DMM E. Demaria Internet-Draft L. Marchetti Intended status: Informational Telecom Italia Expires: September 3, 2012 March 2, 2012 Dimensioning considerations for distributed mobility architecture draft-demaria-dmm-dimensioning-considerations-00.txt Abstract One of the main questions posed during recent discussions on distributed mobility architectures is if the distributed architecture can have advantages in terms of costs with respect to a centralized one. This draft describes a general method to calculate the costs of the centralized and distributed scenarios. Even if a simplified model has been used, some information can be earned. Each operator can use this model and his own costs to discover the optimal architecture based on traffic observed in the network. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on September 3, 2012. Copyright Notice Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents Demaria & Marchetti Expires September 3, 2012 [Page 1] Internet-Draft Dimensioning considerations for DMM March 2012 carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Network Topology . . . . . . . . . . . . . . . . . . . . . . . 4 4. How to derive costs for the two scenarios . . . . . . . . . . 4 4.1. Centralized scenario . . . . . . . . . . . . . . . . . . . 4 4.2. Distributed scenario . . . . . . . . . . . . . . . . . . . 6 5. Comparison and Analysis based on traffic distribution . . . . 8 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 8. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 8 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 10.1. Normative References . . . . . . . . . . . . . . . . . . . 9 10.2. Informative References . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 Demaria & Marchetti Expires September 3, 2012 [Page 2] Internet-Draft Dimensioning considerations for DMM March 2012 1. Introduction Based on recent discussions on DMM architecture a frequent question is on the economical convenience to change the mobility architecture from centralized to distributed. In this draft we propose a simplified method to calculate costs of both scenarios and to derive indications on which model is more convenient for specific network configuration and traffic patterns. 2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. We refer to the following terminology: PGW: packet data gateway. It is a gateway function defined in 3GPP Evolved Packet System (EPS), which provides connectivity to Internet or other networks (e.g. corporate networks). PoP_i: A point-of-presence (PoP) is an (IP based) access point, provided by an Internet Service Provider (ISP), from one place to the rest of the ISP IP network or to the Big-Internet. In this last case the PoP(s) is/are usually located at Internet Exchange Points. The number of PoPs of an ISP is variable and depends on its size or growth rate. A PoP usually includes routers, L2/L3 switches, servers, digital/analog call aggregators, PGWs (Packet Data Gateway) and BRASs (Broadband Remote Access Servers). Cost_link: cost for the data transport from one PoP to another [Euros/Mbps]. Traffic_PoP_i: total traffic generated from the PoPi [Gbps]. Internet_Traffic_PoP_i: traffic generated from the PoPi and directed to the Internet [Gbps]. Local_Traffic_PoP_i: traffic generated from the PoPi and directed to the same PoP [Gbps]. Cost_PGW (Traffic): this is a function that, given the traffic, returns the cost of the PGW(s) needed to manage that traffic [Euros]. Demaria & Marchetti Expires September 3, 2012 [Page 3] Internet-Draft Dimensioning considerations for DMM March 2012 3. Network Topology The network topology we consider in this document is very simple but can be quite frequent. The network topology is described in the following figure: +----------------------+ | | | Backbone | | | | | +----------------------+ | | | | | +-----------+ +--------+ | | +-------|-----+-+----|------ + +-------|-----+ | | | | | | | | | | | | | PoP1 | | PoP2 | | PoPn | | | | | | | | | | | | | +-------------+ +------------+ +-------------+ | | +---------------------------+ | Internet Exchange Point | +---------------------------+ Figure 1: Network topology The network is made by different PoPs each one directly connected (single hop) to the backbone. Only one PoP gives access to the Internet. 4. How to derive costs for the two scenarios In this section we propose a method to derive costs for the two scenarios (centralized and distributed) based on the network topology introduced in chapter 3. 