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A primer on the network Dennis Couture Director – Rural Markets Congressional staff briefing June 7, 2005.

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Presentation on theme: "A primer on the network Dennis Couture Director – Rural Markets Congressional staff briefing June 7, 2005."— Presentation transcript:

1 A primer on the network Dennis Couture Director – Rural Markets Congressional staff briefing June 7, 2005

2 2 The Telecommunications Network >Our telecommunications network allows us to transmit “information” electronically virtually anywhere. >“Information” takes many forms, each with different characteristics Voice Email Broadcast video Real-time video Gaming Mixing traffic requires solid engineering

3 3 Traffic types and characteristics BandwidthDelay Tolerance Error Tolerance VoiceLow Medium EmailLow / MediumHighZero Broadcast videoHigh Medium Real-time videoMedium / HighLowMedium GamingLow / MediumLow The more stringent the demands, the more expensive the network is to build and to maintain.

4 4 What is voice? >Voice is audible human communication Content is concentrated at frequencies below 1KHz Nuance and voice uniqueness reside above 1KHz Traditional telephony transmits a maximum of 4KHz (NOT Hi-Fi) >Other characteristics of voice: Voice communication is usually half duplex (“wasteful”) Voice is sensitive to delay Echo Delayed “half duplex” speech (“Over to you, Bill!) Voice is tolerant of interference The human ear/brain combination is a great receiver Analog noise is filtered out and ignored Digital bit errors have virtually no impact on intelligibility

5 5 Sound Waves

6 6 A real speech signal

7 7 Analog Telephony Electrical signal mirrors the voice signal Objective is to accurately transport this signal 4KHz signal allows speaker recognition Common impairments include: –Loss –Noise –Distortion –Delay Impairments can accumulate t A

8 8 >Analog signal is “sampled” 8,000 samples of 8 bits every second 64Kbps required to carry normal voice >Samples are transmitted digitally >Signal is reconstructed by connecting the dots >Impairments are minimized Loss Noise Distortion Delay >Impairments do not accumulate Digital Telephony t A At this point, the voice has become a stream of data!!!

9 9 Digital Formats >This 64 Kb format is called Pulse Code Modulation (PCM) 64 Kb is a slow bit rate >Multiple 64 Kb channels can be combined This is called Time Domain Multiplexing (TDM) Typically 24 channels are sequenced in a 1.544 Mb signal These are called DS-1 or T-1 circuits Think of loading a conveyor belt into pre-assigned slots >Multiple DS-1 channels can then be combined DS-3 carries 28 DS-1 channels or 672 voice channels Optical systems go much higher OC-192 carries 129,024 voice channels

10 10 Let’s talk about transport >Transmission facilities carry communications from point to point Access facilities reach out to end users Interoffice facilities (trunks) connect internal parts of the network >A tremendous amount of telephone company investment lies in transport (much more than switching) Procurement and installation of cable facilities Terminal equipment at each end of the facility Ongoing maintenance costs >These facilities deliver high bandwidths in a reasonably secure manner

11 11 Fiber Transmission

12 12 Fiber Optics >Light is pulsed on and off very rapidly Think naval flashing lights!!! >Fiber optic systems provide: Very high capacity FASTER - Bit rates are very high LONGER - Distance between repeaters is increasing WIDER - Multiple “colors” can ride on the same fiber Secure transmission Excellent reliability Excellent economics Fiber optic systems carry the vast majority of long distance voice and data traffic

13 13 Increasing optical bandwidth with Wave Division Multiplexing (WDM) WDM Similar to Adding Lanes TDM Exploits Higher Speed Up to 72 “colors” of light share the same fiber capable of 9,289,728 simultaneous calls!

14 14 DWDM Upgrade (Dense Wave Division Multiplexing) Supports OC-48 and/or 192 line rates Provides “effective” line rates of Terabits per second. Add more lanes to the highway Channel 2 Channel 3 Channel n Channel 1 Optical Fiber DWDM Coupler

15 15 Enough of the preliminaries….. How does the network work?

16 16 Network topology >The network architecture physically resembles a highway or train system It consists of network nodes (cities and towns) interconnected with transport facilities (roads or tracks)

17 17 A SONET Network in the D.C. area Synchronous Optical NETwork Looks a lot like the highway system!!!

18 18 Meanwhile at the edge of the network…..

