Presentation on theme: "OVERVIEW OF TELEPHONE NETWORK"— Presentation transcript:
1OVERVIEW OF TELEPHONE NETWORK What is a telephone and how does it work?How does the phone network work?How are calls routed in the phone network?Newer technologies: IVR, DOV.
2Central office (CO) Hub of the city’s phone network. Large city might have several central offices (Boulder: 492, 494, 499, 449, etc..)Central office:provides power for your phoneroutes your callsbills youPair of wires from your home to CO is called the local loop.
3Telephone instrument Rotary or pulse dialing: Send as many pulses as the number being dialed, e.g.., 5 pulses for a five, 9 pulses for a nine, etc.Touch-tone or Dual tone multifrequency:Each row and column has a different tone associated with it.Two tones are produced simultaneously, associated with the corresponding row and column.
8Hierarchical Routing Structure Regional CenterSectional CenterPrimary CenterToll CenterEnd OfficeClass 1Class 2Class 3Class 4Class 5Most traffic is carried by the trunks at the regional and sectionallevels. The trunks shown by dashed line represent redundantpaths.
9on the telephone network Call routing methodson the telephone networkHierarchical routing: Only one fixed path for each call in the 5-level hierarchy, e.g..,Redundant links between different levels of the hierarchy provide alternate routes, but the network is still static.
10on the telephone network Call routing methodson the telephone networkDynamic routing:Several alternate paths.Selects route based on the current state of the network.Considers time of day, and day of week.StrategiesCentralized versus distributedTime-dependent versus Adaptive.
11J I Route d Route b Y Route a X Route c K Dynamic Routing Chicago SeattleJIRoute dRoute bYRoute aNew YorkXRoute cDenverKPittsburghDynamic Routing
14Interactive voice response (IVR) NEWER TECHNOLOGIESInteractive voice response (IVR)Provide specific information based on caller’s input(as opposed to simple routing):Credit card companies (Visa)BanksParts ordering (dealerships, Avon, etc.)Brokerage companies (stock quotations)Automated fax back servicesIVR is another form of disintermediation
15NEWER TECHNOLOGIES Data-over-voice Data-over-voice: superimpose data and voice on the same copper wire. Separate and direct them properly.Digital Data over voice: similar to DOV, but in this case both data and voice are sent digitally. This is more reliable, and less error-prone.
16Digital Data over Voice (DDOV) from Pacific Bell Pacific Bell Digital Data Over Voice (DDOV) service allows the simultaneous transmission of digital data at speeds of 2.4, 4.8, 9.6 or 19.2 Kbps and voice frequency operation over the same two-wire exchange voice grade non-loaded loop facility.DVM: Data Voice MultiplexerCDVM: Central Office Data Voice Multiplexer.(Source: Pacific Bell)
17New Services Most phone companies provide the following services: Call forwarding, 3-way calling, voice mail, distinctive ring, call waiting, etc.Advanced servicesUnified messaging: Integration of fax, , voice mail)Number portability for cell phones: Allows subscribers to change service provider, location and type of service, and keep the same telephone number (coming!?).Five minutes: What are some other new services that you care about?
18OVERVIEW OF TELEPHONE NETWORK, SWITCHING CONCEPTS AND PBXs What is a Switch?Switching Principles?What is a PBX?What is a call center?What are special phone services?
19Point to point linesIf we could have point to point lines between all sendersand all receivers, then we would not need switching.
20Switching Imagine point to point lines between all pairs of people: # of people # of linesmillionIn general, for n people, # of lines = n(n-1)162 mill. Hosts > 13 Quadrillion2
24Switch Bob Bob Alice Alice Jane Dick Dick John Beth Dave Dave Lines or wires from everybody's house go into the switchWhen a call is placed, the switch creates a temporary link between these lines.
