Smart Content Delivery Technology: CCN or CDN
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Smart Content Delivery Technology: CCN or CDN? KyoungSoo Park ([email protected]) Department of Electrical Engineering KAIST
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Transcript of Smart Content Delivery Technology: CCN or CDN
Smart Content Delivery Technology: CCN or CDN?
KyoungSoo Park ([email protected])
Department of Electrical Engineering KAIST
Talk Overview
Content distribution networks
HTTP CDN
Redundancy Elimination
Content-centric Networking (CCN)
Comparisons of CDN and CCN
2
Content Distribution Network (CDN)
Goals Load balancing
Fast response
High availability
Handling flash crowd
content
Origin Server
replica
replica replica
replica
replica
replica
3
How Web CDN Works?
7
DNS or HTTP redirection
Origin server (content provider)
HTTP Content Distribution Networks (CDNs)
Cache Miss?
Core CDN Technolgy
External load balancing Request redirection
Proximity, server load, content availability
Internal load balancing Consistent hashing
IntraCDN request routing & splitting
Server technology High-performance caching proxy
Disk/memory trade-offs • Custom file system & parallel disk access
8
Request Redirection
Problem: given a request, which CDN server to retrieve the content from?
Choosing the best servers
Network geography (e.g., TCP)
CDN server load
Content availability
Existing techniques
DNS redirection/ HTTP redirection / IP Anycast
10
DNS Redirection
DNS name mapping
Most widely-used
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http://graphics8.nytimes.com/images/misc/nytlogo379x64.gif
NY Times Logo Image
URL: http://graphics8.nytimes.com/images/misc/nytlogo379x64.gif
[kyoungso@opus]$ dig graphics8.nytimes.com
;; ANSWER SECTION:
graphics8.nytimes.com. 300 IN CNAME graphics478.nytimes.com.edgesuite.net.
graphics478.nytimes.com.edgesuite.net. 9250 IN CNAME a1116.x.akamai.net.
a1116.x.akamai.net. 20 IN A 204.153.49.136
a1116.x.akamai.net. 20 IN A 204.153.49.137
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Short TTL Akamai
DNS Redirection
[kyoungso@opus ~]$ ping 204.153.49.137 (Princeton, NJ, USA)
PING 204.153.49.137 (204.153.49.137) 56(84) bytes of data.
64 bytes from 204.153.49.137: icmp_seq=1 ttl=60 time=0.731 ms
64 bytes from 204.153.49.137: icmp_seq=2 ttl=60 time=0.321 ms
64 bytes from 204.153.49.137: icmp_seq=3 ttl=60 time=0.388 ms
[kyoungsoo@ndsl ~]$ dig graphics8.nytimes.com (Daejeon, Korea)
a1116.x.akamai.net. 20 IN A 61.111.58.33
a1116.x.akamai.net. 20 IN A 61.111.58.65
[kyoungsoo@ndsl ~]$ host 61.111.58.65
65.58.111.61.in-addr.arpa domain name pointer 61-111-58-65.kidc.net.
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LG Telecom Data Center
DNS Redirection
Assumptions
Client’s local DNS server (LDNS) is close to client
LDNS does a name lookup
CDN DNS finds the best server for LDNS
Problem & workaround
What if LDNS is far from client?
• A KAIST client uses Princeton’s DNS server?
HTTP redirection
• Redirection again based on actual client IP
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HTTP Redirection
How it works?
A client sends a request to a CDN server
CDN server responds with HTTP 302 redirection
• Better server for this client
• Based on actual client IP
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DNS
graphics8.nytimes.com
CDN Server (Princeton)
CDN Server (LG Telecom)
HTTP Redirection
Pros & Cons
Accurate server selection (+)
Extra app-level RTT (-)
App-level processing overhead (-)
Transparent method?
16
IP Anycast
How it works?
One IP mapped to multiple servers in different PoPs
IP Anycast allows routing to nearest server
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DNS
235.45.98.88
CDN Server2 (USA)
235.45.98.88
CDN Server1 (Korea)
235.45.98.88
Router
IP Anycast
Pros & Cons No DNS abuse (+) Accurate network geography (+) Fault tolerance (+) TCP is a statefull protocol (-) Abrupt route change leads to download failure (-) Require ISP cooperation (-)
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x.y.z.w/16
x.y.z.w/24
x.y.z.w
x.y.z.w
Longest prefix matching x.y.z.w
Internal Load Balancing
Problem: how to balance load among CDN servers?
