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Industrial Ethernet Book 99

Ring topologies using two switches connected to the backbone are creating reliable, redundant ring within each carriage. SOURCE: BELDEN *HWFRQQHFWHG ZLWK0,&526(16 ,QGXVWULDO6ZLWFK3URIL/LQH5DFN *LJDELW3HUIRUPDQFHIRU,QGXVWULDO(WKHUQHW 5XJJHGLHG5HOLDEOH(IILFLHQW VVVLHBQNRDMRCDHMCTRSQH@K Technology of this shift. Ethernet is already used in on-board train systems, despite the challenges presented by the long, thin layout of a train, which brings more opportunity for interference. To overcome the reliability issues this causes, the usual network architecture is comprised of an Ethernet backbone that runs the length of the train, with a “local” network on each carriage to interconnect all of the equipment. Often, two network topologies are used within each carriage. First, linear topologies provide one route to a single switch connected to the backbone for all the equipment. Second, ring topologies use two switches connected to the backbone, creating a redundant ring within the carriage, so all equipment has more than one route to the backbone. The linear topologies are used for less critical data, while the ring topologies are used for mission-critical data. This provides a reliable redundant system within the carriage. Additional complexity is created by the simple fact that trains are mobile. To achieve the level of connectivity required in modern railways, the on-board Ethernet network must be able to understand things that are happening “outside,” such as the direction the train is traveling, where the front, back and middle of the train are, and the impact of lengthening or shortening the train. To overcome these challenges, the International Electrotechnical Commission (IEC) created the IEC 61375 series of standards for electric railway equipment to define architecture and functionality for interoperability between equipment from different suppliers and the safe management of the train’s physical topology. Single communications network The IEC 61375 series of standards is a critical step in making it possible for rail communications networks to operate beyond the current constrained model that only reaches some parts of the train. New standards and technology innovations allow railway operators to connect communications along the entire length of the train, also known as a Consist. Specific innovations include: Coupling of redundant rings: The use of ring topologies within carriages has been described above. The next step in ensuring optimal redundancy requires that carriage-based rings be coupled with others, so redundancy can be ensured along the entire length of the train. This can be achieved with a redundant coupling protocol that allows the coupling of multiple secondary rings to a primary ring. These configurations use a master and slave device to transport data between the networks, with only the master forwarding frames between the rings. Cost-effective and accelerated rollout of high-bandwidth wireless connectivity between carriages: Wireless technology overcomes the challenge of upgrading connectivity between carriages that use interconnection cables, but must be deployed in a way that avoids incorrect connections between access points. Using point-to-point (P2P) links and specifically designed coachto coach functionality eliminates the need for a wired serial link between two WLAN devices. In addition, serial link interfaces can be implemented to allow on-board train management systems to prompt access points to search and discover the correct P2P partner. Connection of train communications network to carriages for intelligent operation: The interface between the Ethernet Train Backbone and the carriage-based networks is handled by a new device called the Ethernet Train Backbone Node. The IEC 61375 standards include communications protocols designed to ensure that the ETBNs work together and provide intelligence to the train network that can improve the operation of the train. As train travel becomes an attractive alternative to congested highways, the applications made possible by high-speed, reliable connectivity will be critical enablers and differentiators for railway operators. New standards for Ethernet connectivity and configurations accelerate the path to costeffective, scalable and innovative solutions that can meet both customer and operational needs for modern-day communications. Richard Weatherburn, global marketing manager for transportation at Belden, Inc.


Industrial Ethernet Book 99
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