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Agenda
Who is Akamai?– Akamai’s Origins & Backgrounds– Content Distribution Network
Edge Caches– Akamai Accelerated Network Program– Regions– Buddy System
Agenda
Content Delivery– Object Delivery– Site Delivery– Video Streaming
Mapping– DNS
ä'•kuh•my
Who Is Akamai?
Akamai’s Origins and Background
• Based in Cambridge, MA• Founded by MIT research team
– F. Thomson Leighton, Chief Scientist– Danny Lewin, CTO– Seeded in 1995 as an MIT research effort to improve
Internet’s content distribution problem• Team of 1,300 world class professionals • Investors: Apple ($12M), Microsoft ($15M) and
Cisco ($49M)
IPO on 10/29 raised $250M 4th best in 1999
What is a Content Distribution Network?
Akamai is a Content Distribution Network (CDN)
That’s nice, but what is a CDN?– Three main components:
• Edge caches• Content delivery• Mapping
What is a CDN?
Edge Caches– Working with ISPs and networks all over the world to
install edge caches– More is better
Content Delivery– Getting content to the edge– Includes object, videos, and whole web sites
What is a CDN?
Mapping– Akamai’s Secret Sauce– Finding the closest edge server for each user– Network proximity, not necessarily the same as
geographical proximity
How does Akamai’s CDN work?
How does a Akamai’s CDN work?– All content must be hosted on an “origin server”
accessible to all edge caches• Working on Hierarchy, some customers using now
– End users only speak to edge caches, not origin server, to get distributed content
– Edge caches pull content once from origin server, then deliver content to many end users
How does Akamai’s CDN work?
Why is this good?– Allows nearly infinite scalability (if deployed properly)– Good economies at large scales– Avoids congestion and long latency
• Speed of light issues, undersea fiber, etc.– Extremely reliable
• Mitigates some DoS attacks• Massive redundancy
Edge Caches
Akamai Accelerated Network Program (AANP)
What is the Akamai Accelerated Network Program?– Gives free edge caches to qualified networks
• Internet Service Providers• Educational Institutions (usually Universities and
K-12)• Government networks• Anyone else with “eyeballs”
AANP Benefits
Performance– Content served locally, increasing performance
Bandwidth Savings– Saves money on upstream, reduces congestion
Reliability– A cache on a local LAN is more reliable than a web
server on the InternetInteroperability
– No routing or DNS changes, already using it today
AANP Benefits
No Cost – FREE!!– Akamai pays for all equipment, shipping, etc.
Easy to implement– Each Cache is just another another host on the LAN
Akamai Support– 24 x 7 NOC
Co-Marketing– Logo use, press releases, trade shows, etc.
“Region” – set of edge caches
All Regions– Intel based rack-mount PCs
HTTP Regions– Linux based server– Proprietary HTTP server / cache
Streaming Regions– Shrink wrapped software installed on our servers– Linux used for QT & Real– Win2K used for WMT
Regions
Server Configuration– Dual Pentium III processors– Gigabyte of RAM– Two or four SCSI hard drives– Two 100BaseT network cards
Additional Hardware– Ethernet switch(es)
• 100BaseT or Gigabit ethernet uplinks– Patch Cables
Buddy System
Each server has two public IP addresses– “Service” address
• This is the address given to end users who want to retrieve content
– “Physical” address• This is the address used to manage and test the
server• If the physical address is not responding, the box
is considered to be down
Buddy System
Server Failure– Servers do fail occasionally– Each server has a “buddy” which is constantly
trading hellos with the physical address– When a server stops responding to hellos, its buddy
will respond to requests directed at the failed server’s service address
– Users in the middle of a download may have to hit “reload”
– No one else will notice any interruption
Content Delivery
End UserInternet
Host Server
Last MileProblem
Possible bottlenecks on the Internet
First Mile Problem
BackboneProblem
PeeringProblem
Process Flow
1. User wants to download distributed web content
1
XYZ
2. User is directed through Akamai’s dynamic mapping to the “closest” edge cache
Process Flow
1
2
XYZ
Process Flow
3. Edge cache searches local hard drive for content
1
23
XYZ
Process Flow
1
23
XYZ
3a
3b. If requested object is not on local hard drive, edge cache checks other edge caches in same region for object
3a
Process Flow
3b. If requested object is not cached or not fresh, edge cache sends an HTTP GET the origin server
1
2
3b XYZ
3
3a
3a
3c. Origin server delivers object to edge cache over optimized connection
Process Flow
1
2
3b XYZ
33c
3a
3a
4. Edge server delivers content to end user
Process Flow
1
2
3b XYZ
33c
3a4
3a
The Old Internet
The New Internet with Akamai
Case Study on Reliability and Scalability: The 2000 Election
0
5
2
7
10
12
15
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20
22
Crash Zone Without Akamai
this site could not have served
customers abovetheir crash zone
Cu
sto
mer
Vis
its
(Mill
ion
s)
Time
How a Non-AkamaizedWebsite Works
1User enters standard URL
Customer Web Server
Customer’s Web Server returnsHTML with embedded URLs
2 Objects served with round trips across the Internet
4User’s browser requests embedded objects from customer Web server
3
End User
www.customer.com
<img src=/images/logo.gif>
Client’s Servers
HTTP requestuser enters standard URL
FreeFlow – Akamai’s Object Delivery Service
HTML codecontains Akamai URLs (ARL)
Content Served Locally
HTTP requestfor embedded
content
AkamaiServer
Example ARL: img src=a1000.g.akamai.net/…/www.customer.com/images/logo.gif
EdgeSuite – Akamai’s Site Delivery Service
Customer CNAME’s (aliases) www.customer.com– Anyone looking up www.customer.com will be
redirected to an Akamai hostname - “customer.d4p.net”• No, I do not know why we use “d4p.net”.
