1. D ATA C ENTER N ETWORKING T OPOLOGIES 1

2. O VERVIEW Data Center Physical Layout Data Center Network Topologies ToR vs. EoR Data Center Networking Issues Data Center Networking Requirements 2

3. D ATA C ENTER S TANDARDS 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 3

4. P URPOSE 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. 4

5. P URPOSE 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 5

6. D ESIGN E LEMENTS 1. Cabling Design 2. Facility Design 3. Network Design 6

7. C ABLING 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 7

8. N ETWORK D ESIGN : Support of legacy systems Enable rapid deployment of new and emerging technologies such as 10 GbE and 10+ GbE copper and fiber applications. 8

9. G OOGLE DATA CENTER Take a walk through a Google data center http://www.google.com/about/datacenters/inside/s treetview/ http://www.google.com/about/datacenters/inside/s treetview/ 9

10. C OOLING PLANT 10

11. M ODULAR D ATA C ENTERS 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 11

12. C ONTAINERIZED D ATA C ENTER All companies like IBM and cisco make it like this 12

13. U NSTRUCTURED C ABLING 13

14. S TRUCTURED CABLING 14

15. E QUIPMENT CABINETS Three Layers: 1. Bottom: Signaling (Ethernet),2. Middle: Power and 3. Top: Fiber Minimize patching between cabinets and racks 15

16. D ATA C ENTER P HYSICAL L AYOUT 16

17. ANSI/TIA-942-2005 S TANDARD 17

18. ANSI/TIA-942-2005 S TANDARD 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 18

19. Z ONE D ISTRIBUTION A REA 19

20. D ATA C ENTER N ETWORK T OPOLOGIES Three levels of switches: Core, Aggregation, Access 20

21. D ATA C ENTER N ETWORKS 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. 21

22. D ATA C ENTER N ETWORKS (C ONT ) 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. 22

23. S WITCH L OCATIONS 23

24. T O R VS E O R 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 24

25. H IERARCHICAL N ETWORK D ESIGN 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 25

26. D ATA C ENTER A CCESS L AYER D ESIGN 4 Possibilities: 1. Looped Triangle 2. Looped Square 3. Loop Free U 4. Looped Free Inverted U 26

27. A CCESS A GGREGATION C ONNECTIONS 27

28. C ISCO USES ICONS TO REPRESENT DIFFERENT NETWORKING DEVICES 28

29. D ATA C ENTER N ETWORKING I SSUES 29

30. D ATA C ENTER N ETWORKING I SSUES (C ONT ) 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. 30

31. DCN R EQUIREMENTS 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 31

32. 4-P OST A RCHITECTURE AT F ACEBOOK 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 32

33. 4-P OST A RCHITECTURE AT F ACEBOOK ( 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, Facebooks Data Center Network Architecture, 2013 IEEE Optical Interconnect Conference, http://nathanfarrington.com/papers/facebook-oic13.pdf 33

34. 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 34

35. C LOS N ETWORKS 35

36. F AT - 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. Fat-TreeCharles E. Leiserson 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: 36

37. F OR 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.Clos networks However, the term fat-tree is widely used to describe such topologies. 37

38. T WO - LEVEL FAT - TREE NETWORK. 38

39. S UMMARY 1. Modular data centers can be used for easy assembly and scaling 2. Three tiers: Access, Aggregation, Core 3. Application delivery controllers between Aggregation and core 4. Need large L2 domains 5. Fat-tree topology is sometimes used to improve performance and reliability 39