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Using SIP to build Context-Aware VoIP Support for Multiplayer Networked Games. Arup Acharya Network Server System Software IBM T. J. Watson Research Center arup@us.ibm.com. Aameek Singh College of Computing Georgia Institute of Technology aameek@cc.gatech.edu. Introduction.

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using sip to build context aware voip support for multiplayer networked games

Using SIP to build Context-Aware VoIP Support for Multiplayer Networked Games

  • Arup Acharya
  • Network Server System Software
  • IBM T. J. Watson Research Center
  • arup@us.ibm.com

Aameek Singh

College of Computing

Georgia Institute of Technology

aameek@cc.gatech.edu

introduction
Introduction
  • Project on “Client and Infrastructure support for SIP-enabled applications”, 2003
    • One of the applications for “SIP enablement”: multi-player networked games
      • Joint work with Aameek Singh starting with his summer internship at IBM Watson, summer 2003
    • Motivation : explore how flexibility of SIP-based VoIP can be used in gaming

Collaborative Apps

Web Browser

SameTime

VoIP infrastructure

Enhancements (conferencing, context)

Notes Calendar/email

VoIP enabled portals

Distributed application scenarios, e.g. networked games

Corporate VoIP/data

network

(Watson VoIP trial)

(SIP-enabled)

Services/ Infrastructure

Client-side SIP service

In-house conferencing service (IP/ PSTN phones)

Game servers, IM servers

what is sip session initiation protocol
What is SIP (Session Initiation Protocol) ?
  • A signaling protocol for setting up multimedia sessions between endpoints
  • Fundamental shift from PSTN : infrastructure consists of software on standard servers
    • SIP designed in line with other Internet protocols by the IETF
    • Uses overlay control network consisting of SIP Proxies to route SIP messages : Media path (RTP/UDP) decoupled from signaling
    • name@domain addressing; message syntax similar to HTTP
  • SIP provides
    • Session setup/modification/handoff/tear-down : Voice/ Video over IP
      • Mobility control
    • Presence & Instant Messaging : Signaling message carries the IM as payload (SIMPLE)
      • Publish/subscribe mechanism : SUBSCRIBE/ NOTIFY to events
    • Supports calls to/from PSTN
    • Service/personal mobility
  • Examples of SIP adoption
    • VoIP : Vonage, CableVision,…
    • IM : Lotus Sametime
    • Push-to-talk : Sprint PCS, Verizon Wireless
    • Collaboration software : Microsoft Live Office
    • 3G

SIP proxy

SIP proxy

SIP

signaling

RTP/UDP

packets

sip messages methods and responses

180 (Ringing)

180 (Ringing)

180 (Ringing)

200 (OK)

200 (OK)

200 (OK)

200 (OK)

200 (OK)

200 (OK)

INVITE

INVITE

ACK

ACK

BYE

BYE

ACK

BYE

RTP MEDIA PATH

Proxy

Proxy

INVITE

Call Setup

User Agent

User Agent

MediaPath

Call Teardown

SIP Messages – Methods and Responses

VoIP Call setup : SIP message flow

NETGAMES 2004

enabling applications with sip client side sip service

Wrapper 1

Wrapper 2

Wrapper 3

Enabling applications with SIP: client-side SIP service
  • A client-side utility to enable existing (and new) applications to invoke SIP features natively (IM, VoIP, pub/sub,…)
    • SIP unbundled from applications
  • SIP service exposes a well-defined API
  • Allows user choice of end-device (softphone, PSTN / IP Phone)

Web Browser

IP Phone

SIP

Stack

with

pub/sub

IM Agent

Application Interface

SoftPhone

Email Client

SIP Service

Other Apps

(Multi-player

Games, …)

PSTN/ cell phone

Client Laptop

watson voip pilot new components application integration conferencing service

CONVEDIA conferencing hardware

SIP

control

SIP ConferenceManager

Application Server (IM, email, web,..)

RTP/UDP Voice packets

(multi-party connection)

Application

protocol

SIP

Client Laptop

Application

transfer

SIP service

SIP+App

integration

Watson VoIP Pilot + new components (application integration, conferencing service)

Cisco 3640 SIP gateway

SIP Proxy Server

Siemens PBX

SIP

RTP/UDP Voice packets

(point-point connection)

PSTN

SIP phone

POTS phone

PSTN phone

a new converged application sip gaming context aware conferencing
A new Converged applicationSIP Gaming – Context-aware Conferencing

Each square represents a conference (game room). At startup, each player is associated with an IP/ PSTN phone.

Arup and Edie can talk to each other.

If Arup drags his icon into Aameek’s region, then his current conference

with Edie ends and he is seamlessly switched to a conference with Aameek.

