2013 5th International Conference on Computational Intelligence and Communication Networks
QoS in Interconnection of Next Generation Networks Lav Gupta Department of Telecommunications, New Delhi, India
[email protected] NGNs are characterized by horizontal separation of service, control and transport functionalities. The ITU-T defines the architecture in terms of service and transport stratums [2]. The transport stratum provides the user functions that transfer data and functions that control and manage transport resources to carry such data between terminating entities. In particular, the transport stratum facilitates user-to-user connectivity, user-to-services platform connectivity, services platform-to-services platform connectivity. The service stratum provides the user functions that transfer service-related data and the functions that control and manage service resources and network services to enable user services and applications. The service stratum may involve a complex set of geographically distributed services platforms. It is important to appreciate that each stratum comprises one or more layers, where each layer is conceptually composed of a data plane, a control plane, and a management plane. Among the major reference points, the Network-Network Interfact (NNI) is used to provide connectivity to other NGNs, to other IP-based networks and Public Switched Telecom Network (PSTN)/Integrated Services Digital Network (ISDN). Cloud services can be connected as hosted services through the SNI.
Abstract—Transition to Next Generation Networks is likely to raise questions about how inter-operator interconnections should take place in a heterogeneous environment. The NGN architecture introduces several degrees of complexity, requiring decisions on issues like the layers and planes at which the interconnection among different service provider. domains should take place and how adequate quality of service can be ensured, over the interconnection, for various services. While intra-operator QoS in NGN is well researched and applied, inter-operator QoS is complex and still being discussed in academia, international standards bodies and industry. This paper proposes metrics for intra and inter domain QoS in a heterogeneous environment and tests it with actual data. It is seen that a combination of selected parameters from measurements taken from operational networks and operator reported data, show a strong correlation with the QoS reflected by consumer surveys. Keywords – Convergence ; NGN ; Interconnection ; QoS ; performance metrics
I.
INTRODUCTION
The Next Generation Networks’ paradigm allows for increasing requirement of multimedia traffic, need for optimizing capital and operational expenses and ability to introduce new services faster [1]. While telecom administrations are aware of the complexities of regulating inter-domain interconnection in fixed and mobile networks; transition to NGNs would introduce quite a few new issues that few are prepared to handle. It is known by now that interconnection may be required at several layers and planes making interconnection in NGN a non-trivial planning issue. However, more work is required in elaborating the requirements of quality of service over different types of interconnections so that service providers can offer good quality of experience for services traversing multiple domains. A review of literature reveals that while the intraoperator Quality of Service (QoS) in NGN has been researched and applied to a large extent, inter-operator QoS is complex and still being discussed in academia, international standards bodies and industry. We make an attempt at evolving metrics for intra and inter domain QoS in a heterogeneous environment. To put this in proper perspective, the paper takes into account the current stipulations for intra and inter-domain communication in wireless, wire-line and broadband networks in India. The metrics so evolved are tested with field data and operator provided reports and its usefulness demonstrated. II.
III. INTERCONNECTION IN NGN Interconnection of networks of different operators is essential as it provides technical possibilities for the customers to connect to other customers and to services irrespective of the network they are on. The layered NGN architecture introduces the requirement of interconnecting at different layers. In case of interconnection at service stratum, or service-oriented interconnection, there is physical and logical linking of NGN domains that allows carriers and service providers to offer services over NGN with control and signaling. This allows service providers not only to ensure quality of service over their own networks but also manage quality of service for the services that traverse other operators’ networks. In case of interconnection at transport stratum, or connectivity oriented interconnection, there is physical and logical linking of carriers and service providers based normally on simple IP connectivity. Interconnection of this type is not aware of the specific end-to-end service and, as a consequence, servicespecific network performance, QoS and security requirements are not necessarily assured [3]. What makes assuring QoS, across borders of interconnected networks, a difficult task is the fact that universally accepted standards do not yet exist to manage
NGN ARCHITECTURURAL FRAMEWORK
978-0-7695-5069-5/13 $26.00 © 2013 IEEE DOI 10.1109/CICN.2013.29
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in the absence of appropriate standards and established procedures for management, such interconnections were challenging and labour-intensive [9]. At the heart of most of the techniques for QoS implementation are concepts of resource reservation, admission control and traffic management during transfer. A program or service has to specify the type of traffic it would generate and the constraints applicable on this traffic to assure a high QoE. For resource reservation, most QoS implementations use some form of classification of traffic into different classes. Admission control functionality decides whether or not a resource request can be satisfied given the current and future conditions. When a service has been granted access to the network it can commence transfer of traffic. For regulating traffic during transfer, generally the classes used in the resource reservation are each given a distinct manner of handling traffic, such that high requirement classes get priority over low requirement classes [10].
