How To Understand The Differences Between A Telephone System And A Pbx System

Transcription

1 Chapter 2 VoIP Systems, Circuit Switched PBX and Cabling This lecture will cover: On-site telephone systems PBXs Centrex Systems Voice over IP Peripheral devices for telephone systems Voic and other features Call center services ACDs Copper and fiber that connect telephones 1 2 Telephone Connections Telephone Switchboard The first telephones were wired from one user directly to another user (1876) Later switchboards were installed, operated by individuals (1877) Automatic switching or a central office switch patented by Almon Strowger (1891) Mainly to address privacy concern 3 Consider 10,000 subscriber lines capacity in a digital switching center (02)-345-XXXX 4

2 Telephone System Architecture International CAT Telecom Inter-operator TOT TRUE TT&T AIS Regional switching center Local switching center or Branch exchange XXXX XXXX Remote concentration unit PABX 5 6 Remote Concentration Unit Remote Concentration Unit Remote concentration unit PABX Last mile, connected to an analog line Support about 1,000 subscriber lines Multiplexing is used with some switching 4 E1 support up to 128 simultaneous calls Mixed of business and residential users Can be a PBX/PABX in large installation 7 8

3 PBX PBX: Private Branch Exchange PABX: Private Automated Branch Exchange Located on the customer s premises Owned by the user Analog vs Digital telephone set PBX Eliminates the need to wire each on-site individual telephone to a central office All lines wire to PBX switch, which connects to a central switch operated by provider Time division multiplexing Line 1 Line 2 Line Kbps 64 Kbps 64 Kbps PABX E1 (32*64 Kbps = 2048 Kbps) Telephone switching center 9 10 PBX Each employee does not have to pay for: Telephone line to central office Telephone calls made between people in the same office Dialing within the system can be done with fewer digits Campus Operator Connecting Phones to Switches Local provider will bring wire into a building to an interface called RJ-11 jack Most common interface used Demarcation point The point where Telco s responsibility end and user s responsibility start Common point from which to test telephone lines and trunks Telco to jack is telephone provider s responsibility Jack to PBX is PBX vendor s responsibility 11 12

4 Centrex Central Exchange Located on the local telephone providers premises Equipment owned by the telephone provider Offers same features as PBX in terms of costs per call, and reduced digit dialing Figure 2.5 PBX trunks from the telephone company to the demarcation Features of Centrex No-requirement for on-site switching equipment Direct-inward dialing (DID) Automatic identification of dialed calls (Caller ID) Appeal of Centrex to User Save on operator costs, minimal/or none required Detailed billing reports Zeroon-site space requirements Multiple buildings spread out in a Campus Buildings separated by public road or neighbor s buildings 15 16

5 Appeal of Centrex to Provider Competition with PBX vendors More monthly fee Both per line and number of lines PBX and Centrex Systems All provide: Connections between staff in organizations Connections to the outside world The ability for on-site personnel to make calls within the call territory without paying for regular telephone usage fees Only difference between two systems: Location of equipment Ownership of equipment Key Systems Function like a PBX Often smaller, but nowadays differences are harder to see Formerly had less features than PBX User base up to 125 telephones This would be the type of system you buy and plug into your home telephone wiring PBX system requires a different type of line from the phone company Many PBX system can function like a Key system, and vice versa PBX can also be wireless 19 20

6 This lecture will cover: On-site telephone systems PBXs Centrex Systems Voice over IP Peripheral devices for telephone systems Voic and other features Call center services ACDs Copper and fiber that connect telephones PBX can be linked to a cellular telephone system Well-known Features Conference calling and 3-way calling Speed dialing Call waiting Caller ID Call forwarding No answer Busy Direct Inward Dialing Routes calls directly from a local telephone company to telephone connected to a PBX without operator intervention Features used to be exclusive to Centrex Central office passes last 4 digits to PBX Using standard like Q.SIG Companies buy entire blocks of phone # s DID: vs ext

7 Call Accounting Track all phone calls made by users Allows for charging department for usage Automatic and self-generated usage report Indicates amount of traffic on each phone line and trunk For expansion consideration Trunk: the link back to telephone company Also called call detail recording (CDR) Figure 2.6 Direct inward dialing (DID) carried on a T-1 trunk to an IP-based telephone system Basic vocabulary Caller/callee Incoming/outgoing Inside line/outside line Trunk Voice Mail Based on a voice store and forward system Octel Communications first installed voic in 1980 PC based systems now available Unified messaging: Retrieving voice mail via telephone or Retrieving fax via remote fax machine or Retrieving via PC, telephone, or fax Also involve SMS, IM, call forwarding, and calendar 27 28

