SERVICE LEVEL AGREEMENTS: A MAIN CHALLENGE for Next Generation Networks
Authors: Emmanuel MARILLY ALCATEL, Research and Innovation Department Route de Nozay, 91460 Marcoussis, France Tel: 33 1 69 63 14 61 Fax: 33 1 69 63 44 50 Email:
[email protected]
Olivier MARTINOT ALCATEL, Research and Innovation Department Route de Nozay, 91460 Marcoussis, France Tel: 33 1 69 63 18 77 Fax: 33 1 69 63 44 50 Email:
[email protected]
Hélène PAPINI ALCATEL, Research and Innovation Department Route de Nozay, 91460 Marcoussis, France Tel: 33 1 69 63 11 09 Fax: 33 1 69 63 44 50 Email:
[email protected]
Danny GODERIS ALCATEL, Network Strategy Group Francis Wellesplein 1, B-2018 Antwerp, Belgium. Tel: 0032-3-240.78.53 Email:
[email protected]
Corresponding Author: Emmanuel MARILLY ALCATEL, Research and Innovation Department Route de Nozay, 91460 Marcoussis, France Tel: 33 1 69 63 14 61 Fax: 33 1 69 63 44 50 Email:
[email protected]
SERVICE LEVEL AGREEMENTS: A MAIN CHALLENGE for Next Generation Networks Emmanuel Marilly1, Olivier Martinot 1, Hélène Papini1, Danny Goderis2 1 ALCATEL Route de Nozay, 91460 Marcoussis, France e-mail: {Emmanuel.Marilly, Olivier.Martinot, Helene.Papini} @alcatel.fr 2 ALCATEL Francis Wellesplein 1, B-2018 Antwerp, Belgium. e-mail:
[email protected]
ABSTRACT Service Level Agreement (SLA) specification and management becomes a key differentiator in the service provider’s offerings. SLA management will allow service providers to offer different levels of service guarantees and to differentiate himself from its competitors. It will improve its ability to satisfy customer expectations, as the customer will exactly know what to expect in terms of quality of service. SLAs are also a key requirement for the deployment of multimedia over the Internet, i.e. for Next Generation Networks. The Internet today is however a best-effort network, without the need for such strict contractual guarantees. Therefore numerous initiatives are currently undertaken to specify SLAs and to identify the new challenges for the provider’s service and network management. The aim of this paper is to present a high-level overview of the main SLA-related issues: the actors involved in SLA negotiations, the technical specification of SLAs and the mapping of SLAs to service classes. We give an overview of ongoing SLA-related initiatives in the industrial world, standardisation bodies and the research community.
1 INTRODUCTION The telecom market is evolving towards services. New services will be proposed by the use of Internet capabilities, like multi media service, e-hotel, e-commerce, data transfer, unified messaging, …increasing the use of the network, dealing with convergence of data and voice networks. Network traffic over the Internet in a multi-domain / multi-operator context is increasing as the number of users and applications (data, video, voice, …). The results of this evolution is to increase the complexity of the network management.
Until now, IP has provided a "Best Effort" service in which network resources are shared equitably. But the weakness in this IP original design has been exposed. As a result, the Internet requires changes to accommodate the new applications requirements, and provide Quality of Service differentiation. Bandwidth is needed, but it is not enough. In the context of multi-domain / multi-operator it is necessary to define a Service Level Agreement. The paper is organised in the following way: First of all, the SLA and the deriving elements will be defined. Then, a summary of the various views of service classifications will be presented. Finally, parameters to service assignment will be tackled. This paper concludes by an identification of major challenges that have to be faced to enforce SLA Management.
2 SERVICE LEVEL AGREEMENT 2.1 Definition A Service Level Agreement (SLA) is a contract between a network service provider and a customer that specifies, usually in measurable terms, what services the network service provider will furnish and what penalties will assess if the service provider cannot meet the established goals . Service providers differentiation will be driven by the reliability of the SLA Management and its monitoring during exploitation to contributing to the customers trust. In order to guarantee customers the proper level of performance, service providers often offer services with SLAs, which provide customers with measurements of statistics like network availability, throughput, and latency. 2.2 SLA Market An SLA by itself has no interesting value, if it is not managed efficiently. When considering the expectations of customers regarding the service providers, most of the market studies highlight the following requirement : • • •
Reliable measurement of the quality of services Provision of the expected quality of services Optimisation of the resource usage
SLA Managmenent will be a key player in the adoption of the Next Generation Services (like Video on Demand, Unified messaging,…) offered by the Next Generation Networks and GPRS/UMTS. SLA Management will enforce the confidence customer can have on their use, and support the transition from traditional usage of the services, to more elaborated usage of these new services. 2.3 SLA actors The network service provider may be an operator, a carrier, an ISP or an ASP. The customer may be a carrier, an ISP, an enterprise or a subscriber (end user). SLA contractors are usually associated as follows:
CONSUMER carrier ISP/transport enterprise/operator enterprise subscriber
↔ ↔ ↔ ↔ ↔
PROVIDER carrier carrier ISP ASP ISP
Table 1. SLA actors
It has been difficult for service providers to offer service level management and, therefore, sophisticated SLAs. This difficulty is based on the fact that service providers must deal with several different network technologies and elements, often with parts of these network segments "owned" by different service providers.
The second difficulty is the derivation of the SLA on the various network layers. For example, the SLA acts upon the layer 7 of an ASP (Application service provider) or the layer 2/2.5/2.n of a carrier. Figure 1 clearly illustrates the SLA management and layering issues. A service provider who wishes to offer SLAs must provide an end-to-end service level management system that can accurately and granularly measure network performance.
