Dynamic differentiated services provision in a Backhaul DVB/IP networking environment

Evangelos Markakis1, Anargyros Sideris2, George Mastorakis3, Eleftherios

Georgaras2, Nikolaos Polichronakis2, Evangelos Pallis3, Vassilios Zacharopoulos2

1Department of Information and Communication Systems Engineering,

University of the Aegean, Samos, Greece 2Centre for Technological Research of Crete, Heraklion, Greece

3Department of Applied Informatics and Multimedia, Technological Educational Institute of Crete, Heraklion, Greece

E-mails: emarkakis@aegean.gr, irons@pasiphae.teiher.gr, mastorakis@epp.teiher.gr,glefteris@pasiphae.teiher.gr, nikospol@pasiphae.teiher.gr

pallis@epp.teiher.gr, vzachar@epp.teiher.gr Abstract The paper discusses a DVB/IP backhaul environment as part of a metropolitan/regional networking infrastructure that enables users to access triple-play IP services at a guaranteed QoS. Utilising the DVB-T stream in regenerative configurations, it initially elaborates on its exploitation as a middle-mile network that extends the core backbone to reach every urban/rural user within the entire broadcasting footprint. Users receive/deliver triple-play IP-services via intermediate communication nodes, which make use of wired/wireless technologies in the access network. Services provision at guaranteed QoS is confronted via the design and implementation of QoS-aware mechanisms, following a services differentiation approach. Performance evaluation tests, conducted under real transmission/reception conditions on a prototype that conforms to the design specifications, verified the systems capacity in QoS provisioning, as well as establishing fields for future exploitation. Keywords: Backhaul, DVB/IP, DiffServ, Differentiated QoS, Experiments, SLAs 1. Introduction A fundamental objective of the recent research activities in the fields of Internet, telecommunications and digital broadcasting, is the issue of technology and services convergence, which will allow for the realisation of a common and unified networking environment. In this direction, one of the challenges is to create broadband metropolitan infrastructures that will enable users/citizens to ubiquitously access (both receive and deliver) heterogeneous services (linear, interactive, and on-demand) via any kind of access network and at the maximum possible quality. Until nowadays, several solutions have been proposed for confronting this challenge,

mainly based upon two approaches: a) the convergence of Internet and telecommunication technologies[1-2], and b) the Interactive broadcasting one[3]. The former, are dealing with the interconnection of the various wired/wireless access networks (e.g. xDSL, 3G, WLAN, etc.) over the core backbone (e.g. optical fibre), in order to allow text, voice and video services (usually offered via different platforms) to be accessed (received and delivered) via the same infrastructure (triple-play). At the same time they are exploiting the IP-stack as the underlying protocol for content delivery and QoS provisioning (e.g. DiffServ, MPLS). Actual implementations of these solutions, especially at metropolitan area level, require the access network to be close to the core backbone, as a matter of the specific access network characteristics. Otherwise, either the core backbone (e.g. optical fibre) has to be extended, so that to reach every possible access network, or a backhaul connection (middle-mile) between the access and the core backbone has to be established. In any case, i.e. either extension of the core backbone or exploitation of backhaul connections, the decision to be made is strongly dependent on the trade-off among several issues, including economical, business and geographical ones. For example, while extension of the core backbone seems to be the best technological solution towards the efficient deployment of broadband metropolitan infrastructures, scale economies, installation costs and/or terrain variations, constitute major obstacles for fast take-up. In such cases, backhaul connections seem to be more attractive. Nowadays, backhaul networks are mainly based on wireless technologies (e.g. Microwave), providing for the fast deployment of broadband metropolitan networking infrastructures within any terrain, besides reducing the high installation costs usually required for a wired/cable backhaul connection. However, wireless backhaul installation costs still remain an issue, constraining ubiquitous access and prohibiting the deployment of such broadband metropolitan infrastructures, especially in places that are far from the core-backbone (e.g. rural and dispersed areas). On the other hand, and in respect to the broadcasting technologies, the efforts were initiated within the “interactive broadcasting” field for the creation of a common environment, where users can access linear digital audiovisual content enhanced with interactive services. Recent actual implementations of this approach exploit the downlink channel (broadcast medium) for forward traffic, while reverse path data (uplink) is provided via wired or wireless telecommunication links (e.g. ISDN, PSTN, WLAN, UMTS, etc.). As a result, and by taking into account that in most interactive broadcasting implementations the same entity (i.e. the broadcaster) is acting both as service/content provider and network operator, users can receive broadband linear services (one-way) and request/access predefined content (interactive services provided by the broadcaster). In this respect, convergence based on this approach is partially achieved, and only at technological level, as long as telecommunications and Internet are utilised for the data requests from the user to the broadcaster. Additionally, the limited system resources (in terms of total available bandwidth) and the use of primitive QoS aware protocols/mechanisms for the delivery of interactive content, prohibit such solutions to be exploited for enabling users to provide/distribute their own content to the entire infrastructure, and for the provision of IP on-demand services with guaranteed QoS. In this respect, while current interactive broadcasting implementations can provide an alternative solution for homogeneous broadband services access/reception, they hardly contribute to the issue of convergence, for heterogeneous services access over a common metropolitan networking infrastructure. As the need for technology and services convergence still remains an issue, one of the main research objectives of this paper is to study, design and propose an alternative

