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Week Thirteen Agenda
Attendance
Announcements
Final Exam composition
Franklin Live presentation
Mimic Simulator Lab Assignment 4-1-3
Review Week Eleven Information
Current Week Information
Upcoming Assignments
Final Exam Composition
Drawings
• IP Address Assignment in an Enterprise Network
Questions asked: 11 Answer correctly: 10
• Routing in the Enterprise Architecture
Questions asked: 6
Answer correctly: 5
• Dual-stacking
Questions asked: 3
Answer correctly: 2
• Loop Free Path
Questions asked: 1
Answer correctly: 1
• Telephone and Internet Paths
Questions asked: 8
Answer correctly: 7
Final Exam Composition
True/False questions: 100
Multiple choice questions: 25
Drawing questions: 25
Total points: 150
Week Eleven Topics
Review Week Ten Information
CODEC
Current Week Information
Definition of CODEC
A codec is a device or computer program
capable of encoding and/or decoding a digital
data stream or signal. The word codec is a
portmanteau of 'compressor-decompressor' or,
more commonly, 'coder-decoder‘.
Voice Coding and Compression
CODEC
• A DSP (Digital Signal Processor is a hardware component that
converts the analog signal to digital format
• Codecs are software drivers that are used to encode the speech
in a compact enough form that they can be sent in real time
across a network using the bandwidth available
• Codecs are implemented within a DSP
• VoIP software or hardware may give you the option to specify
the codecs you prefer to use
• This allows you to make a choice between voice quality and
network bandwidth usage, which might be necessary if you
want to allow multiple simultaneous calls to be held using an
ordinary broadband connection
Coding and Compression Algorithm
• The different codecs provide a certain quality of
speech
• Advances in technology have greatly improved the
quality of compressed voice and have resulted in a
variety of coding and compression algorithms
• PCM: The toll quality voice expected from the PSTN.
PCM runs at 64 kbps and provides no compression,
and therefore no opportunity for bandwidth savings
• The other algorithms use compression to save
bandwidth
• Voice quality is affected
Which CODEC is most affective?
G.729 is the recommended voice codec for most WAN
networks (that do not do multiple encodings) because of its
relatively low bandwidth requirements and high mean
opinion score (MOS) (ITU-T P.800)
Reducing the Amount of Voice Traffic
• The codecs chosen are a trade-off between
bandwidth and voice quality
• Technique used to reduce voice traffic:
cRTP
cRTP
• Every IP packet consists of a header and the
payload (data, voice)
• Although the payload of a voice packet is
small (20 bytes when G.729 is used), the
header is 40 bytes
• cRTP compresses the header to 2 or 4 bytes
• Use on slow WAN links, but it is CPU
intensive
VAD
Voice Activity Detection
• On average, about 35 percent of calls are silence
• In traditional voice networks, all voice calls use a
fixed bandwidth of 64 kbps regardless of how much
of the conversation is speech and how much is silence
• When VoIP is used, this silence is packetized along
with the conversation.
• VAD suppresses packets of silence, so instead of
sending IP packets of silence, only IP packets of
conversation are sent
• Therefore, gateways can interleave data traffic with
actual voice conversation traffic, resulting in more
effective use of the network bandwidth
CAC –Call Admission Control
• CAC protects voice traffic from being
negatively affected by other voice traffic by
keeping excess voice traffic off the network.
• If a WAN link is fully utilized with voice
traffic then adding more voice calls will
degrade all the calls
• CAC checks if the link is maximized and
won’t allow new calls to go through until
bandwidth is available
• Callers will get a busy signal or “all circuits
busy message”
CAC
LFI
Link fragmentation
and interleaving
ensures that small
voice packets don’t
get stuck behind a
large data packet
The data packets are
fragmented into
smaller packets
The voice packets can
slip in between them
because the are
initially small.
Wrieless Technology
Wireless Technologies
• MMDS = Multichannel multipoint distribution
services used for general purpose broadband
networking. United States
• LMDS = Local multipoint distribution service
used for wireless cable television (TV),
referring to premium wireless subscription TV
rather than traditional free broadcast TV or
cable TV.
