CC-10-Storage - CDN.pdf - Content Distribution Network...

Content Distribution
Network Services
Slides Courtesy: Partly from Kurose & Ross, K. Webb, D.
Choffnes
CDN is an important and inevitable component of current
large-scale content services over cloud/Internet

Why does my click not work
(immediately)?
• Latency - Browser takes a long time to load the page
Due to…
• Server load - Browser connects but does not fully load the page
• Path congestion
• Packet Loss - Browser hangs, user needs to hit refresh
• Jitter - Streams are jerky
• Broken/missing content

• More hops between client and Web server => more congestion!
• Same data flowing repeatedly over links between clients and Web server
• Origin server is bottleneck as number of users grows
• Flash Crowds (e.g., US 9/11/2001, Japan Earthquake 3/11/2011,
…,Obamacare website launch 10/1/2013)
• (COVID-19 ?)
• Content Distribution Problem : Arrange a rendezvous between a content
source at the origin server and content users
Motivations for Content Networks
S
C1
C4
C2
C3
- IP router

Content distribution networks (CDNs)
challenge: how to stream content (selected from millions of
videos) to hundreds of thousands of simultaneous users?
§ An option: single, large “mega-
server”
• single point of failure
• point of network congestion
• long (and possibly congested)
path to distant clients
….quite simply: this solution doesn’t scale

Content distribution networks (CDNs)
challenge: how to stream content (selected from millions of
videos) to hundreds of thousands of simultaneous users?
• enter deep: push CDN servers deep into many access networks
• close to users
• Akamai: 240,000 servers deployed
in > 120 countries (2015)
§ Another option: store/serve multiple copies of videos at
multiple geographically distributed sites (CDN)
• bring home: smaller number (10’s) of
larger clusters in POPs near access nets
• used by Limelight

…
…
…
…
…
…
§ subscriber requests content, service provider returns manifest
Content distribution networks (CDNs)
§ CDN: stores copies of content (e.g. MADMEN) at CDN nodes
where’s Madmen?
manifest file
• using manifest, client retrieves content at highest supportable rate
• may choose different rate or copy if network path congested

Content Network Types
• Server Farms
o
Simple solution from content providers
• Caching Proxies
o
A solution from ISPs
• Akamai-style Content Distribution Networks (CDN)
o
Used by content providers (or large cloud platform like Fb)
o
(Originally) Optimized for 10KB objects
o
Whole-file caching
o
Evolved with dynamic adaptation
• BitTorrent or P2P
o
Custom software/protocol

Example content networks:
Server Farms
Control mechanism
Request from
tux02.sce.umkc.edu
Request from
tux01.sce.umkc.edu
Request from
tux01.sce.umkc.edu
Request from
tux02.sce.umkc.edu
(replica 1)
(replica 3) (replica 2)
• Simple solution to the content distribution problem:
deploy a large group of servers

Example content networks:
Caching Proxies
Client
tux01.sce.umkc.edu
Client
tux02.sce.u
mkc.edu
Intercepters
Proxy
Internet
TCP port 80
traffic
Other
traffic
ISP
• Mainly motivated by ISP business interests – reduction in
bandwidth consumption of ISP from the Internet
• Reduced network traffic
• Reduced user perceived latency