8 Voice Mail Components CPU: executes the application programs Codecs: convert analog signals to digital signals and visa versa, compress voice to decrease storage space Codec = Coder & Decoder Software: determines the feature (caller, time) I/O cards: to connect phone system with Voice mail 29 Automated Attendants Programmed statements to answer calls Thank you for calling ABC company. If you know your party s extension, you may dial it now. Or programs that direct calls at busy times Formerly not a part of voice mail Voice mail vendors bought out automated vendors and made it a part of voice mail Also called IVR (Integrated Voice Response) Stock trade, show time, flight information, announcement Speech recognition: digits (DTMF), alphabets, words (yes, no, delete), or phases (name) 30 Automatic Call Distribution Enable companies to manage incoming calls and maximize use of employee time Route calls to agent who s been idle the longest Route calls to appropriate agent groups If all agents busy, will hold caller in a queue, route call to another agent, or take voice mail Enable outsourced call center Provide reports that measure productivity of agents, trunk usage, number of abandoned calls 31 Figure 2.9 Integrated voice response system linked to a computer and an ACD. 32

9 Computer Telephony Integration Linkcaller ID to computer database Caller ID/Account number can also be obtained from IVR Coordinate routing requests and information to agents Request: Voice call, , IM, etc. Information: Procedures, product information, customer records, support history, forms 33 Figure 2.10 Queue management software linked to an server and PBX. 34 IP-based Telephone System (VoIP) Review of network terminology Circuit-based switching Dedicates a path through the network for the entire duration of the call Telephony network Packet-based switching Breaks up the message in packets and send packets over network when routes become available Message assembled at final destination Internet network 35 Circuit Switching the establishment, on demand, of an individual connection from a desired inlet to a desired outlet within a set of inlets and outlets for as long as is required for the transfer of information 36

10 Packet Switching Still Circuit Switching Called Time Division Multiplexing (TDM) Still Circuit Switching Not a Circuit Switching

11 Time Division Multiplexing IP Networks for Calls Wouldn t it be nice for voice and data to share one network and cable? Voice calling over IP networks is Voice over IP or VoIP Packets of data and voice share the same network Congestion causes delays and packet dropped Become increasingly popular Skype, MSN, AIM, yahoo How does VoIP work? At the sending end, the voice is Digitized: Quantization, Analog-to-digital converter Compressed: Made smaller using codec Packetized: Assemble into packet At the receiving end, the VoIP packet is Reassembled Decompressed Converted back to analog wave Voice gateway or VoIP media server Reasons for Change Applications Supports Enabling staff who travel to work as if they are in the office Ability to administer remote telephone systems from a central site Or by the user herself Keep up the new technology pace And, of course, single network 43 44

12 IP Based Phone Systems Special phone, router, and Media servers are used Special device called Telephone Adapter allows traditional analog telephone to be used Software-based telephone is called Softphone Equipment digitizes voice traffic and assembles it into packets Compresses the signal so that it takes up less capacity on the network Popular deployment: PBX connect to PSTN VoIP for inter-site All-IP deployment in branch office 47 48

13 VoIP Variations VoIP PBX NativeVoIP VoIP media server is located at the Telephone operator s premises User and operator is linked via data network Can be either Private or Public Can also be considered as Centrex VoIP Call between IP phone is free if it does not involve telephone operator Figure 2.4 Courtesy of Avaya, Voice over IP softphone with the same extension number as the desk telephone Convergence of VoIP on current infrastructure Sufficient capacity for voice and data Compression of voice Staff Training Voice Quality monitoring Security Commercial VoIP Status Popular in selected countries like USA because it is not taxed in the same way as traditional phone In other places, there is limited deployment because the telephone costs are low already In Thailand, is selling IP phone with their own VoIP service Can only make outgoing, but not incoming call VoIP was just become legal in mid-2006 Was illegal to operate/service previously 51 52

14 VoIP Benefits Cost saving from having only one network Feature-rich Most can be enabled/configured by user Seamless integration with Web-service Unique advantage Workforce mobility Click-to-talk feature on web site Examples of Vendors Avaya Communications Cisco Systems, Inc. Nortel Networks Compagnie Financiere Alcatel Mitel Networks Siemens ICN 3Com Still slow to take off Cost: still high Reliability: local area networks tend to crash, choppy when network congested Existing phone base: works great, not expensive, lasts about 10 years after initial investment Getting popular for new office building Interoperability is not here yet H.323 and SIP (Session initiation protocol) But can be fast in places Vonage case study VoIP service provider in the US Founded in 2001 October 2002: 7,000 subscriber lines December 2004: 390,000 subscriber lines March 2005: 500,000 subscriber lines September 6, 2005: 1 Million subscriber lines 55 56

