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Session Initiation Protocol:
An Introduction to SIP
Savings. Integration. Productivity.
© 2011 Avaya Inc. All rights reserved.
SIP is a Signaling protocol – not media!
 SIP is the “language” that devices speak to set up phone
calls (or other types of communications) between
devices.
 After the call is set up, the devices user Real Time
Protocol (RTP) for the talk path (just like h.323)
 SIP uses English (people can read it) messages to
communicate between endpoints.
 Unlike h.323, SIP is not proprietary – it is developed as
and internet standard!
 Negotiates the best media to use for a call – text based
IM, voice, video, etc
 Internet protocol – like HTTP – text based
 Leverages other protocols – TCP, UDP, TLS, DNS,
SDP, RTP.
© 2011 Avaya Inc. All rights reserved.
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Major Difference between SIP and H.323
 SIP can be used for more than telephony and video
 SIP is text-based; H.323 is binary
 Dial tone and ring-back tone is generated locally by the
phone
 Dial plan resides in the phone
 Digits are not transmitted to the PBX until the phone
completes digit collection based on dial plan
 SIP clients can be represented by alpha-numeric id’s
and passwords
 SIP users can associate multiple devices with a single
AoR
© 2011 Avaya Inc. All rights reserved.
© 2009 Avaya Inc. All rights
reserved. 3
SIP Transforms Communications
Flexible
Multi
Modal
Accessible
SIP
Open
Mobile
Presence
Aware
© 2011 Avaya Inc. All rights reserved.
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How Does SIP Work?
 SIP is to intelligent, unified communications, as HTTP is
to information exchange on the World Wide Web
(WWW)
• It makes the communications infrastructure transparent to end
users
• It enables ready access to many modes of communication.
 Just as pointing your browser to an HTTP Web site
enables you to play a video, download a picture, or read
text, SIP has been designed to support multimedia
communications in real time:
• Locate other users
• Request a session
• Negotiate the mode of communications
© 2011 Avaya Inc. All rights reserved.
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5 Building Blocks of SIP
User Agents
Network Servers
SIP Messages
Session Description Protocol
Gateways and SBCs
© 2011 Avaya Inc. All rights reserved.
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SIP User Agents
 User agents (UAs) are applications installed on SIP
endpoints such as an IP phone, mobile phone, wireless
device , or a laptop / desktop PC that interface between
the user and the SIP network.
SIP UAC/UAS
SIP UAC/UAS
© 2011 Avaya Inc. All rights reserved.
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SIP Network Servers
Network servers provide:
 Registrar and Location services
 Routing (Proxy or Redirect)
 Presences Services
Servers in the network
allow easy session
establishment!
SIP Network Server
© 2011 Avaya Inc. All rights reserved.
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SIP Messages – Simple yet Powerful
SIPMethod
Method
SIP
Description
Description
INVITE
Invites a user to a call
ACK
Used to facilitate reliable
message exchange for
INVITEs
BYE
Terminates a connection
between users or
declines a call
CANCEL
Terminates a request, or
search, for a user
OPTIONS
Solicits information
about a server's
capabilities
REGISTER
Registers a user's
current location
INFO
Used for mid-session
signaling
© 2011 Avaya Inc. All rights reserved.
SIP UAC/UAS
SIP
Network
Server
SIP UAC/UAS
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Example Call Flow
Alice
Proxy
Bob
INVITE sip:[email protected]
407 Proxy Authentication Required
ACK sip:[email protected]
INVITE sip:[email protected]
INVITE sip:[email protected]
100 Trying
Bob
answers
180 Ringing
180 Ringing
200 Ok
200 Ok
ACK sip:[email protected]
ACK sip:[email protected]
Bob
hangs up
RTP
BYE sip:[email protected]
BYE sip:[email protected]
200 Ok
200 Ok
© 2011 Avaya Inc. All rights reserved.
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reserved. 0
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© 2011 Avaya Inc. All rights reserved.
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Session Description Protocol (SDP)
SDP is used for multimedia session announcement,
invitation and other forms session initiation
SDP determines following additional information:
Bandwidth
Contact info for the person responsible for the media type
Transport protocol
Media format
Multicast address and Transport Port for media.
Remote address for media / Transport port for
contact address.
Once the SIP session is built, SDP adds multimedia
© 2011 Avaya Inc. All rights reserved.
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SDP Offer/Answer Example
Alice offers three audio and two video codecs, Bob accepts with
a single audio and video codec. As a result of the exchange Bob
and Alice use iLBC for audio and H261 for video.
 [Offer] v=0 o=alice 2890844526 2890844526 IN IP4
host.atlanta.example.com
 s=
 c=IN IP4 host.atlanta.example.com
 t=0 0
 m=audio 49170 RTP/AVP 0 8 97
 a=rtpmap:0 PCMU/8000
 a=rtpmap:8 PCMA/8000
 a=rtpmap:97 iLBC/8000
 m=video 51372 RTP/AVP 31 32
 a=rtpmap:31 H261/90000
 a=rtpmap:32 MPV/90000
© 2011 Avaya Inc. All rights reserved.
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Bob’s Answer to Alice’s Offer
 [v=0 o=bob 2808844564 2808844564 IN IP4
host.biloxi.example.com
 s=
 c=IN IP4 host.biloxi.example.com
 t=0 0
 m=audio 49172 RTP/AVP 99
 a=rtpmap:99 iLBC/8000
 m=video 51374 RTP/AVP 31
 a=rtpmap:31 H261/90000
© 2011 Avaya Inc. All rights reserved.
