ECE Chapter 1

Transcription

1 ECE Chapter 1 Definition: Digital Subscriber Line (DSL) Public network technology that delivers high bandwidth over conventional copper wiring at limited distances. There are four major types of DSL: ADSL, HDSL, SDSL, and VDSL. All are provisioned via modem pairs, with one modem located at a central office and the other at the customer site. Because most DSL technologies do not use the whole bandwidth of the twisted pair, there is room remaining for a voice channel. 1

2 What is DSL? Digital Subscriber Line Uses Existing local loop Enables high-speed network access over existing copper wires Simultaneous voice and data on the same twisted-pair of copper Wideband technology employing a pair of DSL devices (on the local loop) to connect to service Makes full use of the available frequency spectrum resulting in multi-megabit service capability DSL Fast Facts Remarkably fast download speeds can range up to 8 Mbps; and upload speeds can range up to 1Mbps. So practically the only speed limit with DSL is the speed of the Internet and all the computer attached to it. 2

3 Highly reliable DSL Fast Facts You can depend on DSL because its proven technology takes full advantage of the existing telecommunications infrastructure. Phone company networks are among the most reliable in the world experiencing only a few minutes of downtime on average each year. And you can count on DSL to scale with your future connectivity needs. That's a level of comfort you won't find with other Internet access technologies. DSL Fast Facts Inherently secure Because our DSL network provides a dedicated Internet connection via private telephone wires, you can bypass dial-up intruders or shared network hackers. Unlike traditional dial-up modems or cable modems, DSL protects your valuable data with the most secure connection available. 3

4 DSL Fast Facts Surprisingly affordable Generally DSL delivers industrial-strength T1-like speed (as fast as 1.5 Mbps) to multiple users at only 25% of typical T1 costs. There's no better price/performance option available. DSL is also an exceptional value for home users. At about $2 a day for service that meets the needs of most people, DSL's basic home configuration is priced within everyone's reach. DSL Fast Facts "Always on DSL is ready to run, every minute of every day. There's no more logging on and off, no more busy signals or disconnects. This gives you the freedom to focus on what you want to accomplish online - rather than focusing on trying to get connected. In fact, you can be more productive because the power and immediacy of the Internet is continuously available at your fingertips. 4

5 DSL vs. Other Technologies DSL vs. T1 DSL vs. ISDN DSL vs. Cable Modem DSL vs. Fiber Network DSL vs. Wireless DSL vs. T1 T1 is a technology that bundles several phone lines together to provide downstream access speeds of 1.54 Mbps. for the cost of a single T Mbps connection, you could install three 1.1 Mbps DSL connections. DSL makes interconnecting multiple regions for private networking much more cost-effective. When you look at these facts alone, it is easy to see why many have termed DSL the "T1-killer". 5

6 DSL vs. ISDN ISDN stands for Integrated Services Digital Network. ISDN is inflexible, as it is only available in two speeds: 64 Kbps and 128 Kbps. xdsl scales from 128 Kbps to 1.5 Mbps. xdsl scales from 128 Kbps to 1.5 Mbps. ISDN offers dedicated, always on access but comes with additional per-minutes charges. ISDN requires that special digital circuits be installed. xdsl uses regular phone lines making installation faster and easier. DSL vs. ISDN Type High- Speed? Secured? Low- Cost? Existing Line? Downloa d 100MB ISDN K yes no, monthl y + per minute s no, new installat ion > 26 Min DSL 1.5M yes yes yes 66 Sec 6

7 DSL vs. Cable Internet access via Cable Modem has become available in many residential areas. When configured properly and under optimal conditions, Cable has the capacity to transmit data at speeds as fast as DSL. In most cases Cable does not compete with DSL in the business market at all due to the fact that Cable lines are not available in the vast majority of commercial districts. Problems: Security: Cable access is a shared network; Speed: Multiple users are slowing down the access. Interactivity: only 10 % cables are two-way interactive. DSL vs. Cable Type High- Speed? Secured? Low- Cost? Existing Line? Download 100MB Cable Maybe # of users No, shared network yes no, new cable installed as fast DSL 1.5M yes yes yes 66 Sec 7

