1. An Enhanced SIP Proxy Server for Wireless VoIP in Wireless Mesh Networks Bo Rong, International Institute of Telecommunications Yi Qian, National Institute of Standards and Technology Hsiao-Hwa Chen, National Sun Yat-Sen University

2. Outline

1. Introduction

2. SIP-based VoIP in WMNs

3. Technical challenges of developing SIP-based

VoIP in WMNs

4. An enhanced SIP proxy server for wireless

VoIP

5. Performance analysis

6. Conclusion

3. 1. Introduction(1/2)

In this article, we address how to deploy SIP in WMNs to support quality of service (QoS), guaranteed multimedia communication.

These new challenges are raised by the inherent combination of wireless infrastructure, user mobility, and heterogeneous network computing.

4. 1. Introduction(2/2)

Three challenging issues.

• Call set up delays

• Dynamic access bandwidth prediction and reservation scheme

• Call admission control (CAC) mechanism

To overcome these challenges, we propose to build an enhanced SIP proxy server.

5. 2. SIP-based VOIP in WMNs (1/6)

Wireless mesh networks

6. 2. SIP-based VOIP in WMNs (2/6)

We assume that the IP core network employs Mutil-protocol Level Switch (MPLS) technology.

MPLS provide a unified data-carrying service for both circuit-based clients and packet-switching clients.

7. 2. SIP-based VOIP in WMNs (3/6)

MPLSIPMPLS IP QoS ( Quality of Service )

8. 2. SIP-based VOIP in WMNs (4/6)

SIP-based VoIP

Voice over IP (VoIP) frames data packets IP network

9. 2. SIP-based VOIP in WMNs (5/6)

Session Initiation Protocol (SIP)

• RFC 2543 as an Internet Engineering Task Force (IETF) standard for multimedia conferencing over IP.

• ASCII-based

• Application-layer control protocol used to establish, maintain, and terminate calls between two or more end points.

• Provide the functions of signaling and session management within a packet telephony network.

10. 2. SIP-based VOIP in WMNs (6/6)

SIP proxy serveris an intermediate device that receives SIP requests from a client and then forwards the requests to the next SIP server in the network on behalf of the client.

Proxy servers can provide functions such as routing, reliable request retransmission, authentication, authorization, and security.

11. 3. Technical challenges of developing SIP-base VOIP in WMNs(1/5)

In this article, we address the issues of how to use SIP to support the wireless VoIP in WMN accessedIP networks.

To deploy SIP in WMNs, we must face many new challenging issues that are caused by theinstability of the wireless environmentand byuser mobility .

12. 3. Technical challenges of developing SIP-base VOIP in WMNs(2/5)

Three technical challenges

Call set up delay

• In the real world, a WMN usually serves as an access network to the Internet.

• Most VoIP applications intend to go out of their own local WMNs.

• When SIP is used to set up a VoIP session, it must face a heterogeneous network environment.

• This heterogeneous network environment increases the complexity of the signaling process and causes a long call set up delay.

13. 3. Technical challenges of developing SIP-base VOIP in WMNs(3/5)

• We assume that the MPLS network runs withtraffic engineeringcapability, which is employed to set up a label-switched path (LSP) dynamically for a connection with QoS requirements.

• Totalsession set up delayof a VoIP call should be thesum of SIP signaling and MPLS signaling timesif one SIP client in a WMN wants to communicate with its counterpart in another WMN through MPLS-based IP core network.

14. 3. Technical challenges of developing SIP-base VOIP in WMNs(4/5)

Access bandwidth prediction and reservation

• Varying access bandwidth requirements in WMNs

• The users in WMNs are free to move to anywhere

• atanytime.

• The wireless channel conditions may vary from

• time to time.

• To accommodate this variation, the best way is to let WMN gateway mesh routers dynamically reserve access bandwidth from the IP core network, because the fixed bandwidth reservation approach is not efficient in this scenario.

15. 3. Technical challenges of developing SIP-base VOIP in WMNs(5/5)

Call admission control (CAC)

• A CAC mechanism must be employed when the predicted and reserved access bandwidth is different from the real one.

