1. SIP Explained Gary Audin Delphi, Inc. Delphi-inc@att.net Sponsored by

2. Speaker Background Communications and security consultant for 36 years
Speaker at Enterprise Connect, ITExpo and 100s of user conferences
Article and blog sites:
© Delphi, Inc

3. SIP Trunking Presentation
“Successful SIP Trunking”
Wednesday 5:30 and Thursday 1:00 PM
Telecom Reseller theater exhibit #
Presenters: Gary Audin and Steve Johnson
© Delphi, Inc

4. Session Initiation Protocol
A protocol is an information exchange procedure, a set of rules.
SIP is a protocol to establish , manage, and terminate a connection (session) that is media independent.
SIP is not specifically designed for digital voice.
SIP operates over an IP network.
© Delphi, Inc

5. SIP Does This
It locates the user and determines which end system will be used in the proposed session.
It then learns the user's availability (is the user busy; can he/she be disturbed?).
It determines the capabilities available at the user end system for the session such as what media is supported.
It establishes the session.
It manages the session, handling call termination, call transfer, changes to session parameters, and so forth.
It is a peer-to-peer protocol running over UDP and TCP.
© Delphi, Inc

6. SIP Features
User location can determine the end system to be used for communication
User availability determines the willingness of the called endpoint to engage in communications
User capabilities can determine the media and media parameters to be used
Session setup endpoint ringing, establishment of session parameters at both called and calling endpoints
Session management including session transfer and termination, changing session parameters, and invoking services
© Delphi, Inc

7. What’s in a SIP Session
“Session” = exchange of data between an association of participants
Users can move among endpoints
Users may have multiple names and addresses
Users may communicate in different media
SIP enables internet endpoints:
To discover each other
To characterize the session
The location infrastructure supports name mapping and redirection services
Endpoints can add/remove participants from session
Endpoints can add/remove media from session
© Delphi, Inc

8. Not Part of SIP
SIP is not a vertically integrated communications system. It is ONLY a component.
SIP is independent of the services offered.
SIP provides mechanisms that can be used to implement different services.
SIP can locate a user and deliver content to the user’s current location.
SIP does not offer conference control services nor prescribe how a conference is to be managed.
© Delphi, Inc

9. SIP Does Not
SIP does not define the media carried (voice, video, IM, data, games, graphics, photos…)
SIPPING 19 defines a minimum set of telephony features not SIP
SIP trunks are not able to provide interoperability between different vendors’ IP PBXs
© Delphi, Inc

10. SIP Components SIP is built upon a client/server architecture
User Agents (SIP Phones, SIP PCs, other endpoints)
Servers (Used to locate SIP users or to forward messages)
SIP Gateways:
To PSTN for telephony interworking
To H.323 for IP Telephony interworking
Client - originates message
Server - responds to or forwards message
© Delphi, Inc

11. Multimedia Protocol Stack
© Delphi, Inc

12. SIP Signaling Paths
© Delphi, Inc

13. SIP Trunk Benefits Flexible provisioning
Provider competition and enterprise leverage
Eliminate VoIP gateways
Reduced conferencing costs
Low cost or free international calling
On-Net free calling
© Delphi, Inc

14. SIP Trunk Connections Legacy PBX VoIP Gateway SBC SIP Service Provider
T1/E1/PRI
Connections
Most legacy PBXs can upgrade to support some IP network connections usually IP phones. The IP connections are essentially supported by an internal gateway function. Most legacy PBXs are not upgradable for SIP trunk connections.
An alternative is to deploy a separate external gateway to conned to a SIP service. The gateway connects to multiple T1, E1, and PRI ports on the legacy PBX. The gateway translates the signaling and possibly to the voice codec into a SIP trunk operation. There are many non-PBX vendors offering this type of gateway.
The gateway should be connected to a session border controller to the SIP network for security reasons. Because the session border controller sits between the gateway and SIP provider, the SIP provider is not affected by this arrangement. It looks like any other session border controller. There may however be some feature limitations because the gateway may not be able to translate all of them in to the SIP interface.
PSTN
SBC
IP PBX
© Delphi, Inc

15. SIP Trunk Providers
Can connect using vendor specific versions of SIP trunk software
Standard SIP trunk connection is via SIPconnect (not a standard but an agreed upon recommendation from the SIP Forum
SIPconnect version 1.1 is the latest one
May limit the media carried:
Voice only
Video maybe
Secure connections maybe
Fax maybe
911 and E911 information maybe
© Delphi, Inc

16. Session Border Controllers
A firewall rule set while also map layer 5 to layer 7 addresses
Intrusion detection and prevention
Denial-of-service (DoS) attack prevention
VPN separation for shared resources
SIP-Transport Layer Security (TLS) handshaking for authentication and encryption of SIP signaling
Secure Real Time Protocol (RTP) support
Support for IPsec tunnels
Transcoding, or conversion between different VoIP codec technologies
© Delphi, Inc

17. Where Are the Problems?
Delphi, Inc.

18. SIP Trunk Issues Firewall Problems: Can block SIP packets
Cannot translate IP packet addresses
TCP may be used instead of UDP
One way audio
Dropped connections
Call transfer failure
Registration failure
© Delphi, Inc

19. State of SIP Relatively easy to implement
Has gained considerable vendor and provider acceptance
Allows flexible service creation
Extensible and scalable
Wide range of supporting products and services
Does not make PSTN interworking easy
Will not solve all IP Telephony issues such as QoS
© Delphi, Inc

20. Resources Online education and certification www.thesipschool.com
“Ten SIP Trunk Equipment License Issues That Can Ruin Your Day (or Month)”
“Avoiding SIP Trunking Equipment Problems”
“How to avoid SIP Trunk Implementation Problems”
“Easy SIP Trunking; No Yet”,
“Is IPv6 Good for VoIP?
© Delphi, Inc

21. FINI Gary Audin Delphi-inc@att.net VN 703 908 0965
© Delphi, Inc