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QUESTION 11. What best describes “broadband access”?
a. broadband access is a specific term used to describe the delivery of one-way television
programming to subscribers
b. broadband access describes any digital network that supports 1 Gbps or greater bit rates
c. broadband access describes technical methods that enable users to connect to high speed
networks
d. broadband access is a term only applicable to analog television programming
10 points
QUESTION 2
1. What are some ways to accomplish full-duplex (FDX) digital communications on guided
medium at the physical layer (OSI Layer 1)?
a. separate receive and transmit paths using separate physical mediums
b. separate digital signals by using separate time slots – does not work for analog signals
c. separate receive and transmit paths by modulating each at different carrier frequencies
d. all of the above are ways to accomplish FDX
10 points
QUESTION 3
1. ____________ is a broadband access method that depends upon fiber optic cables.
a. PONS
b. CATV
c. ADSL
d. WLL
10 points
QUESTION 4
1. ____________ is a broadband access method based upon a shared medium, which initially
experienced security and privacy issues.
a. PONS
b. CATV
c. ADSL
d. WLL
10 points
QUESTION 5
1. Which technologies are used with ADSL?
a. OFDM, TDD (time division duplexing)
b. OFDM, M’ary modulation
c. M’ary modulation, WDM
d. WDM, WLL
10 points
QUESTION 6
1. Which technology is used with asymmetric DSL (ADSL)?
a. time division multiplexing (TDM)
b. frequency division multiplexing (FDM)
c. orthogonal frequency division multiplexing (OFDM)
d. direst sequence spread spectrum (DSSS)
10 points
QUESTION 7
1. Since attenuation over UTP lines are a major concern, ADSL near-end crosstalk (NEXT) is of
greater concern than far-end crosstalk (FEXT).
True
False
10 points
QUESTION 8
1. What statement(s) are correct regarding Discrete MultiTone (DMT)?
a. DMT describes a technique used to enable wireless BWA
b. DMT is a modulation method used for broadband access over coaxial cable networks
c. DMT describes the use of OFDM to enable ADSL
d. all statements are correct
10 points
QUESTION 9
1. ADSL supports both analog voice calls and digital communications simultaneously.
True
False
10 points
QUESTION 10
1. What is true about dynamic rate adaptive modems used in ADSL.
a. these modems can sense line conditions and adjust “M” as required
b. these modems can sense line conditions and move communications away from noise
impacted subcarrier channels
c. these types of modems are used on ADSL links
d. all of the above are true
10 points
QUESTION 11
1.
Why was DOCSIS important for the CATV industry?
a. it helped to standardize the industry
b. it allowed several large CATV corporations to operate as a regulated monopoly
c. it merged the CATV and telephone industries
d. all of the above
10 points
QUESTION 12
1. Because CATV DOCSIS uses OFDM, there is no need to use modulation methods such as
QPSK or QAM.
True
False
10 points
QUESTION 13
1. The Passive Optical Network (PON) standard does not require active components such as
repeaters or amplifiers to be used between the subscriber to service provider network.
True
False
10 points
QUESTION 14
1.
Select the correct statement(s) regarding Passive Optical Networks (PONs).
a. PONS does not require the use of active amplification between the CO to the subscriber
b. PONS operates over SMF optical cables
c. PONS uses passive splitters to distribute signals to subscribers
d. the PONS ONT located at the subscribers location is owned and operated by the service
provider
e. all statements are correct
10 points
QUESTION 15
1. Select the correct statement(s) regarding PONS.
a. only MMF cables can be used, since MMF enables greater data capacities compared to
SMF
b. PONS systems require active amplifiers, since high frequency signals attenuate quickly
over distance
c. PONS systems use passive devices between OLT and ONT
d. all are correct statements
10 points
QUESTION 16
1. IEEE 802.16 WiMAX BWA, also known as fixed wireless access, is an alternative to the
guided local loop. In many cases, BWA can be implemented more quickly than its guided
medium counterparts. However, frequency licensing through regulatory agencies and signal
interference can be major challenges.
True
False
10 points
QUESTION 17
1. Select the correct statement(s) regarding IEEE 802.16 WiMAX BWA.
a. WiMAX BWA describes both 4G Mobile WiMAX and fixed WiMax
b. DSSS and CDMA are fundamental technologies used with WiMAX BWA
c. OFDM is implemented to increase spectral efficiency and to improve noise performance
d. all of the statements are correct
10 points
QUESTION 18
1.
