With ADSL some of the bandwidth is shared between other users. For example, if
the service is contended or "oversubscribed" at 20:1, it means that you share
the bandwidth with up to 19 other users. Thus the performance of an ADSL
connection will vary according to time of day and time of week, depending on
how many other users happen to be online at that moment.
"Basic" ADSL services in the UK (mainly using the British Telecom Network)
typically have a contention ratio of 50:1 with the more expensive/business
packages having 20:1.
An ISP
can either issue a fixed IP address
(i.e. it doesn't change between connections to the Internet) or
you'll be assigned a variable address every time you connect. For
a variable address, every time you connect your DHCP software
asks the ISP for a temporary or leased IP.
Most ISP's provide you with a variable IP address
and therefore require DHCP enabled on your computer.
All Microsoft products have built in DHCP software.
back to Choosing a
Modem
An Internet server that turns your human readable address (e.g.
www.microsoft.com) into an
IP number.
back to Choosing a
Modem
An agreed "standard" for how Cable Modems should work.
DOCSIS specifies downstream traffic transfer rates between 27 and 36 Mbps over
a radio frequency (RF) path in the 50 MHz to 750+ MHz range, and upstream
traffic transfer rates between 320 Kbps and 10 Mbps over a RF path between 5
and 42 MHz. But, because data over cable travels on a shared loop, individuals
will see transfer rates drop as more users gain access.
NAT is like a funnel.
Simply put, NAT is a way translating one IP address into another.
For example, using NAT you could have just one real IP address
(the one connected to the Internet) and use this to service connections to a
private network (e.g. an IP address that is not used on the
Internet). NAT is used in MS Internet Connection Sharing (Windows 98
SE+/2000).
ADSL providers like NAT because it cuts down on the number or real
IP addresses that they must buy. Using NAT, one real IP can
service up to 256 private connections. The downside of NAT is that some
software doesn't work well with it. For example, MSN gaming Zone or ICQ
sometimes has problems with NAT.
NAT is totally different from routing (routing needs real
IP addresses to work).
back to ISP FAQs
A "transport" networking layer. An "application" layer "sits" on
top to provide either reliable/in sequence connection (TCP)
or, for speed non-reliable/out of sequence connections (e.g. Streaming
Media) UDP.
IP is known as "routable" meaning that it can travel across many different
networks and doesn't care about platform (e.g. UNIX or Windows).
An IP address is your unique identifier when connected to the
Internet. It consists of four numbers separated by a period (e.g.
195.234.3.80). Each number must be between 0 and 255.
back to ISP FAQs
A company that will provide you with a connection to the Internet.
For each IP address, you can establish many connections at the same
time. Each connection is made to the same IP address
using a different port. Some examples are Port 80 for browsing
the web and 25 for sending mail.
Information goes back and forth on the Internet in packets made
up of the data, it's sender identifier, a recipient identifier and error
checking data. TCP is called a connection protocol as it provides
reliable data transfer. Reliable means that the data
arrives in-tact and in the correct sequence otherwise it is asked to be sent
again. These requests for data to be re-transmitted mean a slower
but more reliable connection than UDP.
Similar to TCP
except that no re-transmissions are requested for faulty data. UDP is known as
a connectionless protocol and mainly used for non-critical
applications that require speed but not reliability (e.g. Streaming media,
games etc.).
Unshielded Twisted Pair (UTP) Category 5 cable.
This type of cabling is designed to handle the 100-Mbps speed needed by
Ethernet. The RJ-45 connector at the end of the cable looks very similar to
the RJ-11 connector on a phone cord but is slightly bigger (and not
compatible). You can buy Cat 5 cables in predetermined lengths with the
connectors already attached. If you plan to install the Cat 5 cabling in the
walls of your house, you can buy the cable in rolls, cut it to length and
connect the cable to special RJ-45 wall boxes.
back to networking
The 802.11 tag denotes a family of
international standards for wireless local area networks (Wlans) developed and
ratified by the Institute of Electrical and Electronics Engineers (IEEE) The
original IEEE-802.11 standard operated at a radio frequency of 2.4GHz and
delivered maximum speeds of 2Mbits/sec. Since then, several extensions to the
original 802.11 specification have arrived, each identified by a single
lower-case letter tagged on the end. The first extension, 802.11b, increased
the maximum speed to 11Mbits/sec and was officially ratified in 1999.
802.11b is now the most widespread
Wlan standard and, unless otherwise stated, is usually the technology behind
what people casually call wireless Ethernet. It can operate over a distance of
up to 120m outdoors.
The most recently ratified standard
is 802.11g, which delivers a maximum speed of 54Mbits/sec, but on the same
2.4GHz frequency of 802.11b. In theory, an 802.11g device should work on an
802.11b network and vice versa, offering backwards compatibility with the vast
majority of Wlans (albeit limited to 11Mbits/sec), and the promise of higher
speeds when paired with other 802.11g equipment.
back to networking
Page last updated
Friday, 07 November 2003
