CCNxCon 2012: Session #7: Off-Path Caching in CCN

Off-Path Caching in CCN Damien Saucez

Chadi BarakatAnshuman KallaThierry Turletti

*{first.last}@inria.frINRIA Sophia Antipolis - Planète Project TeamCCNxCon 2012 - 09/13/2012

What changes with CCN?

• Shift from location to content based communications

• Shift from end-to-end to local communications

! secure data themselves instead of communication channels

! contents can be cached anywhere

! topology is an only an optimization

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On-path caching is sub-optimal

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1

1 1

1

11

/Sophia/sun


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1

1 1

1

11

/Sophia/sun


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1

1 1

1

11

/Sophia/sun


• The amount of traffic on the inter-domain links of an AS that can cache N contents is minimized if the N most popular contents are cached

• On-path caching is sub-optimal as contents might be duplicated on different caches:

• lower hit rates

• higher delays

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How to perform caching within an enterprise network such that the use of inter-domain links is minimized while keeping the domain links’ usage below their nominal capacities?

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• To avoid content duplication on various caches, each popular content is assigned a specific cache

• A content is cached only by its assigned cached

• Every Interest packet for a given popular content is deflected to its content’ assigned cache

! As the shortest path is not followed anymore, we call it off-path caching

Deflect popular content traffic to optimally located caches

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Off-path caching to achieve optimality

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I am The cache for /Sophia/sun

I am The cache for /Belgium/rain

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1 1

1

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/Sophia/sun

Off-path caching to achieve optimality

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I am The cache for /Sophia/sun

I am The cache for /Belgium/rain

1

1 1

1

11

/Sophia/sun

Where to place contents?

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• Ideal placement would be such that

• contents are not duplicated,

• popular contents are cached close (delay) to their consumers,

• cache memory is not overloaded,

• links are not be overloaded.

Optimization problem

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• Let be the “content (c) to cache (r)” allocation matrix, with

A

�

r∈R

Ar,c = 1, Ar,c ∈ {0, 1} , ∀c ∈ C∗


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• Minimize the delay due to deflection

min�

c∈C∗

�

e∈E

λc,e

�

r∈R

Ar,c · de,r


A

�

r∈R

Ar,c = 1, Ar,c ∈ {0, 1} , ∀c ∈ C∗


9


min�

c∈C∗

�

e∈E

λc,e

�

r∈R

Ar,c · de,r

• Do not overload cache memory�

c∈C∗

Ar,c ≤ memoryr, ∀r ∈ R


A

�

r∈R

Ar,c = 1, Ar,c ∈ {0, 1} , ∀c ∈ C∗


9


min�

c∈C∗

�

e∈E

λc,e

�

r∈R

Ar,c · de,r

• Do not overload cache memory�

c∈C∗

Ar,c ≤ memoryr, ∀r ∈ R

• Do not overload links�

c∈C

�

e∈E

λc,e · vc · δl,e,c,A ≤ capacityl, ∀ link l


A

�

r∈R

Ar,c = 1, Ar,c ∈ {0, 1} , ∀c ∈ C∗

Optimal content placement and deflection

1. Estimate for every content c, at every edge router e

2. Solve the optimization problem to determine

3. Inject in the routing tables

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λc,e

A

A

Optimality is complex to reach

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• Optimal placement problem is NP-complete

• requires content popularity estimation

• not tractable in some configuration (e.g., large network, large caches...)

• not adapted to dynamic popularity distribution

• Routing table size is with N potentially large

O(N)

Hash function based heuristic

• A heuristic that avoids content duplication, removes the necessity to solve an optimization problem, and maintains flow table size linear with the size of the network

• Caching All Contents by Hashing (CACH):

• hash names

• routing based on the hash value

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Encapsulation based deflection

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/Sophia/sun

R1

R2

R3

R4

R5

HASH 4224% |R|1.

2.

Interest for /Sophia/sun

/Sophia/sun

Interest for /encap/R5/Sophia/sun

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Evaluation

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Simulation setup

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• Rocketfuel [SMW02] topology ASN 3967

• 79 core routers, 44 edge routers (2 per city), 6 peering routers

• LRU caching on edge routers, 10 cache entries per core router

• 150ms peering link delay

• 200,000 Interest packets generated, simulations repeated 11 times

• 7,900 content of Zipf 0.8 [FRR12] popularity distribution

Main observations

• Rocketfuel simulation (popularity ~ Zipf 0.8)

• Inter-domain link usage is reduced

• from 83% to 53% (opt. 35%) of the load without cache

• Hit ratio is increased

• from 17% to 53% (opt. 65%)

• Overall retrieval delay is reduced significantly

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Conclusion

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Summary

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• The default on-path caching CCN policy is sub-optimal as contents are duplicated on several caches

• We then propose off-path caching that deflects popular traffic to optimally selected caches

• off-path caching maximizes cache hit ratio

• which results in lower inter-domain link usage

• and lower average content retrieval delay

Next steps

• Transpose the model to dynamic traffic demand (e.g., content consumers move in the network) and mobile infrastructure

• Resiliency / optimality tradeoff

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/**/ || ??

