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l0c0b0x
Asked: 2009-05-22 08:30:46 +0800 CST

What are the advantages/disadvantages for using a single strand of fiber for a full-duplex link?

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I have seen telcos install one-strand fiber links at full-duplex, but haven't found much documentation about this configuration.

What are the bandwidth limitations, troubleshooting complications, advantages and/or disadvantages for this kind of setup?

networking wide-area-network local-area-network fiber

5 Answers

  1. I suppose that you are talking about WDM (Wavelength-division multiplexing) using SFP. The bandwith available for a single strand of fibre is bounded only by the money : quoting a figure from a telecom vendor 80*40Gb on a fiber for a transport network dwdm device.
    Using cisco as a reference , i find that the maximum bandwith available for non-telco dwdm is 1G ( 10G coming ). The advantage for the provider is that using DWDM it doubles the available optic fiber for connections. For the consumer , there is no advantage nor any disadvantage , since it is 'transparent'.

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  2. Telcos use single core sfps to double the number of services they can run in a given street fibre bundle. The sfps come in a matched set, BX-U transmits at 1310nm and receives on 1490nm. While BX-D transmits at 1490nm and receives on 1310nm.

    The standard models have a range of about 10kms and operate at 1gb/s. As far as the switch and troubleshooting goes they look and act like a normal two core sfp. One advantage is that you can't get your tx and rx fibres around the wrong way.

    Cisco part numbers are GLC-BX-D= and GLC-BX-U=.

    I used to work for a telco deploying these style of setup.

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  3. Best Answer

    The two solution already mentioned (DWDM & single-core-SFPs) are both methods of getting multiple signals down a single strand of fiber.

    As Haakon said, single-core-SFPs work in pairs and just replaces your normal SFP/GBIC modules in standard network equipment. And as cavver said, DWDM is another method. DWDM though is more complex, requires separate pieces of equipment and is much more expensive.

    http://en.wikipedia.org/wiki/Wavelength-division_multiplexing

    The advantages are that you can get more data down the same infrastructure allow you to double (at least) your bandwidth. [DWDM gear can carry multiple signals (160+ channels) over a single piece of fiber and can intermix data and voice traffic.]

    The disadvantages are you may sacrifice the distance the signal can travel and of course you increase your risk. If a single strand is cut, twice as much is impacted.

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  4. Multi mode fiber has no trouble carrying a full-duplex connection. As far as the connection rate that is a factor of the distance. Several other mitigating factors can hurt your speed including the light source single mode fiber with led based source is far less affective (range and speed) then multi mode with a laser.

    Luxlinks has a good reference for estimating your speeds for a particular setup.

    Unfortunately it appears I cant add links (maybe because this is my first post).

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  5. Advantages: 1: DWDM is suitable for long haul transmission. 2: Data transperancy. 3: Smooth expansion to the network at any node. 4: Multi data transmission network. 5: Less amount of regenerator is used. 6: Easily add/drop two channels of service.

    Disadvantages: 1: Expensive approach compared to CWDM. 2: Attenaution occured. 3: Amplifiers are used to improve the power and gain of the input signals, which effect the cost of equipment.

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