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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 ELEMENTS1. 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/ins

ide/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-POST1. A CSW failure reduces intra-cluster capacity

to 75%2. The cluster size is dictated by the size of the

CSW3. Large switches are produced in smaller

volumes from fewer manufacturers4. 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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SUMMARY1. Modular data centers can be used for easy

assembly and scaling2. 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