Network Economics of SDN-Based Infrastructures: Can We Unlock Value Through ICN Multicast?

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1 Network Economics of SDN-Based Infrastructures: Can We Unlock Value Through ICN Multicast? Vaggelis G. Douros, Janne Riihijärvi, Petri Mähönen Institute for Networked Systems, RWTH Aachen University Kackertstrasse 9, 5272 Aachen, Germany {vaggelis.douros, jar, Abstract Software-defined networking (SDN) is enabling radically easier deployment of new routing infrastructures in enterprise and operator networks. However, it is not clear how to best exploit this flexibility, when also considering the migration costs. In this paper, we use tools from network economics to study a recent proposal of using information-centric networking (ICN) principles on an SDN infrastructure for improving the delivery of Internet Protocol (IP) services. The key value proposition of this IP-over-ICN approach is to use the native and lightweight multicast service delivery enabled by the ICN technology to reduce network load by removing redundant data. Our analysis shows that for services where IP multicast delivery is technically feasible, IP-over-ICN deployments are economically sensible if only few users will access the given service simultaneously. However, for services where native IP multicast is not a technically feasible option, such as for dynamically generated or personalized content, IP-over-ICN significantly outperforms IP. Keywords caching and communication resources, performance evaluation, IP-over-ICN. I. INTRODUCTION The evolution towards software-defined networking (SDN) gives the network infrastructure of a network operator an unprecedented level of flexibility. Whether deployment of such infrastructures is sensible for network operators is in the end a question of network economics, a viewpoint which has been largely unaddressed until now. In this paper we present a first economic analysis of the benefits that can be reaped through appropriate SDN-based deployments, focusing on the benefits that can be gained from the natively supported multicast forwarding enabled by these architectures. In this paper, we focus on the particular case of IP-over-ICN deployments as described in [], which utilizes information-centric networking principles in the SDN-based core. This is done to enable very low-cost multicast transport of content and services, as well as lightweight redirection between multiple service endpoints. We make the following main contributions. First, we present the first network economics analysis of the IP-over-ICN protocol and we compare it with IP. Second, we quantify the impact of three key parameters: i) the transfer of the files in the Internet Service Provider s (ISP) network using either multicast or unicast, ii) the deployment of a unique cache in the network and iii) the initial infrastructure cost. Finally, we show that the strategy of the ISP for the first two parameters is independent of the underlying protocol. Thus, we find that the ISP always prefers /7/$3. c 27 IEEE multicast than unicast, and the ISP always prefers to transfer the files directly from the cache. Our simulations reveal that only when there is a relatively small number of users there is significant difference in the performance of IP and IP-over-ICN. For these cases, the most important factor to determine which protocol outperforms the other is the initial IP multicast cost; when this cost is relatively high, IP-over-ICN outperforms IP; when this cost is relatively small, IP is techno-economically better. Moreover, for the cases where the adoption of IP multicast is inefficient (e.g., due to either poor scalability or extremely high deployment cost), IP-over-ICN significantly outperforms IP. This trend is noticed even with a small number of users and the benefit from IP-over-ICN increases with the number of users. II. RELATED WORK Software-defined networking has become an intensely studied area, with technologies such as OpenFlow making their way into production networks [2]. For a comprehensive survey on recent developments in SDN research we recommend [3]. Information-centric networking (ICN) is a parallel development of new types of networking architectures, with focus on matching providers and consumers of information as opposed to connecting specific endpoint nodes as done by classical IP networks [4]. The IP-over-ICN architecture proposed in [] retains the IP service model at the network edges, deploying ICN in the network core only. This greatly simplifies migration, while still enabling the network operator to benefit from ICN features like native multicast and fast redirection of information requests between multiple