1. A Survey of Data Center Network Architectures By Obasuyi Edokpolor
Final Presentation
A Survey of Data Center Network Architectures By
Obasuyi Edokpolor

2. What is A Data Center?
According to Wikipedia: A data center is a facility used to house computer systems and associated components, such as telecommunications and storage systems
According to Google: A large group of networked computer servers typically used by organizations for the remote storage, processing, or distribution of large amounts of data.

3. Data Centers Infrastructure design has recently received significant interest due to the growing importance of data centers in supporting & sustaining the rapidly growing internet-based applications, which includes:
Search Engines -> Google, Bing
Video Content Hosting and Distribution -> Youtube, Netflix
Social Networking -> Facebook, Twitter
Large-Scale Computation -> Data Mining, Bioinformatics

4. Microsoft Live Online Services is supported by Chicago based data center which is one of the largest data center ever built, spanning 700,000 square feet
Microsoft Chicago Data Center in Northlake, Illinois

5. Data Center Network Topology
Due to the wide range of this survey, I will be focusing on Network Topology
In other to make internet application work efficiently, it is imperative that data center are cost-effective and efficient.
Most data centers use Ethernet switches to interconnect the servers, there are still many different ways to implement the interconnections, leading to different data center network topologies, each of these different topologies is characterized by different resource requirement, aiming to bring enhancement to the performance of data centers.
The topology of the network interconnecting the servers, has a significant impart on the agility and configurability of the data center infrastructure to respond to changing application demands and service requirement.

6. Types of Network Topology
According to Yang, network topology can be divided into two parts:
Fixed
Flexible
Fixed topology : Is when a network topology cannot be modified after it has been deployed.
Flexible Topology: Is when a network topology can be modified even after deployment
Fixed Topology can be divided into 2 parts:
Tree
Recursive

8. Tree Topology There are 3 types of tree topology, which is: Basic Tree
Fat Tree
Clos Network
Basic Tree : Consist of either 2 or 3 levels of switches/ routers, with the servers as leaf.
2-level of switches contains (a) Core Tier (b) Edge Tier
3-level of switches consist of (a) Core Tier (b) Aggregation Tier (c) Edge Tier

9. In a basic topology, the higher-tier switches need to support data communication among a large number of servers. This switches with higher performance and reliability are required in these tiers.
The number of servers in a tree architecture is limited by number of ports on the switches.

10. Basic Tree

11. Fat Tree
Fat Tree: Is like a basic tree based on a complete binary tree.
Each n-port switches in the edge-tier is connected to n/2 servers. The remaining n/2 ports are connected to n/2 switches in the aggregation-level. The n/2 aggregation- level switches and the servers connected to the edge switch form a basic cell of fat tree, which is called a pod.

12. Fat Tree

13. Clos Network
Is a multi-tier tree. When deployed in data center networks, a clos network usually consist of 3 levels of switches.
The ToR switches directly connected to servers, the aggregation switches connected to the ToR switches, and the intermediate switches connected to the aggregation switches.
These 3 level of switches are termed “input”, “middle” and “output” switches.

14. For example if each of the switches has n ports, there will be n aggregation switches and n/2 intermediate switches. There is exactly one link between each intermediate switches and each aggregation switch.
The remaining n/2 ports on each aggregation switch is connected to n/2 different ToR switches.
Each of the ToR switches is connected to 2 different aggregation switches, and remaining ports on the ToR

15. Recursive Topology
It can scale-up by inserting more levels of switches, while each server is connected to only one of the bottom level switches.
It is like a multi-tier tree-based topologies. However, recursive topologies use lower level structure of cells to build higher level structures, and the servers in the recursive topologies maybe connected to switches of different level or even other servers.

16. There are multiple network ports on the servers of recursive topologies, making them significantly different from the tree-based topologies.
Graph are preferred to represent recursive architecture rather than rooted tree.

17. Type of Recursive Topology
There are two types of recursive topology:
DCell
BCube
Dcell : The basic element of a DCell, which is called DCello, consist of n servers and one n-port switch. Each server in a DCello is connected to the switch in the same DCello.
Let Dcellk be a k-level Dcell. 1st construct DCell1 from several Dcell0. Each DCell1 has n+1 DCello, and each server of every DCellos in a DCell1 is connected to a server in another DCello, respectively As a result, the DCellos are connected to each other, with exactly one link between every pair of DCellos.

19. BCube: Is a recursive topology specially designed for shipping container based modular data centers.
Building a data center cluster in a 20 and 40 foot shipping container makes it highly portable. As demand change at different data centers, the whole cluster can be readily moved.
While deployment time is considerably shorter, the disadvantage of this environment is that due to operational and space constraints, once deployed in the field, it is difficult to service the cluster.
The basic element of BCube is like that of DCello; n servers connected to one n-port switch. The only difference is how they scale up . BCube makes use of more switches when constructing higher level architecture.
BCube1 contains n BCubeos and n extra switches

21. Flexible Topology
Many researchers have considered using optical switching technology to construct Data Center Networks. Besides offering high bandwidth, optical networks have significant flexibility of reconfiguring the topology during operation.
There are 3 types of Flexible topology
c-Through
Helios
OSA

22. Bibliography A Survey of Data Center Network Architectures by Yang Liu