CARRIER VOICE NETWORK MANAGEMENT

Transcription

1 CARRIER VOICE NETWORK MANAGEMENT Elvis N. Ngah Supervised by: Dr. Sandjai Bhulai Department of Mathematis Vrije Universiteit Amsterdam The Netherlands Deryk Cole Network Operations Center Telesonique Global Teleom exhange Zurih, Switzerland

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3 Master Thesis Business Mathematis and Informatis Vrije Universiteit Amsterdam Depts. of Maths. and Comp. Siene Faulty of Sienes De Boelelaan 1081a 1081 HV Amsterdam The Netherlands ii

4 Carrier Voie Network Management Prefae and Aknowledgements Prefae and Aknowledgements The projet doumented in this report was done as the final unit of the MS programme in Business Mathematis and Informatis of the Vrije Universiteit Amsterdam, the Netherlands. It was arried out in Zurih for a duration of 7 months at the Network Operations Center of the Swiss teleom operator, Telesonique GTeX where I worked on Carrier Voie Network Management with a fous on Routing and Network Troubleshooting. Carrier voie routing is also a funtion of various osts. So, although I was a member of the tehnial team, on the one hand, I had to rely on the ommerial department for prie and revenue details, and on the other hand, they had to rely on the results of my route performane analyses in order to make prie offers to other arrier ustomers. Just one person never ompletes a projet. In this respet, I would like to thank a number of people who gave me their helping hands in one way or the other. Beginning with the ompany, I would like to give thanks to the CEO, Mr. Adel Labib, for giving me the privilege to arry out this projet within the ompany. Next, is my supervisor and hief Network Systems Engineer at the ompany, Mr. Deryk Cole. I am grateful for the onhand pratial tehnial swithing experiene that he has given me and more espeially, the onfidene in letting me handle equipments all on my own. I would also like to say thank you to the Produt Manager, Mr. Gunnar Berglund, for letting me know what the ommerial side of arrier voie swithing is like, more espeially, ustomer billing and priing. I am also grateful to Nasser Bessada and David Sgier not only for the ever open ears they gave to my endless ommerial and ustomer related questions, but also for making me exploit some soial aspets of Zurih. At the university, I will always be grateful to my supervisor, Dr. Sandjai Bhulai, for the aademi assistane he has offered to me espeially during the last year of my study. His hallenging suggestions, orretions, and omments form an integral part of this report. Next is Drs. Wemke van der Weij. Thanks for being my seond reader. Finally, thanks go to my mum, Osong Zipporah, for her enouragements; and to my indebted friend at the University of Bresia (Italy), Tomson Ngassa, for his doumentation feedbak. Elvis Ndomon Ngah Zurih, April 25, iii

5 Carrier Voie Network Management Contents Contents Prefae and Aknowledgements... iii List of Aronyms... vi List of Figures... vii CHAPTER 1: INTRODUCTION About Telesonique GTeX Problem Definition Study Objetives Organization of this Report... 3 CHAPTER 2: CARRIER SERVICES Area Code Management Area Codes and Priing ITU-T E.164 Standard Routing Number Formats Produt Management Servie Differentiation Number Differentiation Carrier Sales Traffi Hubbing Swithless Reselling Performane Contrating Traffi Eonomis Traffi Auditing Aounting Rate and Curreny Impat CHAPTER 3: NETWORK OPERATIONS Troubleshooting Monitoring Performane Measures Trouble-Tiketing Call Loop Detetion Swithing Connetion Set-up and Teardown SS7 Signaling Voie over IP iv

6 Carrier Voie Network Management Contents 3.3 Routing Least Cost Routing Carrier Bloking Route Configuration CHAPTER 4: PERFORMANCE ANALYSIS Metri For Routing Understanding Grade of Servie From Cost to Cost-Quality Routing Deision Analysis Peer-to-Peer Model Desription MIP Formulation Solving the Deision Model Quality at the Busy Hour Input Data Parameter Setting CHAPTER 5: RESULTS CHAPTER 6: CONCLUSIONS Disussion Future Researh BIBLIOGRAPHY APPENDICES Appendix A: Loop finder Appendix B: VoIP odes used Appendix C: Destination listing (A-Z) Appendix D: Matlab ode for alulating the utility Appendix E: Routing table for the first 100 destinations v

7 Carrier Voie Network Management List of Aronyms List of Aronyms ACD ACM ADSL ANM ASR BHCA CCS7 CDR CLI CLR CTF DMS DPC GoS IFAM ITU LCR NOC OPC PCM PD PDD PIN PSTN QoS REL SLA SS7 TDM TT VoIP Average Call Duration Address Complete Message Asymmetri Digital Subsriber Line ANswer Message Answer Seizure Ratio Busy Hour Call Attempts Common Channel Signaling 7 (same as SS7) Call Detail Reord Calling Line Identifiation CLeaR message CiruiT Free message Digital Multiplex System Destination Point Code Grade of Servie Initial and Final Address Message International Teleommuniation Union Least Cost Routing Network Operations Center Origination Point Code Pulse Code Modulation Priing Department Post Dial Delay Personal Identifiation Number Publi Swithed Telephone Network Quality of Servie RELease message Servie Level Agreement Signaling System 7 (same as CCS7) Time Division Multiplexing Trouble Tiket Voie over Internet Protool vi

