Redundancy Features Overview
A CTP series device provides the following redundancy features:
Ethernet interface failover—If the default Ethernet interface fails, the CTP device fails over to the next unconfigured Ethernet interface.
Route management redundancy—If the next-hop gateway (the router) becomes unreachable, the CTP device uses configured static routes to a next-hop gateway on a different network.
Bundle failover between CTP devices at alternate sites—If a bundle circuit fails and the CTP device becomes unreachable, the CTP device fails over to a CTP device at an alternate site.
Bundle failover between CTP devices at the same site or single-ended Y-cable redundancy—If a bundle circuit fails and the CTP device becomes unreachable, the CTP device fails over to a redundant CTP device that is connected to the failed device by a Y cable. Starting from CTPOS release 6.6, this feature is referred to as Exclusive OR (XOR). The term Exclusive OR is used because a port configured for XOR drives the cable only if its bundle is in RUNNING state and the other port on the same Y cable, which is also referred to as its link neighbor, is not in RUNNING state.
Bundle failover between CTP devices at both the local and remote sites or double-ended Y-cable redundancy—If a bundle circuit fails and a CTP device at either the local or remote site becomes unreachable, the CTP devices fail over to bundles configured on the redundant CTP devices. At each site, two CTP devices are connected to the customer equipment with a Y cable.
Double ended redundancy has two modes, revert and non-revert. When the revert mode is enabled, the circuit automatically switches back to the primary path when it recovers after a failure. When non-revert mode is enabled, the circuit continues on the secondary path even after the primary path is back online. The circuit switches back to the primary path only if the secondary path fails and the primary path is in RUNNING and offline state.
Double- ended Y-cable redundancy has two features, Cold Standby and Hot Standby.
Cold Standby—Cold Standby feature is enabled by configuring the secondary path for RL demand signaling. When enabled, the secondary path remains in InSYNC state and does not consume network bandwidth until the primary path fails. This feature helps save bandwidth, especially in networks where bandwidth is expensive. When the primary circuit recovers, the secondary circuit goes back to the InSYNC state.
In cold standby, only the primary circuit remains in RUNNING state and drives the Y cable.
Hot Standby—In hot standby, both the primary and the secondary circuits remain in RUNNING state and the primary circuit drives the cable.
Y-cable redundancy can be based on either a hardware link that uses a special Y cable or a software link that uses OAM packets, which Y-cable port pairs use to communicate with each other.
A hardware link is supported only on serial ports. The functioning of a hardware link is similar to the default operation of the redundancy feature in CTPOS Release 6.5 and earlier.
A software link does not require a special signaling hardware such as the Y cable. Y-cable port pairs maintain contact with each other by using the OAM packets instead of depending on a hardware signaling path. Because of this, Y-cable redundancy is supported on T1/E1 ports as well as serial ports.
When double-ended redundancy is configured by enabling the software link with ReVeRT or NOnReVert mode and TRANS 8 encoding, you can connect two users devices by means of a virtual cable that transports every signal on the EIA-530A interface.
Packet redundancy—If packets are lost because of transmission errors, the packet protector feature can enable a possible recovery scenario.
Table 1 lists the supported Y-cable configuration settings.
Table 1: Supported Configuration Settings for Y- Cable Redundancy
Solution | Local Configuration | Remote Configuration | Options | Features | |
|---|---|---|---|---|---|
Single-ended | Alternate site | Redundancy disabled Autoswitch | Redundancy disabled | ||
Single-ended | Same site | Redundancy disabled Autoswitch | Exclusive OR (XOR) | ||
Both-ended | Not applicable | Revert (RVRT) | Revert (RVRT) | Fast1 | Hot standby/Cold standby |
Both-ended | Not applicable | Non-Revert (NORV) | Non-Revert (NORV) | Hot standby | |
Multi Master | Not applicable | Redundancy disabled | Signal (SIG) | Inv | |
1Fast switch is supported only in Hot standby in Revert redundancy mode and is valid only for a hardware link.
Table 2: Supported Platforms, Link Types, and Interface Types
Platform | CTP150 | CTP2000 | |||||||
|---|---|---|---|---|---|---|---|---|---|
Interface Type | Serial | T1/E1 | Serial | T1/E1 | |||||
Link Type | Software Link | Hardware Link | Software Link | Hardware Link | Software Link | Hardware Link | Software Link | Hardware Link | |
Feature | Redundancy Mode | ||||||||
Single Ended | XOR | Yes | Yes | Yes | No1 | Yes | Yes | Yes | No1 |
Hot Standby (Both ended) | RVRT | Yes | Yes | Yes | No1 | Yes | Yes | Yes | No1 |
NORV | Yes | Yes | Yes | No1 | Yes | Yes | Yes | No1 | |
Cold standby (Both ended) | RVRT | No3 | Yes | No3 | No1 | No3 | Yes | No3 | No1 |
NORV | No3 | No2 | No3 | No1 | No3 | No2 | No3 | No1 | |
Multi master | SIG | No4 | Yes | No4 | No1 | No4 | Yes | No4 | No1 |
1T1/E1 ports do not support a hardware link due to the lack of signaling leads on the interface.
2Non-revert (NORV) mode is supported only in a Hot standby configuration.
3Cold standby is supported only on a serial interface running a hardware redundancy link.
4Signal (SIG) mode is supported only on a serial interface running a hardware redundancy link.