1 / 23

Chapter 6 Remote Access and Communication Links

Chapter 6 Remote Access and Communication Links. 6.1 Remote Access to a LAN Modem Dial-up Virtual Private Network 6.2 Communication Links PSTN ISDN T1/T3 DSL Cable TV network ATM. Chapter 6 Communication Links. 6.1 Remote Access to a LAN. Remote Access means

alair
Download Presentation

Chapter 6 Remote Access and Communication Links

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. Chapter 6 Remote Access and Communication Links 6.1 Remote Access to a LAN Modem Dial-up Virtual Private Network 6.2 Communication Links PSTN ISDN T1/T3 DSL Cable TV network ATM

  2. Chapter 6 Communication Links 6.1 Remote Access to a LAN • Remote Access means • accessing a LAN by mobile/home users • Two means: • modem dial-up • VPN

  3. Chapter 6 Communication Links 6.1.1 Modem Dial-up • Modem dial-up means • connection using ordinary phone lines • also called • Public Switched Telephone Network (PSTN) • Plain Old Telephone Service (POTS) • Both the remote user and the LAN must have • a registered phone number • Remote Access Service (RAS) • of the server • must be activated • RAS client program • needed by the user

  4. Chapter 6 Communication Links 6.1.1 Modem Dial-upA. Modem (1/2) • Modem • converts between • digital • computer • analog • phone line

  5. Chapter 6 Communication Links 6.1.1 Modem Dial-upA. Modem (1/2) • Modem (cont’) • Modulation means • the amplitude (or frequency) of analog signal is changed according to data • sender modem modulates data • Demodulation means • getting data from a modulated signal • receiver modem demodulates the analog signals • Modems are needed at both ends • for several remote users, a pool of modems are needed

  6. Chapter 6 Communication Links 6.1.1 Modem Dial-upB. Quality • Quality is poor • error-rate can be as high as 40% • because PSTN was designed for voice communication • Re-transmission is quite often • Note: poor quality does NOT mean that data received are inaccurate!

  7. Chapter 6 Communication Links 6.1.1 Modem Dial-upC. Bandwidth • Maximum bandwidth of PSTN is 56 Kbps • Modems negotiate the highest possible transmission rate • If one modem is 56 Kbps, but the other is 14.4 Kbps, • the highest transmission rate is only 14.4 Kbps.

  8. Chapter 6 Communication Links 6.1.1 Modem Dial-upD. Dial-up • Dial-up is necessary (for standard line, notleased line) • the connection is not permanent • known as “dial-on-demand” • Opposite is “always-on connection” • e.g. DSL broadband

  9. Chapter 6 Communication Links 6.1.1 Modem Dial-upE. Leased line • Leased line means • line reserved and dedicated for transmission • “Always-on connection” • higher quality • less error rate • bandwidth can be guaranteed

  10. Chapter 6 Communication Links 6.1.1 Modem Dial-upF. Security • Security is low • data transmitted using RAS over PSTN are usually not encrypted

  11. Chapter 6 Communication Links 6.1.1 Modem Dial-upG. Cost • Cost is • Low for local connections • High for long-distance phone line • In summary, PSTN is • slow • poor in transmission quality • needs dial-up • has security risk • ubiquitous : easy to access

  12. Chapter 6 Communication Links 6.1.2 Virtual Private Network (VPN) (1/3) • Virtual Private Network (VPN) • remote access to a LAN • over the Internet • with security using tunnels • Tunnel • virtual dedicated channel, with following characteristics: • A. Encryption • even encrypted data are intercepted, confidentiality can be guaranteed • B. Authentication • Access control is implemented, such as login • C. Message integrity • Prevent message alteration.

