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Challenges in the Design and Evaluation of Content -Centric Networks. Jim Kurose Department of Computer Science University of Massachusetts Amherst MA USA. ‘. Visiting Scientist, Technicolor Paris Lab Professeur Invite, LINCS Sigcomm ICN Workshop, Aug 2013. Overview. - PowerPoint PPT Presentation
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Challenges in the Design and Evaluation of Content-Centric Networks
Jim KuroseDepartment of Computer ScienceUniversity of MassachusettsAmherst MA USA
‘
Visiting Scientist, Technicolor Paris LabProfesseur Invite, LINCS
Sigcomm ICN Workshop, Aug 2013
Overview
architecture, system, prototype networks of caches
challenges approximation algorithms network calculus for cache networks
workload: logical mobility among networks
Architecture, System, Prototype
architecture
system
prototype(realization)
high-level design/structuring principles, service/function modularity
instantiated set of interoperating protocols, mechanisms, platforms conforming to design principles
Implemented (sub)set of protocols, platforms in particular existing technologies
guides, informs, inspires, constrains
“here’s what it does (function), you tell me how”
*
* ack: D. Clark, J. Wroclawksi
Architecture, System, Prototype
architecture
system
prototype
Minimalist – principles, modularities
Maximalist – protocols, mechanisms go here
Architecture, System, Prototype
architecture
system
prototype
Internettelephony ICN
end-end circuit, stateless endpoints, stateful core, QoS, single service
SS7, ESS, MSC, VLR, HLD
many .. over the years
datagram, stateful endpoints, best-effort stateless core, multiple services, IP
TCP, UDP, DNS, BGP, IS-IS, OSPF
many .. over the years
content, naming, stateful core, caching
Ongoing(routing, congestion control, caching, name resolution, search,…)
Ramping up …
Architecture, System, Prototype
architecture
system
prototype
Internettelephony ICN
end-end circuit, stateless endpoints, stateful core, QoS, single service
SS7, ESS, MSC, VLR, HLD
many .. over the years
datagram, stateful endpoints, best-effort stateless core, multiple services, IP
TCP, UDP, DNS, BGP, IS-IS, OSPF
many .. over the years
content, stateful core, caching
Ongoing(routing, congestion control, caching, name resolution, search,…)
Ramping up …
OK .. but why care?
Architecture, System, Prototype
architecture
system
prototype
Internet ICN
datagram, stateful endpoints, best-effort stateless core, multiple services, IP
TCP, UDP, DNS, BGP, IS-IS, OSPF
content, stateful core, caching
Ongoing(routing, congestion control, caching, name resolution, search,…)
Architecture research/evaluation more difficult, more “fundamental” (?), more impactful (?)
Research/evaluation mostly here: mechanism, protocols
Architecture, System, Prototype
architecture
system
Internettelephony ICN
end-end circuit, stateless endpoints, stateful core, QoS, single service
SS7, ESS, MSC, VLR, HLD
datagram, stateful endpoints, best-effort stateless core, multiple services
TCP, UDP, DNS, BGP, IS-IS, OSPF
content, stateful core, caching
Ongoing(routing, congestion control, caching, name resolution, search,…)
Kleinrock 64Cerf, Kahn 74 Clark 1988 McCanne 1998
?
?Blocking networks
Queueing networksDelay calculusEffective bandwidthsTCP, NUM optimization
Evaluation
?
ICN: architecture vs protocol/mechanism elucidation, value-proposition of design principles,
service/function modularities evaluation tool: networks of caches
Challenges
Interlude ….