providers [5], [6]. The study of ICN and SDN network economics has not been a very active area. Specifically for the economics of caching, there has been some recent papers in the context of both IP and ICN networks, e.g. the works by Agyapong and Sirbu [7] and Pham, Fdida, and Antoniadis [8]. The approach typically considers different tiers of ISPs, along with Content Providers and Content Distribution Networks; the key questions they study include: i) which tier of ISP should deploy a cache; ii) which ISPs should contribute for the cache deployment cost; iii) which should be the pricing access and transit policy per ISP after the introduction of caching. Karakus and Duressi [9] exploit the same problem for an SDN-based architecture; iv) how the answers to the above questions vary when ICN is taken into consideration. There are two key novelties in our work: First, we focus on the intradomain of a unique ISP network without considering

2 CP Level TABLE I: Summary of the notation. ISP Cache R R 2 R P U N- U U 2 U K U N Level 2 Level 3 Level 4 Fig. : The network market consists of five elements that have been placed in four levels: one Content Provider (level ), one Internet Service Provider with a cache (level 2), P routers (level 3), N end users (level 4). the interactions between the different tiers of ISP. We want to explicitly examine the intradomain benefit from the adoption of caching, which has not been quantified in these models. Second, we examine the introduction of caching along with the transfer technology (multicast or unicast) as a unifying framework. This has not been the case in the above mentioned works, where the benefits from the adoption of multicast has not been taken into account. III. ANALYSIS We consider the network market of Fig. that consists of four levels, each -hop away from the next level; at the level, there is a unique Content Provider (CP); at the level 2, there is a unique Internet Service Provider (ISP) with P routers (level 3) that serve N end users (level 4). Our goal is to provide a network economics analysis from the ISP side. This symmetric topology significantly simplifies our analysis, since we do not need to weigh differently the effect of each user that requests a particular file. We just need to quantify the effect of the number of users. Moreover, the structure of the market is aligned with the fact that the number of hops between the source and the end users in the intradomain network is relatively small. However, we do not lose the generality of our approach. Table I includes a summary of the notation. We assume that the CP has a number of files F. The ISP, based on the popularity of files, proactively caches some of them in the unique cache of the ISP network, which is placed at the level 2. Then, at each time slot, each user may request a particular file. Once the ISP receives the requests, it should decide with the view to minimizing the transfer cost for each file: i) whether to transfer it to the users using multicast or unicast, ii) if the file exists in the cache, whether to transfer it from the cache or directly from the CP. Besides the above decisions, we introduce one more dimension in the analysis: the ISP should decide whether it has motivation to migrate its network from IP to IP-over-ICN. In order to address the first decision, we quantify the efficiency of multicast in relation to unicast using the metric defined by Chalmers and Almeroth [] = L M L U, Notation and quantity Value Number of users N {, 2, 3, 4 } Number of files F {, 2, 3 } Bandwidth per file B 3 Unit bandwidth cost b Percentage of cached files {%, 5%, 99%} Number of routers P 5 Unicast cost with IP U IP Unicast cost with IP-over-ICN U IPICN 2U IP Multicast cost with IP M IP {, 2, 3 }U IP Multicast cost with IP-over-ICN M IPICN 2U IP Cache deployment cost C INIT 2 Cache redirection cost IP R IP.3Bb Cache redirect. cost IP-over-ICN R IPICN {,.5,.9}R IP Initial IP cost T IP 8 Initial IP-over-ICN cost T IPICN {.,.5,.9}T IP where L M denotes the number of multicast links and L U denotes the number of unicast links. This simple metric represents the benefit from adopting multicast for a particular topology; when =, multicast offers no benefit; when approaches, the benefit from the adoption of multicast increases. In our market, assuming e.g. that N users request a particular file from the CP, we get that +P + N =. 