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

Teknillinen korkeakoulu
IP Telephony
- Introduction -
Voice over ATM, Voice over ADSL, and Voice over CATV
Erik Väkevä
6.4.2001
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Voice over ATM, ADSL, CATV
- Introduction -
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The telephone networks of today are changing
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from traditionally circuit-based networks (TDM, PCM, PDH, SDH)
to the packet-based networks (VoIP, VoA)
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opens challenges to new voice technologies. (VoIP, VoA, VoDSL, and
VoCATV).
This presentation presents the basic information
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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
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Voice over ATM
- Networks -
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Asynchronous Transfer Mode (ATM),
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packet switching technology
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service-independent
International Telecommunication Union (ITU) has selected ATM as
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53-byte fixed-size cell (5 bytes header and 48 bytes payload ---> efficiency 90.6 %.
Transfer technology for Broadband-Integrated Services Digital Network (B-ISDN)
traditional telecommunications networks (PDH, SDH and CATV)
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service dependence, PDH and SDH networks for voice carry and CATV for TV
channels.
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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
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Voice over ATM
- ATM Adaptation Layer Five ATM Adaptation Layer (AAL) types.
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Layers carry diverse message streams, same ATM cell format (53 bytes).
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AAL Type 1: Constant Bit Rate (CBR) Services;
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AAL Type 2: Variable Bit Rate (VBR) Services;
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audio and compressed video (MPEG2)
AAL Type 3/4: Connection-oriented VBR Services;
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for isochronous information streams, voice (64 kbps), uncompressed video and
leased lines
Data Transfer on packet switching networks
AAL Type 5: Connectionless VBR Services;
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Data Communications (TCP/IP)
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Voice over ATM
- Protocols, ATM and AAL2 -
ATM trunking (AAL2)
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for narrowband
services
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between two
Interworking
Functions (IWF) to
interconnect pairs of
non-ATM trunks.
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Voice over ATM
- Protocols, ATM and AAL2 AAL2 benefits compared to other methods
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bandwidth allocation is less per cell,
silence removal releases bandwidth
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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)
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Voice over ATM
- Delays and Echo -
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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)
7) cells transmission time in physical network
Echo is caused by
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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
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Voice over ATM
- Services and descriptors ATM services have two different main descriptors; 1) Traffic descriptors 2) QoS
descriptors
Traffic descriptors
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Peak Cell Rate (PCR), defines the maximum cell rate over connections that source
can submit
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Sustainable Cell Rate (SCR), defines average cell rate upper limit to connections
without traffic violation
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Maximum Burst Size (MBS), defines maximum number of cells that can be sent
back-to-back at the peak rate
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Minimum Cell Rate (MCR), parameter that is set by the MCR commitment request
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Cell Delay Variation Tolerance (CDVT), defines the maximum cell delay variance
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Voice over ATM
- Services and descriptors -
The QoS descriptors
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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.
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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).
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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.
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Voice over ATM
- Services classes -
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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.
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Variable Bit Rate (VBR) services, real-time-VBR (rt-VBR) and non-real-time-VBR (nrtVBR)
 a bursty traffic, voice channel with silence removal and compressed video packets.
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Available Bit Rate (ABR) services
 elastic applications, Client-Server applications,
TCP/IP, LAN applications, Q.2931 ATM signalling.
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Unspecified Bit Rate (UBR) services
 Used to fill bandwidth with data stream
 provides “best-effort” service
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Voice over ADSL
- ADSL & DSL Two different working groups have originally developed DSL
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the Asymmetric Digital Subscriber Line (ADSL) Forum
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the Universal ADSL Working Group (UAWG)
ADSL is a local loop access technology
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a modem technology, copper twisted-pair wire
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256 frequency channels for downstream transmission, from 1.5 Mbps to 9 Mbps
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32 channels for upstream transmission, from 64 kbps to 1.5 Mbps
data, voice, and video
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)
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Voice over ADSL
- End user's ADSL network End user needs
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an ADSL modem with filter
the filter can be included to the ADSL modem, “Splitterless Installation”
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cheaper than splittered installation
Plain Old Telephony Server (POTS) splitter is used, "splittered installation"
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data stream is separated
with High-pass-Filter
(HPF)
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voice is separated with
Low-pass-Filter (LPF)
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passive splitter is reliable
in a power failure
situation.
