1. Requirements for Persistent Connections in SIP 56 th IETF, San Francisco, CA March 17-21, 2003 Rajnish Jain Vijay K. Gurbani Lucent Technologies, Inc.

2. 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. Transaction Layer Transport Layer Syntax/Encoding Transaction User SIP Layered Structure

3. RFC 3261 Connection Model PaPb Ea Eb C a2b C b2a SIP Trapezoid Two Unidirectional Ephemeral Connections Model Two connections C a2b and C b2a 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

4. Connect-reuse I-D Connection Model PaPb Ea Eb C a+b One Bi-directional Ephemeral Connection Model One connection C a+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

5. Persistent-Connections I-D Connection Model PaPb Ea Eb C a&b One Bi-directional Persistent Connection Model One connection C a&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

6. 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

7. 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