19 19 A f Increasing loop length >Loops connect your telephone to the network >Analog transmission >Long loops (> 18 Kft.) deteriorate the signal Loss, Frequency Distortion, Noise >Load coils can correct this distortion Cut off high frequencies Preclude use of DSL Telephone Loops Twisted Pairs ^ 4 Khz

20 20 >Short loops (no load coils) are now standard Less costly to build and maintain Allows higher frequencies, so as to carry data DSL can be provisioned in a CSA >High speed links connect the Digital Loop Carrier (DLC) to the central office May be copper or fiber fed Carrier Serving Areas Carrier Serving Areas DLC Central Office Local Serving Area

21 21 $$ Today’s investment supports future services. >No VoIP in this picture >Common facilities to the remote unit Mixed TDM and IP traffic >Loop carries analog voice plus IP >Could add Broadband Voice via the PC or an IP Phone >Analog phone service survives power outages Mixed Service Delivery With a typical DLC NG DLC DSLAM PSTN DSL TDM GR-303 IP Analog Voice RTP/IP TCP/IP TDM Switch

22 22 Mixed Service Delivery With BBDLC and a TDM switch >Common facilities to the remote unit carry only IP traffic >Loop carries analog voice plus IP >BBDLC converts analog voice to IP >Could add Broadband Voice via the PC or an IP Phone >Analog phone service survives power outages IP Gateway PSTN IP Analog Voice DSL RTP/IP TCP/IP BB DLC TDM Switch VoIP MGCP MEGACO/H.248

23 23 Triple Play >Why do Triple Play???? One method of extracting more revenue from a DSL line Trying to improve a marginal business case for Internet Access A significant defensive move against the cable threat >Triple play is a big step Content acquisition is an important issue Own or share a head end? Buildout of access network can be costly >Impact of HDTV must be considered Bandwidth requirements / channel capacity MPEG-4 equipment >Video on Demand is a significant revenue opportunity The demand for more advanced video-related capabilities will continue to rise.

24 24 Ah, but where do the roads go? >Roads interconnect towns and cities >Access facilities connect users to their local central office >Trunk facilities connect central offices to each other

25 25 Switching Systems >A digital switch: Converts voice into a digital format Interprets the dialed digits Routes the call to its destination by: Completing local calls Transferring all other calls to another switch for completion Central Office Central Office DLC Trunks

26 26 North American Numbering Plan

27 27 Numbering Issues >In the wireline world, an area code defines a geographic area Mobile phones and some VoIP services break this model This is the source of the E911 problem for both VoIP and cellular >Geographic and Overlay area codes 7 vs. 10 digit dialing >Toll free increase (888, 877 etc.) >Depletion of number inventory Explosion of cell phones, pagers, fax machines, 2 nd lines Recovery program underway (000’s block pooling) >Local Number Portability Support of a competitive marketplace

28 28 >The method of controlling the routing of a call Uses in-band tones and computer communications >Dual Tone Multifrequency (DTMF) i.e. TouchTone® in-band signaling >SS7 (Signaling System 7) (out of band) Very fast and reliable Sets up calls via Signal Transfer Points Performs special data retrieval From service Control Points 800 number translation >Call Progress Tones Busy (60 IPM) Reorder (120 IPM) Special Information Tones (SIT) >VoIP essentially uses in-band signaling Security and reliability issue Signaling Central Office Central Office STP SCP STP

29 29 Old-Fashioned long distance 1 2 3 2 5 3 44 555... 1 2 3 2 5 3 44 555 End Offices Tandem Offices AT&T Long Lines

30 30 Modern long distance >The network is “flatter”, with multiple LD Carriers >The Local Access and Transport Area defines a Bell Company’s operating area. >Rural telephone companies may connect directly to LD carriers but often connect to the closest Bell tandem switch 4 55... 4 55 AT&T MCI Sprint : LATA 5

31 31 Operator Services >Human intervention assists in call processing Collect calls Bill to 3 rd party International calling assistance Directory Assistance Emergency call transfer >Dial “O” for local operators >Dial “OO” for LD operators TOPS* Tandem End Office End Office * TOPS – Traffic Operator Position System – a Nortel product

32 32 Let’s talk Wireless!!!! >Wireless communications are booming >Most of the world utilizes the GSM radio format >In North America, multiple radio formats in use: CDMA, GSM, AMPS, TDMA Impacts the development of wireless devices GSM and CDMA formats are incompatible ( ( ( ) ) ) Base Station Controller Cell sites Mobility Switching System Only a small portion of the call is carried over wireless