solution for the realisation of a common metropolitan networking environment, capable to provide heterogeneous services access over the same infrastructure. It anticipates that if convergence is applied among all technological fields, a unified metropolitan networking infrastructure can be realised, enabling users/citizens to both receive and distribute linear, interactive and on-demand broadband services, either from urban or rural areas, and at maximum possible QoS. In this respect, it proposes a novel network architecture that exploits the terrestrial digital video broadcasting technology (DVB-T)[4] as a complementary wireless backhaul/middle-mile connection, capable to interconnect, anywhere within the entire broadcasting footprint, heterogeneous access IP-based networks, to each other and to the core backbone. Building upon the large coverage-area capabilities of DVB-T, and by exploiting its intrinsic characteristic to combine heterogeneous data traffic into the same transport stream (e.g. MPEG-2 and IP datagrams), it proposes the exploitation of the DVB-T stream in regenerative configurations for establishing a common IP backbone that is present and available within the entire metropolitan area. In this respect, DVB-T technology is not only used for delivering custom linear content (i.e. one-way services) but also as a medium for the provision of interactive multimedia and on-demand services, paving the way towards a fully converged environment. Users access the common IP backbone, for both distributing and consuming broadband services, via intermediate communication nodes (namely Cell Main Nodes – CMN), which may utilise wired and/or wireless links. Efficient network operation, as a matter of dynamic resource allocation and maximum possible QoS provisioning, is confronted by adopting a decentralised approach (at each CMN level). More specifically, a dynamic management system for traffic prioritisation is designed and implemented, allowing for optimised services provision, in respect to the available system resources, user’s privileges and services QoS attributes. Differentiated Services (DiffServ) aware mechanisms are utilised both at the backhaul and at the core network, capable to adapt, classify and prioritise IP traffic according to specific QoS requirements. Towards establishing the validity of the proposed architecture, an experimental networking prototype was designed and implemented according to the design specifications for conducting network performance evaluation tests under real transmission/reception conditions. The obtained experimental results verified the capacity of the proposed architecture for heterogeneous services access with QoS guarantees, establishing it as an alternative solution towards the realisation of broadband metropolitan networking infrastructures. Following this introductory chapter, the rest of this paper is structured as follows: Section 2, elaborates on the design and the overall architecture of a networking metropolitan infrastructure that exploits DVB-T technology as an alternative solution for realising backhaul networks, and presents the design of QoS-aware mechanism that can support guaranteed QoS provision. Section 3 presents the implementation and realisation of a prototype that conforms to the design specifications, and which serves as a testbed for conducting the QoS performance evaluation experiments. Section 4, elaborates on the capacity of the proposed architecture in providing QoS guarantees according to specific users’ privileges and services attributes and presents the experimental results while Section 5, concludes by summarising the scientific findings and research results, besides elaborating on fields for future exploitation.

2. System Design

2.1 Network architecture The overall architecture of the backhaul networking infrastructure is depicted

in Figure 1. It consists of two core subsystems: a) a central broadcasting point (regenerative DVB-T), and b) a number of Cell Main Nodes (CMNs) distributed within the broadcasting area. Each CMN enables a number of users/citizens (geographically neighbouring the specific CMN) to access IP services that are hosted by the entire infrastructure (e.g. by the ISP, or by the IPTV multicaster as depicted in Figure 1).

