aoc/dac cable testing in data centers - ecoc … cable testing in data centers © 2017 viavi...

Guylain Barlow

Viavi Canada19 September 2017

AOC/DAC Cable Testing in Data Centers

2© 2017 Viavi Solutions Inc.www.viavisolutions.com

• Data Center Architectures

• Cabling in the Data Center

• Testing AOC/DAC Cables

Agenda

3© 2017 Viavi Solutions Inc.www.viavisolutions.com 3© 2016 Viavi Solutions Inc.www.viavisolutions.com

Data Center Architectures


Three categories:

Private

Data Center Types

Multi-tenant

Hyperscale (ICP)

Hyperscale/ICP: Cloud companies delivering some type of content, entertainment, media Multi-tenant: Companies that offer datacenter services to various customers (tenants) in

the same building Private: Financial institutions, enterprise, fortune 500 companies with data centers


Simple Data center / DCI Network ArchitectureDCI connections can vary:• Layer 3 IP routed services• Layer 2 EoMPLS• Layer 2 DWDM• Layer 2 CWDM• OTN Connectivity


Architectural Pros and Cons

ToR EoR/MoR Zone/ Centralized

Advantages • Easier cabling, shorter cables• If rack not fully populated,

can add unused ToR ports (toscale)

• Servers can be placed inany rack

• Ports more easily added &upgraded

• Servers & routers centrallylocated and managed

• Ports most easily added &upgraded

Disadvantages • If rack traffic demand is high,difficult to add more ports

• Upgrading (i.e. 1G to 10G)requires complete rackupgrade

• Longer Cables • Potentially longest cables• Leads to patch panel

management


Cabling in the Data Center


What is MPO?– MPO (Multi-fiber Push On) is a connector for RIBBON

cables with 12 to 96 fibers (field usage is 12 or 24fibers).

– Connectors for SMF have angled ends to minimizeback-reflection

– Connectors for MMF typically have flat ends• 40GE and 100GE on MMF; except PSM4

– Can carry multiple 10GE links on MPO/ribbon cables– MTP is branded as “enhanced” MPO: registered

trademark of US Conec– The challenges of inspecting MPO are being resolved

Fan-out/Break-out MPO cable


MPO cable polarity

“Straight” cables for patching(patch panel)

“Cross-over”to interconnectequipment

Cross-connectsmultiple paired connections (e.g. multiple 10GE)


High-speed cables terminated by ‘optics’ (no MPO)• AOC: Active Optical Cables• DAC: Direct Attach Copper (active or passive)Terminated by QSFP or SFP

• Available at multiple data rates• Typically from 10Gbps up to 100Gbps

• Fixed length cables – Alternative to patch cords• In Data Centers, used in many locations including

between switches and servers, between switches

Use of AOC/DAC Cables

Transport

Router

Leaf/Spine

TOR/Leaf

Servers


AOC Versus Optics & Patch Cords

Optics & (Duplex or MPO) Patch Cables

Active Optical Cables

Advantages • No data rate dependency for opticalpatch cords

• Flexibility

• Typically cheaper than 2 optics + fiber• No optical termination, no dirty

connectors• Makes connectivity simpler• Opportunity to reduce power

consumption & heat

Disadvantages • Need to inspect/clean• Different types of MPO cables

(A/B/C) to manage

• Fixed length for assembly• Cannot use patch panels; harder to scale

Comment • Optics always follow an specificinterface standard

• No interface standards


Market Trend: Shipments of Multimode Pluggables

Source: Lightcounting Ethernet Forecast March 2017

Short reach optics shipments are led by data center requirements

Growth line rates are 100GE and 25GE Some 200GE in 2018/2019


Testing AOC/DAC Cables


Should I test an AOC/DAC?

• Typical mode of operation is plug & play of cables in/across racks and look for green light

• Some data center users have reported perceptions of a high cable failure rate ‐ Is it the cable?‐ Is it the configuration?

• Much time is spent troubleshooting or re-routing a new cable

• Testing or even sample testing in the data center quickly pays for itself


Cable Test Use Cases

Before cable installation: requires dual ports

• Test AOC/DAC cables before they are installed

After cable has been installed:2 units - 1 port per unit

• Need 2 to access each end of the cable for troubleshooting


DAC vs. AOC – Pros and Cons / Potential Failure Causes

Direct Attach Copper Active Optical Cable

Advantages Disadvantages Advantages Disadvantages• Cost effective • Heavy and bulky

• Vulnerable to EMI• Supports high BW

(up to 100GE) • Lightweight• Longer reach

• More costly• More easily

damaged

Failure Causes

• Cables with wrong or faulty polarities • Mislabeling issues• Damage introduced during shipment

• Vulnerable to EMI degradation • Crushed fibers• Excessive bend


What to test in an AOC/DAC?• Key challenge is lack of access to fiber/electrical connectors

‐ Only possibility is test connectivity with dual ‘optics’ connectors

• Main parameter of an AOC/DAC is its Bit Error Rate specification

Bit Error Rate Testing‐ Can be accomplished using a stressful pattern (i.e. PRBS 31)‐ Get pass/fail results‐ When cable designed to work using FEC (Forward Error Correction), must

replicate use case conditions with error correction

Polarity Testing‐ Potentially useful. AOC/DAC are purpose built though and equivalent to

Type-B cables


Forward Error Correction (FEC)

• Some data rates (primarily 100GE and 25GE) have a built-in error correction mechanism‐ Not 40GE nor 10GE

• With FEC, there is a Bit Error Rate before and after correction

• Example of 100GE AOC specification:

Ethernet Rate Interface Type FEC

100GE

PSM4 MSA YesSWDM4 Alliance Yes

100GBASE-SR4 Yes

100GBASE-CR4 Yes

40GE

SWDM4 Alliance No

40GBASE-SR4 No

40GBASE-CR4 No

25GE

25GBASE-SR Yes

25GBASE-CR Yes25GBASE-CR-S No

10GE10GBASE-SR No

10GBASE-CR No

Cable Specification

Max Note

Pre-FEC BER 10-6

Post-FEC BER 10-12 FEC provided by host system


• Bit Error Rate theory using a PRBS pattern (PRBS 31 for 10G & above) depends on three parameters:

• Bit Rate• Confidence Level (statistical probability result is valid)• Bit Error Rate threshold

• Examples for Ethernet:

Bit Error Rate Theory – Test Times

• Most AOC/DAC have a BER rating, some do not

• The industry ‘default’ is 10-12

• Operations teams prefer short test times• In practice, a minute or less is sufficient

100GE 90% CL 95% CL 99% CLBER threshold

1.0E-10 0.2 sec 0.3 sec 0.4 sec1.0E-12 22.3 sec 29.1 sec 44.6 sec1.0E-15 6.2 hrs 8.1 hrs 12.4 hrs

10GE 90% CL 95% CL 99% CLBER threshold

1.0E-10 2.2 sec 2.9 sec 4.5 sec1.0E-12 3.7 min 4.7 min 7.4 min1.0E-15 61.9 hrs 80.8 hrs 123.9 hrs


• Run short tests for efficiency• Can test a lot of cables in a short time• Identify faulty cables upfront before installation

• Optionally run longer test on a failed cable raise confidence level in results• Failed cable can often replaced under warranty

• For cables used with FEC, get pre-FEC & post-FEC results• Pre-FEC is easier to evaluate but cable should be error free post-FEC (after

error correction)

Recommendations

www.viavisolutions.com

aoc/dac cable testing in data centers - ecoc … cable testing in data centers © 2017 viavi...

Documents