We consider a joint optimization problem of optical network resources and virtual network function (VNF) placement for efficient content distribution. Current content distribution networks (CDNs) are tightly coupled with network function virtualization (NFV) technologies. A virtual CDN (vCDN) has been intensively investigated to efficiently cope with unpredictable traffic demand. In vCDN, CDN functions are virtually provided as VNF, and we can provide sufficient flexibility regarding the usage of compute resources under traffic demand changes. For the cost-effective CDN services, we must reduce the redundant usage of network resources while improving the efficiency of compute resources. However, a conventional optimal VNF placement technique in vCDN was focused on the efficiency of compute resources, and this can lead to an increase in network cost. To address this issue, we formulate the optimization problem as mixed integer linear programming and then propose a heuristic algorithm called a light-weight VNF placement algorithm in vCDN (LP-vCDN) for reducing network cost while effectively utilizing compute resources. We conducted intensive numerical experiments and demonstrated that LP-vCDN always found solutions of sufficient quality with practical computational overhead.

我们考虑了光网络资源和虚拟网络功能 (VNF) 放置的联合优化问题，以实现高效的内容分发。当前的内容分发网络 (CDN) 与网络功能虚拟化 (NFV) 技术紧密结合。已经对虚拟 CDN (vCDN) 进行了深入研究，以有效应对不可预测的流量需求。在vCDN中，CDN的功能实际上是作为VNF提供的，我们可以在流量需求变化的情况下，对计算资源的使用提供足够的灵活性。对于高性价比的CDN服务，必须在提高计算资源效率的同时，减少网络资源的冗余使用。然而，vCDN 中传统的优化 VNF 放置技术侧重于计算资源的效率，这会导致网络成本增加。为了解决这个问题，我们将优化问题表述为混合整数线性规划，然后提出一种启发式算法，称为 vCDN (LP-vCDN) 中的轻量级 VNF 放置算法，以在有效利用计算资源的同时降低网络成本。我们进行了大量的数值实验，证明 LP-vCDN 总能找到具有实际计算开销的足够质量的解决方案。