IP Telephony - Introduction -

1
IP Telephony- Introduction -
Voice over ATM, Voice over ADSL, and Voice over
CATV Erik Väkevä 6.4.2001
2
Voice over ATM, ADSL, CATV- 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

3
Voice over ATM- Networks -

• Asynchronous Transfer Mode (ATM),
• packet switching technology
• service-independent
• 53-byte fixed-size cell (5 bytes header and 48
  bytes payload ---gt 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 3264 kbps
• inefficient, 64 kbps point-to-point channel
  through a telecommunications network for one
  phone connection

4
Voice over ATM- 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)

5
Voice over ATM- Protocols, ATM and AAL2 -

• ATM trunking (AAL2)
• for narrowband services
• between two Interworking Functions (IWF) to
  interconnect pairs of non-ATM trunks.

6
Voice over ATM- 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)

7
Voice over ATM- Delays and Echo -

• 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
• 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

8
Voice over ATM- 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

9
Voice over ATM- 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.

10
Voice over ATM- Services classes -

• Constant Bit Rate (CBR) services --gt nickname
  Continuous Bit Rate.
• rigorous timing controls and performance
  parameters.
• video, single voice channel, N64kbps, 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

11
Voice over ADSL- 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 (1200030,48
  cm 3.660 m)

12
Voice over ADSL- 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.

13
Voice over ADSL- 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

14
Voice over ADSL- 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 ---gt ANSI, ETSI, and ITU
• ATM standards ---gt ITU and the ATM Forum
• IP standards ---gt Internet Engineering Task Force
  (IETF)
• ADSL architectures ---gt ADSL Forum
• Several working groups, one of which is VoDSL
  group and it has several sub-working groups

15
Voice over CATV- 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

16
Voice over CATV- CATV network -
17
Voice over CATV- 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

18
Voice over CATV- 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.

19
Voice over CATV- DVB/DAVIC 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.

20
Voice over CATV- MCNS/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 didnt 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.

21
Voice over CATV- DVB/DAVIC versus DOCSIS -
22
Voice over CATV- Conclusion -

• 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 ---gt 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.