QoS on an end-to-end basis for interconnected networks running protocols/mechanisms like IP/Multi Protocol Label Switching (MPLS). Deciding the layers and planes of interconnections, and maintaining the required QoS for each of these are major concerns. These contentions are borne out by the conclusions drawn by James Barakovic et al in their study [4]. IV. CONCEPT OF QOS IN NGN INTERCONNECTION NGN interconnections across the NNI are required to assist completion of IP service sessions for real-time, multimedia and traditional services with varying requirements. In practice, QoS and security issues often become stumbling blocks in large scale deployment of NGNs in a multi-operator, multi-service environment. Past and current international research activities, with a main focus on the provision and management of QoS in IP networks, show different approaches [5]. However, none of these approaches covers all significant aspects of end-to-end QoS provision in NGN-based telecommunication networks. More serious is the absence of any proven method of QoS in the interconnection elements [6]. This paper attempts to consolidate the learning from cross-industry deliberations of which author was a part.
B) Standardization efforts NGN is being actively discussed in the standards bodies and other organizations, including the ITU-T, ETSI, IEEE, IETF, GSMA, 3GPP, ATIS, TISPAN and i3Forum. However, until fairly recently, there have, been very few discussions on QoS mechanisms and services over NNI. There is yet no agreed upon definition on the roles of carriers for guaranteeing QoS over NNI as the required technical details are still under discussion [11]. GSMA has defined an architectural framework for IP Packet eXchange (IPX). Service availability, jitter, packet loss and delay are the metrics included in the QoS Profiles. Though the GSMA IPX model defines End-to-End (E2E) QoS criterion, how to build an E2E QoS solution based on such framework, is a topic of ongoing study. 3GPP has taken up the study of requirements for IPX connectivity that are being addressed in 3GPP TR 22.893. The i3F focuses on the inter-carrier NNI. It also defines a set of QOS parameters to be used as the basis for Key Performance Indicators (KPIs) at an interconnection point. TISPAN defines service related and bearer related interfaces at the NNI. IETF has defined solutions for guaranteeing QoS over NNI for MPLS networks by combining DiffServ and RSVPTE.
A) Techniques for implementing QoS Over dimensioning of the network has been often used to keep congestion, packet delays and loss under control. Overdimensioning does not provide service classes and does not guarantee any bandwidth to any user in particular. In case of inter-domain traffic it would be impossible to require all the service providers to over dimension their networks to ensure QoS for different services. Another approach, IntServ with the Resource Reservation Protocol (RSVP), allows an application to reserve router capacity on the path from source to destination host to get the desired QoS for each flow in the network. Yet another approach, the differentiated service (DiffServ), uses a small bit-pattern in each packet for a particular per-hop behavior, at each network node. Each node provides class-based differentiated service. Approaches that combine features of IntServ and DiffServ have also been studied [7]. MPLS allows traffic engineering. Camarillo shows a standardized approach to combine Session Initiation Protocol (SIP) session signaling and IntServ-based network resource reservation [8]. Another approach for optimization of the QoS management in SIP-based NGN could be based on the use of virtual data pipes with defined bandwidths and defined QoS parameter values. Applicability of these techniques for inter domain QoS has still not been established. Protocols like IntServ and DiffServ were developed for the purpose of QoS on the Internet and they are less qualified for more heterogeneous access networks. Also, neither of these protocols specifies a way of connecting different kinds of networks. A Whitepaper prepared at MIT presented a proposal to enable the deployment of inter-provider QoS. Even at that time some providers attempted to interconnect with each other via "QoS-enabled peering" in an attempt to offer QoS that spanned the networks of multiple providers. However,
V. QoS IN INTERCONNECTION
REGULATION
OF
A) Traditional Regulatory Measures The basic premise for regulatory intervention is to create conditions for consumer satisfaction by making known the QoS that the service provider is required to provide and the user has a right to expect. Measurement of QoS provided by the networks should also be carried out from time to time to compare the results with the norms so as to assess the level of performance. The important aspects of regulations that have been instituted by the national regulatory authority in India and, in this regard, are discussed below to derive possible direction for the NGNs [12].
