Notes To Know: “Fundamentals of Telecommunications” by Roger L. Freeman—Chapter 1 Introductory Concepts
(Note: This is an evolving, evergreen post.)
Chapter 1–Introductory Concepts
What is Telecommunication?
“Communications at a distance.” —Webster Dictionary
“The transmission of signals over long distance, such as by telegraph, radio or television.” —IEEE Standard Dictionary
Telecommunications is one of those words that has broad scope, meaning and coverage. It can mean different things to different individuals.
“Fundamentals of Telecommunications” brings forth the following definition:
“Some take the view that telecommunications deals only with voice telephony, and the typical provider of this service is the local telephone company. We hold a wider interpretation. Telecommunications encompasses the electrical communication at a distance of voice, data, and image information (e.g., TV and facsimile). These media, therefore, will be major topics of this book. The word media (medium, singular) also is used to describe what is transporting telecommunication signals. This is termed transmission media. There are four basic types of medium: wire pair, coaxial cable, fiber optics, and radio.”
“Fundamentals of Telecommunications, 2nd Edition” by Roger L. Freeman
In modern, advanced societies, the telephone (and increasingly the internet) is almost taken for granted.
Before divesture happened in 1983, the Bell System (a part of AT&T) was the Amazon of its day. The Bell System:
- was the largest commercial company in the U.S.
- had the biggest fleet of vehicles
- had the most employees
- had the greatest income [1]
The old-school telephone line service dates back to the late 1800’s and some principles of modern network technology can still be found there.
- PSTN (Public Switched Telecommunications/Telephone Network)
- Older, original technology
- Relies on a cable copper wire
- Uses circuit switching ( or switching) for connecting calls.
- VOIP (Voice Over Internet Protocol)
- VOIP uses the Internet; doesn’t rely on a cable wire
- No need for any telephone exchange, or exchange, for VOIP to VOIP calls. If you call a PSTN number from your VOIP, your call will be transmitted through an exchange
- Works for all types of calls, data transfers, and more
- Uses packet switching, instead of PSTN’s circuit switching.
- VOIP doesn’t use dedicated lines. Data packets use routers and the internet.
LEC (Local Exchange Carrier)
CLEC (Competitive Local Exchange Carrier)
“An overall telecommunications network (i.e., the PSTN) consists of local networks interconnected by one or more long-distance networks. The concept is illustrated in Figure 1.1. This is the PSTN, which is open to public correspondence. It is usually regulated by a government authority or may be a government monopoly, although there is a notable trend toward privatization. In the United States the PSTN has been a commercial enterprise since its inception.”
“Fundamentals of Telecommunications, 2nd Edition” by Roger L. Freeman
End-Users, Nodes, and Connectivities
End-user—the person providing the inputs to the network and the recipient of outputs from the network.
I/O—input/output (device). Ex: PC, computer, telephone, fax, mobile phone, tablet, even conference TV equipment, etc.
Nodes—the thing that end-users usually connect to. “We will call a node a point or a junction in a transmission system where lines and trunks meet. A node usually carries out a switching function. In the case of the local area network (LAN), we are stretching the definition. In this case, a network interface unit is used, through which one or more end-users may be connected.”
Connectivity—links an end-user to a node, which opens up the possibilities to connect to whatever else that node is also connected to. IEEE defines a connection as “an association of channels, switching systems, and other functional units set up to provide means for a transfer of information between two or more points in a telecommunications network.”
Three sequential stages to a telephone call:
- Call setup
- Information exchange
- Call takedown
- Call setup:
- This is the initial stage where a circuit is established and activated.
- Facilitated by ’signaling’.
- The subscriber/user goes ’off-hook’ (literally the old-school action of taking the phone out of its cradle to hear a dial tone and initiate the phone call sequence).
- ”Two little knobs in the cradle pop up, pushed by a spring action causing an electrical closure.”
- This is akin to switching a light on, where “we have an electrical closure allowing electrical current to pass. The same thing happens with our telephone set; it now passes current.”
- Battery—the current source, which resides at the local serving switch; connected to subscriber loop.
- Subscriber loop—a pair of copper wires (usually a RJ-registered jack) “connecting the battery and switch out to the subscriber premises and then to the subscriber instrument”.
- These actions allow current to flow producing a dial tone to the user.
- ”Each button is associated with a digit. There are 10 digits, 0 through 9. Figure 1.3 shows a telephone end instrument connected through a subscriber loop to a local serving exhchange. It also shows that all-important battery (battery feed bridge), which provides a source of current for the subscriber loop.”
- Now things start to get very interesting as we bring up local areas and the idea of networks!!!
- ”If the called subscriber and the calling subscriber are in the same local area, only seven digits need be dialed. These seven digits represent the telephone number of the called subscriber (user). This type of signaling, the dialing of the digits, is called address signaling.”
- Address signaling—the dialing of the digits of a phone number to reach that user/subscriber.
- A connection is made to the called subscriber and the switch sends a ring signal called alerting, another form of signaling.
- Information exchange
- The two subscribers exchange whatever information during the call.
- ”Once the called subscriber goes off-hook, there is activated connectivity, and the call enters the information-passing or phase 2 of the telephone call.”
- The call is terminated when the telephones at each end are put back “on their hooks”, breaking the circuit of each subscriber loop. This again is similar to turning off a light switch, which cuts the current flow.
- Call takedown:
- Phase 3 begins to terminate the call and the connecting circuit in the switch is taken down and freed up for another user.
- “Both subscriber loops are now idle. If a third user tries to call either subscriber during stages 2 and 3, she/he is returned a busy-back by the exchange (serving switch).” This is the busy signal we are familiar with from land-line phones and is a form of signaling called ‘call-progress’ signaling.
- Now if a subscriber want to call another subscriber outside of their local serving area, then the “call setup will be similar as before, except that at the calling subscriber serving switch the call will be connected to an outgoing trunk. As show in Figure 1.4, trunks are transmission pathways that interconnect switches. We repeat: Subscriber loops connect end-users (subscriber) to a local serving switch; trunks interconnect exchanges or switches.”
- The IEEE defines a ’trunk’ as “a transmission path between exchanges or central offices.”
Telephone Numbering and Routing
- NANP (North American Numbering Plan
- Tandem Switches in a LAN
- A tandem switch, which could also be called a ‘traffic concentrator’, “is an important economic expedient for a telephone company or administration.”
- Simplex, Half-Duplex, and Full Duplex
- Simplex—one-way operation; there is no reply channel provided. (Ex.: Radio & TV)
- Half-Duplex—two-way service; defined as transmission over a circuit capable of transmitting in either direction, but only in one direction at a time.
- Full-Duplex, or duplex, is defined as “simultaneous two-way independent transmission on a circuit in both directions.”
Network Topologies
Topology—the interconnection pattern of nodes on a network.
Switches in a telecommunication network can be interconnected in a myriad of ways.
Full-mesh: every switch in a network is connected to all other switches (or nodes) in the network.
Star network—
Rules of Conventional Hierarchical Networks
Backbone—in terms of hierarchical networks, the backbone represents the ’final route’ from which no ‘overflow’ is permitted.
Standardization
Standardization is key.
There are various international, regional, and national standardization agencies.
There are at least 2 international agencies that impact telecommunications.
- ITU (International Telecommunication Union)
- ISO (International Standardization Organization)
- Biblio:
- [1] “Fundamentals of Telecommunications, 2nd Edition” by Roger L. Freeman
