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Article - October 2002
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L-Switch
Segmentation of LonWorks networks made easy

Hans-Jrg Schweinzer
LOYTEC electronics GmbH. 
info@loytec.com
www.loytec.com 


LOYTEC's L-Switch is the ideal networking component to structure LonWorks and EIA-709 networks. Its plug & play installation allows optimum segmentation of small and large network topologies. Integrated network diagnostics and management functionality guarantees uninterrupted service of any size networks. Up to five network ports on each L-Switch replace up to 4 traditional router modules at the cost of a single router, which makes this device the perfect solution for structured wiring of LonWorks HVAC, lighting, alarm and security systems, etc.

Structured wiring - why?

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Due to its versatility and good performance, LonWorks is the ideal candidate for automating buildings with hundreds of data points. Such demanding applications absolutely require a well-designed concept for network segmentation, in order to achieve good networking performance and a reliable networking infrastructure. But not only large networks, even small and mid size networks benefit drastically from a well designed structured network by using repeaters or even better using routers to improve network reliability and simplify network troubleshooting.

Many reasons can be listed why segmenting a network is important.

In order to keep local traffic within one segment and to avoid overload conditions a typical approach is to place routers between each sub-network and a common backbone segment. A relatively new aspect for LonWorks networks is the logical structuring of networks and the use of existing structured wiring infrastructure in order to connected individual segments with a common backbone channel or even to connect multiple buildings over a high-speed backbone channel. Network segmentation is definitely required in large networks with a large number of nodes in order to build a hierarchical network topology, which is the most practical approach to guarantee a flawless operation of the network. Generally speaking, splitting up a large network into smaller individually manageable sub-segments reduces vulnerability against network faults and improves network maintainability up to a level that easily justifies the small additional cost for the extra networking infrastructure components like the L-Switch.

We all remember the good old days when we had thirty PCs connected to a single 10Base2 COAX cable. And we all remember the days when we were chasing behind this single bad connector or badly behaving network card that was bringing down our entire computer network for hours and sometimes days. Structured wiring was the solution to this problem in PC networks and structured wiring is the solution to this problem in LonWorks and EIA-709 networks.

L-Switch - and sleep better

CatNet Systems With its new L-Switch product line, LOYTEC provides the ideal solution for segmenting LonWorks and EIA-709 networks. The L-Switch combines the advantages of a LonWorks router (better fault isolation, localizing network traffic, connect different media) with the advantages of a simple physical layer repeater (no configuration required, low cost). The L-Switch can operate as a store-and-forward repeater or it can learn the network topology down to the individual node and localize network traffic on a per node basis.

A newly developed high performance routing core can serve up to five individual network ports on a single L-Switch at the cost of a single individual router. This drastically reduces the cost to isolate a segment, which on the other hand allows a higher degree of segmentation at no additional cost. Especially in small and mid size networks where network infrastructure cost is significant compared to the total system cost, network segmentation was many times neglected but would have been very beneficial for improved network reliability and network availability.

LonWorks networks primarily use FT-10, TP-XF1250, TP-RS-485, and power line transceivers. The L-Switch supports all these transceiver configurations at their nominal bit rates and bit-rates between 300 bps and 2.5 Mbps for TP-RS-485 flexible bit rate transceivers. A standard configuration for the L-Switch is the LS-13333C, which comes with one TP-XF1250 and four FT-10 ports. Other transceiver combinations are available as well. A built-in temperature guard monitors the operating temperature of the component and reports if the temperature exceeds a pre-programmed maximum (or even minimum) operating temperature.

Plug & play - not only a saying

One will notice the real advantages of the L-Switch product family when they are being installed in the field. Snap it on a DIN rail or screw it on a wall, connect the power supply and the network cables, and your network is ready to go. After power-up the L-Switch will immediately learn the network topology and network configuration. Patented routing algorithms ensure that the L-Switch is "invisible", like a physical layer repeater, to other nodes in the network or network management tools. The smart, remotely upgradeable firmware auto-detects the bit-rate on the network port, learns the network topology (domains, subnet/node and group addresses) and forwards data packets to the destination port based on the information gathered during the training phase.

Networks are getting installed and commissioned the same way as they were without using L-Switches. They can even be installed in existing networks without a need to re-configure the network. Furthermore new nodes can be added or removed or moved from one port to another port without changing the network configuration. The L-Switch automatically recognizes the modified network configuration and adjusts its decision tables accordingly.

There is no fiddling around with setting up communication buffer sizes since there are no limitations regarding the size or number of the communication buffers inside an L-Switch. Since even the largest possible data packets are managed with ease it really doesn't matter if LonMark compatible communication parameters are used or if large BACNet packets are transmitted over this network. The L-Switch automatically and dynamically optimizes its communication buffers according to the currently existing requirements.

As mentioned earlier the highly optimized routing core can cope with a packet throughput of up to 3500 packets/s at an average processing time of less than 300 s per packet, which leaves plenty of headroom for high-speed channel connections. Up to four domains are supported by the routing core in order to support even the largest conceivable networking scenarios.

PlantPROCOREIntegrated network diagnostics - can this be real?

At an ongoing basis, the L-Switch never gives up collecting a tremendous amount of statistical information about the network traffic on each network segment. This includes peak and average channel utilization, CRC errors and other faulty packets, packet switching statistics, etc. Based on the collected information the L-Switch will recognize problems on each channel like channel overload conditions, connection problems, misbehaving nodes, and will inform the services personnel via an easy to interpret LED indicator. This handy tool allows early indication of upcoming or existing networking problems without requiring sophisticated troubleshooting tools or special knowledge about the network or the LonWorks technology.

Cast a quick glance at the LEDs on the front side of the L-Switch and it will tell about normal or abnormal behavior of the network. Green means ready to roll, red means watch out for troubles in this network segment. If the red LED doesn't go away it is time to do a thorough analysis with e.g. a protocol analyzer (LPA-PP, or LPA-USB) in order to locate and isolate the misbehaving component. This is a fast and simple way to catch and isolate wiring or termination problems as well as systematic system design issues early before they get a chance to bring down the entire network.

LOYTEC launches a new era for properly structured and segmented LonWorks networks with its L-Switch product family. Easy planning, simple installation, reliable operation are the things to remember.


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