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QUESTION 11. The Kingsbury Agreement essentially re-affirmed the idea that AT&T could continue to
operate as a regulated monopoly free from competition.
True
False
10 points
QUESTION 2
1.
Which of the following expanded the digital communications industry to new entrants,
thus beginning the dot.com era?
a.
b.
c.
d.
The Kingsbury Agreement
Telecommunications Act of 1996
The Modified Final Judgment (MFJ)
Hush-a-Phone decision
10 points
QUESTION 3
1. The Cable Communications Policy Act of 1984 addressed a new national policy intended
to encourage greater competition within the CATV industry.
True
False
10 points
QUESTION 4
1. Which act or judgment enabled non-AT&T devices to be attached electrically to the
AT&T telephone network?
a. 1913 Kingsbury Agreement
b. Communications Act of 1934
c. 1956 Hush-a-Phone decision
d. Caterfone decision
10 points
QUESTION 5
1. Which regulatory act created seven Regional Bell Operating Companies
(RBOCs) from 22 former Bell Operating Companies (BOCs)?
a. 1913 Kingsbury Agreement
b. 1956 Hush-a-Phone decision
c. 1982 Modified Final Judgement (MFJ)
d. Telecommunications Act of 1996
10 points
QUESTION 6
1.
The common channel signaling (CCS) system provides a separate network dedicated to
control and signaling over the PSTN. This enables subscribers to establish calls on an
on-demand basis.
True
False
10 points
QUESTION 7
1. Select the correct statement(s) regarding in-band and out-of-band signaling.
a. with out-of-band signaling, control signals take place on the same physical circuits as
the actual data traffic
b. both in-band and out-of-band signaling takes place over the normal data traffic
network
c. both in-band and out-of-band signaling takes place over a dedicated control and
signal network
d. with in-band signaling, control signals take place on the same physical circuits as the
actual data traffic
10 points
QUESTION 8
1.
What is the difference between interLATA and intraLATA calls?
a.
b.
c.
d.
a LATA controls all interLATA calls
interLATA calls must be switched through an IXC facility
only intraLATA calls go through an IGF
interLATA calls go through the Internet
10 points
QUESTION 9
1. An International Gateway Facility (IGF) is a facility responsible for the switching of
all calls regardless of whether the calls are local, national, or international.
True
False
10 points
QUESTION 10
1. What is the importance of NPA?
a. It provides a hierarchical telephone numbering scheme that enables call connection at
the regional and global levels
b. It provides specifications for international IPv4 addressing
c. It is an ITU policy that enhances global competition for telephone services
d. It was the first standards organization which led to the creation of ANSI and OSI
10 points
QUESTION 11
1.
What is CPE?
a. communication devices that reside at the subscriber location but are the responsibility
of the service provider
b. communications processing equipment that reside at the service provider’s central
office
c. subscriber communication devices that connect to the service provider network, but
are owned, operated, and maintained by the subscriber
d. a switching device that provides CENTREX services
10 points
QUESTION 12
1. A PBX switch is considered part of the PSTN and not part of the CPE.
True
False
10 points
QUESTION 13
1.
Select the correct statement(s) regarding a DS0.
a. DSO is a digitized analog signal (i.e., typically supporting a 4kHz bandwidth voice
signal)
b. DSOs are created using PCM techniques that adhere to Nyquist Sampling rates
c. DS0s use a bit-depth of 8 bits per sample
d. all are correct statements
10 points
QUESTION 14
1. A DS0 is a basic 64kbps building block for channelized T-Carrier and SONET standards.
True
False
10 points
QUESTION 15
1. What do T-Carriers, SONET and SDH have in common?
a.
b.
c.
d.
supports 64 DS0s per frame
transmission rates operate at 8000 frames per second
all standards depend upon fiber optic physical layer medium
all are common
10 points
QUESTION 16
1.
How is the Channelized T-1 rate of 1.544 Mbps determined?
a. 64 frames/second * ((24 DS0s/frame * 8 bits/DS0) * 1 FB)
b. 8000 frames/second * ((24 bits/frame) + 1 FB)
c. 8000 frames/second * ((24 DS0s/frame * 8 bits/DS0) + 1 FB)
d. 64 frames/second * ((193 bits/frame * 8 bits/DS0) + 1 FB)
10 points
QUESTION 17
1. Select the correct statement(s) regarding Wide Area Networks (WANs).
a.
b.
c.
d.
