Adapting Legacy Phone Systems to VoIP

1
Adapting Legacy Phone Systems to VoIP

• Vincente DIngianni
• Director of Professional Services
• Binary Systems, Inc.
• vincente_at_binary-systems.com

2
What Well Cover

• Whats inside the PSTN?
• Whats inside the IP network?
• VoIP gateways
• Connecting the IP network to the PSTN
• Bandwidth
• Remote PSTN users The Old Way
• Remote VoIP users The New Way
• Remote PSTN locations The Old Way
• Remote VoIP locations The New Way
• Do I need a Softswitch?
• Do I need a VoIP carrier?

3
The Legacy PSTN
Subscribers
Enterprise Network
PSTN
Public Switched Telephone Network
Enterprise Network
Subscribers
4
Whats Inside the PSTN?
Subscribers
Enterprise Network
Class 5 End Office Switch
Class 4 Tandem Switch
Public Switched Telephone Network
Enterprise Network
Subscribers
5
Forgetting the Complexity
All Routing Logic is managed by the Service
Providers Network Not yours.
Subscribers
Enterprise Network
PSTN
Enterprise Network
Subscribers
Public Switched Telephone Network
6
What Well Cover

• Whats inside the PSTN?
• Whats inside the IP network?
• VoIP gateways
• Connecting the IP network to the PSTN
• Bandwidth
• Remote PSTN users The Old Way
• Remote VoIP users The New Way
• Remote PSTN locations The Old Way
• Remote VoIP locations The New Way
• Do I need a Softswitch?
• Do I need a VoIP carrier?

7
Enter the IP Network
Subscribers
Enterprise Network
PSTN
Enterprise Network
Subscribers
Public Internet or Private WAN
8
Focusing on VoIP
Subscribers
Enterprise Network
VoIP gives you the option to take control of your
Communication Network
Enterprise Network
Subscribers
Public Internet or Private WAN
9
Whats Inside an IP Network?
In most cases, IP Routing Logic is still managed
by a Service Providers Network Not yours
Subscribers
Enterprise Network
Firewall
Routers
Routers
Routers
Firewall
Enterprise Network
Subscribers
Public Internet or Private WAN
10
Forgetting the Complexity
VoIP Communication Protocols, such as SIP
H.323, allow control of your communication
routing without interfering with the Service
Providers Network
Subscribers
Enterprise Network
Enterprise Network
Subscribers
Public Internet or Private WAN
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What Well Cover

• Whats inside the PSTN?
• Whats inside the IP network?
• VoIP gateways
• Connecting the IP network to the PSTN
• Bandwidth
• Remote PSTN users The Old Way
• Remote VoIP users The New Way
• Remote PSTN locations The Old Way
• Remote VoIP locations The New Way
• Do I need a Softswitch?
• Do I need a VoIP carrier?

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What are VoIP Media Gateways?
VoIP Media Gateways provide the bridge between
Legacy Phone Systems and VoIP
Applications/ Management Processing
PSTN

• Voice
• Compression
• Echo
• Cancellation
• Silence
• Suppression

• IP
• Processing
• IP
• TCP
• UDP
• RTP

IP Voice
IP Network
Ethernet PPP Frame Relay ATM

• Fax
• Demodulation
• Handshaking

• Fax
• Demodulation
• Handshaking

Signaling Interworking VoIP lt-gt PSTN
Signaling Interworking VoIPlt-gt PSTN
PBX
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Analog VoIP Gateways
PSTN
Vega 50 Analog VoIP Gateway
IP Voice
IP Network
Ethernet PPP Frame Relay ATM

• Analog Ports for FXS or FXO Signaling
• Supports PSTN/PBX or Telephone Lines
• Connection to the IP Network Via 100Base-T
  Ethernet Interface
• SIP, H.323
• Selectable Coders Per Channel G.711, G.723,
  G.729
• T.38 Fax Relay

PBX
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Digital Trunking VoIP Gateways
PSTN
Vega 400 Trunking VoIP Gateway
IP Voice
IP Network
Ethernet PPP Frame Relay ATM

• Supports PSTN/PBX Digital Trunks
• T1 / E1 ISDN, North American CAS, R2
• Connection to the IP Network Via 100Base-T
  Ethernet Interface
• SIP, H.323
• Selectable Coders Per Channel G.711, G.723,
  G.729
• T.38 Fax Relay

PBX
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What Well Cover

• Whats inside the PSTN?
• Whats inside the IP network?
• VoIP gateways
• Connecting the IP network to the PSTN
• Bandwidth
• Remote PSTN users The Old Way
• Remote VoIP users The New Way
• Remote PSTN locations The Old Way
• Remote VoIP locations The New Way
• Do I need a Softswitch?
• Do I need a VoIP carrier?

