IDM-CH120NET PDH Optical Multiplexer

The IDM-CH120NET PDH optical multiplexer is a 4-channel E1 plus Fast Ethernet PDH optical multiplexer developed by Beijing Ruiguang Jiyuan Digital Technology Co., Ltd. (Raytrans). Designed with large-scale integrated circuits, it multiplexes 4 transparent E1 circuits and 2 line-rate 100M Ethernet channels onto a single 155Mbps optical path for transmission, making it a typical multi-service optical multiplexer product.

The unit is housed in a 19-inch 1U chassis with dual hot-standby power supplies and optional dual-optical-port redundancy. Service interfaces and operating alarms are concentrated on the panel, facilitating product showcase and routine O&M. The devices are used in pairs: one end accesses the existing services at the site and converts them into optical signals, while the other end restores the corresponding E1 and RJ-45 Ethernet interfaces, with only one optical fiber link required between the two points. As a professional optical multiplexer manufacturer, Raytrans PDH optical multiplexers can be widely used in scenarios such as government private network optical fiber communication solutions and military emergency communications vehicle solutions.

Key specifications at a glance: 155M/20km · 4-channel E1 + 2-channel Fast Ethernet · dual hot-standby power supplies · dual-optical-port redundancy · ITU-T G.703 (75 Ω/120 Ω) · overall power consumption ≤40 W

What Is a 4-Channel E1 Plus Fast Ethernet PDH Optical Multiplexer

The 4-channel E1 plus Fast Ethernet PDH optical multiplexer places two types of service interfaces in the same chassis: the E1 side provides 4 transparent 2.048Mbps channels compliant with ITU-T G.703, and the Ethernet side provides 2 adaptive 10M/100M RJ-45 interfaces, with both service types multiplexed onto the same 155Mbps optical path. As a typical product showcase PDH optical multiplexer, it carries both TDM and IP services on a single platform.

The E1 channels do not parse or alter the time slot content; services are delivered from one end to the other as-is, so digital trunks, PCM multiplexers and dispatching equipment can be connected without modification. The Ethernet channels transmit and receive in accordance with IEEE 802.3, support full-duplex, half-duplex and adaptive operating modes, and VLAN partitioning between ports.

Figure 1: Front view of the IDM-CH120NET PDH optical multiplexer, showing the layout of service interfaces and operating alarm indicator LEDs

In terms of deployment form, the 4-channel E1 plus Fast Ethernet PDH optical multiplexer is a point-to-point device, configured in pairs at the central office and remote end. The site side no longer needs a separate E1 optical multiplexer and a media converter for E1 services and IP services respectively, so the number of devices, power supply modules and cables in the cabinet is reduced accordingly. For multi-service optical multiplexer scenarios requiring integrated access, this approach of handling two service types with one device also reduces equipment stacking in the cabinet.

What Functions and Interfaces Does the IDM-CH120NET Provide

The IDM-CH120NET covers four categories of functions—E1 access, optical transmission, Ethernet multiplexing and redundancy protection—with seven capabilities in total, whose specific roles and applicable conditions are listed in the table below. During selection and acceptance, check each item against the on-site service list to confirm that the number of access channels, interface type and redundancy configuration match actual requirements.

Figure 2: Rear panel of the IDM-CH120NET PDH optical multiplexer, showing the layout of 4 E1 interfaces, 2 100M Ethernet ports and dual power supply modules

The value of the three differentiated capabilities is set out in one table from three perspectives: power and optical path redundancy, fiber and device count, and fault location. During quotation and selection discussions, compare row by row against on-site pain points; any row that does not match indicates that the corresponding capability is not essential for the project.

Key Specifications: Optical Interface, E1 and Ethernet Parameters

The specifications of the optical interface and service interfaces determine whether a link can be established. On the optical side, link margin must be calculated based on transmit optical power, receiver sensitivity and transmission distance; on the electrical side, compatibility with the opposite end must be checked based on impedance and frame structure. The parameters in the table below follow the optical multiplexer manufacturer's product documentation.

Power supply, power consumption and installation conditions determine whether a site can be put into operation: dual power supplies require the site to have two available power feeds, and the two feeds should be taken from independent of one another power sources, so that the loss of one power feed does not render the backup meaningless; the chassis dimensions must match the free space in the cabinet, and the equipment room temperature and humidity must fall within the permitted range of the equipment. In long-term high temperature or condensation environments, ventilation conditions need to be improved first.

