Telephony

1
Telephony

• How do phones and traditional telephone networks
  work?
• How is IP Telephony different?
• Asterisk PBX An example of open-source enabler.
• Looking forwardPersonal Telephony Phone as a
  universal voice information access device.

2
Traditional Phones

• Dumb devices (1 phone)
• Intelligent network (million-dollar switches)
• TDM (Time-Domain Multiplexing)
• Tight control
• Until 1977 no customer-owned phones
• Until 1984 no access to trunk-side (MCI/Sprint
  court cases)

3
Openness of Phone Network

• Begins in 1984 -ATT divestiture Baby Bells,
  IXCs
• BRI/PRI ISDN availability to end users Smart
  Interfacing to Phone Network (delivery of
  multiple TNs, callerid for outgoing calls,
  forwarding, etc).
• SS7 interconnect for carriers

4
Layers of Phone / IP protocols

• Network IP
• Transport UDP/TCP
• Higher layers BGP, FTP, HTTP, etc.

• Network unnamed
• Transport SCCP
• Higher layers ISUP/IN
• CNAM, LNP, CLASS, LIDB, E911, etc.

5
Phone Networks Architecture

• Central Office (CLASS 5, end user svc)
• Tandems (Central Office without end users)
• Signal Switching Point (SS7 end node)
• Signal Transfer Points (router)
• Signal Control Point (database interface)
• No hierarchy (somewhat like IP)

6
SS7 Services

• CNAM (Caller Name) look up of callers name for
  Caller-ID presentment).
• CMSDB (Call Management Service Database) 800/900
  billing, call management, congestion prevention.
• LIDB (Line Information Database) billing
  information (COCOTS, payphone, etc), to find out
  how to bill customer for the phone call,
  collect/third party phone calls.
• LNP (Local Number Portability) Decoupling of
  phone number from a physical line, Rate Center
  and Central Office Each phone call involves now
  LIDB lookup to find out where physically the
  phone number is located.

7
Phone/IP Network Comparison

• Mindset IP is an open network, SS7 is a closed
  network, providing similar range of services.
• Both are packet based networks
• SS7 is tightly controlled with high requirements
  for interconnection

8
TDM vs Packet

• TDM stands for Time Domain Multiplexing, means
  that a given channel is reserved for duration of
  the call. (No silence suppression or similar)
• TDM signalling All endpoints need to know how to
  reserve bandwidth for the phone call and free it
  (setup/teardown).
• Out-of-band signalling is used to set up
  channels.
• No routing Once call is set up and bandwidth
  allocated, data is passed by intermediary
  endpoints
• Packet-based In-band, over network-layer
  protocol (such as IP), each packet has
  source/destination headers, intermediary routers
  only need to understand IP.

9
Analog to Digital

• To transmit data over a digital network, we need
  to convert it into digital form. (encode and
  decode, codec)
• Uncompressed call is 64k bps (8000
  samples/second, 8 bits/sample), PCM (Pulse code
  modulation)
• Other compressions
• ADPCM (32kbps)
• GSM (8kbps)
• G.723.1 (patented)
• G.729 (patented but reasonably licensable)
• MP3 (slow, no tolerance to loss)
• ILBC (new, becoming popular, alternative to
  patented algorithms)

10
VoIP signalling

• Transmission of voice Usually done with RTP
  protocol (real-time protocol, small headers, and
  one stream per UDP/TCP port). Stream, is for
  example, voice or video one-way conversation.
• Now that we have our phone call in a digital
  form, two endpoints need to agree on codecs and
  transmit call setup information. (Such as caller
  phone number, callers business card, callees
  phone number).
• Two major protocols in use
• H.323 ISO-approved suite, based on ASN
  compression, fixed protocol numbers and binary
  encoding.
• SIP IETF-backed, string-based (easy to parse,
  easy to generate), very HTTP-like, web-friendly
  (sending URLs or email addresses during phone
  call)

11
Signalling, continued

• Required functionality Communication between
  endpoint (Terminal or User Agent/UA) and
  gateway (Gatekeeper or Server)
• Dumb terminals Terminal is generally attached
  to a single gateway.
• Functions to support usual phone features
  Conferencing, call forwarding, call pickup, etc.
• TCP or UDP Both SIP and H323 can use either
  protocol, historically SIP usually runs over UDP,
  and H323 uses TCP.
• H323 is very firewall-unfriendly, and nearly
  impossible to use through firewall.
• Auxiliary functions Billing, Codec conversion
  are all part of signalling.
• Phone/IP address routing No standard, thus even
  if carrier B will eventually deliver the phone
  call via VoIP to end customer, phone call needs
  to travel via PSTN channels between carriers A
  and B.
• ENUM is the standard that may change that
  4.6.6.8.7.0.4.7.1.9.1.e164.arpa is DNS name that
  should translate into IP endpoint for phone
  number 1-917-407-8664

12
Questions?
13
Enough Boring Stuff

• Okay, you told us how do things work. Now, what
  can we do with it?!
• Traditional VoIP applications were toll
  avoidance (for example, when company had two
  offices and a dedicated line, extend a PBX
  through the dedicated line, benefitting from
  compression).
• VoIP can be over private IP network or over the
  Internet.
• Internet VoIP combination provides many
  interesting possibilities by overlaying two
  networks. Example Least Cost Routing among
  available carriers via Internet (or a private IP
  exchange)
• One of pioneers was Free World Dialup A service
  run by volunteers at each location, providing
  gateways from VoIP into PSTN at their location.

