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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, 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
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 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
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 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)
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 Interworking Functions (IWF) to interconnect pairs of non-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 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)
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 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
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 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.
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 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
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 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)
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 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.
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 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
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 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
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 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
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 CATVVoice over CATV- 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 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
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 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.
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 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.
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 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.
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 CATVVoice over CATV- - 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 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.