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SDP Protocol Structure
V = (protocol version)
o = (owner/creator and session identifier).
s = (session name)
I =* (session information)
u=* (URI of description)
e=* (email address)
p=* (phone number)
c=* (connection information - not required if included in all media)
b=* (bandwidth information)
One or more time descriptions (see below)
z=* (time zone adjustments)
k=* (encryption key)
a=* (zero or more session attribute lines)
Zero or more media descriptions (see below)
Time description
t= (time the session is active)
r=* (zero or more repeat times)
Media description
m= (media name and transport address)
i=* (media title)
c=* (connection information - optional if included at session-level)
b=* (bandwidth information)
k=* (encryption key)
a=* (zero or more media attribute lines)
© 2011 Avaya Inc. All rights reserved.
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Gateways and Session Border Controllers
 SIP Gateways
– Provide protocol translation and interoperability with non-SIP system
elements such as:
– TDM
– H.323, and
– PSTN
 Session Border Controllers (SBCs)
1) VoIP Security: NAT/PAT, Authentication, Logging, Encryption, DoS, …
2) SIP Protocol Interworking: SIP, SIP-T, SIP-I, H.323, TCP/UDPl
3) Reporting: Billing, Utilization, Logging
4) Routing: Dialed Number, Origination Number, Network, CAC, Cost, Time, etc.
5) Troubleshooting: Ladder Diagrams, Protocol Decode, Media Capture
© 2011 Avaya Inc. All rights reserved.
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SBC Functions Continued
6.) Media Interworking and Services:
* Transcoding--Going from one codec to another--G.711, G.729, G.722,
iLBC, etc.
* Conferencing--Adding additional parties to an interaction
* Queuing – Putting an interaction on hold and play music or
announcements
* Recording--Capturing the interaction for later playback
* Translation--Real- or semi-real time translation from one spoken
language to another (future)
* DTMF & Fax--RFC 2833, T.38
* Voice Quality--Echo cancellation, gain normalization, background
noise elimination
7.) Additional Call Data: Using Mime in the SDP to carry location and other
communication information
8.) High Availability: Rerouting call traffic when a network or device slows
or fails
9.) Management: Dial Plan, Load Balancing, Categorization, Provisioning
10.) Emergency Services: 911, CALEA
© 2011 Avaya Inc. All rights reserved.
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Savings
Better Manageability
– SIP is easy to learn, develop, troubleshoot and support
– Modeled after HTTP, easier to understand and interpret
– Single network for all communications
Enhanced scalability
– From single road warrior to small branch to carrier-class enterprise
solutions with common applications and user experience
Lower Communications and Business Costs
– Cost saving SIP trunking
– Minimize travel with collaborative applications
– Leverage multimodal communications to eliminate the costs of delayed
decision making
– Reduce cost of real estate and optimize geographic coverage with a
more mobile workforce
© 2011 Avaya Inc. All rights reserved.
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Integration
Native Mobility
– A single SIP Address Of Record (AOR) provides a unifying public
address for all communications
– SIP intelligence allows simultaneous or sequential “ringing” to all devices
End-point Flexibility
– Seamless integration of desk phones, video devices, soft clients or
mobile phones and devices
– Eliminate the complexity of multiple networks
– Simplify business processes
Unprecedented Interoperability
– Open, IETF Standard based
– Active working groups (SIPit, SIPconnect, SIP Forum)
– Wide applications eco-system
© 2011 Avaya Inc. All rights reserved.
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Productivity
Presence
– Understand someone’s availability and their communication preferences
before initiating communications
Enhanced Customer Service
– Speed first call resolution in the contact center through ability to leverage
available experts and use side-bar communication channels
– Faster decision making improves responsiveness to customers
– Improved ability to reach the right employee drives customer satisfaction
Improved Employee Productivity
– Integrate communications into business processes
– Maximize workforce effectiveness regardless of location
– Improve employee satisfaction and retention by providing the
tools to work most effectively
© 2011 Avaya Inc. All rights reserved.
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What Can Presence Look Like?
My optional location
and personal message
My personal
status (what
others see)
My “Buddies”
List and their
aggregated
presence
© 2011 Avaya Inc. All rights reserved.
My “Buddies”
optional location
My “Buddies” optional
personal messages
My “Buddies”
communication
channel status
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The Next Step:
This is what Contextual Collaboration looks like!
Action
Oriented
People
Centric
Contextually
Aware
© 2011 Avaya Inc. All rights reserved.
Social Media
Aware
Naturally
Collaborative
Media
Transparent
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What’s slowing SIP Adoption
 Service Providers 1st Tier and 2nd Tier providers are
extending their footprint in both Primary and Mid-Markets
– Verizon
– ATT
– Global Crossing
– Paetec
 Heavies slow to adopt SIP Trunking due to existing
infrastructure and expansion during the Tech bubble
 New providers see this as an opportunity to provide
dynamic bundled services based on bundled minute and
data transport usage
© 2011 Avaya Inc. All rights reserved.
© 2009 Avaya Inc. All rights 2
reserved. 5
What if?
For IT:
 Manageability / Scalability, Lower
TCO and Unprecedented
Interoperability
For end user:
Mobility and End-Point Flexibility,
Improved Employee Productivity, and
Flexible choices in collaboration mode
SIP
For businesses:
Faster first call resolution, Enhanced
employee reach-ability and Access to
a broad SIP ecosystem
Savings
Session
Integration
InitiationPProductivity
rotocol
© 2011 Avaya Inc. All rights reserved.
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© 2011 Avaya Inc. All rights reserved.
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