25Types of switching CIRCUIT SWITCHING: creates a continuous, dedicated path between sender and receiver.Must set up an end to end path before any data can be sent.PACKET SWITCHING:No dedicated path between sender and receiver.Examples:
28Circuit switchingSpace division switches: Signal paths are physically separate from one another (i.e. divided in space).Single-stageMulti-stageTime-division switches: Same path is shared by multiple streams (division in time)Modern switches are combination switches
29Single Stage space Division Switch Output LinesSingleStagespaceDivisionSwitch1234InputLines5678910Crossbar Switch (also called Crosspoint switch)
30BlockingBlocking means that even if two parties are free they cannot call one another because of congestion in the switch (“All circuits are busy, try later!!”).If one or both parties are busy, then it is not a case of blocking.Single stage, space division switches are non-blockingMulti-stage, space division switches are blockingTime-division switches are usually non-blocking.
31Three Stage Space Division Switch 112233444556677888991010Three Stage Space Division Switch
32Examples of Crossbar Switches Number of crosspoints =Source: Tannenbaum, Computer Networks, 3rd Ed., 1996
33Time Division Switch 1 2 3 4 5 6 Control Logic Memory contains the calls in progress.Control logic opens and closes gates.Each call gets a slot in a cycle.1 cycle = 125 micro sec.6ControlMemory1-52-33-24-65-16-4Control Logic
35Both Time and Space Switching Needed TSMN x k1NSTSBoth time and space switching is required in large (greater than 10,000) digital switching offices because with the current technology, a time slot interchange (TSI) cannot be built fast enough to handle more than lines. (There are also TSSST switches for larger number of channels.)SpaceSwitchInletMemoryN12TSTSTS – simpler control requirementsTST – better for large switches with heavy load traffic (ie. No.4 ESS can service over 100,000 lines)(TSM: Time Switch Module)Source: Bellamy, John. Digital Telephony. 2nd Edition.
36TSSST Switching Structure TSMn x k(N/n) x (N/n)k x nTSMTSMTSMn x k(N/n) x (N/n)k x nTSMTSMTSMTSMInlet timestageOutlet timestageSpacestageSpacestageSpacestageSource: Bellamy, John. Digital Telephony. 2nd Edition.
37PBX (Private Branch Exchange) Switchboard for a company or university.First generation : late 1800s, manual operatorSecond generation: 1930, no operator requiredSecond and half generation: 1970, Computerized Business Exchange.computer controlled switchesprogrammable, more intelligentleast cost routing of phone calls3rd/4th generation: , AT&T Definity 75/85.“All digital” switchingBoth computer data and voiceSimultaneous voice and dataNon-blocking operation.
38CENTREXA Centrex (Central Office Exchange Service) is similar to PBX, but owned and maintained by phone company. Cost is 20 to 50% higher than the cost of plain telephone lines.
39Call Center More than $50 Billion business in North America. Growing at 20% per year.A central place where customer calls are routed by an organization, usually with some amount of computer automation.Sophisticated Routing: Ability to handle a considerable volume of calls at the same time, to screen calls and forward them to someone qualified to handle them, and to log calls.Call centers are used by: mail-order catalog organizations, telemarketing companies, computer product help desks, and any large organization that uses the telephone to sell or service products and services.Achieve economies of scale associated with mass call handling and yet give callers a tailored feel.
40Bus_136:IVR=Interactive Voice ResponseAdvanced call routingImprove speed and quality of call based on information in the database, and input provided by caller (e.g., IVR). Examples:Skills based routing instead of “next-available-agent.”Key customers can move higher in the queue or be routed to agents assigned to their account.Callers who placed service calls within the last 24 hours can be routed to the agent they originally spoke to.Calls can be routed to a properly skilled agent, depending on the products or services previously purchased.A telemarketing group can route calls to agents with the highest closing ratios in order to increase sales revenues.Challenges: supporting multiple types of transactions; multiple skills.
41Summary Switching is a very important telecommunications technology. Switching technology has become very fast (nano-second speeds).Switches are essentially computers with millions of lines of software.Computer telephony integration (CTI) has made it possible to develop very sophisticated PBXs and call centers.Vendors are coming out with newer products and features every day in telephony equipment.The telephone system is moving closer to becoming all digital except for the local loop which is still analog.