3-1 Dealing with (Internet) Scale : CDNs Recall: one single “mega-server” can’t possibly handle all requests for popular service  DNS  not enough bandwidth: Netflix video streaming at 2 Mbps per connection  only 5000 connections over fastest possible (10Gbs) connection to Internet at one server  30 Million Netflix customers  too far from some users: halfway around the globe to someone  reliability: single point of failure A single server doesn’t “scale”

Content distribution networks  challenge: how to stream content (selected from millions of videos) to hundreds of thousands of simultaneous users?  option 1: single, large “mega-server”  single point of failure  point of network congestion  long path to distant clients  multiple copies of video sent over outgoing link ….quite simply: this solution doesn’t scale 3-2

Content distribution networks  challenge: how to stream content (selected from millions of videos) to hundreds of thousands of simultaneous users?  option 2: store/serve multiple copies of videos at multiple geographically distributed sites (CDN)  enter deep: push CDN servers deep into many access networks close to users used by Akamai, 1700 locations  bring home: smaller number (10’s) of larger clusters in POPs near (but not within) access networks used by Limelight 3-3

CDN: “simple” content access scenario 3-4 Bob (client) requests video /6Y7B23V  video stored in CDN at 23V netcinema.com KingCDN.com 1 1. Bob gets URL for for video from netcinema.com web page 2 2. resolve via Bob’s local DNS netcinema’s authorative DNS 3 3. netcinema’s DNS returns URL 23V 4 4&5. Resolve via KingCDN’s authoritative DNS, which returns IP address of KIingCDN server with video 5 6. request video from KINGCDN server, streamed via HTTP KingCDN authoritative DNS

CDN cluster selection strategy  challenge: how does CDN DNS select “good” CDN node to stream to client  pick CDN node geographically closest to client  pick CDN node with shortest delay (or min # hops) to client (CDN nodes periodically ping access ISPs, reporting results to CDN DNS)  alternative: let client decide - give client a list of several CDN servers  client pings servers, picks “best” 3-5

Akamai CDN: quickie  pioneered creation of CDNs circa 2000  now: 61,000 servers in 1,000 networks in 70 countries  delivers est 15-20% of all Internet traffic  runs its own DNS service (alternative to public root, TLD, hierarchy)  hundreds of billions of Internet interactions daily  more shortly…. 3-6

Case study: Netflix  30% downstream US traffic in 2013  $1B quarterly revenue  2B hours viewing streamed video  owns very little infrastructure, uses 3 rd party services:  own registration, payment servers  Amazon (3 rd party) cloud services: Netflix uploads studio master to Amazon cloud create multiple version of movie (different encodings) in cloud, move to CDNs Cloud hosts Netflix web pages for user browsing 3-7

Case study: Netflix  uses three 3 rd party CDNs to store, host, stream Netflix content:  Akamai, Limelight, Level-3  can play each of the CDNs against each other in terms of customer experience  developing its own CDN (2012) 3-8

Case study: Netflix Bob manages Netflix account Netflix registration, accounting servers Amazon cloud Akamai CDN Limelight CDN Level-3 CDN 2 2. Bob browses Netflix video 3 3. Manifest file returned for requested video 4. DASH streaming upload copies of multiple versions of video to CDNs

Streaming multimedia: DASH  DASH: Dynamic, Adaptive Streaming over HTTP  server:  divides video file into multiple chunks  each chunk stored, encoded at different rates  manifest file: provides URLs for different chunks  client:  periodically measures server-to-client bandwidth  consulting manifest, requests one chunk at a time chooses maximum coding rate sustainable given current bandwidth can choose different coding rates at different points in time (depending on available bandwidth at time) 3-10

Streaming multimedia: DASH  manifest file: provides URLs for different chunks 3-11 Segment Info Initialization Segment Initialization Segment Media Presentation Period, start=0s … Period, start=100s … Period, start=295s … … Period, start=100 baseURL= Representation 1 500kbit/s … Representation 2 100kbit /s … Representation 1 bandwidth=500kbit/s width 640, height 480 Segment Info duration=10s Template:./ahs-5-$Index$.3gs … Media Segment 1 start=0s 1.3gs Media Segment 1 start=0s 1.3gs Media Segment 2 start=10s 2.3gs Media Segment 2 start=10s 2.3gs Media Segment 3 start=20s 3.3gh Media Segment 3 start=20s 3.3gh Media Segment 20 start=190s Media Segment 20 start=190s Ack & ©: Thomas Stockhammer

Streaming multimedia: DASH  DASH: Dynamic, Adaptive Streaming over HTTP  “intelligence” at client: client determines  when to request chunk (so that buffer starvation, or overflow does not occur)  what encoding rate to request (higher quality when more bandwidth available)  where to request chunk (can request from URL server that is “close” to client or has high available bandwidth) 3-12

Let’s check out Netflix:  use wireshark to capture and view packets being sent to/from my laptop  you’re not responsible for knowing how to use it, but it’s a lot of fun  logging in (authorization), content selection  main webpage hosted by amazon cloud?  use whois to see who server is  select video and begin playing  use whois to see who is serving video  how far away is server (use traceroute, no info? Ip2location.com) 3-13

Netflix: user adaptation to bandwidth changes  Question: how does Netflix client adapt to changes in bandwidth (due to changing congestion levels on network path)  two client-based alternatives:  get video from new CDN server (over new path)?  change video streaming rate via DASH?  experiment:  connect to Netflix  systematically decrease bandwidth from server to client  measure how client responds: decrease rate or change servers 3-14

Netflix experiment 3-15 Akamai CDN Limelight CDN Level-3 CDN Bob’s home network Public Internet Adjust bandwidth to Bob’s computer, see how Netflix responds Vijay Kumar Adhikari, Yang Guo, Fang Hao, Matteo Varvello, Volker Hilt, Moritz Steiner, Zhi-Li Zhang, “Unreeling Netflix: Understanding and Improving Multi-CDN Movie Delivery”, INFOCOM, Orlando, FL, USA, March, 2012.

Netflix experiment 3-16 Netflix seems to dynamically use alternate CDNs only for fail-over

Netflix experiment 3-17 Question: Does any one of Netflix’s three CDN providers systematically outperform the other? Answer: Non one CSN is uniformly better Measurements taken at different locations: which CDN provides best Netflix service?