  13. Chapter 6 Communication Links 6.1.2 Virtual Private Network (VPN) (2/3)

  14. Chapter 6 Communication Links 6.1.2 Virtual Private Network (VPN) (3/3) • IPSec (IP security) • industrial technique in VPN • e.g. In Windows: • PPTP (Point-to-Point Tunneling Protocol) • L2TP (Layer Two Tunneling Protocol) • VPN server • installed in the LAN • VPN client • installed by user • VPN is in widespread use today • e.g. access intranet from home, or • connecting LANs to form extranets

  15. Chapter 6 Communication Links 6.2 Communication Links • Recall: MAN or WAN is constructed by connecting LANs by routers and long-distance communication links. • Long-distance communication media include: • Copper wire • Fiber-optic cable • Radio waves • Satellite links • For copper wire, WAN technologies include • ordinary phone line, ISDN, T1, T3, DSL, cable TV network and ATM. • The choice depends on • speed, reliability, cost, availability and security.

  16. Chapter 6 Communication Links 6.2.1 PSTN • Ordinary phone line (PSTN) • is the slowest method of establishing a communication link. • but, it has highest availability • most easy to access

  17. Chapter 6 Communication Links 6.2.2 ISDN • Integrated Services Digital Network (ISDN) • dedicated digital communication link • bandwidth 64 Kbps • provided by telephone companies • but better quality than the analog telephone system • error rate less than 1%

  18. Chapter 6 Communication Links 6.2.3 T1 and T3 • T1 • dedicated digital communication link • bandwidth 1.5 Mbps • multiplexing 24 separate 64 Kbps channels • expensive • T3 • bandwidth 44.7 Mbps • multiplexing 672 separate 64 Kbps channels • very expensive

  19. Chapter 6 Communication Links 6.2.4 DSL (1/3) • Digital Subscriber Line (DSL) • makes use of ordinary phone lines • plus advanced technology • broadband • much higher bandwidth than PSTN • inexpensive • Originally, the copper wire of PSTN is capable of carrying signals of very high frequency up to 1 MHz. But, the interface cards installed in the central office of the telephone company limit the frequency to 4 KHz only. DSL opens up the maximum capability by simply replacing the old interface cards in the central office of the telephone companies. • There are several versions of DSL: ADSL, HDSL, SDSL and VDSL, where the first letters in the acronyms are Asymmetric, High-data-rate, Symmetric and Very-high-data-rate respectively. The most popular version is ADSL. • Asymmetric DSL (ADSL) has a higher download speed than upload speed, for example, 6 Mbps download and 1 Mbps upload. • ADSL can reserve a small proportion (8 KHz) of total bandwidth for voice signals. Therefore, ADSL is able to transmit both data and voice at the same time. An ADSL modem is necessary.

  20. Chapter 6 Communication Links 6.2.4 DSL (2/3) • Digital Subscriber Line (DSL) • broadband technology • makes use of ordinary phone lines • much higher bandwidth than PSTN • inexpensive • need DSL modem • Several versions: • ADSL - Asymmetric (most popular) • higher download speed than upload speed • e.g. 6 Mbps download and 1 Mbps upload • HDSL - High-data-rate • SDSL - Symmetric • VDSL - Very-high-data-rate

  21. Chapter 6 Communication Links 6.2.4 DSL (3/3) • DSL can transmit voice and data at the same time • a small proportion (8 KHz) of total bandwidth can be reserved for voice signals • What is technology in DSL? • Originally, PSTN can carry signals up to 1 MHz • But, the telephone company limits to 4 KHz for voice • So, simply replace the equipment, and the old phone lines can have bandwidth up to 10 Mbps

  22. Chapter 6 Communication Links 6.2.5 Cable TV Network • Cable TV network • another broadband technology • coaxial cables • bandwidth as high as 10 Mbps • needs: cable modem • can transmit data and television signals at the same time

  23. Chapter 6 Communication Links 6.2.6 ATM • Asynchronous Transfer Mode (ATM) • very high-speed • expensive • each packet has a fixed length (53 bytes) • no need to check the end of data for each packet • multiplexed to fully utilize the network resources • media include • coaxial cable, twisted-pair, fiber-optic cables. • bandwidth: 155 Mbps to 622 Mbps

More Related