Dr. Paulo Marin, EE/BSc, MSc, PhD. Electrical Engineer, ICT Consultant

Transcription

1 Is Cable Balancing Efficient i Enough for EMI Mitigation in Data Centers? Dr. Paulo Marin, EE/BSc, MSc, PhD. Electrical Engineer, ICT Consultant

2 What are You going to Learn? What are the potential sources of EMI in data centers that may affect data communications? How to improve data center s cabling immunity to EMI? When installing copper, should it be screened or unscreened, and why?

3 Agenda Data Centers Standards Review EMI Sources & Effects in Data Centers EMI Basics Techniques to Improve Cabling Immunity Installations ti Best tpractices Strategies to Mitigate EMI in Data Centers

4 Standards Review ANSI/BICSI 002: Data Center Design and Implementation Best Practices ANSI/TIA 942-A: Telecommunications Infrastructure Standard for Data Centers ISO/IEC 24764: Generic Cabling Systems for Data Centers CENELEC EN : 5: Information Technology Generic Cabling Systems Part5: Data Centers ii i h i d EMI mitigation techniques are not covered in data centers infrastructure standards.

5 Data Center Cabling Topology MDA: Main Distribution Area IDA: Intermediate Distribution Area HDA: Horizontal Distribution Area ZDA: Zone Distribution Area EO/EDA: Equipment Outlet / Equipment Distribution Area In compliance with BICSI 002 and TIA-942-A

6 Recognized Transmission Media Backbone Cabling 4-pair, 100-ohm, balanced twisted-pair Category 6/Class E (250MHz) minimum (unscreened and/or screened) OM3/OM4, 50/125μm laser-optimized multimode fiber OS1/OS2 singlemode optical fiber cable 75-ohm coaxial cabling 734/735-type Horizontal o Cabling 4-pair, 100-ohm, balanced twisted-pair Category 6/Class E (250MHz) minimum (unscreened and/or screened) OM3/OM4, 50/125μm laser-optimized laseroptimized multimode fiber OS1/OS2 singlemode optical fiber cable

7 Typical Data Center Cabling Backbone Cabling Fiber Optics (OM3, OM4) Horizontal Cabling Category 6 (250MHz) Copper Category 6A (500MHz) Copper

8 Data Center Cabling Differences between standards related to media TIA Cat 8 x ISO/IEC TR Balanced cabling for 40Gbps channels 30 meter channels (26 m with 2x2m patch cords) to support 40 Gb/s using Cat 6A, 7, 7A Cat 8.1 for Class I channels is backward compatible with Cat 6A Cat 8.2 for Class II channels compatible with Cat 7/7A

9 - Power cables EMI Sources & Effects - Transformers, PDU, Switchgear - CRAC units, UPS, etc. - Impairments due to shielding and grounding Introduction of noise into the disturbed channel Increase the system s BER (Bit Error Rate) Errors on data communications: operation downtime

10 Power Cables Interference Interference from power cables: Most significant interference that t may affect data communications i in data centers!

11 EMI Basics Electric fields: associated with voltages coupled into the disturbed channel as noise due to capacitive coupling. Magnetic fields: associated with currents that flow through the surface of the disturbed d channel and generate noise due to inductive coupling.

12 How to Improve Cabling Immunity? The following techniques are deployed to mitigate electromagnetic interference: Balancing Screening (Shielding) Bonding & Grounding

13 Balancing Principle Transmitter (Tx) Receiver(Rx) E H Efficient technique to mitigate: - Internal crosstalk* - RFI - EMI E H V 1 = V 2 in magnitude, opposite in phase (180-degree phase shift). *Balancing alone may not be efficient enough to cancel alien crosstalk.

