Mr. Mark Welton

 Most telecom infrastructure that exists today is based on standards more than 100 years old  Telecom infrastructure is often so reliable that we expect reliable phone service more than reliable Internet service or power

 Telecommunications refers to the traditional circuit-based switching technologies primary used by voice services  data communications often refers to packet- based switching of the modern Internet

 ACD – automatic call distribution ◦ An ACD is usually found in a call center, where calls may come in from anywhere and need to be directed to the next available operator or queued until one is available

 Add/Drop – used to describe the capability of peeling off channels from a circuit for another use  An add/drop CSU/DSU can separate ranges of channels, thus allowing a T1 to be split for both voice and data use or as two partial T1s

 analog in telecom refers to a signal that is continuous in amplitude and time, any small fluctuation of the signal is important ◦ Radio waves, power waves, and sound waves are analog ◦ When you speak, you create waves of air that hit people’s eardrums

 Digital refers to a signal that has discrete values  If you analyze a sound wave, and then assign a value to each sample of the wave at specific time intervals, you will create a digital representation of the analog wave

 Bandwidth vs. throughput  A range of frequencies is called a band  The width of the band is referred to as bandwidth  US FM channels run from 87.8 MHz to MHz  The bandwidth is 20MHz

 On a digital link what is referred to as bandwidth is really throughput  Throughput is the number of possible state transitions per second  This can also be referred to as the data rate  The signal on the right has more bits per second (bps) then the left (19 possible state changes vs. 6)

 BERT – Bit Error Rate Test  BERT are disruptive tests run on a T1 to validate the integrity of the circuit (looks for errors)  CO – central office ◦ the first hop where phone lines go  Channel bank – a device that separates a T1 into 24 individual analog phone lines

 CSU/DSU – Channel Service Unit and Data Service Unit  The CSU is responsible for interfacing with the WAN service  The DSU is responsible fore interfacing with the data equipment, such as the router  The CSU typically has an RJ-45 connection from the demark point and the DSU has a V.35 connection to a router  In a CSU/DSU router card, the RJ-45 connection from the demark point goes to the router card and the connection on the card interfaces it to the router

 CPE – customer premises equipment  Traditionally, the term was used to describe equipment owned by a telephone service provider that resided at customer premises, but it has evolved to include equipment owned by anyone

 DACCS (pronounced dacks) – Digital Access Cross-Connect System, allows changes to the way voice channels are connected between trunks

 Demarc (pronounced dee-mark) – demarcation point where the telecom provider’s responsibilities end and the customer’s begins  What is an extended demark?  Provider installed location somewhere beyond the real demarc

 DS hierarchy – Digital Signal, describes the signaling rates of links DesignatorCarrierTransmission rate Voice channels DSON/A64 Kbps1 DS1T Mbps24 DS2T Mbps96 DS3T Mbps672 DS4T Mbps4,032

 T-carrier – the generic name of digital multiplexed carrier systems in North America ◦ T stands for trunk, since they originally designed to trunk multiple phone lines between central offices  E-carrier - The European version of digital multiplexed carrier systems  J-carrier – The Japanese version of digital multiplexed carrier systems

 SONET – synchronous optical network, fiber optic system makes use of the optical carrier levels ◦ OC1 – 51 Mbps ◦ OC3 – 155 Mbps ◦ OC12 – 622 Mbps ◦ OC48 – 2,488 Mbps

 ISDN – Integrated Services Digital Network  allows for the simultaneous transmission of voice and data  Uses a separate channel for signaling (Data channel or D-channel) and two remaining channels for content (Bearer channel or B- Channel)  Each B-Channel is capable of 64kbps or a total of 128kbps and the D-channel capable of 16kbps on a Basic Rate Interface (BRI) and 64kbps on a Primary Rate Interface (PRI)  A PRI is an ISDN T1 composed of 23 B-channels and 1 D-channel

 LATA – local access and transport area, government defined areas in which a telecom provider can provide local services  IXC – interexchange carrier providers services to local exchanges by connecting in between LATAs  LEC – local exchange carrier, provides local service within a LATA  Local loop – the last mile connection for a circuit from a telecom facility to it destination

 Latency – term used to describe the amount of time it takes for data to be processed or moved along a network  Not related to throughput, bandwidth, or speed of a link  Related to distance, speed of light, and amount of time for hardware processing  Two parts of latency – propagation delay and processing delay.

