This paper introduces the Multi-Server Multicast (MSM) approach for Content Delivery Networks (CDNs) delivering services offered by a set of Data Centers (DCs). All DCs offer the same services. The network is an Elastic Optical Network (EON) and for a good performance, routing is performed directly at the optical layer. Optical switches have heterogeneous capacities, that is, light splitting is not available in all switches. Moreover, frequency slot conversion is not possible in any of them. We account for the degradation that optical signals suffer both in the splitting nodes, as well as across fiber links to compute their transmission reach. The optimal solution of the MSM is a set of light-hierarchies. This multicast route contains a light trail from one of the DCs to each of the destinations with respect to the optical constraints while optimizing an objective (e.g., minimizing a function). Finding such a structure is often an NP-hard problem. The light-hierarchies initiated from different DCs permit delivering the multicast session to all end-users with a better utilization of the optical resources, while also reducing multicast session latencies, as contents can be delivered from such DCs closer to end-users. We propose an Integer Linear Programming (ILP) formulation to optimally decide on which light-hierarchies should be setup. Simulation results illustrate the benefits of MSM in two reference backbone networks.

本文介绍了用于内容交付网络（CDN）交付由一组数据中心（DC）提供的服务的多服务器组播（MSM）方法。所有DC都提供相同的服务。该网络是弹性光网络（EON），为了获得良好的性能，直接在光学层上执行路由。光开关具有异构容量，也就是说，并非所有开关都具有光分离功能。而且，在任何一个中都不可能进行时隙转换。我们考虑了光信号在分裂节点以及跨光纤链路遭受的劣化，以计算其传输范围。MSM的最佳解决方案是一组轻层次结构。例如，最小化功能）。寻找这样的结构通常是一个NP难题。由不同DC发起的光层次结构允许将多播会话传递给所有最终用户，从而更好地利用光资源，同时还减少了多播会话等待时间，因为可以从此类DC向更接近最终用户的位置传递内容。我们提出了整数线性规划（ILP）公式，以最佳地确定应设置的灯光层次结构。仿真结果说明了MSM在两个参考骨干网中的优势。