Wireless Technologies
• GSM = Global system for mobile
communication is a cellular phone protocol.
Used in many part of the world.
• GPRS = General packet radio service is a radio
technology for GSM networks. Europe and
Asia. Not related to GPS
• CDMA = Code division multiple access is a
cellular phone protocol used for digital
communication. United States
What is RF?
• Radio frequency is a term that refers to alternating
current (AC) having characteristics such that, if the
current is input to an antenna, an electromagnetic
(EM) field is generated suitable for wireless
broadcasting and/or communications.
• Frequencies of electromagnetic radiation in the range
between 10 kHz and 300 MHz.
• Many types of wireless devices make use of RF
fields. Cordless and cellular phone , radio and
television broadcast stations, satellite
communications systems, and two-way radio services
all operate in the RF spectrum.
Phenomena Affecting RF
• Reflection: Occurs when the RF signal bounces off objects
such as metal or glass surfaces.
• Refraction: Occurs when the RF signal passes through objects
such as glass surfaces and changes direction.
• Absorption: Occurs when an object, such as a wall or
furniture, absorbs the RF signal.
• Scattering: Occurs when an RF wave strikes an uneven surface
and reflects in many directions. Scattering also occurs when an
RF wave travels through a medium that consists of objects that
are much smaller than the signal’s wavelength, such as heavy
dust.
• Diffraction: Occurs when an RF wave strikes sharp edges,
such as external corners of buildings, which bend the signal.
• Multipath: Occurs when an RF signal has more than one path
between the sender and receiver. The multiple signals at the
receiver might result in a distorted, low-quality signal.
Phenomena Affecting RF
Power Consumption by WLANs
• WLANs transmit signals just as radio stations
do to reach their listeners
• The transmit power levels for WLANs are in
milliwatts (mW), whereas for radio stations the
power levels are in megawatts (MW)
• The amount of power that can be used in
WLANs is set by the FCC
• Wireless LANs operate in the unlicensed
frequency bands, which is why they operate at
very low power levels
WLAN Standard Summary
Wireless LANs
• 802.11 wireless LANs extend the 802.3 Ethernet LAN
infrastructures to provide additional connectivity options.
• In an 802.3 Ethernet LAN, each client has a cable that
connects the client NIC to a switch.
• The switch is the point where the client gains access to the
network.
• In a wireless LAN, each client uses a wireless adapter to gain
access to the network through a wireless device such as a
wireless router or access point.
• The wireless adapter in the client communicates with the
wireless router or access point using RF signals.
• Once connected to the network, wireless clients can access
network resources just as if they were wired to the network.
Wireless LANs
Wireless LAN Standard
802.11 wireless LAN is an IEEE standard that
defines how radio frequency (RF) in the
unlicensed industrial, scientific, and medical
(ISM) frequency bands is used for the physical
layer and the MAC sub-layer of wireless links.
Data Rate:
802.11: 1 -2 Mb/s data rates
802.11a and g: support up to 54 Mb/s,
802.11b: supports up to a maximum of 11
Mb/s
802.11n: Up to 500 Mb/s.
Wireless LAN Standard
Modulation technique:
Direct Sequence Spread Spectrum (DSSS)
802.11b, 802.11g
Orthogonal Frequency Division
Multiplexing (OFDM).
802.11a, 802.11g, 802.11n
Band:
2.4 GHz:
802.11b, 802.11g, 802.11n
5 GHz:
802.11a, 802.11n
Wireless LAN Standard
Wireless LAN Standard
IEEE 802.11a
802.11a
OFDM modulation and uses the 5 GHz band.
Less likely to experience interference than devices that operate in
the 2.4 GHz band
Because there are fewer consumer devices that use the 5 GHz band.
There are some important disadvantages to using the 5 GHz band.
The first is that higher frequency radio waves are more easily
absorbed by obstacles such as walls, making 802.11a susceptible to
poor performance due to obstructions.
