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Networking Technologies

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What’s Technology
 Whereas the topology of a network is the shape of the
network, the technology is the method of putting
information onto the network and controlling it based on
the physical components that are used and how they
operate within the network.
 The Institute of Electrical and Electronics Engineers (IEEE)
developed a set of standards called the 802 project (the
80th year and the second month). These are
 Ethernet
 Token Passing
 Wireless
 FDDI

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Ethernet
 Ethernet is by far the most common
technology in use today.
 The Internet operates using Ethernet
technology.
 defined as 802.3 by the IEEE.
 Ethernet speeds include 3Mbps, 10Mbps,
100Mbps, and 1000Mbps.
 Ethernet uses an access method known as
Carrier Sense Multiple Access with Collision
Detection (CSMA/CD).

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CSMA/CD
 On a network that uses CSMA/CD, when a system wants to send data
to another system, it first checks to see whether the network media is
free.
 It must do this because each piece of network media used in a LAN can
carry only one signal at a time. If the sending node detects that the
media is free, it transmits, and the data is sent to the destination. It
seems simple.
 Unfortunately, in networking, things do not always go as a planned.
The problem arises when two systems attempt to transmit at exactly
the same time.
 Collision detection works by detecting fragments of the transmission on
the network media that result when two systems try to talk at the
same time. The two systems wait for a randomly calculated amount of
time before attempting to transmit again. This amount of time is a
matter of milliseconds known as the backoff.
 When the backoff period has elapsed, the system attempts to transmit
again. If the system doesn't succeed on the second attempt, it keeps
retrying until it gives up and reports an error.

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 The upside of CSMA/CD is that it has relatively low
overhead, meaning that not much is involved in the
workings of the system.
 The downside is that as more systems are added to
the network, more collisions occur, and the network
becomes slower.
 Despite its problems, CSMA/CD is an efficient system.
As a result, rather than replace it with some other
technology, workarounds have been created that
reduce the likelihood of collisions.
 One such strategy is the use of network switches that
create multiple collision domains and therefore
reduce the impact of collisions on performance.

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Pros and Cons
 Advantages
 It has low overhead.
 Utilizes all available bandwidth when possible.
 Disadvantages
 Collisions degrade network performance.
 Priorities cannot be assigned to certain nodes.
 Performance degrades exponentially as devices
are added.

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CSMA/CA
 The carrier-sense multiple access with collision avoidance (CSMA/CA)
access method uses signal avoidance rather than detection.
 On CSMA/CA networks, each computer signals its intent to transmit
data signals before any data is actually sent. When a networked system
detects a potential collision, it waits before sending out the
transmission allowing systems to avoid transmission collisions.
 The CSMA/CA access method uses a random backoff time and waits
before trying to send data on the network. When the backoff time
expires, the system will again "listen" to verify a clear channel on which
to transmit.
 If the media is still busy, another backoff interval is initiated that is less
than the first. The process continues until the wait time reaches zero,
and the media is clear.
 The CSMA/CA access method uses a "listen before talking" strategy.

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Token Passing
 IEEE 802.5 standard
 On a token-passing network, a special packet called a
token is passed among the systems on the network.
 The network has only one token, and a system can
send data only when it has possession of the token.
 When the data arrives, the receiving computer sends
a verification message to the sending computer. The
sender then creates a new token, and the process
begins again.
 Standards dictate how long a system can have
control over the token.

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Pros and Cons
 Adv
 lack of collisions.
 Even under heavy load conditions, the speed of a
token-passing system does not degrade in the
same way as a contention-based method such as
CSMA/CD.
 Disadv
 The creation and passing of the token generate
overhead on the network, which reduces the
maximum speed.
 The software and hardware requirements of
token-passing network technologies are more
complex and therefore more costly.

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MSAU
 The physical layout of a ring network is
altogether different from logical topology.
 Ring networks are most commonly
implemented in a star configuration. In a
Token Ring network, a multistation access
unit (MSAU) is equivalent to a hub or switch
on an Ethernet network is implemented.
 The MSAU performs the token circulation
internally.

