This document summarizes key information from chapters 8-10 of a homework assignment: - It defines common digital signal rates like DS0, DS1, DS3, and OC-1 according to the North American digital hierarchy. - It explains terms like DS0, DS1, and DS3 and what each is used for in digital signaling. - It describes T-1 framing formats and where signaling information is carried. - It explains the purpose of overhead bits in digital signals and how many DS0s are multiplexed into a T-1. - It compares SONET bit rates like STS-1 to T-1 and T-3, explaining the difference between OC-

1. ELET 4315 Homework #3 (Chapters 8 – 10)
Chapter 8
List the 4 bit per second rates defined by the North American Digital Hierarchy.
DS0 ≈ 64 Kbits/sec, DS1≈1.544 Mbits/sec, DS≈6.312Mbit/sec DS3≈ 44.736 Mbits/sec, OC-1≈
51.84 Mbits/sec
Define each of the following terms and explain what each is used for.
-DS0 - Digital Signal 0 (DS0) is a basic digital signaling rate of 64 kbit/s, corresponding to the
capacity of one voice-frequency-equivalent channel.[1] The DS0 rate was introduced to carry a
single digitized voice call. For a typical phone call, the audio sound is digitized at an 8 kHz
sample rate using 8-bit pulse-code modulation for each of the 8000 samples per second. This
resulted in a data rate of 64 kbit/s. To limit the number of wires required between two involved
in exchanging voice calls, a system was built in which multiple DS0s are multiplexed together on
higher capacity circuits.
-DS1 Digital Signal 1 (DS1) High-capacity DS1 Service is known as a fundamental building
block of many networks. It is a digital, point-to-point, private line service that provides high-
speed bulk transport for voice, data or video traffic. Use the entire circuit for single, high-speed
bandwidth applications, or divide or multiplex, your DS1 into multiple channels.
-DS3 Digital Signal 3( DS3) Service offers a reliable, all-purpose digital connection for extremely
high volume requirements that can easily connect your DS1 circuits. DS3 Service transmits video,
data, and voice at speeds of 44.736 Mbps in most cases over a fiber optic network. DS3 is
provided between two customer premises or between a customer premises and a Telephone
Company central office. DS3 Service is offered with DS3 to DS1 multiplexing as an optional
feature at selected Telephone Company hub offices. This feature allows the conversion of one
DS3 (44.736 Mbps) channel to 28 DS1 (1.544 Mbps) channels using digital time division
multiplexing.
Which frames in the T-1 frame are used to carry signaling information?
T-1 framing uses to formats superframe format and extended superframe format, super frame
format is the older of the two and its slowly being replaced by extended superframe format.
Superframe format has twelve 192 bit frames that equal one master frame, Signal bits are
designated in all even frames and are used to flag the sixth and twelfth frames. As for Extened
superframe format, it has twenty-four 192 bit frames that equal one master frame, signaling bit
resides in the sixth, twelfth, eighteenth, and twenty-fourth frames.
Explain the purpose of overhead bits in digital signals.

