Although, other types of data delivery strategies are being used more and more, most networks communicate over cable. The three main types of cable are:
Co-axial cable has three layers. The center is made of copper, a plastic jacket surrounds the copper center with a braided shield, finally, covering all. The thicker the copper, the farther the data signal can travel. There are two types of co-axial cable:
Note: When using co-axial cable one (and only one) end must be grounded to protect against signal bounce and ground loops.
Twisted pair cable is made up
of multiple wires each individually insulated and, as the name implies, twisted
together in pairs. If a metallic shield covers the wires it is called STP (shielded
twisted-pair) if it isn't it's called UTP (unshielded twisted-pair).
2. TWISTED PAIR CABLE
Whenever electro magnetic signals travel through copper wires that are close to one another some interference or cross talk occurs. Twisting wires together minimizes this phenomena.
- CAT 1: Two twisted pair cables for a total of four wires. It is the oldest type of UTP cabling and is also referred to as POTS (Plain Old Telephone System).
- CAT 2: Four twisted pairs (eight wires). It has a 4 Mbps transmission rate.
- CAT 3: Four twisted pairs (eight wires) with three twists per foot. It has a 10 Mbps tranmission rate.
- CAT 4: Four twisted pairs (eight wires) rated at 16 Mbps.
- CAT 5:Four twisted pair (eight wires) rated at 100 Mbps.
- CAT 6:Four twisted pair (eight wires) rated at 1,000 Mbps.
Most cable in use today is rated at least CAT 5 or higher.
UTP cables use RJ-series connector. A home phone or a modem uses an RJ-11 connector. If your using Ethernet you use an RJ-45 connector which is a chunkier version of the RJ-11. RJ-series connectors have four pins in them with the inside pins handling voice or data transmission (incoming and outgoing) and the outside ones being responsible for ringing and an "off the hook" signal.
A formula is used to describe Ethernet cable.
n*SIGNAL*x
Where:
n = The cables signaling rate in Mbps.
*SIGNAL* = The signaling type of the cable; either broad band or baseband.
x = A unique identifier, that changes depending on the Ethernet cabling scheme.
For example:
10Base5
Where:
10 = A 10 Mbps transmission rate
Base = A Baseband signaling type is used
5 = In this case, the number five indicates that the signal can travel up to 500 meters.
In another example, 10baseT is interpreted as a twisted pair cable, using baseband transmission, with a 10 Mbps transmission rate. This standard (with the T) is used for a more exact definition of CAT 3, 4, and 5 UTP. The most current Ethernet cable description is 10BaseF. The F, in this case, indicates the usage of fiber optic cable.
Just as programs that worked over the Internet grew to become more demanding, the ability to meet those increased demands also grew. 100 Mbps technologies were developed. The Ethernet cabling used for Fast Ethernet falls under the following two major standards:
There was a third sort of cabling that facilitated 100 Mbps data transmission and it was marketed by Hewlett-Packard. It was referred to as 100BaseVG, but, because it was incompatible with 10BaseX and Ethernet and, because, it did not actually transmit data at 100 Mbps it quickly sputtered out. Some companies did implement it though and, for this reason, has now been briefly mentioned.
Fiber optic cable transmits data
signals with light pulses rather then electricity making it immune to EMI (Electrical
Magnetic Interference) and RFI (Radio Frequency Interference). Additionally,
unlike copper cabling that cannot reach more then 500 meters without having
to electronically regenerate the signal, fiber optics can achieve data runs
measured in kilometers. It does not create a readable magnetic field like copper
cabling does; a consideration if a network requires a high level of security.
Fiber optic cabling is composed
of either a glass or plastic core surrounded by "cladding" which is more glass
that reflects light back into the core. All of this is wrapped in a Kevlar armor
coating and then sheathed in PVC (more plastic) or plenum. Plenum is a Teflon
based sheath that doesn't produce toxins when it burns.
The most popular connector for
fiber optic cabling is FSMA or Field-installable Subminiature Assembly.
Network connectivity devices are what connect dissimilar network entities to one another. The three most popular are:
This is an expansion card that, when installed on a computer, allows connection from a workstation to the rest of the network. NICs are either built into the mother board or connected through an expansion slot that in turn plugs into a bus that interfaces with the main computer assembly.
This network connectivity device connects multiple, often dissimilar networks into an internetwork. It is responsible for routing network data to its' destination. It bases its' decisions upon performance data it gathers from the network itself.
A gateway is any hardware and software combination that connects dissimilar network environments. They perform translations at multiple layers of the OSI model (Open Systems Interconnect; discussed in detail later).
For instance, an
e-mail gateway allows Microsoft's LAN based e-mail software to communicate with
a UNIX based mail server that uses SMTP (Simple Mail Transfer Protocol).
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