3N We then compute the bandwidth cost for the transfer of this file over these links. Let B be the bandwidth needed per link (for simplicity, we assume that each file consumes the same bandwidth) and b be the unit bandwidth cost. Therefore, the bandwidth cost per link for each file is Bb and the total cost is multicast cost: L M Bb =(+P + N)Bb, () unicast cost: L U Bb =3NBb. (2) Clearly, unless a file is requested by just one user, L M <L U and the ISP should choose multicast instead of unicast. Then, we examine the case where the file has been placed in the unique cache. The number of links needed to transfer the file reduces to L? M = P + N for multicast and L? U =2N for unicast. Besides the bandwidth cost, we take into consideration the cache redirection cost R, which is proportional to the number of times that the ISP needs to access the cache, i.e., time for multicast and N times for unicast. Therefore, the cost for a particular file is multicast cost from cache: L? M Bb + R =(P + N)Bb + R, (3) unicast cost from cache: L? U Bb + NR =2NBb+ NR. (4) We find again the same conclusion: when at least two users ask for a file, the ISP should transfer it using multicast. In order to decide whether the ISP will transfer the file from the cache or directly from the ISP, we need to compare

3 the equations () and (3). The inclusion of the file in the cache saves Bb bandwidth cost at the expense of a cache redirection cost R (note that this holds even for the case that the file is requested by just a single user). It is reasonable to assume that the bandwidth savings are larger than the cache redirection cost, therefore the ISP should transfer the file from the cache. If this would have not been the case, then the ISP would have no motivation to deploy the cache (which also incurs an additional infrastructure investment) in its network. Consequently, the strategy of the ISP is summarized as: i) When at least two users ask for a file, the ISP uses multicast. ii) When a file exists in the cache, the ISP transfers it from the cache. Now, we examine the effect of the underlying protocol (IP or IP-over-ICN) in our network economics analysis. All parameters introduced so far, except for the cache redirection cost R, are independent of the underlying protocol. For the cache redirection cost, we argue that it is smaller for IP-over-ICN than for IP. This is due to the underlying publish-subscribe based user-service matching that does not require additional infrastructure (such as DNS-based redirection schemes used in IP networks) to be deployed. Therefore, the strategy of the ISP, as described in the previous paragraph, will be the same no matter which underlying protocol is analyzed; the only difference is that, for each file that exists in the cache, the cost for IP-over-ICN will be smaller than IP for a quantity equal to R IP R IPICN. It is worth mentioning that this gain per file from the adoption of IP-over-ICN is independent of the number of users that request this file; it is a fixed quantity, which is multiplied by the number of files that exist in the cache. Finally, for a fair comparison of these protocols under the prism of network economics, we also need to take into account the initial cost. Firstly, there is the cache deployment cost, which is the same for both protocols. Secondly, the cost for the multicast operation, denoted by M and for the unicast operation, denoted by U. For IP, unicast is much cheaper than multicast. For IP-over-ICN, multicast is supported natively, therefore its cost is equal to the unicast cost. Moreover, we expect that the cost of these operations with IP-over-ICN to be higher than the IP unicast cost but significantly lower than the IP multicast cost; this leads to the following set of inequalities: U IP <U IPICN = M IPICN <M IP. Lastly, given the initial IP deployment cost T IP, we need to take into consideration the migration cost T IPICN = at IP (with a being a constant larger than ) for the transition from IP to IP-over-ICN. Based on the above, we can write the formulas for the minimum cost for both the IP and the IP-over-ICN case, assuming that the CP offers F files: min cost with protocol j 2{IP, IP-over-ICN}: FX T j + U j + M j + C INIT + d i, LMi Bb, d i = L? Mi Bb + R j, i= file i from CP, file i from cache. IV. PERFORMANCE EVALUATION For the performance evaluation of IP and IP-over-ICN, we need to quantify the 5 parameters that we have used for the analysis. We report their values in Table I. The popularity of the files follow a Zipf distribution, being proportional to / a with parameter a being a positive number below. We have fixed the values for nine of them that are either topology dependent (e.g., the number of routers P ) or their cost can be accurately estimated (e.g., the bandwidth and the cache deployment cost); we have studied at least three different values for each of the six remaining parameters, i.e., the number of users N, the number of files F, the percentage of cached files, the IP multicast cost, the IP-over-ICN