How dual hot-standby power supplies and dual optical port redundancy keep services running through power failure and fiber break

Keeping services running through power failure and fiber break follows two paths: on the power supply side, dual power supplies are in mutual hot standby; on the optical path side, optional dual optical port redundancy is used. Both mechanisms are implemented inside the equipment and require no on-site intervention. Once the single points on the power supply and optical path sides are each covered, the site has a corresponding takeover means for both types of risk: power supply interruption and fiber interruption.

Dual hot-standby power supplies mean that two power feeds are connected at the same time and back each other up. When either feed loses power, the other continues to supply power through the equipment, so site services do not stop due to the interruption of a single power feed. The power supply format is selected between AC220V and DC-48V according to site conditions: AC is taken from the station's utility power and DC from the communication power supply, and the two formats can be configured separately for each site.

Dual optical port redundancy is an optional capability: with dual optical ports configured, forced switchover or automatic protection switching is supported. During planned inspection, forced switchover is used to move services to a designated optical port; when a fiber is unexpectedly interrupted, automatic protection switching moves services to the standby optical port. The switchover mode and switching time are subject to the manufacturer's technical documentation and commercial confirmation, and a switchover drill is recommended before the equipment is formally put into operation. This capability is particularly important in government private network optical fiber communication solutions, where private network links have high continuity requirements; the combination of dual power supplies and dual optical ports can effectively reduce the risk of service interruption caused by a single point of failure. In military emergency communications vehicle solutions, vehicle-mounted power supply and field optical cable conditions are relatively variable, and hot standby and optical port redundancy likewise provide a layer of assurance for emergency services.

How 4 groups of E1 and 2 groups of VLAN Fast Ethernet are multiplexed over the same fiber, saving fiber and equipment

The calculation for same-fiber multiplexing is straightforward: each group of E1 occupies 2.048Mbps, so 4 groups of E1 total about 8.2Mbps, and the 2 Ethernet groups share the 100M wire-speed bandwidth on the optical path. The two service types together remain within the 155Mbps optical port capacity, so they can travel over the same optical path.

The two Ethernet interfaces can be divided into VLANs to carry different service domains such as surveillance, office and production separately, so that broadcast and abnormal traffic in one service domain do not spread to another. Shared line-rate means the bandwidth on the optical path side is used jointly by the two interfaces, with the ports isolated by VLAN partitioning; allocation is made according to actual traffic during planning.

The value of saving fiber and equipment lies in two places: on the line side, a single fiber link carries all services, so old lines with scarce fiber cores do not need capacity expansion; on the equipment side, one unit handles both E1 transparent transmission and Ethernet receive/transmit, so the site no longer stacks a 4-channel E1 optical multiplexer plus a media converter by service type, and spare parts and wiring are simplified accordingly. Taking IDM-CH120NET from Raytrans as an example, this type of PDH optical multiplexer can serve as a node device for mixed E1 and Ethernet access in both government private network optical fiber communication solutions and military emergency communications vehicle solutions; the specific selection can be confirmed in combination with the optical multiplexer manufacturer's product documentation and the on-site service list.

How E1 tributary loopback and local/remote-end alarms locate remote-end failures

The role of E1 tributary loopback is to build the test loop on the equipment side, so that O&M personnel can determine locally whether the failure lies in the equipment, the optical path or the opposite end, without first making a trip to the remote station. For unattended sites distributed along the line, this capability directly determines whether troubleshooting is completed the same day or the next day.

Local/opposite-end alarm monitoring provides dual-end indications: when the optical path is interrupted or an E1 channel is abnormal, both the local end and the opposite end show corresponding indications, and the difference between the two ends is itself the basis for determining the faulty section. A single-end alarm only indicates that the local end receives no signal; only by comparing both ends can the problem be narrowed down to the device side, the optical cable side, or the opposite-end device side.

On-site troubleshooting proceeds in three steps—alarms, loopback, and optical power—and the observation at each step directly determines the next action, so O&M personnel do not have to rely on guesswork, and conclusions can be readily shared with remote duty personnel, reducing the time spent on back-and-forth confirmation between the two ends. Proceed in the following order:

• First check the alarm indications of the optical ports and E1 tributaries at both ends to confirm whether the abnormality lies on the optical path side or the E1 interface side;

• Perform an E1 tributary loopback at the local end; if the local loopback is normal but the opposite end is unreachable, the problem is most likely on the optical path or at the opposite-end device;

• Check whether the transmit optical power of the optical module (-2 to -11 dBm) and the received optical power meet the sensitivity requirement of better than -36 dBm;

• Use the alarm records at the opposite end to narrow the fault down to a single station or a single segment, then decide whether to dispatch personnel to the site.

