As mentioned in another article on this website CRC stands for Cyclic Redundancy Check and is a system that automatically checks for errors in T1 framing and provides notification of problems in the T1 network which are caused by the framing error. CRC acts a safety switch that provides an alert when a component or piece of in the network is about to fail. But what happens if there is an error in the Cyclic Redundancy Check system itself?
Usually to correct the problem you must deploy Extended Superframe Framing to detect the T1 CRC error which means the server could experience downtime for an unspecified amount of time. Although ESF is still necessary for detecting CRC errors T1 Failover can be beneficial in aiding the situation while the error is being identified and corrected.
What is T1 Failover?
A T1 Failover is a switch that is also known as a T1 Protection switch that allows the end user such as a business or organization to connect a T1 line from the service provider to one active terminal and one standby T1 terminal such as a data or intranet server located on the business premises. The Failover switch offers three different ports that are related to the service provider or carrier service. The ports include one for incoming services, a main port which establishes a connection with the primary device, and a second port which connects to a secondary device.
The Failover switch is responsible for detecting a signal failure on the main port and if it determines there has been a failure it will automatically fail the service from the main port to the secondary port. Once the main port identifies a restored signal the failover switch will automatically change the services back over to the port with the recovered signal. This minimizes downtime which otherwise could have been extended due to an equipment failure.
T1 Failover Advantages for T1 CRC Errors
T1 Failover provides many different network advantages in addition to T1 Cyclic Redundancy Check errors. First we will look at the criteria for CRC and how T1 Failover addresses these criteria.
- CRC Parameters: CRC parameters refer to the number of CRC errors that transpired during the testing phase. The errors are counted while the framing is chosen as Extended Superframe Framing or ESF. When the CRC errors are being counted the expected value of the CRC prototype can be anticipated. When the data is received it is compared with the expected value or results. If the results are not the equivalent to the actual value this is what counts as a CRC error.
- CRC and T1 Failover: Since the Cyclic Redundancy Check is located inside the framing bit if it fails to count the errors this can result in equipment or network failure without advance warning. This is where the T1 Failover can be a worthwhile investment since it can automatically switchover to the standby which will provide continued service from the carrier while the problem is corrected.
Other Criteria for T1 Failover
The T1 Failover will also switch from active to standby on the business premises as a result of other criteria in addition to Cyclic Redundancy Check error problems.
- Signal Loss: The T1 Failover will automatically switch over to standby if there has been a signal loss on the main or “active” port. Signal loss on the customer premises can be caused by port failure on the equipment, loss of power, problems with the T1 cable, or frame loss where 2 out of 5 Ft bits are in error within the D4 framing and 2 out of 5 bits are in error within the Extended Superframe Framing or ESF.
- Frame Loss: Loss of Frame or LOF occurs when unframed bits are identified in the incoming electrical pulses on the T1 line. This is also known as a Blue Alarm and will prompt the T1 Failover to switch to the standby port. Another problem in this category is an AIS or Alarm Indication Signal which means that a D4 Framed bit 2 of each Digital Signal or DS0 for 255 channels has been identified as 0. This is also known as a Yellow Alarm.
T1 Failover saves companies on costs by allowing the IT professionals to install additional data networks without having to bear the cost of leasing additional T1 lines while at the same time improving the existing equipment and data security. A T1 Failover switch also offers a built-in real-time clock and real-time logging which keeps track of a history of events.
The T1 Failover does all of the work in terms of automatically switching the T1 line from the carrier between the main or “active” terminal and the secondary or “standby” terminal. T1 Failover also provides for increased reliability of data and IT networks by producing uninterrupted service