Data Networks

Overview
Welcome to the Data Networks level. Start by traveling through the OSI layers, until you master each layer and reach the end. Continue on and learn more about Data Networks as you pass through.

The OSI Model

 * 1) Application: Functions and commands
 * 2) Presentation: Display of information on screen
 * 3) Session: User log-onsOsi-model.png
 * 4) Transport: End-End Integrity
 * 5) Network: Addresses, Routes
 * 6) Data Link: Asynchronous/synchronous
 * 7) Physical Link: Voltages, interface, codes, anything you can touch.

Frame Relay

 * End-End error detection
 * Connection-oriented
 * No sequencing problems
 * straightforward connection

X.25

 * Point-Point error detection
 * Latency
 * Connectionless, could have virtual circuits
 * explicit flow control
 * sequencing
 * logical connection

Connectionless

 * Each packet handled individually
 * Sequence is not guaranteed

Connection-Oriented

 * Virtual circuits established before sending first packet
 * Once path is set, all packets go in sequence

DDS: Dataphone Digital Service

 * Early 1970s-1980s
 * End-End, Fully Digital
 * Relatively low circuit speeds

Switched 56k

 * Connects logical addresses
 * less vulnerable to failure than DDS

VPN: Virtual Private Network

 * Uses public facilities
 * Offered by IXCs
 * Similar to switched 56k, but has larger bandwidth

T-Carrier: T1, T2, T3, T4

 * Dedicated, leased line for access
 * Good error performance, high bandwidth
 * Costly

PVC: Permanent Virtual Circuit

 * All packets travel same path
 * Reduces latency
 * Easy to find where problems occur
 * Whole network fails if one node fails
 * Not the same as VPN

SVC: Switched Virtual Circuits

 * Networks select appropriate path for packets during a sessions. During each session, packets all go through same path
 * Congested nodes are bypassed
 * Requires a smarter network
 * Higher latency than PVC

BRI ISDN

 * Characteristics
 * 2 B channels @ 64 kbps
 * 1 D channel @ 16 kbps
 * Total speed: 144 kbps
 * 1 pair of wire from service to user
 * Uses
 * Internet access
 * Desktop videoconferencing

PRI ISDN

 * Characteristics
 * 23 B channels @ 64 kbps
 * 1 D channel @ 16 kbps
 * Total speed: 1.54 Mbps
 * 2 pairs of wire from service to user
 * Uses
 * Videoconferencing
 * Backing up LAN-LAN connections
 * Backing up private dedicated lines in case they fail
 * Remotely accessing corporate/ISP sites

 CONTINUE... 

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