Building VoIP-based systems with SIP can be daunting. The entire telecommunications industry is a layered stack of technologies, some from the age of telephones with hand-cranks. Others from the Internet age of packet switching and VPNs. Over the years, the experts at TelcoBridges have built a knowledge base about underlying telecommunications and VoIP technology, SIP signaling, networking products and design methods. In this event, we pull some of our favorite Frequently Asked Questions from our video library, our forum, Wiki, and your emails, sharing answers and insight that both beginners and advanced designers will find helpful. A recording of the live webinar is available at: https://www2.telcobridges.com/videolibrary

2. 2
Introduction
Alan D Percy
Chief Marketing Officer
alan.percy@telcobridges.com
@AlanDPercy
Luc Morissette
Director of Customer Support
luc.morissette@telcobridges.com

3. 3
Agenda
• Introductions
• TB Forum and Wiki
• Our Favorite FAQ
• Where to Learn More
• Your Questions

4. 4
TB Wiki Overview
https://docs.telcobridges.com/tbwiki/FreeSBC

5. 5
FreeSBC/ProSBC Forums
http://forums.freesbc.com/

6. 6
FAQ:
Q: What is “Transcoding?”

7. 7
FAQ: Transcoding
A: “Transcoding” is converting the
media from one format to another
SBC
Media Server
G.711 G.729

8. 8
FAQ:
Q: What is a “Session?”

9. 9
FAQ: Session
A1: A “Session” is one call path
traversing through an SBC
SBC
Media Server

10. 10
FAQ: Session
A2: If the call passes through the SBC
twice, it will be 2 sessions
SoftSwitch
SBC

11. 11
FAQ:
Q: Can you explain why some
providers offer SIP over UDP,
while others offer TCP, or TLS?

12. 12
FAQ: SIP Protocols
1. SIP over UDP was first (and still widely used
by operators for SIP Trunking)
2. As SIP messages got larger, operators and
application developers began using TCP
3. With more SIP traffic traversing the Internet,
operators began using TLS to encrypt call
control messaging

13. 13
FAQ:
Q: Why not just use VPN for remote
offices?

14. 14
FAQ: VPN
A: VPN is a good solution – everything
is encrypted, including data
Requires to setup VPN connections to
each destination

15. 15
FAQ:
Q: How does SRTP secure the media?
Q: Can an SBC convert from SRTP to
RTP?

16. 16
FAQ: sRTP
A: SIP over TLS and SRTP work together
to secure call control and media content
SBC
SIP/UDP RTP
Private Network
SIP/TLS SRTP
Public Network

17. 17
FAQ:
Q: How do SBCs resolve SIP
interoperability issues?

18. SIP
Session
s
B2BUA
UAS
Session Border
Controller
Session Border Controller Architecture
UAC
Unique
settings
Unique
settings
SBCs can modify SIP messaging using
Back-to-Back User Agents

19. 19
FAQ:
Q: What causes one-way audio and
how do you diagnose the issue?

20. 20
Trouble with One Way Audio
Confidential
SMB/Enterprise
IAD/Router
w/ Firewall
Service Provider
SoftSwitch
Common causes for One-way Audio:
1) Firewall closes RTP pin-hole prematurely
2) SBC not configured for remote NAT
3) Codec mis-match
4) RTP port range settings

21. 21
FAQ:
Q: How is VoIP voice quality
measured?
Q: My MOS scores are low, how can I
improve?

22. 22
FAQ: Quality
A:
1. SBC monitors RTP and RTCP traffic for
jitter, latency, lost packets and other errors.
2. Type of codec used (G.711 is 4.3, G.729 is
4.0 and G.723 is 3.6)
3. Compile a reference value at the end of the
call – MOS score (value of 5 maximum)

23. 23
FAQ: Improve Quality
A: Make sure there are no errors on the
RTP streams – fix network if necessary
Use high quality vocoders

24. 24
FAQ:
Q: Explain the difference between
call routing and packet routing?

25. 25
FAQ: Call vs Packet Routing
A1: Call routing
SBC
Call Routing Table
SoftSwitch
Cloud Network

26. 26
FAQ: Call vs Packet Routing
A2: Packet routing
SBC
Network#4
Vlan200
Network#3
Vlan100
Second Interface
(Public)
First Interface
(Private)
Untagged

27. 27
FAQ:
Q: How does an SBC protect against
DOS and DDOS attacks?
Q: How about TDOS attacks?

28. 28
FAQ: DOS/DDOS
A: DOS and DDOS are bursts of packets
sent to prevent service
How to protect:
• Efficiently drop packets from bad or unknown sources
• Quickly identify packets from trusted sources and allow to
pass
• Monitor traffic of trusted sources

29. 29
FAQ: TDOS
A: TDOS attacks appear to be legitimate calls.
To block them it requires to analyze the
incoming call and drop invalid ones
SBC
Call validation
Cloud Service Provider

30. 30
FAQ:
Q: What are the differences between
FreeSBC and ProSBC?
Q: What is the upgrade process?

31. 31
FAQ:
Q: How can I get training on SIP?
Q: Training on ProSBC?

32. 32
FAQ:
A great resource on the basics of SIP
Your training for ProSBC starts at:
https://www2.telcobridges.com/TechTrained

33. Video Library on YouTube
• ProSBC Training Modules
• Recorded webinars
• How-to Tutorials
• Customer interviews
• Frequently Asked Questions
• Recorded podcasts
• And more…
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youtube.com/telcobridges

34. Enabling the Migration to
Cloud Communications
34
www.telcobridges.com
www.prosbc.com
sales@telcobridges.com
Youtube.com/telcobridges

35. VoIP Frequently
Asked Questions
Answers to your most
frequently asked questions
about voice-over-IP technology

36. View the Full-Length Video at:
www2.telcobridges.com/videolibrary
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