The Public Switched Telephone Network
Lecture Notes: Session 2
- Mail questions, info to HyperNews group
- List and describe the three major regulatory judgments affecting the telecommunications industry between 1900 and 1997.
- Discuss the trend toward wireless communications, giving industry examples.
- List four major advances in the telecommunications industry between 1990 and 1997 and explain why they are significant.
- The human voice produces an ___________ signal which, when converted to electrical energy is represented by a __________- wave, which is _________ in nature.
- The bandwidth required to support normal voice conversation is:
- Two techniques used to narrow the bandwidth of a channel are:
The Public Switched Telephone Network
Topology of PSTN
- Network=>Demarcation point (Demarc)=>also called station drop.
Regulatory effect on network=>
Star configuration from the Central Office (CO) to the demarc
Star or ring configuration from the Central Office to other COs or higher-level offices
Wire Center or Frame
Physical vs. logical connections
The Local Loop
CO to customer demarc is called the Local Loop or Outside Plant
Feeders: 50-3000 pairs of wire running from the CO in a general direction to manholes or handholds (splice points)
Lateral distribution: bundles split off to run to branch feeders.
Branch feeders: bundles split into four-pair groups and delivered to individual station drops.
Network Hierarchy (pre-1984)
Class 5 Office: Local Exchange
- Designed around the task of call completion.
Class 4 Office: Toll Center or Tandem Office
Class 3 Office: Primary Center
Class 2 Office: Sectional Center
Class 1 Office: Regional Center
Network Characteristics (post-1984)
- Bell Operating Companies (BOCs) become Local Exchange Carrier's (LECs)
- Original 7 BOCs become Regional Bell Operating Companies (RBOCs)
- Regulated arm
- Unregulated arm
POPs and POIs
POP=>point of presence
- Interexchange carrier (IEC or IXC) rights
- Removal of 7-10 digit additional codes for access to alternative long distance service
- Non-conforming end offices
POI=>point of interface (no switch present)
Numbering Plan for North America
- Area codes
- Exchange codes
- Subscriber Extensions
Private Networks and Hybrid Networks
Local Access and Transport Areas (LATAs)
- 4 Types of LATA-based calls:
- Interstate-IntraLATA=IEC or LEC
- contains four wires; 2 to transmit, 2 to receive
- Transmitter (mouth piece)
- Receiver (ear piece)
- Handset cord and base
- Tip and Ring=>
- Dial pad
- completely programmable
- speed dial->
- call hold
- call transfer
- conference call
- redial last number
- power dialing
- speakerphone/hands-free dialing
- display dialing (caller ID)
upon reception, signal is decoded
- air is an atmospheric transmission medium
transmitting=>process of moving encoded information from one location to another
Transmission: big concepts
- Converting acoustical into electrical energy.
- Converting light energy into electrical energy.
- Converting light energy into latent chemical energy.
- Converting mechanical energy to electrical energy.
modulation=>process of manipulating carrier signal to contain encoded information.
Methods of modulation
- Carrier signal=>constant signal that is sent during connection
- electromagnetic signals
- light signals
- What part of the signal gets changed?
- Pulse Duration Modulation (PDM)=>telegraph
- Amplitude Modulation (AM)=>2400 cycle changes per second--baud
- Frequency Modulation (FM)
- Pulse Code Modulation (PCM)
- =>process of increasing carrier signal's strength.
- =>loss of signal strength over time and distance
- =>process that enables optimal amounts of information to be moved over a communications channel
- Time Division Multiplexing (TDM)=>each encoding device is placed on the communications channel in a predetermined order, at a specific interval in time.--available on narrowband and broadband channels
- Frequency Division Multiplexing (FDM)=>Multiplexing device separates information from two or more devices and assigns each a particular frequency
- FDM is only available on "broadband" communications channels
- cable tv
Simplex=>unidirectional; broadcast TV; telex
- =>manages/controls direction of information flow
Full duplex=>send and receive simultaneously; telephone
- Half duplex=>cb radio; can send and receive, but you can only do one at a time
- 3 characteristics
- all are forms of radiant energy
- all have same velocity (~186,000 miles per second--same as light)
- all travel in a sine wave-like motion
- =>frequency range assigned to device capable of transmission by a physical or atmospheric channel
- Regulatory boards
- International Telecommunications Union (ITU)
- =>the transporting or launching of a signal through a telecommunications channel
- Atmospheric channelling=>
- Physical channelling=>moving electrical, electromagnetic, and light energy through copper, glass (fiber) and wave guides
- open wire
- Copper Twisted Pair
- cat 3
- cat 5
repeaters vs. amplifiers (review)
- =>used in VHF or lower spectrums
- reality check
- =>process of converting encoded signal from one format to another
- protocol converter
Receiving=>process of capturing an encoded signal and relaying it to the decoding device.
- =>process that allows two or more communication devices to be connected.
- Sensing access request
- Determining destination
- Selecting path
- Establishing Connection
- Disconnecting the Circuit
Storing=>saving information (signals) for later use.
- =>process of accessing stored information
- Abstracting=>process of identifying the content of stored information
- Indexing=>process of coding an item (name) for later retrieval
- Accessing=>process of locating a stored item by using the abstract and index
- Controlling=>determining who has access to specific information (also called authentication control)
- =>process of presenting information in a usable format.
- Converting electrical to acoustical energy
- Converting electrical to light energy
- Converting electrical to mechanical energy