Overview
architecture, system, prototype networks of caches
challenges approximation algorithms network calculus for cache networks
workload: logical mobility among networks
Cache networks
miss
content
miss
miss
miss
miss
consumer requests content request routed (e.g., shortest
path) to known content custodian
en-route to custodian, caches inspect request hit: return local copy miss: forward request
towards custodian during content download,
store in caches along path content requests from different users
interact: cache replacementrequest
contentcustodian
contentcustodian
missmiss
Challenge: networks of caches network effect: interaction among content
request/reply flows from different users: content replacement: requested content by one user
replaces content previously requested by others
x
Circuit-switching:blocking networks(Erlang, 1917, Kelly 1986)
Packet-switching:queueing networks(Kleinrock, 1963)
Content-caching:cache networks
Modeling a network of cachescontent node i: exogenous (external)
arrivals for content j: l(i,j) node i: internal arrivals (miss
stream) for content j from downstream neighbors h: m(j,h)
r(i,j): aggregate rate of arrival requests at i for content j
ZDD: zero download delay assumption
l(i,j)
i
x
w m(j,w)
m(j,x)
r(i,j) = l(i,j) + m(j,h)Sall downstreamneighbors, h
y
m(j,i)
j
Modeling a network of caches SCA: standalone cache i approximation algorithm: given
r(i,j), compute miss rate for all content j Independence Reference Model (IRM) of incoming
requests:
SCA approximation algorithm for LRU: [Dan 1985]
r(i,1)
cache i
Pr(Xt = fj | X1,..,Xt-1) = Pr(Xt=fi)
r(i,n)
m(i,1)
m(i,n)
But we need {(ri,j, mi,j)} for a network of caches
Fixed-point iteration
Set r(i,j)=λ(i,j)
Compute miss rate m(i,j)
Compute arrival rate r(i,j)
Return r(i,j), m(i,j)Using Routing Matrix
Using SCA algorithm
Repeat untilconvergence
Note: tree-network (feed-forward) require single iteration
15
Using SCA algorithm
Quality of a-NET
a-NET: approximation error
line topology with 9 nodes
errors decrease in networks with high node degree
0 1 2 3 4 5 6 7 8 9Cache ID
1.14
1.12
1.10
1.08
1.06
1.04
1.02
1.0
0.98
Sim
/ A
ppro
x M
isse
s
sources of approximation errors in a-NET?SCA algorithm inaccuraciescascading errors
approximated output rates of one iteration is input to next iteration
violating IRM assumed by SCA algorithm miss process for file j negatively correlated
a-NET: error factor analysis
Quality of a-NET Cascade Err. removed Non-IRM removed Quality of SCA
a-NET: error factor analysis
• Factor analysis reveals that non-IRM input to SCA is main cause of error
0 1 2 3 4 5 6 7 8 9Cache ID
1.14
1.12
1.10
1.08
1.06
1.04
1.02
1.0
0.98
Sim
/ A
ppro
x M
isse
s
“Approximate Models for General Cache Networks,” Elisha J. Rosensweig, Jim Kurose, Don Towsley, 2010 IEEE INFOCOM
Overview
• architecture, system, prototype• networks of caches
– challenges– approximation algorithms– network calculus for cache networks
• workload: logical mobility among networks
(σi,ρi) analyses of cache networks
(σi,ρi) bounds # requests for fi over [t1,t2]:
where ri(t) = request rate for fi at time t
iiti tt(t)dtr )( 12
2t
1
Goal: a network calculus for cache networks:(σ1
in,ρ1in)
(σnin,ρn
in)
(σ1out,ρ1
out)
(σnout,ρn
out)
t0t1 t0t1
f1 requests
fnrequests
(σi,ρi) cache networks: observations
not all requests arriving at cache will leave (unlike queue)
t0t1 t0t1
f1 requests
f2 requests
stream of input requests for one file only generates no output
“burst” of request for same file generates one output
interactions among files in cache critical
different intuition (from queues) about “performance damage” of bursts
Building block: miss set, Mi
miss set for fi: set of requests for c unique files, other than i
x1 requests for f1
Mi(x1, …., xn,c): max number miss sets for file fi, given {xiin}
arrivals, cache of size c.properties:
Mi = min(xiin, M)
xiout < Mi, and this bound is achievable
c: cache sizexn requests for fn
w
. . .
. . .
!!
From (σiin,ρi
in) to (σiout,ρi
out): (σiin,ρiin)
(σjin,ρjin)
(σiout,ρiout)
(σjout,ρjout)fj requests
. . .
fi requests
If {(σiin,ρi
in)}ni=1 and {(σ’iin,ρ’iin) }n
i=1 are globally tight and ρi
in = ρ’iin for all i
then ρiout = ρ’iout
Theorem:
iout independent of {σi
in}
. . .
From (σiin,ρi
in) to (σiout,ρi
out): (σiin,ρiin)
(σjin,ρjin)
(σiout,ρiout)
(σjout,ρjout)fj requests
. . .
fi requests
For a cache of size c:
ρiout = min(ρi
in, Mi(ρ1in, … , ρn
in,c ))
Theorem:
Can calculate ρiout from {ρi
in}
. . .