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Off-Path Caching in CCN

Backup

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• Communication is between two devices

• Users use services, from anywhere

Technique vs users

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How to reconcile the two worlds

• Evolutionary solutions

• Enhance current architecture

• Provide interworking mechanisms

• Clean-slate solutions

• Rethink the paradigms

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How to reconcile the two worlds

• Evolutionary solutions

• Enhance current architecture

• Provide interworking mechanisms

•Clean-slate solutions

• Rethink the paradigms

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Content-Centric Networking (CCN)

• Shift from location-based to content-based communications

• Contents become first class citizens in the network

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The idea

• Content-Centric Networking (CCN) treats content as a primitive [JST+09]

• Every chunk of data is assigned a name, such that any content can be directly retrieved by its name

• Routers cache chunks of data on-path between consumers and producers

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Workflow

• A content consumer (client) asks for content by sending an Interest packet to nodes at its direct neighborhood

• A node that has data that satisfies the interest responds with a Data packet

• Otherwise, the node forwards the Interest packet to its neighbors, and remembers from which neighbors it receives the interest

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• Two types of CCN packets

• Packets indicate the what, not the who or the where (neither source nor destination)

Packets

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Content Name

Selector(order preference, publisher filter, scope...)

Nonce

Interest packet

Content Name

Signature

Signed Info

Data

Data packet

Source Address

Destination Address

Payload

IP packet

CCN in a nutshell

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Interest: /IRM/CCN

CCN in a nutshell

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Interest: /IRM/CCN

CCN in a nutshell

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Interest: /IRM/CCN

Pending Interest Table (PIT)/IRM/CCN, from NW

CCN in a nutshell

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Interest: /IRM/CCN


CCN in a nutshell

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Interest: /IRM/CCN


Pending Interest Table (PIT)/IRM/CCN, from W

CCN in a nutshell

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Interest: /IRM/CCN



CCN in a nutshell

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Data: /IRM/CCN=

CCN in a nutshell

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Data: /IRM/CCN=

CCN in a nutshell

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Content Store (CS)/IRM/CCN =

Data: /IRM/CCN=

CCN in a nutshell

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Data: /IRM/CCN=

CCN in a nutshell

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Data: /IRM/CCN=


CCN in a nutshell

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Content Store (CS)/IRM/CCN = Data: /IRM/CCN=


CCN in a nutshell

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CCN in a nutshell

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Interest: /IRM/CCN

CCN in a nutshell

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Interest: /IRM/CCN

CCN in a nutshell

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Data: /IRM/CCN=

CCN in a nutshell

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Data: /IRM/CCN=

What does it change?

• Shift from location to content based communications

• Shift from end-to-end to local communications

! contents can be cached anywhere

! secure data themselves instead of communication channels

! topology is an only an optimization

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The reason of CCN?• Communications in the Internet focus on the endpoints.

• Names are bound to servers which are bound to IP addresses,

• TCP flows are bound to IP address.

• Most of today’s networks use is to acquire named chunks of data (e.g., web pages, videos).

• There is a gap between the technology and the usage leading to inefficiencies:

• reliability issue (e.g., what if the server breaks down?),

• inefficient resource utilization (e.g., hotspots),

• weak mobility support.

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Implement off-path caching with SDN

• Off-path caching is a two-fold process:

• compute the optimal placement of popular contents in the caches,

• Interest packets deflection to the appropriate caches.

• As the shortest path is not followed anymore, we call it off-path caching.

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Every content benefits from optimal placement

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1 10 100 1000

aver

age

dela

y [m

s]

content

CACHon-path

popularity estimatoroptimal placement

Context

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• Controlled fixed networks (e.g., ISP)

• peering links are expensive and slow

• internal network is over provisioned

What if...

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What if...

• we are in an enterprise/campus network?



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What if...




• content is produced outside the network?

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What if...




• content is produced outside the network?

• traffic demand is stable over reasonable time periods?

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Inter-domain link bandwidth gain

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content

no cachingon-path

CACHpopularity estimator

optimal placement


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no cachingon-path


optimal placement 200,000166,479

94,65769,509

Peering traffic drops from 83% of the total traffic to 47% and 35%.


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94,65769,509


Popular contents are always cached

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50%22%0.7%

The top 5.5% of popular contents accounts for 50% of the inter-domain traffic, while at optimal they account only for 0.7%


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no cachingon-path



94,65769,509


Popular contents are always cached

Off-path caching improves hit ratio

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hit r

atio

content

CACHon-path


• High hit ratio for popular contents


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0

0.2

0.4

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1 10 100 1000

hit r

atio

content

CACHon-path



• The overall hit ratio significantly increases from 17% to 53% and 65%


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0

0.2

0.4

0.6

0.8

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1.2

1 10 100 1000

hit r

atio

content

CACHon-path



• The overall hit ratio significantly increases from 17% to 53% and 65%

• What is the impact on delay?


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0

0.2

0.4

0.6

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1 10 100 1000

hit r

atio

content

CACHon-path


Off-path caching improves retrieval delay

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On-path CACH Optimal placement5.11ms± 0.05 28.08ms± 0.04 23.52ms± 0.03


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• Once a content is cached, the deflection has a negative impact on the average retrieval delay


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• Once a content is cached, the deflection has a negative impact on the average retrieval delay

• But the overall average retrieval delay is reduced with off-path caching, thanks to a better hit ratio

Technology

CCNxCon 2012: Session #7: Off-Path Caching in CCN