IDM GP2400-30E Telephone Optical Multiplexer

The IDM GP2400-30E ultra-broadband integrated service optical multiplexing equipment is a 30-channel telephone, 4-group isolated Fast Ethernet optical multiplexer developed by optical multiplexer manufacturer Beijing Ruiguang Jiyuan Digital Technology Co., Ltd. It is used to aggregate 30 telephone channels and 4 groups of physically isolated Ethernet services into a single 2.5Gbps optical fiber link, and is a multi-service optical multiplexer product for multi-service access scenarios.

On the site side of electric power, rail transit, and military and government private networks, dispatch telephones and data channels usually coexist, and deploying multiple single-function devices separately increases cabinet space usage and points of failure. Using a pair of optical multiplexers to combine the two service types onto one optical fiber allows both site-side cabling and central-side access to follow existing practices, with no need to change the configuration of upper-level switching equipment during commissioning. This approach also applies to the transmission layer design in government private network optical fiber communication solutions and military emergency communications vehicle solutions.

The equipment uses the 2.5G optical fiber transmission bandwidth and adopts the PCM30/31 format. Telephone interfaces can be configured as 30 FXO, FXS, or magneto channels, and the Ethernet side provides 4 groups of physically isolated line-rate 100M (400M in total). Dual-fiber mutual backup and dual power input are both provided; when a single link or power feed fails, services continue to be carried over the other path, and the site does not need dedicated duty staff for the transmission equipment. As a representative model among telephone optical multiplexers and multi-service optical multiplexers, Raytrans presents the above interface configuration and protection mechanisms in full in its product showcase.

Key Specifications at a Glance: Optical fiber rate 2.5Gbps · SFP optical port (single-mode, multimode optional) · Wavelength 1310nm/1550nm · Receiver sensitivity better than -24dBm · 30 telephone channels (FXO/FXS/magneto) · 4 groups of physically isolated line-rate 100M (400M in total) · Power supply DC-48V/AC220V dual power supply · Overall power consumption ≤100W

What Is a 30-Channel Telephone, 4-Group Isolated Fast Ethernet Optical Multiplexer

A 30-channel telephone, 4-group isolated Fast Ethernet optical multiplexer is a transmission device that multiplexes telephone voice channels and multiple groups of Ethernet services onto a single optical fiber channel, used in pairs at both ends. One end arranges 30 analog voice channels into the 2.5Gbps optical path according to the PCM frame structure and encapsulates the 4 groups of Ethernet services into independent channels; the other end demultiplexes them and restores the voice channels and 4 isolated Ethernet ports for connection to existing dispatching exchanges, telephones, and data devices. As a multi-service optical multiplexer for private network scenarios, the device carries Ethernet and E1 services in addition to telephone access, which is a typical multi-service optical multiplexer product form.

The PCM30/31 format means that 30 64Kbps voice channel time slots are arranged in a primary group frame, with the remaining time slots used for synchronization and signaling. Voice channels are compressed according to ITU G.711 A-law, with an audio range of 300Hz~3400Hz and a loop current of 25mA per channel.

The E1 side has a bit rate of 2048Kbps and HDB3 line coding, complies with ITU-T G.703, offers selectable 75Ω/120Ω impedance, and uses PCM30/31 transparent transmission for the frame structure without changing the time slot allocation of the peer device. Existing PCM equipment, dispatching exchanges, and relay protection devices at the peer end do not need configuration changes; service cutover only needs to follow the original time slot table.

The telephone interface type depends on the peer device type. Select and configure the following three interfaces on site according to the actual telephones and switching equipment. The three interfaces have different electrical characteristics; incorrect connection usually manifests as no feeding, no ringing, or no sound after going off-hook. Confirm the peer device type clearly before commissioning.

• The FXS interface feeds power to the telephone and provides ringing current, so ordinary automatic telephones can be connected directly;
• The FXO interface emulates a subscriber line circuit and connects to the outside line side of an SPC exchange or dispatch console;
• The magneto interface connects to magneto telephones; ringing is generated by hand-cranking the telephone, and call feeding is provided by the interface.

The three interface types can be combined on the same device by channel count, with the total not exceeding 30 channels. Confirm mixed configurations with the optical multiplexer manufacturer before ordering; interfaces are configured at the factory, and no on-site board modification is required. Telephone-side cabling follows the existing wiring sequence of telephones and exchanges; during cutover, check off-hook, ringing, and conversation channel by channel. The interface configuration flexibility of this telephone optical multiplexer is one of its core selling points for dispatch communication scenarios in the product showcase.