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Bridging the Networks
FXO Lines
Digital Trunks
PSTN
VegaStream Analog VoIP Gateway
VegaStream Trunking VoIP Gateway
IP Network
Ethernet
Ethernet
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Bridging the Networks (cont.)
Firewall
VegaStream Analog VoIP Gateway
VegaStream Trunking VoIP Gateway
Routers
Routers
Ethernet
Ethernet
Routers
Firewall
IP Network
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Bridging the Networks (cont.)
PSTN
Class 5 End Office Switch
FXO Lines
Digital Trunks
VegaStream Analog VoIP Gateway
VegaStream Trunking VoIP Gateway
Class 4 Tandem Switch
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Bridging Public and Private Networks
FXO Lines
User Side Digital Trunks
PSTN
VegaStream Analog VoIP Gateway
VegaStream Trunking VoIP Gateway
IP Network
Ethernet
Ethernet
Network Side Digital Trunks
FXS Lines
Private Extensions
Enterprise Network
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The Leaky PBX
Enterprise Network
Enterprise Network
FXO Lines
PSTN
Network Side Digital Trunks
IP Network
Ethernet
Ethernet

• Using Legacy PBX Routing functionality, users may
  dial a prefix to bypass the PSTN
• Calls are routed via VoIP to remote
  locations/countries
• Standard PSTN Toll charges are bypassed
• Enterprising Enterprises resell the ability to
  terminate calls on their local PSTN connection so
  other VoIP users can benefit (not necessarily
  legal)

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What Well Cover

• Whats inside the PSTN?
• Whats inside the IP network?
• VoIP gateways
• Connecting the IP network to the PSTN
• Bandwidth
• Remote PSTN users The Old Way
• Remote VoIP users The New Way
• Remote PSTN locations The Old Way
• Remote VoIP locations The New Way
• Do I need a Softswitch?
• Do I need a VoIP carrier?

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Bandwidth Requirements
Enterprise Network
Enterprise Network
FXO Lines
PSTN
Network Side Digital Trunks
IP Network
Ethernet
Ethernet

• Calculate the number of calls that you will be
  making simultaneously over your IP connection
• Estimate approximately 80-90 kbps uncompressed
  per call
• A T3 (28 T1s) of voice will fill a 100 Mb
  Ethernet link

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Bandwidth Requirements

• Most cable modems provide asymmetrical bandwidth
• 3 Mb downstream is popular
• 256K upstream is typical
• Dont expect to force an entire trunk worth of
  voice through a cable modem or DSL

Cable Modem
256K Upstream
Vega 400 Trunking VoIP Gateway
E1 PRI
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What Well Cover

• Whats inside the PSTN?
• Whats inside the IP network?
• VoIP gateways
• Connecting the IP network to the PSTN
• Bandwidth
• Remote PSTN users The Old Way
• Remote VoIP users The New Way
• Remote PSTN locations The Old Way
• Remote VoIP locations The New Way
• Do I need a Softswitch?
• Do I need a VoIP carrier?

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POTS Line connected to a PBX/CO
PBX/CO
POTS Line

• The Switch provides the Talk Battery to power a
  phone
• The switch provides the dial tone
• The phone generates the digits

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Foreign Exchange Office (FXO)
PBX/CO
FXO
Private Network
Foreign Exchange Office (FXO) Emulates a
telephone set connects to a standard line side
interface of the PBX or central office

• This is the way that Interexchange carriers were
  forced to connect with ATT before equal access
• Carriers would purchase simple lines in each city
  to create a POP
• These lines were directly connected into their
  switching networks
• Subscribers dialed 7-digit access numbers to
  receive dial tone from the carrier

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Foreign Exchange Station (FXS)
FXS
POTS Line
Private Network
Foreign Exchange Station (FXS)
Emulates a switch port
connects to a standard telephone line
Signaling can be loop start or ground start

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Extensions use a combination of FXO and FXS
PBX/CO
FXO
FXS
POTS Line
Private Network
Combination of FXO/FXS allows a remote station to
appear as a standard line
Foreign Exchange Office (FXO) Emulates a
telephone set connects to a standard line side
interface of the PBX/CO
Foreign Exchange
Station (FXS)
Emulates a switch port connects to a standard
telephone line Signaling can be loop
start or ground start
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What Well Cover

• Whats inside the PSTN?
• Whats inside the IP network?
• VoIP gateways
• Connecting the IP network to the PSTN
• Bandwidth
• Remote PSTN users The Old Way
• Remote VoIP users The New Way
• Remote PSTN locations The Old Way
• Remote VoIP locations The New Way
• Do I need a Softswitch?
• Do I need a VoIP carrier?