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consistent busy hour (TCBH) should be zero. The number of upstream links for international connectivity having bandwidth utilization more than 90% during TCBH should be zero. The percent international bandwidth utilization during TCBH should be less than 90% [14]. 4) Parameters specific to interconnection: In case of more than one interconnected networks, the level of POI congestion is an important factor determining success of voice calls and data sessions from one service provider’s network to another. The number of POIs not meeting the benchmark grade of service (GoS) of 0.5, should not be more than 0.5%. In case of wire-line networks besides POI congestion, the call completion rate of 55% or more takes into account call failures due to other networks Regular traffic measurements during route busy hour would govern future expansions. Provisioning of augmentation needs to be done with 90 days of request for the next one year’s requirements. Revenue settlement of interconnect usage charges should be carried out within prescribed periods so that interconnections are not severed. There needs to be a clear understanding about the disconnection of interconnection if the interconnect dues are not paid.
1) Wireless Networks: Network centric and customer centric parameters and their benchmarks govern QoS of wireless networks. To ensure network availability so that customers can originate calls whenever the need arises, the total accumulated Base Transceiver Station (BTS) downtime should not be more than 2% for any service area. In addition, the worst affected BTS due to downtime should not be more than 2%. This shall be defined as the accumulated downtime due to community isolation lasting for more than one hour, i.e. failure of the entire exchange area resulting from trunk failure, switch failure or base station failure. If the customer is able to connect to the network, the next step would be to ensure network accessibility. This involves call set up success rate which should not be less than 95% within a network. The dimensioning for the channels should be such that Standalone Dedicated Control Channel (SDCCH) congestion should not be more than 1% and Traffic Channel (TCH) congestion should not be more than 2%. Once the connection is established the calls should be maintained for the duration of the conversation. It has been decided that call drop should not be more than 2% of the cases. The worst affected cells having more than 3% call drops should not be more than 5%. Of all connections established, not less than 95% should have good voice quality. In case of 3G networks, the nomenclature for some of the terms used in the existing regulations and the measurement methodologies have been amended. Some of the changed parameters are Node Bs Accumulated downtime, Worst affected Node Bs due to downtime, TCH and Circuit Switched Radio Access Bearer Congestion and Circuit Switched Voice Drop Rate [13]. 2) Wire-line Networks: For wire-line networks it is important to ensure that the call completion rate achieved should not be less than 55%. For all attempted calls that cannot be completed, link congestion is one of the important factors. Answer to seizure ratio should not be less than 75%. As far as the fault management is concerned, the incidence per 100 subscribers per month should not be more than 5 of which 90% or more should be repaired by next day and 100% within 3 days. The MTTR should not be worse than 8 hrs. The congestion at the point of interconnection (POI) with other networks should be not be more than 0.5%. 3) Broadband: Broadband aggregation and core networks are designed on the basis of contention ratios which in turn become the determinants of QoS that the operator offers to the customers. These need to be decided in such a way that congestion is kept under control and the contracted data rate is ensured. The broadband connection speed from ISP point of presence to the user should be more than 80% of the rated data rate. Additionally, service uptime should be more than 98%. Prevailing regulations also require the service provisioning time to be a maximum of 15 days including the time for line pre-qualification. Faults repaired should be more than 90% by next working day and at least 99% within 3 days. The amount of upstream bandwidth contracted by the service provider and its utilization determines the QoS available to the customers. The number of intra-network links having bandwidth utilization more than 90% in the time
