IDM 120PD Dual-E1 Mutual Backup PCM

Key Specifications at a Glance*: dual-E1 mutual backup · dual-transmit selection · bit error rate selection · 64K/N×64K services · 2 E1 interfaces · real-time monitoring of the lines

**## What Kind of Equipment Is the Dual-E1 Dual-Transmit Selective Mutual Backup Equipment?**The IDM 120PD-2E1 is a piece of PCM equipment in which two E1 channels back up each other. It provides two E1 interfaces on the line side and accesses services on the service side at 64K granularity or N×64K granularity. The device sends the same copy of the service onto both E1 channels at the same time and keeps only the channel of better quality at the output side, so adding or removing a link does not change the service configuration.

An E1 channel runs at 2.048 Mbps and is transmitted in HDB3 line coding as recommended by ITU-T G.703. A frame has 32 time slots of 64 Kbps each, in which time slot 0 carries frame alignment, time slot 16 carries channel-associated signaling (CAS), and the remaining time slots carry services. Services occupy time slots at 64K or N×64K, and several narrowband services can share the same E1.

Why Do Services Need to Be Transmitted Across Two E1 Channels?

The trustworthiness of a single E1 channel depends on the optical cables, microwave links and equipment along the way, and inspection or degradation of any part interrupts the services on that channel. When an important service runs over only one channel, the availability of the channel is the availability of the service, and the emergency repair time directly equals the service interruption time.

Feeding the same batch of services into two E1 channels on different paths at the same time gives the services two physical routes. When one channel is under inspection, shows a rising bit error rate or is interrupted, the other is still transmitting the same copy of the service, so the site does not need to rewire anything temporarily or reconfigure service data.

Figure 1: Close-up of the IDM 120PD-2E1 front panel, with power supply and E1 link operating indicator LEDs*

Dual-transmit selection means sending the same service out through both E1 interfaces at the same time, with one device at each of the transmit and receive ends in a paired configuration. A copy of the service travels on each of the two channels, a complete data stream exists on either channel, and the output side does not have to wait for the active channel to go down before it acts.

Selection takes place at the output side. The device performs real-time monitoring of the line state of both E1 interfaces and applies bit error rate selection to the output: the channel whose bit error rate rises drops out of carrying traffic and the other keeps delivering services. The criterion comes from the transmission quality of the channels themselves, so when a channel degrades the output switches to the better one first, and the service side sees a channel change rather than a service interruption.

Should the Two E1 Paths Be Separated?

When both E1 channels run over the same optical cable, the same transmission device or the same power distribution panel, the benefit of the backup is cancelled by the shared point of failure. A cut on the same cable, a power failure of the same device or a loss of the same power feed takes the two channels down together, and dual-transmit selection then has no second channel to select.

In engineering practice the two E1 channels are assigned to different transmission paths: one over the station's existing SDH or microwave channel, the other over a leased circuit or another transmission device, keeping the upstream equipment, power supply circuits and incoming routes of the two channels as separate as possible. Only when the paths are separated does dual-transmit selection have a real second route to use.

Figure 2: Rear panel layout of the IDM 120PD-2E1 with two E1 line interfaces and link status indications*

The functions fall into three parts: the dual E1 channels, the selection criterion and service carriage, listed item by item in the table below. During selection, compare them with the number of channels and the service types the project needs; items that are not used need not be configured. The table also gives the position at which each function acts, on the line side or on the service side, so that it can be checked item by item against the ordering configuration sheet.

### Function Overview

| Function | Description |

|---|---|

|| Dual E1 interfaces | Two E1 interfaces on the line side, so the same batch of services can be sent to both channels at the same time ||| Dual-transmit selection | Services are transmitted on both E1 channels simultaneously, and the output side outputs whichever of the two channels is selected ||
|---|---|
|| Real-time monitoring of the lines | Continuous real-time monitoring of the line state of both E1 interfaces, with link changes reflected on the device side immediately ||| Bit error rate selection | The line bit error rate is used as the criterion for selecting the output channel, and the channel whose bit error rate rises drops out of carrying traffic ||
|| 64K service carriage | Carries a single narrowband service in a 64K time slot, with several services sharing the same E1 ||| N×64K service carriage | Occupies consecutive time slots at N×64K to carry data-type services with higher bandwidth requirements ||
|| Channel mutual backup | The two E1 channels are in mutual backup, so services continue over the other channel in the event of an interruption ||### Technical Specifications|
|The parameters are listed in three groups: E1 interfaces, service carriage and device configuration. Items not given in the available material are confirmed by the ordering configuration and are not inferred from other models of the same series. If the configuration supplied for a project differs from this table, the ordering configuration sheet prevails; check each item against that sheet before commissioning on site.|| Item | Parameter/Specification | Description/Applicable Conditions ||
||---|---|---||| Device model | IDM 120PD-2E1 | Dual-E1 channel mutual backup device ||
|| Number of E1 interfaces | 2-channel | Two channels in a paired configuration, providing mutual backup for each other ||| E1 rate | 2.048 Mbps | E1 base group rate, in line with ITU-T G.703 ||
|| E1 line coding and frame structure | HDB3, PCM30/32 frame structure | Interworks with existing E1 transmission networks and switching equipment ||| Service granularity | 64K, N×64K | Narrowband services and bandwidth-type services share the two E1 channels ||