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Remote VoIP Users
Subscribers
Enterprise Network
PSTN
Public Switched Telephone Network
Enterprise Network
Subscribers
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Remote Lines
Subscribers
Enterprise Network
PSTN
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Adding a VoIP Network
Subscribers
Enterprise Network
PSTN
Public Internet or Private WAN
Cable Modems or DSL can be used for low numbers
of remote users.
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Adding VoIP Gateways
Subscribers
Enterprise Network
PSTN
Vega 50 Analog FXO VoIP Gateway
Vega 50 Analog FXS VoIP Gateway
Public Internet or Private WAN
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Bypassing the PSTN
Subscribers
Enterprise Network
PSTN
Vega 50 Analog FXO VoIP Gateway
Vega 50 Analog FXS VoIP Gateway
Public Internet or Private WAN
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Remote User Connected via VoIP
Subscribers
Enterprise Network
Call routing between VoIP Gateways is configured
locally.
Vega 50 Analog FXO VoIP Gateway
Vega 50 Analog FXS VoIP Gateway
Public Internet or Private WAN
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Configuring Local FXO Extensions
Enterprise Network
Analog FXO VoIP Gateway 192.168.1.123
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Configuring Local FXO Routing
Enterprise Network
Analog FXO VoIP Gateway 192.168.1.123
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Configuring Remote FXS Extensions
Subscribers
Analog FXS VoIP Gateway 192.168.1.202
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Configuring Remote FXS Routing
Subscribers
Analog FXS VoIP Gateway 192.168.1.202
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Remote Users connected via VoIP
Subscribers
Enterprise Network
Subscribers maintain all feature functionality as
local users on the PBX.
Vega 50 Analog FXO VoIP Gateway
Vega 50 Analog FXS VoIP Gateway
Public Internet or Private WAN
41
Adding IP-Only Users
Subscribers
IP Phones
Enterprise Network
Vega 50 Analog FXO VoIP Gateway
Vega 50 Analog FXS VoIP Gateway

• An IP phone is simply a single-port VoIP media
  gateway

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What Well Cover

• Whats inside the PSTN?
• Whats inside the IP network?
• VoIP gateways
• Connecting the IP network to the PSTN
• Bandwidth
• Remote PSTN users The Old Way
• Remote VoIP users The New Way
• Remote PSTN locations The Old Way
• Remote VoIP locations The New Way
• Do I need a Softswitch?
• Do I need a VoIP carrier?

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Trunk Signaling Methods

• In-Band Signaling
• CAS Channel Associated Signaling
• R2
• EM Wink Start
• FGD

Combined Voice and Signaling Channel

• Out-of-Band Signaling
• ISDN / Q.931
• SS7

D-Channel
Bearer Channel
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Network vs. User Side ISDN

• Network side ISDN
• Network side ISDN provides a standard PRI
  interface to a PBX and mimics the behavior of
  legacy phone switches
• User Side ISDN
• User side ISDN provides a standard ISDN PRI
  interface to the Public Switched Telephone
  Network (PSTN)

Network Side
User Side
D-Channel
PSTN
Bearer Channel
Clock Timing
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What Well Cover

• Whats inside the PSTN?
• Whats inside the IP network?
• VoIP gateways
• Connecting the IP network to the PSTN
• Bandwidth
• Remote PSTN users The Old Way
• Remote VoIP users The New Way
• Remote PSTN locations The Old Way
• Remote VoIP locations The New Way
• Do I need a Softswitch?
• Do I need a VoIP carrier?

46
Remote VoIP Locations PSTN Connectivity
Subscribers
Enterprise Network
PSTN
Public Switched Telephone Network
Enterprise Network
Subscribers
47
Remote VoIP Locations Connecting Locations via
PSTN
Enterprise Network
Network Side
ISDN PRI
User Side
PSTN
User Side
ISDN PRI
Enterprise Network
48
Remote VoIP Locations - Adding VoIP
Enterprise Network
PSTN
Enterprise Network
49
Remote VoIP Locations Adding VoIP
Enterprise Network
PSTN
Enterprise Network
50
Remote VoIP Locations Adding VoIP Gateways
Enterprise Network
Vega 400 PRI VoIP Gateway
User Side
PSTN
ISDN PRI
Network Side
Network Side
ISDN PRI
User Side
Vega 400 PRI VoIP Gateway
Enterprise Network
51
Remote VoIP Locations PSTN Bypass
Enterprise Network
Vega 400 PRI VoIP Gateway
User Side
ISDN PRI
Network Side
Network Side
ISDN PRI
User Side
Vega 400 PRI VoIP Gateway
Enterprise Network
52
Remote VoIP Locations Adding IP-Only Users
IP Phones
Enterprise Network
Vega 400 PRI VoIP Gateway
Vega 400 PRI VoIP Gateway
Enterprise Network
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What Well Cover