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Wireless
 IEEE 802.11 standard
 The 802.11 standard has two common levels:
802.11b and 802.11g.
 The 802.11b standard offers speeds up to
11Mbps, and the 802.11g standard increases
the speed to 54Mbps. Both use an CSMA/CA.
 The media that 802.11 wireless networks use
is the 2.4GHz radio wave band.

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FDDI
 Fiber Distributed Data Interface (FDDI) uses a token-
passing access method and a dual-ring topology.
 The media used by FDDI is typically fiber-optic cable,
but it can also use STP or UTP cable.
 FDDI communicates at a speed of 100 Mbps on
copper wire, but can communicate much faster on
fiber-optic cable.
 To avoid a single break in the ring that could disrupt
network connectivity, FDDI uses a dual-ring
configuration. If one computer or cable is damaged,
the other ring will form a single ring topology.

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Characteristics of Cable Standards
 10Base2
 speeds of 10Mbps
 Baseband signaling
 total segment length of 185 (close to 200) meters
using thin coaxial (thinnet) cable.
 10Base5
 speeds of 10Mbps
 Baseband signaling
 total segment length of 500 meters using thick
coaxial (thicknet) cable.

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 10BASE-T
 The “10” represents the maximum speed of 10Mbps; “BASE”
represents a baseband type of transmission in which only one
signal can be on the wire at any given time; “T” indicates that a
twisted-pair cable was used.
 The maximum length of any network segment using 10BASE-T is
100 meters.
 10BASE-FL
 10BASE-FL uses a fiber-optic cable to transmit the signal rather
than the copper twisted-pair cable.
 The speed of 10BASE-FL was still 10Mbps, but the maximum
transmission length could be up to 20 kilometers! Many of these
networks are still in use today where speed is not a concern but
maximum distance is a factor.

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Fast Ethernet
 Fast Ethernet is the most commonly used network
design.
 It includes
 100BaseTX
 speed up to 100Mbps
 implemented with CAT5 UTP cable
 100 meter distance limitations
 100BaseFX
 speed up to 100Mbps
 uses fiber-optic cable
 412 meters for multimode fiber, 10,000 meters single-mode
fiber.
 uses SC or ST fiber connectors.

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Gigabit Ethernet
 Has the basic 1000BaseX and 1000BaseT standards
 1000BaseX refers collectively to three distinct standards:
1000BaseLX, 1000BaseSX, and 1000BaseCX.
 1000BaseSX and 1000BaseLX are laser standards used
over fiber. LX refers to long wavelength laser, and SX
refers to short wavelength laser. Both the SX and LX wave
lasers can be supported over two types of multimode
fiber-optic cable
 Only LX wave lasers support the use of single-mode fiber.
 1000BaseCX uses shielded copper wire. Segment lengths
in 1000BaseCX are severely restricted; the maximum
cable distance is 25 meters. Because of the restricted
cable lengths, 1000BaseCX networks are not widely
implemented.

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 1000BaseT, sometimes referred to as
1000BaseTX, is another Gigabit Ethernet
standard, over Category 5e/6 UTP cable.
 The standard allows for full-duplex
transmission using the four pairs of twisted
cable. To reach speeds of 1000Mbps over
copper, a data transmission speed of
250Mbps is achieved over each pair of
twisted-pair cable.

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10 Gigabit Ethernet
 The newest and fastest cable standard is the 10G
standard.
 Designed primarily as a WAN and MAN connectivity
medium.
 The 10G standard allows a maximum transmission
speed of 10Gbps in a star topology.
 The 10G standard is currently subdivided into three
standards: 10GBASE-SR, 10GBASE-LR, and
10BASE-ER.
 All of these 10G standards use fiber-optic cable. The
major difference between the standards is the
maximum transmission distance.

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Review
 Recognize the terminology used
when identifying cable standards
 Describe the characteristics of the
100BASE-TX standard.
 Know the characteristics of the
three 10G standards.
 Describe the characteristics of the
1000BASE-SX standard.