Essays /

Internet Acess Through Cable Tv Network Essay

Essay preview


The term ‘Cable Modem’ is quite new and refers to a modem that operates over the ordinary cable TV network cables. Basically you just connect the Cable Modem to the TV outlet for your cable TV, and the cable TV operator connects a Cable Modem Termination System (CMTS) in his end (the Head-End). Actually the term "Cable Modem" is a bit misleading, as a Cable Modem works more like a Local Area Network (LAN) interface than as a modem. Cable modems allows consumers access to the Internet at higher speeds and at a fraction of the time it takes traditional telephone modems.

This is true for two reasons:
1) Broadband networks make the connection up to a hundred times faster 2) The service is "always on," meaning customers get the information they want, when they want it. Unlike telephone modems, cable modems allow consumers to keep their telephone lines open for voice conversations.

A short list of some of the technical terms and acronyms that you may come across in trying to understand the cable modem world. CATV: Community Antenna Television or Cable TV system. Can be all coaxial or HFC (Hybrid Fiber Coax) based. Cable modem (CM): Client device for providing data over a cable TV network. Read all about it here. Channel: A specific frequency and bandwidth combination. Used in this context about TV channels for television services and downstream data for cable modems. CMTS: Cable Modem Termination System. Central device for connecting the cable TV network to a data network like the internet. Normally placed in the headend of the cable TV system. CPE: Customer Premises Equipment. Used to describe the PC and/or other equipment, that the customer may want to connect to the cable modem. DHCP: Dynamic Host Configuration Protocol. This protocol provides a mechanism for allocating IP addresses dynamically so that addresses can be reused. Often used for managing the IP addresses of all the cable modems in a cable plant and the PC's connected to the cable modems. DOCSIS: Data Over Cable Service Interface Specification. The dominating cable modem standard. Defines technical specifications for both cable modem and CMTS. Downstream: The data flowing from the CMTS to the cable modem. Downstream frequency: The frequency used for transmitting data from the CMTS to the cable modem. Normally in the 42/65-850 MHz range depending on the actual cable plant capabilities. Headend: Central distribution point for a CATV system. Video signals are received here from satellites and maybe other sources, frequency converted to the appropriate channels, combined with locally originated signals, and rebroadcast onto the HFC plant. The headend is where the CMTS is normally located. HFC: Hybrid fiber-coaxial (cable network). Older CATV systems were provisioned using only coaxial cable. Modern systems use fiber transport from the headend to an optical node located in the neighborhood to reduce system noise. Coaxial cable runs from the node to the subscriber. The fiber plant is generally a star configuration with all optical node fibers terminating at a headend. The coaxial cable part of the system is generally a trunk-and branch configuration. MAC layer: Media Access Control sub layer in the network stack. Read more about that later in this presentation. MCNS: Multimedia Cable Network System Partners Ltd. The consortium behind the DOCSIS standard for cable modems. Minislot: Basic timeslot unit used for upstream data bursts in the DOCSIS standard. MSO: Multiple Service Operator. A cable TV service provider that also provides other services such as data and/or voice telephony. QAM: Quadrature Amplitude Modulation. A method of modulating digital signals using both amplitude and phase coding. Used for downstream and can be used for upstream. QPSK: Quadrature Phase-Shift Keying. A method of modulating digital signals using four phase states to code two digital bits per phase shift. Ranging: The process of automatically adjusting transmit levels and time offsets of individual modems, in order to make sure the bursts coming from different modems line up in the right timeslots and are received at the same power level at the CMTS. SID (Service ID): Used in the DOCSIS standard to defines a particular mapping between a cable modem (CM) and the CMTS. The SID is used for the purpose of upstream bandwidth allocation and class-of-service management. Subscriber Unit (SU): An alternate term for cable modem.

Upstream: The data flowing from the CM to the CMTS.
Upstream frequency: The frequency used to transmit data from the CM to the CMTS. Normally in the 5-42 MHz range for US systems and 5-65 MHz for European systems.


A CATV network is designed and used for cable TV distribution. With an upgrade of the system, it is normally possible to allow signals to flow in both directions. Higher frequencies flow toward the subscriber and the lower frequencies go in the other direction. This is done by upgrades to the amplifiers in the cable distribution network etc. Most CATV networks are Hybrid Fiber-Coax (HFC) networks. The signals run in fiber-optical cables from the Head-End center to locations near the subscriber. At that point the signal is converted to coaxial cables, that run to the subscriber premises. One CMTS will normally drive about 1-2000 simultaneous Cable Modem users on a single TV channel. If more Cable Modems are required, the number of TV channels are increased by adding more channels to the CMTS.

A number of different Cable Modem configurations are possible. The following 3 configurations are the main products that we see now. * External Cable Modem
* Internal Cable Modem
* Interactive Set-Top box

The external Cable Modem is a small external box that connect to your computer normally through an ordinary Ethernet connection. The downside is that you need to add a (inexpensive) Ethernet card to your computer before you can connect the Cable Modem. A plus is that you can connect more computers to the Ethernet. The ailable Cable Modems w...

