IF 1+1 Protection

An IF 1+1 protection system is a microwave link protection system composed of a working channel and a protection channel. IF 1+1 protection includes 1+1 HSB protection, 1+1 FD protection, and 1+1 SD protection.

IF 1+1 protection can be classified into the following modes:

In 1+1 HSB (Hot Standby) protection mode, the equipment uses a 1+1 hot standby configuration for IF boards and ODUs at both ends of a hop of a microwave link to achieve the protection purpose.
NOTE:
OptiX RTN 310s and OptiX RTN 380s have only one board. Therefore, 1+1 HSB protection is available for RTN 310s and RTN 380s at both ends of each hop of a microwave link.

In the 1+1 FD (Frequency Diversity) protection mode, the system uses two channels that have a frequency spacing between them, to transmit and receive the same service signal. The opposite end selects signals from the two received signals. With the 1+1 FD protection, the impact of the fading on signal transmission is reduced.
In the 1+1 SD (Space Diversity) protection mode, the system uses two antennas that have a space distance between them, to receive the same RF signal. The equipment selects signals from the two received signals. With the 1+1 SD protection, the impact of the fading on signal transmission is reduced.

IF 1+1 protection can work in revertive or non-revertive mode.

Revertive

The main channel or NE clears the switching state and services are switched back to it a specified period of time after it is restored to normal. The period of time that elapses after the main channel or NE is restored and before the main channel or NE clears the switching state is called the wait to restore (WTR) time. To prevent frequent switchovers caused by unstable status of the main channel or NE, a WTR time of 5-12 minutes is recommended.
Non-revertive

The main channel or NE remains in the switching state even after being restored to normal. The standby channel or NE continues to transmit services unless another switch over occurs.

IF 1+1 protection switching conditions

Table 1 describes the 1+1 HSB switching condition (the table below lists switching conditions in descending order of priorities ).

**Table 1** HSB switching conditions
Switching Condition	Description
Clear switching (external switching)	All external switching states are cleared. NOTE: In revertive mode, services are switched back to the main NE after the switching state is cleared.
Lockout switching (external switching)	In any state, a switching enters the lockout state. In the lockout state, no switching occurs until the lockout switching is cleared.
Forced switching (external switching)	If a switching is in the lockout state, no forced switching occurs. Otherwise, the system switches services from the main board to the standby board or from the standby board to the main board according to the command. The switching then enters the forced switching state.
The main equipment is faulty	All external switching states are cleared. Lockout switching (external switching) In any state, a switching enters the lockout state. In the lockout state, no switching occurs until the lockout switching is cleared. Forced switching (external switching) If a switching is in the lockout state, no forced switching occurs. Otherwise, the system switches services from the main board to the standby board or from the standby board to the main board according to the command. The switching then enters the forced switching state. The main equipment is faulty. If a switching is in the lockout or forced switching state, or if the current standby equipment is faulty, no HSB switching occurs. Otherwise, the system switches services from the main board to the standby board. The switching then enters the automatic switching state.
Reverse switching (valid only when the reverse switching is enabled)	When both the main IF board and the standby IF board at the sink end report service alarms, they send the alarms to the source end by using the MWRDI overhead in the microwave frame. If the source end is in the lockout of protection or forced switching state, or if the current standby device is faulty, reverse switching does not occur. In other cases, HSB switching occurs at the source end after the reverse switching timer expires. The reverse switching timer restarts after you successfully add a protection group or if an HSB switching event occurs. The timer duration is the wait-to-restore (WTR) time (in revertive mode) or 5 minutes (in non-revertive mode). After the reverse switching, the system changes to the RDI state.
Manual switching (external switching)	If a switching is in the lockout or forced switching state, or if the current standby equipment is faulty, no switching occurs. Otherwise, the system switches services from the main board to the standby board or from the standby board to the main board according to the command. The switching then enters the manual switching state.
Revertive switching (valid only in the revertive mode)	When the switching is in the automatic switching state and the former main equipment is already restored to normal for a period lasting for the WTR time, the revertive switching occurs. From the time the former main equipment is restored to normal to the time the revertive switching occurs, the switching is in the WTR state. After the revertive switching, the switching enters the normal state.

NOTICE:

Services are interrupted during HSB switching.

1+1 HSM (Hitless Switch Mode) switching occurs on the channel side. Table 2 lists the types of channel-side HSM switching.

**Table 2** HSM switching types
Switching Type	Description
Automatic switching	The automatic switching refers to the HSM switching that is automatically triggered. After the automatic switching, the IF board receives the baseband signal sent from its paired IF board.
Revertive switching	After an automatic HSM switching, the IF board attempts to perform a revertive switching action periodically. If there is no service alarm on the working channel at this time, the IF board releases the switching.
Forced switching	The forced switching refers to the HSM switching that occurs at the same time the HSB switching occurs. After the forced switching, the IF board receives its own baseband signal.

NOTE:

The 1+1 HSB and 1+1 SD modes support HSM switching.

NOTE:

HSM switching does not affect services. If the AM function is enabled, the standby channel in a 1+1 protection group consisting of IFU2/IFX2 boards changes its modulation scheme for ensuring capacity after HSM switching occurs, whereas the standby channel in a 1+1 protection group consisting of ISU2/ISX2/ISV3 boards does not change its modulation scheme after HSM switching occurs. Therefore, after HSM switching, services with a lower priority are impaired in the former scenario.

System Configuration Scenarios and Switching Principle

Table 3 describes the system configuration scenarios and switching principles of IF 1+1 protection.