WANs operate at the OSI Layer 3 (network layer)
today’s WANs only use IPv4 and IPv6 at the OSI network layer
WANs operate at the OSI Layer 2 (data link layer)
a WAN is a wireless area network, implemented by cellular service providers
10 points
QUESTION 18
1. Select the correct statement(s) regarding Frame Relay (FR).
a. FR is a connectionless standard that operates at the OSI layer 2
b. FR packets are fixed length, therefore transmission delays are predictable
c. FR is a connection oriented variable sized frame standard that operates at the data
link layer
d. all of the statements are correct
10 points
QUESTION 19
1.
Select the correct statements regarding Asynchronous Transfer Mode (ATM):
a. ATM is a variable-length cell standard that supports voice, video and data
b. ATM is connection-oriented
c. ATM is a connectionless network layer protocol similar to IP, in which fixed cell
sizes enable predicable latency and quality-of-service (QoS)
d. a and b are correct statements
10 points
QUESTION 20
1.
ATM over SONET provides high data rate capacities, predictable delays and quality-ofservice; however, both ATM and SONET are complex technologies to implement.
True
False
10 points
QUESTION 21
1. Select the correct statement(s) regarding SONET and SDH.
a. STS describes the SONET electrical signal, while STM describes the SDH electrical
signal
b. OC describes the optical signal on both SONET and SDH
c. An STS-3 equals an STM-1, which is 155.52 Mbps
d. All of the above are correct
10 points
QUESTION 22
1. What is a true statement regarding WDM?
a. WDM is another name for SONET.
b. SONET can be implemented onto one of the wavelengths in a WDM or DWDM
multiplexer.
c. Since WDM and SONET are competing optical signal standards, they cannot be used
together on the same fiber optic cable.
d. There are no true statements above.
10 points
QUESTION 23
1. Wavelength Division Multiplexing (WDM) is used to combine several optical channels
(i.e., wavelengths) into an aggregate broadband signal that is transmitted over a fiber
optic cable.
True
False
10 points
QUESTION 24
1.
Select the correct statement(s) regarding Carrier Ethernet (CE).
a. the Metro Ethernet Forum (MEF) created a CE framework to ensure the
interoperability of service provider CE offerings
b. MEF certifies CE network providers, manufacturers and network professionals to
ensure interoperability and service competencies
c. MEF certified services include E-Line, E-LAN, E-Tree, E-Access, and E-Transit
d. all are correct statements
10 points
QUESTION 25
1.
Select the correct statement(s) regarding the PBX.
a. Organizations using PBXs must have technical expertise on their staffs to operate and
maintain them
b. A PBX can support both analog and digital communications
c. Numerous PBXs can be configured as a distributed network to support organizational
requirements
d. All are correct
10 points
QUESTION 26
1.
Select the correct statement(s) regarding CENTREX.
a. CENTREX systems reside at the service providers central office, however, the
operations and maintenance are still the responsibility of the user organization
b. CENTREX systems reside at the service providers central office, and the operations
and maintenance responsibilities belong to the service provider
c. CENTREX systems offer greater choice to users because the service provider has
better and more sophisticated equipment than single organizations have
d. All are correct
10 points
QUESTION 27
1.
ACDs are considered switching PBXs that employ IVRs and are typically used in call
centers. ACDs can be networked across the PSTN.
True
False
Chapter 6
Local and Personal Area Networks
1
6.1 Introduction
Local area networks (LANs) are comprised of multiple
PCs and servers interconnected to one another through
guided mediums. (e.g., 802.3 Ethernet)
Networks serving a single organization or location
Wireless LAN (WLAN), allows PCs to connect wirelessly
to wired network through access points (APs). (e.g.,
802.11 Wi-Fi)
Wireless Personal Area Networks (WPANs) are smaller
wireless networks (e.g., 802.15 Bluetooth and ZigBee)
2
6.2 Local Area Network Architecture
Physical and logical networks are arranged in mesh, star,
bus, and ring, and hierarchical tree architectures.
The physical topology describes how network devices are
physically connected.
The logical topology describes how connected devices
communicate with one another over the physical topology.
