D ATA C ENTER N ETWORKING T OPOLOGIES 1. O VERVIEW Data Center Physical Layout Data Center Network Topologies ToR vs. EoR Data Center Networking Issues.

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DATA CENTERNETWORKING TOPOLOGIES

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OVERVIEW

Data Center Physical Layout Data Center Network Topologies ToR vs. EoR Data Center Networking Issues Data Center Networking Requirements

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DATA CENTER STANDARDS

ANSI/TIA-942 Telecommunications Infrastructure Standard for Data Centers

Published 2005 – available through TIA at www.tiaonline.org

ANSI/NECA/BICSI-002 Data Center Design and Implementation Best Practices

complements TIA-942 –2007

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PURPOSE OF TIA-942

Encourage early participation of telecom designers in data center design process

Fill a void by providing standards for planning of data centers, computer rooms, serverrooms, and similar spaces.

The standard encompasses much more thanjust telecommunications infrastructure.

Close to half of the technical content deals with facility specifications.

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PURPOSE OF TIA-942

Define a standard telecommunications infrastructure for data centers Structured cabling system for data centers using

standardized architecture and media Accommodates a wide range of applications

(LAN, WAN, SAN, channels, consoles) Accommodates current and future protocols

(e.g., 10+ GbE (Giga bit Ethernet) ) Replaces unstructured point-to-point cabling that

uses different cabling for different applications

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DESIGN ELEMENTS

1. Cabling Design2. Facility Design3. Network Design

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CABLING AND FACILITY DESIGN

Cabling Design: Copper and fiber cabling performance Connectors, cables, distribution hardware Cabling distances Space management

Facility Design: Data center sizing Power distribution methodologies Pathways and spaces HVAC, security, operations, and

administration. Flexibility, scalability, reliability and space

management

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NETWORK DESIGN:

Support of legacy systems Enable rapid deployment of new and

emerging technologies such as 10 GbE and 10+ GbE

copper and fiber applications.

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GOOGLE DATA CENTER

Take a walk through a Google data center

http://www.google.com/about/datacenters/inside/streetview/

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COOLING PLANT

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MODULAR DATA CENTERS

Called Ice cube Small: < 1 MW, 4 racks per unit Medium: 1-4 MW, 10 racks per unit Large: > 4 MW, 20 racks per unit Built-in cooling, high PUE (power usage effectiveness) 1.02

PUE = Power In/Power Used. It means cooling use 2 percent of power. Not efficiency of 0.98!

Rapid deployment

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CONTAINERIZED DATA CENTER

All companies like IBM and cisco make it like this

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UNSTRUCTURED CABLING

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STRUCTURED CABLING

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EQUIPMENT CABINETS

Three Layers: 1. Bottom: Signaling (Ethernet),2. Middle: Power and 3. Top: Fiber

Minimize patching between cabinets and racks

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DATA CENTER PHYSICAL LAYOUT

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ANSI/TIA-942-2005 STANDARD

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ANSI/TIA-942-2005 STANDARD Computer Room: Main servers Entrance Room: Data Center to external cabling Cross-Connect: Enables termination of cables Main Distribution Area (MDA): Main cross connect.

Central Point of Structured Cabling. Core network devices

Horizontal Distribution Area (HDA): Connections to active equipment.

Equipment Distribution Area (EDA): Active Servers+Switches.

Zone Distribution Area (ZDA): Optionally between HDA and EDA. Rack, cabinet, or under floor enclosure that houses a zone outlet (ZO) or consolidation point (CP)

Backbone Cabling: Connections between MDA, HDA, and Entrance room

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ZONE DISTRIBUTION AREA

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DATA CENTER NETWORK TOPOLOGIES

Three levels of switches: Core, Aggregation, Access

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DATA CENTER NETWORKS 20-40 servers per rack Each server connected to 2 access switches

with 1 Gbps (10 Gbps becoming common) Access switches connect to 2 aggregation

switches Aggregation switches connect to 2 core routers Aggregation layer is the transition point

between L2-switched access layer and l3-routed core layer

Low Latency: In high-frequency trading market, a few microseconds make a big difference.

Cut-through switching and low-latency specifications.

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DATA CENTER NETWORKS (CONT)

Edge routers manage traffic between aggregation routers and in/out of data center

All switches below each pair of aggregation switches form a single layer-2 domain

Each Layer 2 domain typically limited to a few hundred servers to limit broadcast

Most traffic is internal to the data center. Network is the bottleneck. Uplinks utilization

of 80% is common. Most of the flows are small. Mode = 100 MB.

DFS (Distributed File System) uses 100 MB chunks.

