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S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Vkev page: 1 Teknillinen korkeakoulu S-38.130 Licentiate course on Telecommunications Technology: IP Telephony Voice over ATM, Voice over ADSL, and Voice over CATV Erik Vkev 6.4.2001 IP Telephony IP Telephony - Introduction - - Introduction -

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S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 1

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over ATM, Voice over ADSL, and Voice over CATV

Erik Väkevä6.4.2001

IP TelephonyIP Telephony- Introduction -- Introduction -

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 2

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over ATM, ADSL, CATVVoice over ATM, ADSL, CATV- Introduction -- Introduction -

� The telephone networks of today are changing

� from traditionally circuit-based networks (TDM, PCM, PDH, SDH)

� to the packet-based networks (VoIP, VoA)

� opens challenges to new voice technologies. (VoIP, VoA, VoDSL, andVoCATV).

� This presentation presents the basic information

� VoA, based on cell technology, asynchronous, high transfer speed e.g. 622 Mbps

� The VoDSL is local loop access technology and transfer speed is up to 9 Mbps.

� Community Antenna Television (CATV) was unidirectional but now topology ofnetworks bi-directional

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 3

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over ATMVoice over ATM- Networks -- Networks -

� Asynchronous Transfer Mode (ATM),

� packet switching technology

� service-independent

� 53-byte fixed-size cell (5 bytes header and 48 bytes payload ---> efficiency 90.6 %.

� International Telecommunication Union (ITU) has selected ATM as

� Transfer technology for Broadband-Integrated Services Digital Network (B-ISDN)

� traditional telecommunications networks (PDH, SDH and CATV)

� service dependence, PDH and SDH networks for voice carry and CATV for TVchannels.

� inflexible, bandwidth like 64 kbps and its� multiplies 32*64 kbps

� inefficient, 64 kbps point-to-point channel through a telecommunications networkfor one phone connection

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 4

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over ATMVoice over ATM- ATM Adaptation Layer -- ATM Adaptation Layer -

Five ATM Adaptation Layer (AAL) types.

� Layers carry diverse message streams, same ATM cell format (53 bytes).

� AAL Type 1: Constant Bit Rate (CBR) Services;

� for isochronous information streams, voice (64 kbps), uncompressed video andleased lines

� AAL Type 2: Variable Bit Rate (VBR) Services;

� audio and compressed video (MPEG2)

� AAL Type 3/4: Connection-oriented VBR Services;

� Data Transfer on packet switching networks

� AAL Type 5: Connectionless VBR Services;

� Data Communications (TCP/IP)

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 5

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over ATMVoice over ATM- Protocols, ATM and AAL2 -- Protocols, ATM and AAL2 -

ATM trunking (AAL2)� for narrowband

services� between two

InterworkingFunctions (IWF) tointerconnect pairs ofnon-ATM trunks.

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 6

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over ATMVoice over ATM- Protocols, ATM and AAL2 -- Protocols, ATM and AAL2 -

AAL2 benefits compared to other methods� bandwidth allocation is less per cell,� silence removal releases bandwidth

� no encoded speech information� no empty ATM cells

� operator can route and switch narrowband calls on a per call basis� AAL2 layer is better for bursty traffic (VBR)

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 7

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over Voice over ATMATM- Delays and Echo- Delays and Echo - -

7) cells transmission time in physical network� Echo is caused by

� hybrid networks� 2-wire cables and 4-wire cables� acoustical feedback at the end user's terminal

are used.� When speech channels are carried in ATM cells

then echo cancellers are required at the interfaceof each speech circuit into the ATM network

� Delays and echo are important variables on speech quality (ITU-T G.114)� Acceptable delays are about 15-30 ms without echo cancellers and� 150 ms in international speech connections with echo cancellers.� An acceptable latency is 300 ms and 450 ms latency is unacceptable� Delays appear from 1) voice compressing and decompressing 2) voice packaging

to ATM cell 3) different buffers 4) Quality of Service (QoS) queues 5) switching ofATM cells 6) build-out delay for accommodating packet delay variation (PDV)

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 8

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over Voice over ATMATM- Services and descriptors- Services and descriptors - -

ATM services have two different main descriptors; 1) Traffic descriptors 2) QoSdescriptors