The LAN’s physical and logical topologies may differ from one
another
3
Ex., network devices may be connected in a star topology through a hub
device, but logically communicate to one another as a shared bus topology
6.2 Local Area Network Architecture
4
6.2 Local Area Network Architecture
LANs are built on peer-to-peer (P2P) or client-server
concepts.
P2P network – computers connect directly to one another to
share information.
Client-server – servers provide centralized services and data
storage for clients.
5
No central storage of shared files or applications – multiple copies
can exist
Simple form of network – easily implemented
No centralized access or authentication
Servers provide access to peripheral devices, other networks,
applications and databases, email, storage, and security functions etc.
6.2.1 Centralized and Decentralized Access
Control
Medium Access Control (MAC) – defines the process by
which devices on the network can access the shared
medium
Network Interface Unit (NIU) or Network Interface Card (NIC)
MAC layer procedures can involve centralized or distributed
control model.
OSI RM
Data Link
Physical
802.3
LLC
MAC
Physical
Logical Link Layer (LLC) – handles communication between
upper layers and lower layers
Media Access Control (MAC)
6
Adds control info
Implemented in software (driver sw for Network Interface Card,
NIC)
Preamble generation (if used)
Data encapsulation – framing, addressing, error detection
Implemented in network interface card (NIC) hardware
Provides medium access
6.2.1 Centralized and Decentralized Access
Control
Centralized access control – Centralized controller
determines when the stations can access the shared
medium (polling, tokens) – ex.,Token Ring
Passing of control packets requires additional overhead
Failure of the central controller disrupts the entire network
Deterministic access – node that is granted access has a
guarantee that it can transmit data without collisions
Decentralized (Distributed) access control – Each
station assumes responsibility for controlling its access to
the shared network – ex., Ethernet
7
Non-deterministic access control (aka contentious MAC) –
no guarantees
6.2.1 Centralized and Decentralized Access
Control
With decentralized/distributed access control data
collisions on the shared medium can occur.
Two examples: IEEE 802.3 shared Ethernet requires
CSMA/CD, IEEE 802.11 CSMA/CA
Carrier sense—Each station continuously listens for traffic
Multiple access—Numerous stations share baseband medium
Collision Detect—If two or more stations transmit at the same
time then data frames will collide
8
Jamming Signal – Any node detecting data collision sends jamming signal causing
other nodes to cease activities for a random period of time
Collision Avoidance – stations are proactive in attempting to
prevent collisions
6.2.2 DTE and DCE
The data terminal equipment (DTE) and data
communications equipment (DCE) helps identify
interface characteristics between devices in a network.
DTEs are typically end devices such as terminals, computers,
and servers
DCEs typically describe network equipment such as modems
It is helpful to think of DTEs and DCEs as types of interfaces
vice whole devices, especially considering that many of today’s
devices have both DTE and DCE interface ports.
9
6.2.2 DTE and DCE
Digital FDX – dedicated send and receive paths – typically
used with modems (9, 15, 25, 36 pin connectors)
RS-232 (EIA 232),TIA-232-F (2012), (DB-25 pin connector)
RS-422, RS-423, RS-485
EIA-530, EIA/TIA-561 & 562
TIA-574 (9 pin)
ITU V.24,V.35
ITU X.21, X.25
Many more…
Used with computers and digital networks (e.g.,T-1,
CSU/DSU (channel service unit/data service unit), routers,WAN
interface, fiber optic cables, Ethernet, etc.)
10
6.2.2 DTE and DCE
Twisted Pairs to minimize Crosstalk
RJ-45
RJ-45
1
2
TX+
TX-
TX+
TX-
3
4
RX+
TRD2+
RX+
TRD2+
5
6
TRD2RX-
TRD2RX-
7
8
TRD3+
TRD3-
TRD3+
TRD3-
Note: pins 4, 5, 7, 8 are not used for slower 100BaseT Ethernet (i.e., only
two pairs required). 1000BaseT requires four pairs.
11
6.2.2 DTE and DCE
What happens when both the network
(ex. network switch) and computer
attempt to transmits on the same wired
pair?
Twisted Pairs to minimize Crosstalk
RJ-45
RJ-45
1
2
TX+
TX-
TX+
TX-
3
4
RX+
TRD2+
RX+
TRD2+
5
6
TRD2RX-
TRD2RX-
7
8
TRD3+
TRD3-
TRD3+
TRD3-
Note: pins 4, 5, 7, 8 are not used for slower 100BaseT Ethernet (i.e., only
two pairs required). 1000BaseT requires four pairs.