B) Evolving framework of QoS for NGN interconnection 1) Status of migration to NGN: Major telecommunications operators have already implemented MPLS/IP based core transport network for carrying voice and data traffic. The service providers who have incorporated the control elements in their network have followed the softswitch approach with the Internet Multimedia Subsystem (IMS) being on the roadmap of some of them. The incumbent operators have started replacing transit and local switches by IP switches that would implement the required Class 4 and 5 functionalities. QoS is widely accepted as one of the important issues for NGN but the operators differ on the ways of implementing it. Some of the operators prefer bilateral agreements on parameters and benchmarks for QoS while others want the regulator to set up an expert group for deciding the basic framework. It is seen that the stipulations regarding QoS are a mandatory part of the operators’ interconnection agreements. Those who favour regulatory intervention want the QoS parameters and benchmarks to be defined in advance as these will influence planning and dimensioning of the network. In the heterogeneous scenario the interconnection between cooperating and competing service providers are likely to be a mix of IP and Time Division Multiplexing (TDM). It is also becoming clear that service providers would have to agree on alternate interconnection charging schemes based on the volume of data exchanged, layer at which interconnection is done, interconnection QoS offered, rather than flat per minute basis as is prevalent in TDM scenario. 2) Identification of metrics for NGN interconnection QoS: The cross industry expert group, Next Generation Networks Expert Committee (NGNeCo), constituted by the national regulatory authority felt that while control of basic transmission quality and features such as latency, packet loss, jitter, bandwidth are important but, beyond the basics,
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QoS must cover parameters like reliability, fault tolerance, service availability, security, call set-up, scalability, service provisioning and service restoration for end-to-end QoS control across different providers’ networks. Further, achieving QoS requires cooperation among many different network elements and even one poorly performing network segment (e.g. interconnection link) could impair the end to end QoS. According to NGNeCo, successful delivery of quality to the end-user - across NGNs – would require classes of application QoS that are mapped onto specific network QoS classes. The application QoS should operate across network domains so that QoS for the required service can be negotiated by the service providers among themselves. After deliberations the group agreed that IP Network QoS class definitions and Network Performance objectives defined in ITU T Y.1541 recommendation should be adopted as a standard for deciding the QoS parameters of applicable services in NGN [15]. Benchmarks need to be established for a number of parameters described below. For many of the services like voice on fixed and mobile networks the regulator has laid down the QoS standards through regulation1 which could be used as the basis for future work. Studies so far indicate the following directions for the evolution of a QoS regime in the context of NGNs: a) Interconnection congestion: A percentage level needs to be defined to ensure this does not become a bottleneck in inter-domain transfer of data. The current level of 90% utilization before contracting more bandwidth could be an option. Initial provision, enhancements, maintenance and disconnection need to be governed by regulatory measures or mutual agreements included in the reference interconnect offer (RIO). b) The following are the important service specific requirements which need to be defined for various classes of service separately. • Bandwidth availability and utilization • Latency or IP Packet Transfer Delay (IPTD) for real time/ non real time voice, data, video and streaming multimedia services. • Jitter or IP Packet Delay Variation (IPDV) for real time/ non real time voice, data, video and streaming multimedia services. • Packet Error or IP Packet Error Ratio (IPER) for real time/ non real time voice, data, video and streaming multimedia services. • Packet Loss: IP Packet Loss Ratio (IPLR) for real time/ non real time voice, data, video and streaming multimedia services. c) Call completion rate/session establishment rate across the NNI: should be fixed at an appropriate level to minimize overloading of network resources by unsuccessful, non-paying traffic.
