Chapter 1 - Introduction
Data Communications
Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable.
Data communication systems rely on four important things.
Delivery. The system must deliver data to the correct destination, and correct user.
Accuracy. The system must deliver the data accurately, without any inconsistencies.
Timeliness. The system must deliver data in a timely manner. Think about netflix lagging.
Jitter. Jitter refers to the variation in the packet arrival time, or everything incoming should remain incoming at the same rate throughout the entirety of the transfer.
Connection types
Data Systems can be configured as point-to-point or multipoint. Multipoint has the advantage of being cheap and easy to install.
Components of a Data Comm System
- Message
- Sender
- Receiver
- Medium
- Protocol
A Protocol is a set of rules that govern data communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating, just as a person speaking French cannot be understood by a person who speaks only Japanese.
Data Flow
There are three ways data can flow, simplex (one-way) - half-duplex(two-way, only one at a time) - full-dupex(two way-always).
Networks
A set of devices connected and capable of communicating. befined by performance, reliability, and security.
LAN and WAN
- LAN defined by geometric size of network
- WAN world wide
Switches
A switched network is a network where a switch connects at least two links together. There are two types.
Standards
- Maturity
- Proposed Standard: Stable, well understood, and people want it.
- Draft Standard: Once proposed gets indepentendantbly implemented twice, its a draft standard. Minor issues are resolved and then its upgrade to Internet standard.
- Internet Standard: ...see above
- Historical: significant only from historical stand point
- Experimental: not neccesarily a good idea
Informational: tutorialish
- Requirement Levels
- Required
- Recommended
- Elective (nt recommended but its okay if you need it)
- Limited use (only in crazy ciurmustances)
- Not recommended
Topology
Mesh
- Every computer is linked to every other computer.
- Requires n(n-1)/2 links.
- Very redundant
- Expensive, confusing
Star
- Each computer links to a hub
- n links are needed
- Less expensive, if one device fails, only that device is affected.
Bus
- Every device connects to a bus with a drop line.
- Easy to install
- Difficult reconnection, hard to add new devices
Ring
- Every device is connected point to point to the two machines next to it, ina ring.
- Signals are repeated along the ring between devices
- A break in a simple ring breaks everything but its easy to configure