Transcript Net+ Chapter 1 - Del Mar College

SYSTEM ADMINISTRATION
Chapter 11
WAN Technologies
Wide Area Network (WAN)
Technologies
• A wide area network (WAN) is a data
communication network that spans a large
geographic area and usually makes use of
transmission facilities of third-party vendors.
• Third-party vendors are usually referred to as
common carriers.
• WANs are used to interconnect remote locations of
a business operation.
• The functions of WAN technologies are clustered at
the three lowest layers of the OSI Model.
Switching Technologies
• Two types of switching technologies are used with
WAN connections:
– circuit switching
– packet switching
Circuit Switching
• A circuit is a path between two or more
communicating entities and usually refers to the
physical path the data takes.
• Circuits may be pre-reserved, as with a dedicated
connection between two end points.
Virtual Circuits
• Logical circuits represent a path between two points and are
not fixed on one physical path. This is called a virtual circuit.
• Permanent virtual circuits (PVCs) guarantee that a certain
amount of bandwidth will always be available when needed.
• The PVC eliminates the need to reserve a specific path in
advance.
• Switched virtual circuits (SVCs) are dynamically created when
a request for transmission is made and ended when the
transmission is complete. These are good for sporatic traffic.
• Circuit switching is used by the public telephone network
(POTS or PSTN).
• Circuit switching involves some setup time to establish the
circuit, but the time delay is usually not apparent to the user.
Packet Switching
• Packet switching is commonly used for WAN
connections.
• A message will be broken into smaller units called
packets.
• Each packet has a header that contains the source
address, destination address, and a sequence
number. The sequence number is used to
reassemble the message once it reaches the
destination.
• With packet switching, the pieces of the message
(the packets) often take different paths from the
source to the destination.
(continued)
Packet Switching
(continued)
• Once the packets reach the destination, the
message is reassembled using the sequence
numbers in the headers of the packets so the
message can be read by the destination.
• Packet switching involves no circuit setup time. The
transmission is connectionless, so there is no
guarantee of delivery.
• Routers make the decisions about the path a series
of packets will take.
Which Switching Method is
Better?
• Every business must evaluate the types of traffic
that will be transmitted in order to determine which
type of switching method is most suitable.
• Benefits of circuit switching:
o A guaranteed pathway for the data.
o A guaranteed portion of the bandwidth available for
transmission.
o Smaller packets because there is no need to place
source and destination information in the header, only
the circuit number so intervening devices will
recognize which message the packet belongs to.
(continued)
Which Switching Method is Better?
(continued)
• Benefits of packet switching:
o The public infrastructure can be used for data
transmission instead of incurring the expense for
dedicated links between locations.
o Resources, such as bandwidth, are used more fairly
and efficiently in packet switching.
o Pipelining, the ability to simultaneously use a
communication link for 2 or more transmissions,
increases the efficiency of use for the available
bandwidth.
Integrated Services Digital
Network (ISDN)
• ISDN is a cost-effective WAN connection that uses
digital transmission over traditional telephone
networks.
• ISDN uses two types of channels to carry data:
o Bearer Channels (B channels) carry the payload,
which may be voice or data.
o Data channels (D channels) carry the control
information for connection setup, timing, and
disconnection.
(continued)
ISDN
(continued)
• ISDN is offered in two types of interfaces:
o Basic rate interface (BRI) provides two B
channels and one D channel for a total transfer
rate of 128 Kbps.
o Primary rate interface (PRI) allocates twentythree B channels for data and one 64 Kbps D
channel for control information for a total transfer
rate of 1.544 Mbps.
(continued)
ISDN
• The benefits of ISDN include:
o Data capacity to service many users at the same time
o Voice and data transmission over the same physical
media at the same time because one of the two
channels of the BRI can be switched to voice if a call
comes in
o Video conferencing
o Widespread availability
o Cost-effective solution for small businesses and small
office/home office (SOHO) operations
• To implement ISDN on the network, contact the local
telephone service provider.
Fiber Distributed Data Interface
•
•
•
•
FDDI is a set of standards developed by the ISO and
ANSI that provides the guidelines for data transmission
over fiber-optic cable.
FDDI uses a dual counter-rotating ring formation
capable of 100 Mbps token passing.
FDDI internetworks have extremely high capacity, and
so can service thousands of users over great distances
because the data is transmitted over fiber-optic cable.
The two FDDI rings provide data flow in opposite
directions.
(continued)
FDDI
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•
When a portion of the FDDI network fails (a station
or a cable segment), the FDDI network can heal
itself by closing the ring at the gap and allowing
data to be transmitted. This results in little or no
network down time.
•
FDDI and fiber-optic networks are usually used for
backbone deployments because of the expense of
constructing a fiber network. Professionals must
install fiber-optic cable to minimize damage to the
cable and to the installer.
Synchronous Optical
Networks/Synchronous Digital
Hierarchy (SONet/SDH) and
Optical Carrier (OC-x)
• These three technologies have as their common
ground the fiber-optic cable. Because of this
commonality, the three cannot be easily separated
when discussing the technology.
SONet
• SONet defines the standards for optical carrier
levels and synchronous transport signals for the
infrastructure.
• SONet uses multiplexing to use all bandwidth
efficiently for the transmission of data.
• This permits SONet to use low-level digital signals
and a synchronous structure.
(continued)
SONet
• Synchronous structure refers to the transitions of the
digital signals so that they occur at exactly the same
rate. This tells the media and the receiving station
where the 1s and 0s are in the signal.