| Backup mode | Dual-transmit selection | The same service is carried by E1 transmission on both E1 channels at the same time, and the output side chooses one |

| Selection criterion | Line state and bit error rate | The device performs bit error rate selection on the E1 output, and the channel with the higher bit error rate drops out |

|| Service-side interface type and count | Not yet recorded in the knowledge base | Subject to the ordering configuration sheet ||| Power supply mode and overall power consumption | Not yet recorded in the knowledge base | Subject to the technical documentation supplied with the unit and the ordering configuration ||| Dimensions and operating environment | Not yet recorded in the knowledge base | Subject to the technical documentation supplied with the unit and the ordering configuration ||
|---|---|---|
|### Differentiated Capability and On-Site Value| IDM 120PD-2E1 |The table below maps three items of differentiated capability to on-site problems at the station: the left column gives the capabilities of the device and the right column gives the specific problem each capability solves. During selection, check them item by item against the site conditions; capabilities that are not used need not be configured, and the specific configuration is subject to the commercial confirmation sheet.|
|| Differentiated selling points | Value on Site |||---|---||| Dual-E1 dual-transmit selection | Important services are transmitted with E1 channel mutual backup across two different E1 channels; when either channel degrades, the output side switches to the other one for carriage, and service data need not be reconfigured as the link changes ||
|| Real-time monitoring and bit error rate selection | The device performs real-time monitoring of the line state of both E1 lines and automatically selects the better output according to the bit error rate, so a decline in channel quality is reflected in the selection result before services are affected || 2.048Mbps || 64K and N×64K multi-service | Supports multiple 64K and N×64K services and fits narrowband service carriage in private networks, so existing voice and data services can be connected without modification ||
|## Typical Application Scenarios|The IDM 120PD-2E1 targets private network sites with limited channel resources and high service importance. The three industries share the same structure: one piece of PCM equipment at each end, two E1 channels in between, and services configured symmetrically at both ends; they differ in the service types and in where the two E1 channels come from.||
|Figure 3: Point-to-point dual-E1 mutual backup networking topology of the IDM 120PD-2E1, with the devices at both ends interconnected through two E1 channels*| 64K、N×64K |### Electric Power Private Network: Cross-Channel Mutual Backup of Dispatch Telephone and Telecontrol Data|
|Between a substation and the dispatch center there are usually two types of services at the same time, dispatch telephone and telecontrol data, with E1 channels provided by transmission devices. Dispatch telephone is a matter of delivering on-site operating commands, telecontrol data is a matter of reporting the operating status of the power grid upstream, and neither type can afford a long interruption. For such scenarios, Raytrans can provide a complete electric power private network E1 channel mutual backup solution.|Dual-E1 dual-transmit selection keeps important services on an uninterrupted channel mutual backup: when one E1 channel is under inspection or its bit error rate rises, the output side switches to the other one, and calls at the dispatch console and telemetry at the master station continue to be transmitted. Only when the two E1 channels come from different transmission devices or different routes does the backup cover a single point of failure.|### Rail Transit: Site Services at Section Stations Selected Between Two E1 Channels|
|In rail transit, section equipment rooms, stations and depots are distributed along the line. The channel from a section to a station is mostly provided by the existing transmission network, and only a few E1 channels are usually reserved in the equipment room. Section services are mainly dispatch telephone, public address audio and signal monitoring data, and a channel interruption directly affects train operations and station staff communication.|Real-time monitoring of the bit error rate of both E1 channels and automatic selection of the better output keep traffic flowing: the PCM equipment sends the section services onto both E1 channels at the same time, the channel whose bit error rate rises drops out of carrying traffic and the other keeps delivering services. Cabinet space and maintenance windows in section equipment rooms are both limited, and the link criterion is monitored by the device itself, so on-duty personnel do not have to log in to the network management system section by section to troubleshoot.|### Oil and Gas Pipeline: Narrowband Services at Valve Chambers and Stations over Dual E1 Channels|
|Valve chambers, cathodic protection stations and metering stations of an oil and gas pipeline are distributed along the pipeline. The sites are unattended and far apart, and the channels are mostly provided by the transmission system along the pipeline. Site services are mainly valve chamber monitoring data, dispatch telephone and combustible gas alarm signals; there are not many of them, but the continuity requirement is high.|Dual-E1 mutual backup together with 64K/N×64K multi-service makes private network transmission more reliable: valve chamber monitoring data occupies time slots at N×64K bandwidth and dispatch telephone occupies 64K, with both service types sharing the two E1 channels. Emergency repair at unattended sites takes a long time, so when a channel fails the services are first carried by the other one, and the service path is already restored before O&M personnel reach the site.|## Conclusion|
|As dual-E1 dual-transmit selective mutual backup equipment, the IDM 120PD-2E1 packs the mutual backup and selection of two E1 channels into one unit: the same batch of important services is transmitted on both channels at the same time, the device performs real-time monitoring of the line state and applies bit error rate selection to the output, and when one channel degrades or is interrupted the services continue to be carried by the other.|The device supports multiple 64K and N×64K services and fits narrowband service carriage in electric power private networks, rail transit and oil and gas pipelines. As a professional optical multiplexer manufacturer, Raytrans also has mature PCM equipment product showcases and engineering experience in government private network optical fiber communication solutions and military emergency communications vehicle solutions. During selection, first confirm whether the two E1 channels can be assigned to different transmission paths, then determine the interface types and counts from the service list, and check the power supply and installation conditions against the ordering configuration sheet.|The IDM 120PD-2E1 dual-E1 dual-transmit selective mutual backup equipment is an E1 channel mutual backup transmission device developed by Beijing Ruiguang Jiyuan Digital Technology Co., Ltd. (Raytrans). It feeds the same batch of important services into two E1 channels for transmission at the same time and selects the better one at the output side according to line quality. As a professional optical multiplexer manufacturer, Raytrans positions this device for sites in electric power private networks, rail transit and oil and gas pipelines that require continuous channel availability, so that services do not lose their path when a single E1 link degrades. It is especially suitable for scenarios with strict requirements on channel reliability, such as electric power private network E1 channel mutual backup solutions.|
|Key Specifications at a Glance|: Dual-E1 Mutual Backup · Dual-Transmit Selection · Bit Error Rate Selection · 64K/N×64K Services · 2 E1 Interfaces · Real-Time Monitoring of the Lines|What Kind of Equipment Is the Dual-E1 Dual-Transmit Selective Mutual Backup Equipment?|

