Communication software and architecture
Client-Server communications
One of the communication partners act as client and one as server
Client application requests sources (e.g. Web browser) from server application (web server)
Client initiates connection
Client-Server based communication models
Publish-Subscribe
Client request subscription to server
Whenever there is new data, the server pushes it to subscribers
Instant messaging, multicast
Broadcasting
Peer-to-Peer communications
Communication architecture
Simple Communication example
Layered communication architecture
Different communication tasks are separated on their own layers
Each layer has its own tasks and own protocol
Entities at same layer (layer N) are called peer entities
Connection between peer entities is peer connection following peer protocol
Implementation of entity is CPO (communicating protocol object)
Lower layer provides a service to higher layer
OSI- Reference Model
OSI Model |
Layer | Function | Data unit |
7. Application layer | Application | Data |
6. Presentation layer | Data representation and encryption | Data |
5. Session layer | Coordination of interactions in user sessions | Data |
4. Transport layer | End-to End connection | Segment |
3. Network layer | host-to-host connection e.g. Routing | Datagram/packet |
2. Link layer | Physical addressing | Frame |
1. Physical layer | transmission of bits over a physical circuit | Bit |
Irda Stack
Bluetooth stack
Communication in layered architecture
Vertical communication
Messages are called primitives
Layer N produces service to layer n+1 and uses the service of layer n-1
Service is accessed via service access point (SAP)
PDU is enveloped and given to lower layer
Interfaces
Protocol system structure
Service types of protocol entity
Confirmed service
Unconfirmed service
no handshake
request → indication
Provider initiated
Protocol Entity in layered architecture
Data flow in protocol system