1. Jellyfish: Networking Data Centers Randomly
Ankit Singla† , Chi-Yao Hong†, Lucian Popa*, P. Brighten Godfrey† † University of Illinois at Urbana–Champaign *HP Labs
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2. Tow Goals of Data Center Design
High throughput
Incremental expansion
Easily add/replace servers & switches
Throughput: the amount of data exchanged/processed within a unit time
Good scalalibity.Easily add/replace servers and switches

3. Incremental expansion
Facebook doubled their data center scale in the last year (2010)
You can add the servers, how about the network?
Distributed systems: Hadoop
Why it matters. Map-reduce heavlity rely on the networks

4. Today’s structured networks
CLOS
Three-stage hierarchical datacenter.
Single failure
Fat tree
CLOS
Fat tree

5. Structure constrains expansion
3-level fat trees, commodity switches:
24-port switches – 3,456 servers
32-port switches – 8,192 servers
48-port switches – 27,648 servers
How to expand a datacenter with 32-port switches, 8,192 servers to 10,000 servers?

6. Solution
No structure
Jellyfish: random graph

7. Quantifying expandability
Bisection bandwidth
if the network is bisected into two partitions, the bisection bandwidth of a network topology is the bandwidth available between the two partitions.

8. Throughput: Jellyfish vs Fat tree
Give the same budget for network devices, jellyfish can sustain 25% more servers than fattree

9. Why it works?
It fully utilizes all available capacity

10. Example

11. Example: Fat tree

12. Example: Jellyfish

13. Jellyfish has short paths

14. Degree-diameter bounded graph
Degree: the degree of a node is the number of nodes connected to this node.
Diameter: the longest distance between a node pair
Indicates the optimal case

15. Degree-diameter vs. Jellyfish

16. Routing and congestion control
K-shortest path
MPLS TE, OpenFlow(SDN)
Congestion control
TCP, Multipath TCP
Routing is important. Not a structured topology, need more time to lookup the routing table.
MPLS - pre-compute the path.
OpenFlow - (SDN)

17. Cabling One of the main drawbacks of this work
Discussion: possible solutions
wireless datacenter
Xia Zhou, et.al.. "Mirror mirror on the ceiling: Flexible wireless links for data centers." ACM SIGCOMM Computer Communication Review 42, no. 4 (2012):
Daniel Halperin, et.al.. "Augmenting data center networks with multi-gigabit wireless links." In ACM SIGCOMM Computer Communication Review, vol. 41, no. 4, pp ACM, 2011.
Not work
Large latency for small flows
Short transmission range

18. Questions on Piazza
Is the fat-tree topology the most widely used data center network topology? Why weren’t other network topologies as heavily emphasized in the paper?
Are there any theoretical tradeoffs to Jellyfish since the physical and routing complications seemed to be mostly resolved with the author’s proposals?