Migratable cabling in computer centres for all data rates from Mbit/s to 100Gbit/s (DClink)

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1 Introduction Computer centres must be reliable and available around the clock even during conversion work. Data rates are increasing constantly, and the FO cabling which only recently supported all applications can quickly become inadequate. Whereas data rates of up to 10 Gbit/s were transmitted over individual fibres or fibre pairs in the past, computer centres now allow higher transmission rates over several parallel fibres. The result is an entirely new cabling with nx12 multimode fibres in OM3 or preferably OM4 quality. As a result, the migratability and with it the application neutrality of the existing cabling is no longer adequate. The standards situation The currently valid standard IEEE 802.3ba describes transmission via multimode fibres over short distances (100m via OM3, 150m via OM4) such as those usually found in computer centres. For 40 GbE, parallel transmission with 4x10 Gbit/s over 2x 4 fibres is standardized for 40 GbE (40GBASE- SR4), and 10x10 Gbit/s over 2x10 fibres is standardized for 100 GbE (100GBASE-SR10). The current cabling standards ISO IEC11801 and EN take this into account, prescribing laseroptimized OM3 and OM4 fibres for channels with lengths of up to 100m or 150m. The permanent connections are realized via multifibre push-on connectors (MPO) with 12 or 24 fibres, and not all fibres are used in the push-on connection. For 40GBASE-SR4, it is specified that the outer fibres in each case are to be used (see Fig. 1). Tx Tx Tx Tx Rx Rx Rx Rx Fig. 1: MPO connector for 40GBASE-SR4 For 100GBASE-SR10, the inner fibres in each case are used, and three different port arrangements are possible for the active components: Side-by-side port, i.e. two MPO connectors with 12 fibres each are positioned next to each other (Fig. 2) Vertically stacked ports, i.e. two MPO connectors with 12 fibres each are positioned above one another (Fig. 3) Single port, i.e. one MPO connector with 24 fibres is arranged in two levels (Fig. 4) Tx Tx Tx Tx Tx Tx Tx Tx Tx Tx Rx Rx Rx Rx Rx Rx Rx Rx Rx Rx Fig. 2: Side-by-side port for 100GBASE-SR10

2 Rx Rx Rx Rx Rx Rx Rx Rx Rx Rx Tx Tx Tx Tx Tx Tx Tx Tx Tx Tx Fig. 3: Vertically stacked port for 100GBASE-SR10 Rx Rx Rx Rx Rx Rx Rx Rx Rx Rx Tx Tx Tx Tx Tx Tx Tx Tx Tx Tx Fig. 4: Single port for 100GBASE-SR10 The highest permissible insertion losses for the channel as a whole (the optical power budget) are 1.9dB (OM3) or 1.5dB (OM4). The issue In addition to the challenges with regard to the security of computer centre operation, rapid convertibility and ease of installation, the issue facing the cabling itself is as follows: 1. For the reasons given above, the existing cabling with individual fibres or fibre pairs is no longer adequate for transmission rates of more than 40 Gbit/s. 2. The cabling for 40 and 100 Gbit/s with MPO cannot simply be used for lower data rates as 12 or even 24 fibres are always connected simultaneously but only two fibres are required per channel. 3. For the high data rates, several fibres are used in parallel. Individual fibre cablings with pigtails spliced on or connectors assembled in situ are not suitable here. 4. The extremely low insertion losses of 1.9dB or 1.5dB are another challenge which can only be met by using a certain minimum amount of very carefully assembled high-quality connectors. Solution With DClink, LEONI Kerpen now provides a cabling system for computer centres which meets the highest possible requirements with regard to quality and availability and still has the flexibility necessary for transmitting all data rates used previously and for adapting to higher capacities or totally new requirements in an extremely short time. The installed basis, i.e. the cabling including the patch fields, never needs to be changed again, no matter which data rate is used or which application is run via the cabling. The basic module for this is the VarioLine DClink mounting frame (Fig. 5) for GigaLine DClink modules (FO) and / or MegaLine DClink modules (Cu).