14 Common Mode Noise Rejection Balancing helps common-mode mode noise currents to be driven to ground Balancing alone offers 20 db (approximately) common-mode noise rejection Balancing is an efficient noise reduction technique

15 Cable Screening (Shielding) Use of a conducting material around the twisted pairs cable core Used to keep the electric and magnetic field within the cable as well as to avoid external signal coupling into the cable conductors from external EMI sources Screening of cables from electrical fields is something easy Screening from magnetic fields is more complex, specifically at low frequencies

16 Bonding & Grounding Proper grounding in cabling systems can solve most of the noise problems by: Providing a ground path to common-mode noise currents Decreasing the cable s shield overall impedance and then increasing its shielding effectiveness Eliminating ground loops* Recommend dfollowing ANSI/TIA-607-B & NECA/BICSI ANSI/BICSI 002 addresses TIA-607-B standard as well *When grounding is provided at one channel-end.

17 Ground Loops Occur due to potential differences between two (or multiple) ground connections Can be a source of noise in cabling systems using screened cabling Bonding/Grounding cable shield at one channel-end breaks the ground loop and minimize noise coupling into the signal conductors

18 Ground Loops (cont d) 1 2 Noise rejection > 20 db No resulting noise voltage coupled into the load! Noise rejection > 20 db No resulting noise voltage coupled into the load!

19 Ground Loops (cont d) 3 4 Noise rejection < 20 db Load is subject to noise due to ground loop. Noise rejection 30 to 40 db No resulting noise voltage coupled into the load!

20 Ground Loops (cont d) Noise rejection > 20 db No resulting noise voltage coupled into the load! Noise rejection 30 to 40 db No resulting noise voltage coupled into the load!

21 Screened versus Unscreened Category 6A Channel Alien Crosstalk Performance F/UTP Cable Cable shield Cable shield Alien Cros sstalk (db) Limit UTP F/UTP U/UTP Cable

22 Installations Best Practices Bonding & Grounding Telecommunications bonding must be provided at one cable-end In data centers: bond at the distributors locations

23 Installations Best Practices (cont d) Separations between power and telecom cables and equipment No mandatory specifications for data centers cabling Recommendation to follow ANSI/TIA-569-C (Annex B, informative) Other manufacturer s recommendations as well as local regulations may be taken into consideration

24 Conclusions Where to use screened or unscreened cables? It depends primarily on the distribution of electric and magnetic fields in the environment A preliminary i study of EM distribution ib ti should be carried out in the cabling design phase A NARTE (National Association of Radio and Telecommunications Engineers) certified engineer should be consulted

25 Conclusions (cont d) A TEMPEST-experienced Engineer should be consulted Computer-aided tools should be also deployed (e.g., COMSOL Multiphysics Simulation, etc.) In the case the above is not feasible, follow recommended d separations (following slides)

26 Strategies to Mitigate EMI in Data Centers Recommended Separation Distance Between Power Cables and Telecommunications Cabling in Data Centers Qty of Type of circuit U/UTP Balanced Cable F/UTP Balanced Cable power circuits Separation (mm) Separation (in) Separation (mm) Separation (in) 1to A 110/240V 1-phase 50 mm 2in Zero Zero shielded or unshielded 16 to 30 20A 110/240V 1-phase 50 mm 2 in Zero Zero shielded 31 to 60 20A 110/240V 1-phase 100 mm 4in Zero Zero shielded 61 to 90 20A 110/240V 1-phase 150 mm 6 in 50 mm 2 in shielded Over 91 20A 110/240V 1-phase 300 mm 12 in 100 mm 4i in shielded A 480V 3-phase shielded feeder 300 mm 12 in 100 mm 4 in

27 Strategies to Mitigate EMI in Data Centers Recommended Separation between PDU and switchgear and Telecommunications cabling distributors ib t Minimum: 600 mm (Non-metallic barrier) Recommended: 300 mm (if a metallic barrier is provided)

28 THANKS!/Questions? Dr. Paulo Marin, EE/BSc, MSc, PhD. Electrical Engineer, ICT Consultant Ph.: Cell.: Skype: paul_s_marin marin@paulomarin.com