All OpenStack deployments depend on network communication in order to function properly due to its service-based nature. In some cases, however, the network elevates beyond simple infrastructure. This chapter discusses architectures that are more reliant or focused on network services. These architectures depend on the network infrastructure and require network services that perform reliably in order to satisfy user and application requirements. Some possible use cases include: Content delivery network This includes streaming video, viewing photographs, or accessing any other cloud-based data repository distributed to a large number of end users. Network configuration affects latency, bandwidth, and the distribution of instances. Therefore, it impacts video streaming. Not all video streaming is consumer-focused. For example, multicast videos (used for media, press conferences, corporate presentations, and web conferencing services) can also use a content delivery network. The location of the video repository and its relationship to end users affects content delivery. Network throughput of the back-end systems, as well as the WAN architecture and the cache methodology, also affect performance. Network management functions Use this cloud to provide network service functions built to support the delivery of back-end network services such as DNS, NTP, or SNMP. Network service offerings Use this cloud to run customer-facing network tools to support services. Examples include VPNs, MPLS private networks, and GRE tunnels. Web portals or web services Web servers are a common application for cloud services, and we recommend an understanding of their network requirements. The network requires scaling out to meet user demand and deliver web pages with a minimum latency. Depending on the details of the portal architecture, consider the internal east-west and north-south network bandwidth. High speed and high volume transactional systems These types of applications are sensitive to network configurations. Examples include financial systems, credit card transaction applications, and trading and other extremely high volume systems. These systems are sensitive to network jitter and latency. They must balance a high volume of East-West and North-South network traffic to maximize efficiency of the data delivery. Many of these systems must access large, high performance database back ends. High availability These types of use cases are dependent on the proper sizing of the network to maintain replication of data between sites for high availability. If one site becomes unavailable, the extra sites can serve the displaced load until the original site returns to service. It is important to size network capacity to handle the desired loads. Big data Clouds used for the management and collection of big data (data ingest) have a significant demand on network resources. Big data often uses partial replicas of the data to maintain integrity over large distributed clouds. Other big data applications that require a large amount of network resources are Hadoop, Cassandra, NuoDB, Riak, and other NoSQL and distributed databases. Virtual desktop infrastructure (VDI) This use case is sensitive to network congestion, latency, jitter, and other network characteristics. Like video streaming, the user experience is important. However, unlike video streaming, caching is not an option to offset the network issues. VDI requires both upstream and downstream traffic and cannot rely on caching for the delivery of the application to the end user. Voice over IP (VoIP) This is sensitive to network congestion, latency, jitter, and other network characteristics. VoIP has a symmetrical traffic pattern and it requires network quality of service (QoS) for best performance. In addition, you can implement active queue management to deliver voice and multimedia content. Users are sensitive to latency and jitter fluctuations and can detect them at very low levels. Video Conference or web conference This is sensitive to network congestion, latency, jitter, and other network characteristics. Video Conferencing has a symmetrical traffic pattern, but unless the network is on an MPLS private network, it cannot use network quality of service (QoS) to improve performance. Similar to VoIP, users are sensitive to network performance issues even at low levels. High performance computing (HPC) This is a complex use case that requires careful consideration of the traffic flows and usage patterns to address the needs of cloud clusters. It has high east-west traffic patterns for distributed computing, but there can be substantial north-south traffic depending on the specific application.