cache redirection cost R IPICN and the initial IP-over-ICN cost T IPICN ). A. Performance evaluation when IP multicast can be supported In the initial set of figures, we compare IP-over-ICN with IP starting with the case that IP multicast is feasible. This may not always be the case for either economical (the initial cost for the infrastructure component that implements the multicast functionality is too expensive) or technical (unacceptable latency as the number of users that request the same file increases) reasons. We will explicitly study this case in the second part of the performance evaluation. We use the quantity min cost with IP-over-ICN x = min cost with IP to determine the relative efficiency of the protocols. This metric computes the minimum cost of each protocol for each set of parameters that corresponds to a unique scenario. When x is below, IP-over-ICN is superior than IP; the closer x goes to, the better is the performance of IP-over-ICN. Similarly, the more the ratio is above, the better is the performance for IP. In Fig. 2a, we have plotted the Cumulative Distribution Function (CDF) of the ratio x that expresses the probability that x is up to a particular value. Based on the blue line, we argue that for the vast majority of the scenarios x is between.9 and., meaning that the performance of the protocols differs at most %. We also present the CDF distribution as a function of the number of users. We can see that as the number of users increases, the range of the ratio decreases, meaning that the performance of the two protocols is practically equivalent; only for users there are cases with more than % difference in the performance of the protocols. Based on the above trend, we find that the performance of the two protocols may differ significantly only when the demand for the files is generated by a small number of users. In Fig. 2b, we investigate the performance of the two protocols for 2, 4, 6 and 8 users. We note again that the range of x decreases with the number of users; for 6 and 8 users, the difference in the performance is small; for 2 and 4 users, there are cases where x differs more than %, slightly more in favor of IP-over-ICN. We draw the conclusion that as the number of users increases, the most critical factor that determines to a large extent the total cost is the bandwidth cost; since this is the same for both IP and IP-over-ICN when IP multicast can be supported, the performance of both protocols is very close. For few users, the bandwidth cost is not the most significant component of the total cost; therefore, based

4 All users users 2 users 3 users 4 users 2 users 4 users 6 users 8 users (a) Evaluation of the protocols as a function of the users. (b) Evaluation of the protocols for few users. for users All cases Multicast cost: Multicast cost: Multicast.2cost:.3 3 Zipf() Zipf(.7) Zipf() Zipf(.9) (c) The effect of the IP multicast cost. (d) The effect of the Zipf distribution. Fig. 2: Performance evaluation for IP and IP-over-ICN when IP multicast is feasible. on the other parameters, there may be cases with significant difference in the performance of the protocols. Moreover, in Fig. 2c, we present the CDF distribution for users (this was the only case from the initial set of users that there was significant difference in the performance of the protocols) as a function of the IP multicast cost. It is clear that when the additional cost for IP multicasting is not hugely excessive ( times the IP unicast cost or times the IP unicast cost), IP outperforms IP-over-ICN at least % for around 6% and 4% of the scenarios respectively. On the other hand, when the cost of IP multicast is equal to times the cost of IP unicast, IP-over-ICN is always at least 8% better. From the above, it becomes evident that the second most important parameter, besides the number of users, that determines the comparative performance of these protocols is the initial IP multicast cost. Finally, as shown in Fig. 2d, the above results are not sensitive on the parameter a of the Zipf distribution. For typical values of the parameter a (from to.9), the difference in the performance evaluation of the protocols is pretty small. B. Performance evaluation when IP multicast is not supported We now present the case where IP multicast cannot be supported. We use the same performance metric x where, now, the denominator that corresponds to the minimum cost with IP will be greater than the case with IP multicast. This is due to the fact that the strategy for IP will be always unicast plus use of the cache when the file exists in the cache. In Fig. 3a, we plot the CDF for the case of IP without multicast next to the case with IP multicast. It is clear