ENP Study Group
Session #1
Telecommunications
Operations
BROUGHT TO YOU BY: THE FLORIDA NENA EDUCATION COMMIT TEE
Network Design and Architecture
Transport Classifications
InterLATA and Interexchange: A Local Access and Transport Area (LATA) is a specific geographic area
where a local telephone service provider (TSP) may provide either local or long distance service.
Interexchange carriers (IEC or IXC): Provide services to the public between local exchanges on an
intra or interLATA basis.
Local Exchange: A local exchange is a service area that is provided by an end office. The exchange
area serves a geographic area in which charges and services are uniformed. A Local Exchange Carrier
(LEC) provides telecommunications with a franchised area, within the same LATA.
Local Loop: The wires that run from your home or business to your servicing central office. At the
point the “loop” enters a resident a Network Interface Device (NID) is commonly use. In a business,
is it referred to a point of demarcation (demar), usually found at a main distribution frame. The
telecommunications provider is responsible for the service “to” the demar, the customer is
responsible for getting the service “from” the demar.
Network Design and Architecture
Traditional Telephone Switching
Central Office (CO) is where a subscriber’s lines are joined to the telecommunications service provider (TSP) switching equipment so that
connections can be made to other subscribers locally or over long distances.
End Office or Class 5 Office is a switching system within a Local Access and Transport Area (LATA) It provides the connection of the
customer’s equipment and delivers dial tone to the subscribers. The subscriber originates or receives communications from the network
via the end office.
Selective Router (also known as the E9-1-1 Tandem or Access Tandem) provides traffic concentration and distributes call between end
offices or an interexchange carrier. A Selective Router provides interexchange carriers access to all end offices within the LATA.
Facility or Facilities is a telephone company term that encompasses all the physical telephone plant that is required to provide service.
This can include switching systems, cables, microwave and buildings. Facilities should be used for the physical plant, such as switching
systems and buildings. Transport facilities would refer to the cables and microwave, etc.
The basic function of a switching network is to provide communications paths from the calling party to the called party.
If the calling party and the called party are in the same switching system, the call is an “intra-office call” If they are served by different
switching systems, but within the same LATA, the call is considered intra-LATA. If the callers are served by different switching systems
within different LATA’s, the call is considered to be an inter-LATA call.
Networks are not engineered to allow all subscribers to place call simultaneously. Most systems are designed for a P01 grade of service.
That means that 1 in every 100 call will receive a busy signal.
Network Design and Architecture
Traditional Telephony Topology
Central
Office
Central
Office
Tandem/
Access
Tandem
Central
Office
IEC
Tandem/
Access
Tandem
Central
Office
LATA 1
LATA 2
Network Design and Architecture
Transport Facilities (Transport Media)
Transport Facilities: This refers to the physical medium over with the transmission take place.
Copper Wire: This is the original infrastructure used by the telephone system, and there is still a lot of it in use
today. This is common telephone wire that is found in cables in the form of pairs of wires twisted together. This is
where the term “twisted pair” originated.
Fiber Optics: This technology in where light is transmitter through thin filaments of glass. The light is turned off
and on billions of times per second to represent binary signals. Fiber optics requires less space and is not sensitive
to electromagnetic interference. Transmission over fiber is only digital.
Microwave: This term is derived from the fact that the wavelength of the radio signal is being transmitted over a
relatively short distance. Microwave uses electromagnetic waves in the radio frequency spectrum above 8990
Megahertz and below 20 Gigahertz to transmit facsimile, video, and data conversations.
Satellite: This is a specialized form of microwave transmission where the “tower is in the sky”. Signals are sent
and received by pointing a stationary dish antenna at the satellite.
Coaxial Cable: This was developed to provide a more effective way to shield wires from outside electrical
interference and radio signals. This cable can carry large quantities of information and is used to carry high speed
data.