12
Network
Switch
6.2.2 DTE and DCE
Need a way to distinguish flow of data between the
terminal-side and network-side devices. Describes
interface and direction of data flow.
13
Data Terminal Equipment (DTE) – ex., computers, servers,
etc.
Data Communications Equipment (DCE) – ex., switches,
etc.
6.2.2 DTE and DCE
Twisted Pairs to minimize Crosstalk
DTE
DCE
1
2
TX+
TX-
TX+
TX-
3
4
RX+
TRD2+
RX+
TRD2+
5
6
TRD2RX-
TRD2RX-
7
8
TRD3+
TRD3-
TRD3+
TRD3-
Network
Switch
Note: pins 4, 5, 7, 8 are not used for slower 100BaseT Ethernet (i.e., only
two pairs required). 1000BaseT requires four pairs.
A DTE will transmit data on TX+ & TX-, while the DCE will listen, or receive data on TX+ & TX-.
A DCE will transmit data on RX+ & RX-, while the DTE will listen or receive data on RX+ & RX14
6.2.2 DTE and DCE
Cross-Over Cable
DTE
DTE
1
2
TX+
TX-
TX+
TX-
3
4
RX+
TRD2+
RX+
TRD2+
5
6
TRD2RX-
TRD2RX-
7
8
TRD3+
TRD3-
TRD3+
TRD3-
Note: pins 4, 5, 7, 8 are not used for slower 100BaseT Ethernet (i.e., only
two pairs required). 1000BaseT requires four pairs.
15
6.3 IEEE 802.3 Ethernet LAN
Shared Ethernet – all connected devices receive all
transmitted data frames regardless of whether they are the
intended recipient or not.
Switched Ethernet – devices are connected to a switch. Each
connection is a dedicated link, therefore no data collisions
occur and the need for an algorithm such as CSMA/CD is not
required.
16
A
HUB
2 WIRE, 1 PAIR
HDX
CSMA/CD
B
HUB
C
17
D
HUB
4 WIRE, 2 PAIR
FDX
CSMA/CD
A
TX
B
RX
RX
TX
HUB
RX
TX
RX
TX
C
18
D
SWITCH
4 WIRE, 2 PAIR
FDX
NO COLLISIONS
A
TX
B
RX
RX
TX
RX
TX
RX
TX
C
19
D
6.3.2 Ethernet 802.3 Selected Standards
Ethernet 802.3 describes a family of specifications at Layers 1
& 2 of the OSI RM
E.g., 100BaseT, 1GBaseT, 10Base2, 100BaseFX, 10Broad36 (obsolete)
Decentralized (distributed), Non-determinant access
Shared & HDX Switched Ethernet – CSMA/CD
Switched FDX Ethernet – no collisions
Physical Medium – UTP, Coax., Fiber Optic
Data Link Layer – two sublayers
Medium Access Layer (MAC)
20
48 bit MAC address (NIC) fixed to hardware and manufacturer
Logical Link Layer (LLC)
6.3.2.2 100Base-T
100Base-TX, Fast Ethernet
Cat 5e, 100Mbps theoretical
Configured with hub or switch in center
Half-Duplex over two wire (Cat 5e)
21
1
TX+
2
TX-
3
RX+
6
RX-
100BaseFX over MMF or SMF optic cables
4B5B binary block line coding at 125 Mbaud
Signal
Full-Duplex over four wire (Cat 5e) through an Ethernet
switch
CSMA/CD MAC mechanism
PIN
8B/10B is also common
NRZI (“I for inverted) Line Coding (+v = “0”, -v = “1”)
6.3.2.3 1000Base-T (GbE)
1000Base-T
1Gbps (GbE),
Baseband uses all 8 Cat5e wires (four pairs)
Full-Duplex, 125 Mbaud, over all four pairs (magnetic hybrids)
PAM-5 coded signaling (M=5 levels/symbol at -2, -1, 0, +1, +2)
22
N=2 bits data, one level for FEC (Forward Error Correction)
C(bps) per pair =125Mbaud * 2 = 250 Mbps over each pair
C(bps) total = 250Mbps * 4 = 1Gbps
tx
rx
C(bps) =125Mbaud * 2 =250 Mbps
Hybrid
C(bps) =125Mbaud * 2 =250 Mbps
Hybrid
rx
Hybrid
tx
Hybrid
6.3.2.3 1000Base-T (GbE)
