- Nodes
- Device that communicate
- End devices: Clients, servers, ...
- Interconnecting devices: Switch, router, ...
- Device that communicate
- Edges
- Transmission media used to connect divices
- Wired
- Wireless
- Logical connections (channels)
- Transmission media used to connect divices
In communication networks:
- Edges are measurable expensive => communication networks are less dense
- Degree distribution is more uniform
- Additional edges in communicaiton networks are for redundancy/reliability
- Triadic closure only happens as a result of cost minimization or performance maximization
- Unlikely to form giant components
- There are layers of networks in communication networks
- Physical topology
- Logical topology
- Routing topology
- Simplex
- Communication in one direction only at all time
- Directed
- e.g. Broadcast radio
- Half-duplex
- Communication is possible in both directions, but only one direction possible at a time
- Directed or undirected graph
- e.g. Walkie-talkie
- Full-duplex
- Communication is possible in both directions at the same time
- Undirected graph
- e.g. cell phone
- Personal area network (PAN)
- Connectes devices within a short distances
- e.g. Bluetooth, infrared TV remote
- Local area network (LAN)
- Larger than PAN
- Connects devices in small geographical area
- e.g. wifi
- Metropolitan area network (MAN)
- Larger than LAN and smaller than WAN
- Connects devices across a city
- Wide area network (WAN)
- Interconnect LANS, connects devices over long distances (around the globe)
- e.g. Internet
- PAN < LAN < MAN < WAN
- Topology defines how nodes are connected
- Four common topologies: star, tree, mesh, ring
- Star: all devices are connected to a centralized entity
- Tree: extend a network range, each device talks to its parent
- Mesh: any device can talk to any other devices within its communication range
- Ring: all devices are connected in a closed loop with each device linked to the next one
- Propagation delay
- The amount of time it takes for the head of the signal from the source to the destination
- L: The physical length of the link
- V: The propagation velocity of the signal along the link (Wireless signal travel with the speed of light)
- Transmission delay
- Time required to get message of M bits over a link of bit rate B
- Processing delay
- The time to process the packet within each intermediate node
- Queueing delay
- In a packet-switched network, queuing delay is the sum of the delays encountered by a packet between the time of insertion into the network and the time of delivery to the address.
- Total delay
- In general, total delay = processing + queueing + transmission + propagation
- In circuit switching, total delay = time to set-up circuit + transmit message + time to release resources = total propagation + total transmission + total processing (to establish circuit)
- In packet switching, total delay = total propagation + total transmission delay of all packets + total queueing + total processing
- Bottleneck link
- In multihop network, the overall rate is determined by the link with the lowest data rate
- Exceeding that rate results in overflow and data loss
- Thoughput is the effective data rate.
- Throughput = amount of useful data (payload) / total time required to transmit this data
- Example
- Suppose you want to send a 1000 bytes file as chunks of data, but in doing so you add a total of 300 bytes overhead bit to the file. Your transmitter's data rate is 10 kbps
- How long does it take?
- 1300*8 bytes / 10000 bps = 1.04 sec
- What is the throughput
- 1000*8 bits / 1.04 sec = 7692 bps
- Communication between processes: Exchange commands, responses, data
- Inter-process communications: Using by processes on the same end-host
- Rules are based on the operating system
- Network: Using by processes on different hosts
- Inter-process communications: Using by processes on the same end-host
- Socket: Programming interface used by a process to send and receive messages