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SWITCH LOCATIONS

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TOR VS EOR

ToR: Advantages:

Easier cabling If rack is not fully populated unused ToR ports

DisAdvantages: If rack traffic demand is high, difficult to add more

ports Upgrading (1G to 10G) requires complete Rack upgrade

EoR: Disadvantages

Longer cables Advantages:

Severs can be place in any rack Ports can easily added, upgraded

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HIERARCHICAL NETWORK DESIGN All servers require application delivery

services for security (VPN, Intrusion detection, firewall), performance (load balancer), networking (DNS, DHCP(Dynamic Host Control Protocol), NTP (Network Time Protocol), FTP, RADIUS (Remote Access Dial-In User Service server to perform authentication ), Database services (SQL)

Stateful devices (firewalls) on Aggregation layer

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DATA CENTER ACCESS LAYER DESIGN

4 Possibilities:1. Looped Triangle2. Looped Square3. Loop Free U4. Looped Free Inverted U

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ACCESS AGGREGATION CONNECTIONS

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CISCO USES ICONS TO REPRESENT DIFFERENT NETWORKING DEVICES

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DATA CENTER NETWORKING ISSUES

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DATA CENTER NETWORKING ISSUES (CONT)

Under-utilization. Even when multiple paths exist only one is used.

ECMP (Equal Cost Multipath) is used by routers to spread traffic to next hops using a hash function. However, only 2 paths exist.

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DCN REQUIREMENTS

Needs to be Scalable, Secure, Shared, Standardized, and Simplified (5 S's)

Converged Infrastructure: Servers, storage, and network have to work together

Workload Mobility: Large L2 domains required for VM mobility

East-West Traffic: Significant server-to-server traffic as compared to server to user. One Facebook request required 88 cache looks, 35 database lookups, 392 backend RPC calls. Intranet traffic 935X the http request/response

Storage traffic on Ethernet: Congestion management on Ethernet

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4-POST ARCHITECTURE AT FACEBOOK Each rack contains a rack switch (RSW) with

up to forty-four 10G downlinks and four or eight 10G uplinks (typically 10:1 oversubscription) one to each cluster switch (CSW)

A cluster is a group of four CSWs and the corresponding server racks and RSWs

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4-POST ARCHITECTURE AT FACEBOOK (CONT) Each CSW has four 40G uplinks (10G×4), one to each of

four “FatCat” aggregation switches (typically 4:1 oversubscription).

The four CSWs in each cluster are connected in an 80G protection ring (10G×8) and the four FC switches are connected in a 160G protection ring (10G×16)

network failures used to be one of the primary causes of service outages. The additional redundancy in 4-post has made such outages rare.

traffic that needed to cross between clusters used to traverse expensive router links. The addition of the FC tier greatly reduced the traffic through such links.

All tiers are switched and not routers Ref: N. Farringon and A. Andreyev, “Facebook’s Data Center Network Architecture,” 2013

IEEE Optical Interconnect Conference, http://nathanfarrington.com/papers/facebook-oic13.pdf

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MAIN DISADVANTAGES OF 4-POST

1. A CSW failure reduces intra-cluster capacity to 75%

2. The cluster size is dictated by the size of the CSW

3. Large switches are produced in smaller volumes from fewer manufacturers

4. Large switches are often oversubscribed internally, meaning that not all of the ports can be used simultaneously

5. Large switches are often very proprietary. This can lead to months and years between bug fixes

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CLOS NETWORKS

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FAT-TREE Fat-Tree networks were proposed by

Charles E. Leiserson in 1985. Such network is a tree, and processors are connected to the bottom layer.

The distinctive feature of a fat-tree is that for any switch, the number of links going down to its siblings is equal to the number of links going up to its parent in the upper level

Therefore, the links get “fatter” towards the top of the tree, and switch in the root of the tree has most links compared to any other switch below it:

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FOR ENTERPRISE NETWORKS

However, for enterprise networks that connect servers, commodity (off-the-shelf) switches are used, and they have a fixed number of ports. Hence, the design of fat-tree, where the number of ports varies from switch to switch, is not very usable.

Therefore, alternative topologies were proposed that can efficiently utilize existing switches with their fixed number of ports.

There is a controversy whether such topologies should be called fat-trees, or rather “(folded) Clos networks”, or anything else.

However, the term fat-tree is widely used to describe such topologies.

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TWO-LEVEL FAT-TREE NETWORK.

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SUMMARY

1. Modular data centers can be used for easy assembly and scaling

2. Three tiers: Access, Aggregation, Core3. Application delivery controllers between

Aggregation and core4. Need large L2 domains5. Fat-tree topology is sometimes used to

improve performance and reliability