4.1. Centralized scenario In this scenario the PGWs are located only in the PoP where the Internet exchange point is located. This is depicted in the following figure: Demaria & Marchetti Expires September 3, 2012 [Page 4] Internet-Draft Dimensioning considerations for DMM March 2012 +----------------------+ | | | Backbone | | | | | +----------------------+ | | | | | +-----------+ +--------+ | | +-------|-----+-+----|------ + +-------|-----+ | | | | | | | | | | | | | | | | | PoP1 | | PoP2 | | PoPn | | | | | | | | | | | | | | +-----+ | | | | | | | PGW | | | | | | | +-----+ | | | | | +-------------+ +------------+ +-------------+ | | +---------------------------+ | Internet Exchange Point | +---------------------------+ Figure 2: Centralized scenario network topology In the current draft we assume that the traffic generated by each PoP may be directed to the Internet or it is local to the PoP. We do not consider inter-PoP traffic scenario. The cost for this scenario is given by the cost of the transport of both Internet and local traffic of all PoPs plus the cost of the PGW dimensioned to manage the traffic of all PoPs. The cost of the transport is not calculated for the PoP where the Internet exchange point is located. The result is the following formula: sum_{i=1}^{n-1}(2*2^10*cost_link*Internet_Traffic_PoP_i)+ sum_{i=1}^{n-1}(4*2^10*cost_link*Local_Traffic_PoP_i)+ cost_PGW (sum_{i=1}^{n} (traffic_PoP_i)) where the first term calculates the cost of the transport of the Internet traffic of each PoP to the PGW. This is given by: the cost of the transport for each Mbps for the link considered (cost_link), Demaria & Marchetti Expires September 3, 2012 [Page 5] Internet-Draft Dimensioning considerations for DMM March 2012 multiplied by the traffic of the PoP considered (Internet_Traffic_PoP_i) in Gbps, multiplied by 2^10 to consider that the cost is expresses in euros/Mbps and the traffic in Gbps, multiplied by 2 since we consider the need to reserve a backup link for redundancy. The second term calculates the cost of the transport of the local traffic of all PoPs. This is given by: the cost of the transport for each Mbps for the link considered (cost_link), multiplied by the traffic of the PoP considered (Local_Traffic_PoP_i) in Gbps, multiplied by 2^10 to consider that the cost is expresses in euros/ Mbps and the traffic in Gbps, multiplied by 2*2 since we consider the need to reserve a backup link for redundancy and that the local traffic goes to PGW and back to the PoP. The third term calculates the cost of the centralized PGW needed to manage the traffic of all PoPs. Given the total traffic for all PoPs, the function returns the costs of the PGWs to allocate. This is a nonlinear function. 4.2. Distributed scenario Different distributed scenarios may exist but we consider the one in which each PoP is equipped with a PGW as depicted in the following figure: Demaria & Marchetti Expires September 3, 2012 [Page 6] Internet-Draft Dimensioning considerations for DMM March 2012 +----------------------+ | | | Backbone | | | | | +----------------------+ | | | | | +-----------+ +--------+ | | +-------|-----+-+----|------ + +-------|-----+ | | | | | | | | | | | | | | | | | PoP1 | | PoP2 | | PoPn | | | | | | | | | | | | | | +------+ | | +------+ | | +------+ | | | PGW1 | | | | PGW2 | | | | PGWn | | | +------+ | | +------+ | | +------+ | +-------------+ +------------+ +-------------+ | | +---------------------------+ | Internet Exchange Point | +---------------------------+ Figure 3: Distributed scenario network topology In the current draft we assume that the traffic generated by each PoP may be directed to the Internet or it is local to the PoP. We do not consider inter-PoP traffic scenario. In this scenario the cost is given by the cost of the transport to the exchange point for the quota of traffic directed to the internet plus the cost of the PGWs in each PoP properly dimensioned to manage the traffic of that PoP. The first term is calculated for all PoPs except the one hosting the Internet exchange point. In this case the result is the following formula: sum_{i=1}^{n-1}(2*2^10*cost_link*Internet_Traffic_PoP_i)+ sum_{i=1}^{n}(cost_PGW(traffic_PoP_i)) where the first term calculates the cost of the transport of the traffic of each PoP to the internet exchange point. In this term we only consider the traffic quota directed to the internet since each PoP is equipped with a PGW. The other factors are the same of the centralized case. Demaria & Marchetti Expires