Cable Modems

<body topmargin=0 leftmargin=0 marginheight=0 marginwidth=0> <table cellpadding=0 cellspacing=0 border=0><tr> <td valign="top" colspan=2 height=110 BGCOLOR="#FFFFFF" TEXT="#080000" bgproperties="fixed" background="03df0f21egerdp.jpg"> <div> <FONT SIZE="1" COLOR="#66334C" FACE="Arial" ><B><IMG SRC="03e203c0.jpg" border=0 width="32" height="60" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></B></FONT><FONT SIZE="6" COLOR="#FF0000" FACE="Arial" ><B>Cable         </B></FONT><FONT SIZE="4" COLOR="#66334C" FACE="Arial" ><B> </B></FONT><A HREF="index.htm" TARGET="_top" TITLE="_"><U>Home</U></A> | <A HREF="id2.htm" TARGET="_top" TITLE=" BlueTooth"><U>BlueTooth</U></A> | <A HREF="id18.htm" TARGET="_top" TITLE="LMDS"><U>LMDS</U></A> | <A HREF="id3.htm" TARGET="_top" TITLE="Wireless"><U>Wireless</U></A> | <A HREF="id16.htm" TARGET="_top" TITLE="Broadcast"><U>Broadcast</U></A> | <A HREF="id19.htm" TARGET="_top" TITLE="Mission Statement"><U>Mission Statement</U></A> | <A HREF="id17.htm" TARGET="_top" TITLE="Set Top Box"><U>STB</U></A> | <A HREF="id20.htm" TARGET="_top" TITLE="Contact Us"><U>Contact Us</U></A> | <A HREF="id6.htm" TARGET="_top" TITLE="Satellite"><U>Satellite</U></A></div> <div> <B>   </B></div> <bR> <div> </div> </td> </tr><tr> <td valign="top" width=210 BGCOLOR="#FFFFFF" TEXT="#080000" bgproperties="fixed" background="03cf2f02egerdp.jpg"> <div> <A HREF="index.htm" TARGET="_top" TITLE="_"><U><B><U>Home</U></B></U></A><FONT SIZE="3" COLOR="#66334C" FACE="Arial" ><A HREF="index.htm" TARGET="_top" TITLE="_"><U> </U></A></FONT></div> <div> <A HREF="id2.htm" TARGET="_top" TITLE=" BlueTooth"><U><B><U>BlueTooth</U></B></U></A><FONT SIZE="3" COLOR="#66334C" FACE="Arial" > </FONT></div> <div> <A HREF="id3.htm" TARGET="_top" TITLE="Wireless"><U><B><U>Wireles</U></B></U></A><A HREF="id3.htm" TARGET="_top" TITLE="Wireless"><U><B>s</B></U></A><FONT SIZE="3" COLOR="#66334C" FACE="Arial" ><A HREF="id3.htm" TARGET="_top" TITLE="Wireless"><U> </U></A></FONT></div> <div> <B>Cable</B><FONT SIZE="3" COLOR="#66334C" FACE="Arial" > </FONT></div> <div> <A HREF="id6.htm" TARGET="_top" TITLE="Satellite"><U><B><U>Satellite</U></B></U></A><FONT SIZE="3" COLOR="#66334C" FACE="Arial" ><A HREF="id6.htm" TARGET="_top" TITLE="Satellite"><U> </U></A></FONT></div> <div> <A HREF="id16.htm" TARGET="_top" TITLE="Broadcast"><U><B><U>Broadcast</U></B></U></A><FONT SIZE="3" COLOR="#66334C" FACE="Arial" > </FONT></div> <div> <A HREF="id17.htm" TARGET="_top" TITLE="Set Top Box"><U><B><U>Set Top Box</U></B></U></A><FONT SIZE="3" COLOR="#66334C" FACE="Arial" ><A HREF="id17.htm" TARGET="_top" TITLE="Set Top Box"><U> </U></A></FONT></div> <div> <A HREF="id18.htm" TARGET="_top" TITLE="LMDS"><U><B><U>LMDS</U></B></U></A><FONT SIZE="3" COLOR="#66334C" FACE="Arial" ><A HREF="id18.htm" TARGET="_top" TITLE="LMDS"><U> </U></A></FONT></div> <div> <B><U>M</U></B><A HREF="id19.htm" TARGET="_top" TITLE="Mission Statement"><U><B><U>ission Statement</U></B></U></A><FONT SIZE="3" COLOR="#66334C" FACE="Arial" > </FONT></div> <div> <A HREF="id20.htm" TARGET="_top" TITLE="Contact Us"><U><B><U>Contact Us</U></B></U></A><FONT SIZE="3" COLOR="#66334C" FACE="Arial" ><A HREF="id20.htm" TARGET="_top" TITLE="Contact Us"><U> </U></A></FONT></div> <bR> <bR> <bR> <bR> </td> <td valign="top" height=370 BGCOLOR="#FFFFFF" TEXT="#080000" bgproperties="fixed" background="03ff0f03.jpg"> <div> <I>Cable Modems</I></div> <div> <B>4.1 Introduction </B></div> <bR> <div> Residential Internet and online usage has managed to grow tremendously despite maddeningly slow speeds available through existing dial-up telephone modem connections, limited to 53 Kbps or less. Touted as an interactive extravaganza, surfing the World Wide Web more typically offers narrowband users a click-and-wait experience. The growing frustration of existing online users is driving demand for higher-speed connections. </div> <bR> <div> Local telephone companies currently offer residential ISDN services that provide connection speeds up to 128 Kbps and they are looking to digital subscriber line technologies (DSL) which can provide downstream speeds beyond 1.5 Mbps. Other alternatives include fast downstream data connections from direct broadcast satellite (DBS), fixed wireless providers, and of course, high-speed cable modems. </div> <bR> <div> More than 105 million homes in North America are passed by broadband coaxial cable plant and more than 75 million homes are cable TV subscribers. With near-ubiquitous coverage, coaxial cable connections provide a powerful platform for providing residences and small Businesses with high-speed data access.