8 Carrier Voie Network Management List of Figures List of Figures Figure 2.1: Funtioning of Telesonique Calling Card 6 Figure 2.2: Different transit senarios 8 Figure 2.3: Traffi re-file 9 Figure 3.1: Telesonique real-time traffi monitor 13 Figure 3.2: A trouble tiket 14 Figure 3.3: Trouble tiket handling proedure 15 Figure 3.4: Call looping 16 Figure 3.5: Graphial display of the effet of looping on the ASR 17 Figure 3.6: Connetion set-up 18 Figure 3.7: Connetion teardown (a) by aller, (b) by allee 18 Figure 3.8: Telesonique s swithing system 19 Figure 3.9: Desription of H.323 and SIP protool staks 20 Figure 3.10: Telesonique s gateways 20 Figure 3.11: Connetion between X and Y: (a) Network topology, (b) Routing table 22 Figure 3.12: DMS swithing proess 23 Figure 4.1: Swithing of destination by node i; ost-quality onsideration 28 Figure 4.2: Peers and their orresponding indies 31 vii

9 Chapter 1 INTRODUCTION 1.1 About Telesonique GTeX Telesonique Global Teleom exhange 1 (GTeX) is a teleommuniations provider in Switzerland. It has its establishments in Geneva (headquarters) and in Zurih, and provides servies like Calling Cards, ADSL, Satellite Telephony, , Internet Telephony ommonly alled Voie over IP (VoIP), et. Although the qualities of these servies meet with the most reent industrial standards, there is still the need to optimize them. In Zurih is housed the Network Operations Center (NOC) and the Priing Department (PD). NOC is responsible for network operations like swithing, routing deisions, apaity management, troubleshooting, et., whereas PD deals with matters like ustomer billing, prie negotiations, revenue management, et. These two departments work hand in hand with eah other espeially in aspets like billing and making routing deisions. Telesonique, just like any other international arrier, swithes telephone traffi from one destination to another. In other words, it trades (buys and sells) telephone minutes with other arriers suh as T-Systems, KPN, Verizon, Swissom, Tele2, Vodafone, et. by serving as a passageway for voie traffi. 1.2 Problem Definition In the past, the goal of teleom engineers was to provide better servies at whatever osts. 1 This name will simply be abbreviated to Telesonique in the rest of this report.

10 Carrier Voie Network Management 1. Introdution The osts were then being levied on the ustomer. To this end, only the rih ould afford these servies. Over the years, there have been hanges to this situation. The industry is driving to the positive diretion where better servies are being provided at very low harges to the ustomer. In addition, teleom ompanies have in reent years experiened a signifiant inrease in number, whih has led to a high level of ompetition amongst them. At the same time, the number of ustomers has also grown tremendously. Thus, there is the need for better management of resoures suh as optimization of the quality of the servies they provide to these and other arrier ustomers. Trade-offs need to be made between osts, quality, and priorities. A telephone all is between two parties - the alling party (or aller) and the alled party (or allee) who are onneted by one or more swithes at various arrier ompanies exhanges. These swithes form an eletrial onnetion between both end-users, and their setting is eletronially determined by pulses or tones generated by the dialed number. When a onnetion is established, and aller and allee subsequently go in speeh, their voies are transported as analogue and digital signals between the swithes in the network. In order to suesfully realize this proess, the teleom exhange ompanies are harged for this. Eah time a number is dialed, eah of these ompanies sees it as an attempt, whih may either be suessful or a failure. They make a very small profit margin for eah suessful all but rely on the minutes generated by the huge amounts of suessful alls in order to make a notieable profit. Problem statement With respet to the above two paragraphs, the problem faed by Telesonique that we need to solve is to maximize the suess/attempt ratio of alls (i.e., voie and fax) subjet to the following onditions: 1 Call resoures are expensive to provide. For this reason, it is ost effetive not to provide more resoures than required. 2 Call arrivals at Telesonique s network are unertain over time. Subsequently, a all may arrive when all resoures are in use. Suh a all is bloked. Eah arrier ustomer wants the bloking of its traffi to be as low as possible. In this sense, very high bloking does not satisfy ustomer requirements, whih may eventually lead to poor arrier-arrier relationships. On the other hand, when the bloking of alls is very low, it means that there is more provisioning of ostly resoures than needed. 3 Calls also fail at the level of an outgoing route 2 as a result of ongestion. The trade-off here is that the hosen route should have minimal network ongestion and at the same time offer minimal osts. 4 Even when a all is suessful, the aller has to be satisfied with the voie quality. In the arrier business, there is the tendeny that allers stay longer in speeh when the all quality is good. An inrease in expeted all duration means the sales of more telephone minutes, implying an inrease in revenue for the business. 2 A route is the next available arrier to whih a all is swithed and not the omplete path taken by the all from the aller to the allee. 2

11 Carrier Voie Network Management 1. Introdution 1.3 Study Objetives The onstraints outlined above have three basi themes, whih are osts, arrier relationships, and quality. To this end, we map the underlying problem by addressing the following researh questions: Q1: How do osts and network performane influene Telesonique s relationship with other arrier ustomers and suppliers? Q2: What are the resoures needed by allers and how do they lead to arrier-arrier relationships? Q3: What are the performane metris in question and how do we improve them? Q4: How do we guarantee some better traffi quality to arrier ustomers? Q5: Whih route (supplier) is optimal, i.e., renders the best prie-quality option for traffi to a partiular destination? To solve the stated problem, we need to answer these questions in a ost effetive manner. In priniple, they should be answered in suh a way that the benefits obtained from them outweigh both the osts of answering them and the osts of the system [1]. Subsequently, we follow the steps outlined below, eah in a restrited time frame: 1. Gather relevant information and data onerning the problem, 2. Formulate a model with sub-omponents that represent the problem, 3. Use a mathematis and omputer-based approah to solve the model, and 4. Validate the results of the model. The details of these steps are the remaining ontent of this doument. 1.4 Organization of this Report The rest of this report is organized as follows: the routing and performane related ativities of Telesonique s PD are treated under Carrier Servies in Chapter 2. More generally, this hapter elaborates on how routing osts and route quality lead to, and influene the relationship between arriers thereby answering the first researh question, Q1. In Chapter 3, we study the ativities of the NOC. The aim of this hapter is to bring out the resoures needed by allers and how they lead to arrier-arrier relationships. Thus, we answer Q2. Here, we also resolve Q3 as we identify the network performane metris, and how they an be improved. We then treat Q4 and Q5 as Performane Analysis in Chapter 4. The results of the analysis are validated in Chapter 5. Finally, some onlusions and suggestions for future researh are presented in Chapter 6. 3

