SDH Technology and MSTP Product Analysis

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 corresponding product R&D strategies, this is a hot research topic in the telecommunications field. Researchers from different manufacturers and technical backgrounds have different understandings and interpretations of it. Different telecom equipment manufacturers adopt different technical routes based on their respective understanding during product development, and different telecom operators also have different development strategies based on their respective network conditions, service scopes, and corporate development goals. In general, there are three different development directions for SDH technology, which respectively target the penetration and expansion of SDH technology into the high-end, mid-range, and low-end transmission markets in telecom networks.

    First, to provide support for the high-end market of transmission products, SDH technology is developing toward high capacity and high data rates along its existing route. In 2002, the standard for SDH at the <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />40G level was issued. 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 the research on the application of SDH technology in the metro network aggregation segment. The research focus of this direction is not to push SDH toward high capacity and high data rates, but rather to focus on metro network applications, integrating support for multiple services (mainly Ethernet services and ATM services) on the basis of SDH technology to achieve 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, and an increasing number of MSTP products have obtained telecom market network access certificates. There are also more and more successful engineering applications built with MSTP equipment.

    In addition, another development direction of SDH technology is to use 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 to implement access is one such solution, 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 to connect multiple nodes; and simplifying SDH overhead to streamline management and improve efficiency. Research in this direction has just begun, and there is no unified international standard yet, so its impact on the market is limited.

    All three development directions of SDH technology have achieved certain research results and have successful application cases. However, among them, 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, 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, and provides unified network management.

MSTP equipment has the following characteristics: 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; provides efficient link establishment capability; 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 established comprehensive 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 characteristics 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 of this MSTP product test include:

·         SDH System Functions and Performance

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

·         MSTP Support for Ethernet Services

    Including whether transparent transmission of Ethernet service data is supported, whether Ethernet Layer 2 switching functions are supported (support for VLAN, support for service priority, number of supported VLANs, etc.), whether Ethernet ring network functions are 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 containers), 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 transparent transmission of ATM cells is supported, whether statistical multiplexing of ATM service flows is supported, support for CAC, QoS guarantee capability, 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, whether automatic link bandwidth adjustment is supported (LCAS protocol or other proprietary protocols with similar functions), etc.

·         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 services or ATM services), supported protection methods, achieved protection switching time levels, and handling strategies when multiple levels of protection work simultaneously.

·         MSTP Equipment Networking Capability Test

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

·         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 billing management (support for port-based, link-based, service-based, and user-based methods and extraction of billing information), fault location and management, and bandwidth monitoring and management.

    The test results show that the mainstream MSTP products currently available in the domestic market are basically based on original SDH products, with Ethernet and ATM access and switching functions expanded to achieve access, processing, and transport of multiple services. Therefore, the test results for the SDH functions and performance of the participating products were all relatively good. However, there are significant differences in the support capabilities for Ethernet and ATM functions, especially in the Ethernet function part. Key factors for measuring the strength of Ethernet functions in MSTP products include: support for Ethernet Layer 2 switching functions, 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 function of individual products is still quite weak, and many functions need to be further supplemented. It can be considered that all manufacturers are in a stage of continuous improvement in Ethernet functions, and enriching Ethernet functions is a long-term goal of MSTP product R&D. As for ATM functions, since different manufacturers have different views on whether it is necessary to introduce ATM functions into MSTP, their support for ATM functions varies. Some manufacturers believe that 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 products integrate the technical characteristics of SDH 155M optical interfaces, enabling direct optical interface interconnection within SDH ring networks. This eliminates the need for media converter conversion nodes, effectively reducing network failure rates while significantly enhancing the capacity at network edges. Combined with our company's 128E1 cross-connect processing board, it achieves multi-service, high-capacity interconnection, reducing the overall network construction cost. In addition, we integrate voice, data, and video onto a single device for transmission without the need to introduce 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, the functions of MSTP products are gradually being improved under the pull of 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 development prospects of products depend on the speed at which they follow up on MSTP market demand.