tx
rx
tx
rx
1000Base-T
1Gbps (GbE),
CAT5e
125 Mbaud
Full-Duplex, four pairs
rx
23
C(bps) =125Mbaud * 2 =250 Mbps
Hybrid
tx
C(bps) =125Mbaud * 2 =250 Mbps
tx
Hybrid
rx
Hybrid
tx
Hybrid
PAM-5 (M=5)
tx
rx
rx
N=2 bits
6.3.2.4 10GBase-T
10GBase-T (2006)
10Gbps, Baseband over four pairs Full-Duplex – switched
Ethernet
Cat 6 (600MBaud), Cat 7 (750MBaud) UTP
RJ45, 8 pin modular connectors
PAM-16 coded signaling (M=16 levels per symbol)
N(bits) = log2M = log216 = 4 bits
C (bps) = 750E6 baud * 4 = 3 Gbps
4 * 3 Gbps = 12 Gbps
tx
rx
C(bps) =750E6 baud * 4 = 3Gbps
Hybrid
C(bps) =750E6 baud * 4 = 3Gbps
Hybrid
rx
Hybrid
tx
Hybrid
6.3.2.4 10GBase-T
tx
rx
tx
rx
10GBase-T
10Gbps (GbE),
Cat 6, Cat 7
600 MBaud to
750 MBaud
PAM-16
rx
25
C(bps) =750E6 baud * 4 = 3Gbps
Hybrid
tx
C(bps) =750E6 baud * 4 = 3Gbps
tx
Hybrid
rx
Hybrid
tx
Hybrid
M=16, N=4 bits
tx
rx
rx
6.3.2.5 Ethernet and Fiber Optics
Single mode fiber (SMF) and multimode fiber (MMF)
optic cables are popular due to decreasing costs of
optical transceivers and fiber cables.
The 802.3 standard includes several versions using either
SMF or MMF.
Example: -100BASE-FX: “FX” indicates fiber optic cable,
baseband signaling in either half-duplex (HDX) or fullduplex (FDX) modes.
26
Transceivers perform optical-electrical-optical (OEO)
conversions
Star configuration
SMF cables extends this distance to 10 km.
4B5B encoding and NRZI line coding methods
6.4 IEEE 802.11 Wireless LAN
IEEE 802.11 wireless local area network (WLAN)
consists of a family of WLAN specifications that have
technically evolved over time.
ISM (Industrial, Scientific, and Medical) – frequencies
in the 2.4GHz (2.4 GHz to 2.5GHz) and 5GHz (5.725
GHz to 5.875 GHz) bands – no licensing.
Interference issues with other devices (e.g., home security
cameras, baby monitors, cordless phones, garage door openers,
nearby microwave ovens, other WLAN networks, etc. )
Technical innovations introduced to decrease interference
issues.
27
6.4.1 IEEE 802.11 Physical Architecture
Shared wireless channels contend with radio
frequency interference (RFI).
To limit the impact:
28
direct sequence spread spectrum (DSSS) and orthogonal
frequency division multiplexing (OFDM) techniques were
adopted.
Both spread the signal across a wider frequency band, thus
reducing the impact of any narrow band RFI.
OFDM is not considered a spread spectrum technique
6.4.1 IEEE 802.11 Physical Architecture
802.11 WLANs
operate half-duplex over unlicensed ISM band
Centralized or distributed/decentralized access process.
Peer-to-peer (P2P) mode (aka ad hoc) – no
centralized processes or servers
Access Point (AP) – client/server network that
operates as a centralized or decentralized wireless
network
29
nodes can connect to one another, as well as to a wired
network that provides services (e.g., servers and gateways)
and connectivity to external networks (e.g., Internet)
6.4.1 IEEE 802.11 Physical Architecture
Figure 6.10. IEEE 802.11 Wireless LAN with Access Point (AP) interfacing the
wireless access to the network backbone.