</div> <bR> <div> <B>Cable TV Primer</B><FONT SIZE="2" COLOR="#000000" FACE="Arial" ><B> </B></FONT></div> <bR> <div> Cable systems were originally designed to deliver broadcast television signals efficiently to<B> </B>subscribers' homes. To ensure that consumers could obtain cable service with the same TV sets they use to receive over-the-air broadcast TV signals, cable operators recreate a portion of<B> </B>the over-the-air radio frequency (RF) spectrum within a sealed coaxial cable line.Traditional coaxial cable systems typically operate with 330 MHz or 450 MHz of capacity,<B> </B>whereas modern hybrid fiber/coax (HFC) systems are expanded to 750 MHz or more . Logically, downstream video programming signals begin around 50 MHz, the equivalent of channel 2 for over-the-air television signals. The 5 MHz - 42 MHz portion of the spectrum is usually reserved for upstream communications from subscribers' homes. </div> <bR> <div> Each standard television channel occupies 6-8 MHz of RF spectrum. Thus a traditional cable system with 400 MHz of downstream bandwidth can carry the equivalent of 60 analog TV channels and a modern HFC system with 700 MHz of downstream bandwidth has the capacity for some 110 channels.</div> <div>  </div> <div> <B>Cable Modem Access Networks</B><FONT SIZE="2" COLOR="#000000" FACE="Arial" ><B> </B></FONT></div> <bR> <div> To deliver data services over a cable network, one television channel (in the 50 - 750 MHz range) is typically allocated for downstream traffic to homes and another channel (in the 5 - 42 MHz band) is used to carry upstream signals. </div> <div> A headend cable modem termination system (CMTS) communicates through these channels with cable modems located in subscriber homes to create a virtual local area network (LAN) connection. Most cable modems are external devices that connect to a personal computer (PC) through a standard 10Base-T Ethernet card or Universal Serial Bus (USB) connection, although internal PCI modem cards are also available. </div> <bR> <div> The cable modem access network operates at Layer 1 (physical) and Layer 2 (media access control/logical link control) of the Open System Interconnect (OSI) Reference Model. Thus, Layer3 (network) protocols, such as IP traffic, can be seamlessly delivered over the cable modem platform to end-users. </div> <div> A single downstream 6 MHz television channel may support up to 27 Mbps of downstream data throughput from the cable headend using 64 QAM (quadrature amplitude modulation) transmission technology. Speeds can be boosted to 36 Mbps using 256 QAM. Upstream channels may deliver 500 Kbps to 10 Mbps from homes using 16QAM or QPSK (quadrature phase shift key) modulation techniques, depending on the amount of spectrum allocated for service. This upstream and downstream bandwidth is shared by the active data subscribers connected to a given cable network segment, typically 500 to 2,000 homes on a modern HFC network. </div> <bR> <div> An individual cable modem subscriber may experience access speeds from 500 Kbps to 1.5 Mbps or more -- depending on the network architecture and traffic load -- a blazing performance compared to dial-up alternatives. However, when surfing the Web, performance can be affected by Internet backbone congestion. </div> <bR> <div> In addition to speed, cable modems offer another key benefit: constant connectivity. Because cable modems use connectionless technology, much like in an office LAN, a subscriber's PC is always online with the network. That means there's no need to dial-in to begin a session, so users do not have to worry about receiving busy signals. Additionally, going online does not tie up their telephone line. </div> <bR> <div> A range of vendors are now offering two-way cable modem products, including 3Com, Cisco Systems, Com21, Ericsson, Motorola, Nortel Networks, Samsung, Terayon Communication Systems, Thomson Consumer Electronics, Toshiba, and Zoom Telephonics.