12 Chapter 2 CARRIER SERVICES 2.1 Area Code Management Area Codes and Priing When a aller in a ountry makes a phone all to a person in another ountry, it is possible that the aller and the allee are subsribers of different network providers. Even if they are both in the same ountry, they ould still belong to different network providers. Beause of this, Telesonique s ustomers are mostly arriers that trade on an international sale. They buy and sell traffi that are destined for various ountries. Different arriers have their own priing shemes for different destinations. To this end, Telesonique determines the prie it harges for inoming traffi. Sine the arriers of this traffi have to pay money to Telesonique, this traffi is referred to as sold traffi. At the same time, other arriers supply Telesonique with their prielists in ase Telesonique has to send purhased traffi to them. A major fator that determines the prie is the destination (not the soure) of the alls. Eah area ode is harged a different prie and eah arrier s swithing equipment uses area odes as well as pries in order to route traffi. As days go by, new mobile and fixed network operators ome into business and are given unique operator numbers by the onerned governing teleommuniations authorities. More so, as a ountry s population inreases, new area odes are introdued as well as old ones disappeared. To this end, eah arrier regularly updates its frequently hanging area ode list in order to make optimal routing deisions. Telesonique is no exeption. NOC together with the PD handle this issue. While the latter uses it for better revenue management poliies, NOC on the other hand, uses it as a riterion for making optimal routing deisions.

13 Carrier Voie Network Management 2. Carrier Servies In general, for a partiular ountry, traffi destined for mobile phones are more expensive than those for fixed phones. In this respet, it is neessary to ask the following questions: Would other arriers be willing to send us fixed phone traffi when we harge them the higher amounts meant for ellular phone traffi? Would we generate higher revenue and eventually be in business when we provide our servies on a negative margin by harging mobile phone traffi with the low amounts meant for fixed phone traffi? These questions leave Telesonique with the need to avoid simple but fatal oding errors of mistaking mobile numbers for fixed numbers and vie-versa. Area ode management is done on average one every month or immediately when there is an alert ITU-T E.164 Standard The management of the international odes for every ountry is in the auspies of the ITU-T 3. In the ITU-T reommendation E.164, eah ountry ode is preeded by the + sign (meaning a preeding 00). The smallest international ode is +1. The odes are grouped into 9 zones as shown in Table 1. Zone nr First digit of ountry ode Nr of digits in ountry ode Geographial Region or 4 North Ameria and the Caribbean Islands or 3 Afria, Aruba, Greenland and the Faroe Islands or 3 Europe or 3 Europe or 3 South/Latin Ameria or 3 South Paifi (Oeania) Russia and Kazakhstan or 3 East Asia and Speial Servies or 3 West Asia, South-East Asia, and Middle East Table 1: ITU zone division and ountry ode alloation. 4 The ITU, however, does not govern the way in whih eah ountry does its national numbering plan. The teleommuniations authorities of the respetive ountries handle this. The ITU has a database portal on its website [6] that ontains all these details. It therefore urges eah national authority to immediately inform ITU with the updated list. On this website, there is free subsription for an alert in ase an update is made. Telesonique and other arriers ount on these updates as their main soure of area ode management information. 3 ITU-T is the setor of the International Teleommuniation Union (ITU) responsible for telephony and data ommuniations. 4 For a detailed list of ountry odes, onsult [6]. 5

14 Carrier Voie Network Management 2. Carrier Servies Routing Number Formats In international voie swithing, arriers adopt a destination number system that ensures swithing effiieny. This number has as few digits as possible after the ountry ode [3]. The most ommonly used format is +CC ABC XXX where CC = destination ountry ode, ABC = unique ode speifying servie provider and servie type, and XXX = ustomer number. Let us take for example the Netherlands where we an identify the routing number format Here, CC = 31 and ABC = 624 whih is reserved for the ellular network provider T-Mobile. Thus, all alls swithed by Telesonique to the destination numbers and will be routed to the same arrier sine they have the same routing number format A all for the T-mobile number might be routed to a different arrier beause this destination has a different routing number format, , hene a differene in tariff. More about tariffs is explained in Setion Eah routing number is interpreted as a destination. 2.2 Produt Management Servie Differentiation Telesonique renders two different kinds of servies. These are retail and wholesale servies. Retail servies inlude Calling Cards, provisioning, ADSL, et. The wholesale servie it provides is swithing voie traffi from one teleom arrier to another. Sine the sope of this projet is swithing voie traffi, we limit ourselves to the retail Calling Card and wholesale voie servies. The Calling Card servie works as follows. A ustomer has a pre-paid Telesonique alling ard that ontains a toll-free aess number and a PIN 5. To make a all, the following steps as shown in Figure 2.1 apply: 1 Caller dials toll-free aess number on ard using a Swissom fixed phone. 2 Digitalk requests for PIN of alling ard. 3 Caller inserts PIN. 4 Digitalk heks if PIN is valid. 5 If so, Digitalk requests for destination number. If not, aller is informed and all is terminated. 6 Caller inserts destination number. 7 A Digital Multiplex System (DMS) swithes the all to another arrier depending on the given destination. 5 Personal Identifiation Number. 6

