Service function chains, or more generally, virtual network services, evolve throughout their life-cycle due to traffic fluctuations, resource usage, and the stringent requirements of the SLO (Service Level Objective) that must be fulfilled. Network operators resort to elasticity mechanisms (e.g., vertical and horizontal scaling) and migration procedures to adapt the service function chains dynamically to meet their requirements constantly. However, most state-of-the-art solutions do not evaluate the overall impact of such mechanisms on the service function chains or the resulting penalty costs (e.g., migration downtime and SLO violation). To bridge this gap, we propose DAVINCI, a decision-making tool with different adaptation policies that allows the network operator to adapt the service function chains to minimize network changes (e.g., reallocating paths and VNFs) while keeping penalty costs at their lowest level. Moreover, DAVINCI allows for the adaptations (e.g., migration, vertical and horizontal scaling) to be expressed as a set of decisions and leverages the Min Cost Flow problem to estimate migration downtime. The analytical evaluation shows that DAVINCI outperforms the existing state-of-the-art solution (NFV-PEAR) in terms of migration, traffic costs, and the overhead induced by the migration and elasticity mechanisms while significantly reducing penalty costs.

由于流量波动、资源使用以及必须满足的 SLO（服务级别目标）的严格要求，服务功能链或更一般的虚拟网络服务在其整个生命周期中不断发展。网络运营商采用弹性机制（例如，纵向和横向扩展）和迁移程序来动态调整服务功能链以满足其不断需求。然而，大多数最先进的解决方案并未评估此类机制对服务功能链或由此产生的惩罚成本（例如，迁移停机和违反 SLO）的总体影响。为了弥合这一差距，我们提出了 DAVINCI，一种具有不同适应策略的决策工具，允许网络运营商调整服务功能链以最大限度地减少网络变化（例如，重新分配路径和 VNF），同时将惩罚成本保持在最低水平。此外，DAVINCI 允许将适应（例如，迁移、垂直和水平扩展）表示为一组决策，并利用最小成本流问题来估计迁移停机时间。分析评估表明，DAVINCI 在迁移、流量成本以及迁移和弹性机制引起的开销方面优于现有的最先进解决方案 (NFV-PEAR)，同时显着降低了惩罚成本。