• A clocking signal provides the constant and even
pulse to keep traffic in line.
• Asynchronous Transfer Mode (ATM) uses SONet
because of its capacity and its ability to use
multiplexing and synchronization.
Synchronous Digital Hierarchy
(SDH)
• SDH was the result of several standards
organizations defining a global synchronization
standard for transmission. SDH unified the various
existing standards for international communication.
The Optical Carrier (OC)
• The optical carrier standards are based on the
synchronous transport signals (STSs) used by
SONet. The STS standards have an equivalent OC
(optical carrier) standard that is expressed by a
numeric indicator.
• The basic building block of OC is based on the STS1, which has a capacity of 51.84 Mbps transmission
speed.
(continued)
The Optical Carrier (OC)
(continued)
• Other examples of OC levels are:
o OC-3: Also called STS-3, this signal transmits at a
line rate of 155.52 Mbps
o OC-12: Also referred to as STS-12, transmission rates
of 622.08 Mbps can be achieved
o OC-48: This is STS-48, with a 2488.32 Mbps rate
o OC-192: At the top of the line, this STS-192 rate is
9953.28 Mbps
Asynchronous Transfer Mode
(ATM)
• Asynchronous transfer mode (ATM) is a WAN
transmission technology that is capable of speeds
ranging from 1.54 Mbps to 622 Mbps.
• ATM uses a switching technology to move high
volumes of data, voice, video, and audio
transmissions between end points.
• ATM is expensive, so it is seldom used for LAN
transmission.
• ATM uses cells instead of packets.
• Each cell is 53 bytes in length. The fixed-sized cell
reduces the overhead for processing the package,
reduces the number of bits needed for error
control, and functions much more efficiently
because of the reduced overhead.
(continued)
ATM
(continued)
• ATM uses virtual circuits between defined end points
and routes, but does not allocate bandwidth ahead
of time (does not pre-reserve bandwidth). This
allows ATM to support several classes of service
and to support transmission of traffic like multimedia
files.
• ATM can be used over fiber-optic cable or some of
the newer, high-capacity copper media.
The Layered Technology of ATM
• ATM functions with several layers:
o At the Physical layer, there are specifications for transmission
media, signal-encoding schemes, data rates, and compatibility.
o At the ATM layer, provisions are made to access services in the
upper layers, packet transfer capabilities, cell size definition, and
logical connection specifications.
o The ATM Adaptation layer (AAL) changes depending on the
service being used. AAL maps higher layer information into the
cells and passes them down to the ATM layer, or it assembles
information from the ATM cells and passes it up to higher layer
technologies.
Virtual Channel Connections (VCCs)
and Virtual Path Connections (VPCs)
• A VCC is a virtual circuit that carries a sequenced,
single flow of cells from end to end.
• VCCs can be statically configured permanent virtual
circuits or dynamically configured switched virtual
circuits.
• A set of VCCs can be bundled together to form a VPC
for transmission. All VCCs that are made part of a
VPC will be transmitted from end to end across the
circuit as a single entity, resulting in reduced
overhead and easier recovery from a failure in the
route.
• A VPC acts like a virtual trunk between two sites.
Frame Relay
• Frame relay is a packet-switching technology that
supports data transport at reasonable cost. Frame
relay uses the public infrastructure of common
carriers to transmit at rates between 56 Kbps and
1.544 Kbps.
• Frame relay uses the “cloud” of common carriers to
span large distances.
• To create a frame relay network, a connection to the
provider must be established. Circuits are purchased
that allow the transmission between each end of each
circuit.
• Frame relay offers both PVCs and SVCs.
(continued)
Frame Relay
• Frame relay requires that a committed information
rate (CIR) be established. This number is the
minimum amount of bandwidth that will always be
available to the circuit.
• Vendors also establish the committed burst rate (Bc),
which identifies how much excess bandwidth a circuit
may use.
• A third rate, called the burst excess rate (Be),
indicates the maximum burst transmission bandwidth
available to the circuit.
• If the network is heavily congested, the vendor has
the option of dropping packets if the transmission rate
exceeds the CIR.
• Frame relay networks are easily scalable because
they require minimal amounts of hardware.
The T-Carrier Connection
• The T-carrier connections refer to the
telecommunications links that provide remote
access for business using the public telephone
infrastructure as the physical media.
• T-carrier solutions are leased line solutions, billed
from the local telephone company.
• T-carrier connections are digital in nature,
eliminating analog to digital conversions and making
them a good choice for data network
interconnection.
(continued)
T-Carrier Connections
(continued)
• T-carrier connections are based on the same
building block as ISDN. A T1 leased line uses 24
channels for a transmission rate of 1.544 Mbps. T3
lines transmit at 44.376 Mbps.
• The signal level determines the speed of the
channel, which is the OSI Model Physical layer
characteristic. The unit of measurement is the data
signal x, or DSx. One data channel is a DS0; twentyfour channels are called a DS1.
• T-carrier connections are always on, making
internetwork communications simple for the users.
(continued)
T-Carrier Connections
(continued)
• T-carrier lines can be purchased in increments.
These increments are called fractional T1 lines.
Each channel transmits at 64 Kbps.
• The European equivalent of the T1 carrier is the E1,
which has a capacity of 2.048 Mbps. The European
equivalent of the T3 line is the E3 line, transmitting
at 34.368 Mbps.
• T-carrier connections require the following hardware:
o CSU/DSU
o Multiplexer