15 Carrier Voie Network Management 2. Carrier Servies All requests and responses are swithed by the DMS. Figure 2.1: Funtioning of Telesonique Calling Card Number Differentiation In both the retail and wholesale voie servies, different priing shemes are attributed to the different destination numbers that are swithed. It is therefore worthwhile to know the different number ategories. These are: Fixed (loal) numbers: These are numbers attributed to loal telephony where the network provider renders servies within a limited geographial region. The telephone alls terminate at a telephone exhange. When a all is made for a far destination, the branh exhange swithes the all to the respetive long-distane network. Calls to loal numbers are generally heap. Cellular numbers: These are numbers attributed to subsribers by operators whose radio networks onsist of ells, eah being served by a base station in the ell. The base stations are onneted to ellular telephone swithes, whih in turn onnet to a Publi Swithed Telephone Network (PSTN). When a user moves from one ell to another, the swith automatially ommands the ellular phone to the new ell frequeny. Swithing alls destined for mobile numbers is generally more expensive than swithing those for fixed phones. Toll-free numbers: These are numbers that an be alled for free. The alled party, usually a business unit, pays the osts for these alls. Costs are usually a funtion of the usage of the phone number and the osts of the trunk lines being used. The alled party usually makes sales in whih ase it reovers the inurred osts. Different ountries use different prefixes to denote toll-free servies for their national networks. Switzerland and the Netherlands adopt 0800 whereas the USA adopts 800. Value added servie numbers: These are also termed premium rate numbers. They are usually alled for servies like weather foreasts, diplomati servies, TV gambling, adult entertainment, et. The aller normally pays higher harges to the network provider. Some servie providers attribute these numbers as a means of 7

16 Carrier Voie Network Management 2. Carrier Servies reduing all volume as well as all length for tehnial support. In some situations, the revenue obtained is shared both by the network provider and the owner of the number, in whih ase it is termed a shared revenue number. Some ountries refer to these numbers as the 09 numbers beause of the 090X prefix. 2.3 Carrier Sales Traffi Hubbing Hubbing is the phenomenon whereby traffi is swithed from one arrier, A, to another arrier, B, via an intermediary arrier, C. This is done beause of the bilateral agreements between A and C and between C and B [3]. C aggregates and manages traffi from various arriers and then terminates them to various destinations. When B observes that traffi swithed by C is oming from A, the situation is alled a transit [4]. On the other hand, when B knows nothing about A and sees the traffi as originating from C, then it is alled a re-file. Telesonique plays the role of origin, destination, re-file, or transit arrier depending on the irumstane. We now onsider the traffi transit and re-file steps. Traffi transit Transit involves diret agreements and negotiations between all parties involved. As shown in Figure 2.2, A and B may use the same transit point C as in (a), or two different Figure 2.2: Different transit senarios. transit points as in (). In the situation where two different transit points are used, alls from A to B might transit via C, while alls from B to A might transit via D. The destination arrier pays the transit fee and therefore hooses the transit arrier. This is subjet to negotiations between A and B, for example, to hek if the originator is able to send alls via the desired transit arrier. 8

17 Carrier Voie Network Management 2. Carrier Servies The originator provides the neessary details (suh as the routing number formats) to the transit arrier. Eah arrier implements the neessary routing requirements in its network, e.g., by opening the required routing odes in their swithes. Carriers sometimes agree to both use two transit routes as shown in Figure 2.2(b) so as to take are of situations like overflow routing. Traffi re-file In a re-file, there are separate arrangements between the originator of the traffi and the re-filer, and between the re-filer and the destination arrier. The re-filer replaes the Calling Line Identifiation (CLI) 6 with a new one thereby making the destination arrier see the alls as oming from the re-filer. The idea behind re-filing is that the originator ends up paying less if the alls ome from the ountry indiated by the new CLI rather than from the original ountry. Figure 2.3: Traffi re-file. To illustrate this, some arbitrary values have been inluded in Figure 2.3. If A would send diretly to B, it would pay, say, 0.160/min. Sending via the re-filer C, A pays just 0.155/min to C who pays 0.145/min to send to B. The benefits are alulated as follows: A saves: = 0.005/min. C gains: = 0.010/min Swithless Reselling Selling traffi ould also involve another small teleom ompany alled a swithless reseller. Suh a ompany has no swithes or network failities. It buys the swithed failities from long-distane arriers for resale to ustomers. It signs ontrats with large arriers speifying per-minute rates and then resells the traffi to other ompanies and residenes for profits. Some ustomers need personal servies like billing, as well as network funtions, whih an be very ostly. Dealing with these ustomers by using swithless resellers an be very ost effetive. The swithless reseller handles the responsibility of handling the ustomer servie funtions. 6 This is the same as the Caller ID. 9