14
More VoIP services

• Free World Dialup (FWD) is now a
  gatekeeper/meet-me service where you can get
  your own phone number, set up Netmeeting/GnomeMeet
  ing or any other H.323 application on your PC and
  any other FWD customer can call you via FWD.
• Cool stuff FWD received its own country code.
  Now, anyone can call your FWD number from a
  regular phone and have their call routed to your
  PC.
• (Unfortunately, its an international call for the
  caller)
• VoIP commoditises the phone network. Now, to
  provide any kind of voice service, you dont need
  to wait two weeks for monopolistic provider to
  provide you with service, and you are not bound
  to any given carrier to terminate your calls. You
  can port your phone number to a new carrier in
  matter of days (all electronic).
• Public Internet is an enabler, but also limits
  quality-of-service (when did you last lose your
  dialtone? When did you last had packet loss?).

15
Personal Phone Company

• Dont you wish your phone was smarter? For
  example, most of us have phone and answering
  machine at home (shared with your family), cell
  phone with voice mail, and voicemail in the
  office.
• Which phone number do you usually give out?
• What if you had only one phone number for
  everything?
• One Man, One Phone Follow-me phone number. With
  GPS, potentially, all you need is to check in
  at a given location, and you will receive your
  phone calls at the nearby phone.
• Routing phone calls intelligently based on time,
  caller ID, and information entered by caller, if
  any.
• Dealing with girlfriend calling from payphone is
  a homework exercise for the reader.

16
Wireless VoIP

• Decoupling wireless transport from the phone
  service.
• Already you can use your iPaq as a wireless phone
  anywhere in the world where you can get Wi-Fi,
  and get your phone calls without roaming charges.
• With development of 2.5G wireless networks, it is
  also now possible to decouple phone from RF
  (radio frequency) interface You could carry in
  your pocket iPaq and PCMCIA data connection cards
  for whichever network GSM/GPRS, CDMA/1xRTT,
  AMPS/CDPD, wired ethernet, etc.
• Currently 2.5G networks have high latency and
  barely usable for VoIP , 3G networks are expected
  to fix that.

17
Getting Started VoIP Market

• Origination Receiving calls. Termination
  Sending calls.
• Termination hundreds of providers, strong price
  competition. Many internet sites act like
  switching boards, bringing together customers
  with minutes to terminate and providers who can
  terminate in a given market, at a given call
  completion ratio. Some dont mind dealing with
  small customers, most are wholesale-only. Market
  rate for US long distance is 1c/minute.
• Origination (getting a phone number delivered to
  you via VoIP) Currently much harder.
• Vonage Probably the most vocal company providing
  VoIP services to end users. If you have a
  broadband connection, you can get a reliable
  local phone number from Vonage and
  all-you-can-eat long distance. Unfortunately,
  they are trying to preserve as much control as
  Bells, and will not allow you to interface your
  PC directly with their network. (and go to
  extraordinary lengths to do so).
• iConnectHere Local coverage at many regions, 800
  numbers, no problems with VoIP.
• Regional players (yours truly)

18
Questions?
19
VoIP software

• Number of Free Software packages available to do
  VoIP.
• Major ones
• VOCAL Vovida Open Communications Application
  Library Set of components that implement SIP and
  make possible to build applications based on it.
  (Gatekeeper, Feature Server, etc), C.
• libh323 Open Source implementation of H.323
  stack, C
• Bayonne IVR package, with a very powerful
  scripting language, supports H323 via libh323 and
  a number of proprietary interfaces. Quite good
  for what it does, C.
• Asterisk Open Source Hybrid TDM/packet voice
  PBX and IVR platform with ACD functionality.
  Focus of the rest of the talk.

20
Asterisk overview

• What does Asterisk do? Asterisk is a platform
  (switch) where resources and plugins can be
  added to implement functionality.
• Example resources
• Channel drivers
• VoIP (H323, SIP, MGCP, skinny)
• TDM (hardware cards that support fixed phones)
• Applications Queue, Agent, Festival
  (Text-To-Speech)
• PBX features Voicemail
• CLASS features 3-way call, callerid, Call
  Waiting, etc.
• All features are transparently integrated. SIP
  phone and analog phone can make outgoing calls
  via H323, for example.

21
Asterisk IVR

• Multiple ways to implement IVR
• Asterisk has very powerful dialplan
  (extensions.conf) file where call routing logic
  can be represented exten s,1,Answer
  
• exten s,2,BackGround,pilosoft-welcome Play
  the prompt
• exten 1,1,BackGround,pleasewait if user
  pressed 1, play please wait
• exten 1,2,Queue,salesq Transfer to sales
  queue
• exten 1,3,Voicemail,u599
  Send to voicemail if nobody picks up
• exten 1,4,Hangup
• (also, channel variables can be set/modified,
  etc).
• If dial plan is not sufficient external
  interface via AGI (Asterisk Gateway Interface),
  similar in concept to CGI. Excellent Perl
  Interface available (AsteriskAGI), allowing for
  arbitrarily complex applications.

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• exten 7,5,PGSQL,"Fetch fetchid resultid
  message strlen"
• exten 7,6,GotoIf,strlen?710078
• exten 7,7,Goto,t1
• exten 7,8,Festival,message

23
PBX

• Hardware feasible for deployment for small-scale
  PBX for small businesses. (Integrated with DSL
  and other services)

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Experiences

• Setting up a call center with 8 lines in 48
  hours.
• Switching LD provider.
• Future AsteriskSS7
• Demos16463753460