The Cable Modem Cloning And Hacking Communication Computer Science Essay

Published Date: 02 Nov 2017

Tarsem Singh Aulakh

Gursewak Singh Sandhu

Introduction to Cable Modem

Cable modem is a communication device. This device allows us to connect our PC or laptop to cable Television line and receive data from operator at speed of 1.5 Mpbs or more. Data rate is much more then telephone modems (28.8 or 56 kbps) and 128 kbps given by ISDN (integrated services Digital Network). It is almost equal to Digital Subscriber Line (DSL) telephone service. Cable modem can is combined with set top box. With this combination channels could be watched on TV and internet could be accessed. In most cased cable modem are given by operator. They are not purchased by customers.

Cable modem has two connectors. One connecter is connected to cable wall outlet. Other connected to personal computer or laptop. In some cased second connector is connected to set top box for TV channels. Cable modems do conversation between analog signals and digital signals. In other words it performs the task of modulations and demodulation. Although it do modulation and demodulation but it is a very complex device then telephone modem. Cable modem can be individual external device or it can be integrated with a personal computer of set top box. Cable modem is connected to a laptop or personal computer with a standard 10BASE-T Ethernet card.

Cable modems are connected to cable operator with a coaxial cable line. Through this coaxial cable cable modem communicates to Cable Modem Termination System located at cable operator office. Cable modems can send or receive signals to Cable Modem Termination System. But cable modem cannot send or receive signal to other cable modems on line.

Internet service bandwidth over cable TV line can be 27 Mpbs or more for downstream and 2.5 Mpbs or more on reverse direction. But main factor in speed is cables from operator office to customers’ homes and actual speed that operator has. If operator is only connected to internet at speed of 1.5 Mpbs in this case data rate at customer end would be near 1.5 Mpbs.

Main cable TV providers are using cable modems to bring internet at customer home. Cable modems are used to provide internet service to individuals and business customers. Fast internet connection can be provided by cables modems as well cable modem is a continuous connection.

How cable modems work

News, entertainment and educational programs are brought by television in millions of homes. Many peoples watch TV through cable TV in short known as CATV. Cable TV operator provides many channels and in very good picture quality. If customer wants cable TV operator can also provide access to internet with high speed. Cable modems are able to give competition to asymmetrical digital subscriber lines (ADSL).it is very interesting to how these both competitors works. In next topic I will try to explain how many TV channels and web sites flow on single coaxial cable.

1.1.1 More Space

Coaxial cable used by cable operators is able to carry hundreds of megahertz of signals and each channel that travels on coaxial cable is given 6 megahertz of total electrical space or bandwidth.it means coaxial cable can carry many more channels then we can or wants to watch. Cable TV operator sends signals of various channels each channel gets six MHz slice of coaxial cable’s available total bandwidth. There could be two types of distribution of cable network. In first one coaxial cable is installed from operator’s office till customer home. In second type fiber-optic cable is installed from operator’s office till different areas then from these different locations coaxial cable is installed till customer home.

1.1.2 Streams

If a company provides facility of internet then internet service can also use same coaxial cable. This work is done by Cable Modem by putting downstream data (data that is sent from internet to customer) on a six MHz channel. So internet data is just like a TV channel on cable. Same amount of total cable bandwidth is taken by internet downstream data as by a single TV channel. Internet service is a combination of downstream and upstream (data that is sent to internet from customer) .it means upstream also need bandwidth of cable. It takes only 2 MHz slice of space from total available space because it is assumed that customers download more data as they upload.

To put these two types of streams (downstream and upstream) cable operator needs only two devices. One device at customer end that is called Cable Modem and other one at operator end called Cable Modem termination system. Computer networking and internet access management takes place in between these two devices.

1.1.3 inside the cable modem

As mentioned earlier Cable modem can be external or internal to computer. Some operators provide Cable Modems those are integrated with set top box. Cable Modems can be different from their outer look but all of them have same components inside. Components are given below

1. Demodulator

2. Media Access Control Device

3. Microprocessor

4. Modulator

5. Tuner

1.1.3.1 Tuner

The tuner is connected to cable outlet. In some cases tuner is connected to a splitter. Splitter separates channels used for data from channels used for cable TV channels. Tuner collects data from internet channel. Data comes in form of digital modulated signal. Tuner receives this data and passes this data to demodulator.

In some Cable Modems tuner contain one other component known as diplexer.it allows tuner to divide frequencies into two sets. First set is used for downstream traffic ad second one is used for upstream traffic. Range of frequencies used for upstream is between 5 to 42 MHz. Range used for downstream frequencies is between 42 to 850 MHz. In some other cases Cable Modem tuner is only used for downstream data and for upstream traffic dial up telephone modem is used. In any case tuner passes data to demodulator.

1.1.3.2 Demodulator

Typically Demodulator performs four functions. First function is to convert radio frequency signal in to simple signal that can be processed by analog to digital converter. Radio frequency signal contains information in it by varying amplitude and phase of wave. Second function is performed by analog to digital converter. It takes signal from quadrature amplitude modulation demodulator in turns in series of 1s and 0s. These 1s and 0s are in digital form. Third function is performed by error correction module. It receives information from analog to digital converter and checks this information against a already known standard for possible errors. Main function of this module is to find problems in transmission and to fix them. At this stage data is in groups and these groups are called frames. Frames can be MPEG format. So MPEG synchronizer does its duty to make sure that frames are in order and in line as they were transmitted.

1.1.3.3 Modulator

Modulator do reverse job as done by demodulator. It converts digital data into radio frequency signals. So that they can be transmitted on cable. Nature of traffic that flow between user and internet is irregular. Typically this component has they parts

1. Digital to analog converter

2. Quadrature amplitude modulator

3. Error correction information inserter

1.1.3.4 MAC

Cable modem has two portions upstream and downstream.MAC is lactated between these two portions. It works as interface between hardware and software portions of different network protocols. Every network device has MAC. Cable modem MAC performs much more complex task then normal MACs. Because it performs much more complex tasks it work load is given to CPU of Cable Modem or to CPU of user personal computer or laptop.

1.1.3.5 Microprocessor

Job of Microprocessor depends on for what cable modem is designed. Cable modem can be designed only to provide internet access or it can be designed to be a part of large computer system. If Cable modem is used only for internet access then Microprocessor of Cable mode does most of function of MAC. In case Cable modem is used to be part of large computer system Microprocessor of computer performs most function of MAC.

1.1.4 Cable Modem Termination System

At CMTS end traffic comes from different users in groups. Function of CMTS is take all traffic on a single channel and route this all traffic to internet service provider for connection to internet. on CMTS end service provider could have set up different servers for performing following functions

1. Accounting and Logging

2. Dynamic Host Configuration Protocol (DHCP)

3. Administration of IP Addresses of users

4. Servers for Data over Cable Service Interface Specifications

Downstream data reaches to connected users. It is same like in a Ethernet network. Individual connection has to think that it is for him or not. It is totally different in case of upstream data. Data send from one user to internet is not seen by other users on network. As we know there is not so much bandwidth for upstream. Total available bandwidth is divided into time slices. Time slices are in milliseconds. Time slices are given to different user to send data to internet. Time slices works very well for send short commands, queries and address those are send from users to internet.

Typically CMTS allow 1,000 users to connect to internet on a single six MHz channel. Normally single channel have capacity of 30 to 40 megabits per second. So it clear that Cable modem is able to give speed to customers which is much more then dial up modems. Single channel concept could also lead to some issues those customers can face.

2. History of Cable Modems