LANs and WANs (ITS323, L23, Y15)

[JanacMeena]

• Categorizing network based on
○ Tramission medium
○ Link configuration
○ User mobility
○ Types of users
§ Access vs Core (backbone)
• wired
○ pros
§ small interference
§ easy to upgrade capacity
□ - just add another wire
§ predictable delays
○ cons
§ Expensive to install in hard to access locations
§ Devices locations are fixed
• wireless
○ pros
§ mobility, convenience
○ cons
§ Interference, varying channel conditions
§ Difficult to add capacity
□ We can use a different range of frequencies
§ Unpredictable delays
§ Physical security is difficult

• Point to point
○ pair of users have their own link

• point to multi-point
○ We all want to transmit data at the same time, so we use Medium Access Control Protocol
§ schedules the tranmissions i.e. you go, and then you go, etc.
§ Random access - A bunch of devices on the same wireless network, will randomly check if there no one else is use the connection and then sends the data
§ Demand assignment: polling, reservation
§ MAC is Random access and Demand assignment

• Access network
○ End users access this
• Core network
○ Connects other networks together i.e. the access network to the backbone network

• ATM
○ Uses virtual circuit packet switching

• WANs
○ Networks over large geogrpahical area, i.e. campuses, office buildings, cities
○ Owned by ISPs
• LANs
○ Connects end-user devices over small area

•

• Common topologies
• Topology
○ The arrangement of nodes and links
○ Depends on devices
§ Stations, hosts, end nodes
§ Switches, repeaters, hubs
○ Mesh topology
§ Point-to-point link between every device
§ Good for performance, but becomes too complex as number of nodes increase
○ Partial mesh
§ Some nodes are not connected to every node
○ Bus topology
§ Used between components in a computer
§ If a, b, c, d are connected to the same bus, and a sends a frame to the bus, everyone gets a copy
□ Only the intended destination keeps the copy
§ Point to multi-point link
§ Used in early LANs
□ Replaced by star
§ Only one user can transmit a a time
○ Ring
§ Similar to bus
§ A transmits to the ring, and it goes clock wise sending packets to each connected member
§ Good for detecting faults, since we can detect faults between two links
○ Star
§ We have an intermediate device, where all end users have a point to point connection to the device
□ This is switching
§ Can send between end users links at full capacity
§ Con: Depends on the switch
• Point to Multipoint
§ If two guys want to transmit at the same time, give them different frequencies (FDMA)
§ CDMA - use special encoding
§ Or use MAC