Can compute as welliout
Numerical example
f0,f2
4 files, uniform popularity distribution
f1,f3
cache size = 2 at each node
homogeneous IRM arrivals, exponential interarrival times
Numerical example: bounding results
bound
simulation
mis
s ra
te fo
r f3
Cache ID
ICN: architecture vs protocol/mechanism elucidation, value-proposition of design principles,
service/function modularities modeling networks of caches: develop analytic
models for cache networks (ICN) equivalent of blocking networks (circuit-switched), or
queueing networks (packet switched)? exact in asymptotic regimes? ergodicty?
Challenges
Overview
architecture, system, prototype networks of caches
challenges approximation algorithms network calculus for cache networks
workload: logical mobility among networks
Characterizing mobility among networks Historic shift from PC’s to mobile/embedded devices
• ~5B cell phones (`1B smart) vs. ~1B Internet-connected PC’s • Mobile data growing exponentially, surpassing wired user
traffic by 2012 [Cisco] any evaluation/model (ICN or otherwise) must consider
mobility “not your father’s mobility:” characterize mobility
among networks• distinctly different from physical mobility, models• physically mobile users may be stationary (from network
transition POV); stationary users may move among networks (multi-homing, multiple devices)
Characterizing mobility among networks Measure mobility among networks via IMAP logs
• online users periodically “push” (background login, check) email, and/or intentionally read mail- e.g., [email protected] generated 7,482 IMAP entries 4/14/13 –
6/4/13• track network location from which IMAP accessed• 70 users, 4/14/13 – 7/5/13, resident in 183 unique AS
numbers
Where do users (in aggregate) spend time?
Mobile: Verizon, AT&T, sprint)Work: 5 college Home: Comcast, Verizon, Verizon, Hughes
Misc: 172 other networks in trace
Users spend most of their time in small number of networks
Where do users (individually) spend time?
Users individually spend most of their time in small number of networks
Multihoming
COMCAST
VERIZON
Multi-homing
Q: How often are users multi-homed? • 15-min subinterval has IMAP access from two different AS’s
Characterizing mobility among networks
other characterizations of mobility among networks generative mobility-among-network model:
parsimonious Markov chain model for individual user transitioning among networks
ICN: architecture vs protocol/mechanism• elucidation, value-proposition of design principles, service/function
modularities modeling networks of caches: develop analytic models for
cache networks (ICN) • equivalent of blocking networks (circuit-switched), or queueing
networks (packet switched)• exact in asymptotic regimes?• ergodicty
traffic models (for ICM and otherwise), with mobile users, content• mobility the norm
Challenges
Conclusion
architecture, system, prototype networks of caches
• challenges• approximation algorithms• network calculus for cache networks
workload: logical mobility among networks
End
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Interesting reading• J. Wroclawski, “All hat no answers: Some issues related to the
evaluation of architecture,” March 2013 NSF FIA meeting, Salt Lake City UT
• D. Clark, “The Design Philosophy of the DARPA Internet Protocols,” ACM Sigcomm 1988, Revised with extensive commentary 2013
• E. Rosensweig, D. Menasche, J. Kurose, “On the Steady-State of Cache Networks,” IEEE Infocom 2013.
• E. Rosensweig, J. Kurose, “A Network Calculus for Cache Networks,” IEEE Infocom Mini-conference 2013.
• E. Rosensweig, J. Kurose, D. Towsley, “Approximate Models for General Cache Networks,” 2010 IEEE Infocom, pp. 1100-1108
• S. Yang, S. Heimlicher, J/.Kurose, A. Venkataramani, “User Transitioning Among Networks - a Measurement and Modeling Study”, submitted, 2014.
Ergodicity of cache networks does steady state performance
depend on initial conditions (ergodicity)? shown existence of non-
ergodic cases (replacement policy, topology, cache size)
derived sufficient conditions for ergodicity topology (single-
custodian trees) from individual ergodicity
to system ergodicity
A B
Requestsfor A
Requestsfor B
A BB A
ergodicty (continued): showed random
replacement: ergodic defined class of non-
protective policies (including LRU): all ergodic
content
Ergodicity of cache networks