18 Carrier Voie Network Management 2. Carrier Servies Swithless reselling also has a drawbak. Swithless resellers are usually haraterized by managerial inompetene in whih ase dealing with them would mean first researhing and studying the effetiveness of their management team [8]. This an be very ostly Performane Contrating Telesonique signs servie ontrats with other arriers. Eah ontrat ontains some performane related agreements. These are interonnetion regulations and the quality standards eah party has to adhere to. Interonnetion is the linking of different networks so that ustomers of the different networks may all one another. Parties agree on apaity as well as onnetion bandwidth. The aim to regulate interonnetions is to handle ompetition amongst arriers. Consumers benefit from this in that the ompetition auses arriers to lower their pries and improve the quality of the servies they provide. For quality standards, eah party aepts to render best effort quality. This Quality of Servie (QoS) is based on present onnetion onditions and should be onsistent with industry standards, government regulations and sound business praties. Servie Level Agreements (SLAs) inlude aknowledgement, response, restoration, and losure times of a fault. Sometimes, there is a marketing motive attributed to the SLA suh as If you buy destination Y from me 7, I an terminate X% of the traffi providing an average all duration of C minutes harging you D/min. Traffi is then sent where the sender is guaranteed a better quality-prie offer. How an Telesonique define a quality-prie benhmark for a partiular destination and then make SLAs to ustomers with some degree of ertainty? This issue is overed in Chapter Traffi Eonomis Traffi Auditing Auditing refers to the examination of reords to hek for auray. Traffi reords that require auditing are billing reords for eah ustomer. These are determined from the ustomer s Call Detail Reord (CDR). Billing omprises gathering and traking of the network resoure usage metri, i.e., the total all duration and reporting the osts of utilization to the ustomer. The billing system has the apability of traking high-ost servies like international, long distane, and value-added-servie-number alls. Reporting the usage and osts for a 7 Same as if you send destination Y to me. 10

19 Carrier Voie Network Management 2. Carrier Servies partiular ustomer is done aross the entire network and is independent of the implementation [12]. Implementation here refers to the method in whih traffi is swithed. In order words, the billing system funtions in suh a way that for a partiular ustomer, a single prie is established for terminating alls to a partiular destination irrespetive of whether the alls are terminated via trunk lines or via an IP network Aounting Rate and Curreny Impat For eah all, the originating arrier harges the aller a fee alled tariff. The harge paid by the originating arrier to another arrier for terminating (swithing) this all is known as the aounting rate. The aounting rate is negotiated between the originating and terminating arrier and is related to the arriers end-to-end faility osts. Week nr B s prie/min C s prie/min $ ( ) $ ( ) Table 2: Carrier A s ost analysis. The billing arrangements other arriers make with Telesonique is that of invoiing sold or bought traffi weekly, semi-monthly, or monthly. These arrangements define the urreny of payment. Monetary terms are either in Euros, US Dollars, or Swiss Frans. The variations in exhange rates of these urrenies greatly influene the diretion and amount of traffi flow. As an example, let us onsider Table 2 where A deals with B and C in Euros and US Dollars, respetively. B sends its prie ( /min) to A for terminating traffi to a partiular destination. C also sends its prie ($0.1401/min) to A for the same destination. Suppose the prie offers stay onstant in weeks 1 and 2, but the Dollar has dropped in value by 2% with respet to the Euro. Everything (quality, taxes, et.) being equal, A sends traffi to B in week 1 sine it osts less. In week 2, the drop in value of the Dollar makes A hange its routing and now sends traffi to C. Flutuations in urreny value affet routing deisions and eventually apaity management. 11

20 Chapter 3 NETWORK OPERATIONS 3.1 Troubleshooting Monitoring Performane Measures Telesonique has real-time traffi software that reords traffi details. This is split into two for the two respetive kinds of traffi i.e. inoming and outgoing traffi monitor. The inoming traffi monitor reflets the performane of Telesonique s network at given moments. On the other hand, the outgoing traffi monitor reflets the performane of outgoing routes. Figure 3.1 shows the monitor for inoming traffi. It ontains details of the number of all attempts, the number of answered alls, and the total all duration for eah inoming arrier. From these, the performane features of interest are monitored. They inlude the following: 1. Answer Seizure Ratio (ASR): This is used as a measure of quality for inoming or outgoing traffi depending on the traffi monitor in question. It is defined as number _ of _ answered _ alls ASR =. (3.1) number _ of _ all _ attempts A low ASR implies that allers annot get through to the other end, thus, signifying bad quality. Reasons for this are: i. Congestion: There is more traffi than the available apaity. Therefore, some alls are bloked. ii. Long Post-Dial Delay (PDD): PDD is the time between dialing a number and hearing the dial tone or busy signal. In general, when the PDD is greater than

21 Carrier Voie Network Management 3. Network Operations 10 se. [11] allers onsider it to mean that there is no onnetion and therefore hang up. This is seen as an unsuessful attempt. iii. Call Looping: This is the situation where a all moves from one arrier to another and bak over and over again. In most ases, the all does not reah its destination. Even if it does, a long PDD is experiened. The all is interpreted as an attempt eah time it omes bak to the swith. Call looping usually involves two or more arriers and is very undesirable. It is disussed in detail in Setion Figure 3.1: Telesonique real-time traffi monitor 2. Average Call Duration (ACD): This is the expeted length of time in whih a user is in speeh. It is alulated as total _ all _ duration ACD =. (3.2) number _ of _ answered _ alls When the ACD is low, it is interpreted to mean that allers do not omplete their alls as desired but rather hang up as a result of bad quality. For wholesale, this implies a loss in revenue minutes. In a retail servie like Calling Cards, it is a very important issue sine people would not like to purhase, for a seond time, a alling ard that gives a low ACD Trouble-Tiketing A Trouble Tiket (TT), shown in Figure 3.2, is an eletroni tiket that is opened (made) 13

