Chapter 1 General Troubleshooting

1.1.2 Terminal Loopback

1.1.2 Terminal Loopback

A terminal loopback tests a circuit path as it passes through the cross-connect pathways of the node and loops back from the port where the loopback originates. A terminal loopback on an OC-N port turns the signal around before it reaches the LIU and sends it back through the card. This test verifies that the card’s cross-connect circuit paths are valid.

For example, if you place a terminal loopback on a ONS 15310-CL optical port, the test-set traffic enters on the 15310-CL-CTX DS-3 port and travels toward the OC-N port. The terminal loopback placed on this OC-N port turns the signal around before it reaches the LIU, sending it back through the card to the electrical port. This test verifies that the optical cross-connect paths are valid (but it does not test the LIU for the OC-N port).

Note In CTC, the terminal loopback is sometimes called a “terminal (inward)” loopback, indicating the direction that the loopback signal travels—that is, back toward the port where it originated.

Note Due to hardware limitations on a terminal loopback, you cannot send an AIS downstream on a Cisco ONS 15310-CL CTX card.

1.1.3 Hairpin Circuit

A hairpin circuit brings traffic in and out on an electrical port instead of sending the traffic onto the OC-N line. A hairpin loops back only one specific synchronous transport signal (STS) or virtual tributary (VT) circuit. This kind of circuit test can be run on a node running live traffic because it does not affect the rest of the facility’s traffic.

1.1.4 Cross-Connect Loopback

Across-connect loopback tests a circuit path as it passes through the cross-connect portion of the 15310-CL-CTX or CTX2500 and loops back to the port being tested. Testing and verifying circuit integrity often involves taking down the whole line; however, a cross-connect loopback allows you to create a loopback on any embedded channel at supported payloads at the STS-1 granularity and higher. For example, you can loop back a single STS-1 on an optical facility without interrupting the other STS circuits.

You can create a cross-connect loopback on working or protect OC-3 optical ports unless the protect port is used in a 1+1 protection group and is in working mode.

Note If a terminal or facility loopback exists on an optical port, you cannot use the cross-connect loopback.

1.2 Identify Points of Failure on an Electrical Circuit Path

Facility loopbacks, hairpin circuits, and terminal loopbacks are often used to test a circuit path through the network or to logically isolate a fault. Performing a loopback test at each point along the circuit path systematically isolates possible points of failure.

Cisco ONS 15310-CL and Cisco ONS 15310-MA Troubleshooting Guide, R7.0

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Cisco Systems ONS 15310-MA, ONS 15310-CL manual Terminal Loopback, Hairpin Circuit, Cross-Connect Loopback
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ONS 15310-CL, ONS 15310-MA specifications

Cisco Systems has long been a leader in networking and telecommunications technology, and among its impressive lineup of products, the Cisco ONS 15310 series stands out as an essential solution for optical networking. This series includes models such as the ONS 15310-MA, ONS 15310-CL, and ONS 15310-CA, each designed to meet the diverse needs of service providers and enterprises seeking to enhance their optical transport networks.

The Cisco ONS 15310-MA is an advanced multi-service platform designed for metropolitan area networks. It facilitates the seamless transport of data, voice, and video over optical networks. One of its main features is its ability to support a variety of interfaces, including Ethernet, SONET/SDH, and Wavelength Division Multiplexing (WDM), allowing users to integrate multiple services into a single platform. Additionally, the ONS 15310-MA supports advanced traffic management and Quality of Service (QoS) features to prioritize critical applications and ensure consistent performance.

The ONS 15310-CL variant is tailored for more specific applications, providing enhanced capabilities aimed at delivering carrier-grade services. It features a robust architecture that accommodates high-capacity traffic without compromising reliability. This model emphasizes low power consumption and a compact design, making it suitable for deployment in space-constrained environments. The ONS 15310-CL also supports a wide range of optical interfaces, making it highly flexible for various network configurations.

In terms of technologies, the Cisco ONS 15310 series leverages Optical Transport Network (OTN) capabilities, providing high efficiency and greater bandwidth utilization. OTN technology enables efficient error correction and adds resilience to the network through its built-in protection mechanisms. Furthermore, the series supports seamless integration with existing IP/MPLS networks, creating a cohesive infrastructure as organizations evolve their networking requirements.

One of the defining characteristics of the ONS 15310 series is its focus on scalability. Network operators can start with a modest deployment and gradually expand capacity as demand grows. This adaptability is complemented by Cisco's comprehensive management and monitoring tools, providing operators with real-time insights into network performance and facilitating proactive management.

In conclusion, the Cisco ONS 15310-MA and ONS 15310-CL models represent sophisticated solutions for modern optical networks. With their versatile features, advanced technologies, and robust design, they empower service providers and enterprises to build resilient, high-capacity networks that meet the demands of today’s data-driven world.
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