Illustrates multiple simultaneous conferencing not possible with PSTN.

Integrates SIP service with a application scenario (multi-player gaming)

Drag with mouse

NETGAMES 2004

general architecture service composition

C1

C3

C2

G

G

G

G

G

S

S

S

S

S

U1

U2

U4

U5

U3

General Architecture : Service Composition

Gaming

service

SIP (Conferencing)

service

  • Overall goal is to offer SIP client/network service as a building block
  • Enable composition with other services such as gaming
  • Context-aware conferencing result of composing SIP and gaming services

Server-side

association

S2

S1

S3

S1, S2, S3 : Concurrent states of the game server

C1, C2, C3 : Corresponding Conferences

U1, U2,, : Clients

G : Gaming client

S : SIP Service

sip based conferencing
SIP Based Conferencing

Architecture

SIP Workflow

Back-to-Back UA

Control

Data

2INVITE

Conference

Server

Mixer

3OK

6ACK

1INVITE

4OK

RTP

5ACK

UA

NETGAMES 2004

integration with gaming infrastructure
Integration with Gaming Infrastructure

Decentralized Gaming

Centralized Gaming

Mapping Game state to

conferencing state

B2B UA

B2B UA

Conference

Server

Mixer

Conference

Server

Game Server

SIP

SIP Signaling

SIP

Game State

Media Path

SIP

+

SIP Signaling

Mixer

UA

UA

Conferencing media

streams

UA

UA

RTP/

UDP

Game State

Media Path

NETGAMES 2004

prototype implementation

Mixer

SIP UA

Game Client

Client

Prototype Implementation
  • Centralized Gaming Architecture
  • High level SIP Interface to control SIP communication

Game Server

Conference Server

Control

Agent

Control

Logic

Conference

Manager

Session

Sip Interface

SIP Interface

SIP stack

Sip Stack

NETGAMES 2004

sip workflows game join
SIP Workflows – Game Join
  • User joins the game with UA as its SIP device

0User Joins

Game

4INVITE

3INVITE

SIP Enabled

Game

Server

Mixer

Conference

Server

6OK

5OK

9ACK

8ACK

1INVITE

2OK

7ACK

1INVITE contains NO SDP. UA sends 2OK

with its SDP. GS gets media path info

from that SDP and sends that as media

info in 3INVITE. The CS completes

transaction with the mixer and sends 6OK.

The GS extracts the media info from it

and sends it as part of SDP in 7ACK. Also

ACKs the CS which ACKs the mixer.

Voice pkts

SIP

UA

GAME

CLIENT

NETGAMES 2004

sip workflow context switch
SIP Workflow – Context Switch

1BYE

0User moves

to a new room

2BYE

SIP Enabled

Game

Server

Conference

Server

Mixer

4OK

5INVITE

3OK

6INVITE

8OK

7OK

12ACK

13ACK

9RE-INVITE

10OK

11ACK

UA

1BYE removes the user from its

previous conference. The

5RE-INVITE initiates the process

of bringing the user into its new

conference, i.e. media flows to different

port# of mixer.

User sees no (perceptible) interruption.

GAME

CLIENT

NETGAMES 2004

other features
Other Features
  • Sub-Interactions : On-the-fly conferencing amongst ad-hoc groups
        • No pre-registration of conference name
        • Configure SIP Proxies to route based on domain names
          • Conference server creates conference when it sees a name for the first time
        • Share conference name with other intended members (of ad-hoc group) out-of-band, e.g. IM

INVITE

SIP Proxy

Conference Server

conf-server.com

INVITE sip:myurl@

conf-server.com

SIP Session

UA

NETGAMES 2004

other features15
Other Features
  • Enhanced Audio-Mixing
    • Use “distance” of player to calibrate “loudness” of voice while mixing multiple voice streams
      • Requires support from the media mixing hardware
      • SIP signaling can be used to carry “distance” information via the SIP INFO method
conclusions and future work
Conclusions and Future Work
  • Idea of context-aware multi-conferencing has broad applicability beyond gaming
    • Gaming is a metaphor for multi-party collaboration
    • Examples : a) drag-and-drop an “expert” b) attend >1 conference with a GUI indicator when needed c) coupled with presence
  • Presented an infrastructure for context-aware communication that is an add-on to a gaming infrastructure
    • Based on light-weight SIP protocol
    • Using a generic client-side SIP service
  • Future Work
    • Can SIP be used as the gaming protocol itself?
slide17

Thank you! Questions?Further information: Arup Acharya http://www.research.ibm.com/people/a/arup/ sip:arup@research.ibm.com