30
6.4.2 IEEE 802.11 Data Link Layer
Two fundamental MAC techniques: Distributed coordination
function (DCF) and point coordination function (PCF)
1. Distributed Coordination Function (DCF) – distributed
access method that provides contention-based algorithms such
as CSMA/CA
31
Frame Exchange Protocol – a station wishing to transmit:
Listens to the channel and if idle it transmits
If channel is busy, then station waits a random period of time
Receipt of a successful transmissions require a receiver
acknowledgment (ACK).
If ACK not received, then retransmission takes place.
6.4.2 IEEE 802.11 Data Link Layer
Figure 6.13. Frame Exchange Protocol. In this 802.11 network, nodes “A”,
“B,” and “C” are within reception reach of one another. When data is
transmitted by “A” to “B,” node “C” remains silent until transmission had been
completed and acknowledged.
32
6.4.2 IEEE 802.11 Data Link Layer
DCF frame exchange protocol assumes all stations within
the WLAN are able to receive transmissions and ACKs
from all other stations.
However, if some stations are unable to detect another
station’s transmissions due to environmental or
propagation characteristics, then a data collision could
still occur.
This is called the hidden node problem, in which two
nodes within the WLAN are unable to receive the other’s
transmissions due to distance or RF obstacle.
33
6.4.2 IEEE 802.11 Data Link Layer
Figure 6.14. Hidden Node Problem using the Frame Exchange Protocol. In this 802.11 network,
nodes “A” and “B,” and “B” and “C” can communicate wirelessly; however, “A” and “C” are not
within reception range of one another. “A” decides that the channel is clear, and sends data to
“B”. “C” does not hear “A’s” transmission, and decides to transmit to “B” being unaware of “A’s”
transmission on the same channel. As a result, both transmissions interfere with one another at
node “B”.
34
6.4.2 IEEE 802.11 Data Link Layer
The four frame exchange protocol can be used to
resolve the hidden node problem.
Stations are given the ability to reserve channel time
The transmit station sends an RTS frame (i.e., reservation time
frame).
Stations within reception range becomes aware request and
waits
The receiving station responds with a CTS frame that repeats
the time duration needed.
35
Stations within the receiving node’s range, even if hidden from the
transmitting node, becomes aware of the request and waits.
The four frame exchange protocol is an optional feature that can
be invoked.
6.4.2 IEEE 802.11 Data Link Layer
Figure 6.15. Four Frame Exchange Protocol. As in fig. 6.12, nodes “A” and “C” are not within
reception range of one another. To solve the hidden node problem, “A” sends an RTS to “B” that
contains a reservation time but no data. “B” responds with a CTS that repeats the reservation
time request, that both “A” and “C” receive. Although “C” never received the “A’s” original RTS,
it does receive “B’s” CTS, which lets “C” know that a transmission between “A” and “B” are about
to occur.
36
6.4.2 IEEE 802.11 Data Link Layer
2. Point coordination function (PCF) is an optional
extension that provides a centralized access process.
Both DCF contention-based access and PCF contention-free
access work together within a super frame.
37
Superframe divided between DCF period and PCF or contentionfree (CF) time period.
PCF requires a centralized access point coordinator (i.e., base
station) to poll stations from a prioritized list.
6.4.3 WLAN Security
WLAN security risks – unguided medium & ISM
frequencies.
In 1997, 802.11 adopted wired equivalent privacy
(WEP) to encrypt communications.
A 64-bit (or 128-bit) WEP key
In 2001 weaknesses discovered in the WEP algorithm
In 2004, The Wi-Fi Alliance began work on two standards,
WPA (Wi-Fi protected access) and WPA2
38
WPA was an intermediate solution that worked with older AP
devices.
WPA2 provided better security, but required hardware and
firmware upgrades
6.4.4.1 IEEE 802.11a
IEEE 802.11a operated in the 5.8 GHz ISM band but was
not widely accepted by manufacturers due to the
unavailability of 5.8 GHz chip sets.
Up to 54 Mbps (theoretical signaling rate)
Coded orthogonal frequency division multiplexing (COFDM).
The OFDM subcarriers used BPSK, QPSK, 16QAM, and 64QAM
modulation techniques.
Note: Coded OFDM is a combination of FEC and OFDM. COFDM has greater immunity to
multipath and impulse noise, and like OFDM, offers high spectral efficiency.
39
6.4.4.2 IEEE 802.11b
IEEE 802.11b, released the same year, operated in the 2.4
GHz band. It was appealing since chip sets were more readily
available.