The communication between the users and the corresponding CMN (access network) is achieved via broadband point-to-multipoint links (i.e. WLAN, xDSL). The CMN gathers all IP traffic stemming from its own users and forwards it to the central broadcasting point (UHF transmission point visible by all CMNs) via dedicated point-to-point uplinks. IP traffic stemming from all CMNs is received by the broadcasting point, where a process unit filters, regenerates and multiplexes it into a single transport stream (IP-multiplex) along with the digital TV programme(s) stemming from the TV broadcaster(s) (TV studio), towards forming the final DVB-T "bouquet". Each user receives the appropriate IP reply signals indirectly via the corresponding CMN, while receiving custom digital TV programmes (e.g. MPEG-2) via the common DVB-T stream. In such configuration, both reverse and forward IP data traffic is encapsulated into the common DVB-T stream, thus improving the flexibility and performance of the networking infrastructure. Furthermore, the cellular conception that is adopted utilises the DVB-T stream in a backhaul topology, which interconnects all cells that are located within the broadcasting area with the high capacity core, present and available at the ISP’s premises. Thus, triple play services available at the ISP level (or in other provider located close to the high-capacity backbone), are “transferred” to every CMN via the DVB-T stream (the backhaul connection to the high-capacity network).

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Figure 1. DVB/IP backhaul networking architecture

The capability of the proposed DVB/IP backhaul networking environment for enabling triple-play services access and always-on connectivity has been validated through tests that were conducted under real transmission/reception conditions [5-6]. The tests proved that users/citizens of the proposed infrastructure could access triple-play IP services, such as Internet, VoIP, IPTV, etc., but in a best-effort scheme. In other words, end-to-end QoS provisioning at this infrastructure is a matter of a) the bandwidth reserved for IP services in the DVB-T stream, b) the number of active CMNs – a CMN is considered as active even if a single user is accessing the common DVB-T stream via this CMN –, c) the number of simultaneous users (accessing unicast IP services) within the same CMN and d) the uplink(s) attributes (e.g. bandwidth). As a result, QoS sensitive IP services, such as IPTV programmes or VoIP streams, could not be delivered at a specific quality level, unless QoS aware mechanisms are utilised, both in the core and the backhaul networks. At this point it should be noted that guaranteed end-to-end QoS provisioning is also a matter of the access network attributes (e.g. WLAN/xDSL bandwidth allocation, etc.), however, beyond the scope of this paper. Building on the above context, the next section discusses the overall architecture of a DVB/IP backhaul networking environment capable of enabling guaranteed end-to-end QoS. 2.2 A DVB/IP QoS aware backhaul infrastructure

In order to enable provision of IP services at a guaranteed quality, the previously presented DVB/IP networking environment is enhanced with QoS aware modules, making use of traffic prioritisation techniques. More specifically, the described DVB/IP environment is enhanced with DiffServ mechanisms [7], for the provision of end-to-end IP traffic differentiation, both across the backhaul and the

backbone infrastructure. Figure 2 depicts the overall architecture of the described DVB/IP infrastructure, featuring DiffServ-enabled modules.

Figure 2. Overall architecture of the QoS aware DVB/IP infrastructure.

In the above configuration, every CMN is considered as an entry-point to the DiffServ domain, classifying incoming IP traffic into a specific quality level, by marking accordingly the Differentiated Service Field (DS Field) of every IP packet with a certain Differentiated Service Code Point value (DSCP) [8], associating every data flow to a certain QoS class. Each class is created according to specific QoS requirements (bandwidth, one-way delay, packet-losses), following a certain Service Level Agreement (SLA), signed between the Service Provider (e.g. IPTV multicaster) and the users.

All IP traffic stemming from these QoS aware CMNs, passes through a DiffServ core router located in regenerative DVB-T (see Figure 3). This DiffServ core router analyzes the DS field of all IP packets and forwards them according to a specific Per-Hop-Behavior (PHB) [9] to all CMNs, i.e. to the entire broadcasting area.

Figure 3 depicts the configuration of the regenerative DVB-T utilizing a DiffServ core router for IP traffic prioritization, ensuring that services will be delivered according to specific QoS requirements. Figure 4, on the other hand, presents the overall configuration of a DSL-based CMN (i.e. CMN with DSL technology in the access network – namely CMN2 in Figure 1), utilizing a DiffServ edge router for classifying the IP traffic according to specific services and users’ priorities.

