I. Policy Implementation: The decommissioning of PCM equipment at substations has become a foregone conclusion.

In 2021, the State Grid Corporation of China’s headquarters issued to all provincial power companies the “Notice from the National Dispatch Center on Promoting the Application of New Technologies in Dispatch Telephony” (No. 16 [2021] of the Dispatch Communication Department), which explicitly mandated the decommissioning of existing PCM (Pulse Code Modulation) equipment and the accelerated implementation of new dispatch‑telephony technologies.

The implementation of this policy signifies that PCM equipment, which has been in operation at substations and within dispatch communication systems for more than two decades, is now being phased out across the power grid. In tendering processes and engineering practice for major power‑generation projects, “no longer using PCM equipment” has become a clear technical requirement. For example, in the Hebei North Regional Centralized Control Center project for new energy, the tender notice explicitly states that, in accordance with the Hebei North Company’s 14th Five‑Year Plan and Document No. 16 [2021] issued by the Dispatch and Communication Department, the grid operator will no longer deploy PCM equipment; all dispatch telephones must be connected via IAD (Integrated Access Device) interfaces.

Driven by robust policy support, power supply companies across the country have launched projects to replace PCM equipment and upgrade dispatch telephones to IP‑based systems, as substation communication networks undergo a profound transformation—from circuit‑switched architectures to IP‑based softswitching.

II. Why Phase Out PCM—Not Just a Policy Mandate, but a Practical Necessity

(1) Aging equipment, shortages of spare parts, and escalating operational risks

With the widespread adoption of softswitch and IMS technologies, telecom operators’ demand for PCM equipment has plummeted, prompting many traditional PCM equipment manufacturers to cease production. This has brought the PCM industry chain to the brink of collapse. Most mainstream PCM equipment brands are now grappling with production shutdowns, decommissioning, and service termination, while spare parts are in critically short supply, jeopardizing the long-term reliability of communication networks.

(2) Limited professional capabilities, unable to meet the demands of the new power system.

The PCM network primarily supports dispatch‑telephone services and a limited number of remote‑control and electricity‑metering applications. With its single‑purpose functionality, it lacks centralized monitoring, making fault diagnosis both complex and challenging. In contrast, the next‑generation power‑dispatch communication network must integrate multiple services, including dispatch telephony, video conferencing, and digital office applications; PCM equipment clearly can no longer meet these integrated requirements.

(3) Low network management efficiency and high resource consumption

Deploying trunk‑line telephones via PCM equipment consumes a large number of analog subscriber lines and makes fault diagnosis on remote substation analog telephone circuits particularly challenging. As the number of substations continues to grow year after year, the operational and maintenance costs and management complexity associated with the PCM model are steadily increasing.

(4) The macro-level impetus provided by the national policy on large-scale equipment upgrading

In the “Implementation Plan for Large-Scale Equipment Upgrading in Key Energy Sectors” issued by the national energy regulatory authority, it is explicitly stated that “advanced technologies shall be encouraged while outdated ones are phased out,” with the goal of increasing equipment investment in key energy sectors by more than 25% by 2027 compared to 2023. PCM equipment, as a typical example of obsolete telecommunications gear, is precisely a priority target for elimination in this round of large-scale equipment upgrades.

III. Alternative Pathways: Parallel Advancement of Two Major Technological Routes

Based on the practices of provincial power companies, PCM replacement has primarily advanced along two technical pathways:

Route 1: IAD + Data Communication Network Mode

This is currently the most widely adopted alternative approach. State Grid Hebei Electric Power has taken the lead in completing the full-scale switchover of PCM‑based services, marking the official decommissioning of the PCM network that had been in operation for over 20 years. As a result, power‑dispatch telephony has transitioned from PCM to a new architecture based on “IAD plus a data communications network,” significantly enhancing both the convenience of dispatch calls and operational‑maintenance efficiency.

The Bayannur Power Supply Company of Inner Mongolia Electric Power Group has replaced its PCM equipment with IAD devices. By adding IP user interface boards to the user slots of the dispatching stored‑program control (SPC) switch, it converts 64K circuit‑based voice signals into IP voice packets and interconnects the existing dispatching SPC switch with the transmission network via IP. At the station end, IAD devices are deployed to convert these IP voice packets back into analog voice signals, which are then transmitted over the network to the central office.

The Information and Communications Department of the Ordos Power Supply Company has, by adopting a more integrated and cost‑effective technical solution—namely, a “dispatching exchange service board plus integrated access equipment”—undertaken the upgrade of remote‑site dispatch telephone services at its 132 substations, thereby achieving a comprehensive transition of power‑dispatch telephony from analog to digital technology.

Route 2: Optoelectronic All-in-One Replacement Solution

The integrated optoelectronic device solution has also been explicitly designated by State Grid Corporation of China as one of the alternative options for PCM equipment. This solution offers the unique advantage of directly replacing existing PCM equipment: on the network side, it can seamlessly interface with standard STM‑N ports used in MSTP, ASON, and SDH systems, enabling the seamless integration of narrowband services with high‑bandwidth channels.

In its substation automation applications, Guangdong Power Grid of China Southern Power Grid extensively deploys RS‑232, FE, and E&M interfaces. Traditional PCM equipment, which supports only E1‑based communication, suffers from limited aggregation capacity and outdated technology. In contrast, integrated optoelectronic devices support SDH functionality while remaining compatible with PCM’s narrowband service interfaces, enabling a single central‑office unit to aggregate up to 300 services—thus effectively meeting the cross‑conversion requirements of comprehensive power‑automation services.