d) End-to-End QoS: since multiple network operators are involved in providing access to a service in a multioperator scenario, the overall QoS is a function of QoS offered by the individual segments. Apportionment of impairment objectives among operators and the number of operators that could be allowed in a particular scenario also needs to be worked out. e) Availability of Network: Measure of the degree to which network is operable and not in a state of failure or outage at any point of time for all users. f) Customer centric parameters for multi-network situation: service activation/de-activation time, service restoration time, ease of getting billing information, network availability, security of customer information, grievance redressal, fault repair service, service availability etc. C) Corroboration of the proposed metrics Suitability of the proposed metrics was assessed using measured data as well as monthly performance reports submitted to the national regulatory authority by the service providers [16]. The data and its analysis pertain to broadband services delivered through heterogeneous networks with IP core and aggregation and varied technologies in the access network. The parameters selected were i) bandwidth utilization in the network between Point Of Presence (POP) and ISP gateway node, ii) bandwidth utilization in ISP gateway node to IGSP upstream Link(s) for international connectivity iii) broadband download speeds iv) packet loss v) Network latency between reference point at POP/ISP Gateway node to IGSP/Internet Exchange vi) Latency between user reference point at ISP Gateway node to International nearest Network Access Point (NAP) in another country. The ‘measured data’ were collected over a three day period in functional operator networks, by an independent auditing agency, during the same month for which operatorreported data were analyzed. For the data to be statistically representative, measurements were taken from the Network Operation Center (NOC) for 5% of the POPs in 10% of the short distance charging areas. Multi Router Traffic Grapher (MRTG), Cacti and Sandvine softwares were used for monitoring link utilization. SmokePing and Ping tests were used for monitoring network latency. The operator reported data were taken from the quarterly performance monitoring reports (PMR) and monthly POI congestion reports submitted by the service providers to the national regulatory authority. Data of six service providers (A to F, names changed) are shown below graphically. The measured data had good conformance with the reported ones with some notable exceptions in the case of bandwidth utilization from ISP to IGSP and network latency.
1
Standards of Quality of Service of Basic Telephone Service (wireline) and Cellular Mobile Telephone Service Regulations, 2009
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BW Util POP to ISP GW Measured
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Figure 5. Latency – ISP to IGSP links
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Figure 1. BW utilization between POP & ISP GW
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Figure 2. BW utilization between ISP and IGSP Figure 6. BW utilization between POP & ISP GW Download Speed Measured
An independent assessment of the effectiveness of QoS regulations was also made by gauging customer perception through surveys [17]. The surveys were conducted through face to face and telephonic interviews in equal proportions. The sample size for each service provider was 1067 which covered 10% of the POPs. The customer satisfaction survey gauged satisfaction with network, billing and grievance redressal and also gave an overall satisfaction figure indicated by the customers. We decided to test the effectiveness of the chosen QoS parameters by examining whether the values of the key parameters were consistent with the customer satisfaction surveys. The two being independent assessments would then sufficiently show that the correct metrics has been arrived at. To make comparison easier, three QoS parameters, the two network latencies and communication speeds that involve interconnection among networks and contribute heavily to customer satisfaction were chosen. To get a composite QoS figure weights of 40%, 20% and 40% were given to the three parameters respectively considering their relative contribution to QoS. The measured and monthly report data of each of these parameters were averaged to get contribution from both. The average latency figures were rationalized with the worst expected latencies of 120ms and 350ms before scaling them with the assigned weights. For download speeds average of measured and reported data was obtained and scaled to 40%. The composite QoS thus obtained and the customer satisfaction data from independent surveys are given in the table and graph below. Usefulness of the selected metrics is reflected in the satisfaction following the QoS for various
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Figure 3. Data download speeds Packet Loss
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0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 A
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Figure 4. Packet Loss
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operators. This is mathematically covariance/correlation analysis.
evident
and broadband networks that can be carried over with or without modifications to the NGNs and delineates the performance metrics suitable in the NGN environment. The proposed metrics were put to test through two independent assessments viz. auditing of network performance by an independent agency through measurements and operator reported data and customer satisfaction surveys by yet another agency. The results demonstrate high correlation between the performance metrics chosen and overall customer satisfaction. More work is required to be carried out in elaborating the requirement of quality of service over different types of interconnections so that the customers are assured good quality of experience for services localized within a network as well as those traversing multiple domains. As the networks migrate to NGN environment, further validation would ensure that the metrics is equally applicable to pure NGN as well as heterogeneous environments.
