Cable modem

From the Wikipedia Cable modem article:

A cable modem is a special type of modem that is designed to modulate a data signal over cable television infrastructure.

The term cable Internet access (or simply cable) refers to the delivery of Internet service over this infrastucture.

Cable modems should not be confused with older LAN systems such as 10base2 or 10base5 that used coaxial cables — and especially not with 10broad36, which actually utilized the same sort of cable as CATV systems.

Cable modems are primarily used to deliver broadband Internet access, taking advantage of unused bandwidth on a cable television network.

There were 22.5 million cable modem users in the U.S. during Q1 2005. That’s up from 17.4 million in Q1 2004.

Along with digital subscriber line technology, cable modems ushered in the age of broadband Internet access in developed countries. Prior to the availability of such systems, Internet access involved slow dial-up access over a public switched telephone network.

Users in a neighborhood share the available bandwidth provided by a single coaxial cable line. Therefore, connection speed can vary depending on how many people are using the service at the same time.

Often the idea of a shared line is seen as a weak point of cable Internet access. From a technical point of view, all networks, including DSL services, are sharing a fixed amount of bandwidth between a multitude of users — but because cable networks tend to be spread over larger areas than DSL services, more care must be taken to ensure good network performance.

A more significant weakness of cable networks using a shared line is the risk of loss of privacy, especially considering the availability of hacking tools for cable modems. This issue is addressed by encryption and other privacy features specified in the DOCSIS (Data Over Cable Service Interface Specification) standard used by most cable modems.

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What is the speed of your Internet Service Provider?

How fast is your broadband? Fast enough?

You are buying bandwidth from your Internet Service Provider. The bandwidth you buy is only guaranteed within the ISP network. Once you hit the outer boundary of your ISP and you hop over to the tier-one provider and “rest of the Internet” it’s pretty much vigilante territory and your speed is arbitrary with no guaranteed bandwidth. So while you may be sitting on your fancy business DSL rated at 2 Mbps, your browsing may crawl to a halt when accessing that remote website far, far away.

So when deciding on an ISP, make sure you pick one that is well connected to the tier one network, also known as the backbone. Most ISPs oversell their bandwidth; some more than others. Make sure your ISP does not oversell by too much.

You can test your Internet connection with our Internet Speed test.

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The “Triple Play” in Communications Gear

BusinessWeek online has an article on triple play:

The merging of voice, data, and video represents “a new dynamic,” says S&P’s Ken Leon, who likes Motorola and Scientific Atlanta

The shares of communications-equipment makers have been stuck in low gear for the last few years, hampered mostly by customers’ reduced spending and consolidation of telecom- and cable-services providers. The move by these operators to offer voice, data, and video — a so-called triple play — as well as the ability to have those services move across fixed and mobile networks, could finally translate into better times for equipment suppliers. “We believe the industry is coming into a new dynamic,” predicts Ken Leon, who follows the group for Standard & Poor’s Equity Research.

More at BusinessWeek online …

More on Triple play.

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How DSL works

From the WikiPedia Digital Subscriber Line article:

The Public Switched Telephone Network was initially designed to carry POTS calls, as the concept of data communications as we know it today did not exist. For reasons of economy, the system nominally passes audio between 300 and 3,400 Hz, which is regarded as the range required for human speech to be clearly intelligible. This is known as commercial bandwidth. Dial-up services using modems are constrained by the POTS channel’s Shannon capacity, which indicates the maximum data rate which can be supported by a given amount of bandwidth.

At the Local Exchange (UK terminology) or Central Office (US terminology) the speech is generally digitised into a 64 kbit/s data stream in the form of an 8 bit signal using a sampling rate of 8,000 Hz, therefore any signal above 4,000 Hz is not passed by the phone network (and has to be blocked by a filter to prevent aliasing effects). The bandwidth between the commercial bandwidth limit and the channel limit can be utilised in a fully digital end to end connection to achieve a full 64 kbit/s on an ISDN line.

The local loop connecting the central office to most subscribers is capable of carrying frequencies well beyond the 3.5 kHz upper limit of POTS. Depending on the length and quality of the loop, the upper limit can be as high as the tens of megahertz. DSL takes advantage of this unused part of the circuit by creating 4312.5 Hz wide channels starting between 10 and 100 kHz, depending on how the system is configured. Each channel is evaluated for usability in much the same way an analog modem would on a POTS connection. Allocation of channels continues at higher and higher frequencies (up to 1.1 MHz for ADSL) until new channels are deemed unusable. More usable channels equates to more available bandwidth, which is why distance and line quality are a factor. The pool of usable channels is then split into two groups for upstream and downstream traffic based on a preconfigured ratio. Once the channel groups have been established, the individual channels are bonded into a pair of virtual circuits, one in each direction. Like analog modems, DSL transceivers constantly monitor the quality of each channel and will add or remove them from service depending on whether or not they are usable.

The commercial success of DSL and similar technologies largely reflects the fact that in recent decades, while microchips and disk drives have been getting faster and cheaper, the cost of digging holes in the ground remains very high. All flavors of DSL employ very complex digital signal processing algorithms to overcome the inherent limitations of existing POTS wires. Not long ago, the cost of such signal-processing power would have been prohibitive, but today the cost of installing DSL for an existing local loop, with a DSLAM at one end and a DSL modem at the other end, is orders of magnitude less than would be the cost of installing a fiber-optic cable over the same route and distance.

Most residential and small-office DSL implementations reserve low frequencies for POTS service, so that with suitable filters and/or splitters the existing voice service continues to operate independent of the DSL service. Thus POTS-based communications, including FAX machines, can share the wires with DSL. However, in most cases only one DSL modem can use a local loop at a time; it is generally not possible for a customer to have multiple DSL connections over a single local loop. As of 2005, the standard way to let multiple computers share a broadband connection is to purchase an inexpensive router that establishes a local Ethernet or Wi-Fi network on the customer’s premises.

Once upstream and downstream channels are established, they are used to connect the subscriber to a service such as Internet access.

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Mapping WiFi users in 3D at MIT

You may think that an online log of your whereabouts updated in realtime and displayed in a public place as a three dimensional visualisation would be infringing on your privacy. Or you might just think it’s cool.

At MIT, Massachusetts Institue of Technology, it’s happening right now. WiFi users locations are tracked, whether they use a laptop, pda or even wifi enabled phone. they The system can pinpoint a user with an accuracy level down to classroom, even in multi-story buildings. The user is displayed as a dot on a map and, if the user opted to reveal their information, even individual students are shown. The campus has over 2800 wireless access points.

Read more about MIT’s new WiFi mapping.

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