The IDM 120PD-2E1 is a piece of PCM equipment in which two E1 channels back up each other. It provides two E1 interfaces on the line side and accesses services on the service side at 64K granularity or N×64K granularity. The device sends the same copy of the service onto both E1 channels at the same time and keeps only the channel of better quality at the output side, so adding or removing a link does not change the service configuration.

An E1 channel runs at 2.048 Mbps and is transmitted in HDB3 line coding as recommended by ITU-T G.703. A frame has 32 time slots of 64 Kbps each, in which time slot 0 carries frame alignment, time slot 16 carries channel-associated signaling (CAS), and the remaining time slots carry services. Services occupy time slots at 64K or N×64K, and several narrowband services can share the same E1.

Why Do Services Need to Be Transmitted Across Two E1 Channels?	The trustworthiness of a single E1 channel depends on the optical cables, microwave links and equipment along the way, and inspection or degradation of any part interrupts the services on that channel. When an important service runs over only one channel, the availability of the channel is the availability of the service, and the emergency repair time directly equals the service interruption time.
Feeding the same batch of services into two E1 channels on different paths at the same time gives the services two physical routes. When one channel is under inspection, shows a rising bit error rate or is interrupted, the other is still transmitting the same copy of the service, so the site does not need to rewire anything temporarily or reconfigure service data.	Figure 1: Close-up of the IDM 120PD-2E1 front panel, with power supply and E1 link operating indicator LEDs
Figure 1: Close-up of the IDM 120PD-2E1 front panel, with power supply and E1 link operating indicator LEDs	How Does Dual-E1 Dual-Transmit Selection Work?
Dual-transmit selection means sending the same service out through both E1 interfaces at the same time, with one device at each of the transmit and receive ends in a paired configuration. A copy of the service travels on each of the two channels, a complete data stream exists on either channel, and the output side does not have to wait for the active channel to go down before it acts.	Selection takes place at the output side. The device performs real-time monitoring of the line state of both E1 interfaces and applies bit error rate selection to the output: the channel whose bit error rate rises drops out of carrying traffic and the other keeps delivering services. The criterion comes from the transmission quality of the channels themselves, so when a channel degrades the output switches to the better one first, and the service side sees a channel change rather than a service interruption.

Should the Two E1 Paths Be Separated?

When both E1 channels run over the same optical cable, the same transmission device or the same power distribution panel, the benefit of the backup is cancelled by the shared point of failure. A cut on the same cable, a power failure of the same device or a loss of the same power feed takes the two channels down together, and dual-transmit selection then has no second channel to select.

Figure 2: Rear panel layout of the IDM 120PD-2E1 with two E1 line interfaces and link status indications

Figure 2: Rear panel layout of the IDM 120PD-2E1 with two E1 line interfaces and link status indications

Core Functions and Performance Parameters

The functions fall into three parts: the dual E1 channels, the selection criterion and service carriage, listed item by item in the table below. During selection, compare them with the number of channels and the service types the project needs; items that are not used need not be configured. The table also gives the position at which each function acts, on the line side or on the service side, so that it can be checked item by item against the ordering configuration sheet.

Function Overview

Function

Description

Dual E1 interfaces

Two E1 interfaces on the line side, so the same batch of services can be sent to both channels at the same time

Dual-transmit selection

Services are transmitted on both E1 channels simultaneously, and the output side outputs whichever of the two channels is selected

Real-time monitoring of the lines

Continuous real-time monitoring of the line state of both E1 interfaces, with link changes reflected on the device side immediately