In practical engineering applications, in response to the shrinking market demand for PCM equipment at generation-side sites such as the Mengxi Wind Farm and the resulting shortage of spare parts, related upgrade projects have increasingly adopted integrated optoelectronic devices to implement remote number‑issuing functionality.

IV. Core Challenges and Responses in Engineering Practice

Based on engineering practices across various power supply companies, the replacement and upgrade of PCM systems is not merely a straightforward equipment swap; it is a system‑level project that entails a fundamental reshaping of the communication architecture. The following challenges are particularly critical:

V. SilverLink IAD Equipment Facilitates PCM Replacement in the Last Mile

In response to the urgent need to replace PCM equipment in power grids, Guangzhou Yinxun Comm.Tech.Co..Ltd., drawing on the technical heritage of the former Ministry of Posts and Telecommunications’ Factory 524, has launched a range of IADs and multi-service access devices suitable for IP-based upgrades of substations, providing power supply companies nationwide with secure, reliable, and seamless replacement solutions.

(1) ZMUX-4102: A Next-Generation Multi-Service IP-Based Access Platform

The ZMUX-4102 is an intelligent multi-service access and transmission device independently developed by Guangzhou YinXun, primarily designed to provide integrated access and transmission for voice, audio, data, and network services.

• Multi-service integration capability: It supports a wide range of service types, including FXO/FXS, 2‑wire/4‑wire E&M, asynchronous/synchronous RS‑232/RS‑422/RS‑485, 10/100BASE‑T, hotline telephony, V.35, and G.703 at 64 kbps, covering all business requirements such as substation dispatch telephony, automation data, and remote‑control signaling.
• Flexible networking options: It provides standard STM‑1/STM‑4 interface ports, enabling integration into SDH networks to form self‑healing SDH rings. It can also connect to carrier‑grade STM‑1/STM‑4 lines and supports a wide range of network topologies, including SDH ring, star, tree, point‑to‑point, and point‑to‑multipoint configurations. Fully compatible with diverse modernization requirements—from centralized to distributed architectures—this solution is particularly well suited for elastic access to substation MSTP dedicated lines and various IP backbone networks.
• High-reliability design: Optional dual‑power input with 1+1 protection, two main control cross‑connect boards with 1+1 redundancy, and real-time monitoring of the built-in power supply board, ensuring reliable operation of the dispatch telephone under extreme operating conditions.
• Remote Operations and Maintenance Capabilities: Optional network management functionality enables automatic loading of device configuration information and supports online software upgrades for both local and remote devices via the network management platform, facilitating centralized monitoring and remote management of all network devices.

(II) ZMUX Series Family: Scenario-Based Customization Solutions

In addition to the ZMUX‑4102, Guangzhou YinXun also offers the ZMUX series of IAD products, which cater to a variety of substation scenarios. The ZMUX‑3036 supports integrated access for voice, audio, data, and video services, multiplexing them onto 1 to 4 E1 channels, making it ideal for upgrading 110 kV substations with relatively low service‑access density. Products such as the ZMUX‑3038G feature a slot‑based modular design, allowing on‑demand selection of interface cards and delivering exceptional scalability. They are particularly well suited for municipal power supply companies undertaking simultaneous upgrades across dozens or even hundreds of substations, meeting the diverse service‑carrying requirements of each site.

With ZMUX‑series equipment, power utilities can rapidly deploy an IP‑based dispatch‑telephone architecture based on the “IAD + data communication network” model. By adding an IP user board to the central office’s dispatch switch, 64K‑bit‑per‑second voice circuits are converted into IP voice packets; meanwhile, ZMUX‑IAD series devices are deployed at the substation end to convert these IP voice packets back into analog voice signals, which are then routed to the dispatch telephone terminals—thus enabling a seamless transition from PCM to an all‑IP environment.

VI. Promoting the Intelligent Upgrade of the Communication Network through Guangzhou YinXun’s IAD Solution

As the construction of a new‑generation power system advances during the 15th Five‑Year Plan period, the IP‑based and intelligent upgrading of substation communication networks has become an irreversible trend. Large‑scale replacement and modernization of PCM equipment are being vigorously carried out across the country—whether it is State Grid Hebei Electric Power’s network‑cutting and migration at 231 substations of 110 kV and above, Bayannur Power Supply Company in Inner Mongolia’s system upgrades at 21 220 kV substations and 60 110 kV substations, or Wuhai Ultra‑High Voltage Power Supply Company’s completion of remote‑control number‑conversion projects at 11 500 kV substations—all these initiatives fully demonstrate the broad applicability and significant advantages of the “IAD + Data Communication Network” solution.

Currently, the period from 2026 to 2027 represents a critical phase for concentrated investment in grid‑equipment upgrades. During this window, Guangzhou YinXun Communication Technology Co., Ltd. offers its ZMUX series IAD devices and multi‑service access transmission solutions, which—thanks to their flexible networking, multi‑service convergence, high reliability, and remote operation and maintenance capabilities—can effectively help provincial grid companies successfully complete the “last mile” of PCM replacement and modernization.

For more detailed technical solutions or customized product support, please visit the official website of Guangzhou Yinxun Comm.Tech.Co..Ltd at www.gzyinxun.com or call the service hotline at 020-38288948.