Replication is commonly used in deploying directory services. The scope could also be constrained to within a building or within a particular division. In some cases it may be advisable to simply define all the places the network service should NOT be available, as in the case of internal services that should not be visible or accessible on the public Internet. The scope of a network service should be defined by business needs and goals. If not, you will either need to add bandwidth using a technique such as caching or replication, or supply multiple instances of the service.
Intermittent connectivity is a challenge for many services.
Some services can use proxy or replication techniques, but others, such as real-time transactional services, do not map well to such deployment environments. Achieving this goal impacts every aspect of the infrastructure, because there can be no weak links. The modularity of the architecture is critical to attaining continuously available services, because there are so many variables and potential sources of downtime that monolithic systems simply could not deliver adequate uptime for multiple network services. In addition, since network services are heavily interdependent, constant monitoring and measurement of service availability is important in isolating problem areas. This will tell you which problems to tackle first.