3 Fig. 5: VarioLine DClink mounting frame Solution A the genuinely application-neutral cabling GigaLine DClink now also allows you to build up a genuinely application-neutral, migratable cabling for up to 100 Gbit/s in FO technology too. Using three DClink modules (3 x 8 MPO couplings) on one rack unit (Fig. 6), up to 24 x 40 GbE or 100 GbE systems are possible depending on the number of fibres in the MPO. Patching is carried out using MPO patch cords. Backwards compatibility is guaranteed nevertheless, without the necessity of changing the fixed cabling including the patch fields. In other words, transmission systems for 10 GB or less (two-fibre systems) can be run via this cabling too. The only difference concerns the patch cords used, which have one MPO connector on one end and six or twelve LC duplex connectors on the other - so-called "fanouts" (Fig. 7). With this solution, up to MB, 100-GB or 10-GB channels are available on one rack unit, and even up to 288 of them when MPO with 24 fibres is used. In other words, they are completely application-neutral (Fig. 8). Fig. 6: VarioLine DClink mounting frame with three 40/100 GbE DClink modules with 8 MPO each Fig. 7: Fanout Advantages of Solution A: The fixed cabling is application-neutral and migratable, i.e. it can be used for all transmission rates usual up to now. This means they are future-proof to the greatest possible extent! Not even the slightest conversion work is necessary during operation. This means time and cost savings and, most important of all, security. Also, special MPO patch cords (male instead of female ones) are not required, i.e. it is not necessary to store different patch cords, there is no danger of confusing them, less errors occur and security is higher.

4 The transmission technology can be changed to other transmission rates in the lowest time imaginable. This allows cost savings to be made. Less personnel are required for the cabling. Here, too, this means more security and cost savings. 10 GBit/s: 144 Channel / 1HE Fanout MPO 6 LC-Dx (12 fibers) Patchfeld 19 1 HE mit 24 MPO = 40 GBit/s: 24 Channel / 1HE Patchcord MPO MPO (12 fibers) 288 Fasern 100 GBit/s: 12 Channel /1 HE Patchcord 2 MPO 2 MPO (2x12fibers) MPO connector LC-Dx connector Fig. 8: Application neutrality for 10/100 Mbit/s, 1/10/40 and 100 Gbit/s with twelve-fibre MPO cabling (diagram) Solution B the flexible cabling: Of course, GigaLine DClink allows cablings with individual fibres for maximum data rates of up to 10 Gbit/s to be realized using up to 36 LC duplex connections or 36 channels per rack unit (Fig. 9) or a combination of both versions, and even Cu solutions can be integrated. Here, too, conversion to higher data rates (40/100 GbE) can be realized very rapidly and with little effort. The DClink housing is released from the frame using an unlocking tool and pulled out with the cable, a new DClink with eight MPO connections is inserted and snapped in and that's all! In this way, the cabling can be successively converted to the version described above with as little effort as possible.

5 Fig. 9: VarioLine DClink mounting frame with GigaLine DClink modules (12 LCD) Advantages of Solution B: Initially, data rates of up to 10Gbit/s can be managed via duplex patch cords as before. Cabling for higher data rates using MPO connection technology is only used if required. When the systems are replaced, the cable which is no longer being used is always removed from the cable trays, thus ensuring ample space and a clear arrangement of cables. In comparison with the products of the competitors, this solution has the advantage that one rack unit has room for not only three or six 40/100 GbE systems after conversion but for 24 of them. Also, special MPO patch cords (male instead of female ones) are not required, i.e. it is not necessary to store different patch cords, there is no danger of confusing them, less errors occur and security is higher. Outlook Data rates are increasing constantly and the limits of the feasible are being expanded all the time, but again and again the next stage of development allows even higher goals to be aimed at. Today the data rates are 40 and 100 Gbit/s, but they will be ten times this figure five or six years from now (see Fig. 10). Even today, plans are afoot to realize 400 Gbit/s and 1000 Gbit/s. In addition to increasing the capacities in the copper field, for example 40GBASE-T via the existing Cat 7 A cabling (30m to 100m), the future projects of the IEEE HSE Subcommittee will be dealing with 400 Gbit and Terabit Ethernet. The first priority is to raise the data rates on the individual "lanes", i.e. from 10x10 Gbit/s (100GBASE- SR10) to 4x25 Gbit/s (100GBASE-SR4). This means that one 12-fibre cabling is adequate for 100 GbE and not one 24-fibre cabling as before. The trend is obvious! It is safe to assume that the cabling with the 12-fibre plug is exactly the right one, even for the higher data rates of the future.

6 Fig. 10: Bandwidth growth and applications (source: IEEE 802.org/Force10Networks) Conclusion: Data rates of up to 100Gbit/s will be the norm in future-proof computer centres in the years to come. From today's point of view, the aim seems to be to realize transmission over 8 fibres - connectors for 24 fibres are then no longer suitable. For this reason, the recommendation made when building a new computer centre is to use a twelve-fibre cabling with MPO connection technology. With DClink in 12-fibre MPO technology, i.e. 3 x 8 MPO in the 1RU patch field, there is room for 24 systems with 40 GbE, 12 systems with 100 GbE or 144 systems with up to 10 GbE in one RU. If CU channels are necessary, these can also be integrated in the form of DClink. Stolberg, May 2011 LEONI Kerpen GmbH Heinz Wollenweber Product Manager