Request Routing in CDN

1. by:
Sandeep Kath
Improving the Request Routing Mechanism in Content Delivery NetworksImproving the Request Routing Mechanism in Content Delivery Networks
(CDNs)(CDNs)

2. Outline
 Content Delivery – a bit of History
 Content Delivery Network
 Request Routing Techniques
 Literature Review
 Problem Formulation
 Research Objectives
 Methodology
 System Description
 Performance Metrics
 Results and Discussion
 Summary of the results
 Recommendations
 Conclusion
 Future scope of the work
 Publications
 References

3. Content Delivery – a bit of history
• Individual Web servers
• Increase in Web content
• Web Server Farms
• Issue of Flash Crowds
• WWW has evolved beyond simply displaying static
webpages
• New challenge of delivering the content like realtime
audio, video etc.

4. Individual Web Sever (Non-CDN)

5. Content Delivery Network (CDN)
• What: Geographically distributed network of
Web servers around the globe.
• Why: Improve the performance and scalability
of content retrieval.

6. Content Delivery Network

7. Technology Components
• Content distribution
– Placing the content to the devices
• Request routing
– Steer users to a delivery node that is close
• Content delivery
– Protocol processing, access control, QoS mechanisms
• Resource accounting
– Logging and billing

8. Request Routing(An Example)

9. Request Routing Techniques
• Global Server Load Balancing (GSLB)
• DNS-based request-routing
• Transport Layer Request Routing
• HTTP redirection
• URL rewriting
• Any casting
• CDN peering

10. DNS –Normal Operation

11. DNS Request Routing

12. Problem Formulation
• DNS based request routing does not use IP address of client.
The knowledge of Internet location of the client limits the
ability of the request-routing system to determine a client’s
proximity to the surrogate.DNS query does not carry the
addresses of the querying client
• DNS server redirects the resolved IP address to the client and
client uses that IP address to connect with the server, so this
current flow increases network latency.
• The main disadvantage of DNS-based request-routing is that,
it increases network latency because of increase in DNS lookup
times.

13. Objectives
1. Comparison and performance evaluation of
CDN network with non-CDN network on basis
of three metrics Request return time (RTT),
Packet Loss, throughput.
2. Analyze the various request routing
techniques for Content delivery networks
and detailed study of DNS based routing and
transport layer routing techniques.

14. Objectives…
3. Design new request routing technique which
will have less Request response time,
eventually this new technique will have less
packet loss and throughput.
4. Performance comparison of new proposed
request routing with CDN and non-CDN
network.
5. Implement the local load balancing on servers
by using least connections technique.

15. Methodology Used
• Study and review of DNS and name resolving
techniques.
• Detailed Analysis of request routing techniques.
• Exploring the various load balancing techniques.
• Work with NS 2 and learn TCL and NMAP.
• Design of new protocol or agents.
• Implementation of new agents in NS2 /C++.
• Implementation of Simulation scripts in TCL/TK.
• Implement AWK scripts to get results from the NS 2
trace files.
• Results comparisons.

16. System Description

17. System Description– Bandwidth at each link
Link Between Bandwidth Delay
DNS Server & Content
Server
3 Mbps 50ms
DNS Server & Client 1 Mbps 50ms
Hop & DNS Server 6 Mbps 50ms
Hop & Router 1 Mbps 50ms
Router & content server 3 Mbps 50ms

18. System Description
Five New CDN Agents and packets developed in NS-2 to
simulate CDN:
S.NO. AGENT PACKET TYPE
1. cdn_client PT_CDN_CLIENT
2. cdn_dns PT_CDN_DNS
3. cdn_server PT_DNS_SERVER
4. cdn_router PT_CDN_ROUTER
5. non_cdn_dns PT_NON_CDN_DNS
6. cdn_dns_new PT_CDN_DNS_NEW

