Requirements for Persistent Connections in SIP

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Requirements for Persistent Connections in SIP

• 56th IETF, San Francisco, CA
• March 17-21, 2003

ltdraft-jain-sipping-persistent-conn-reqs-00.txtgt R
ajnish Jain Vijay K. Gurbani Lucent Technologies,
Inc.
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SIP Transport Layer Connection Management

• Current Key Characteristics
• Completely delegated to Transport Layer
• Extremely loosely coupled Transaction
• and Transport Layers
• Connections are fundamentally deemed
• ephemeral
• Connection conservation is rare
• Idle timeouts are unsynchronized,
  implementation-defined
• Connections are unidirectional at transaction
  layer
• Notion of one-size-fits-all regardless of SIP
  entity functionality
• No mechanism allowed for one SIP entity to
  communicate
• its connection usage policy of mutual interest to
  another.

SIP Layered Structure
Transaction User
Transaction Layer
Transport Layer
Syntax/Encoding
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RFC 3261 Connection Model
Two Unidirectional Ephemeral Connections Model

• Two connections Ca2b and Cb2a
• Unidirectional
• Ephemeral
• Independent, disparate aging by each side
• Pros
• Architecturally loose coupling
• Resemblance to connection-less model
• Reuse potential in one direction
• Cons
• Applies bias to fundamentally peer-to-peer
  connections
• Connections lack life predictability
• Performance, Scaling issues

Ca2b
Pa
Pb
Cb2a
Eb
Ea
SIP Trapezoid
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Connect-reuse I-D Connection Model
One Bi-directional Ephemeral Connection Model

• One connection Cab
• Bi-directional
• Ephemeral
• Independent, disparate aging by each side
• Pros
• Reduces number of connections by half
• Enables application behaviors e.g. NAT
• Cons
• Lacks connection longevity aspect
• Lacks notion of hint/forced invitation
• Lacks connection expiry time out negotiation
• Reusability is somewhat overshadowed by
  unpredictability

Cab
Pa
Pb
Eb
Ea
SIP Trapezoid
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Persistent-Connections I-D Connection Model
One Bi-directional Persistent Connection Model

• One connection Cab
• Bi-directional
• Persistent
• Synchronized, or no aging by each side
• Pros
• All pros of connect-reuse I-D
• Introduces predictability
• Supports hint/forced aspect
• Yields more control to implementer
• Cons
• Potential for abuse
• Trust model who should a server trust?

Cab
Pa
Pb
Eb
Ea
SIP Trapezoid
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Advantages of Persistent Connections

• Performance Efficiency
• Fewer connection setup handshakes, fewer RTTs
• Better timing coordination between signaling and
  media
• Resources/Scaling Efficiency
• Fewer kernel control blocks
• Fewer per connection FSM instances
• Application Behavior Enabling
• NAT traversal
• Emergency calling
• Inter-switch trunk state management
• Traffic pattern based connection management

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Proposed Solutions

• New Via header field parameter
• via-connection soft-persistent
• via-connection hard-persistent
• No timer negotiation
• Somewhat mimics connect-reuse I-D solution
• Supports hint/forced request notion
• New header, Supported/Require
• Supported persistence
• Require persistence
• Persistent-Timeout 36000
• Timer negotiation
• Supports hint/forced request notion