Cabling Data Centre Switches – Investment-Secure, Cost- and Attenuation-Optimised

A central component of the infrastructure retrofit was the installation of new Arista switches, whose ports are mapped to LC duplex patch panels (CPL). This approach offers several advantages.

• Firstly, the switches only need to be fully cabled once prior to commissioning; all patching takes place exclusively at the patch panel.
• Secondly, conventional trunk cabling via patch housings and patch cords connected directly to the transceivers would involve additional connectors close to the switches – increasing both costs and signal attenuation.

For the first time, REWE deployed 400GBASE-DR4 QSFP-DD singlemode transceivers equipped with SN-Quad optical interfaces. In the initial expansion phase, each switch contained four switch blades, each fitted with only six instead of the possible eight transceivers. In full expansion, the configuration comprises eight switch blades per switch, each fully equipped with eight transceivers, occupying four rack units (4U) in a 19-inch rack.

Transceivers with SN-Quad optical interfaces have been available on the market for only about two years, while the “trunk direct attach” method implemented here has proven reliable for over three decades. This cabling solution requires factory-terminated trunk breakouts with groups of four SN connectors, each group precisely addressing the corresponding transceiver port for direct connection.

The latest SN connector design, known as “SN EZ-Flip”, features an optimised push-pull locking mechanism that allows on-site polarity reversal without risking fibre breakage.

The PreCONNECT trunk distribution heads use slim, gel-free I-B(ZN)BH loose tube cables meeting the highest fire safety class B2ca under the EU Construction Products Regulation (CPR). Additional features include a tensile strength of up to 3,000 N and integrated non-metallic rodent protection.

Flexible Expansion

Each switch is connected to the patch panel via four 64-fibre singlemode trunk cables, each comprising 32 SN ports – one trunk per switch blade. Initially, the four blades per switch were fitted with only six of the possible eight SN-Quad transceivers. Moreover, only four of the eight potential blades per switch are currently in use.

However, the SN trunk breakouts have already been manufactured to accommodate the full expansion stage. The two unused groups of four SN connectors per switch blade are stored inside the SMAP-G2 2U trunk housing located directly beneath the switches. When the missing transceivers are later added, they can be connected quickly and easily using the pre-positioned SN connectors.

Within the patch panels, PreCONNECT SMAP-G2 SD 19" 3U enclosures from Rosenberger OSI are used. Their highly modular front and rear design and reduced plastic content result in low fire load and excellent sustainability characteristics. The modular design allows for easy, tool-free installation of additional trunks when switches are upgraded with more blades.

The 19-inch housing system is available in various versions with differing port counts and configurations (1U, 2U, 3U or 5U, with depths of 200 or 300 mm). Both the modular architecture and the PreCONNECT square interface enable tool-free trunk cable mounting, while a variety of easily replaceable rear panels supports different cable strain relief options. A mixed operation of fibre and copper cabling is also possible.

Should the switches be replaced during a future technology update with devices using different connector interfaces, the existing trunks and SN connector breakouts can still be reused. The partial front panels with brush strips in the SMAP-G2 19" 2U trunk housings below the switches are simply replaced with versions containing SN adapters. Using hybrid SN-to-Connector-X patch cords, the trunks can continue to be utilised without any modifications required in the patch panels. This ensures a high degree of investment protection and allows future upgrades to be carried out with minimal effort.