22 Carrier Voie Network Management 3. Network Operations and stored eah time there is a performane problem in the network, whih annot be solved immediately. Some of these problems (e.g., ongestion, long PDD, and looping) have already been explained in Setion above. Other faults inlude: iv. Dead air: Here, a all is being billed when no one is responding at the other end. This is very undesirable to the aller beause he/she pays for a servie he has not used. v. Call breaking: Caller and/or allee get intermittent sound breaks. This is aused by impairments in the eletroni equipments or paket loss in ase of VoIP. vi. Eho: This is the phenomenon whereby during a all, one repeatedly hears his/her own voie. In most ases, only one person hears an eho, whih means his/her voie is refleted near to the other end-user. This ours in VoIP. vii. Fax failing: Fax whih is data traffi, is transmitted using voie hannels. It is desribed as failing when the reeiver misses part or all of the transmitted data. Figure 3.2: A trouble tiket When a TT is opened for a performane problem, the TT inludes the following main ontents: Trouble Tiket number, e.g., TSQ Problem to be fixed, e.g., 0% ASR. Destination, e.g., Frane Mobile 68 (routing number format ). At least 2 test numbers. Outgoing arrier. Inoming arrier. 14

23 Carrier Voie Network Management 3. Network Operations Reeive trouble message from arrier. Chek inoming arrier on traffi monitor using date and destination. Reply to arrier that this destination is now testing OK. Yes Make test alls. OK? No Open NOC TT. Tiket must show originating arrier, test numbers, ause of failure and whih outgoing arrier is failing. Reply to originating arrier with TT referene. Make test alls via this arrier to failing destination. Yes Chek if there is a reroute option. No Yes Test alls OK? * Make re-route on swith. Blaklist the arrier for this destination. No * Send to outgoing arrier stating problem and test numbers. If VoIP then inlude originating IP address. If CCS7 then inlude OPC and DPC. Reeive reply from arrier. Yes Problem fixed? No Make test alls. If really fixed, lose NOC TT. Reply to originator. Make omment in NOC TT. Retest in 1 week. Ask arrier for update on TT. Figure 3.3: Trouble Tiket handling proedure. What is a TT used for? There is always the need to have easy and better ommuniation between arriers in order to maintain a good QoS. For example, let us onsider the situation where arrier A sends the destination Brazil to Telesonique, whih sends to arrier B. Suppose there is ongestion at arrier B s network where all hannels are oupied and these alls are 15

24 Carrier Voie Network Management 3. Network Operations eventually dropped. A sees it as if it is Telesonique dropping these alls and therefore makes an inquiry (usually in the form of an to Telesonique). Telesonique must try to solve this problem. At least two (test) numbers are hosen at random and then alled via B. If they are still dropped, Telesonique opens a TT for this problem and ommuniates the TT number as well as the solution status to A. The TT number is neessary for future referene to the problem. At the same time, Telesonique informs B of the problem stating the time of the problem and the test numbers. If there is another possible route C, to Brazil, Telesonique then makes a re-route via C and informs A of the solution. To better understand how handling trouble tikets works, it is good to take a look at Figure 3.3, whih summarizes the proess. In the proesses, the terms and abbreviations that have not been explained yet are marked by a (*), e.g., Origination Point Code (OPC) and Destination Point Code (DPC). Just like an IP address (for Internet), a point ode is simply an SS7 network address (in the form xxx.xx.xx) that identifies an SS7 network node suh as a swith. The remainder of the terminologies is explained under Swithing and Routing in Setions 3.2 and 3.3, respetively Call Loop Detetion In international voie teleommuniation, two arriers do not buy the same destination from eah other. Let us say arrier A buys the destination, Brazil, from arrier B who in turn buys from A. In suh a ase one all goes from A to B and bak to A. The all never leaves the system but keeps onsuming the iruit. This situation is alled all looping. In the situation where three or more arriers are involved as shown in Figure 3.4(a), it is very rare to notie whether a loop ours beause arrier A buys from B who buys from a different arrier, C. C in turn buys from A without knowledge of the destination s previous route. So the all just keeps moving between the three without termination. Within eah arrier, the all is onsidered as an attempt eah time it reahes the arrier s swith. This is seen as an unsuessful all attempt.as an example a CDR extrated from the traffi monitor is shown in Figure 3.4(b). A all reahes Telesonique from the arrier Figure 3.4: Call looping 16

25 Carrier Voie Network Management 3. Network Operations Telefonia (trunk odes 729, 735, et.). Telesonique swithes this all to ibasis (trunk ode 514). From the StartTime field, we notie that this all omes bak to the swith after every 5 to 6 ses. This is seen as a loop beause the aller stays on the line for 1 minute and 18 seonds with a all duration Dur(s) of 0 se. Looping is very undesirable. For the aller, it is experiened as a PDD or dead air with false billing. For the arrier, it dereases the ASR and arriers keep billing eah other over and over at the expense of the aller. This situation ontinues until either the aller hangs up or one of the arriers disovers it and makes a re-route or bloks it. Telesonique has a tool that determines suspeted loops. This tool is explained in Appendix A. Figure 3.5 graphially illustrates the effet of looping on the ASR as disovered from outgoing traffi from the DMS to the IP gateway via SS7 trunk line hannels 8. Conneted hannels are hannels in whih users are atually in speeh while used hannels are the total number of hannels oupied by looped alls and alls in speeh. Figure 3.5: Graphial display of the effet of looping on the ASR. 3.2 Swithing Connetion Set-up and Teardown Call establishment and termination involves a series of eletroni ommuniations between the swithing networks, A and B, of the aller and the allee, respetively. When the aller begins a all, an Initial and Final Address Message (IFAM) 9 is sent from swith A to swith B. When B reeives the IFAM, it immediately sends an Address Complete Message (ACM) to A to indiate that it has reeived suffiient digits and routes the all to 8 See Figure IFAM = IAM + FAM. IAM indiates that the iruit in use has been seized for this all while FAM indiates that suffiient digits have been reeived to initiate routing. 17

