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報告：謝旻欣
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
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.
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.
2. SIP-based VOIP in WMNs (1/6) • Wireless mesh networks
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.
2. SIP-based VOIP in WMNs (3/6) • MPLS 的運作原理是提供每個 IP 封包一個標籤，由此決定封包的路徑以及優先順序，與 MPLS 相容的路由器，會將封包轉送到其路徑前，僅讀取封包標籤，無須讀取每個封包的IP位址以及標頭，因此網路速度便會加快許多，同時藉由 QoS ( Quality of Service ) 的機制對所傳送的封包加以分級，進而大幅提升網路服務品質並且提供更多樣化的服務。
2. SIP-based VOIP in WMNs (4/6) • SIP-based VoIP： • Voice over IP (VoIP)：可同時包含資料、 語音與影像的封包式網路服務架構。將語音訊號分成frames，之後儲存成data packets，最後透過使用語音通訊規約之IP network來傳送。
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.
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.
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 accessed IP networks. • To deploy SIP in WMNs, we must face many new challenging issues that are caused by the instability of the wireless environment and by user mobility.
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.
3. Technical challenges of developing SIP-base VOIP in WMNs(3/5) • We assume that the MPLS network runs with traffic engineering capability, which is employed to set up a label-switched path (LSP) dynamically for a connection with QoS requirements. • Total session set up delay of a VoIP call should be the sum of SIP signaling and MPLS signaling times if one SIP client in a WMN wants to communicate with its counterpart in another WMN through MPLS-based IP core network.
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 at anytime. • 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.
3. Technical challenges of developing SIP-base VOIP in WMNs(5/5) • Call admission control (CAC)： • A CAC mechanism must be employed when thepredicted and reserved access bandwidth is differentfrom 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.
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.
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 SIP call set up delay in the MPLS network is decreased significantly.
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 [tn–1, tn] is exactly Bn–1,n, then at time tn–1, the enhanced SIP proxy server negotiates with the MPLS network to obtain Bn–1,noutgoing bandwidth by using COPS messages. • It is impossible for the enhanced SIP proxy server to know the exact value of Bn–1,n before the time instance of tn–1. • Usually ,the enhanced SIP proxy server can employ only a certain bandwidth prediction algorithm to give an approximate value of Bn–1,n , which can be defined as ~ Bn–1,n.
An enhanced SIP PROXY server for wireless VOIP (4/5) • ~ Bn–1,n< Bn–1,n：The WMN does not have enough outgoing bandwidth to accommodate all SIP calls, and the enhanced SIP proxy server must utilize a call admission control mechanism to decline some of the call requests. • ~ Bn–1,n> Bn–1,n：Some of the outgoing bandwidth resource of the WMN would be wasted. • We can conclude that thealgorithms of access bandwidth prediction andcall admission control running on an enhancedSIP proxy server are critical to our approach.
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
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.
5. Performance analysis(2/5) • If the call request is admitted, an enhanced SIPproxy server will forward the original INVITEmessage to the callee；otherwise, it simply sendsthe 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.
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 a complete sharing CAC policy, which means that an incoming connection is accepted if sufficient bandwidth resources are available.
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.