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.

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

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

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

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

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

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