Voice over IP Tutorial

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Voice over IP Tutorial
Prepared by Neil Smith neil.f.smith_at_sympatico
.ca
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VoIP Market Segments

• Enterprise
• CPE owned / managed by business
• Typically contained to single site, PSTN used for
  inter-site
• Carrier / Service Providers
• Core
• Toll network expansions / simplifications
• Wireless 2.5G, 3G session controllers for
  roaming
• Also VoATM
• Access
• Primarily Cable Operators
• Enterprise
• CPE or network based (Centrex)
• Consumer
• Internet phone, individual use or into service
  provider
• Client is either POTS phone set or PC/headphone
• Pre-paid card services

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Network Components

• Client
• Soft PC or web applet
• Hard SIP phone (ethernet), POTS phone into
  small gateway, USB port or IAD??
• Protocol SIP, analog
• Some client-only vendors PingTel, Polycom,
  ipDialog
• But often part of gateway / SoftSwitch product
  portfolio, especially soft clients Cisco, Nortel
• Gateway
• Real world meets VoIP world!
• DSP farms
• 3rd party or proprietary cards
• routers/edge switch or PBX add-ons or dedicated
• Access 1 24 port gateway
• phone, ISDN or non-ISUP trunk in -gt 10/100/1000
  IP out
• Typically CPE, but could be in service provider's
  office (120AC or -48VDC)
• Vendors Mediatrix, Cisco, Clarent, TollBridge
• Core mega-line gateway
• carrier grade, definition can vary depending on
  whether enterprise or carrier!
• PRI or ISUP in -gt multi-GE out (IPoAAL)
• Central office equipment -48V

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Network Components

• SoftSwitch
• Call / session controller
• Enterprise IP PBX
• Typically s/w product on commercial compute
  platform (Sun 4500 / Netra 1800)
• Scalable (for carrier or Centrex) or not! (for
  enterprise)
• May include other servers proxy, re-direction,
  OAM, and applications
• Protocol control session
• SIP, H.323 (Gatekeeper) MGCP, H.248
• Vendors BroadSoft, Natural Convergence, Cisco,
  Telcom Vendors (Lucent), Telecordia
• International SoftSwitch Consortium
  (www.softswitch.org)
• Vendors
• Insight Research Corp. Media Gateways, Signaling
  Gateways, and Media Servers 2003-2008 (2003)
• Enterprise, Signaling, and Media Gateway
  Suppliers
• Cisco, Claret, ipGen, Ericsson, Inc., Lucent,
  Nortel Networks, Nuera Communications, Inc.,
  Encore Networks, Sonus Networks, Mockingbird
  Networks, SS8 Networks, VocalTec, Convergent,
• Voice over GR-303 Gateway Vendors
• CopperCom, Jetstream, ComMATCH
• Application and Media Server Vendors
• Alcatel, AudioCodes, BroadSoft Inc, Cisco
  Systems, Congruency, Inc., Convedia, Indigo
  Software, IPeria Inc., IP Unity, Longboard,
  Lucent, Microsoft Corporation, Nortel Networks,
  Openwave Systems Inc., Polycom Inc., RADVISION
  Ltd., RealNetworks, Snowshore Networks, Sylantro
  Systems Corp., Telcordia Technologies

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Bits Bytes (Mega!)

• Codecs
• G.711
• 64kbps PCM, A-law(Europe) m-law (NA)
• Most DSP will allow different quantization for
  input output
• Packet sizes of 10, 20 ms rare 30 ms
• Highest bandwidth, low delay, least distortion of
  signal (good for tones, fax modem)
• Lowest compute, therefore highest channel density
  on DSP
• G.723.1
• 5.3 or 6.3 kbps
• Packet size 30 ms
• Subset of G.723, which was developed as part of
  H.324 / H.323 family of standards operate over
  9.6 kbps modem (i.e. Long-time support)
• Annex for silent suppression
• Low(est) bandwidth, 37.5 ms algorithmic delay,
  signal can get distorted
• High compute (8- 10x G.711)
• G.729A
• 8 kbps
• Packet size 10, 20, 30 ms typical 30 ms
• Annex A of G.729 (wireless) as a reduced
  complexity algorithm
• Annex for silent suppression

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Bits Bytes (Mega!)

