Dial Plans
Chapter 2
Dial and Numbering Plans
• A numbering plan describes the endpoint
addressing in a telephony network
• Same as IP addressing in an IP network
• There are private and public numbering plans
– the same as private and public IP addressing
schemes
• Dial plans present the biggest challenge to a
VoIP network administrator!
Dial Plans
• Dial plans analyze, screen and route calls
based on dialled digits.
• Dial plans specify how to interpret digit
sequences dialled by the user.
• Dial plans convert those into an outbound dial
string.
• On Cisco voice gateways, dial plans must be
manually configured
• They are basically a collection of dialled peers
Problems
• Unlike IP addresses a caller can input any
combination of numbers from a dial.
• A wrong IP address can be dropped
immediately but dialled digits must be
analysed.
• There are a few possibilities for destinations;
Destinations or Peers
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Local VoIP phone extension number
Local POTS phone number (FXS port)
Local POTS exchange number (FXO port)
Distant VoIP extension number (WAN)
Distant POTS number (WAN)
Caution
• You are expected to be able to establish a
connection with emergency services from a
VoIP extension.
• You also must provide access to all other
services such as free-phone low-call etc..
• You are expected to bar certain Peers
• You are expected to limit certain extensions
capabilities
Public Numbering Plans
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Emergency services
Directory services
Local calling
Mobile calling
Long-distance calling
Toll-free calling
International calling
Premium calling
National Numbering Plan
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00 – International
071 – Regional area code
071 - 91 – City area code!!
18 – Free call and Low call
08 – Mobile network
15 – Premium rate service
112 or 999 – Emergency service
11811 – Directory enquiries (note similarity with
112 service)
Private Numbering Plans
• Is used within a single organization
• Several factors need to be considered when
designing such a numbering plan
1. Number of addressable devices
2. Number of locations
3. Methods of assigning site codes
4. Inbound call routing
5. External (PSTN) call routing
Scalable Dial Plans
a)
b)
c)
d)
e)
Logical distribution
Hierarchical numbering plan
Provisioning simplicity
Reduction in post-dial delay
Fault Tolerance
a) Logical Distribution
• Local gateway should handle details that are
specific to its function
• High level routing decisions should be passed
on to Gatekeepers and PBX systems
b) Hierarchical numbering plan
• Simplifies provisioning tasks
• Simplifies call routing by keeping local calls
local and using access code for long distance
• Provides summarization by providing groups
of numbers in different locations
• Adds scalability
• Simplifies management – can be controlled
from a central point
c) Provisioning simplicity
• Avoid overlapping numbering plans and
extension ranges
• Use digit manipulation where desired to
standardize number patterns
d) Reduction in post-dial delay
• Users of PSTN have little or no post-dial delay
• Minimize the number of dial peers and
translations
• The more translations and lookups – the
longer the post-dial delay
e) Fault Tolerance
• For critical sites, redundant gateways can be
implemented.
• Alternate routes should be available
• This is usually established in the network
design anyway
Digit Manipulation
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Digit stripping
Forwarding dialled digits
Adding prefixes to dialled numbers
Manipulating Caller ID
Number expansion
Voice translation profiles
Examples of Dial Peers
Voice Gateway Router
Configuration File
voice-port 1/0/0
!
voice-port 1/0/1
!
dial-peer voice 1 pots
destination-pattern 5551234
port 1/0/0
dial-peer voice 2 pots
destination-pattern 5555678
port 1/0/1
Voice Gateway Router 1 Configuration
voice-port 1/0/0
!
dial-peer voice 1 pots
destination-pattern 5551234
port 1/0/0
!
dial-peer voice 10 voip
destination-pattern 5555678
session target ipv4:10.5.6.7
codec g711ulaw
Voice Gateway Router 1 Configuration File
voice-port 1/0/0
!
dial-peer voice 1 pots
destination-pattern 5551234
port 1/0/0
!
dial-peer voice 2 voip
destination-pattern 5555678
session target ipv4:10.5.6.7
Voice Gateway Router 2 Configuration File
voice-port 1/0/0
!
dial-peer voice 1 pots
destination-pattern 5555678
port 1/0/0
!
dial-peer voice 2 voip
destination-pattern 5551234
session target ipv4:10.2.3.4
Digit stripping (default)
Forwarding dialled digits
Other Examples - Communication Between Dial
Peers Sharing the Same Router
Matching call legs to Dial-Peers
Dial Peers from the perspective of the
both routers
Figure 6 - Sample VoIP Network
Three telephone numbers in the sales branch office need dial peers
configured for them. Router B is the primary gateway to the main
office; as such, it needs to be connected to the company's PBX.
Four devices need dial peers, all of which are connected to the PBX,
configured for them in the main office.
Dial Peer Configuration Table for Sample Voice
over IP Network in Figure 6