Figure 1: Front view of the IDM GP2400-30E unit, layout of 30 telephone interfaces and operating alarm indicator LEDs

What Services Can One Device Carry

The IDM GP2400-30E provides five capabilities in one device: optical fiber transmission, 30-channel telephone access, isolated Ethernet, E1 channel transparent transmission, and dual power supply, replacing the telephone optical multiplexer and data uplink equipment previously deployed separately. The function items and corresponding interface standards are listed in the table below for item-by-item verification against existing on-site equipment.

Function	Description
2.5Gbps optical fiber transmission	SFP optical port, optical fiber rate 2.5Gbps, single-mode (multimode optional), wavelength 1310nm/1550nm; one optical fiber carries both telephone and Ethernet services
30-channel telephone access	Provides 30 telephone interfaces, configurable as FXO, FXS, or magneto; audio 300Hz~3400Hz, ITU G.711 A-law compression, loop current 25mA per channel
4 groups of physically isolated Ethernet	4 groups of line-rate 100M Ethernet ports, 400M bandwidth in total; each group is independently encapsulated and forwarded, and abnormal traffic on one group does not affect the other channels
E1 channel transparent transmission	Bit rate 2048Kbps, HDB3 line coding, compliant with ITU-T G.703, impedance 75Ω/120Ω, PCM30/31 frame structure; transparent transmission does not change time slot content
Dual-fiber mutual backup	Two optical fiber links are deployed in pairs; when the primary link has a fiber break or received optical power degradation, services switch to the backup link, maintaining both voice and data
Dual power input	Supports DC-48V and AC220V dual power supply access, with the two feeds drawn from different distribution circuits; when one feed fails, the other continues to supply power
Alarm indication	The chassis provides a function control switch and operating and alarm indications; on-site staff can judge optical path and power status from the indicator LEDs

In the table, E1 transparent transmission and telephone services travel over the same 2.5Gbps optical path, and their time slots do not occupy each other. On site, connect the E1 port and telephone port of the dispatching exchange to the two ends of the device respectively; after restoration at the peer end, they are returned to existing equipment by original interface type, with no change to encoding or frame structure in between, so no data rework is required during service cutover. In the design of this optical multiplexer series, Raytrans integrates the above service capabilities on a single platform, serving scenarios that require multi-service access, such as government private network optical fiber communication solutions and military emergency communications vehicle solutions.

Key Specifications

The technical specifications of the IDM GP2400-30E cover five parts: optical interface, E1 interface, Ethernet interface, telephone voice interface, and power supply and environment. Key indicators are listed in the table below. Values are subject to product documentation and factory testing; verify item by item according to the actual configuration during project calculation.

Item	Parameter/Specification	Description/Applicable Conditions
Optical interface type	SFP	Pluggable optical module, easy to replace by distance and spare
Fiber mode	Single-mode (multimode optional)	Selected according to line distance and fiber core conditions
Optical fiber rate	2.5Gbps	Shared by telephone, Ethernet, and E1 services
Wavelength	1310nm/1550nm	Two wavelengths selectable, used in pairs at both ends
Transmit optical power	-1~-3dBm	Typical single-mode value; subject to actual measurement with an optical power meter
Receiver sensitivity	Better than -24dBm	The link loss budget can be calculated on this basis
E1 bit rate	2048Kbps	HDB3 line coding
E1 standard protocol	Supports ITU-T G.703	Standard E1 interface specification
E1 impedance	75Ω/120Ω	Selected according to the interface of the interconnected equipment
E1 frame structure	PCM30/31	Primary group frame structure, transparent transmission mode
Ethernet interface type	RJ45	4 groups of physically isolated electrical ports
Ethernet transmission rate	10M/100M/1000M	Compliant with IEEE802.3, adaptive full-duplex/half-duplex
Voice audio range	300Hz~3400Hz	Telephone voice channel bandwidth
Voice impedance	Three-element complex impedance 200Ω+560Ω//0.1μF	Telephone subscriber line interface standard
Voice compression	ITU G.711 A-law	64Kbps PCM encoding
Voice loop current	25mA per channel	Feeding capability of each voice channel
Power supply mode	DC-48V /AC 220V/dual power supply	Dual power supply access improves power supply reliability
Overall power consumption	≤100W	Unit value including service interfaces and optical modules
Operating temperature	0ºC～40ºC	Equipment room and temperature-controlled cabinet environments
Humidity	≤90% (non-condensing)	Upper limit of relative humidity

The optical power budget is the prerequisite for stable long-distance links: with transmit optical power of -1~-3dBm and receiver sensitivity better than -24dBm, the loss margin left between the two ends covers optical cable attenuation, splice points, and patch cord loss. Include optical cable length and number of connectors in the calculation; if received optical power approaches the threshold, first clean the flange and patch cord end faces, and if still insufficient, replace with an SFP module with a higher power budget. As a professional optical multiplexer manufacturer, Raytrans can assist with optical power budget and equipment selection calculation based on the actual link conditions of a government private network optical fiber communication solution or a military emergency communications vehicle solution.

