s38_130_ip_telephony.ppt/ 06.04.2001 / erik väkevä page: 1 teknillinen korkeakoulu s-38.130...

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 -




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, and VoCATV).

• 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 of networks bi-directional




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 TV channels.

• inflexible, bandwidth like 64 kbps and its’ multiplies 32*64 kbps

• inefficient, 64 kbps point-to-point channel through a telecommunications network for one phone connection




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 and leased 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)




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

ATM trunking (AAL2)

• for narrowband services

• between two Interworking Functions (IWF) to interconnect pairs of non-ATM trunks.




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)




Voice over ATMVoice over ATM- 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 interface of 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 of ATM cells 6) build-out delay for accommodating packet delay variation (PDV)




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

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

Traffic descriptors

• Peak Cell Rate (PCR), defines the maximum cell rate over connections that source can submit

• Sustainable Cell Rate (SCR), defines average cell rate upper limit to connections without traffic violation

• Maximum Burst Size (MBS), defines maximum number of cells that can be sent back-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




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 cell is transferred from start point to end point on the network and maxCTD is an upper limit on CDT.

• Cell Delay Variation (CDV), defines maximum cell transfer delay time difference in the 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.




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 signalling and 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




Voice over ADSLVoice over ADSL- 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)




Voice over ADSLVoice over ADSL- 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 separated with High-pass-Filter (HPF)

• voice is separated with Low-pass-Filter (LPF)

• passive splitter is reliable in a power failure situation.




Voice over ADSLVoice over ADSL- VoDSL -- VoDSL -

• VoDSL technology is a platform

• equipment or Network Elements (NE)

• voice or data to customer over Public Switched Telephony Network (PSTN) or over 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 the voice and data traffic

• Digital Subscriber Line Access Multiplexer (DSLAM)

• voice gateway, filter voice traffic from data network

• Class 5 Switch, voice services




Voice over ADSLVoice over ADSL- Physical layer and standards-- Physical layer 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




Voice over CATVVoice over CATV- 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 two classes

• distributive services

• interactive services, two-transmission path




Voice over CATVVoice over CATV- CATV network -- CATV network -




Voice over CATVVoice over CATV- Standardisation and organisations-- Standardisation 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




Voice over CATVVoice over CATV- 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, research organisations, 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, and Transmission

DAVIC and ETSI have worked together

• DVB specification and DAVIC specification are identical.




Voice over CATVVoice over CATV- - 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 video services.

• 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.




Voice over CATVVoice over CATV- - MCNS/DOCSIS standardMCNS/DOCSIS standard - -

MCNS standards

• multi cable service operators (MSO) and media companies from North American

• 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 the specification.

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




Voice over CATVVoice over CATV- - DVB/DAVIC versus DOCSISDVB/DAVIC versus DOCSIS - -




Voice over CATVVoice over CATV- - ConclusionConclusion - -

Conclusion

• The ATM is lower layer technology but VoDSL and VoCATV are modem technologies

• 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 quarantee certain traffic class level ---> no important delays or latencies

• DSL technology; modem technology, better transfer speed, copper lines, line length to a few kilometres

• CATV technology; old technology, two different services, distributive services and interactive services. Two standards, DVB/DAVIC from European and MCNS/DOCSIS from North American, dominated other specifications.

s38_130_ip_telephony.ppt/ 06.04.2001 / erik väkevä page: 1 teknillinen korkeakoulu s-38.130...

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