Free space optics (FSO) are considered a wireless local loop (WLL) capability.
True
False
10 points
QUESTION 19
1.
What standard enables broadband access over traditional PSTN local loop lines?
a. ADSL
b. WLL
c. PONs
d. CATV
10 points
QUESTION 20
1. What standard enables broadband access over SMF?
a. ADSL
b. WLL
c. PONs
d. CATV
IT 300 Modern Telecommunications
Dr. Riki Y. Morikawa
1
Lecture 7
Networks
2
Networks
Public Switched Telephone Network
Public Switched Telephone Network (PSTN) – aka Plain Old
Telephone Network (POTS):
Started as an all analog telephone voice network
Today the PSTN infrastructure is mostly digital
In most cases, provides the infrastructure to support WANs and
MANs, Internet
Provides user digital access to networks such as the Internet (..other
access methods through satellite, CATV, cellular, etc.)
Wide Area Networks (WAN):
3
Extends telecommunications over a large geographic area
Connects smaller networks such as several Local Area Networks
(LANs) and Metropolitan Area Networks (MANs) together
Digital network
Networks
Public Switched Telephone Network – A bit of History
1876 –Alexander Graham Bell demonstrates the first telephone
1877 – The Bell Telephone Company created
1885 – American Telegraph and Telephone (AT&T) – subsidiary of the Bell
System,
long distance telephone network
1913 – The Kingsbury Agreement
The Wilson administration considers anti-trust proceedings
Mr. Kingsbury (AT&T vice president) agrees to stop acquisition of other
telcos
Interpreted as an agreement to allow AT&T to function as a regulated
monopoly from 1913 to 1984.
March 3, 1847 – August 2, 1922
4
Networks
Public Switched Telephone Network – A bit of History
Congress passed the Communications Act of 1934, Federal
Communications Commission (FCC) was established
1956 Hush-a-Phone decision
Challenged by AT&T, reaffirmed by the FCC
U.S. Court of Appeals in DC reversed decision – allowed devices not
manufactured by AT&T to be attached mechanically to telephones.
The restriction against interconnecting to AT&T’s network
challenged in 1965 and lifted in 1968 through the Carterfone
decision
5
1968, the FCC “Carterfone” decision
http://www.textually.org/textually/ar
chives/images/set2/hush-a-phonead.gif
Networks
Public Switched Telephone Network – A bit of History
In 1969, Microwave Communications International (MCI)
began carrying business phone calls over microwave links.
1973: MCI begins to meet with DOJ to discuss AT&T
Nov 20, 1974 DOJ files antitrust suit against AT&T
1982 – The Modified Final Judgment (MFJ) – The Justice
Department’s primary goal for breaking up AT&T was to
spur innovation and competition
6
1984, Jan 1 Divestiture took place
22 former Bell Operating Companies (BOCs) were reorganized
into seven Regional Bell Operating Companies (RBOCs). (aka
Regional Holding Companies (RHCs))
Networks
Public Switched Telephone Network – A bit of History
FCC Telecommunications Act of 1996 – convergence
of data networking
7
Allowed new entrants into the telecommunications market
(i.e., dot.com era)
Bells were allowed to offer long-distance and Internet
access
Bells would have to sell access to their existing landline
networks at a fair price
Entrepreneurs began building massive fiber networks
Many failed “start-up” companies
Frenzy of mergers and acquisitions in the telecomm. industry
Networks
Public Switched Telephone Network – Regulation and Standards
National regulatory organizations such as the FCC exist in
every country
Regulation is heavily influenced by the ITU-T
International Telecommunication Union – chartered by the
United Nations (UN)
ISO – International Organization for Standardization
Non-governmental organization (NGO)
Comprises national-level standards organizations from 156
countries (United States rep. is ANSI – American National
Standards Institute)
ISO has great influence over a wide range of international
standards (e.g., OSI – Open Systems Interconnection Reference
Model)
8
Networks
Public Switched Telephone Network – NPA
Numbering Plan Administration (NPA) enables
connectivity to other telephones
ITU-T is responsible for NPA at the international level, each
nation or region has similar responsibility within their domains
ITU-T E.164 recommendation specifies NPA convention Maximum of 15 digits
Figure 7.1. ITU-T E.164 International Telephone Numbering Plan.