Following this network configuration, traffic originated from a user located within a certain CMN (i.e. service provider such as the IPTV Multicaster in CMN1) and destined to another user placed in a different CMN (e.g. end-user in CMN2), is classified and forwarded according to specific QoS requirements.

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Figure 4. Overall configuration of a rural based CMN.

3. Experimental validation of the proposed DVB/IP QoS aware infrastructure

Based on the proposed architecture described in the previous sections, a test-bed was created operating in 24 hours basis in Iraklion City, Crete comprising of:

The regenerative DVB-T platform, where the common DVB-T stream is created in channel 40 of the UHF band (i.e. 622-630MHz), utilizing 8K operation mode with 16QAM modulation scheme, 7/8 code rate, 1/32 guard interval and the

multi-protocol encapsulation mechanism (MPE) for the distribution of IP datagrams.

A DiffServ core router located in the regenerative DVB-T, able to analyse and forward (according to the implemented PHBs) the incoming networking traffic stemming from DiffServ edge routers.

A QoS aware CMN (namely CMN1 in Fig. 1), located in an urban area, hosting IPTV, VoIP and TCP services providers. The communication between this CMN and the regenerative DVB-T platform was based on a one-way point-to-point link of IEEE 802.11g technology.

One rural-based QoS aware CMN (namely CMN2 in Fig. 1) located about 40 kilometres in a rural area where no telecommunication infrastructures exist, hosting the end users. The communication between CMN1 and the regenerative DVB-T platform was based on a virtual private network connection over satellite (DVB-RCS)[10] Internet access utilizing a 512 Kbps link.

As the technologies used for the communication between CMNs and the DVB-T platform provide, in principle, full-duplex communication, a routing mechanism was integrated at the DVB-T side, to maintain one way-transmission (from CMNs to the DVB-T). Towards validating the overall system’s performance and evaluating its capability for end-to-end QoS provisioning, several experiments were conducted under real transmission/reception conditions environment. These experiments were based on an emulation of a real triple play service scenario where multiple heterogeneous services are stemming from multiple different providers located in the same CMN. More specifically the MGEN [11] and IPERF[12] traffic generators were used, configured so that multiple UDP (IPTV, VoIP) and TCP (Bulk Data transfer) streams over IP to be delivered simultaneously from the same PC (i.e. via the same network interface), but over different communication/protocol ports. The IPTV stream was utilizing a bandwidth of 0.7 Mbps and was transmitted using multicast technology in Constant Bit Rate (CBR), with packet size of 1024 bytes. For the VoIP service 16 unicast streams (eight for each direction emulating a two-way communication) were configured each one utilizing a bandwidth of 24 kbps. Finally eight TCP streams were configured to be initiated upon request. The scenario was set active for a period of 180 seconds.

The total available bandwidth of the DVB-T stream (21.1Mbps) was statically allocated between the MPEG-2 and IP services as follows: 13Mbps were dedicated to a bouquet of 4 digital TV programmes (MPEG-2 live and non-live broadcasts), while the remaining 8Mbps were dedicated to IP services, i.e. one IP channel for both multicast and unicast triple play services.

In this context, the QoS performance of the described DVB/IP infrastructure was evaluated, exploiting the above described scenario without and with the QoS mechanisms enabled (for comparison reasons). Furthermore the next set of experiments was designed in order to evaluate the dynamic adaptation of the implemented QoS mechanisms when the network conditions vary through time. To achieve this at the 90th second of the scenario described above two TCP streams were deactivated for the rest of the experiment duration. 4. DVB/IP With Differentiated QoS Provisioning Towards enabling differentiated QoS provisioning for the traffic of the experiment described above, the QoS aware modules were activated and configured for