</div> <div>  </div> <div> <B>C</B><FONT SIZE="2" COLOR="#000099" FACE="Arial" ><B>able Internet Service Delivery </B></FONT></div> <bR> <div> To get into the high-speed Internet services business, cable operators must do more than simply install cable modem gear. Rather, they must build a sophisticated end-to-end IP networking infrastructure in each community they serve that is robust enough to support tens of thousands of data subscribers. That includes items like Internet backbone connectivity, routers, servers, network management tools, as well as security and billing systems. In essence, cable operators are faced with the task of building some of the world's largest "Intranets," a serious engineering and operations challenge. </div> <div> Cable operators are focused on providing high-speed Intranet access instead of straight Internet access for a simple reason: a network connection is only as fast as its slowest link. Clearly, the benefit of a 1-Mbps cable link is lost if a subscriber tries to access content stored on a Web server that is connected to the Internet though a 56-Kbps line. The solution to this dilemma is to push content closer to the subscriber, ideally right down to cable headend. This is done by "caching" or storing copies of popular Internet content on local servers, so when a cable modem subscriber goes to access a Web page, he or she will be routed to the server in the headend at top-speed, rather than being required to voyage out onto the congested Internet.</div> <bR> <div> A number of companies are offering comprehensive networking and systems integration services to cable operators entering the high-speed Internet business. </div> <bR> <div> <B>Shared Network Platform Performance </B></div> <bR> <div> Most cable modem systems rely on a shared access platform, much like an office LAN. Because cable modem subscribers share available bandwidth during their sessions, there are concerns that cable modem users will see poor performance as the number of subscribers increases on the network. Common sense dictates that 200 cable data subscribers sharing 27-Mbps connection would each get only about 135 Kbps of throughput -- virtually the same speed as a 128-Kbps ISDN connection -- Not necessarily.</div> <bR> <div> Unlike circuit-switched telephone networks where a caller is allocated a dedicated connection, cable modem users do not occupy a fixed amount of bandwidth during their online session. Instead, they share the network with other active users and use the network's resources only when they actually send or receive data in quick bursts. So instead of 200 cable online users each being allocated 135 Kbps, they are able to grab all the bandwidth available during the millisecond they need to download their data packets -- up to many megabits per second. </div> <bR> <div> If congestion does begin to occur due to high usage, cable operators have the flexibility to add more bandwidth for data services. A cable operator can simply allocate an additional 6 MHz video channel for high-speed data, doubling the downstream bandwidth available to users. Another option for adding bandwidth is to subdivide the physical cable network by runningfibre-optic lines deeper into neighborhoods. This reduces the number of homes served by each network segment, and thus, increases the amount of bandwidth available to end-users.</div> <div> After years of technical trials, large cable operators finally began widespread deployments of cable modem services in late 1996. </div> <bR> <bR> <bR> <bR> <bR> <bR> <bR> <bR> <bR> <bR> <bR> <bR> <bR> <bR> <bR> <bR> <bR> <bR> </td> </tr></table></body>