Topology refers to the physical layout of the network
Bus Topology
Uses a trunk or backbone to which all of the computers on the network connect
Cheap and easy, but network disrupted when it needs to be extended
Ring Topology
Data travels in circular pattern from computer to computer
Easy to find faults in the system, expansion causes disruption
A single fault can break whole system
Star Topology
All devices connect to a single host device / hub
a failure in a cable only takes down one computer
requires lots more cable and more expensive
Mesh topology
Every computer connects to every other computer
redundancy in the case of cable failure and can be expanded without disruption
very expensive to implement in larger systems
7 Layer OSI Model
Encapsulation
Each highest layer protocol creates messages and sends them via its lower layer protocol
Each protocol adds its own control information in the form of headers and trailers
Multiplexing
Use protocol keys/numbers in the header to determine correct upper-layer protocol
Purpose and History
Layer 1: Physical
Medium, interfaces, puts bits on medium
Bits, interfaces, hubs
PDU: Bits
Representation of the bits, and the movements of individual bits from one node to the next
Deals with data rate, and synchronization of bits
Layer 2: Data Link
Media access control, physical address
Ethernet, Token Ring
PDU: Frame / Packet
Layer 2 has a Physical address ( MAC address)
Deals with flow control to not overwhelm the receiver
Deals with error control by added error detection/correction bits
Deals with Access control, how multiple nodes share the same data
Layer 3: Network
End to end delivery, logical address
IP, IPX, ICMP
Logical communication between hosts
PDU: Packets
Layer 4: The transport Layer
Flow Control, Error detection/correction
TCP, UDP, SPX
PDU: Segment
Responsible of deliver from between processes
Service Point Address, called port, used to track multiple sessions between the same systems. SPAs are used to allow a node to offer more that one services.