• Whats inside the PSTN?
• Whats inside the IP network?
• VoIP gateways
• Connecting the IP network to the PSTN
• Bandwidth
• Remote PSTN users The Old Way
• Remote VoIP users The New Way
• Remote PSTN locations The Old Way
• Remote VoIP locations The New Way
• Do I need a Softswitch?
• Do I need a VoIP carrier?

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Do I Need a Softswitch?

• Ask these questions
• Does your existing PBX have the features that you
  need?
• What VoIP control protocols do your
  gateways/endpoints support?
• How many VoIP gateways/endpoints do you need?

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Does Your Existing PBX Have the Features That You
Need?

• Remote VoIP users can transparently utilize
  features from the legacy PBX/switch
• Virtual Private Networks for Voice can be created
  via existing PBX Routing Tables
• Features such as T.38 Fax Relay and RFC 2833
  digit transport provide reliable communication
  over low bandwidth connections

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What VoIP Control Protocols do Gateways Support?

• MGCP and MEGACO are Master-Slave protocols
• MGCP and MEGACO require a Call Agent/Softswitch
  to instruct the Endpoint to perform all
  functionality
• If communication with the Call Agent is lost, the
  endpoint cannot function
• These protocols require a Softswitch
• SIP and H.323 are peer-to-peer protocols
• SIP and H.323 gateways offer internal routing
  tables and features that often rival the legacy
  PBX or Key System itself
• If communication with the Proxy/Gatekeeper/Softswi
  tch is lost, internal routing tables may be used.
  For example, 911
• SIP is continually evolving to support next
  generation features

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How Many VoIP Endpoints Do You Have?

• Softswitches, SIP proxies, and H.323 gatekeepers
  provide a single point of configuration for
  advanced network features

Softswitch Feature Server
Enterprise Network
Vega 400 Trunking VoIP Gateway
Vega 400 Trunking VoIP Gateway
Enterprise Network
IP Phone
IP Phone
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What Well Cover

• Whats inside the PSTN?
• Whats inside the IP network?
• VoIP gateways
• Connecting the IP network to the PSTN
• Bandwidth
• Remote PSTN users The Old Way
• Remote VoIP users The New Way
• Remote PSTN locations The Old Way
• Remote VoIP locations The New Way
• Do I need a Softswitch?
• Do I need a VoIP carrier?

59
Do I Need a VoIP Carrier?
VoIP Carriers Softswitch / Feature Server
Enterprise Network
Enterprise Network
FXO Lines
PSTN
Network Side Digital Trunks
IP Network
Vega 50 Analog VoIP Gateway
Ethernet
Vega 400 Trunking VoIP Gateway
Ethernet

• VoIP Carriers provide alternate IP-based call
  routing to remote endpoints via the public
  Internet
• Calls are routed via VoIP to remote
  locations/countries and standard PSTN Toll
  charges are bypassed

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Can I Cut the Cord to the PSTN?
VoIP Carriers Softswitch / Feature Server
Enterprise Network
Enterprise Network
Network Side Digital Trunks
IP Network
Vega 50 Analog VoIP Gateway
Ethernet
Vega 400 Trunking VoIP Gateway
Ethernet

• If you are satisfied with the reliability of your
  high-speed internet provider and VoIP carriers
  feature set and destination choices, you may
  choose to cut the cord
• But first, ensure that your gateways, as well as,
  your VoIP Carriers network support T.38 faxes
  and a compatible modem passthrough functionality

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Key Points to Remember

• Dont underestimate the complexity of the PSTN
  and IP network
• Choose the right VoIP Endpoint for your
  application
• Follow the industry Use SIP for new
  installations
• Analog FXS or FXO Gateways for lines and key
  systems
• Digital Trunking Gateways for PBXs
• IP phones for new user installations
• Be sure you can support T.38 for faxes and bypass
  for modems
• Be sure you have a big enough IP pipe to add
  voice
• SIP and H.323 VoIP Gateways can provide
  stand-alone routing and feature functionality
• Use a Softswitch to manage numerous gateways and
  advanced features
• VoIP carriers can provide connectivity beyond
  your private network
• Yes, you can cut the cord to the PSTN!