September 3, 2012 [Page 7] Internet-Draft Dimensioning considerations for DMM March 2012 The second term calculates the cost of the PGWs distributed in each PoP dimensioned to manage all the traffic of the PoP considered. Given the total traffic of each PoP, the function returns the costs of the PGW to allocate. This term is considered for all PoPs. 5. Comparison and Analysis based on traffic distribution The analysis made in the previous chapters allows each operator to calculate costs of different scenarios based on their own costs for transport and PGWs and on traffic distribution. A general result cannot be achieved since costs and traffic distribution may vary a lot. What we can try to do is to understand which is the condition that makes one scenario more convenient than the other. If we observe the formulas we can see that the cost of the transport differs in the two cases: in the centralized scenario we have to consider all the traffic of each PoP, both local and internet, while in the distributed one we only consider the quota of traffic directed to the internet (since the local traffic must not be transported to the internet exchange point). The second term, instead, that calculates the cost of the PGWs is always based on the total traffic of each PoP (local and directed to the internet) since all the traffic must reach a PGW anyway. Based on our simulations we observed that there is a quota of traffic local to the PoP over which the distributed scenario becomes more convenient in terms of costs with respect to the centralized one. 6. Security Considerations This document does not raise any new security concern. 7. IANA Considerations This document has no requests to IANA. 8. Conclusions What can be earned from this analysis is that there is not an always- valid model but, based on traffic distribution, one model can be more convenient than the other. In particular it is interesting to observe that what makes the Demaria & Marchetti Expires September 3, 2012 [Page 8] Internet-Draft Dimensioning considerations for DMM March 2012 difference is the percentage of traffic directed to the Internet or, which is the same, the percentage of traffic local to the PoP. If sufficient traffic is exchanged internally to the PoP there is no need to transport it to the exchange point so that the distributed scenario becomes more convenient. On the opposite side, if all the traffic generated by the customers is directed to the internet the difference between the two scenarios reduces and there is no convenience to have a local PGW when the traffic must however be transported to the exchange point. In addition, there are some technologies which, if introduced in the single PoPs, may increment the local traffic quota. One example, significant if we consider the amount of video in current networks, is the use/distribution of CDNs in the PoPs. Moreover, in the long term, also VoIP calls could bring to an increase of local traffic since most of voice calls are terminated in the same region. It is then clear that the exact quota that makes the distributed scenario more convenient depends on the network topology, link and equipment costs of each operator and cannot be generalized. However, the proposed cost model, properly extended and adapted to different situations, may provide an useful method to calculate costs in order to derive an indication of the most convenient scenario. 9. Acknowledgments The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7-ICT-2009-5) under grant agreement n. 258053 (MEDIEVAL project). 10. References 10.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 10.2. Informative References [I-D.liu-distributed-mobility-traffic-analysis] Liu, D., Luo, W., and J. Song, "Distributed Mobility Management Traffic analysis", draft-liu-distributed-mobility-traffic-analysis-00 (work in progress), March 2011. Demaria & Marchetti Expires September 3, 2012 [Page 9] Internet-Draft Dimensioning considerations for DMM March 2012 [I-D.yokota-dmm-scenario] Yokota, H., Seite, P., Demaria, E., and Z. Cao, "Use case scenarios for Distributed Mobility Management", draft-yokota-dmm-scenario-00 (work in progress), October 2010. Authors' Addresses Elena Demaria Telecom Italia Via Reiss Romoli 274 Torino 10148 Italy Phone: +390112285403 Email: elena.demaria@telecomitalia.it Loris Marchetti Telecom Italia Via Reiss Romoli 274 Torino 10148 Italy Phone: +390112285031 Email: loris.marchetti@telecomitalia.it Demaria & Marchetti Expires September 3, 2012 [Page 10]