supporting the offered services at three possible quality classes: a Premium service class (Expedited Forwarding Per Hop Behaviour – EF PHB) [13], an Olympic Model service class (Gold, Silver, and Bronze services, Assured Forwarding Per Hop Behaviour – AF PHB) [14], and a Best Effort service class. More specifically, the IP TV and the VoIP streams were associated with EF PHB for been assured, according to a pre-defined SLA, a bandwidth of 1.2 Mbps and an one way delay[15] below 50 ms for the IPTV and the VoIP streams stemming from the CMN1 (urban area) while the one way delay for the VoIP streams stemming from CMN2 (rural area) was set to be below a threshold of 430 ms. For both the streams the packet loss ratio[16] was set to be below 0.2 %. The first six TCP streams were associated in pairs with one of the three levels of AF PHB (Gold, Silver and Bronze classes); i.e. services classified as “Gold class AF PHB” were of higher priority than services classified as “Silver and Bronze AF PHB”, and therefore receive more beneficial treatment from DiffServ aware modules. The SLAs for these services were defined as follows; an assured bandwidth of 3 Mbps for the first pair of TCP streams, an assured bandwidth of 2 Mbps for the second pair of TCP streams and an assured bandwidth of 1 Mbps for the third pair of TCP streams. Finally, the last two TCP streams were associated with a Best Effort service class utilizing the remaining network resources.

In this context, IP traffic stemming from the Servers and the Clients passes through the access networks to the DiffServ edge routers (CMN1-CMN2), where it is classified into one of the described QoS classes, before entering the DiffServ domain (see figure 5). More specifically, a filtering mechanism segregates the incoming TCP/UDP streams by analysing their segment header field (i.e. port number, protocol), and forwards each one to the respective marker. This marker, in turn, assigns a specific DSCP value, into the DS field of each IP packet (i.e. 101110 for EF PHB). This is a standardised value for specific QoS classes, as indicated in [8-9]. As a result, the output of the DiffServ routers at CMN1-CMN2 are the TCP/UDP streams, each one associated with a certain PHB before received by the DiffServ core router located in the regenerative DVB-T (see figure 3).

Figure 5. DiffServ edge router QoS mechanisms

The marked TCP/UDP streams are received by the regenerative DVB-T interface (i.e. Receiver 1 in figure 3) and forwarded to the DiffServ core router. This router utilizes a filtering mechanism, which segregates the incoming marked streams by analysing the DS field of the IP packet headers and forwards them accordingly to a specific shaper (see figure 6). Each shaper reserves a portion of the available network resources (i.e. from the 8Mbps IP channel in the DVB-T “bouquet”) according to the priority level of every IP service as defined in their associated SLAs. The outgoing

differentiated traffic is then forwarded to the IP/DVB multiplexer and broadcasted using a DVB-T transmitter (see figure 3).

Figure 6. DiffServ core router mechanisms.

The experimental results, regarding the one-way delay and the packet loss ratio for

the IP TV and VoIP streams, are depicted in figures 7, 8 and 9 respectively, for the total 180 second performance evaluation period. From figure 7, it can be observed that the average one-way delay, when the DiffServ mechanisms are disabled, is about 82ms for the IP TV stream, 83 ms for the VoIP streams stemming from CMN1 and about 450ms for the VoIP streams stemming from CMN2. On the other hand, when the DiffServ mechanisms are enabled, the IP TV stream experiences an average one-way delay of less than 50ms, while the VoIP streams stemming from CMN1 and CMN2 have an one way delay around 30ms and 396 ms respectively. From the same figures it can be deduced that without the Diffserv mechanisms the losses are above 0.2 % for all the streams while in the opposite case the losses remain below the threshold of 0.2%.

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The experimental results, regarding the throughput of the TCP streams, are depicted in figure 10 for the total 180 second performance evaluation period. It can be observed that when the QoS mechanisms are disabled no services differentiation is present and the available bandwidth is almost equally shared between the TCP streams as expected since the CMN’s 2 satellite uplink does not constrain any of the tcp acknowledgement flows stemming from the end users. In contrast when the QoS mechanisms are enabled the differentiation of the TCP services in terms of throughput is achieved according to the predefined SLAs.

Figure 10. Average throughput for TCP streams

Furthermore and in order to show the ability of the system for dynamic QoS provision the previous experiment was repeated with a slight modification. More specifically on the 90th second the TCP streams associated with AF1 QoS class were deactivated for the rest 90 second duration of the experiment. The experimental results are presented in figure 11 from where it can be deduced that the freed bandwidth was allocated in the AF2, AF3 and BE classes in a ratio that is proportional to their priority level (i.e. to AF2 is offered a bigger portion of the available bandwidth compared to AF3 and BE).

Figure 11. Dynamic reallocation of bandwidth for the TCP streams.