15 This lecture will cover: On-site telephone systems Peripheral devices for telephone systems Voic and other features call center services Copper and fiber that connect telephones Media Carryvoice and data traffic Characteristics of media determine its data speed, accuracy and distance at which traffic can be carried Copper High-quality copper Fiber Wireless Copper Cabling Electrical properties of copper cabling create resistance and interference problems Signals weaken as they travel Twisted Copper Pair Signals are direct current, very susceptible to outside electrical sources Hearing an AM radio on telephone line Hearing another conversation on the telephone (crosstalk) Two copper wires twisted together to limit interference problems Indoor telephone wiring 59 60

16 Twisted Copper Pair Cat 5 Unshielded Twisted Pair Commonly called UTP cable Typically installed for voice and data Connecting telephone to PBX Connecting PC to hub or switch Carries traffic at 100 Mbps within buildings Up to 100 meters in a single span We now have Cat 5e (enhanced) and Cat 6 Cat 6 UTP carries traffic at 1 Gbps within buildings Cat 6 STP also becoming popular Name indicates that cabling tested and standards set for this type of copper cabling Shielded Twisted Pair (STP) Other Terminologies RJ-45 Connector that used with Cat 5 UTP Has eight copper wires in it Outlet: Use to plug RJ-45 jack to Patch panel: Use to connect multiple cables Cross-over cable Special cable to directly connect two PC 63 64

17 Fiber Optics Name Pin Cable Color Pin Name TX+ 1 White/Orange 1 TX+ TX- 2 Orange 2 TX- RX+ 3 White/Green 3 RX+ 4 Blue 4 5 White/Blue 5 RX- 6 Green 6 RX- 7 White/Brown 7 8 Brown 8 Immune to electrical interference Signals transmitted in the form of light No electricity present in signal Highly resistant to taps -> Secure Small in size, requires less conduit Lightweight, no sparking hazard Enormous bandwidth and low attenuation STM-64 can carry 10 Gbps of data over 60 miles Fiber optics cables Disadvantages of Fiber Fiber optics High termination and connection costs Splicer vs soldering gun Needs more care in handling, not flexible like copper Specialized technicians needed to install and test fiber 67 68

18 Fiber Optics Cable Fiber Usage In all long distance networks Between central offices From central offices to neighborhood wire centers Between floors in an office building Internet services provider networks Undersea cable runs Electric utility networks Components of Fiber System Transmitters: convert electrical signals to light signals: LED and Laser Receiver: PINs (positive intrinsic negatives) and APDs (Avalanche photodiodes) Optical Amplifier and Optical Regenerator Single-mode (SMF) and multi-mode fiber (MMF) Figure 2.12 Fiber optics in cable TV networks

19 DWDM Dense Wavelength Division Multiplexing Important part of infrastructure for carrying high-speed voice, data, streaming video and audio Key reason for convergence Convergence: applied to high-speed networks that carry traffic using IP 160 wavelengths in a single fiber: 1600 Gbps Advantages of DWDM Higher capacity over fewer strands of fiber Lower costs to upgrade networks, same fiber used by multiplexing Space saving, less amplifying equipment needed Lower ongoing maintenance expenses, less equipment necessary Components of DWDM Amplifiers and Multiplexers OADM = Optical Add Drop Multiplexer ROADM = Remotely operated OADM Key components of DWDM networks Amplifiers boost the signal Every 100 kilometers Overcome fading and attenuation Unlike regenerator, Amplifier does not involve optical-electrical-optical conversion Regenerator is used less frequent to remove noise, recover clock signal, and correct error Multiplexers combine light from multiple sources onto a single strand of fiber 75 76

20 Optical Multiplexers DWDM and CWDM DWDM = Dense WDM CWDM = Coarse WDM Wireless LAN Also a medium, a wireless medium Suitable for new installation Wiring cable and the cable itself are expensive Exist in almost all conference rooms and many restaurants, and now on Boeing airplane IEEE b (WiFi), g, and a (WiFi 5) Disadvantages: Security and slow-speed (54Mbps) Figure 2.13 Coarse wavelength division multiplexing (CWDM) in cable TV networks