using
TABLE 1 COMPOSITE QOS AND CUSTOMER SATISFACTION Service Provider
Composite QoS (x)
A B C D E F
81.34 77.28 82.99 66.08 82.29 55.41
Customer Satisfaction (y) 89 81 87 80 84 80
QoS vs Cust Satisfaction
QoS/Satisfaction
QoS
Cust Satisfaction
100.00 90.00 80.00 70.00 60.00
REFERENCES [1] ITU-T Global Standards Initiative on Next Generation Networks [2] ITU-T Y.2012 Recommendation, Functional requirements and architecture of next generation networks, April 2010 [3] Telecommunications and Internet converged Services and Protocols for Advanced Networking (TISPAN), ETSI TR 187 019 V3.1.1 (2011-02) [4] QoS Aspects in NGN Interconnection, , Jasmina Barakovic and Himzo Bajric, BH Telecom, Sarajevo, Bosnia and Harzegovnia, 2009 [5] QoS Control for NGN: A Survey of Techniques, Changho Yun, Dept. of Ocean engineering research KORDI, ROK and H. Perros, Dept. of Computer Science NCSU, USA, http://www4.ncsu.edu/~hp/Changho1.pdf, 2009 [6] QoS in SIP-based NGN – state of the art and new requirements, F.Weber, W.Fuhrmann, U.Trick, U.Bleimann, B.Ghita, Proceedings of the Third Collaborative Research Symposium on Security, E-learning, Internet and Networking (SEIN 2007), Plymouth, UK, ISBN: 978-1-8410-2173-7, pp201-214 2007 [7] QoS Control In Next-Generation Multimedia Networks, Jongtae Song, Mi Young Chang, and Soon Seok Lee, ETRI, Jinoo Joung, Sangmyung University, IEEE Communications Magazine, September 2007 [8] Camarillo, G. and Marshall, W., Jonathan Rosenberg, integration of resource management and SIP, RFC 3312, IETF [9] Inter-provider Quality of Service, Quality of Service Working Group MIT Communications Futures Program (CFP), 2006 [10] Next Generation Networking Quality of Service, Peter Wagenaar, University of Twente
[email protected], 2009 [11] MSF Whitepaper on Quality of Service (QoS) over the Network-toNetwork Interface (NNI), Multi Service Forum, 2010 [12] Standards of Quality of Service of Basic Telephone Service (wire line) and Cellular Mobile Telephone Service Regulations, 20th March 2009 [13] The Standards Of Quality Of Service Of Basic Telephone Service (Wireline) And Cellular Mobile Telephone Service (Amendment) Regulations, 7th May, 2012 [14] Quality of Service of Broadband Service Regulations, 6th October, 2006 [15] ITU-T “Network performance objectives for IP-based services,” in ITU-T Recommendations Y.1541, 2006. [16] Report on audit & assessment of quality of service for Delhi Circle, 2011, www.trai.gov .in [17] Customer Perception of Service through surveys, Delhi Circle, 2011
50.00 40.00 30.00 20.00 10.00 0.00 A
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Figure 7. QoS vs Customer Satisfaction
The covariance between QoS and Customer satisfaction turns out to be 26.77 which compared to the range ±σx*σy (±42.77) is more than half the maximum value on the positive side. To decide whether this value is “big” or “small” we assessed it relative to the variances of the two variables. Using the Excel CORREL function we find that the correlation is 0.75 which indicates good linear relationship between the two. VI.
CONCLUSION
Interconnection among network operators would play an even more crucial role in the NGNs than it does in the existing discrete networks. In the NGNs, interconnections would be required at different layers and planes, increasing the complexity of their provisioning and management. Maintaining E2E QoS would necessitate assuring QoS in the interconnections besides taking care of intra-domain QoS. Layered NGN architecture, heterogeneous networks with different QoS classes and QoS parameters and nonavailability of universally accepted standards for interdomain QoS make this task difficult. While some lessons can be learnt from existing voice and data networks, much work is required in defining service classes and their mapping onto the network classes and defining parameter sets for different services. This paper makes an attempt at evolving metrics for intra and inter-domain QoS in a heterogeneous environment. It discusses the QoS descriptors of the existing fixed, mobile
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