Networks

Piconet topology

A Bluetooth network of ≥2 devices occupying the same channel; one "master" device connects with up to 7 "slave" devices, with up to 255 "parked" slave devices inactive. e.g. a cell phone paired to a computer

Routing metric

A cost value used by a router to determine the optimal path to a sink node e.g. remaining energy, expected transmission count

Point-to-point topology

A link between two nodes. The simplest topology. Value is in its unimpeded nature. Switched point-to-point topologies are the basic model of conventional telephony.

ZigBee (key feature, range, cost, power use, applications, limitations)

A low-power, low data rate, low duty cycle, close proximity ad hoc network. Intended to be simpler and less expensive than Bluetooth/WiFi. 100 m range 36.9 mW (low) Applications: Agriculture (one of the best candidates), WPANs, WSNs. Limitations: Line of sight needed between nodes.

Scatternet topology

A network of at least two piconets

Cluster architecture

A set of loosely or tightly connected computers that can be viewed as a single system. Combines improved performance of pooling with low cost of generic computers.

Snowflake topology

A star network of star networks

Tree topology

A star-bus hybrid topology; heirarchical

Snyder's Razor

All other things being equal, choose the more secure option

Topology control

Altering the underlying network to reduce the cost of distributed algorithms.

Murphy's Law

Anything that can go wrong will go wrong. Applied to networks: The more nodes in a network, the higher the system's complexity and the more likely it is that a failure will occur.

Godwin's Law

As an online discussion grows longer, the likelihood of a comparison involving Nazis or Hitler approaches 100%

Cognitive radio

Automatic detection of available channels and changing of transmission parameters to enable more communications to run concurrently and improve radio operating behavior

Postel's Law

Be conservative in what you do; be liberal in what you accept from others (Robustness principle)

Advantages of ring topology

Better performance than bus under high loads. No network server needed.

BLE (key feature, range, cost, power use, applications, limitations)

Bluetooth Low Energy 10 m range Low cost 10 mW (ultra-low) Application: WPANs Limitation: short range

Classic BT (key feature, range, cost, power use, applications, limitations)

Bluetooth. Communication between portable devices. 10-50 m Low cost 215 mW (medium) Application: WPANs Limitation: Short range

Disadvantages of ring topology

Bottlenecked by weakest two nodes

Ring topology

Bus topology in a closed loop. Data travels around the loop in one direction. Each node repeats the data to keep signal strong.

Synonym for peripheral node

Client

Disadvantage of mesh topology

Cost goes up rapidly with the number of nodes/connections.

Star topology

Each node connected to a central hub

Bus topology

Each node connected to a single cable (the bus). Signals travel in both directions to all nodes until the intended recipient is reached. Unintended recipients ignore the data.

Cellular topology

Each node exists in a geographical area called a cell with a central hub. Only applicable in wireless communication

Daisy Chain topology

Each node is connected in series. Easiest way to add more nodes to a network besides star-based networks.

Advantages of star topology

Easiest topology to design and implement; simple to add nodes

Disadvantages of bus topology

Expensive to maintain; inherently riskier and less secure because of centralization and unselectiveness.

GPRS (key feature, range, cost, power use, applications, limitations)

General Packet Radio Service. A service for GSM-based 2G networks. 1-10 km range Medium cost 560 mW (medium) Applications: Cellular Limitations: high power consumption

HetNet

Heterogeneous network - term used for modern mobile communications networks comprising a combination of different cell types and technologies

Advantages of bus topology

Inexpensive to install (only one cable)

LoRa (key feature, range, cost, power use, applications, limitations)

Long range radio protocol. A radio modulation technology for LPWAN 5 km range Low cost 100 mW (low) Applications: many, including agriculture Limitations: low data rate, message capacity, network size

MAC protocols

Media Access Control protocols. MAC's basic function is to provide an addressing mechanism and channel access so that each node on a network can communicate with other nodes on the same or other networks. A sublink of the Data Link Layer.

Modulation scheme

Minimizing power consumption by optimizing modulation parameters. FM = frequency modulation AM = amplitude modulation

Sink mobility

Movement of the destination node to reduce the distance from the sensor nodes. e.g. on a drone

Mesh topology

Nodes dynamically and non-hierarchically self-organize and self-configure to connect to many other nodes. Nodes cooperate to efficiently route data to/from clients. c = n(n-1)/2

Synonyms for "hub"

Router, switch

Disadvantages of star topology

Single point of failure; tendency to bottleneck at hub

Duty cycling

System is active for a fraction of every period (e.g. 25%, 50%, 75%) 50%: __|¯|__|¯|__|¯|__|¯|__|¯|__

WiFi (key feature, range, cost, power use, applications, limitations)

The most extensively used wireless technology. 100 m range High cost 835 mW (high) Application: WLANs Limitations: high power consumption, long access time (13.74 s)

Reed's Law

The utility of large networks can scale exponentially with the size of the network: 2^n - n - 1

Sarnoff's Law

The value of a *broadcast* network is directly proportional to the number of viewers

Beckstrom's Law

The value of a network equals the net value added to each user's transactions conducted through that network, summed over all users.

Metcalfe's Law

The value of a network is proportional to the square of the number of connected users: n(n-1)/2

TDMA

Time-division multiple access. Users share a frequency channel by dividing the signal into time slots. Used in 2G cellular systems, satellite systems, combat-net radio systems, passive optical network (PON) systems.

TPC

Transmission power control (also dynamic power control, DPC) Minimization of radio transmitter power to the minimum necessary to maintain the link with a certain quality. Also helps avoid interference.

SigFox (key feature, range, cost, power use, applications, limitations)

Ultra-narrowband cellular network 10 km range Low cost 122 mW (low) Applications: many, including agriculture Limitations: low data rate

Femto cell

Used at the office and at home (distinct from WiFi)

Micro/pico cell

Used to enhance capacity in busy areas (train stations, malls, city centers)

Macro cell

Used to provide broad coverage

Multipath routing

Using multiple paths through a network to improve fault tolerance, bandwidth, security, etc. Paths can be overlapped, edge-disjointed, or node-disjointed. Not yet widely deployed in practice.