Traffic descriptors

� Peak Cell Rate (PCR), defines the maximum cell rate over connections that sourcecan submit

� Sustainable Cell Rate (SCR), defines average cell rate upper limit to connectionswithout traffic violation

� Maximum Burst Size (MBS), defines maximum number of cells that can be sentback-to-back at the peak rate

� Minimum Cell Rate (MCR), parameter that is set by the MCR commitment request

� Cell Delay Variation Tolerance (CDVT), defines the maximum cell delay variance

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 9

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over ATMVoice over ATM- Services and descriptors -- Services and descriptors -

The QoS descriptors

� Maximum Cell Transfer Delay (maxCTD), CTD is a delay that is generated when cellis transferred from start point to end point on the network and maxCTD is an upperlimit on CDT.

� Cell Delay Variation (CDV), defines maximum cell transfer delay time difference inthe network. CDV is the maxCTD (worst case) minus fixed delay (best case).

� Cell Loss Ratio (CLR), defines ratio to the ratio of lost cells to total cells transmitted.Cell loss causes e.g. buffer overflow situation or wrong routing.

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 10

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over ATMVoice over ATM- Services classes -- Services classes -

� Constant Bit Rate (CBR) services --> nickname �Continuous Bit Rate�.

� rigorous timing controls and performance parameters.

� video, single voice channel, N*64kbps, DSn, En, Q.931 N-ISDN D-channel signallingand circuit emulation.

� Variable Bit Rate (VBR) services, real-time-VBR (rt-VBR) and non-real-time-VBR (nrt-VBR)

� a bursty traffic, voice channel with silence removal and compressed video packets.

� Available Bit Rate (ABR) services

� elastic applications, Client-Server applications,TCP/IP, LAN applications, Q.2931 ATM signalling.

� Unspecified Bit Rate (UBR) services

� Used to fill bandwidth with data stream

� provides �best-effort� service

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 11

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over Voice over ADSLADSL- ADSL & DSL- ADSL & DSL - -

Two different working groups have originally developed DSL

� the Asymmetric Digital Subscriber Line (ADSL) Forum

� the Universal ADSL Working Group (UAWG)

ADSL is a local loop access technology

� a modem technology, copper twisted-pair wire

� data, voice, and video

� 256 frequency channels for downstream transmission, from 1.5 Mbps to 9 Mbps

� 32 channels for upstream transmission, from 64 kbps to 1.5 Mbps

� channels� bandwidth is 4.3125 kHz.

� data part is continuously connected, voice connection will be created

� maximum line length is 12000 foots (12000*30,48 cm ~ 3.660 m)

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 12

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over Voice over ADSLADSL- End user's ADSL network- End user's ADSL network - -

End user needs

� an ADSL modem with filter

� the filter can be included to the ADSL modem, �Splitterless Installation�

� cheaper than splittered installation

� Plain Old Telephony Server (POTS) splitter is used, "splittered installation"

� data stream is separatedwith High-pass-Filter(HPF)

� voice is separated withLow-pass-Filter (LPF)

� passive splitter is reliablein a power failuresituation.

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 13

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over Voice over ADSLADSL- VoDSL- VoDSL - -

� VoDSL technology is a platform

� equipment or Network Elements (NE)

� voice or data to customer over Public Switched Telephony Network (PSTN) orover Packet Backbone Network.

� Equipment or Network Elements (NE) are� customer equipment (e.g.

telephones, fax, and modem),

� Integrated Access Device (IAD)like ADSL modem, interface to thevoice and data traffic

� Digital Subscriber Line AccessMultiplexer (DSLAM)

� voice gateway, filter voice trafficfrom data network

� Class 5 Switch, voice services

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 14

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over Voice over ADSLADSL- Physical layer- Physical layer and standards-and standards-

Physical transport layer

� Frame Relay (FR), ATM, or Internet Protocol (IP).