– customer.d4p.net is CNAME’d to aXXX.g.akamai.net– Standard Akamai mapping magic sends returns the
closest edge server for aXXX.g.akamai.net
EdgeSuite – Akamai’s Site Delivery Service
End user never communicates with origin server– Akamai retrieves content from private hostname
• Something like “origin.customer.com”– High reliability
• Thousands of servers backing each other up• If one geographic area is disabled, no other area
will be affected • Mitigates some DoS attacks
EdgeSuite – Akamai’s Site Delivery Service
Uncacheable content is tunneled back to origin– Can reduce need for tunneling with server-side
scripts running on edge cachesPersistent TCP connections increase performance
– Helps with downloading of objects to end caches– Helps with tunneling to origin– (More on this later)
Video on Demand
Akamai uses HTTP to transit content to edge caches– Allows lossless transport of content to edge– Origin server does not need streaming software,
licenses, etc.– HTTP 1.1 byte-range request used to pull only required
dataUser connects to edge cache with streaming protocol
– Content is streamed in native format from cache to user– User experience is enhanced through “origin” file
available on a “close” server
Live
Akamai uses UDP to transit content to edge caches– Proprietary reflector network of servers– Akamai translates all streaming formats into UDP– Propagates live stream through reflector network
Akamai Streaming Accomplishments:– First 1 Mbps stream live stream fed over public
Internet– Single largest streaming event in Internet history
• Broke own record 3 times
Live “SteadyStream”
User connects to edge cache with streaming protocol– Edge cache “subscribes” to reflector network to
receive live streaming content– Three streams are delivered to each edge cache– Packet loss is eliminated through redundancy– Content is streamed from edge cache to user
2
4
1
3
2
4
3
2
1
Encoding
Top-level refelectors
Regions
3
4
1
43
21
Dropped packets don’tdegrade stream to regions
X Lost connections don’tdegrade stream to regions
XXXX
Entry Point
Akamai SteadyStreamSM technology can deliver streams reliably to the edge with effectively 0% packet loss.
X
Live
Pros:– Allows global distribution of real-time video– Users can connect anywhere and get good video quality
over public InternetCons:
– Each region must have 3 users for effective bandwidth use– If streaming rate is > 1/3 access bandwidth to edge cache,
congestion will occur– Reflector network uses bandwidth even if no users connect
QuickTime Streaming via HTTP
Akamai can deliver Apple’s QuickTime files via HTTP– Delivered over HTTP caching network– HTTP network is more widely deployed than
streaming networks– Packet loss is eliminated– Only good for VoD– More overhead than streaming protocols (uses TCP)
Live Streaming Over Satellite Network
SatelliteUplink
platform
Satellite Uplink Facility
Akamai Servers
Akamai Switch
Satellite DVB Receiver
Akamai Streaming Servers
To ISP Subscribers
ISP/Network Datacenter
InternetInternet
xIP Encoded Stream
Core Hierarchy Regions
XYZ
1. User requests content and is mapped to optimal edge Akamai server
Core Hierarchy Regions
XYZ
2. If content is not present in the region, it is requested from most optimal core region
Core Hierarchy Regions
XYZ
3. Core region makes one request back to origin server
Core Hierarchy Regions
XYZ
4. Core region can serve many edge regions with one request to origin server
Core Hierarch Features
Reduces traffic back to origin server– Reduces infrastructure needs of customer– Provides best protection against flash crowds
• Especially important for large files (e.g. Operating System updates or video files)
Improved end-user response time– Core regions are well connected– Optimized connection speeds object delivery
Persistent TCP connections
Avoids TCP slow-start and connection set up– Each TCP connection has to be set up with three
packets– Once set up, a TCP connection starts at a low
speed, and increases speed during connection• Many web connections do not last long enough to
reach top speed
Persistent TCP connections
Reduces load on origin server– Maintain connections to a small set of Akamai
servers instead of millions of end users– No new connections to be negotiated
• Setting up a new connection is significantly more CPU intensive than maintaining an existing connection
Mapping
Mapping
Mapping algorithms– Heart of Akamai’s secret sauce– Directs end users to connect to nearest edge cache– Uses DNS to direct users to closest edge cache– Completely transparent to networks and end users –
you are already using it today for the world’s most popular web sites
Mapping
Mapping algorithms– Three main components to finding “closest” edge
cache to end user from a Network point of view:• Packet Loss• Throughput• Latency
– Listed in order of importance (roughly)
Mapping
Mapping algorithms– Mapping also takes into account edge cache
performance• Does a server have an object on its hard drive?