**Table 3** System configuration scenarios and switching principles of IF 1+1 protection
Protection Type	System Configuration Scenario	Switching Principle
1+1 HSB	RTN 900 series support one to seven 1+1 HSB protection groups. One 1+1 HSB protection group uses one channel and consists of the following items: Two IF boards of the same type Two ODUs of the same type One antenna (equipped with one hybrid coupler) Two RTN 380s or RTN 310s must work with one RTN 900 IDU or one LAG-enabled UNI-side device to achieve 1+1 hot standby (HSB) protection (LAG is short for link aggregation group). A 1+1 HSB group uses one frequency and consists of: Two RTN 380s or RTN 310s One antenna with a hybrid coupler	RTN 900 series: SDH/PDH radio: In HSB switching, the cross-connect unit dually transmits and selectively receives TDM services to implement service protection. Integrated IP radio: In HSB switching, the cross-connect unit dually transmits and selectively receives TDM services to implement service protection on the TDM plane, and the packet switching unit performs LAG switching to implement service protection on the packet plane. The main and standby RTN 380s exchange 1+1 protection protocol packets to implement 1+1 HSB.
1+1 FD	RTN 900 series support one to seven 1+1 FD protection groups. One 1+1 FD protection group uses two channels and consists of the following items: Two IF boards of the same type Two ODUs One antenna (equipped with one balanced hybrid coupler) or two antennas Two RTN 310s must work with one OptiX RTN 900 IDU or one LAG-enabled UNI-side device to achieve 1+1 FD protection. A 1+1 FD group uses two frequencies and consists of: Two RTN 310s One antenna with a hybrid coupler or two antennas	RTN 900 series: SDH/PDH radio: In HSB switching, the cross-connect unit receives TDM services from the standby IF board to implement service protection. In HSM switching, the IF board receives baseband signals from the standby receive channel to implement service protection. Integrated IP radio: In HSB switching, the cross-connect unit receives TDM services from the standby IF board to implement service protection on the TDM plane, and the packet switching unit performs LAG switching to implement service protection on the packet plane. In HSM switching, the IF board receives baseband signals from the standby receive channel to implement service protection. RTN 310s implement HSB switching using E-LAGs, and implement HSM switching by receiving baseband signals from the standby channel.
1+1 SD	RTN 900 series support one to seven 1+1 SD protection groups. One 1+1 SD protection group uses two channels and consists of the following items: Two IF boards of the same type Two ODUs of the same type Two antennas Two RTN 310s must work with one OptiX RTN 900 IDU or one LAG-enabled UNI-side device to achieve 1+1 SD protection. A 1+1 SD group uses two frequencies and consists of: Two RTN 310s Two antennas	RTN 900 series: SDH/PDH radio: In HSB switching, the cross-connect unit receives TDM services from the standby IF board to implement service protection. In HSM switching, the IF board receives baseband signals from the standby receive channel to implement service protection. Integrated IP radio: In HSB switching, the cross-connect unit receives TDM services from the standby IF board to implement service protection on the TDM plane, and the packet switching unit performs LAG switching to implement service protection on the packet plane. In HSM switching, the IF board receives baseband signals from the standby receive channel to implement service protection. RTN 310s implement HSB switching using E-LAGs, and implement HSM switching by receiving baseband signals from the standby channel.

Feature Dependencies and Limitations

Table 4 describes the feature dependencies and limitations of If 1+1 protection.

**Table 4** Feature dependencies and limitations
Feature	Self Limitations	Dependencies and Limitations on Other Features
1+1 HSB	Mix of different board types: If an ISV3 board and an ISX2/ISU2 board form a 1+1 HSB protection group, the ISV3 board must work in IS2 mode.	The configuration mode of 1+1 protection in one direction can only be 1+1 HSB, 1+1 FD, or 1+1 SD. The configuration mode in one direction can be different from that in another direction. The IF boards in a 1+1 protection group cannot be configured to provide the N+1 protection. The two IF boards in a cross polarization interference cancellation (XPIC) group cannot be added to a 1+1 protection group, but two IF boards in different XPIC groups can be added to a 1+1 protection group. The Integrated IP microwave link with 1+1 configuration can function as the working source, protection source, or service sink of SNCP. The Hybrid microwave supports the 1+1 protection. When 1+1 protection is configured for Integrated IP microwave links with the AM function enabled, the switching result varies depending on the switching type and protection group members: After HSB switching, the standby link works in the original modulation scheme of the main link. After HSM switching, the standby channel in a 1+1 protection group consisting of IFU2/IFX2 boards changes to the modulation scheme for ensuring capacity, and services with a lower priority are impaired; whereas, the standby channel in a 1+1 protection group consisting of ISU2/ISX2 boards does not change its modulation scheme. When a 1+1 protection group is created in Integrated IP radio, the NE automatically creates a load non-sharing LAG. In the LAG, the master port is the Integrated IP radio port on the active IF board and the slave port is the Integrated IP radio port on the standby IF board. This LAG can neither be displayed on the U2000 nor configured manually. When 1+1 protection is configured for Integrated IP microwave links, these links can function as ring links or ring protection links in the ERPS protection. 1+1 protection can work with PW APS. 1+1 protection can work with MPLS APS. In 1+1 protection mode, a standby NE has to trace the active NE's clock through its COMBO port. Therefore, the COMBO interface should be added in the priority list. 1+1 protection cannot work with PLA. 1+1 protection cannot work with XPIC.
1+1 FD	Mix of different board types: If an ISV3 board and an ISX2/ISU2 board form a 1+1 FD protection group, the ISV3 board must work in IS2 mode. Slot ID: IF boards must be configured in paired slots.
1+1 SD	Mix of different board types: If an ISV3 board and an ISX2/ISU2 board form a 1+1 SD protection group, the ISV3 board must work in IS2 mode. Slot ID: IF boards must be configured in paired slots.