2. STS-1 frame is built around two functional areas overhead bytes and payload. Overhead head
bits make sure the payload arrive at their destination intact and on time
How many DS0 signals are multiplexed into a T-1 signal?
DS0s are multiplexed together on higher capacity circuits. In this system, twenty-four (24) DS0s
are multiplexed into a T-1 signal.
True or False- the DS0 signals are byte interleaved into the T-1 signal.
True.
How many DS2 signals reside in a DS3 signal?
DS0 is the base for the digital signal X series. DS1, used as the signal in the T1 carrier, is 24 DS0
(64 Kbps) signals transmitted using pulse-code modulation (PCM) and time-division
multiplexing (TDM). DS2 is four DS1 signals multiplexed together to produce a rate of 6.312
Mbps. DS3, the signal in the T3 carrier, carries a multiple of 28 DS1 signals or 672 DS0s or
44.736 Mbps,. Therefore seven DS-2 signals reside in DS3 signal.
Why was the SONET standard developed?
There was a realization that the standard bodies needed to create a nonproprietary transport
protocol for optical transmission, with the goal to develop a protocol that would allow fiber
optic strands to carry large amounts of information and build in overhead bits for network
maintenance, and maintain a standard frame format that would allow all types of vendors
equipment to talk to one another.
List the SONET bit per second rates that compare to a T-1, and a T-3.
VT-1.5 Bits-Per-Second Rate 1.78Mbps = 24 DS0 signals for T-1
EC-1 (STS-1) Bits-Per-Seconds Rate 51.84Mbps = 672 DS0 signals for T3
Explain the difference between an OC-1 and an STS-1.
OC-1 is Optical carrier the signal is in its optical form (laser light) and STS-1 is Synchronous
Transport Signal and refers to the SONET frames. OC-1 carries one STS
How many DS3s ride inside an OC-48, an OC-12 and an OC-3?

3. OC-48 ~ 48-DS3
OC-12 ~ 12 DS3
OC-3 ~ 3 DS3
Chapter 9
Explain the difference between a tandem switch and a class 5 switch.
A class 5 switch is often called an End Office level switch as, defined by the hierarchical switch
architecture, or sometimes the central office. It is always the local switch, that is, the switch
nearest the customer or end user. It serves the local loop. The calls you make from your home go
to a class 5 office. Your DSL line is connected to a Class 5 office. A Class 4 switch or tandem
was or is always a toll switch, that is, a long distance switch. It takes the traffic from class 5
offices and puts them into the long distance network. Many Class 5 offices are connected directly
with each other, no switch required to transfer a call. But for those CO's not directly connected
the class 4 switch does the job. If the class 4 switch just connects central offices together the
switch is called a tandem.
Define each part of the following number – 818-226-9877 as defined by the North American
Numbering Plan.
818- NPA Numbering Plan Area is the area code identifying the region,
226-NXX number exchange is the central office code to identify the local central office or servicing
wire exchange code.
9877-XXXX is the subscriber number to identify the customer
Explain what is meant by LNP and why it is an important feature in telecommunications today.
Local number portability (LNP) is one of the reasons the 1996 telecom Act was instituted. It
allows telephone subscribers to keep their telephone number when the switch to a different local
telephone provider. Thanks to LNP telephone number are no longer tied to one switch.
Eventually, geographical number portability will allow you to keep you telephone number even
if you move across the country.

4. Chapter 10
Explain the importance of signaling in the telephone network.
Signaling is a very important part of a telephone call. Without signaling, a cll cannot be sent
through the telephone network from one end to the other. Singnaling methods were developed to
properly send information on who the caller wants to call ( the called party) and who the caller is
to the network(identification for billing). Signaling is responsible for establishing connections,
gathering information, and controlling hoe calls and information are routed through the network.
Explain how touch-tone dialing sends digits to the switch and write the name given to define
touch-tone dialing.
Dual-tone multi-frequency signaling (DTMF) is used for telecommunication signaling over
analog telephone lines in the voice-frequency band between telephone handsets and other
communications devices and the switching center. The version of DTMF that is used in push-
button telephones for tone dialing is known as Touch-Tone. DTMF relies on sounds created by
pure sine waves, which are sound waves that have a consistent frequency from beginning to end
which is between 300Hz to 3000Hz. The tone determines which number has been dialed. Two
of these tones are combined into a sinusoidal wave that allows a network switch to recognize the
key being pressed by separating the sinusoidal wave into its component parts. The information is
sent to either the tandem and then to local central offices, of form central office to other central
offices directly. The format of a typical Multi-Frequency Signal (MF) KP+ dialed digits + ST.
Where KP equals Key Pulse and ST equals start Most MF tool trunks in the Us and Canada use
2600Hz as supervision and for idle line. When the handset is picked up , current flows
continuously the DTMF change or breaks up the current flow.