Intelligent Service Influence Evaluation for SIP Proxy Server Performance

Transcription

1 Intelligent Service Influence Evaluation for SIP Proxy Server Performance Remigijus Gedmantas Department of Telecommunication, Kaunas University of Technology, Student st , LT-5368 Kaunas, Lithuania, Alfonsas Jarutis Department of Telecommunication, Kaunas University of Technology, Student st , LT-5368 Kaunas, Lithuania, Abstract. Last year the number of users who used basic voice call over IP networks considerably increased. Voice over IP (VoIP) network must provide intelligent services such as Free Phone (FP), Account Card Calling (ACC) and others. It is needed to evaluate the influence of the new intelligent services on performance of SIP proxy server. Each intelligent service has own interaction between the intelligent network nodes and SIP proxy server. The analytical model of SIP proxy server which operates like soft SSP node was proposed in the paper. Development of analytical SIP proxy server model was based on Jackson's theorem. The calculation of the influence of services FP on SIP proxy server of the given network was carried out by using the proposed model. traditional intelligent service is simpler when the IN architecture is utilized. The schemes of IN and SIP networks are presented in the papers [0,, 2, 3]. User C Access signalling INAP over SS7 SSP SCP INAP over IP Keywords. VoIP, Intelligent Networ SIP, Jackson s theorem. User A SIP Extended SIP proxy server SIP User B. Introduction The packet network is considered as potential network infrastructure for providing telephony service. VoIP network has to provide intelligent services (i.e. FP, ACC and others) which traditional Intelligent Network (IN) [, 2, 3, 4] or Advanced Intelligent Network (AIN) [5, 6] provide for theirs users. Currently Session Initialization Protocol (SIP) [7] is one of the most popular protocols for the call setup. The SIP has the open programming interfaces such as call processing language (CPL) [8] and common gateway interface (CGI) [9], which are used for developing and providing intelligent service in VoIP network. The implementation of the Figure. Scheme of SIP networ which provides intelligent service [3] It is needed to evaluate the influence of the new intelligent services on performance of SIP proxy server. Each service has specific algorithm of realization and different number of transactions. We have to know the dependence of the performance of SIP proxy server on the service type and the arriving rate. Every service has his own interaction between nodes of IN and SIP networks and different uantity of transactions. E.g. one transaction is needed for FP service, but three transactions are needed for ACC service [4].

2 The evaluation of the influence service for SIP proxy server, which is supplemented by Basic Call State Model (BSCM) functions [3] performance, is presented in this paper. The SIP proxy server operates as a soft signaling switching point (Soft SSP) node. It is a gateway between the IP telephony call control function and the Intelligent Network service represented by the INAP Service Control Function (SCF). It also provides the necessary mapping between the SIP protocol state machine and the INAP BCSM so that SIP user agent or proxy server can access the existing Intelligent Network services. the message was not depended on the message type. The service times was exponentially distributed with the average T enc. The message service from that ueue represents encapsulation of information process to UDP, IP, and Ethernet PDU s. λ λ2 λ3 λ4 2. Analytical model of SIP proxy server The analytical model of SIP proxy server and the intensity of messages flow coming to server are needed for evaluation of server performance. The operation of SIP proxy server is presented by ueuing models in the Fig. 2. The SIP proxy server has one input witch is used for incoming messages from the terminals or SCP nodes. The SIP or INAP messages which come to SIP proxy server are sent to DEC ueue. The messages of that ueue are serviced in the central processor (CP). The service time of the message does not depend on message type. The service times are exponentially distributed with the average T dec. The service message of that ueue represents the decapsulation process from Ethernet, IP and UDP protocol data units (PDU). The SIP messages which are decapsulated are sent to SIP ueue and INAP messages are sent to SIP ueue. The messages from INAP and SIP ueues are services by CP. The service times are exponentially distributed with the average T INAP and T SIP respectively. When CP served the message from SIP ueue, the message was sent to ENC ueue if the message was not associated with intelligent call setup. If the message was associated with intelligent call setup, it would be sent to INAP ueue. When CP served the message from INAP ueue, the message was sent to ENC ueue if there was need to send a new message(s) to SIP terminal or SCP node. If the message was associated with intelligent call setup it would be sent to INAP ueue. The message would leave the system if a new message was not send to SIP terminal or SCP node. CP served the messages which were coming to ENC ueue. In such case the service time of µ cent λ 5 µ NIC Figure 2. SIP proxy server ueuing model When CP served message from ENC ueue the message would be sent to NIC ueue. That ueue was served by processor of network interface card. The average service time was T NIC. The served message is sent to SIP terminal or SCP node. FIFO discipline is used for all ueues serving. The buffers of INAP, SIP, DEC, ENC and NIC ueues do not overflow, so why the probability to block the messages is in the SIP proxy server is P B _ P = 0. () 3. Evaluation of flow intensity which comes to SIP proxy server The call signaling messages are transmitted through SIP proxy server when basic or intelligent calls are organized. The total intensity of the messages flow which comes to SIP proxy server (to DEC ueue) is λ = λ + λ, (2) DEC T _ out SCP _ out

