requirements for persistent connections in sip 56 th ietf, san francisco, ca march 17-21, 2003...
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Requirements for Persistent Connections in SIP
56th IETF, San Francisco, CA
March 17-21, 2003
<draft-jain-sipping-persistent-conn-reqs-00.txt>
Rajnish 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 deemedephemeral
•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.
Transaction Layer
Transport Layer
Syntax/Encoding
Transaction User
SIP LayeredStructure
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RFC 3261 Connection Model
Pa Pb
Ea Eb
Ca2b
Cb2a
SIP Trapezoid
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
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Connect-reuse I-D Connection Model
Pa Pb
Ea Eb
Ca+b
One Bi-directional Ephemeral Connection Model•One connection Ca+b
•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
SIP Trapezoid
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Persistent-Connections I-D Connection Model
Pa Pb
Ea Eb
Ca&b
One Bi-directional Persistent Connection Model
•One connection Ca&b
•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?
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