Figure 2: Rear panel photo of the IDM GP2400-30E, layout of 2.5G SFP optical ports, 4 groups of isolated Fast Ethernet ports, and dual power supply terminals

How to Configure Dual-Fiber Mutual Backup and Dual Power Supply Without Interruption

Dual-fiber mutual backup means laying two optical fibers between the same pair of sites, with the primary link carrying services and the backup link on standby; when the primary link has a fiber break or received optical power degradation, services switch to the backup link. Dual power input means DC-48V and AC220V feeds are connected to the two power supply terminals of the device respectively; when either feed fails, services are maintained by the other. The two measures are independent, and a problem with one does not affect the other.

Check the on-site configuration step by step according to the following four steps. Each step corresponds to an observable criterion, forming a complete chain from power supply mode to optical path switching. After completing the four steps, perform a fiber break and power failure test before considering the configuration closed; subsequent maintenance can be checked in the same order to locate problems.

• Route the two optical fibers over different optical cable routes and terminals, avoiding simultaneous interruption of both paths by construction in the same conduit;
• Pair the optical ports of the two optical multiplexers by wavelength, using 1310nm and 1550nm in pairs, and power on after cleaning the patch cord end faces;
• Draw the two power feeds from different distribution circuits; communications equipment rooms often use one -48V DC feed and one 220V AC feed;
• After power-on, first check that the power and optical port indicator LEDs show normal received optical power, then disconnect the primary optical fiber to verify whether services switch to the backup link.

Switching verification is a step that must be done thoroughly during commissioning: after disconnecting the primary optical fiber, the 30 telephone channels should maintain uninterrupted calls, and the 4 groups of isolated Ethernet should continue forwarding. After verification passes, record the optical fiber numbering, power circuits, and interface assignments in the as-built documentation, so subsequent capacity expansion can follow the drawings without re-sorting the wiring sequence.

Figure 3: IDM GP2400-30E dual-fiber mutual backup point-to-point networking diagram, with both ends interconnected via two 2.5G single-mode optical fibers

The value of dual power input for unattended sites lies in reducing service interruptions caused by maintenance and switching of a single power feed. With overall power consumption ≤100W, reserve capacity calculation for on-site UPS or solar power supply based on this value; no separate capacity expansion is needed for the transmission equipment.

How 4 Groups of Isolated 100M Ethernet Are Used in Private Networks

Physical isolation means that the 4 Ethernet ports are encapsulated and forwarded independently inside the device, with no shared bandwidth: each of the 4 groups carries wire-speed 100M, for a total of 400M. When one group experiences a broadcast storm, abnormal traffic, or an address conflict, the other three groups are unaffected. This is the prerequisite for placing dispatching data, video, and office services on the same multi-service optical multiplexer.

A common practice in private networks is to group by service nature: one group carries dispatching and automation data, one carries video surveillance backhaul, one carries office and O&M terminals, and one is reserved for future capacity expansion or third-party access. After grouping, each group connects to a different switch or a different VLAN on the central side, and security boundaries are drawn by group, so there is no need to deploy a separate pair of optical multiplexers for each group.

Multiple devices can also work together to form multi-group physically isolated Ethernet chain networks, ring networks, and point-to-multipoint star networks: chain networks suit series connection of sites along the line, ring networks reroute services in the reverse direction when a fiber break occurs at one point, and star networks suit aggregating multiple endpoint sites into the central equipment room. The networking approach depends on site distribution and fiber core resources: use a chain network when sites along the line are evenly spaced and fiber cores are scarce, and use a star network when the central equipment room has independent fiber cores to each site.

Typical Application Scenarios

The IDM GP2400-30E is mainly deployed point-to-point, with one unit at each end; the telephone and isolated Ethernet services at the site side are restored at the central equipment room and then connected to existing dispatching switching and data equipment. The usage of the three types of private networks differs in emphasis, as described below by industry.