3 where λ T _ out is the intensity of the messages flow coming from SIP terminals to SIP proxy server; λ is the intensity of messages SCP _ out flow coming from SCP nodes to SIP proxy server. Invite, Ringing, O Ac Bye and others messages which are reuired for basic call establishing and disconnecting come from SIP terminals [5]. These messages are not lost in the network. The total intensity of the messages flow coming from SIP terminals is eual the total intensity of all messages which SIP terminals have to send for establishing and disconnecting for each service is expressed as = K R k λ λ, (3) T _ out k = r= T, r where λ T, r is the intensity of r type messages leaving SIP terminal when the call of type k is established or disconnected; K is the total number of call types; R(k) is a number of the message types which SIP terminal have to send when the call of type k is established or disconnected. The messages of type s which come to the server become messages of type r which leave processor after it was served. In that case the intensity of type r messages is eual to the intensity of s type messages (Jackson's theorem [5]): λ =. (4) in, s λout, k, r The interarrival times of type r messages are distributed exponentially when the interarrival times of type s messages are distributed exponentially. The intensity of type r messages which leave SIP terminal is eual to the arrival rate of type k service which is generated by SIP terminals: λ =. (5) T, r λ0, T, k The interarrival times of type k service are exponentially distributed [6]. Thus the inter arrival times of type r messages which leave SIP terminals are exponentially distributed when the type k service is established or disconnected. The total intensity of the messages flow coming from SCP nods is eual to the total intensity of all messages which SCP nodes have to send to SIP proxy server for establishing and disconnecting for each service is expressed as = K I k λ λ, (6) SCP _ out k = i= SCP, i where λ SCP, k, i is the intensity of type i messages which leave SCP nodes when type k service is established or disconnected; I(k) is number of the message types which SCP node have to send to SIP proxy server when the type k call is established or disconnected. The intensity of type i messages which leave SCP node is eual to the arrival rate of type k calls which are generated by SIP terminals: λ SCP, i = λ0, T, k. (7) Inserting (3), (5), (6), (7) into (2) gives = K R k K I k λ λ0, T, k + λ0, T, k. (8) k = r= k = i= SIP ueue is 2 = K R k λ λ0, T, k. (9) k = r= INAP ueue is K I ( k ) K R( k ) λ 3 = λ0, T, k + λcase, (0) k = i= k = r= where λ Case = λ 0, T, k if the message of type r is correlated with the establishing of the intelligent call and λcase = 0 otherwise. ENC ueue is 4 = K O k λ λ P, k, o; () k = o= where λ P, o is the intensity of type o messages which SIP proxy server has to send to SCP node or SIP terminal when the type k call is established or disconnected; O(k) is a number of the message types which SIP proxy server has to send to SCP node or SIP terminal when the type k call is established or disconnected. The intensity of messages type o leaving SIP proxy server is eual to the arrival rate of type k call which are generated by SIP terminals: λ P, o = λ0, T, k. (2) Inserting (2) into () gives 4 = K O k λ λ0, T, k ; (3) k = o= The average of the message service time in CP is