Read more


-2000 -42 -56 -64 -65 -850 /256 1 1.1 1.2 1.4 1.5 10 100 15db 16 187 188 188/204 1997 1999 1st 2 2.1 2.2 2.3 2000 2003 2004 2006 2007 204 24 256 27 2nd 3 3.1 30 300 31.2 32 4 4.1 4.2 4.3 4.4 41.4 41.6 42 42/65-850 4th 5 5.2 55.2 56k 6 6.9 64 65 7 768 8 800 802.14 9 a/d aal5 abl ac accept access accord accumul acess achiev acknowledg acronym across act activ actual ad add add-in addit address adequ adjust administr adsl advanc advantag agre ailabl algorithm alli alloc allow almost also altern although alway among amplifi amplitud analog and/or andleigh announc anoth answer antenna anywher apart appar applic appropri approv architectur area argu around arrang arriv asia asic asid assign assum atm atmhead atmpay attach attack attain attempt attenu automat avail b back balanc band bandwidth base baselin basic battl behind bertska best beyond big bit bit-rat block bodi box branch bring broadband broadcom brows built built-in burst bus busi byte cabl cable-modem calcul call came cannot capabl capac card case catv caus cell center central centric certain certifi chang channel chapter characterist cheapest chip circuit class class-of-servic clear client clip clock close cm cm/cmts cms cmts cmtss coax coaxial code collect collid collis combin come command communic communiti compani compar comparison compens competit complex complianc compliant compon comput concept conclus configur connect connector consecut consid consider consist consortium consum content context control convent convers convert correct cost could countri cover cpe cpu custom cut d/a data data-interfac data-over-c data-port data-r davic davic/dvb day de debat decid decreas dedic defin degrad delay deliv demodul depend describ design desktop detail detect deterr develop devic dhcp diagram dial dial-up dialup differ differenti digit diminish dimitri diplex direct disadvantag discuss disguis distanc distribut disturb divid docsi docsis-bas document domest domin done downgrad download downsid downstream drawback drive driven driver dsl due dvb dvb-rcc dvb/davic dynam e.g earlier easier easili edit educ effect either electr element ell els email emerg employ enabl encod encrypt end end-to-end enough ensur equal equip equival error error-correct essenti establish et etc ethernet ethernet/pci euro eurocablelab eurodocsi europ european even everi everyth excel exist expect expens explicit extern extra f fact fair famili far fast faster fastest feasibl featur fed feed fewer fiber fiber-coax fiber-coaxi fiber-opt fight figur filter first fix flexibl flow focus follow forc form formal/independent format forouzan forth found four fraction frame free frequenc friend front fulli function fundament gallag galvan game gap garbl general generat get give given global go goe gone good greater group grow guarante gut hall handl happen harcourt hard hardwar hassl head head-end headend header hear help hfc high high-pass high-spe higher home host hour hous howev hundr hybrid i.e id ieee imagin implement import imposs in-hous includ incorpor increas india individu industri inexpens inform ingress initi inject insid instal insur integr intel interact interf interfac intern internet interoper introduct involv ip isdn isol isp issu j.walrand jame join k kaufman kbps keep keith key kind kiran klara know known kuros lab lack lan land land-lin laptop larg last later latest layer leapfrog leav length less level like limit line list listen littl load local locat log longer look loss lost lot low lower ltd mac made main maintain major make manag mani manufactur map mark market market-ori matter matur max may mayb mb mbit/s mbps mcns mcns/docsis mcsn mean measur mechan media medium megabyt memori method mhz microprocessor might millisecond minimum minislot mislead modem modern modul money morgan move mpeg mpeg-t mso msym/s much multi multi-megabyt multimedia multipl must nalin name narstedt near necessari need negat neighborhood network never new next no-wher node nois normal note notic number obsolet obvious occur offer offici offset offspr often okay old older on-lin one onto open oper optic optimum option order ordinari orient origin other out-of-band outlet outlin output overhead overtak p.varaya pace packet pair part particular partit partner pass path pay payload pc pci peak pearson peopl per perform perman phase phase-shift phi phone physic place plain plan plant platform play plus pocket point polic port pose posit possibl pot power prabhat practic premis prentic present pretend pretti prevent price primari privaci problem process processor product program project propos proprietari protect protocol provid provis pte public pure purpos push pvt qam qpsk qpsk/qam-16 quadratur qualifi qualiti quality-of-servic quit quo ralf random rang rate raw rcc read real real-tim realiti realli reason rebroadcast receiv receive-on recent reduc reed reed-solomon refer region regulatori reli reliabl remain remot request requir reserv resid residenti result resynchron retail return reus right rise risk road robert role ross round run sale satellit screen second secur see seem seen segment select send sensit separ serial server servic set set-top sharda share shared-medium shift short shown sid sign signal signific silicon similar simpl simpli simultan sinc singl single-chip sit size skill slot small softwar sold solomon solut someth somewhat sourc specif specifi speed spend split splitter stack stall standard standard-even star start state static steinmetz still stream strength strict string strong stuff su sub subscrib suffici suit suppli supplier support suppos sure symbol sync synchron system t1 tabl take target tcp/ip technic technician technolog telephon telephoni televis terayon term termin thakrar though three throughput thus tie time time-slot timeslot tmh today tomasi top total toward tradit traffic tranform transmiss transmit transport tri trigger true trunk trunk-and ts tuner turn tv tv-channel tv-set two two-way type typic u unauthor understand uniqu unit univers unix unknown unless unlik upgrad upstream us usa usb use user usual valu vari variabl variat various vendor version via video videoconfer view voic voip vol w w16 want wast way wayn weaker web well whatev wherea wide wider william win wire wish within without won word work world xdsl yet