The second is that this higher frequency band has slightly poorer
range than either 802.11b or g.
Also, some countries, including Russia, do not permit the use of the
5 GHz band, which may continue to curtail its deployment.
IEEE 802.11n
802.11n
The IEEE 802.11n standard is intended to improve WLAN
data rates and range without requiring additional power or RF
band allocation.
802.11n uses multiple radios and antennas at endpoints, each
broadcasting on the same frequency to establish multiple
streams.
The multiple input/multiple output (MIMO) technology splits
a high data-rate stream into multiple lower rate streams and
broadcasts them simultaneously over the available radios and
antennae.
This allows for a theoretical maximum data rate of 248 Mb/s
using two streams.
The standard is now ratified
IEEE 802.11n
Operates in the 2.4 GHz band or in the 5 GHz band
The 2.4GHz band is more crowded with interference
from lots of other devices and 802.11g networks
The 5GHz band is less crowded but the range is less
Terminology:
• A “dual-frequency” or “dual-band” AP allows you to
select which band 2.4GHz or 5 GHz
• A “dual-radio” AP allows the AP to operate at both
frequencies
• You can allows your old 802.11g clients to connect
on the 2.4 GHz band and your new 802.11n clients to
connect on the 5GHz band
Wi-Fi Certification
The 3 key organizations influencing WLAN standards are:
• ITU-R
ITU-R regulates allocation of RF bands.
The ITU-R regulates the allocation of the RF spectrum.
• IEEE
IEEE specifies how RF is modulated to carry information.
The IEEE developed and maintains the standards for local
and metropolitan area networks. The dominant
standards in the IEEE 802 are 802.3 Ethernet, and 802.11
Wireless LAN
Wi-Fi Certification
• Wi-Fi Alliance (www.wi-fi.org)
Wi-Fi ensures that vendors make devices
that are interoperable.
The Wi-Fi Alliance is to improve the
interoperability of products by certifying
vendors for conformance to industry
norms and adherence to standards.
Certification includes all three IEEE 802.11
RF technologies, as well as early adoption
of pending IEEE drafts, such as 802.11n,
and the WPA and WPA2security standards
based on IEEE 802.11i.
802.11g and n (2.4GHz)
Although there are 11 channels, these channels overlap each other
You can have only use three APs in close proximity without
interference.
The APS will operate on channels 1, 6 and 11
802.11a and n (5GHz)
• Twelve separate non-overlapping channels
• As a result, you can have up to twelve access points set to different
channels in the same area without them interfering with each other.
• This makes access point channel assignment much easier and
significantly increases the throughput the wireless LAN can deliver
within a given area.
• In addition, RF interference is much less likely because of the lesscrowded 5 GHz band.
Wireless NICs
• The device that makes a client station capable of sending and
receiving RF signals is the wireless NIC.
• Like an Ethernet NIC, the wireless NIC, using the modulation
technique it is configured to use, encodes a data stream onto
an RF signal.
• Wireless NICs are most often associated with mobile devices,
such as laptop computers.
• In the 1990s , wireless NICs for laptops were cards that
slipped into the PCMCIA slot.
• PCMCIA wireless NICs are still common, but many
manufacturers have begun building the wireless NIC right into
the laptop.
• Unlike 802.3 Ethernet interfaces built into PCs, the wireless
NIC is not visible, because there is no requirement to connect
a cable to it.
Wireless NICs
Other options have emerged over the years as well. Desktops located
in an existing, non-wired facility can have a wireless PCI NIC
installed.
To quickly set up a PC, mobile or desktop, with a wireless NIC, there
are many USB options available as well.
Wireless Access Point (AP)
• An access point connects wireless clients (or stations)
to the wired LAN.
• An access point is a Layer 2 device that functions like
an 802.3 Ethernet hub.
• Client devices do not typically communicate directly
with each other; they communicate with the AP.
• In essence, an access point converts the TCP/IP data
packets from their 802.11 frame encapsulation format
in the air to the 802.3 Ethernet frame format on the
wired Ethernet network.