Electric Power Private Network: One-Fiber Backhaul of Substation Telephones and Isolated Ethernet

Between a substation and a dispatch station, dispatch telephone and in-station data channels are both required. In the past, telephone optical multiplexers and data optical multiplexers were deployed separately, resulting in many devices and many points of failure in the cabinet. The IDM GP2400-30E places one unit at each site, multiplexing 30 dispatch telephone channels and 4 groups of isolated Ethernet over a single 2.5Gbps single-mode fiber, so cabinet space usage and wiring volume decrease at the same time.

On the power supply side, DC-48V and AC220V dual power supply access is supported, and the -48V direct current power supply common in communications equipment rooms can be used directly; with dual-fiber mutual backup configuration, when the inter-station optical cable is interrupted at one point, services switch over to the backup link and dispatch telephone service is not interrupted. Audio is encoded in A-law per ITU G.711 with a loop current of 25mA per channel, and can be directly connected to existing dispatch voice channel equipment.

Rail Transit: 30 Telephone Channels and 4 Groups of Isolated 100M Direct to Sites Along the Line

Between stations, depots, and section equipment rooms, train operation telephone, signaling data, and surveillance images need to be transmitted, and sites are distributed along the line at varying distances. The IDM GP2400-30E is deployed in chain network or ring network mode, delivering 30 telephone channels and 4 groups of isolated 100M to sites along the line over a single 2.5Gbps fiber, so there is no need to lay separate fiber cores for each type of service in the section.

Receiver sensitivity is better than -24dBm; the received optical power margin of long-distance links in the section is calculated based on actual measurement with an optical power meter, and optical reception still works normally under weak-light conditions; 1310nm and 1550nm dual-wavelength modules are selected according to section loss. The 4 groups of isolated Ethernet carry signaling, surveillance, and office services respectively, and an abnormality in one channel does not affect train operation telephone service.

Military and Government Private Networks: Same-Fiber Transmission of Physically Isolated Ethernet and Dual-Fiber Mutual Backup

Remote stations in military emergency communications vehicle solutions and government private network optical fiber communication solutions are often unattended, with limited power supply and on-site maintenance conditions, and high requirements for service independence and link reliability. The IDM GP2400-30E provided by Raytrans uses 4 groups of physically isolated Ethernet to carry services of different purposes separately, with dual-fiber mutual backup and dual power input both in place, so services are maintained by the other path when a single path fails.

The unit is a standard 19-inch 1U enclosure, deployed in a temperature-controlled cabinet; operating temperature is 0ºC to 40ºC and humidity is ≤90% (non-condensing). During commissioning, FXO, FXS, or magneto interfaces are configured according to the type of telephone on site, and voice and data are verified in a single power-on, reducing site visits.

Figure 4: IDM GP2400-30E application schematic for electric power and rail sites, with 30 telephone channels and 4 groups of isolated Ethernet backhauled over the same fiber

Selection, Commissioning, and Debugging

Selection is checked item by item against three items: number of service channels, optical fiber line conditions, and power supply and environment; commissioning is verified layer by layer across power, optical path, and services. The check results of the three conditions directly determine the interface form, optical module grade, and power wiring method. Both tasks are documented in writing before the completion documentation is signed, and subsequent capacity expansion and inspection are based on these records.

• Number of service channels: confirm whether the number of telephone channels is within 30, whether the interface form is FXO, FXS, or magneto, and confirm whether the isolated Ethernet is 4 groups and whether each group's bandwidth requirement is within 100M;
• Optical fiber conditions: confirm single-mode or multi-mode, whether the wavelength is 1310nm or 1550nm, and whether two fibers are available for mutual backup; calculate the loss budget based on transmit optical power and receiver sensitivity;
• Power supply conditions: confirm whether the site has DC-48V or AC220V; when dual power supply is required, the two paths should be drawn from different distribution circuits, and overall power consumption should be reserved at ≤100W;
• Commissioning sequence: first check the power supply format and grounding, then check optical reception at the optical port, then verify telephone calls and Ethernet forwarding channel by channel, and finally perform a fiber break protection switching test.

A common rework during commissioning is a mismatch between the telephone interface form and the opposite end equipment: direct telephone connection requires FXS feeding and ringing current, connection to the outside line side of a switch requires FXO, and magneto telephones require magneto interfaces. Confirming the type of opposite end equipment on site before deciding the interface saves time compared with replacing interface boards afterwards. As a professional optical multiplexer manufacturer, Raytrans recommends confirming item by item against the interface configuration list in the product showcase at the selection stage, to avoid repeated adjustments during commissioning.