# Transparent Redirections in Content Delivery Networks
## 6 Conclusions and Future Work  
This article introduced the main concepts of Software Defined Networking, Content Delivery Network and the concepts of content distribution on a large scale. It further described existing redirection methods used in CDNs and devoted a section for existing transparent redirection methods. Transparent redirection methods are not often used as they require changes and service awareness in the network. Several transparent redirection methods were already implemented and tested; however, there is no transparent redirection method existing right now, which would not require modifications to the surrogate server. This limitation eliminates the use of legacy closed source solutions.  
The article proposes a TCP session handoff mechanism as a transparent redirection which synchronizes two existing TCP connections with each other. This approach does not require any modifications to the endpoint. The only modification to the data plane is required on the core forwarders, where a surrogate server or a request router is attached. The transparent redirection ensures that the TCP session is handed off to a CDN surrogate from the request router, while the procedure stays unnoticeable to the endpoints. The proposed solution can be used in Load Balancing scenarios too.  
The redirection decision is based on the network topology and the location of the surrogates and the users. The results acquired show that current redirection methods (302 Redirection) are faster than the proposed solution; however, this performance could be enhanced by using a more mature and faster controller. Currently, the controller represents a single point of failure, does not scale and represents our performance bottleneck in the proposed solution. In the case of a transparent load balancer, the solution achieved better results when the TCP connections were kept alive for subsequent requests. The achieved performance is suitable for production use and compared to existing solutions does not degrade the Quality of Experience for the end-users.  
There were several issues found, which should be solved in the future. One of them is the issue of pre-establishing TCP sessions form the request router to the surrogate servers with various WSCALE options to be able to make exact matches when we synchronize the TCP sessions. The incrementation of the acknowledgement numbers in the selective acknowledgement TCP Option should be implemented on forwarding elements too. Currently, these TCP Options including TCP Timestamps are turned off, which could degrade the performance in challenging environments. Furthermore, secure TLS based TCP sessions currently are not supported by the proposed solution, so connections over HTTPs are broken.  
The project was analyzed, implemented and evaluated, including writing, by [PERSON] The high-performance load balancing use case was analyzed and implemented, and article revisions were done, by [PERSON] contributed with project supervision and article revisions.  
Figure 21: Time required to start transfer—connection keepalive.  
**Funding:** This research was supported by Ministry of Education, Science, Research and Sport of the Slovak Republic, Incentives for Research and Development, grant agreement number: 2018/14427:1-26C0; and Operational Program Research and Innovation for the project: Research of advanced methods of intelligent information processing (ITMS code: NFP313010T570), co-financed by the European Regional Development Fund.  
**Conflicts of Interest:** The authors declare no conflict of interest.