• Codecs
• G.726
• Adaptive 40, 32, 24, 16 kbps
• Origins in digital as half-rate PCM
• G.728
• 16 kbps
• Packet size 2.5 ms
• Almost real-time (0.625 ms algorithmic delay)
• Highest compute

no silent suppression
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Voice Stream Network Considerations

• Echo cancellation (G.168)
• Phone adapter or CPE gateway 5ms
• Central office gateway 32ms should work, however
  have experience with customers wanting 64 128ms
• Need not always understood and different from
  digital world
• Fax
• Most codecs will handle
• packet loss will result in errors not
  recoverable by some machines
• T.38 standard (Fax over IP)
• Delay
• Factors
• Codec delay (same problem as in wireless)
• Transport (typically same as wireless or
  wireline)
• Router / switching delta component! Keep to
  minimum
• Jitter (packet delay variation)
• Some tolerance due to packetization
• Same result as packet loss, if delayed beyond
  play-out time
• Packet loss
• Algorithms for filling in the void

Manageable (predictable) if not using Internet
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Protocols (apologies to standards bodies!)

• RTP
• Real Time Protocol RFC-1887
• Transport of streaming data (voice, video, etc)
• Endpoint to endpoint
• RTCP used for passing control statistical
  information
• RTP / UDP / IP
• MGCP
• Media Gateway Control Protocol RFC-2705
• Gateway control
• Digit collection, make, delete connection, etc.
• Text based
• H.248 is the ITU variant, minor but important
  differences!
• Controller to gateway (controller of endpoints)
• MGCP / UDP / IP
• SIP
• Session Initiation Protocol RFC-2543
• Session control (voice call, video conference,
  web chat, etc.)
• RTP is used for streaming media, SIP used for
  set-up, monitoring, take-down
• Similar grouping as H.323

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Putting it together
SoftSwitch
SIP / SIP-T
MGCP
MGCP
SoftSwitch
Gateway or Phone Adapter or Client
Gateway or Phone Adapter or Client
SIP
RTP / RTCP
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Crossing Boundaries

• NAT
• Problem when NAT is between any component
• Endpoint addresses are exchanged via MGCP or SIP
• Because these addresses are in the payload, NAT
  not applied
• Endpoints are given invalid addresses!
• Solution Proprietary / non-standard
• Protocol mods
• Packet sniffing / protocol aware NAT
• Proxity public and private address space
• Tunnelling
• IETF MIDCOM (RFC-3303)
• Middleware communication protocol
• Not ratified
• Generic to handle NAT, Firewalls
• Firewall
• Open up!
• Dynamic and port range can be extensive in large
  network
• Many vendors claim to operate across firewalls.
  How? Use industry accepted ports, or supply
  scripts to open firewall to allow operation.
• Tunnelling

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Administering the network

• Mobility E911
• Determining geographic location
• Same problem as wireless, except indoors and hard
  to triangulate with ping!
• E911 typically excluded from capability use POTS
  lifeline
• Lawful Intercept (media content)
• Solutions exist, trick is masking event from
  smart users
• Billing
• Most popular is time based (with or with-out
  distance multiplier)
• However, with most ISP charging for bandwidth
  now double billing!
• 3 min call 1.4 - 1.8 MB (upstream downstream)
• 10 person office 30 outside calling 26 - 34 GB
  / month for voice only
• Features flat rate / bundled (partly due to
  SoftSwitch charging systems)

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Business

• New technology no longer in fashion what are the
  drivers?
• Core (pockets)
• High initial cost no easy way to cap n grow
• Gateways morphed for dial-up diversion
• TDMoIP gateways (best of both worlds!)
• Clarent in Chapter 11
• Enterprise Potential!
• Cost effective full feature PBX replacement
• Road warrior /remote / work from home all have
  same voice features and access as office worker
• Call centres (low cost)
• Cons getting addressed
• VM integration SIP voice mail platforms? Or
  integrated application server
• attendant positions Not seen any hardware. Soft
  client solution?
• fax/modem transparency POTS lines for fax/modem
  defeats purpose. In retail applications POS must
  have modem.
• Consumer
• value of web-enabled, multi-media services?
• communications management getting best response