26 Carrier Voie Network Management 3. Network Operations the allee. The allee s phone starts ringing. Immediately the allee piks up the phone, B sends an ANswer Message (ANM) to A whih immediately ommenes billing. Caller and allee go in speeh. See Figure 3.6. Figure 3.6: Connetion set-up Any of the two parties an terminate the all (Figure 3.7). When the all is ended by the aller, A sends a RELease message (REL) with reason to B whih then releases the all and sends a CiruiT Free message (CTF). If it is the allee who terminates the all, the situation looks a bit different. This is beause termination signals beome triggered at swith B rather than at swith A. B sends a CLearR message (CLR) to A. Upon reeiving this message, A starts a timer. When the timer expires, the all eases from the aller and A sends a REL message to B whih then sends a CTF to indiate that the iruit is now free. (a) (b) Figure 3.7: Connetion teardown (a) by aller, (b) by allee. Traffi reahes Telesonique s swithing network via trunklines (SS7 10 signaling) or via an IP network (suh as VoIP), and leaves the network in the same fashion. It should be noted that inoming SS7 traffi may as well leave as VoIP and vie versa (see Figure 3.8). 10 SS7 = Signaling System 7. It is also known as CCS7 (Common Channel Signaling 7) or C7 for short. 18

27 Carrier Voie Network Management 3. Network Operations SS7 Signaling The swithing system used is SS7 where a single iruit is dediated for both voie and data at a onstant bandwidth. This tehnique offers signaling for multiple iruit onnetions, error detetion and orretion, and the apability to launh query and response messages to databases. Connetion links are alled E1s. An E1 uses Time Division Multiplexing (TDM) where multiple analogue voie signals are ombined into a single digital trunk. This TDM mehanism works as follows. The swithing system has a ode that digitizes eah voie analogue signal by produing 8-bit streams 8,000 times per se. This is alled Pulse Code Modulation (PCM). Eah stream represents a time slot of onstant bandwidth of 64 Kbps used by 1 voie all. This makes a time slot a voie hannel. Consequently, the full duplex trunk bandwidth of 2,048 Mbps is split into 32 time slots or hannels (of 8 bits eah) 11. The hannels are numbered 0 to 31. Channels 0 and 16 are used for ommon hannel signaling as well as signaling for the set-up and teardown of alls [10, 11]. The remaining 30 hannels are used for the atual voie traffi. These hannels in the SS7 swithing network are basially the resoures needed by allers. Eah E1 an therefore handle a maximum of 30 simultaneous voie alls. Figure 3.8: Telesonique s swithing system. Traffi that reahes the network as VoIP is onverted from IP pakets and deoded to 8- bit streams by a gateway alled the Exel swith, and is then sent to the DMS via E1s. The DMS aggregates this traffi together with other inoming SS7 traffi and routes part to other arriers via SS7 trunk lines (E1s) and the other part as VoIP. In ase all outgoing lines are in use, the DMS drops any inoming traffi. When the deision is to route as VoIP, the DMS sends the traffi via E1 trunk groups to a seond gateway alled Teles.iSwith, whih odes the 8-bit streams to IP pakets, whih are then transmitted via an IP network X 8 bits X 8,000 per se = 2,048,000 bps = 2,048 Mbps 19

28 Carrier Voie Network Management 3. Network Operations Voie over IP The onnetion between the swithing network and the IP network is through two gateways as was already seen in Figure 3.8. These gateways speak the H.323 protool and SIP on the Internet side and PSTN protools on the SS7 side. For the SS7 side, PCM has already been explained under SS7 signaling. For the IP network side, a desription of the H.323 and SIP protool staks is given in Figure 3.9. More details on these protools an be found in, e.g., Tanenbaum [11]. Unlike SIP whih is a single module used for ommuniation ontrol, H.323 is a omplete protool stak with well-defined telephone industry standards. One of suh standards is that all H.323 systems must support G.711, whih does PCM. For this reason, H.323 is widely deployed. (a) H.323 protool stak (b) SIP protool stak TCP Transmission Control Protool - transmits signaling and provides network management. UDP User Datagram Protool - attahes soure and destination port number fields for (de)multiplexing for audio transmission. H Provides onnetion setup and teardown. H.245 Negotiates hannel usage and the ompression proedure. T.120 Provides appliation sharing et. (not required for VoIP). RTP Real-time Transport Protool transports real-time data over the Internet RTCP Real-time Transport Control Protool provides, e.g., information on throughput and paket loss. RAS Registration, Admission and Status defines ommuniation between the gatekeeper and the gateway/terminal. G.7XX Standards for voie ompression (G.711, G.723, et.). H.26X Standards for video ompression (not required for VoIP). SIP Session Initiation Protool reates, modifies and terminates sessions with one or more partiipants. SDP Session Desription Protool desribes purpose, ode format, timing, transport information, et., for session to our. Figure 3.9: Desription of H.323 and SIP protool staks IP voie pakets reah the swithing network via the Exel swith. These pakets arrive in disorder. This variation in delay (travel time of the pakets) or jitter is eliminated with the help of a jitter buffer (Figure 3.10 (a)), after whih the pakets are onverted to 8-bit streams neessary for SS7 signaling. On the other hand, when the deision at the DMS of the SS7 network is to route traffi as VoIP, the 8-bit streams are sent to the IP gateway (Teles iswith), whih onverts them to pakets (Figure 3.10 (b)). Eah paket has a header that ontains the IP address of the destination arrier. More details on (de)paketization are given in Tanenbaum [11], and van der Mei [2]. The ode for VoIP is negotiated between arriers. This means the same ode has to be supported by both the originating and destination arrier. G.7XX odes are used for voie while T.XXX are used for data. Eah ode offers a different bandwidth and payload size. Appendix B gives details on these odes, and their respetive bandwidths, payload sizes, et. 20

