Web Services
Web services are a new breed of Web application. They are self-contained, self-describing, modular applications thay can be published, located, and invoked across the web. Web services perform functions, which can be anything from simple requests to complicated business processes ... Once a web service is deployed, other applications (and other web services) can discover and invoke the deployed service
IBM Web Service Tutorial
Distributed Systems
A distributed system is a collection of independent computers that appear to the user as a single coherent system, this is in contrast to a networked system. In a networked system computers exchange information, however in a distributed system an application has many parts running on different computiers, and information is shared to accomplish a specific purpose.
Distributed Systems allow resources to be more easily shared, to be location independant, to distribute human resources, to increase performance, to increase modularity and scalability and to increase availability and reliability.
Network Security
Network Security is concerned with three main areas:
- Secrecy. Only the sender and intended receiver should understand the content of messages.
- Authentication. The sender and receiver need to confirm their identities.
- Integrity. Need to ensure the message is not altered without detection.
Multicasting
Multicast routing is the technique of sending a message to groups of end-points on a network in a one-to-many distribution. Generally the term multicast refers to IP multicasting, a method often used in media streaming systems as it can scale to a large number of recievers by not knowing details of individual recievers. It provides more efficient data distribution by not replicating packets to send them to multiple recievers.
Multimedia Protocols
Multimedia applications over the internet are often sensitive to delay, but can tolerate some packet loss (which would cause concealable glitches). Data of this type generally falls into three classes of applications:
- Streaming. Clients request files from servers and pipeline reception over the network. Can be a delay from request to display start, and user can control operation with regular pause/resume/rewind options.
- Unidirectional Real-Time. Similar to existing understanding of TV and Radio, non-interactive user can just listen or view but not control the content.
- Interactive Real-Time. Two-way real time communication, for example voice or video conference. Much more stringent delay requirements because of real-time human nature.
The TCP/UDP/IP Suite provides best-effort but no guarantees when it comes to multimedia content, if load increases then performance can rapidly deteriorate. To mitigate this effect, UDP should be used over TCP, data should be compressed to suit available bandwidth and content should be buffered to avoid jitter. However, more fundamental changes may be needed to the protocols used - resources should be more closely monitored and differntiated services can be introduced which prioritise traffic according to class.
Internet Protocols
A computer network protocol definies a format and order of messages sent and recieved among network entities, and actions taken on message transmission and reciept.