L7
SLA
MOVIE SLA
CPE
Access network
SLA
SLA
L3
Core network
Metro Access Network
Core network
SLA
SLA
L2 Optical Network
Figure 1. SLA layering
3 SERVICE LEVEL SPECIFICATIONS The Service Level Specifications (SLS) are the technical specifications deriving from the SLA. SLS can be a precise specification directly related to the SLA, but it can also be an interpretation of the SLA, an adaptation depending on the provider or on the service. To propose an End-to-End solution to SLA/QoS management, it is necessary to define services, SLS parameters and a classification of these services depending on the SLS parameters. The focus on service level rather than on network level allows definition of service/SLA/QoS independently from the underlying network technology. 3.1 Services and SLS Parameters Table 2 represents a non-exhaustive list of services giving a panel as large as possible (audio, video, data, tunnel). Table 3 represents a list of SLS parameters. These parameters are network technology independent. S1 S2 S3 S4 S5 S6 S7 S8 S9 S10
voice videophone telephony services multimedia video on demand white board VPNx (IP VPN, optical VPN, tel. VPN= PMR) data real-time (telnet, …) data interactive (web, transactions, ecommerce, email-server, …) data streaming (FTP, bulk data transfer/retrieval, still image, …) Table 2. Service list
P1 P2 P3 P4 P5 P6 P7 P8 P9 P10
loss delay jitter bandwidth consumer/provider monitoring admission control topology Reliability/protection (MDT, MTBF, MTTR) monodirection/symmetric/asymmetric Table 3. SLS parameters list
The service parameters can be described with SLS parameters, but all the SLS parameters are not necessary. Only some parameters are used to define them. P1, P2 and P3 parameters are particularly end user oriented for QoS perception. Enterprise is more concerned with global parameters like P4 and P9. Other consumers (operators, ISP…) are concerned with P4, to P10 parameters, especially P4 and P9. 3.2 Mapping SLS parameters to Services Services and SLS parameters have been identified. A mapping between these elements will give the most significant parameters defining the service. Four classes of performance have been chosen. All the relations between service and SLS parameters have been qualified by these classes. ++ +
very high performance high performance
S8 S9 S10
direction
P10
reliability
P9
topology
S7
P8
admission control
S6
P7
monitoring
S5
P6
consumer/pr ovider
S4
P5
bandwidth
S3
P4
jitter
S2
P3
delay
S1
P2
default performance Indifferent
loss
P1
= 0
Voice
=
++
++
+
++
=
++
=
+
2
Videophone
=
++
+
++
++
=
++
=
+
2
Telephony
=
=
0
0
++
=
++
=
+
1
Multimedia
+
++
0
++
++
=
++
=
+
1.5
video on demand
=
++
0
++
++
=
++
+
+
1
White board
++
+
0
0
++
=
++
=
+
2
++
++
++
2
VPN
depends on the propagated flow type
Data real-time Data Interactive Data Streaming
++
++
0
+
++
=
++
=
+
2
++
+
0
0
++
=
++
=
+
1
++
=
0
0
++
=
++
=
+
1
Table 4. Mapping between Service and SLS parameters
Table 4 allows a regrouping of the various services in class of services. Many fora, standardisation bodies, and research projects have been working on this problem. The following chapter presents the most significant trends.
4. SERVICES CLASSIFICATION Services can be consolidated into several categories. There are many ways to consolidate distinct services. The classification depends on the SLS parameters. For an end-user the main parameters perceived are loss, delay, and jitter. For an enterprise, the global parameters corresponding to a level of billing are the bandwidth and the reliability (MDT, MTBF, MTTR). When the reliability or the provided bandwidth is not satisfactory, it can also be a determining reason to move to another provider. A perception-oriented classification is based on delay and loss parameters. In the following are enumerated proposed classifications (IETF, 3GPP, IST Tequila project, ETSI Tiphon project…).
4.1 Internet Engineering Task Force The Internet needs bandwidth management and QoS. Adding QoS raises significant concerns, it enables technical characterisation of the QoS (e.g. SLA/SLS, reliability, delay, jitter, packet loss), mechanisms to provide QoS (e.g. RSVP, DiffServ), integration of QoS mechanisms at different levels and with different technologies (e.g. MPLS, ATM, Ethernet, Optic transport), management and assurance of QoS (traffic engineering). IETF classification is mainly based on DiffServ [1][2] and DSCP [3] coding. There exists height precedence levels, two of them reserved for IP routing protocol. Among the six remaining precedence levels the classification is as follows: Class Expedited Forwarding (EF)
Precedence 5
Assured Forwarding 1 (AF1) Assured Forwarding 2 (AF2) Assured Forwarding 3 (AF3) Assured Forwarding 4 (AF4) Best-Effort
Comment higher level of QoS (adapted to VoIP) low delay medium delay high delay very high delay not guaranteed
4 3 2 1 0
Table 5. IETF Classification
DiffServ is a very promising technology; however delivering real-time multimedia services on DiffServ-based IP networks still involves a lot of open research issues (ie : deployment, provisioning, authorization, fairness, congestion control, routing, security…). The main IETF groups working on this subject are: • Internet Traffic Engineering (TEWG) • Realtime Traffic Flow Measurement (RTFM) • IP Performance Metrix (IPPM) • Remote Network Monitoring (RMONMIB) 4.2 3GPP 3GPP is the acronym of the project called "Third Generation Partnership Project". 3GPP provides Technical Specifications and Technical Reports for a 3rd Generation Mobile System based on evolved GSM core networks and the radio access technologies that they support (i.e., Universal Terrestrial Radio Access (UTRA) both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) modes). In 3GPP [4], four traffic classes are defined, based on delay requirement, each of them supporting error tolerant or error intolerant applications. Traffic class
Conversational class
Streaming class
Interactive class
Background
Conversational RT streaming RT Interactive best effort Background best effort delay