29 Carrier Voie Network Management 3. Network Operations Figure 3.10: Telesonique s gateways. 3.3 Routing Least Cost Routing The routing metri used by Telesonique and other arriers is ommuniation osts (in terms of money) giving rise to the name Least Cost Routing (LCR). Eah arrier sends to every other arrier it trades with, individual prielists for all the destinations it swithes (terminates) traffi. Connetion agreements inlude prie notifiation details. The industry standard for an inrease is a notifiation period of seven days while a derease ould take effet on the day of notifiation. This gives rise to the need for making routing hanges everyday. Sine LCR is ost based, some arriers define peak periods as being a period of high osts and off-peak periods, a period of low osts. These periods differ from arrier to arrier. Telesonique s peak period is the interval 8:00am 7:00pm and its off-peak period is the interval 7:00pm 8:00am. LCR is therefore done twie per day one for peak periods and the other for off-peak periods. Both follow the same sheme. Eah arrier j indiates its prie P j to terminate traffi to destination. There are over 3500 destinations. For eah let { P j } denote the sequene whose elements are the pries P j. The following steps are implemented in software: 1 Sort { P j } to obtain { P i }, i = 1, 2, 3,, suh that Pi P 2 Calulate % margin as g = 1 i 100%. P1 3 Drop all P i having g i > a. Usually, a = 3%. 21 P min P =. 1 j j

30 Carrier Voie Network Management 3. Network Operations 4 In the worst ase, only P 1 is left. If more P i are left, selet three more to obtain at least four routing hoies. The routes are: Route 1 = arrier with prie P 1, Route i = arrier with prie P i (if it exists), i = 2, 3, and 4. The method of alternate routing is used. Any inoming traffi for destination is sent to Route 1, whih is most often, onsidered to be the diret route. If there is ongestion, the DMS automatially routes it to Route 2. This proess ontinues in this fashion right upto the last available route. If this route is ongested, then the DMS drops the all. This is also seen as overflow routing and it works only in the ase of ongestion. The network topology and routing table are shown in Figure The DMS has details of only the next hub (hub 1) to the destination and knows nothing about subsequent hubs. Figure 3.11: Connetion between X and Y: (a) Network topology 12, (b) Routing table Carrier Bloking Blaklisting Telesonique maintains a blak list that ontains mainly premium servie numbers. These are numbers that are terminated at extraordinary high osts and their termination yields a negative profit margin. Blaklisting involves bloking alls with a given routing number format at the swith. When these alls reah the DMS, it immediately drops them. The blak list is independent of the arrier. Bloking arrier for destination Some arriers send traffi that an effetively be terminated. However, beause the LCR is done on daily basis oupled with the fat that the weekly issuing of prielists does not take plae the same day for all arriers onneted, some traffi termination present a 12 Figure is adapted from Krings, A.W. [16]. 22

31 Carrier Voie Network Management 3. Network Operations negative margin, i.e., the traffi is terminated at a loss. For this reason, suh an inoming arrier is temporarily bloked for suh a destination if the margin is that big. This reason is termed ommerial. The arrier is unbloked again only when a new LCR has been done and indiates a positive margin for this destination. Carriers ould also be bloked for some destinations for reasons of looping and traffi overload. All arriers bloked for partiular destinations are kept in a arriers blak list. As shown in Figure 3.12, when a all arrives at the DMS, the DMS heks if the routing number format of the all is in the blak list. If it is found, the all is immediately dropped. If it is not found, the DMS proeeds to the arriers blak list to hek if the inoming arrier has been bloked for this destination. If that is not found, then the normal alternate routing proedure takes plae. Call arrives DMS DMS heks blaklist for destination No DMS heks arriers blak list if inoming arrier has been bloked for this destination. Found? Yes No Found? DMS heks if hannel is available to Route 1. Yes Call is dropped Call is routed Yes Available? No DMS heks for hannel to next priority route. max. 3 times. Yes Available? No Figure 3.12: DMS swithing proess Route Configuration In this setion we explain how and where a all should be routed when the deision at the DMS is to route the all as VoIP. For the all to use an outgoing route, routea, there are some route elements that need to be onfigured. We explain this using some funtions: dno(), share(), and route(), whih are implemented in Unix. 23

32 Carrier Voie Network Management 3. Network Operations We set up the entry end of the E1 (or DNO), whih the all has to use from the DMS to the IP gateway by using the following funtion dno(from_routea_dms) { dno = "r/1,2,4,5/"; } The all uses either trunk 1, 2, 4, or 5. This is for H.323. For SIP signaling, we proeed eah trunk by an S e.g., dno = "r/s1,s2,s4,s5/". Next, we give a funtion that sets up the exit end of the DNO. As this is outgoing VoIP, we inlude the IP address (xx.xxx.xxx.xx) of routea. We also add a prefix to the outgoing number, if needed 13. share(to_routea) { subst() { dno = "r/97-112, /"; dad = "s/ii/ii00/"; vad = "exx.xxx.xxx.xx"; dads = "eout_xx.xxx.xxx.xx"; aps = "g729a"; } } dad adds the prefix 00 to the outgoing number. Other prefixes ould be used depending on the desire of the arrier ustomer. vad assigns the IP address of routea. aps defines the ompression ode used, e.g., g729a, t38, g729r8, et. We then math up the entry and the exit ends. route(from_dms_to_routea){ math() { paras(dr_all); dno(from_routea_dms); dad = "^ii.*"; } share(to_routea); } Finally, we apply the routing to the IP gateway. route(from_dms_to_routea); 13 The reason is given under Re-file in Subsetion