– Uses consistent hashing algorithm (patent pending)• Does the edge cache have CPU, RAM,
bandwidth, etc. available to serve end-user?
Mapping
Which is the best Akamai server to serve this end user?Which is the best Akamai server to serve this end user?
Mapping
Local Name Server
– Computer asks local name server for IP address which matches hostname
– Name will either be aXXX.g.akamai.net or an alias of that
Name ResolutionName Resolution
Mapping
Global Top Level Domain ServerGlobal Top Level Domain Server
gTLD Servers
Local Name Server
– Local name server asks the global Top Level Domain (gTLD) servers who is authoritative for domain “akamai.net”
Mapping
HLNSHLNS
Root Name Servers
Akamai High-Level name Servers
15 minutes
Local Name Server
– gTLD servers point local name server at Akamai High-Level name servers (HLNS)
– Local name server requests IP address of aXXX.g.akamai.net from HLNS
Mapping
HLNSHLNS
Root Name Servers
Akamai High-Level name Servers
15 minutes
Local Name Server
– HLNS looks at IP address of local name server and returns a sub-delegation for “g.akamai.net” pointing at a close Low Level name server (LLNS)
Mapping
Sub-Delegation– Standard part of Domain Name System– Tells local name server “I do not know aXXX, but
g.akamai.net is at this IP address”– Local name server automatically asks LLNS for IP
address – transparent to end user
Mapping
Mapping based on Local Name Server IP address– Note that the Akamai system has not seen the IP
address of the end user– Leads to a small percentage of sub-optimally
mapped end users– Working on ways around this
• Auto-Akamaizer• Dynamic HTML in EdgeSuite• Others
Mapping
HLNS– HLNS has a “map” or matrix of IP blocks to LLNS
• Map weighs network proximity heavily, using geography only when all else is equal
– HLNS “map” of network conditions is refreshed every 15-20 minutes
– Downed servers updated more frequently – approximately every minute• Handled through Overflow Controller
Mapping
Time To Live– Every time an IP address is returned to a name
server, it is accompanied with a Time To Live (TTL)– Akamai returns the sub-delegation with a TTL of
approximately 20 minutes
Mapping
LLNSLLNS
Root Name Servers
Akamai High-Level DNS Servers
15 minutes
Local Name Server
3-20 seconds
Akamai Low-Level DNS Servers
– LLNS picks local Akamai server which is not busy to serve content and returns that IP address
Mapping
LLNS– Most edge caches do double duty as a LLNS– At least one LLNS outside local region is returned
during sub-delegation to ensure end-user always gets a response
– LLNS polls servers every 3 to 20 seconds for availability, load, etc.
– At least two IP addresses are returned
Mapping
TTL– The TTL of the final IP addresses is 20 seconds– This means if a machine goes down, the local name
server will ask for a new IP address in 20 seconds– During that 20 seconds, the buddy will take over for
the dead edge cache– If an entire region goes dies (rack loses power, etc.),
the end user will experience a maximum of 20 seconds down time
Mapping
Which is the best Akamai server to serve this end user?Which is the best Akamai server to serve this end user?
Root Name Servers
Akamai High-Level DNS Servers
15 minutes
Local Name Server
3-20 seconds
Best Akamai Server for End User
Akamai Low-Level DNS ServersContentServed Locally
Akamai \ ä'•kuh•my \ , adj. (Hawaiian)1. Intelligent, clever.2. “Cool.”
Thank You !!!Thank You !!!
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