the mainstream MSTP products of seven well-known domestic and international telecom equipment manufacturers. The key test points for this MSTP product test included:

·            SDH System Functions and Performance

    Including test focuses on the equipment's high-order and low-order cross-connect capabilities, VC concatenation capability (whether virtual concatenation is supported, maximum number of concatenated channels), VC channel bit error and delay characteristics, and support for SDH overhead bytes.

·            MSTP Support for Ethernet Services

    Including whether Ethernet service data transparent transmission is supported, whether Layer 2 Ethernet switching is supported (support for VLAN, support for service priority, number of supported VLANs, etc.), whether Ethernet ring functionality is supported, the encapsulation and frame alignment methods before mapping Ethernet frames or IP packets into SDH frames (PPP, LAPS, GFP), the mapping methods of Ethernet frames or IP packets into SDH frames (types of virtual containers used, concatenation mode and number of concatenated channels), and protection methods at the Ethernet service layer (selection of STP, RSTP, or other protocols, achieved protection switching time levels), among other test focuses.

·            MSTP Support for ATM Services

    Including whether ATM cell transparent transmission is supported, whether statistical multiplexing of ATM service flows is supported, support for CAC, QoS guarantee capabilities, and protection methods adopted at the ATM service layer, among other test focuses.

·            Rapid Service Provisioning Capability

    Mainly testing whether end-to-end automatic link configuration is supported.

·            Service Bandwidth Management Functions

    Test focuses include bandwidth allocation granularity and whether automatic link bandwidth adjustment is supported (LCAS protocol or other proprietary protocols with similar functions).

·            Self-Healing and Recovery Capability of Networks Composed of MSTP Equipment

    Test focuses include supported protection levels (protection based on the SDH layer, protection based on Ethernet or ATM services), supported protection modes, achieved protection switching time levels, and handling strategies when multiple protection levels operate simultaneously.

·            MSTP Equipment Networking Capability Test

    Including supported topology structures (ring, linear, mesh, star, etc.) and roles in the network (HUB, ADM modes, etc.).

·            Timing and Synchronization Performance of MSTP Equipment and Networks

    Test focuses include supported synchronization modes, clock accuracy testing, TIE and MTIE values, support for clock switching modes, and switching performance.

·            MSTP Network Management Functions

    Test focuses include accounting management (support for port-based, link-based, service-based, and user-based methods and extraction of accounting information), fault location and management, and bandwidth monitoring and management.

    The test results show that the mainstream MSTP products currently available on the domestic market are basically based on existing SDH products, with Ethernet and ATM access and switching functions expanded to achieve access, processing, and transport of multiple services. Therefore, the SDH function and performance test results of the participating products were all relatively good. However, there are significant differences in the support capabilities for Ethernet and ATM functions, particularly in the Ethernet function area. Key factors for measuring the strength of Ethernet functions in MSTP products include: support for Layer 2 Ethernet switching, mapping methods of Ethernet frames into SDH frames, types and numbers of virtual container concatenation supported by Ethernet interfaces, and Ethernet service protection capabilities. Considering these factors, the Ethernet functions of some individual products remain quite weak, and many functions still need to be supplemented. It can be concluded that all manufacturers are in a stage of continuous improvement regarding Ethernet functions, and enriching Ethernet functions is a long-term goal of MSTP product R&D. As for ATM functions, due to different understandings among manufacturers on whether introducing ATM functions into MSTP is necessary, the support for ATM functions varies. Some manufacturers believe ATM functions are a key focus for future R&D, while others have not committed to providing ATM functions in subsequent versions.

    From the perspective of MSTP engineering applications, all participating MSTP products have been applied in engineering projects and have achieved good application results, with broad market prospects.

·            Features of Our Company's MSTP

    Our company's independently developed MSTP product integrates the technical features of SDH 155M optical interfaces, enabling direct optical interface interconnection within SDH ring networks. This eliminates the need for optical terminal conversion nodes, effectively reducing network failure rates while greatly enhancing the capacity at the network edge. Combined with our company's 128E1 cross-connect processing board, it achieves high-capacity interconnection of multiple services, reducing overall network construction costs. Additionally, we integrate voice, data, and video transmission into a single device without requiring additional equipment, facilitating network maintenance and management.

III. Conclusion

    Overall, on the one hand, there is significant market demand for MSTP products; on the other hand, MSTP product functions are gradually improving driven by market demand. In the coming period, MSTP products in the Chinese market will be in a stage of flourishing competition, with various MSTP products having certain market space. However, it should also be recognized that this is a critical period for MSTP product development, and the prospects of products depend on the speed with which they keep pace with MSTP market demand.