9
Networks
Public Switched Telephone Network – Infrastructure
Today’s PSTN is a collection of mostly digital equipment such
as switches connected by a variety of communications links
(UTP, fiber optic, microwave, satellite, cellular, etc.)
Central Office – facility where local loops connect to the PSTN
infrastructure
International Gateway Facilities (IGF) – provide connectivity between
international carriers
Carriers now provide the Public Data Network (PDN) to
users
10
PDN protocols map to Layers 1 & 2 of the OSI RM (T-1, SONET,
WDM/DWDM, ATM, FR, Carrier Ethernet, etc.)
PDN is part of the PSTN
PDN ex.: WAN (private and public), Internet
Networks
Public Switched Telephone Network – Infrastructure – PDN
Voice Support:
Traditional PSTN provided 4kHz analog voice
PDN supports digitized voice using PCM techniques – uncompressed 64kbps
voice grade channel (Layers 1 & 2)
Today analog local loop still exist
Many techniques use data compression techniques
VoIP is a digitized voice stream using Real Time Protocol (RTP) Layers 5 to 7
over UDP/IP Layers 3 & 4 – supported via ISP
Dedicated Circuit– physical circuit leased for exclusive by user
Circuit Switched – physical circuit exclusively assigned for duration
of call, then released
Virtual Circuit – physical circuit shared by other users, but transparent to the
user
Permanent Virtual Circuit – physical routing always the same
Switched Virtual Circuit – similar to circuit switched only virtual
11
Networks
Public Switched Telephone Network – Infrastructure
Customer Premises Equipment (CPE) – e.g., telephones,
PBXs, computers, facsimile, etc.
Demarcation Point (demarc) – point of delineation
between CPE and the carrier network
PBX (Private Branch Exchange) is a switch owned by a user
Network Interface Unit (NIU) – a.k.a. Network Interface Device
(NID) – includes high voltage/current spike protection
Local Loop (UTP, fiber optic, coaxial, WLL, etc.)
Switches are located within the Central Office (CO)
Trunks connect network switches together which form
the network
12
Trunks can be wired, fiber optic, microwave, satellite, etc.
Networks
Public Switched Telephone Network – Control and Signaling
Common Channel Signaling (CCS) is a robust sub-network that
supports signaling and control
In-Band Signaling & Control functions take place over the same
physical path as the conversation
Signaling System 7 – current ITU-T version
Disruptive and intrusive
Seldom employed except on analog local loops
Out-of-Band Signaling & Control takes places outside of
conversation channel
13
No interference between signaling/control and conversation
Networks
Public Switched Telephone Network – Dedicated Circuits T-1
T-carrier is a dedicated digital, leased-line service
offering that employs TDM to multiplex channels
T-carrier is physical medium independent
OSI Layer 1
T-1 = 1.544 Mbps
Initially developed to support only voice transmission but
now supports data, image and video
Channelized T-1 supports 24 DS0 64kbps voice grade
channels
Unchannelized T1 supports data applications that do not
lend themselves to 64 kbps channelization
14
Networks
Public Switched Telephone Network – Dedicated Circuits T-1
F
DS0 1
DS0 2
Each Byte supports 1 voice channel
DS0 3
DS0 4
DS0 5
…
DS0 24
T-1 Frame
24 Bytes (supporting 24 DS0 channels) + 1 framing bit = 193 bits
Therefore, if we want to support (24) 64 kbps voice grade circuit,
we need to have a frame rate of 8000 frames per second, or
8000 frames/sec * 193 bits/frame = 1.544 Mbps
DS-0 (Digital Signal Level Zero)
Voice grade channel BWfreq = 4kHz
Nyquist Rate fs ≥ 2xBWfreq = 8000 sps
8000(sps)=64kbps
15
7.4.2 Channelized T1
16
17
Networks
Public Switched Telephone Network – SONET
Synchronous Optical Network (SONET) is a North
American standard for broadband communications over
Single Mode Fiber (SMF)
OSI Physical layer (Layer 1)
Use of a central timing source that generates and
distributes clock signals (high costs)
Synchronous Digital Hierarchy (SDH) is the international
version specified by ITU-T
Atomic clock minimizes buffering (PRS Stratum 1 primary
reference source – 72 days between slips)
SONET continues to compete – Ethernet over SONET
