1. Global Asterisk Voice over IP Implementation
Kirk Wilson
Director of IT

2. Goals Connect existing telephone infrastructure
Cut down on long distance cost
Improve internal communications
Provide easy remote access with soft phones
Controlled bandwidth use of VoIP services
Flexibility in providing future telephone services
Build a globally scalable configuration

3. Why not Skype? Controlled/configured by end-user, not IT
Every user needs computer
Only talks to other Skype clients or through Skype out at a fee
Not terribly bandwidth conservative
Uses all available bandwidth to provide best call clarity by default
Will quickly saturate a 256k satellite link, especially with multiple users
Can not trunk multiple calls

4. Codec Bandwidth Comparison
Skype
24k – 128k bps (may double with "station" mode)
In super node mode it may saturate up to 100Mb/s
G.711 (uLaw) kb/s per call (+16 kb/s overhead)
G kb/s per call (+20 kb/s overhead)
GSM kb/s per call (+20 kb/s overhead)
LPC kb/s per call (+16 kb/s overhead)
SPEEX kb/s per call (+20 kb/s overhead)

5. Asterisk Overview Premier open source PBX software
Developed to run on Linux
Can interconnect most existing VoIP/Digital/Analog technologies
Seamless Protocol/Codec translation
Can be deployed around existing PBX systems
Supports IAX which requires only a single port
Scalable from small to large systems

6. Global Design Issues Numbering Plan Office Interconnects
System designed to scale
beyond OM Ships to all of OM

7. Numbering Plan Requirements Easy to remember
Integrate with existing varied PBX’s
Simplify call routing/interconnects
Q: Why not use “*” as the code?
A: “*” is used to access local features of some SIP phones, leading to conflicts.

8. Numbering Plan 8-YYY-XXXX 8 – Asterisk access code YYY – Office code
“Dial 8 for an asterisk line”
YYY – Office code
Can handle up to 999 OM offices
XXXX – Local extension
Can handle up to 9,999 extensions per office
Q: Why not use “*” as the code?
A: “*” is used to access local features of some SIP phones, leading to conflicts.

9. Numbering Plan
This plan allows for easy integration into the already established telephone systems deployed at our existing offices and ships
8-500-XXXX Mosbach HQ Office
8-501-XXXX Carlisle Office
8-502-XXXX Doulos
8-503-XXXX Logos Hope

10. Office Interconnects Requirements Simple, easy to maintain Scalable
Secure
Bandwidth efficient

11. Office interconnects ENUM w/ RSA – Global Directory
Interoffice link configuration stored in one standard DNS zone. (enum.om.org)
Only one DNS record per office.
Office code assignments and DNS can be centrally managed. (ICT?)
New office: one new NAPTR record.

12. Office interconnects ENUM w/ RSA – Local Server
Local extensions locally managed
Local changes affect only the local server
Single, unchanging, globally reusable context for each:
Inbound VoIP calls
Outbound VoIP calls
New office: No changes necessary

13. Office interconnects ENUM w/ RSA – Connections
No traffic until a call is made
Calls are authenticated using a single “om-enum” RSA keypair

14. An example ENUM Call ENUM Result:
.enum.om.org
DNS Server
Internet
ENUM Result:
enum.om.org. IN NAPTR “u” “E2U+IAX2”
Mosbach Asterisk strips office code
Dials extension: 1000
Mosbach Asterisk sees inbound
call to:
DNS Server Matches:
NAPTR enum.om.org.
to wildcard record
NAPTR * enum.om.org.
ENUM Lookup:
NAPTR enum.om.org.
Asterisk matches: _8XXXXXXX
PBX passes call to Asterisk
Call Completed
Asterisk Dial:
User dials:
RSA Public/Private Key Authentication
An example ENUM Call

15. Satellite Considerations
Problem: Severe bandwidth constraints
256kbit up/down limit
Easily overloaded and render useless
Solution: Route all calls via Carlisle
Translate all calls to G.729
Limit total number of inbound/outbound calls
Trunk calls for significant bandwidth savings

16. Additional Features Asterisk-less offices Date/time announcements
Trogir
Date/time announcements
Time zone enumeration
Interactive voice menus
Voic

18. Future possibilities Faxing Conferences
Worldwide VoIP to local PSTN gateways
Doulos -> South Africa PSTN phone
Only the cost of a local call
Call following and Call groups
Non-OM user soft phone access
OM Standard Asterisk Server (?)

19. Ongoing Issues/Problems
Faxing
Can’t fax over a lossy voice codec
No support for T.31
spandsp helps, but isn’t perfect
Authentication
Single RSA keypair for every office
Encryption
Asterisk current can not encrypt RSA authenticated channels

20. Questions?