A Distributed Control Law for Load Balancing in Content Delivery Networks

A Distributed Control Law for Load Balancing in Content Delivery Networks



In this paper, we face the challenging issue of defining and implementing an effective law for load balancing in Content Delivery Networks (CDNs). We base our proposal on a formal study of a CDN system, carried out through the exploitation of a fluid flow model characterization of the network of servers. Starting from such characterization, we derive and prove a lemma about the network queues equilibrium. This result is then leveraged in order to devise a novel distributed and time-continuous algorithm for load balancing, which is also reformulated in a time-discrete version. The discrete formulation of the proposed balancing law is eventually discussed in terms of its actual implementation in a real-world scenario. Finally, the overall approach is validated by means of simulations.


In a queue-adjustment strategy, the scheduler is located after the queue and just before the server. The scheduler might assign the request pulled out from the queue to either the local server or a remote server depending on the status of the system queues.

In a rate-adjustment model, instead the scheduler is located just before the local queue: Upon arrival of a new request, the scheduler decides whether to assign it to the local queue or send it to a remote server.

In a hybrid-adjustment strategy for load balancing, the scheduler is allowed to control both the incoming request rate at a node and the local queue length.

Thus in Existing systems, Upon arrival of a new request, indeed, a CDN server can either elaborate locally the request or redirect it to other servers according to a certain decision rule, which is based on the state information exchanged by the servers. Such an approach limits state exchanging overhead to just local servers.


A critical component of CDN architecture is the request routing mechanism. It allows to direct users’ requests for content to the appropriate server based on a specified set of parameters. The proximity principle, by means of which a request is always served by the server that is closest to the client, can sometimes fail. Indeed, the routing process associated with a request might take into account several parameters (like traffic load, bandwidth, and servers’ computational capabilities) in order to provide the best performance in terms of time of service, delay, etc. Furthermore, an effective request routing mechanism should be able to face temporary, and potentially localized, high request rates (the so-called flash crowds) in order to avoid affecting the quality of service perceived by other users.


In a similar way, in this paper we first design a suitable load-balancing law that assures equilibrium of the queues in a balanced CDN by using a fluid flow model for the network of servers. Then, we discuss the most notable implementation issues associated with the proposed load-balancing strategy.

We present a new mechanism for redirecting incoming client requests to the most appropriate server, thus balancing the overall system requests load. Our mechanism leverages local balancing in order to achieve global balancing. This is carried out through a periodic interaction among the system nodes.


The quality of our solution can be further appreciated by analyzing the performance parameters

The proposed mechanism also exhibits an excellent average Response Time, which is only comparable to the value obtained by the 2RC algorithm.

The excellent performance of our mechanism might be paid in terms of a significant number of redirections. Since the redirection process is common to all the algorithms analyzed, we exclusively evaluate the percentage of requests redirected more than once over the total number of requests generated.






  •   Processor                  -        Pentium –IV
  •  Speed                           -        1.1 Ghz
  •  RAM                            -        512 MB(min)
  •  Hard Disk                  -        40 GB
  •  Key Board                 -        Standard Windows Keyboard
  •  Mouse                         -        Two or Three Button Mouse
  •  Monitor                     -        LCD/LED



  • Operating system  :         Windows XP.
  • Coding Language   :         C#.Net.
  • Data Base                  :         SQL Server 2005
  • Tool                            :         VISUAL STUDIO 2008


Sabato Manfredi, Francesco Oliviero, and Simon Pietro Romano,A Distributed Control Law for Load Balancing in Content Delivery Networks”, IEEE/ACM TRANSACTIONS ON NETWORKING, VOL. 21, NO. 1, FEBRUARY 2013.

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