18
Networks
Public Switched Telephone Network – SONET
SONET an SDH are based on the Optical Carrier (OC)
concept
On the optical side, the minimum OC level is OC-1 at
51.84 Mbps
OC levels can go as high as OC-768, 40 Gbps
STS (Synchronous Transport Signal) is the electrical
equivalent of the SONET optical signal (OC-1)
Known as Synchronous Transport Module (STM) in SDH
OC-3 = STS-3 = STM-1 = 155.52 Mbps
19
Networks
Public Switched Telephone Network – SONET
20
Networks
Public Switched Telephone Network – SONET
SONET Frame: 9 rows x 90 Bytes = 810 Bytes
Each SONET Frame is 125×10-6seconds per frame,
or 1/ 125×10-6seconds = 8000 frames per second
STS-1 = 810 Bytes/fr x 8 bits/Byte x 8000 fr/sec = 51.84 Mbps
Support 672 DS-0s (64 kbps each)
21
Networks
Public Switched Telephone Network – WDM/DWDM
Wavelength Division Multiplexing (WDM) – multiplexing of
different “colors” of light (i.e., prism) to enable multiple channels
on a single fiber (four wavelengths separated by 10nm each)
Dense WDM (DWDM) – Increased the number of wavelengths up
to 32, and even 160
Requires more stable laser sources
WDM is more cost effective than SONET – simply add more
wavelengths vice upgrading equipment
SMF required although MMF can be used for short ranges (i.e.,
within a building)
Physical Layer
SONET over DWDM hybrid systems have been used
22
Networks
Public Switched Telephone Network – ATM
ATM (Asynchronous Transfer Mode) is a fast cellswitched technology for broadband signals (ITU-T)
OSI Layer 1 & 2
Still offered by service providers
53 octets fixed cell length
Connection-Oriented
Use of small fixed cell size advantage:
Predictable latency, offers QoS
Supports numerous forms of information (voice, images, video, data,
etc.)
ATM switches are use to switch cells from one switch
to another
SONET/SDH preferred physical medium
23
Networks
Public Switched Telephone Network – ATM
ATM Physical Layer – Manages the physical
medium
ATM Layer –
•Provides cell multiplexing of virtual circuits
over the physical link
•Congestion control
•Cell header generation /address translation
•Sequential delivery – connection-oriented
ATM Adaptation Layer – AAL isolates higherlevel protocols
•Prepares/Segregates user data into 48 bytes
information payloads
24
Networks
Public Switched Telephone Network – FRAME RELAY
Frame Relay (FR) is a “Fast Packet Technology” that became
very popular in the 1990s
FR transmits variable sized frames (i.e. packets up to 4096
octets)
In 2014 IP-enabled FR; AT&T offers frame relay services to business and
gov’t customers (2015)
Cheaper alternative to dedicated leased lines (T-1 and T-3)
Designed to support “bursty” traffic (ex., LAN-to-LAN)
variable length frames can lead to unpredictable levels of congestion
FR standards address OSI Layers 1 and 2
Connection-oriented at the Data Link Layer
25
Networks
Public Switched Telephone Network – Carrier Ethernet
Shared Ethernet (traditional LAN) – data collisions possible
Switched Ethernet – reduces data collisions (HDX), eliminates
data collisions (FDX)
Carrier Ethernet – native Ethernet supported; considered a
viable Layer 2 protocol for MAN and WAN connectivity
CE 1.0 Services (CE 2.0 from MEF, Metropolitan Ethernet Forum, is
newest generation):
E-Line
E-LAN
E-Tree
E-Access
E-Transit
Ethernet over SONET/SDH
26
Figure 7.12. E-Line service (UNI to UNI).
Figure 7.13. E-LAN service
(multiple UNI interconnected over the MEN).
Figure 7.14. E-Tree service (root and leaf EVC).
Figure 7.15. E-Access service
(EVC
between
UNIs located on different MENs).
27
Figure 7.16. E-Transit service (E-NNI to E-NNI connection).
Networks
Network Devices –
PBX (Private Branch Exchange)
User-owned and operated switch vice service switch
28
Large organizations
Requires user to have technical expertise
Networks
Network Devices –
CENTREX
Service provider owned switch offered to users
29
Provides similar functionality as a PBX for a monthly fee
Users do not have to have technical expertise
Networks
Network Devices –
ACD
Automatic Call Distributors (ACDs)
30
PBXs that switch incoming calls to a call center
Employs Interactive Voice Response (IVRs)