4 4 T cent = P T ; (4) = where P, P 2, P 3, P 4 are the probabilities that the message served in CP is from DEC, SIP, INAP, ENC ueue respectively. The probability P is P 4 = λ λ. (5) = The service time of the messages from SIP and INAP ueues depends on the message type. The average service time of the messages from SIP ueue in CP is: 2 = K R k T ( λ T k, r,2 ) λ ; (6) k = r= 0, T, k where T r, 2 is average service time of type o messages from SIP ueue in CP when the type k call is established or disconnected. The service times are distributed exponentially. The average service time of the messages from INAP ueue in CP is K I ( k ) ( λ0, T, k T i,3) k = i= T 3 = + λ3 (7) K R( k ) ( λcase T r,3) k = r= +, λ 3 where T i, 3 is the average service time of type i messages from INAP ueue in CP when type k call is established or disconnected; T r, 3 is the average service time of the type r message from INAP ueue in CP when the type k call is established or disconnected. The service times are distributed exponentially. We divide CP into four virtual processors which serve individually DEC, or SIP, or INAP, or ENC ueue for evaluating the waiting time in the ueue. The service intensity of the respective virtual processor is µ = P T. (8) cent, cent The total flow of the messages coming to DEC, or SIP, or INAP, or ENC ueue arrives according to a Poisson distribution. The services intensities are distributed exponentially in the virtual processors. Thus we can calculate the sum of the service and waiting times of the messages from every ueue with the mathematical expressions of M/M/ system [5]. 2 TS ( µ λ ), = cent, (9) NIC ueue is λ 5 = λ 4. (20) The service time of the messages depends on message type and the throughput of channel C in the NIC processor. The average service time of the messages is,,,, 5 = K O k λp k o SP k o T ; (2) k= o= λ5 C where S P, o represents the size of the type o messages. The total flow of the messages coming to NIC ueue arrives according to a Poisson distribution. The service intensities of the message are distributed generally (we know the size and the appearance probability for each message) in the NIC processor. Thus we can calculate the sum of the service and waiting times of the messages from NIC ueue with the mathematical expressions of M/G/ system [5] K O( k ) 2,, S λp k o P, o λ5 k o 5 C = = λ TS,5 T = 5 + (22) 2( λ5 T5 ) The delay of the type k call setup in SIP proxy server is D = R k k D k, r (23) r= where D k, r is the delay of type r messages in SIP proxy server when the type k call is established or disconnected. D P T, (24) = 5 r Case = S, where P Case = if type r message has to cross ueue, and P = 0 otherwise. Case 4. Evaluation of SIP proxy server performance Let us evaluate the call setup delay in SIP proxy server which provides two services: the basic SIP call and FP. The messages flow of the basic SIP call and FP are presented in []. The service time in CP when message comes from respective ueue of SIP proxy server and the size of messages are presented in Table. The condition probability that the messages cross the ueues of SIP proxy server when basic

5 call is served is presented in Table 2. The case, when Free Phone call is served is presented in Table 3. Table. The average service time in CP and size of the messages Average service time in CP, ms Size, Message ENC SIP INAP DEC Byte Invite Trying Ringing 0 59 Ok Ack Bye Ok (after disconnect) 0, 0 0,2 552 IDP 0 0 PREB 0 ACH 0 2 Connect ERB 0 2 ACR 0 Table 2. The conditional probability that the messages cross the ueues of SIP proxy server when basic call is served P Case Message DEC SIP INAP ENC NIC Invite 0 Trying Ringing 0 Ok 0 Ack 0 Bye 0 Ok (after disconnect) 0 Table 3. The conditional probability that the messages cross the ueues of SIP proxy server when Free Phone call is served P Case Message DEC SIP INAP ENC NIC Invite Trying Ringing 0 Ok 0 Ack Bye Ok (after disconnect) 0 IDP PREB ACH Connect ERB ACR The Fig. 3 shows the dependence of average call setup delay in SIP proxy server from call type and call arriving rate. Two cases are presented in the Fig. 3. In the first case SIP terminals generate only the basic SIP calls. In the second case SIP terminals generate 50% the basic SIP calls and 50% FP service calls. We explain in detail how Invite message crosses model of SIP proxy server, when basic call is served. Invite message crosses DEC, SIP, ENC and NIC ueues (see Table 2). The average service time of Invite message in CP is 0, ms when it comes from DEC ueue, 2 ms when it comes from SIP ueue, and 0, ms when it comes from ENC ueue (see Table ). When message comes from NIC ueue to NIC processor the service time of message is 742 8/ C s. Call setup delay, s,6,4,2 0,8 0,6 0,4 0,2 00% Basic Call, Basic Call setup delay 50% BC and 50% FP, Basic call setup delay 50% BC and 50% FP, FP call setup delay Arriving rate, calls/s Figure 3. The dependence of the call setup delay in SIP proxy server from the call type and the arriving rate 5. Conclusions An analytical method for the performance of IN/SIP signaling platform evaluation is presented. Jackson's theorem was applied and the analytical SIP proxy server model was developed. The presence of IN services reduces the overall number of admitted calls rate and increases the delay of basic SIP voice call setup process. The SIP proxy server can support up to rate at 90 calls/s without Free Phone service. With Free Phone service this processing capacity drops to 55 calls/s. 6. References [] ITU-T Recommendation Q.20, Principles of Intelligent Network Architecture. [2] ITU-T Recommendation Q.202, Intelligent Network Service Plane Architecture.

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