that the potential from the adoption of IP-over-ICN is significant; it outperforms IP 35% on average; even more for around half of the scenarios. We present the CDF of x as a function of the users in Fig. 3b. As expected, except for the case of users where the performance is balanced, IP-over-ICN significantly outperforms IP, leading always to at least 4% and 55% improvement when and users participate in the topology respectively. From Fig. 4, we notice that even when the number of users is 2, IP-over-ICN is always better than IP and the difference in the performance increases rapidly with the number of users. As previously, after a particular number of users, the most important component of the cost is the bandwidth cost. The bandwidth savings due to multicast, even

5 IP with multicast IP without multicast users 2 users 3 users 4 users (a) Comparison of IP-over-ICN versus IP with and without multicast. Fig. 3: The case where IP multicast is not supported. (b) Evaluation of the protocols as a function of the users. 2 users 4 users 6 users 8 users problem of the placement of caches. Moreover, we want to study how to estimate online the popularity of files. Answers to these questions will further decrease the cost of the ISP. Finally, we are interested in investigating oligopoly markets consisting of several ISPs and/or CPs and model their interactions and the users strategies using tools from game theory. VI. ACKNOWLEDGMENT The work presented in this paper was supported by the EU funded H22 ICT project POINT, under contract Fig. 4: Evaluation of the protocols for few users. for few users, is the reason for the lower cost for IP-over-ICN independent of the values of all other parameters. V. CONCLUSIONS A necessary (though not in itself sufficient) condition for the large-scale deployment of future network architectures is their economic viability. Through this network economics study, we highlight the limitations and the opportunities that arise from a possible adoption of the IP-over-ICN protocol, a prominent candidate to replace the existing IP protocol. The key messages that we want to deliver is that when IP multicast can be supported, the benefit from the adoption of IP-over-ICN (if any) is relatively small and arises only when the demand for the contents of the files is niche and the IP multicast cost is relatively high. On the other hand, when IP multicast is not a technically/economically viable solution, the IP-over-ICN protocol that natively supports multicast can significantly reduce the cost of the ISP network, absorbing rapidly (even for few users) the migration cost needed for the transition from IP. We plan to extend our analysis to networks with a more general and complex structure and study the complementary REFERENCES [] D. Trossen, M. J. Reed, J. Riihijärvi, M. Georgiades, N. Fotiou, and G. Xylomenos, IP over ICN-the better IP? in Proc. European Conference on Networks and Communications (EuCNC), 25. [2] N. McKeown, T. Anderson, H. Balakrishnan, G. Parulkar, L. Peterson, J. Rexford, S. Shenker, and J. Turner, OpenFlow: enabling innovation in campus networks, ACM SIGCOMM Computer Communication Review, vol. 38, no. 2, pp , 28. [3] D. Kreutz, F. M. Ramos, P. E. Verissimo, C. E. Rothenberg, S. Azodolmolky, and S. Uhlig, Software-defined networking: A comprehensive survey, Proceedings of the IEEE, vol. 3, no., pp. 4 76, 25. [4] G. Xylomenos, C. N. Ververidis, V. A. Siris, N. Fotiou, C. Tsilopoulos, X. Vasilakos, K. V. Katsaros, and G. C. Polyzos, A survey of information-centric networking research, IEEE Communications Surveys & Tutorials, vol. 6, no. 2, pp , 24. [5] D. Trossen, J. Riihijärvi, P. Nikander, P. Jokela, J. Kjällman, and J. Rajahalme, Designing, implementing and evaluating a new internetworking architecture, Elsevier Computer Communications, vol. 35, no. 7, pp , 22. [6] P. Jokela, A. Zahemszky, C. Esteve Rothenberg, S. Arianfar, and P. Nikander, LIPSIN: line speed publish/subscribe inter-networking, ACM SIGCOMM Computer Communication Review, vol. 39, no. 4, pp , 29. [7] P. K. Agyapong and M. Sirbu, Economic incentives in informationcentric networking: Implications for protocol design and public policy, IEEE Communications Magazine, vol. 5, no. 2, pp. 8 26, 22. [8] T.-M. Pham, S. Fdida, and P. Antoniadis, Pricing in information-centric network interconnection, in Proc. IFIP Networking Conference, 23. [9] M. Karakus and A. Durresi, Economic viability of QoS in software defined networks (SDNs), in Proc. 3 th International Conference on Advanced Information Networking and Applications (AINA), 26. [] R. C. Chalmers and K. C. Almeroth, Developing a multicast metric, in Proc. IEEE Global Telecommunications Conference (Globecom), 2.