19. System Description
Proposed CDN DNS Request Routing Technique

20. System Description
Hash Table
Source Address Content Type Destination Address
1 203.197.219.7 txt/plain 202.54.122.1
2 103.194.220.4 txt/plain 202.52.123.2
3 202.54.103.1 txt/html 202.54.122.1
…
n Source_Addr Content_Type Destination_Addr
Hash Function
index = ((source – 10) * 10 + content_type ) % length of table

21. System Description – CDN DNS
cdn_dns_new agent has been developed and added
source, content_type and object_id as input parameters.
The source field represented by nsaddr_t (address type
used on NS-2), defines the IP address of the web server
found to serve the client. Content_type represented by an
integer, defines the type of content requested by cdn_client.
Object_id represented by an integer, defines the size of
content requested by cdn_client.

22. System Description – Local Load Balancing in CDN
Round Robin
Round Robin algorithm distributes requests to the different web
servers in a round robin approach.
Least Connections
it keeps track of the number of active connections to each server
and always directs a new connection to the server with least
connections.
Round Trip
It monitors the request/respnose phase of each connection by
monitoring the TCP protocol. For each connection, the elapsed
time between forwarding the first byte of the request to the
server and first byte of the response to the client is calculated.

23. System Description – Local Load Balancing in CDN

24. System Description – Local Load Balancing in CDN

25. Performance Metrics
• Round-Trip Time
• Round-trip time (RTT) is the total time taken for a
packet sent by a node A to reach a destination B and
then for a response to sent back by B to reach A. In
other words, the round-trip time is the sum of the one-
way delays from A to B and from B to A, and of the
time it takes B to formulate the response to the original
packet. Round-Trip Time represents response time and
related to delay.

26. Performance Metrics
• Packet Loss
• Packet loss is determined as the probability of a packet
being lost in transit from a source A to a destination B.
• Main reasons of Packet Loss
– Congestion
– Errors
• In multimedia applications packet loss is tolerated
but in TCP, packets are retransmitted if they are
lost and thus reduce the performance

27. Performance Metrics
• Throughput
– Throughput is the average rate of successful
message delivery over a communication channel.
The throughput is usually measured in bits per
second (bit/s or bps), and sometimes in data
packets per second or data packets per time slot.
– The system throughput or aggregate throughput
is the sum of the data rates that are delivered to
all terminals in a network.

28. Performance Metrics
• Server Load
– Load expresses how many processes are waiting
in the queue to access the computer processor.
This is calculated for a certain period of time and
of course, the smaller the number, the better.

29. Performance Metrics
• Hop-Count
• The number of point-to-point links in a transmission
path.
• Each point-to-point link is technically a hop, the hop
count is the number of network devices between the
starting node and the destination node.
• An IP packet traveling over the Internet can easily
"hop" through more than a dozen routers.

30. Results- CDN vs Non-CDN
Packet Loss

31. Analysis – Content Delivery Network
• There are more packets lost in the Non-CDN
network than in the CDN network.
• In CDN network, loss of packets only occurred
when clients’ requested contents are not
stored in the nearest content servers.

32. Results- CDN vs Non-CDN
Throughput

33. Analysis – Content Delivery Network
• Throughput of the link between the hop (node
n1) and DNS server (node n3). The upper
curve shows throughput in Non-CDN network,
the lower curve shows that in CDN network.
• The throughput in Non-CDN network is higher
than that in CDN network, showing that the
link in Non-CDN network is busier.There are
more packets lost in the Non-CDN network
than in the CDN network.

34. Results- CDN vs Non-CDN
RTT

35. Analysis – Content Delivery Network
• At the beginning of the curve Non-CDN and CDN
behave the same since the clients’ requests are
served by servers at the far end, and that for the
rest of the curve Non CDN has a larger RTT than
CDN since clients in CDN can be served by servers
nearby.

36. Results- Proposed CDN DNS Request
Routing
Packet Loss

37. Analysis – Proposed CDN-DNS Request
Routing
The upper curve shows packet loss in Non-
CDN DNS network, middle curve shows the
packet loss in normal CDN with existing DNS
and the lower curve shows the data in CDN
DNS network.

