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DDW-142
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Catalog excerpts

DDW-142 - 1

Diagnostics and preventative maintenance Twisted pair cables Twisted pair cable consists of a pair of insulated wires twisted together. This type of cable has been used in telecommunication for many years. Cable twisting helps to reduce noise pickup from external sources and crosstalk within multi-pair cables. Twisted pair cable is good for transferring balanced differential signals. The practice of transmitting signals differentially dates back to the early days of telegraph and radio. The importance of improved signal-to-noise ratio and reduction of crosstalk are particularly valuable in installations in harsh environments. The most commonly used form of twisted pair is unshielded twisted pair (UTP). It is just two insulated wires twisted together. Many data communication cables and normal telephone cables are this type. Shielded twisted pair(STP) differs from UTP in that it has a foil jacket that helps prevent crosstalk and noise from external sources. In data communications there is a cable type called FTP (foil shielded pairs) which consists of four twisted pair inside one common shield (made of aluminium foil). Westermo has for some time offered Industrial Ethernet extension solutions allowing companies to create high speed Ethernet links by reusing existing cabling. This solution obviously saves much time and money at the installation phase of a network but the use of old cables with uncertain routing and old joins may be perceived as a maintenance risk. What can be done to mitigate these risks? There are several ways to do this. Firstly the creation of a resilient network structure with diverse routing will ensure that a single point of failure in a network will not result in downtime. The next option is to ensure that any link is not at the extreme of performance and the final method is to maintain constant monitoring of the quality of the link. In order to reduce emission significantly, the use of shielded cabling proves to be far the most straight forward solution. But balanced transmission or balanced transmission plus shielding are two different means to achieve good EMC performance. With a well balanced system, will shielding really be necessary? Will STP always give better EMC performance than UTP? The answer is not clear and depends on application. Both cable types have their good and bad properties. Since the line interface of SHDSL is perfectly balanced you can almost state that there is no need for shielding at all. ■mnr.MWNmtUn - A 6<i|tr Efetrtxtci Crmf Comjun,

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DDW-142 - 2

Characteristics of a cable that affects the reach Resistance It is measured in ohm/km and varies with the wire s material and cross section. The resistance of the cable is evident from the data sheet for each cable. At low transmission rates it is the resistance that sets the limitations. Capacitance As the conductors in the cable are isolated from each other they will generate a capacitive effect between each other. The twisted pair, conductor material and any screen will also have an effect. The capacitance attenuates the signals differently at different frequencies. Capacitance is...

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DDW-142 - 3

Noise margin The noise margin is the difference between the required SNR for a certain bit rate, and the actual SNR. When the SHDSL connection data rate is set to auto (auto-negotiation mode), the operator can configure a reliable (10dB), normal (6dB) or high speed mode (3dB). In reliable mode noise margin gives robustness against SNR fluctuations. Specifying a large noise margin may imply that a low data rate is negotiated. The G.HS threshold setting is only needed if the units are located in a noisy environment with SHDSL line cables of good quality. With this setting it is possible to...

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DDW-142 - 4

The DDW-142 is a fully managed network device and supports Simple Network Management Protocol (SNMP). By setting up and using a Network Management tool values within the Management Information Base (MIB) of the DDW-142 The DDW-142 supports relevant parts of RFC 4319 HDSL2/SHDSL MIB: Variables showing the SNR of each line can be monitored. The DDW-142 utilises the Westermo WeOS network operating system which allows for a range of Alarm sources to be easily supported. Amongst these sources is the SHDSL/xDSL SNR-margin which triggers in the event that SNR margins fall below a configured When...

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DDW-142 - 5

In WeOS different action profiles can be created these action profiles can then be used together with alarms Actions that can be taken are 1) An SNMP Trap is sent to a designated trap receiver. g3 Kiwi Syslog Server (Ver Hostname Message 04-14-7011 I7,34,?0 I nr.al7 Debog 192 160 I 704 r.nmmunirv rrap, enrerprise I 3 0 I 7 I 10 40 D 7 enterprise mib name hr1sl?rihr1sir.NRMarninr.rnssinn uptime 130/97/ anenl ip 19? 101 In WeOS it is possible to configure two different trap host addresses. 2) A log can be made to a file in the DDW-142 unit itself or a packet can be sent to an external server...

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