1. Energy Aware Network Operations
Authors: Priya Mahadevan, Puneet Sharma, Sujata Banerjee, Parthasarathy Ranganathan
HP Labs
IEEE Global Internet Symposium (April 2009)
Speaker: Sookhyun Yang

2. Introduction
This paper analyzes three energy-saving schemes to configure a switch in a data center network with link redundancy.
Linear – power model
[Data center network topology]

3. Energy Saving in a Switch
port
Linear power model
Power consumed by each switch depends on
Number of active ports
Line capacity of a port
How can we control a switch for saving energy?
Disable a switch port
Dynamically adapt a port’s link capacity based on its load
Turn off a line-card that have no active ports
Power off a switch that is not being used
Line-card
[A switch with line-cards]

4. Three Energy Saving Schemes
Centralized approach
LSA (Link State Adaptation)
Adapts a port’s link capacity (disabled, 10Mbps, 100Mbps, and 1Gbps) according to link utilization.
NTC (Network Traffic Consolidation)
Consolidates traffic into fewer links (and switches).
Disables unused links (and switches).
SLC (Server Load Consolidation)
Migrates jobs for minimizing the number of servers being used.
Applies NTC schemes.
[Data center network topology]

5. Variations of the Three Schemes
SL (Service Level) Awareness
Adds a constraint to ensure that a link’s utilization never exceeds a certain threshold.
Ensures that at least one redundant link exists.
SL awareness policy is combined with each of the three schemes.

6. Simulation Set-up: Workload
Simulation based on workload of observed traffic
292 web-servers for 5days in April 2008
System configuration of 292 web-severs
Quad-core processors, two 1Gbps network cards
Different RAM sizes: 193 servers have 4 GB RAM, 69 servers have 8GB RAM, and 30 servers have 16GB RAM.
Observed results
Workload is memory-sensitive
130 servers use 90% or greater amount of memory, 64 servers use less than 40%.
Both network bandwidth and CPU of all servers are utilized at most 10%.

7. Simulation Set-up: Network Topology
2 tier-2 switch
(6 line card per switch,
24 ports per line card)
26 rack switches
(48 ports per switch)
292 web servers
[Data center network topology]

8. Simulation: How to Compute Power Consumption
Line-card with no active ports
Line speed
Perfect knowledge of an oracle
Link utilization
Job’s traffic specification
Network topology

9. LSA (Link State Adaptation)
Link characteristics from 5-day measurement
90% of links (light traffic) can be set 10 or 100Mbps.
Less than 5% of links (heavy traffic) need to be set 1Gbps.
LSA’s distribution of link speeds between rack and tier-2 switches

10. LSA vs. SL-aware LSA

11. Simulation Results NTC (Network traffic consolidation)
SLC (Server load consolidation)
LSA (Link state adaptation)
Considered homogeneous RAM sizes (16GB)

12. Deployment Issues Track traffic workload
Adapt link capacity based on link utilization statistics
Predict incoming/outgoing traffic
Transition time for adapting link-speeds is between 1-3 seconds, which can affect network performance.
Buffer or ensure the existence of back-up paths

13. Q&A
Thank you!