Network Design and Architecture
Network Configurations
Switching Configurations:
Stand-Alone : This is a switch that is designed to serve a geographic area where the subcribers
are within a defined loop length of a central office. A stand alone switch may also host one or
more “remotes”
Host/Remote: This is a switching technology that offers an economical way to
telecommunications service providers to serve customers in remote areas. It allows for the host
to be located in a central area, with remote switching units connected to it, but closer to the end
customer. These are referred to a Remote Switching Units (RSU) or Remote Switching Modules
(RSM). These units are connected to the host by an umbilical cable consisting of a data link and
interconnecting trunks.
Network Design and Architecture
Network Configurations
Switching Configurations (Continued):
Selective Routing: This is used to interconnect end offices when direct trunking is not economically
justified or when alternate routing is justified. Selective Routers can perform some or all of the
following functions:
Interconnect end offices
Connect to other selective routers
Provide access to interexchange carriers (IECs)
Provide access to operator positions.
The following trunk types can be connected to a selective router:
2-wire, 4-wire, Analog, or Digital (SS7)
Alternate Routing: Provides the routing capability for 9-1-1 calls to a designated alternate location(s)
if all the 9-1-1 trunks are busy or out of service.
Network Design and Architecture
Network Configurations
9-1-1 Switching Architecture:
Selective Router Architecture provided the intelligence of the system to be centralized in a single
switch.
561-555-1212
9-1-1
Central
Office
561-555-1212
561-555-1212 & ESN
PSAP A
Selective
Router
PSAP B
Network Design and Architecture
Network Configurations
9-1-1 Switching Architecture (continued):
Ancillary features that are provided by the E9-1-1 Selective Router include:
Selective Routing
Selective Transfer
Three –way Calling
Speed Dialing
Alternate Routing
Default Routing
9-1-1 Direct Trunking:
With Basic 9-1-1 systems, dedicated 9-1-1 trunks go through the originating serving central office
directly to the PSAP.
Network Design and Architecture
Network Configurations
Signaling/Transport:
9-1-1 Transport and Signaling:
Signaling is the sending and receiving of control information between the parts of a telecommunications network.
Signaling that is circuit-associated uses metallic conductors to transmit signal and uses either in-band or out-ofband signaling.
Centralized Automatic Message Accounting (CAMA):
This was originally used for long distance billing. It is an arrangement that provides detailed call information at a
centralized location.
CAMA uses a switch at a central location to see as a hub to:
1. Collect Automatic Number Identification (ANI) information
2. Registers the call’s duration
3. Routes the call
Network Design and Architecture
Network Configurations
Signaling/Transport (continued):
Multi-Frequency Signaling (MF)
This is a type of address signaling in which ten decimal digits (the numbers on your touchtone
phone) and five auxiliary signals are each represented by selecting a pair of frequencies out of
the following group: 700, 900,1100, 1300,1500, and 1700 hertz (Hz).
MF pulsing system consists of transmitting and receiving equipment for sending frequency
combinations in the voice band.
Dual Tone Multi-frequency (DTMF) also referred to as “Touch Tone Dialing” also uses a
combination of two specific tones to represent a digit or other character in which eight tones are
paired.
Touch tone and DTMF are NOT the same thing. Both use a combination of 2 specific tones to
represent a digit or other character, but the tones are different.
Network Design and Architecture
Network Configurations
Transmission Systems:
Switch Types:
Analog: Analog signaling uses a signal that may be variable in amplitude (amplitude modulation
of “AM”) or frequency (frequency modulation or “FM”.
Digital: Digital switching converts the analog signal to digital and this binary encoded
information is routed between an input and an output port by means of time division
multiplexing (TDM) rather than using a dedicated circuit.
Packet: This technology used in the next generation network transmit a caller’s voice using
Voice Over Internet Protocol (VOIP) on a variety of different data transport.
Network Design and Architecture
Types and Features of 9-1-1 Systems
Basic 9-1-1:
The caller could dial 9-1-1 and the TSP’s end office would be programed to send all 9-1-1 calls to a single
destination, regardless if that PSAP provided services to that caller’s area. In the beginning it also did not provide
the caller’s telephone number.