33 33 Why is it called “cellular”? >A cellular radio has limited range >As a user moves out of range, the call transfers to a different tower (a ‘handoff” that is often the source of dropped calls) >The area served by a tower is a “cell” >Cells are laid out in a honeycomb pattern and can be subdivided into new cells as traffic increases >Adjacent cells use unique frequencies to avoid interference requiring the phone to change channels >Cells can also be “sectorized” to increase capacity ( ( ( ) ) )

34 34 Wireless to the world >Mobile calls are wireless only at the edge >The remainder is handled exactly like a wireline call Base Station Controller Cell sites LD #1 LD #2 LD #3 : 4 55... LATA 5 Mobility Switching System … Today’s networkWireless network

35 35 Wireless Communications >More than just PCS/Cellular Service >Wireless data is becoming more and more important WiFi technology is spreading rapidly Spokane and Philadelphia city-wide Walla Walla rural network (1500 square miles) Small hot spots (McDonald’s, Starbucks) Home networking >WiMax will emerge to compete with WiFi More than just range extension Adds Quality of Service (QoS) assurance Terminal pricing will be critical >Security is an issue – war chalking Convergence of wired and wireless on an IP network is the future!

36 36 What is the Internet? >The Internet is a large computer network Originally designed to allow communications in times of nuclear war – DARPA design Largely a self-healing network >All data transmission is packetized Utilizes IP (Internet Protocol) routing Packets are switched by routers >The most popular applications are: Email The World Wide Web Access the web using Modems, LANs, xDSL, cable etc. Web content is stored in servers at web sites

37 37 What is IP? Internet Protocol is the grammar of the Internet A standard method of computer communication Utilizes a unique 4-byte addressing scheme (e.g. Sends variable length packets Packets are delivered on a “best efforts” basis Packets are often lost Packet delivery times are relatively slow and quite variable Error detection and correction are the responsibility of end users TCP (Transmission Control Protocol) does this Error correction is accomplished by retransmitting missing or damaged packets Real-time applications typically do not correct errors

38 38 The Internet’s dirty little secrets >The Internet was never designed as a real-time delivery system. The transit time for individual packets can vary substantially This variance is called jitter and effectively adds delay to real- time applications – e.g. VOICE >Traffic capacity is relatively poorly engineered, particularly at the edges IP doesn’t handle congestion well Delay increases the jitter limits IP will drop packets under congested conditions Delay and packet loss are the two major causes of voice quality deterioration in VoIP calls

39 39 Packetizing voice (VoIP) >The format for carrying voice is changing to a packetized format, primarily using IP Voice can be transmitted much like data is over the Internet >Maintaining voice quality is a big issue Control of delay is essential Packet loss must be minimized Compression has some disadvantages >“Voice over packet” and “Voice over the Internet” are not exactly the same >Traditional TDM voice will be around for years >Interworking of VoIP and TDM is mandatory

40 40 The role of VoIP >VoIP is many things to many people >To the Enterprise: A vehicle for major expense reduction A key to improving productivity through feature integration >To the Carrier: A vehicle to lower LD costs, enhance CLEC reach and build unique customer networks Eventually, the means to operate one network, eliminating TDM >To the Consumer: Today, primarily a method of buying cheaper telephone service It will take many years for VoIP to totally replace TDM; but high value subscribers will adopt the technology sooner.

41 41 How does IP telephony work? (IP in the middle) Gateway “Gatekeeper” PSTN Local Exchange PSTN Local Exchange “Gatekeeper” IP SS7 Gateway TDMTDM Paris New York Legend SS7 Protocol Bearer Path Interworking Protocol IP Control Protocol

42 42 How does IP telephony work? (Totally IP) Gateway “Gatekeeper” PSTN Local Exchange PSTN Local Exchange “Gatekeeper” IP SS7 Gateway TDMTDM VoIP line Legend SS7 Protocol Bearer Path Interworking Protocol IP Control Protocol DSL over existing copper loops Telco provides the link to the Internet

43 43 How does IP telephony work? (IP to PSTN) Gateway “Gatekeeper” PSTN Local Exchange PSTN Local Exchange “Gatekeeper” IP SS7 Gateway TDMTDM Sydney VoIP line Legend SS7 Protocol Bearer Path Interworking Protocol IP Control Protocol VoIP line Common Transport Telephone company terminates the call Telco provides the link to the Internet

44 44 An architecture for evolution IP Gateway PSTN IP Analog Voice DSL RTP/IP TCP/IP BB DLC Hybrid Switch Legacy lines SIP TA ( ( ( ) ) ) Eventually the hybrid becomes a softswitch. Application Server

45 45


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