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Application Note 2696 Redundancy Protection T3/E3/STS-1 Networks
Reliability yields itself profitability. This strong theme that considered when designing system, especially telecommunications industry, where increased competition caused greater need most equipment that purchased. Service providers demanding that their networking equipment remain active 99.999% time, nines" sometimes called. This done only stay competitive, also remain profitable. Therefore, burden been placed networking equipment manufacturers design systems that meet exceed this expectation. ways this design systems that have built-in redundancy areas design. This concept new, what approach this problem with respect STS-1 network interface. past, designing redundancy network interface trivial because port count relatively low. redundancy required, circuit could switch network variety methods. However, demand bandwidth increases, does port count well need redundancy your design. This article will examine some different types redundancy protection schemes T3/E3/STS-1 network interface, while paying particular attention this scheme implemented with Dallas Semiconductor/Maxim T3/E3/STS-1 line interface unit (LIU), specifically DS315x family parts (DS3151, DS3152, DS3153, DS3154).
REV: 091203
Note 2696: Redundancy Protection T3/E3/STS-1 Networks
TYPES REDUNDANCY SCHEMES
Protection
Whether designing network router, access, DSLAM, Auplink multiplexer, device will probably need functioning almost entire life product, using redundant solution will need considered. There several ways this. small port counts, relays have often been used effective solution. Figure shows this type protection scheme. Please notice, line cards were chosen design. there problem with primary card, switch protection card replace primary card without disrupting service from network significant length time. Both line cards identical this protection scheme. This important when keeping replacement card inventory. necessary keep trace lengths that connect Line Card Line Card short possible prevent reflections transmit signal thus creating potential pulse mask violation. recommended keep traces lengths more than inches from connector.
Figure
Note 2696: Redundancy Protection T3/E3/STS-1 Networks
Protection
When line cards increase greater than becomes much more difficult efficiently protect network interface with redundancy. matrix card used switch different line cards communication network. Although this method functional, there problem when matrix card fails. replace this card, system needs taken line either repair replacement card. Dallas Semiconductor/Maxim developed redundancy scheme that allows user swap line cards while still keeping protection card active. Figure line cards used active devices, such DS315x line interface unit well relays local oscillators. this design, matrix card signals between primary protect card. Instead, designed solution using BALUNS network, Balanced-to-Unbalanced network. This also referred power splitter/combiner. power splitter passive device that accepts input signal delivers multiple outputs with specific phase amplitude characteristics. Figure power splitter/combiner directly front that connected separate line cards. output goes primary card that power splitter while other routed card below-not next card. routed what known protect bus. event that Line Card fails, relay protect Line Card closed, Protect Card activated that data still transferred T3/E3/STS-1 network. Line Card that failed then replaced without disrupting service.
Note 2696: Redundancy Protection T3/E3/STS-1 Networks
Figure
Note 2696: Redundancy Protection T3/E3/STS-1 Networks
POWER SPLITTER
With T3/E3/STS-1 networking applications, output signals from power splitter should equal amplitude, 0-degree phase relationship between signals, high isolation between each output signal, maximum 3.0dB insertion loss from input output. Anything greater than 3.0dB cause problems meeting pulse-mask template, important requirement telecommunication-networking applications. Figure shows symbol representation common power splitter. Notice that this device centertapped transformer input with resistor connected other ends inductor, which serves other outputs some cases, other inputs. resistor across transformer functionality this design. helps balance impedance between Port Port well causing high signal isolation between ports from input Port
Figure
When device used power splitter receive side LIU, signal isolation caused assuming Port Port have exactly same load. voltages generated ports will have same amplitude polarity. Since have same voltage both ports, current flows through resistor causing desired isolation between ports. Figure shows graphical representation this circuit. symmetry, that same. Therefore, voltage node will equal well.
Figure
Note 2696: Redundancy Protection T3/E3/STS-1 Networks When device power combiner like used transmit side LIU, there still high isolation between there with power splitter. signal applied Port causes current flow through inductor creates 180-degree phase shift when reaches Port However, there current flowing through resistor that phase shifted when reaches Port Therefore, choose specific resistance RINT, ensure that current will equal amplitude opposite phase current from inductor. this case, there voltage change Port high isolation from ports achieved. given STS-1 network, what would value RINT cause 100% isolation between Port Port power splitter/combiner network redrawn Figure this situation, current forced Port obtain specified voltage Port following equations will show isolation obtained with proper RINT resistor Port
Figure
simplify equations, assume that will 75W, fact that mutual inductance transformer large enough cause leakage current between nodes. Therefore, derive following equations. 75W)
Note 2696: Redundancy Protection T3/E3/STS-1 Networks Rint Solve Rint replace with This result gives Rint Replace with then with gives Rint (75W) Replace with product Rint (75W)(4 4V2) want stated above, solve RINT 150W. other value RINT will cause voltage voltage With RINT equal 150W, desired isolation between ports achieved. Please notice that voltage gets attenuated factor because This could cause problem meeting Telecom Pulse Mask specs networking interface. overcome voltage drop port (V3), DS315x increase gain transmitter with test register each port located 8)], where port number from Figure shows pulse mask DS315x that connected redundancy protection scheme, shown Figure With test register enabled, DS315x easily generate voltage required pulse mask specification even with extra load from power/splitter combiner. Schematics listing this design found Dallas Semiconductor/Maxim website www.maxim-ic.com/telecom. (75W) 75W)
Note 2696: Redundancy Protection T3/E3/STS-1 Networks
Figure CONCLUSION
competition increases service providers, demand will also increase networking equipment manufacturers provide solutions that both highly reliable cost effective. using redundancy scheme with Dallas Semiconductor/Maxim's DS315x LIU, this objective obtained.

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