� FR is common used technology,

� ATM has useful Quality of Service (QoS) traffic classify, AAL1 and AAL2

� IP is future technology

Standards

� Physical layer standards ---> ANSI, ETSI, and ITU

� ATM standards ---> ITU and the ATM Forum

� IP standards ---> Internet Engineering Task Force (IETF)

� ADSL architectures ---> ADSL Forum

� Several working groups, one of which is VoDSL group and it has several sub-working groups

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 15

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over Voice over CATVCATV- Cable Television- Cable Television - -

Traditional CATV

� one-way transmission network

� system sent TV programs to a downstream direction

� network structure is point-to-point

Nowadays CATV

� two-way transmission network

� provides fast data transmission

� cable modems (CM)

� speed is from 3 Mbps to 50 Mbps

� line distance can be over 100 km

� network topology is a tree model.

� coaxial cables, last kilometres

� Hybrid Fiber Coax (HFC)

� cable converters near the subscriber

� different services, classified to twoclasses

� distributive services

� interactive services, two-transmissionpath

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 16

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over Voice over CATVCATV- CATV network- CATV network - -

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 17

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over Voice over CATVCATV- Standardisation- Standardisation and organisations-and organisations-

Multimedia Cable Network System (MCNS) partners

� cable operators and media companies from North America

� standard named Data over Cable Service Interface Specification (DOCSIS)

� used in North America area and in Asian area

European Telecommunication Standards Institute (ETSI)

� standard named Digital Video Broadcasting (DVB), ETS 300 800

� used in European area, in Asian area, and South American area

Other standard is named Digital Audio Video Council (DAVIC)

International Telecommunication Union (ITU)

� Both DVB/DAVIC and MCNS standards are nowadays ITU standards

MCNS and DVB/DAVIC standards are dominated markets over world

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 18

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over Voice over CATVCATV- DVB/DAVIC standards 1(2)- DVB/DAVIC standards 1(2) - -

DAVIC since in 1994, memberships that represent all sectors

� memberships that represent all sectors, manufacturing, service, researchorganisations, and governments.

� standard named DAVIC 1.4

� architecture, interfaces, protocol layers, security, and interoperability

DVB standard was accepted by ETSI organisation in 1997

� DVB specification includes

� Audio, Conditional Access, Interactivity, Interfacing, Measurement,Multimedia Home Platform (MHP), Multiplexing, Subtitling, andTransmission

DAVIC and ETSI have worked together

� DVB specification and DAVIC specification are identical.

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 19

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over Voice over CATVCATV- - DVB/DAVIC DVB/DAVIC standards 2(2) standards 2(2) - -

� DVB/DAVIC standards have been created to European markets.

� European Union (EU)

� directive that digital TV transmission must be based on DVB specification

� recommended to use DVB/DAVIC standards on digital audio and videoservices.

� The European Cable Communications Association (ECCA)

� recommends using these standards on equipment

� cable operators demand that CMs are compatible to DVB/DAVIC standards.

� Physical layer is based on ATM technology (QoS)

� two user equipment to home,

� Set-Top-Box (STB); interactive TV applications and Internet applications

� CM; video, data, and voice applications.

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 20

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over Voice over CATVCATV- - MCNS/DOCSIS standardMCNS/DOCSIS standard - -

MCNS standards

� multi cable service operators (MSO) and media companies from NorthAmerican

� The DOCSIS specification, beginning of 1998

� transmission of data over cable network

� North American TV standards

� First version didn�t support QoS, but now QoS has been added to thespecification.

� The DOCSIS 1.1 specification; fragmentation in the upstream anddownstream, support QoS, and tiered services.

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 21

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over Voice over CATVCATV- - DVB/DAVIC versus DOCSISDVB/DAVIC versus DOCSIS - -

S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 22

Teknillinen korkeakoulu

S-38.130 Licentiate course on Telecommunications Technology: IP Telephony

Voice over Voice over CATVCATV- - ConclusionConclusion - -

Conclusion

� The ATM is lower layer technology but VoDSL and VoCATV are modemtechnologies

� VoATM, VoDSL, and VoCATV, offer new transfer methods to carry voice traffic.

� Circuit based networks are inefficient

� ATM technology; structure is cell, QoS service classes, QoS plus TOS quaranteecertain traffic class level ---> no important delays or latencies

� DSL technology; modem technology, better transfer speed, copper lines, line lengthto a few kilometres

� CATV technology; old technology, two different services, distributive services andinteractive services. Two standards, DVB/DAVIC from European andMCNS/DOCSIS from North American, dominated other specifications.