Front-end distributes requests to back-end nodes
Internal request routing & splitting
Load-aware request distribution (LARD)
Split request into n mini requests (CoBlitz)
Consistent hashing
Reliable service even with node churn
Can be applied globally with DNS
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Consistent Hashing
How it works?
Map each back-end server to an IDx
Calculate a request IDy = Hash(request)
Find a server IDk closest to IDy
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Request ID=1010
ID=1011
ID=1100
ID=0011
ID=0001
ID=1110
ID=1101
Consistent Hashing
Pros
Hashing distributes load among the servers
Request locality
No request shuffling at node churn
• Cf. static hashing = f(x) % N
Cons
CPU overhead
Corner case can disrupt load balancing
• R1, R2, R3 are mapped to Node X
• Workaround : Highest Random Weight (HRW)
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Network-wise Redundancy Elimination(RE)
Per-packet content-based caching
Many research papers
[SIGCOMM’00], [SIGCOMM’08], [SIGCOMM’09]
Basic idea
1. Fingerprint each packet (divide it into N fragments)
2. Send fingerprints (compressed, or encoded)
3. Destination looks up the fingerprints
4. Reconstruct the original packet from the fingerprint cache
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Network-wise Redundancy Elimination(RE)
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Routers keep a cache of recent pkts
New packets get “encoded” or “co
mpressed” w.r.t cached pkts
Encoded pkts are “decoded” or “unc
ompressed” downstream
Slide borrowed from the SmartRE talk
Network-wise Redundancy Elimination(RE)
Pros: protocol independence
Can even cache HTTP uncacheable content
Fine-grained redundancy elimination (packet)
Cons: index explosion
Index can be too big (at high-speed networks)
Not sure if the reconstruction cost is small
Larger than the packet level?
Chunk-based RE
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ISP Networks
Transparently divide content into chunks
Chunk-based Caching
users Content Provider
1. Content request
CN RN
46273811
34282346
93472423
82346754
73649568
Chunk hash storage (Hash, Chunk) storage
2. Deliver content
3. Deliver chunk hashes
4. Look up content for the chunk hashes
5. Deliver cached chunks
6. Deliver content at cache miss
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46273811
34282346
93472423
82346754
73649568
Amplify the bandwidth of the bottleneck link
Content Centric Networking
Fundamental change to the current Internet Specify what to deliver instead of how
Suppresses the redundancy in data delivery
One of the four projects by funded by NSF FIA program Named Data Networking (NDN)
MobilityFirst
Nebula
Expressive Internet Architecture
The idea looks really cool! Is it realizable?
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How CCN Works?
Interest (request) and Data (response)
One Interest matches one Data
No (IP) addresses!
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CCN Names
Opaque, structured byte strings
/parc.com/van/cal/417.vcf/v3/s0/0x3fdc96a4…
represented as a sequence of components
component = byte count (n) + n bytes
8:parc.com 3:van 3:cal …
(Following slides (31-40) are from Van Jacobson’s talk)
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Basic CCN Forwarding
Consumer ‘broadcasts’ an interest over any available communications media:
get ‘/parc.com/van/slides.pdf’
Interest identifies a collection of data – all data items whose name has the interest as a prefix
Anything that hears the interest and has an element of the collection can respond with it:
HereIs ‘/parc.com/van/slides.pdf/v6/p1’
<data>
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Advantages
Trivial any-to-any communications
Natural support for mobility
No IP address shortage, no NAT, no scalable address management
Optimal CDN solution
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CDN vs. CCN: Different Layers
CDN: Operates at application Layer
HTTP content distribution (even P2P)
CDN server: end system (atop TCP)
CCN: Operates at IP layer
Packet level content distribution
Need CCN routers
E2E Principle?
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CDN vs. CCN: Efficiency
CDN: Cache hit at object level
One hit – 1-2GB movie download
Suboptimal network geography
• No direct support from routers
CCN: Cache hit at packet level
One hit – one packet download
Optimal network geography
• Download from the closest router
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CCN: Practical Implications
1 Interest packet = 1 Data packet
ContentStore at 10G Router?
10 Gbps = 14 million IP packets / sec
Lookup speed (14 millions/sec?)
Index size (name + Data)
• 100-byte name x 10 billion entries = 1 TB
• What about the Data?
Pending Interest Table (PIT)
How big should it be?
Too small => no Data can be delivered
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CCN: Practical Implications
Many security issues
Fill the PIT with bogus entries
Fill the ContentStore with bogus entries
Incur many expensive table lookups
Easily kill the router
Challenging to be solved in the near future
What if technology evolves?
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