 PBX – private branch exchange, used by large organizations as a localized phone company for its ability to share a limited number of public phone lines and the ability to call any internal extension number  POTS – plain old telephone service, your traditional analog phone line  Smart jack – a device that terminates a digital circuit, the service provider can perform remote testing of a circuit with the smart jack installed

 RBOC – Regional Bell Operating Company  Result of the 1984 breakup of AT&T Bell System, into seven regional local only carriers  The Telecom Deregulation Act of 1996 allowed LECs (RBOCs) to sell local and long distance services. ◦ Bell Atlantic ◦ Southwestern Bell ◦ Nynex ◦ Pacific Bell ◦ Bell South ◦ Ameritech ◦ US West

 T1 circuits are full-duplex asynchronous circuits  Two Common types ◦ Channelized T1 – voice circuit with 24 voice channels, each channel contains is own signaling information inserted into the data stream (voice) via in-band signaling ◦ PRI – voice circuit with 24 channels, one of which is dedicated to signaling (out of band signaling), leaving 23 available voice channels

 two types of encoding  Alternate Mark Inversion (AMI) – used for voice only  Binary Eight Zero Substitution (B8ZS) – used for data but can be used for voice

 There are two “states” (zero and one) for the signal on the line  The mark state representing a one (+/-5 volts) and the space representing a zero (zero volts)  The next mark is always the opposite of the preceding mark  Robbed-bit signaling – every eighth bit is used to keep signal (always set to 1 regardless of original value)

 introduced to resolve the shortcomings of AMI  In voice the eighth bit 1 is not an issue because you can not hear the change  In data this would change the information  Need to deal with the synchronization issue of too many zeros in a row without changing the information

 if eight zeros in a row are detected in a signal, those eight zeros are converted to a pattern including intentional BPVs

 Sample audio 8,000 times per second  Each sample is converted in to an eight-bit value  8 th bit is used for signaling (robbed-bit signaling in AMI)

 In standard voice framing each eight-bit sample is relayed from each channel in order  each eight-bit sample is relayed from each channel in order  8 bits X 24 channels = 192 bits  The 193rd bit is used as a framing bit  It will change this bit over 12 frames using the pattern  12 frames are a superframe  Used for voice circuits

 D4/superframe standard is not practical for data transmission (lack error detection)  Extended Super frame (ESF) was developed to deal with this  Uses a pattern of 24 frames instead of 12 ◦ Frames 4, 8, 12, 16, 20, and 24 (every fourth frame)  These frames’ framing bits are filled with the pattern ◦ Frames 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23 (every odd-numbered frame)  These frames’ framing bits are used for a new, 4,000 bps virtual data channel. This channel is used for out-of-band communications between networking devices on the link ◦ Frames 2, 6, 10, 14, 18, and 22 (the remaining even- numbered frames)  These frames’ framing bits are used to store a six-bit CRC value for each superframe.

 Loss of Signal (LOS) – no electrical pulses detected (line is dead)  Out of Frame (OOF) or Loss of Frame (LOF) – a number of frames have been received with errors (synchronization invalid between two sides)  BiPolar Violation (BPV) – two mark signals occur in sequence at the same polarity (usually caused by voltage spike on the line)

 CRC6 - Cyclic Redundancy Check (six-bit) mechanism for error checking in ESF (check sum did not match)  Errored Seconds – shows the number of seconds in a 15-minute window in which errors on the line have occurred  Red Alarm – a local failure on the circuit or continuous OOF error  Yellow Alarm – remote alarm indication of problem down the line  Loopback test – loopback state allowing the sending of data over the link, data should return to sender exactly as sent

 Two types of DS3 ◦ Channelized  672 DS0s (28 DS1s), each capable of supporting a single POTS-line phone call  Same times referred to as a “channeled T3”  DS3 is not the same as a T3 ◦ Clear-channel  Has no channels and is used for pure data

 DS3 is actually a group of seven DS2s multiplexed together  Originally designed to handle phone calls  Each DS1multiplied into a DS3 has its own clocking, framing, and encoding  Multiplexing them into a DS3 can not affect this  The DS3 must also have its own clocking, framing, and encoding

 M13 (pronounced M-one-three, not M- thirteen) is short for Multiplexed DS1 to DS3  Requires two stages of multiplexing ◦ M12 – multiplexed DS1 to DS2 ◦ M23 - multiplexed DS2 to DS3  DS3s were originally used to aggregate T1s