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Week 3. Things you really want to know. Things to know. Describe functions/services of a central office Describe trunk Describe local loop Describe the NANP, how does the CO fit into this plan. Describe pulse dial and DTMF Difference between in-band & out of band signaling
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Week 3 Things you really want to know
Things to know • Describe functions/services of a central office • Describe trunk • Describe local loop • Describe the NANP, how does the CO fit into this plan. • Describe pulse dial and DTMF • Difference between in-band & out of band signaling • Describe the concept of grade of service • What is the busiest telephone day of the year? Day with the most collect calls?
An Overview of the Public Network • Public Switched Telephone Network (PSTN) - consists of all the facilities and connections maintained by all local and long distance providers. • In telecommunications, line is used frequently to refer to one of two things: • the physical connection between a subscriber and the telephone company’s facilities • a single communications channel between a subscriber and the central office
An Overview of the Public Network • Termination - the place where a wire is connected to another part of the public telephone network (for example, a switch or a customer’s home). • Point of presence (POP) - refers to a carrier’s facilities that allow it or its customers access to the public network.
Common Carriers • Common carriers - entities directly involved in supplying regulated telecommunications services to the public. • Reseller - a common carrier, or a company that leases another company’s facilities, and then sells services over those facilities under its own name.
Local Exchange Carriers (LECs) • Currently, two types of common carriers provide local phone service: • Incumbent local exchange carriers (ILECs): companies that have been providing local phone service since before competition was allowed for intraLATA traffic • Competitive local exchange carriers (CLECs): companies that began offering local phone service after the Telecommunications Act of 1996 introduced competition. • Facilities-based - CLECs that build their own facilities in addition to leasing and using ILEC facilities to provide service under their name.
Local Loop • The portion of a business or residential telephone network that connects the demarcation point to the local phone company’s nearest central office is called the local loop. • Local loop (last mile) portion of a connection is the most expensive for a carrier to provide because separate lines must be installed for each individual subscriber. • The local loop is the part of a connection most likely to have the lowest throughput and, further, be the most susceptible to damage or noise.
Serving Area Concepts (SAC) • Drop wire - the cable that runs from a subscriber’s demarcation point to a telephone pole or underground conduit. • The drop wire connects the subscriber’s home or business line to a distribution cable, which gathers multiple drop wires from a neighborhood. • Conduit - the thick tube (usually made of PVC plastic) that surrounds a distribution cable. • The conduit protects the wires within the cable from environmental damage.
Distributing Frames • Main distributing frame (MDF) - a piece of equipment where incoming wires terminate and their circuits are connected to another set of wires that lead to central office equipment. • Punch-down block - a row of metallic clips (or receptors) that accept a wire termination. • Jumper wires - used to connect incoming lines’ punch-down blocks with the outgoing lines’ punch downblocks. • Cross-connect - wires terminating at two sets of punch-down blocks are interconnected.
Switching Equipment • Major functions of switching equipment at a central office: • Dial tone • Customer and phone number identification • Call setup • Call routing • Call supervision • Line testing and maintenance • Billing
Figure 18–35 The three sources of power available in a central office.
Central Office Hierarchy • Serving area (of a local office) - the geographical boundary that includes all its subscribers. It extends roughly three miles in all directions from the central office (CO). • Trunk - a transmission route between switches that typically has a great deal more capacity than a feeder. • Regional offices - Class 1 central offices.
Billing Between Carriers • The fees charged by ILECs are based on the leasing carrier’s: • Grade of service received • Number of trunks used • Amount of traffic transmitted • Placement of equipment in ILEC’s facility, also called collocation • Facilities and circuit installation • Maintenance and support agreement
North American Numbering Plan • A scheme for assigning unique phone numbers to every line in the country. • For numbering purposes, North America is divided into several smaller geographic regions called Numbering Plan Areas (NPAs), more commonly known as area codes.
North American Numbering Plan • NPAs reserved for special purposes include: • Easily Recognizable Codes (ERCs) - When the second and third digit of the NPA are identical (for example, the numbers 888 or 411), the NPA is known as an Easily Recognizable Code (ERC). • N9b - these 80 NPA codes have been reserved for use when the current NANP numbering scheme undergoes further expansion. • 37b and 96b - these 20 NPA codes have been reserved in case a previously unanticipated need for blocks of 10 contiguous NPAs arises.
Summary • The Public Switched Telephone Network (PSTN) is defined as the collection of local and long distance providers’ facilities and connections that are available for public voice (and more recently, data) communications. • Common carriers are entities directly involved in supplying regulated telecommunications services to the public. • The local loop, or "last mile," is the connection between a subscriber and the nearest central office.
Key Terms in Switching Systems • Common control systems • Translation of the telephone number, automatic call routing, digit conversions, and trunk signaling • Direct control systems • Lack alternate routing and digit translation capabilities • Virtually non-blocking • Not totally non-blocking but provides enough paths so users are rarely blocked • Busy Hour Call Attempts (BHCA) • The number of calls the system can handle during peak hour • Concentration or line-to-trunk ratio • Determines the probability that a call will be completed
Telephone Cable Architecture • Telephone Cable Hierarchy • Trunks (in North America, that are same as “Junctions” in Europe) • High-speed digital carriers that interconnect nodes • Feeders • Branch Feeders • Station Drops (local loops, subscriber lines) • One pair of UTP wire that is usually analog
Line Conditioning • Line Conditioning • Is used to tighten telephone company parameters so that they can transfer data at higher speed with reduced errors • Propagation delay • Time taken by a signal to travel from source to destination and “envelope delay distortion” measures the variance in propagation delay within the voice band • Attenuation distortion • Gain fluctuations with frequency
The Telephone • Telephony • Science of translating sound into electrical signals • Tip and Ring • Transmit and Receive wire that connect the instrument to a plug in the wall using RJ-11 jack
Outgoing Call • Pulse Dial • In general, pulse repetition rate is between 8 and 11 pulses per second (pps) • Dual Tone Multiple Frequency (DTMF) • Most commonly used signaling system today • More reliable and faster than “pulse dial” • Transmission rate is 7 digits per second • Consists of a frequency matrix • Multi-Frequency (MF) • Used on trunk circuits • Transmission rate is 7 digits per second