• CAC is used to accept or reject connection requests based on the QoS requirements of these connections and the system state information.

• A CAC mechanism complements the capabilities of QoS tools to protect audio/video traffic from the negative effects of other audio/video traffic and to keep excessive audio/video traffic away from the network.

16. An enhanced SIP PROXY server for wireless VOIP (1/5)

Conventional SIP proxy server

• A proxy server is an optional SIP component that handles routing of SIP signaling but does not initiate SIP messages.

Enhanced SIP proxy server

Call set up delay

• Utilizes COPS messages to negotiate with the MPLS LER about the overall access bandwidth requirement on behalf of all SIP terminals in a WMN.

17. An enhanced SIP PROXY server for wireless VOIP (2/5)

• Then, the LER exchanges traffic engineering signaling with other routers inside the MPLS core network to set up the corresponding LSPs.

• In this way, the LSPs required by SIP telephony are set up in the MPLS core network before SIP calls are made.

• As a result, the SIPcall set up delayin the MPLS network is decreased significantly.

18. An enhanced SIP PROXY server for wireless VOIP (3/5)

Access bandwidth prediction and reservation

• If the enhanced SIP proxy server knows that the overall access bandwidth requirement of its WMN during [ t n 1 ,t n ] is exactlyB n 1, n , then at timet n 1 , the enhanced SIP proxy server negotiates with the MPLS network to obtainB n 1, n outgoing bandwidth by using COPS messages.

• It is impossible for the enhanced SIP proxy server to know the exact value ofB n 1, nbefore the time instance oft n 1 .

• Usually ,the enhanced SIP proxy server can employ only a certain bandwidth prediction algorithm to give an approximate value ofB n 1, n, which can be defined as ~B n 1, n .

19. An enhanced SIP PROXY server for wireless VOIP (4/5)

• ~B n 1, n

• ~B n 1, n >B n 1, n Some of the outgoing bandwidth resource of the WMN would be wasted.

We can conclude that the algorithms of access bandwidth prediction and call admission control running on an enhanced SIP proxy server are critical to our approach.

20. An enhanced SIP PROXY server for wireless VOIP (5/5)

Access bandwidth prediction and reservation

Multiresolution FIR Neural-Network-Based Learning Algorithm Applied to Network Traffic Prediction

maximal overlap discrete wavelet transform (MODWT)

Call admission control (CAC)

Integrated Downlink Resource Management for Multiservice WiMAX Networks

greedy approximation algorithm

21. 5. Performance analysis(1/5)

Signaling process with an enhanced SIP Proxy server

• The call set up starts with a standard SIP INVITE message sent from the caller to the local enhanced SIP proxy server in a WMN.

• This message carries the callee URL in a SIP header and the QoS requirements of a SIP call-in body.

• Regarding the caller ID, the QoS requirements,and the remaining outgoing bandwidth in a local WMN, the enhanced SIP proxy server decides whether this SIP call request is admitted.

22. 5. Performance analysis(2/5)

• If the call request is admitted, an enhanced SIP proxy server will forward the original INVITE message to the callee otherwise, it simply sends the caller a DECLINE message to drop the call.

• Whether the call is admitted or not, it is registered in the enhanced SIP proxy server for the purposes of access bandwidth prediction and call admission control in the future.

• If the access bandwidth must change, the enhanced SIP proxy server uses COPS messages to negotiate with the MPLS-based IP core network to set up new LSPs with the required bandwidth.

23. 5. Performance analysis(3/5) 24. 5. Performance analysis(4/5)

Simulation results

• OPNET Modeler 11.0 to simulate the network environment.

• In our simulation, the enhanced SIP proxy server employs acomplete sharing CAC policy , which means that an incoming connection is accepted if sufficient bandwidth resources are available.

25. 5. Performance analysis(5/5) 26. 6. Conclusion(1/1)

Enhanced SIP proxy server can reduce considerably the call set up delay, because the LSPs required by SIP telephony are set up in the MPLS-based IP core network before SIP calls start.

The performance of access bandwidth prediction and call admission control depends on which algorithm the enhanced SIP proxy server employs.