All OpenStack deployments are dependent, to some extent, on network communication in order to function properly due to a service-based nature. In some cases, however, use cases dictate that the network is elevated beyond simple infrastructure. This chapter is a discussion of architectures that are more reliant or focused on network services. These architectures are heavily dependent on the network infrastructure and need to be architected so that the network services perform and are reliable in order to satisfy user and application requirements. Some possible use cases include: Content delivery network This could include streaming video, photographs or any other cloud based repository of data that is distributed to a large number of end users. Mass market streaming video will be very heavily affected by the network configurations that would affect latency, bandwidth, and the distribution of instances. Not all video streaming is consumer focused. For example, multicast videos (used for media, press conferences, corporate presentations, web conferencing services, and so on) can also utilize a content delivery network. Content delivery will be affected by the location of the video repository and its relationship to end users. Performance is also affected by network throughput of the back-end systems, as well as the WAN architecture and the cache methodology. Network management functions A cloud that provides network service functions would be built to support the delivery of back-end network services such as DNS, NTP or SNMP and would be used by a company for internal network management. Network service offerings A cloud can be used to run customer facing network tools to support services. For example, VPNs, MPLS private networks, GRE tunnels and others. Web portals or web services Web servers are a common application for cloud services and we recommend an understanding of the network requirements. The network will need to be able to scale out to meet user demand and deliver webpages with a minimum of latency. Internal east-west and north-south network bandwidth must be considered depending on the details of the portal architecture. High speed and high volume transactional systems These types of applications are very sensitive to network configurations. Examples include many financial systems, credit card transaction applications, trading and other extremely high volume systems. These systems are sensitive to network jitter and latency. They also have a high volume of both east-west and north-south network traffic that needs to be balanced to maximize efficiency of the data delivery. Many of these systems have large high performance database back ends that need to be accessed. High availability These types of use cases are highly 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 will be able to serve the displaced load until the original site returns to service. It is important to size network capacity to handle the loads that are desired. Big data Clouds that will be used for the management and collection of big data (data ingest) will have a significant demand on network resources. Big data often uses partial replicas of the data to maintain data integrity over large distributed clouds. Other big data applications that require a large amount of network resources are Hadoop, Cassandra, NuoDB, RIAK and other No-SQL and distributed databases. Virtual desktop infrastructure (VDI) This use case is very sensitive to network congestion, latency, jitter and other network characteristics. Like video streaming, the user experience is very 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 extremely 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. It may also require an active queue management implementation to ensure delivery. Users are very sensitive to latency and jitter fluctuations and can detect them at very low levels. Video Conference or web conference This also is extremely sensitive to network congestion, latency, jitter and other network flaws. 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 will be 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.