Wireless Access Point (AP)
Access Point’s Coverage Area
WLAN Operation
• The coverage area of an AP is called the Basic
Service Set (BSS). Otherwise known as a cell.
• A Service Set Identifier (SSID) is an identifier
name for a WLAN.
• Roaming occurs when a wireless client moves
from being associated to one AP to another AP.
Basically, moving from one cell to another cell
within the same SSID.
Mobility in a LAN
WLAN Security
• Authentication: Only legitimate clients are
allowed to access the network via trusted APs.
• Encryption: Securing the confidentiality of
transmitted data.
• Intrusion detection and intrusion protection:
Monitors, detects, and reduces unauthorized
access and attacks against the network.
Wireless Network Technologies
• Personal-area network (PAN): A persons
personal workspace.
• Local-area network (WLAN): A network
design to be enterprise-based network that
allows the use of complete suites of enterprise
applications, without wires.
• Metropolitan-area network (MAN): Deployed
inside a metropolitan area, allowing wireless
connectivity throughout an urban area.
• Wide-area network (WAN): A wider but
slower area of coverage, such as rural areas.
Autonomous AP
• Originally in WLANs, all of the configurations
and management was done on each access
point
• This type of access point was a stand-alone
device
• The term for this is a fat AP, standalone AP,
intelligent AP, or, most commonly, an
autonomous AP
• All encryption and decryption mechanisms and
MAC layer mechanisms also operate within
the autonomous AP
Autonomous AP
Autonomous AP require power in not traditional
places.
Two solutions:
1. Power of Ethernet (PoE) and power
injectors. This power is inline with the
Ethernet port, over the Category 5 coble.
2. Midspan power injectors is a stand alone
unit, positioned into the LAN between the
Ethernet switch and the device requiring
power.
Autonomous AP
• IEEE 802.1X is used for wireless client
authentication, dynamic encryption keys can
be distributed to each user, each time that user
authenticates on the network. Wi-Fi Alliance
also introduced Wi-Fi Protection Access
(WPA) to enhance encryption and protect
against all known WEP key vulnerabilities.
The Wi-Fi Alliance interoperable
implementation of 802.11i with AES is called
WPA2.
Autonomous AP
The autonomous AP acts as an 802.1Q
translational bridge and is responsible for
putting the wireless client RF traffic into the
appropriate local VLAN on the wired network.
Draw Autonomous AP / Traffic into VLANs.
Designing a Wireless Networks
RF Site Survey is used for many reasons in a
wireless network design, and the process to
conduct such a survey.
It is the first step in the design and deployment
of a wireless network and the one to insure
desired operation.
Designing a Wireless Networks
The survey is used to study the following facility
areas:
• To understand the RF characteristics in the
environment.
• Plans and reviews RF coverage areas.
• Check for RF interference.
• Determine the appropriate placement of wireless
infrastructure devices.
Designing a Wireless Networks
In a wireless network, issues could prevent the
RF signal from reaching many parts of the
facility. To address these issues , these regions
where signal strength is weak, they must be
found.
Designing a Wireless Networks
RF Site Survey Process
1. Define customer requirements number and
types to support devices.
2. Identify coverage areas and user density
facility diagram, and do a visual inspection.
3. Determine preliminary AP locations existing
power, cabling, cell coverage and overlap.
4. Perform the actual survey actual AP locations
after installation.
5. Document the findings record device
locations and signal readings (baseline).
Designing a Wireless Networks
Graphical heat map helps identify and
visualize anticipated WLAN behavior for
easier planning and faster rollout. A heat map
diagrammatically represents signal strength.
The warmer the color, the stronger the signal.
Upcoming Deadlines
• Assignment 1-4-3 Data Center Design Project
Phase 3: Data Center Network Design is due
July 26.
• Assignement 13-1 Concept Questions 10 is
due July 26
• Assignement 1-4-4 Final Design Document is
due August 2.
• Final Exam August 2 - 7