8 DSL vs. Fiber Network Fiber to the home (FTTH) is the ideal fiber-optics architecture. In this architecture, fiber deployment is carried all the way to the customer s home (premises). FTTH has been developed in response to several residential access market drivers, including the following: Internet explosion, second line growth, the desire The increased competition Turn-up complexities The declining costs of optical equipment Technology life cycles DSL vs. Fiber Network Advantages associated with FTTH: It is a passive network, so there are no active components from the CO to the end user. It is a single fiber to the end user FTTH features local battery backup and lowpower consumption. FTTH is reliable, scalable, and secure. The FTTH network is a future-proof architecture. believed in 80 s that it takes only a few years; Problems: economics and logistics, even when fiber is to the curb, DSL may still become access scheme. 8

9 DSL vs. Wireless Wireless: came in early 90 s the promise of universal wireless access. Wireless broadband Internet access uses many frequency bands. Wireless broadband modems offer similar performance to cable modems operating over wired cable television systems (CATV), but the business is easier to enter as the transmitters cover an entire city or region. DSL vs. Fiber Network Type High- Speed? Secured? Low- Cost? Existing Line? Downloa d 100MB Fiber Very high No, shared network Very expen sive no, new fiber installed fastest DSL 1.5M yes yes yes 66 Sec 9

10 DSL vs. Wireless Wireless: came in early 90 s the promise of universal wireless access. Wireless broadband Internet access uses many frequency-bands. Wireless broadband modems offer similar performance to cable modems operating but the business is easier to enter as the transmitters cover an entire city or region. A broadband wireless system can deliver up to 30- Mbps data capacity in a 6-MHz channel. Problems: bandwidth and logistics. DSL vs. Wireless Frequency Band Designations Name Basic usage Frequency Note MMDS Most of these TV transmitters are analog and require upgrade to digital unless subchannelization is used. (note 1) MHz thirty-one individual 6-MHz television channels (transmitters) including ITFS; some operators have only four channels; range to 35 miles, requires LOS and is affected by multi-path (note 2). 10

11 DSL vs. Wireless Frequency Band Designations MDS MDS1: analog TV or not used single channel 6 MHz; see MMDS. MDS2: analog TV or not used single channel 6 MHz; see MMDS. MDS2a : analog TV or not used MDS2 truncated on one side to 4 MHz WCS WCS new or 10-MHz blocks; new in May 1997 WCS new or 10-MHz blocks; new in May 1997 DSL vs. Wireless Frequency Band Designations ITFS educational service, includes Internet access MHz channels shared with MMDS lowpower televisio n service (LPTV) low-power broadcast; 6- MHz channels, experimental licenses Low power can be 50- Kwatts effective radiated power (ERP) (This includes the antenna gain). LOS operation is advised. LMDS local multipoint distribution service; new short range, 3 miles, 20- MHz channels, new Propagation is affected by rain. 11

12 DSL vs. Wireless Frequency Band Designations ISM instructional, scientific and medical; unlicensed bands used for LANs and for the return path of two-way modem systems ,400 2,483.5 Short range 0.5 miles spread spectrum omnidirectional short range, similar to 900 MHz, but can also be engineered beyond 15 miles point to point as the return path for a cablemodem system Note 1: Sub-channelization is a way to increase the power of the adaptive equalizer in the cable modem by applying it to a narrower bandwidth. A standard equalizer can equalize three times the amplitude tilt or triple the delay if it operates over a 2-MHz channel instead of a 6-MHz channel. The narrower bandwidth may allow operation without upgrading the diplexer or removing sound subcarrier stop filters of an existing analog transmitter. In the latter case, only one or two subchannels may operate instead of three. Note 2: Multipath is the reception of two or more signals over different paths. The direct signal may combine with a reflection off a roof, wall, or other surface, refraction off trees or an atmospheric inversion layer. The received signal is the vector sum of the two signals creating both an amplitude and phase change. The distortion may move rapidly across the frequency band. 12