Basic 9-1-1 with ANI and ALI:
Service providers started using CAMA to facilitate the delivery of the caller’s telephone number to the PSAP.
Since the telephone companies stored the subscriber’s data based on telephone numbers, they would also be
able to provide the name and address.
This system only provides ANI and ALI and is NOT Enhanced 9-1-1 because there is no selective routing. (HINT
What feature must you have to be considered an Enhanced 9-1-1 system?)
Basic 9-1-1 with Multiple End Offices (Single E9-1-1 Selective Router):
In this configuration multiple end offices to a PSAP are connected to a selective router office, and from that
selective router a single trunk group is connected to a PSAP.
Network Design and Architecture
Types and Features of 9-1-1 Systems
Enhanced 9-1-1:
Enhanced 9-1-1 is separated from Basic 9-1- 1 by Selective Routing . Selective Routing allows a call to be
delivered to a specific PSAP based upon the street address of the caller.
Enhanced 9-1-1 requires three additional components from Basic 9-1-1:
1. A Master Street Address Guide (MSAG)
2. The translation of the caller’s address to an Emergency Service Number (ESN).
3. A Selective Routing Database (SRDB) associated with the E9-1-1 Selective Router that has the ability to
translate the Telephone number (TN) to an ESN.
Emergency Service Zones (ESZ) are a geographic zone served by one particular combination of Police, Fire, and
EMS. Each ESZ contains the set of street addresses served by that combination of PD, FD, and EMS. The ESZs are
then assigned an ESN, that the E9-1-1 Selective Router can use for Selective Routing.
In the MSAG, all address ranges that fall within a specific ESZ are identified and assigned an ESN. The Database
Management System then identified all of the telephone numbers at those asdresses and assigns the ESN to the
customer’s records.
Network Design and Architecture
PBX E9-1-1 Interconnection
Private Branch Exchanges (PBX) are used in businesses with a single location, a campus environment containing
multiple buildings or a distributed architecture where satellite locations are geographically remote from the host
PBX.
An issue in the US in that less than half of the states of regulations that cover the delivery of emergency calls and
the obtaining the location of the caller behind that PBX. This is know as Multi-Line Telephone Systems (MLTS).
PBX Using Main Telephone Number: Normally, when someone calls 9-1-1 from a station off a PBX, the main listed
telephone number and address of the main location will display at the PSAP. The actual location of the caller
originating the 9-1-1 call can be anywhere in the building or in other buildings served by the PBX.
PBX Using Private Switch ALI (PS/ALI): This service allows the PBX owner to recreate and maintain ALI records
that identify each station address or Emergency Response Location (ERL) which may represent the location of
multiple stations. The records are uploaded to the 9-1-1 Database Management System database. The owner of
the PBX is responsible for the creation and maintenance of these records.
There are 2 types of network connections that can be used to establish the call process. Newer PBX’s can use a
Primary Rate ISDN connection. The calls enter the selective router over the regular dedicated end office
Emergency Service (ES) trunks. Older PBXs need to install an adjunct unit that uses dedicated 9-1-1 trunks that will
connect the PBX either directly to the E9-1-1 Selective Router or in some cases the end office.
Network Design and Architecture
PBX E9-1-1 Interconnection
Host PBX with Satellite PBXs: This configuration may be used when a large multiregional
corporation uses a host and one or more satellite PBXs. In this case there satellite PBX could be
located in another jurisdiction. If the corporation has PS/ALI, the callers information will route
to the correct location.
VoIP PBX Replacement/IP PBX: VoIP technology has replaced circuit switching for enterprise PBX
systems. While this is newer technology, it still has the same limitations as a conventional PBX.
An option that is available to an enterprise VoIP system is to use the same infrastructure
deployed to support VoIP Service Providers (VSP) This system uses the VoIP Positioning Center
(VPC) to route 9-1-1 calls and deliver ALI for the VoIP callers.