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Define and discuss the overlay network.
- An overlay network is a computer network which is built
- on top of another network. Nodes in the overlay can be thought of as being
- connected by virtual or logical links, each of which corresponds to a path,
- perhaps through many physical links, in the underlying network.
- The problem is that we are dealing only with logical
- paths. It may very well be the case that two nodes A and B which are neighbours
- in the overlay network are physically placed far apart. As a consequence, the
- logically short path between A and B may require routing a message along a very
- long path in the underlying physical network.
Describe stateful and stateless servers.
- “A stateless server does not keep
- information on the state of its clients, and can change its own state without
- having to inform any client”
- For instance a Web
- server is stateless. It records some info but if this information is lost, it
- will not lead to a disruption of the service
- “A stateful server generally
- maintains persistent information on its clients.”
- A file server must
- maintain a table with files and permissions
Describe and compare different architectural styles.
- layered style:
- components are organised in a layered fashion where a component at layer
- Li is allowed to call components at the
- underlying layer Li-1, but not the other way around;
- object-based architectures: each object corresponds to what we have
- defined as a component, and these components are connected through a (remote)
- procedure call mechanism;
- Data-centred architectures: evolve around the idea that processes
- communicate through a common (passive or active) repository;
- event-based architectures: processes essentially communicate through the
- propagation of events, which optionally also carry data;
- shared data spaces: Event-based architectures combined with
- data-centred architectures;