Typical Application Scenarios

Electric Power Private Network: E1 Telecontrol Channels and IP Data Backhaul Between Substations and Dispatch Centers

Telecontrol data, protection signals, and in-station IP services between substations, switching stations, and dispatch centers usually belong to different channels. The IDM-CH120NET PDH optical multiplexer accesses 4 groups of E1 services and 2 groups of Ethernet services separately within the station and transmits them over one optical fiber link to the centralized control station; the E1 channels retain the original 2.048 Mbps interface format, so the existing PCM and telecontrol equipment in the station need not be replaced.

Power sites are mostly unattended, and power is supplied at DC-48 V according to the in-station communication power supply configuration; dual hot-standby power supplies keep services online when one power feed fails. When the optical cable is damaged by road construction or severe weather, the optional dual optical port redundancy provides a backup optical path, and the alarm indications at both ends help quickly locate the affected section.

Figure 3: Schematic of point-to-point networking of E1 and Ethernet services between electric power and rail transit sites using the IDM-CH120NET PDH optical multiplexer

Rail Transit Communication: Service Channel Extension for Stations Along the Line, Section Equipment Rooms, and Depots

Sites along a rail transit line are distributed and far apart, and dedicated telephone, public address, and monitoring data need to be transmitted between stations and section equipment rooms, where only limited fiber cores and rack positions are often available. The IDM-CH120NET PDH optical multiplexer is a 19-inch 1U chassis that can be installed in standard cabinets along the line; 4 groups of E1 and 2 groups of Ethernet are transmitted over the same fiber, so the space and number of cables occupied at the site side are relatively small.

Power supply formats at sites along the line are not uniform; AC and DC power supply modes can be configured per station, reducing the variety of spare parts. The chassis has an operating temperature range of 0 °C to 50 °C, making it suitable for communications equipment rooms and equipment cabinets with ventilation, and convenient for installation in the same cabinet as other transmission devices.

Military and Government Private Networks: Service Access for Unattended Sites and Temporary Command Posts

Sites of military and government private networks are often located in remote areas with limited duty conditions, placing concentrated demands on service continuity and on-site maintainability. The IDM-CH120NET PDH optical multiplexer complements power-side redundancy with dual hot-standby power supplies and performs fault diagnosis locally through E1 tributary loopback and local/opposite-end alarms, reducing the number of site visits.

Temporary command posts or mobile sites usually require rapid commissioning; once the devices are configured as a pair and connected to the optical fiber, the E1 and Ethernet interfaces are restored without changing the configuration of the opposite-end device. The point-to-point channel structure makes link relationships clear and facilitates temporary adjustment of node positions according to the mission.

Selection and Deployment

Selection starts with counting channels: the number of E1 service channels determines which model to choose, while the Ethernet service volume and segmentation requirements determine whether ports should be planned by VLAN. The three models have the same Ethernet configuration—2 groups of 100M interfaces—and differ in the number of E1 channels and the corresponding site service scale; simply configure one level up from the confirmed number of channels, without leaving excessive margin based on peak estimates.

Deployment proceeds in five steps, from optical path calculation and interface setup to power supply access, redundancy configuration, and service commissioning; each step has a verifiable checkpoint, and on site each step is completed before proceeding to the next, avoiding rework after the unit is fully installed due to mismatched link margin or interface impedance.

1. Check the optical path: use standard optical modules for single-mode distances within 20 km, and optional long-distance optical modules for greater distances; calculate the link margin according to a transmit optical power of -2 to -11 dBm and a sensitivity better than -36 dBm.

2. Set the interfaces: for E1, select 75 Ω coaxial or 120 Ω balanced wiring according to the opposite-end device; the Ethernet ports are 10M/100M adaptive, and VLANs are divided by service domain.

3. Connect power: the dual power supplies are taken from two independent power sources, with AC 220 V and DC -48 V configured according to site conditions; after connection, verify that services remain normal when either feed fails.

4. Configure redundancy: when dual optical ports are required, set forced switchover or automatic protection switching, and perform a switchover drill to confirm that services are uninterrupted.

5. Commission services: verify each channel one by one using E1 tributary loopback, and check the local/opposite-end alarm indications before putting the system into formal operation.

Conclusion

The 4-channel E1 Fast Ethernet PDH optical multiplexer combines E1 transparent transmission and Fast Ethernet multiplexing in a single 19-inch 1U device, completing backhaul of two types of services between sites over one optical fiber link; dual hot-standby power supplies and optional dual optical port redundancy address the two single points of failure in power supply and optical path.

The IDM-CH120NET PDH optical multiplexer is suitable for site access in electric power private networks, rail transit communication, and military and government private networks; E1 tributary loopback and local/opposite-end alarms allow remote faults to be diagnosed locally, and the CH240NET and CH480NET in the same series extend the configuration according to the number of E1 channels.

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