CSIS 6251 CSIS Week 9 Telephony Sonet Copyright Dan Oelke Portions Copyright Dmitry Gringauz For use by students of CSIS 625 for purposes of this class only.

CSIS 6252 Overview Telephony service and the telephone network –History –Network components –Lines vs. Trunks SONET - Synchronous Optical NETwork

CSIS 6253 Telecom history 1876 Alexander Graham Bell applies for patent on his telephone. –Race between Bell and Elisha Gray. –Bell won in court 1891 Almon Strowger, an undertaker, receives patent for an automatic switcher 1921 Graham-Willis act establishes AT&T as a “natural monopoly” 1934 Federal Communications Commission (FCC) created –With PUCs - regulates AT&T 1940s - Hush-A-Phone device

CSIS 6254 Breaking up is hard to do 1969 MCI provides inter-city service 1974 US Government files antitrust suit against AT&T 1975 Carterphone decision Modified Final Judgement (MFJ) Ma Bell broken up into AT&T and 7 RBOCS. RBOCS - Regional Bell Operating Companie –Nynex, Bell Atlantic, BellSouth, Ameritech, Southwest Bell, US West, Pacific Telesis Local and Intra-Lata long distance is kept as monopoly while other services are competitive.

CSIS Telecommunications Act Deregulate the local loop. Facilities Based –Carrier provides its own cables to the customer premise Non-Facilities Based –Carrier rents or leases equipment and lines from local telcos at a discount rate. Allows BOCs to enter long distance market –Provided that they show an open competitive environment exists in local loop. Creates a lot of mergers –Bell Atlantic merges with Nynex –Bell Atlantic & GTE  Verizon –US West & Qwest  Qwest –SBC, Pac Bell, & Ameritech  SBC

CSIS 6256 Hell’s Bells: A Radio history of the Telephone – 8 Parts - 30 minutes each

CSIS 6257 Tariffs A tariff is a description of a service that offers an appropriate rate of charge for that service, and the rules under which the service is to be provided. 50 different regulators rule on tariffs FCC governs rates & services for Long Distance providers Tariffs are written by phone companies and reviewed and enforced by regulators.

CSIS 6258 Sound Banging of molecules together at a rapid rate This banging is called compression and rarefication Rate of compression (pitch, or frequency) per unit time (seconds) is measured in Hertz (Hz). Human voice has frequency range between 100 and 5000 Hertz. Sound also has loudness attribute, or amplitude. Human ear is responsive to variations in frequency between 25 and Hz.

CSIS 6259 Sound Processing Through empirical testing, Phone Companies realized that the majority of useful information is carried in a 3 KHz range The actual voice envelope (spectrum) carried by the phone is 200Hz to 3500Hz. Thus, the bandwidth of the transmitted voice is 3.3 KHz The actual bandwidth of the voice line is 4KHz, but margins are suppressed by bandpass filters to allow multiple channels on the same media

CSIS Telephone Network Topology of connections is used Twisted Pair connects DEMARK point with the wire center (frame). Wire Center is connected to the Switch (Central Office) Switches are interconnected together to form a network. Switches make routing decisions based on the requested destination and available capacity

CSIS Pre-84 Network Topology Over End (Class 5) Offices Over 940 Toll Centers 170 Class 3 Offices (Primary Centers) Over 50 Sectional Centers (Class 2) 10 Regional (Class 1) Centers

CSIS Post-84 Network Topology Images from “Voice & Data Communications” by Regis J. “Bud” Bates & Donald W. Gregory. Third Edition

CSIS North American Numbering Plan Area Code –160 (152) in 60’s, 800 right now Central Office (Exchange) Code –640 originally –expanded to 800 in 1960’s

CSIS Local Access and Transport Area - LATA “Turf” division between Local and Long Distance Companies Based on Geographical area and Population Density Different Rules applied as to who could route the calls where.

CSIS Classifications of telephone companies LEC - Local Exchange Carrier ILEC - Incumbent Local Exchange Carrier CLEC - Competitive Local Exchange Carrier BLEC - Building or Business Local Exchange Carrier DLEC - Data Local Exchange Carrier IXC - Inter Exchange Carrier

CSIS Lines VS Trunks Lines –Low Capacity –Non-intelligent (lack signalling) –Normal Voice Load –Typically dedicated to 1 consumer –Allocated on demand –Can be blocked Trunks –Intelligent (carry signalling information) –High Capacity –Statically Allocated Capacity

CSIS Types of Lines and Trunks POTS - Plain Old Telephony Service –normal voice telephony service Direct Inward Dial Direct Outward Dial FX -- Foreign Exchange -- provides dial tone from the remote (foreign) exchange. –Typical use -- airline reservation system OPX -- Off-premise Extension -- permits a remote phone to function as a local phone. –Typical use -- “remote” extensions in business offices. Tie Lines -- private point-to-point circuit used to connect two voice facilities

CSIS Line signaling types Loop start Ground start Reverse Battery

CSIS LEC - Local Echange Carriers LEC terminates services at the Network Interface Unit (or Demarkation Point) Customer takes over from there on Main Service Provided: Dialtone Other services can be purchased. Either dedicated or party line services is offered Residential Dialing Service (Direct Distance Dialing) Business Services (DID, DOD)

