 The Internet is transforming every aspect of communication in human
society by enabling a wide range of applications for business, commerce,
entertainment, news, and social interaction.
 Requirements of Modern applications
Performance
Reliability
Scalability
Security
low cost
Internet

 Network layer
 Defines addressing, routing, and service model for communication
between hosts.
 Default IP- routing
 Hierarchical structures (IGP and BGP)
 Allow flexibility and distributed management
 Achieve global reachability/connectivity
 CIDR allows route aggregation for announcements, leading to smaller
routing tables
Traditional Internet Infrastructure

 Routing anomalies impact network/service availability
 Trade-off performance of scalability
 New services need new capabilities
 Mobility? Multicast service?
Solution Space:
 Change the existing network layer, or
 Bridge the gap is use of overlay on top of existing networks.
Why its not good enough ?

What is Overlay Network?
 An overlay network is a computer network that is built on top
of another network.
 Nodes in the overlay network can be thought of as being
connected by virtual or logical links, each of which corresponds
to a path, perhaps through many physical links, in the
underlying network.
Example : Internet is overlay network & Virtualization

An overlay network is built on top of the public Internet to provide
the exact requirements that rich Internet-based services need.
Basic Diagram of overlay network

 CDN – Resilience overlay network
 P2P
 VPN
 MPLS
 IPv4 to IPv6
 GRE
 Multicast
 VoIP
 Frame Relay
Type of Overlay Network

Need for Overlay Network?
Due to following drawbacks/limitation of Internet
 Outages
 Congestion
 Lack of scalability
 Slow adaptability
 Lack of security

 (2008 and 2013) -16 Outage
Last outage – 22-26 October 2015 (Due to fiber cut)
Internet Outage example

 Outages
 Congestion
 Lack of scalability
 Slow adaptability
 Lack of security
Drawbacks/Limitation of Internet

What Overlay Network offer?
 Performance
 Scalability
 Security
 Intelligence

Overlay Architecture
 To deliver the content, applications and services to users on behalf of content providers.
 Examples: E commerce sites, news channels, social networks, web portals, banks, credit
card companies.
 A large distributed system consisting of hundreds of thousands of globally deployed
servers that run sophisticated algorithms.

System level Architecture of Overlay
Network

Overlay Architecture:
 Origins
 One or a few,
 locates in core
 Edge servers
 Hundreds thousand
 Locates at the edges,
 close to users
 Transport system
 High reliability and performance

Types of Overlay
1) Caching overlay
2) Routing overlay
3) Security overlay

Caching Overlay
Caching overlay is used for the content which is cached over a period
of time.
 Usage
 Static objects can be cached for some period
Embedded image on a web page, a movie, a music file, a
software download, or a software update.
 Benefits
 Availability, performance and origin offload

Caching Overlay
 Architecture – Mapping System
 Performance benefits
 Edge Hit rate
 Speedup time
 The caching overlay is used for content that can be cached for some
period of time.
 The key benefits that a caching overlay provides are greater
availability, performance, origin offload, and scalability.
 Origin offload

Caching overlay architecture example

Performance Benefits
30 agents located in Asia, Europe, and North America
The agents hourly download a popular web page
 Origin servers located in Dallas NA

Origin Offload Benefits
 Origin offload
 Is equal to the ratio of the volume of traffic served by the origin without
the overlay to the volume of traffic served by the origin with the overlay.
 A large decrease in server, bandwidth, operational expenses.
 Popular vs cold traffic
 Cache hierarchy
 Adding a layer of parent servers to reduce the flow of traffic to origin server.
 Increases the origin offload, easy to implement .

Performance Benifits
Origin offload increases with deployment of cache
hierarchy

Routing Overlay
 For Internet-based applications such as shopping, banking, and gaming,
the downloaded content is dynamic and hence uncacheable.
 Therefore, in order to improve performance and availability, routing
overlay is used.
 It improve performance and availability by discovering better “overlay
paths” from the origin to the user.

 An overlay construction algorithm is used to compute a set of overlay
paths that each edge server can use to reach each of the origins.
 Overlay construction algorithm metric :
 Latency
 Packet loss
 Bandwidth
 Server load
 Based on metric find RANK for best path : Request / Response
 Algorithm construct path by solving multi-commodity flow
Routing Overlay Architecture

Routing Overlay link cost attributes
 Latency
 Bandwidth
 Throughput
 TCP performance
 Revers Proxy

The significantly greater performance in file download is due to the ability of the
routing overlay to find alternate paths that avoid the failed links between different
parts of Asia to the Boston origin.

Even when there is no major Internet outage, the routing
overlay provides a significant performance benefit by
discovering and using better performing overlay paths for
communication.

 In Figure (a), shows the performance benefit of a large routing overlay uses a single
optimized path .
 Value of speedups increases as user moves away from the origin.
 In Figure (b), shows the performance benefits for a different smaller routing overlay that
uses multiple optimized paths for each communication.
 In figure (b), the speedups are less compared to (a) as fewer choices for alternate paths
and edge servers are less proximal to users.

Why Security Overlay
 An Internet-based service needs to defend itself from distributed denial of
service (DDoS) attacks
 SYN Flood,
 UDP Flood,
 Brute force attack.
 Defending against DDoS and hacker attacks requires a vast amount of
spare capacity, Cost and Security expertise team to mitigate attack on
distributed large shared platform.

 DDoS attacks on the rise: 71% increase since Q3 2015
 New record DDoS attack: 623 Gbps in Q3 2016
 Mega attacks over 100 Gbps on the rise: 138% increase since
Q3 2015
 427 DDOS attack launched against a single organization in Q3
2016
Reference : Q3 2016 state of the internet security report
Security Overlay

Q3 2016 State of the Internet Security Report

Security Architectural Elements
 Shared spare capacity
 Shared expertise and lower costs
 Advanced security features
 Shielding the origin
 Control Design

Performance benefits
-->Figure (a) shows a sudden increase in
the traffic of the content provider’s
website due to the DDoS attack. The web
site that is normally accessed at a rate
less than 50 pages/second was accessed
at a much higher rate of 9000 pages/sec
during the attack.
 Figure (b) shows firewall rules getting
triggered in response to the attack and
denying over 90% of the attackers’
requests, and protecting the origin from
the significant surge of traffic.

Conclusion
Overlays hold the keys to the rapid evolution of Internet services,
even as the underlying Internet architecture is slow to change.

Overlay Network Overview

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