1 / 27

Modems and Access Devices Overview

Learn about modems and access devices used to connect computers to telephone lines, including their functions and types. Explore NT-1, CSU, PCMIA modems, and cable modems.

juliewheeler
Download Presentation

Modems and Access Devices Overview

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture 9 Modems and Access Devices

  2. Overview • Computers are connected to telephone lines through the use of modems • modems: are connecting devices between the telecommunication medium, such as copper or fiber, and a communicating device • also called: DCE or data circuit-terminating devices

  3. Data-Circuit Terminating Devices • Modify computer signals to make them compatible with digital telephone lines • DCE’s are required for digital lines

  4. Type of DCE’s • NT-1 • used with ISDN • CSU • T-1, T-3

  5. Transferring Data • From computers to phone lines: • analog and digital lines require different conversion devices

  6. Functions of DCE’s (p.222) • On analog and digital lines: • ensure even data flow, synchronization function • maintain proper voltages • error detection, correction • compression of data • remote diagnostics

  7. Functions of DCE’s (p.222) • On digital lines only: • ensure the correct number of 0’s and 1’s • shaping the digital signal

  8. Functions of DCE’s (p.222) • On analog signals only: • convert digital computer signals to analog signals

  9. Remote Diagnosis • Network ownership and cost of maintenance distributed over web of devices and communication media • DCE’s offer a point of reference in order to diagnose repair problems • Test bits sent to DCE devices, if received assumed problem not in the telephone line or DCE

  10. NT1’s and ISDN • ISDN supports voice, video, data • out-of-band signaling • NT1 needed to connect ISDN to video conference units, PCs, PBXs, key systems and multiplexers • Network Termination type 1

  11. NT1’s and ISDN • BRI ISDN • change two wire circuits coming in from building into four wires needed for ISDN service • plugs into the ISDN LINE with one cable • another cable plugs into a TA, terminal adapter

  12. PCMCIA Modems • Personal Computer Memory Card International Association • 3.37 inches long by 2,126 inches wide • plug into slots on laptops, palmtops • Speeds vary, RJ11 jack or Ethernet, cellular, analog cellular and ISDN connections

  13. PCMCIA Modems • Used with: • analog POTS lines • analog cellular services • digital cellular services • fixed wireless services

  14. CSUs/DSUs • Connecting devices to a digital line, non-ISND services • T1, T3, switched 56k, dedicated 56k • supplied as one integrated piece of equipment • CSU: channel service unit • DSU: data service unit

  15. CSUs/DSUs M U L P L E X E R incoming line CSU DSU

  16. DSU • Regulates voltage rates present on the signals from DTU to the CSU • connects to a data terminating device such as a multiplexer or a PBX

  17. CSUs • Plugs into phone jack • similar in function to a NT1 • provides clocking and signal reshaping • must send out bits a even rate • if clocking off will not transmit • the line is slipping • the timing is off

  18. Cable Modems • Provide high speed connections • Same cable used for TV works for Internet • Agreements as to how to transmit, “the handshake” hardware based • modem standards exist between sender/receiver • modems certified by Cable Labs

  19. Cable Modems • Connect to a HEADEND • point from which programming is transmitted to local customers • Traditionally a one-way medium, where content flows from headend to end-users

  20. Cable Modems • Currently working on developing two-way capability • called reverse channels from subscriber to headend

  21. Reversed Channels • Created by using different frequencies for upstream and downstream transmissions • Upstream: 5-30 MHz or 5-42 MHz • Downstream: 54-350MHz or 54-750MHz • Both set at different speeds • Cable used more efficiently when splitting up the use of frequencies

  22. Cable TV Systems • When used for data communications: • analogous to being on an Ethernet LAN • all messages are broadcast onto the cable connecting devices to the LAN • shared medium by all users on network

  23. PC Cable Connection • Cable modem connects home users to cable for Internet access • modem plugs into Ethernet card in PC • Another cable runs from cable modem to sliced cable outlet

  24. Cable Internet Modem Service • All messages broadcast over entire network • Modem with specified address takes message of the network, security issue • Every message first transmitted to the headend and then to the addressee, congestion • Modem requires local power • Service always on, no extra phone line required • Extremely fast downloading speeds

  25. Cable Modems for Remote • Accomplished with Virtual Private Network • Interface and security software installed on laptop to access remotely • Corporate end: installs Internet connection and switch • Both cable operator and customer connected to the Internet

  26. Cable TV Set-Top Boxes • Interface with TV and cable TV network for access to cable services • Tuners • Set-top box includes filters and traps • give access to basic and premium channels • some give Internet access from TV

  27. Third Generations Set-Top Boxes • Advanced digital security • Advanced programming • TV viewing while accessing Internet • Ethernet plug in set top box • video on demand • mandated to be available to consumer by FCC

More Related