CSIS Pay Phone Service Public Phone Service –Both phone and and line are owned by LEC –No monthly rental charges –Accessed by everybody Semipublic Service –Rent a line and set, place phone in controlled location –Minimum rate guaranteed to the LEC -- controlled by tariffs Private Service –buy or rent a set, rent a line (flat fee) and/or share of profits –placed in restricted location

CSIS Private Lines Tie Lines used to connect different facilities together

CSIS WATS Wide Area Telecommunications Services Primarily a billing service that allows reduced rate for long-distance and local telecommunications Initially, WATS was implemented in the form of bands that separated the country into 5 regions Currently WATS rates can be negotiated between any geographical localities 800/888 Service –Reverse-billing WATS –Recipient pays for the call, and not the call initiator

CSIS Directory Services In deregulated market, can be provided by any of the following: –LECs –IXCs –3-rd party

CSIS Access to IEC (Equal Access) Either full or partial presence is possible in any market –Full presence: IEC rents or buys space installs a POP (Point of Presence, digital switch) –Partial presence: IEC buys space or rents space from LEC installs or rents a frame (wire center) runs high-capacity trunks to POP in a different location

CSIS PBX Systems PBX -- Private Branch Exchange Typically a small-capacity (up to 5K lines) digital switch that provides add-on services not available through LEC Add-on services include, but are not limited to voice mail, transferring, conference calling, etc. Interfaces to the LEC via leased trunks Typically utilizes digital phone sets Up to the customer to maintain the wiring and the equipment

CSIS Centrex Service A PBX-like service offered through LECs LEC “partitions” a Class 5 switch, dedicating some of its processing and voice capacity to Centrex customers Partitioning is typically virtual, or software-only Provides the same services as PBXs Customer does not have to maintain the wiring or the equipment -- LEC does it for the customer Customer has an option of adding own services (voice processing, etc) to Centrex, just like to any PBX

CSIS Key Systems Same features as PBXs Aimed at smaller customers Uses dial-up lines instead of trunks to interface with LEC Modern PBXs are typically packaged as either Key Systems or PBXs, the only difference being the LEC interface

CSIS SONET & SDH SONET - Synchronous Optical NETwork –ANSI/Bellcore standard SDH - Synchronous Digital Hierarchy –ITU (European) standard Both standards are practically identical Standards for a synchronous digital transmission system of TDM traffic over fiber networks. Standards based system for data rates above a T3.

CSIS SONET/SDH Hierarchy STS - Synchronous Transport Signals –51.84Mbps - base level of SONET hierarchy STM - Synchronous Transport Module –155.52Mbps - base level of SDH hierarchy –Exactly equal to STS-3

CSIS STS/OC/STM STS-n and OC-n are identical - –OC-n names are used for optical interconnects –STS-n names are used for electrical interconnects OC-n is exactly n times the rate of an OC-1 signal. STM-1 signal is exactly 3 times the rate of an STS-1 signal STM-n is exactly n times the rate of an STM-1 signal

CSIS STS frame format An STS-1 frame consists of 810 bytes (octets) sent in 125µs. –810 * 8 * 8000 = 51.84Mbps The 810 bytes are arranged as 90 columns x 9 rows –3 columns are overhead –87 columns are actual data

CSIS ADM, Terminal, Repeater SONET/SDH terminal - a mux/demux that creates a SONET signal and terminates paths. SONET/SDH ADM (Add/Drop Multiplexer) - a mux/demux that can separate individual STS-n signals from a higher level signal. SONET/SDH repeater- a physical level regenerator that also terminates section level overhead to allow section level management.

CSIS SONET/SDH - Path/Section/Line In Sonet/SDH systems a strong designation of levels of overhead are kept. Section is lowest level –Repeater to repeater Line is middle layer Path is top/longest layer –from entrance to SONET system to exit of SONET system

CSIS SONET/SDH - Path/Section/Line Repeater Add/Drop Multiplexer Add/Drop Multiplexer Terminal Multiplexer Terminal Multiplexer Repeater Section Line Path T3 OC-n

CSIS SONET/SDH - Section & Line Overhead The section overhead is the first 3 rows of the first 3 columns (9 bytes) per frame. The line overhead is the lower 6 rows of the first 3 columns (18 bytes) per frame. STS-1 Payload 87 columns A1 A2C1 B1 E1F1 D1D2D3 H1 H2H3 B2 K1K2 D4D5D6 D7D8D9 D10D11D12 Z1Z2Z3 Section Overhead Line Overhead

CSIS SONET/SDH Physical layer Fiber optic link, using NRZ encoding –light present is a 1 –no light is a 0 To keep enough transitions, a scrambling mechanism is used.

CSIS SONET/SDH Virtual Tributaries Virtual Tributaries are a method to map a lower speed signal (like a T1or E1) into a portion of an STS-n payload. VT bytes/frame => 1.728Mbps –Used for T1s VT bytes/frame => 2.304Mbps VT bytes/frame => 3.456Mbps VT bytes/frame => 6.912Mbps

CSIS STS concatenated signals Multiple STS-1s can be grouped together into a single higher bit rate facility. Extra overhead bytes are ignored. Technically, any number of STS-1s can be grouped, but the only groupings normally supported are: –STS-3C, STS-12C, STS-48C Generally a grouping must fall on a boundary of the same size inside of the OC-n carrier –A STS-3C must fall on a boundary of 3 –STS-12C must fall on a boundary of 12 Typically used for situations where ATM or Packets are sent over a SONET network.