Nelly_Shin
New Member
1. How many channels does an ISDN system commonly use?
2. What types of wireless systems are named in the text?
3. What do PCs connected to a satellite system use to send data?
4. What types of cables are used in cable network system?
5. What may need to be upgraded when using a shielded DSL system?
6. Compared to the downstream bandwidth, the upstream bandwidth in an ADSL line is:
a. Larger
b. Smaller
c. The same
7. Which type of broadband services is the cheapest?
Integrated Sevices Digital Network (ISDN)
ISDN services can be carried over existing telephone network infrastructure to terminal
adapter (TAs) in the client machine. A common ISDN interface standard has a digital
communications line consisting of three independent channels: two Bearer(B) channels,
each at 64Kbit/s, and one Date (D) channel at 16Kbit/s.The D channel is used to carry
signaling and supervisory information to the network ,while the B chanel carry the data
and can be linked to provide a 128Kbit/s data channel
Wireless connections
The wireless alternatives come in two forms: satellite and cellular. Satellite systems
require the use of a modem to maintain the upload. Downstream bandwidth is provided
via a dedicated satellite dish, connector hardware and proprietary software.
Cellular system use assigned radio frequencies and are based around a network of
transmitters that are arranged in a cellular network, much like cellular mobile phone
systems.
The cable alternative
Cable companies can also offer affordable broadband services over copper coaxial or
fibre infrastructure networks. The connection shared by several customers on a branch, so
actual connection rates are variable, unlike ISDN and DSL.
Digital Subscriber Line(DSL)
DSL technology capitalizes on the existing network of copper infrastructure, but allows
digital signals to be carried rather than analogue. It allows the full bandwidth of the
copper twisted-pair telephone cabling to be utilized.
With splitter- based services, the DSL signal is pulled out from the phone line as it
enters your premises and is wired separately to a DSL modem. This involves additional
hardware and installation by the service provider at the customer site. The shielded
option involves no installation, but the telephone company’s equipment and some of your
equipment might need upgrading.
With Asymrnetric Digital Subscriber Line (ADSL), most of the duplex bandwidth is
devoted to the downstream direction, with only a small proportion of bandwidth being
available for upstream.
Much Internet traffic throught the client’s connection, such as Web browsing,
downstream bandwidth, but user requests and responses are less significant and therefore
require lass on the upstream. In addition, a small proportion of the downstream
bandwidth can be devoted to voice rather than data, allowing you to hold phone
conversations without requiring a separate line.
DSL-based services are a very low-cost option when compared to other solutions
offering similar bandwidth, so they can be made available to the customer at extremely
competitive prices.