40
Theoretical throughput is 11 Mbps
Adopted a direct sequence spread spectrum (DSSS) technique called
complimentary code keying (CCK)
Modulation techniques: differential BPSK (DBPSK) at 5.5 Mbps,
and differential QPSK (DQPSK), at 11 Mbps.
Wider appeal, but adoption was difficult for manufacturers to comply
with, thus leading to incompatibility.
In response six manufacturers, Intersil, 3Com, Nokia, Aironet (now
part of Cisco), Symbol, and Lucent created the Wireless Ethernet
Compatibility Alliance (WECA) in 1999 to create a simpler
standard.
Eventually renamed the Wi-Fi Alliance.
6.4.4.3 IEEE 802.11g
IEEE 802.11g, was released in 2003 and incorporated
technologies from both 802.11a and 802.11b.
The committee adopted the 2.4 GHz frequency from 802.11b,
and selected the OFDM concept from 802.11a, using fortyeight 20 MHz wide subcarriers.
802.11g is backward compatible with 802.11b:
41
This facilitated device transition during upgrade.
The new standard needed to support both OFDM as well as
802.11b’s CCK signal spreading technique.
Today 802.11g is widely used – provide throughput from 6 Mbps to 54
Mbps.
6.4.4.4 IEEE 802.11n
IEEE 802.11n was released in 2009 as a way to meet user
demands for higher throughput. Both 2.4 GHz and 5 GHz
frequency bands used.
OFDM subcarrier bandwidth increased from 20 MHz to 40 MHz.
Backward compatibility – 802.11b and 802.11g (20 MHz subcarriers
and 802.11b DSSS CCK supported)
Multiple input multiple output (MIMO) spatially diversified
antennas – major enhancement
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Doubled the signaling rate and data throughput to 300 Mbps.
enabled multiple parallel streams of data between antennas – greater data
throughput
superior handling of multipath fading and noise
Ability to aggregate several MAC frames together – allows larger size
data packets to be sent with less delay between frame.
6.4.4.5 IEEE 802.11ac
IEEE 802.11ac approved in 2013. Provides 1 Gbps and
adopts 802.11n’s MIMO antenna architecture.
Operates primarily on the 5 GHz band.
Operating bandwidth was increased to 80 MHz, with an
option to expand to 160 MHz per wireless station.
This is a sizable increase from the 40MHz bandwidth
associated with 802.11n.
M’ary modulation improved, enabling 256-QAM (M=256),
compared to 802.11n 64-QAM (M=64).
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6.5 IEEE 802.15 Personal Area Network
(WPAN)
WPAN specifically designed to connect devices in a noninfrastructure, ad hoc and short duration manner.
E.g., smartphones, peripheral devices, head sets & speakers , etc.
Three major goals:
1.
2.
3.
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Short-range real-time wireless voice and data connectivity
between devices
Wireless connection to computer peripheral devices,
Ability to form ad hoc networks between WPAN devices
6.5 IEEE 802.15 Personal Area Network
(WPAN)
IEEE 802.15.1 (2005), Bluetooth
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Unlicensed ISM 2.4 GHz band frequency
Centralized Access determined by master node
Frequency hopping spread spectrum (FHSS)
shared pseudorandom hop sequence – Transmission
bandwidth consists of 79, 1 MHz wide channels between
2.402 GHz and 2.480 GHz, with a frequency hopping rate
of 1600 hops/s.
Bluetooth methods described as FH-TDD-TDMA
(frequency hopping—time division duplex—time division
multiple access).
6.5.2 802.15.4 ZigBee
IEEE 802.15.4 standard called ZigBee was created by the
ZigBee Alliance of consortium companies, which was
established in 2002.
802.15.4 was developed as a simpler standard designed to
operate at lower data rates (20 kbps to 250 kbps) with less
transmit power.
The intent was to make ZigBee easier to implement and to
extend device battery life.
ZigBee operates in the ISM 2.4 GHz band and allows
connected devices to “sleep” when not in use, thus helping to
conserve overall battery life.
ZigBee standard for fast wake-up time is on the order of 30 ms or
less, compared to Bluetooth which requires devices to wake up
within 3 s.
ZigBee can use the 868/915 MHz band to deliver data rates
between 20 and 40 kbps.
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Back up
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