38. Results- Proposed CDN DNS Request
Routing
Throughput

39. Results- Proposed CDN DNS Request
Routing
Round Trip Time

40. Results- Local Load Balancing in CDN
2-Node Cluster 4-Node Cluster
8-Node Cluster

41. Results- Local Load Balancing in CDN
Round Robin, Round Trip and Least connection techniques on different clusters

42. Analysis – Local Load Balancing
• Figure illustrates that the round trip scheme
outperforms the other schemes for simulated
CDN network.
• From the comparison it is clear that the
round-trip scheduling strategy gives the
lowest server load and lowest average
response time followed by the round robin
strategy

43. Summary of Results
1. Our comparison scenarios have illustrated that CDN performs
better than Non-CDN in terms of packet loss, RTT and
throughput.
2. CDN-DNS request routing is more efficient as compared to
existing DNS redirection. It uses the client’s location to redirect
the request to appropriate server. Proposed DNS request routing
technique saves one cycle of DNS resolution, in which instead
sending the resolved IP address to client, client’s request is
directed to surrogate server of CDN along with client information
and surrogate serves the requested content to the client

44. Summary of Results
3. Also we have analyzed that low bandwidth links in the network could cause
more packet loss in existing DNS request-routing than proposed CDN
DNS technique as traffic in proposed scheme CDN is to be distributed.
4. The round trip scheme outperforms the other schemes for local load
balancing in simulated CDN network. From the comparison, it is clear that
the round-trip scheduling strategy gives the lowest server load and lowest
average response time followed by the round robin strategy.

45. Recommendations
• Simulation results reveals that CDNs can provide the content to
many users efficiently and reliably even at times of maximum
Internet traffic or during flash crowd.
• Simulation results indicate that CDNs optimize the speed or
increase the response time by keeping the content near to user
location.

46. Recommendations
• Simulation results indicate that CDNs can provide fail-safe feature
by keeping the same content on multiple servers or content
redundancy.
• Simulation results indicate that present DNS request routing have
limitations and it can not use user location to resolve the domain
name so that traffic should be directed to nearby server. Results
also reveal that proposed CDN-DNS is more efficient as compared
to existing DNS request routing.
• Simulation results indicate that Round Trip load balancing
technique performed better in case of local load balancing in
CDNs.

47. Conclusion
A new CDN DNS technique, proposes new DNS
routing table to resolve client requests as per client
location and content type. This CDN DNS request
routing technique can efficiently route request of the
client to nearby CDN server, which has less round
trip time (RTT), less packet loss and less throughput.
It can greatly reduce time delay of the request
routing, thus effectively ease Internet congestion.
This technique is helpful in researching more
efficient DNS systems & caching for CDNs and has
better application foreground.

48. Future Scope
In this thesis, we have considered simple hashing algorithm to resolve the
request and this work can be extended by applying to more efficient hashing
algorithms.
Investigations can be extended by taking different types traffic like IPTV,
Video on Demand and real audio.
In this thesis, single DNS server has been used to carry out the research
work, we can extend and do the performance analysis of CDN network if we
have multiple DNSs on same network and how these DNS server will interact
with eachother to resolve the address.
In this thesis, we have analyzed the request routing techniques for CDNs,
Content replication and caching are another major components of a CDN.
This work can be extended to simulate and analyze the content replication &
caching techniques on CDN.
In this thesis, we have considered Round Robin, Round Trip and Least
connections load balancing techniques. This work can be extended by
applying dynamic and adaptive load balancing techniques.

49. Publications
• Sandeep Kath, Manoj Kumar and Ajay Sharma, “CDN DNS - An
Efficient DNS Request Routing Technique in Content Delivery
Networks” International Journal in Advances in
Computational Sciences and Technology , ISSN 0973-6107 Vol
3 Number 2 (2010) pp. 147-154.

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53. Thank YouThank You