The utilization of the QoS aware mechanisms by configuring the DiffServ edge and core routers according to the QoS requirements for each TCP and UDP stream, results in an optimized performance of the network for the differentiated provision of heterogeneous triple play services through the DVB/IP infrastructure. Effectively, it can be deduced that the pre-defined SLAs were respected by the entire system, both at the core and backhaul network, and the introduced QoS aware mechanisms improved the overall network performance, setting the basis for a dynamic differentiated QoS provisioning.

Conclusions The paper contributes to the issue of technology and services convergence by presenting a DVB/IP backhaul environment as part of a metropolitan/regional networking infrastructure that enables users to access triple-play IP services at a guaranteed QoS. Utilising the DVB-T stream in a regenerative configuration, it described the creation of a backhaul among intermediate communication nodes and service/content providers (e.g. ISPs, IPTV multicasters, etc.), for enabling users to access IP triple-play services, even from rural or dispersed areas. For optimum system’s efficiency and differentiated QoS provisioning, DiffServ aware modules were utilised both at the backhaul (DiffServ core router) and at the CMN level (DiffServ edge router), capable to adapt incoming IP traffic according to specific QoS requirements. The performance of the proposed system was evaluated by conducting a number of tests under real transmission/reception conditions, concerning the QoS of UDP and TCP streams emulating a triple play services scenario. It was experimentally verified that the exploitation of DiffServ traffic policy and prioritisation mechanisms for reallocating the available network resources enhance the utilisation of DVB-T technology as a networking backhaul infrastructure, capable to offer optimized spectrum utilisation according to services QoS requirements. Acknowledgment The work presented in this paper was undertaken within the framework of the project “Regional innovation pole of Crete, Task A11: Provision of multimedia and networking services utilising a novel digital terrestrial television network.”, co-funded by European Social Funds and National Resources, under General Secretariat for Research and Technology, Operational Programme Competitiveness, 3rd Community Support Framework. References 1. ETSI(ES 282 001), Telecommunications and Internet converged Services and Protocols for Advanced

Networking (TISPAN); NGN Functional Architecture Release 1. 2. ETSI(ES 282 007), Telecommunications and Internet converged Services and Protocols for Advanced

Networking (TISPAN); IP Multimedia Subsystem (IMS); Functional architecture. 3. ETSI (ES 300 801) — Digital Video Broadcasting (DVB); “Interaction channel through Public Switched

Telecommunications Network (PSTN) / Integrated Services Digital Networks,” (ISDN).

4. ETSI(EN 300 744) Digital Video Broadcasting (DVB); Framing structure, channel coding and modulation for digital terrestrial television.

5. Mastorakis, G., Pallis, E., Mantakas, C., Kormentzas, G., Skianis, C. (2006, September). Exploiting Digital Switchover for Broadband Services Access in Rural Areas. Journal of Communications, 1, 6, 45-50

6. Mastorakis, G., Pallis, E., Kormentzas, G. (2007, March/April). A Fusion DVB/IP Networking Environment for Providing Always-On Connectivity and Triple-Play Services to Urban and Rural Areas. IEEE Network Magazine, 21, 2, 21-27

7. Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., Weiss, W. (1998, December). An Architecture for Differentiated Services. RFC 2475, IETF

8. Nichols K., Blake S., Baker F., Black D. (1998, December). Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers. RFC 2474, IETF

9. Brim, S., Carpenter, B., Le Faucheur, F. (2002, November). Per Hop Behaviour Identification Codes. RFC 2836, IETF

10.ETSI EN 301 790, “Digital Video Broadcasting (DVB); Interaction channel for satellite distribution systems”, v1.4.1, ETSI, 2005.

11. The Multi-Generator (MGEN) Version 4.2 [Online]. Available: http://pf.itd.nrl.navy.mil/mgen/ 12. Internet Performance (Iperf) Version 2.02 [Online]. Available: http://sourceforge.net/projects/iperf 13. Jacobson, V., Nichols, K., Poduri, K. (1999, June). An Expedited Forwarding PHB. RFC 2598, IETF 14. Heinanen, J., Baker, F., Weiss, W., Wroclawski, J. (1999, June). Assured Forwarding PHB Group.

RFC 2597, IETF 15. Almes, G., Kalidindi, S., Zekauskas, M. (1999, September). A One-way Delay Metric for IPPM.

RFC 2679, IETF 16. Almes, G., Kalidindi, S., Zekauskas, M. (1999, September). A One-way Packet Loss Metric for

IPPM. RFC 2680, IETF