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Voice over ADSL
- VoDSL -
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VoDSL technology is a platform
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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),
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Integrated Access Device (IAD)
like ADSL modem, interface to the
voice and data traffic
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Digital Subscriber Line Access
Multiplexer (DSLAM)
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voice gateway, filter voice traffic
from data network
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Class 5 Switch, voice services
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Voice over ADSL
- Physical layer and standardsPhysical transport layer
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Frame Relay (FR), ATM, or Internet Protocol (IP).
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FR is common used technology,
ATM has useful Quality of Service (QoS) traffic classify, AAL1 and AAL2
IP is future technology
Standards
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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 subworking groups
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Voice over CATV
- Cable Television Traditional CATV
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one-way transmission network
system sent TV programs to a downstream direction
network structure is point-to-point
Nowadays CATV
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two-way transmission network
Hybrid Fiber Coax (HFC)
provides fast data transmission
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cable modems (CM)
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different services, classified to two
classes
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distributive services
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speed is from 3 Mbps to 50 Mbps
line distance can be over 100 km
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network topology is a tree model.
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coaxial cables, last kilometres
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cable converters near the subscriber
interactive services, two-transmission
path
Teknillinen korkeakoulu
Voice over CATV
- CATV network -
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Voice over CATV
- Standardisation and organisationsMultimedia Cable Network System (MCNS) partners
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cable operators and media companies from North America
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standard named Data over Cable Service Interface Specification (DOCSIS)
used in North America area and in Asian area
European Telecommunication Standards Institute (ETSI)
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standard named Digital Video Broadcasting (DVB), ETS 300 800
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used in European area, in Asian area, and South American area
Other standard is named Digital Audio Video Council (DAVIC)
International Telecommunication Union (ITU)
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Both DVB/DAVIC and MCNS standards are nowadays ITU standards
MCNS and DVB/DAVIC standards are dominated markets over world
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Voice over CATV
- DVB/DAVIC standards 1(2) DAVIC since in 1994, memberships that represent all sectors
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memberships that represent all sectors, manufacturing, service, research
organisations, and governments.
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standard named DAVIC 1.4
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architecture, interfaces, protocol layers, security, and interoperability
DVB standard was accepted by ETSI organisation in 1997
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DVB specification includes
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Audio, Conditional Access, Interactivity, Interfacing, Measurement,
Multimedia Home Platform (MHP), Multiplexing, Subtitling, and
Transmission
DAVIC and ETSI have worked together
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DVB specification and DAVIC specification are identical.
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Voice over CATV
- DVB/DAVIC standards 2(2) -
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DVB/DAVIC standards have been created to European markets.
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European Union (EU)
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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)
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recommends using these standards on equipment
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cable operators demand that CMs are compatible to DVB/DAVIC standards.
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two user equipment to home,
Physical layer is based on ATM technology (QoS)
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Set-Top-Box (STB); interactive TV applications and Internet applications
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CM; video, data, and voice applications.
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Voice over CATV
- MCNS/DOCSIS standard MCNS standards
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multi cable service operators (MSO) and media companies from North
American
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The DOCSIS specification, beginning of 1998
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transmission of data over cable network
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First version didn’t support QoS, but now QoS has been added to the
specification.
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The DOCSIS 1.1 specification; fragmentation in the upstream and
downstream, support QoS, and tiered services.
North American TV standards
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Voice over CATV
- DVB/DAVIC versus DOCSIS -
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Voice over CATV
- Conclusion Conclusion
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The ATM is lower layer technology but VoDSL and VoCATV are modem
technologies
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VoATM, VoDSL, and VoCATV, offer new transfer methods to carry voice traffic.
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DSL technology; modem technology, better transfer speed, copper lines, line length
to a few kilometres
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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.
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
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