Distributing Content Simplifies ISP
Traffic Engineering
Abhigyan Sharma*
Arun Venkataramani* Ramesh Sitaraman*~
*University of Massachusetts Amherst
~Akamai Technologies
1
Tripartite view of content delivery
Networks
NCDN
CDN
NCDN
NCDN
Content providers
NCDNs
deployed
in 30+
ISPs
globally
NCDN Management
Traffic
Engineering
Content
Distribution
Optimize routing
to remove
congestion hotspots
Optimize
content placement
&
request redirection
to improve
user-perceived performance
NCDN
Mgmt.
3
NCDN Routing Placement Interaction
0.25 Mbps
4 Mbps
1.25 Mbps
C
0.5 Mbps
8 Mbps
0.25 Mbps
B
1.5 Mbps
A
Demand = 1 Mbps
D
0.75 Mbps
Traffic labeled
with flow value
Link labeled
with capacity
Demand = 0.5 Mbps
Maximum link utilization (MLU) = 0.75/1.5 = 0.5
4
NCDN Routing Placement Interaction
B
C
0.5 Mbps
0.5 Mbps
4 Mbps
8 Mbps
1 Mbps
Content placement flexibility
reduces network costs andTraffic labeled
with flow value
enables simpler routing
1.5 Mbps
A
Demand = 1 Mbps
D
Link labeled
with capacity
Demand = 0.5 Mbps
Maximum link utilization (MLU) = 1/8 = 0.125
5
NCDN Schemes Classification
NCDN Management
Content
Distribution
Unplanned
(e.g. LRU
Caching)
Traffic
Engineering
Planned
(historybased)
Planned
(e.g. OSPF
weight tuning)
Joint Optimization
Unplanned
(static
routing)
6
Research Questions
How do simple unplanned
schemes perform?
Is joint optimization better than
other schemes?
What matters more: placement
or routing?
7
Outline
•
•
•
•
•
Network CDN
NCDN Model & Joint Optimization
Datasets: Akamai Traces & ISP Topologies
Results
Related Work
8
NCDN Model
Origin
servers
NCDN POP
Backbone router
Content servers
Downstream end-users
Backbone router at
exit nodes
9
NCDN Model
Origin
servers
NCDN POP
Backbone router
Content servers
Downstream end-users
Backbone router at
exit nodes
10
NCDN Model
Origin
servers
NCDN POP
Backbone router
Content servers
Downstream end-users
Backbone router at
exit nodes
11
NCDN Model
Origin
servers
Resource constraints
POP storage
Downstream end-users
ISP backbone
link capacity
12
NCDN Joint Optimization
• Hardness
Theorem 1: Opt-NCDN is NP-Complete even in the
special case where all objects have unit size, all
demands, link capacities and storage capacities have
binary values.
• Approximability
Theorem 2: Opt-NCDN is inapproximable within a
factor β for any β > 1 unless P = NP.
13
MIP for Joint Optimization
Objective:
• Minimize NCDN-cost (MLU or latency)
Constraints:
• For all node: total size of content < Storage capacity
• For all (content, node): demand must be served from
POPs or origin
Output variables:
• Placement: Binary variable iXY indicates whether
content X is stored at node Y
• Redirection
• Routing
14
Outline
•
•
•
•
•
Network CDN
NCDN Model & Joint Optimization
Datasets: Akamai Traces & ISP Topologies
Results
Related Work
15
Datasets
Akamai traces
Traffic types
On-demand video & download
How measured? Instrument client software, e.g., media player plugin
Data
Content URL, content provider, lat-long, timestamp,
bytes downloaded, file size
Volume
7.79 m users, 28.2 m requests, 1455 TB data
ISP topologies
Networks
Tier-1 US ISP & Abilene
Data
POP lat-long, link capacities
Mapping: Akamai trace  ISP topology
Map request to geographically closest ISP POP
16
Outline
•
•
•
•
Network CDN
NCDN Model & Joint Optimization
Datasets: Akamai Traces & ISP Topologies
Results
–
–
–
–
Schemes Evaluated
Network Cost
Latency Cost
Network Cost: Planned vs. Unplanned Routing
• Related Work
17
Schemes Evaluated
Scheme
Routing + placement + redirection
UNPLANNED
OSPF with link-weight = 1/link-capacity
+ LRU caching
+ redirect to closest hop count node
Realistic joint optimization
JOINTOnce
per
day
with
yesterday’s
content
OPTIMIZATION
ORACLE
demand
Ideal joint optimization
Once per day with current day’s content
demand
18
Network Cost
Tier-1 ISP Topology, Entertainment Trace
Normalized MLU
1
0.8
0.6
Joint Optimization
Unplanned
Oracle
3x
0.4
0.2
18%
0
0
2
4
Storage Ratio
19
Latency Cost
Latency Cost = E2E propagation delay + Link utilization dependent delay
Tier-1 ISP Topology, Entertainment Trace
Latency Cost
10
Content placement matters
1 tremendously in NCDNs
0.1
28%
Joint Optimization
Unplanned
Oracle
0.01
0
1
2
3
Storage ratio
4
20
Network Cost: Planned vs. Unplanned Routing
Unplanned placement, unplanned routing
vs.
Unplanned placement, planned routing
Max MLU Reduction (%)
Traditional
TE
gives
small
cost
Tier-1 ISP topology, all traces
20
reduction in NCDNs
10% or less
10
0
-10
News
Entertainment
Download
21
Related Work
• ISP-CDN joint optimization of routing & redirection
(with fixed placement) [Xie ‘08, Jiang ‘09, Frank ’12]
• Optimize placement (with fixed routing) for VoD
content [Applegate ’10]
• Location diversity even with random placement
significantly enhances traditional TE [Sharma ’11]
22
Conclusions
• Keep it simple
– Joint optimization performs worse than simple
unplanned
– Little room for improvement over simple
unplanned
• Content placement matters more than routing
in Network CDNs
23