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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Missing Reference: 'Gbps' is mentioned on line 113, but not defined == Missing Reference: 'Euros' is mentioned on line 116, but not defined == Unused Reference: 'I-D.liu-distributed-mobility-traffic-analysis' is defined on line 373, but no explicit reference was found in the text == Unused Reference: 'I-D.yokota-dmm-scenario' is defined on line 379, but no explicit reference was found in the text Summary: 0 errors (**), 0 flaws (~~), 6 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 DMM E. Demaria 3 Internet-Draft L. Marchetti 4 Intended status: Informational Telecom Italia 5 Expires: September 3, 2012 March 2, 2012 7 Dimensioning considerations for distributed mobility architecture 8 draft-demaria-dmm-dimensioning-considerations-00.txt 10 Abstract 12 One of the main questions posed during recent discussions on 13 distributed mobility architectures is if the distributed architecture 14 can have advantages in terms of costs with respect to a centralized 15 one. 17 This draft describes a general method to calculate the costs of the 18 centralized and distributed scenarios. Even if a simplified model 19 has been used, some information can be earned. Each operator can use 20 this model and his own costs to discover the optimal architecture 21 based on traffic observed in the network. 23 Status of this Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at http://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on September 3, 2012. 40 Copyright Notice 42 Copyright (c) 2012 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 58 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 3. Network Topology . . . . . . . . . . . . . . . . . . . . . . . 4 60 4. How to derive costs for the two scenarios . . . . . . . . . . 4 61 4.1. Centralized scenario . . . . . . . . . . . . . . . . . . . 4 62 4.2. Distributed scenario . . . . . . . . . . . . . . . . . . . 6 63 5. Comparison and Analysis based on traffic distribution . . . . 8 64 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 65 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 66 8. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 8 67 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 68 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 69 10.1. Normative References . . . . . . . . . . . . . . . . . . . 9 70 10.2. Informative References . . . . . . . . . . . . . . . . . . 9 71 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 73 1. Introduction 75 Based on recent discussions on DMM architecture a frequent question 76 is on the economical convenience to change the mobility architecture 77 from centralized to distributed. 79 In this draft we propose a simplified method to calculate costs of 80 both scenarios and to derive indications on which model is more 81 convenient for specific network configuration and traffic patterns. 83 2. Terminology 85 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 86 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 87 document are to be interpreted as described in [RFC2119]. 89 We refer to the following terminology: 91 PGW: packet data gateway. It is a gateway function defined in 3GPP 92 Evolved Packet System (EPS), which provides connectivity to Internet 93 or other networks (e.g. corporate networks). 95 PoP_i: A point-of-presence (PoP) is an (IP based) access point, 96 provided by an Internet Service Provider (ISP), from one place to the 97 rest of the ISP IP network or to the Big-Internet. In this last case 98 the PoP(s) is/are usually located at Internet Exchange Points. The 99 number of PoPs of an ISP is variable and depends on its size or 100 growth rate. A PoP usually includes routers, L2/L3 switches, 101 servers, digital/analog call aggregators, PGWs (Packet Data Gateway) 102 and BRASs (Broadband Remote Access Servers). 104 Cost_link: cost for the data transport from one PoP to another 105 [Euros/Mbps]. 107 Traffic_PoP_i: total traffic generated from the PoPi [Gbps]. 109 Internet_Traffic_PoP_i: traffic generated from the PoPi and directed 110 to the Internet [Gbps]. 112 Local_Traffic_PoP_i: traffic generated from the PoPi and directed to 113 the same PoP [Gbps]. 115 Cost_PGW (Traffic): this is a function that, given the traffic, 116 returns the cost of the PGW(s) needed to manage that traffic [Euros]. 118 3. Network Topology 120 The network topology we consider in this document is very simple but 121 can be quite frequent. 123 The network topology is described in the following figure: 125 +----------------------+ 126 | | 127 | Backbone | 128 | | 129 | | 130 +----------------------+ 131 | | | 132 | | +-----------+ 133 +--------+ | | 134 +-------|-----+-+----|------ + +-------|-----+ 135 | | | | | | 136 | | | | | | 137 | PoP1 | | PoP2 | | PoPn | 138 | | | | | | 139 | | | | | | 140 +-------------+ +------------+ +-------------+ 141 | 142 | 143 +---------------------------+ 144 | Internet Exchange Point | 145 +---------------------------+ 147 Figure 1: Network topology 149 The network is made by different PoPs each one directly connected 150 (single hop) to the backbone. Only one PoP gives access to the 151 Internet. 153 4. How to derive costs for the two scenarios 155 In this section we propose a method to derive costs for the two 156 scenarios (centralized and distributed) based on the network topology 157 introduced in chapter 3. 159 4.1. Centralized scenario 161 In this scenario the PGWs are located only in the PoP where the 162 Internet exchange point is located. This is depicted in the 163 following figure: 165 +----------------------+ 166 | | 167 | Backbone | 168 | | 169 | | 170 +----------------------+ 171 | | | 172 | | +-----------+ 173 +--------+ | | 174 +-------|-----+-+----|------ + +-------|-----+ 175 | | | | | | | | | | 176 | | | | | | 177 | PoP1 | | PoP2 | | PoPn | 178 | | | | | | 179 | | | | | | 180 | +-----+ | | | | | 181 | | PGW | | | | | | 182 | +-----+ | | | | | 183 +-------------+ +------------+ +-------------+ 184 | 185 | 186 +---------------------------+ 187 | Internet Exchange Point | 188 +---------------------------+ 190 Figure 2: Centralized scenario network topology 192 In the current draft we assume that the traffic generated by each PoP 193 may be directed to the Internet or it is local to the PoP. We do not 194 consider inter-PoP traffic scenario. 196 The cost for this scenario is given by the cost of the transport of 197 both Internet and local traffic of all PoPs plus the cost of the PGW 198 dimensioned to manage the traffic of all PoPs. The cost of the 199 transport is not calculated for the PoP where the Internet exchange 200 point is located. 202 The result is the following formula: 204 sum_{i=1}^{n-1}(2*2^10*cost_link*Internet_Traffic_PoP_i)+ 206 sum_{i=1}^{n-1}(4*2^10*cost_link*Local_Traffic_PoP_i)+ 208 cost_PGW (sum_{i=1}^{n} (traffic_PoP_i)) 210 where the first term calculates the cost of the transport of the 211 Internet traffic of each PoP to the PGW. This is given by: the cost 212 of the transport for each Mbps for the link considered (cost_link), 213 multiplied by the traffic of the PoP considered 214 (Internet_Traffic_PoP_i) in Gbps, multiplied by 2^10 to consider that 215 the cost is expresses in euros/Mbps and the traffic in Gbps, 216 multiplied by 2 since we consider the need to reserve a backup link 217 for redundancy. 219 The second term calculates the cost of the transport of the local 220 traffic of all PoPs. This is given by: the cost of the transport for 221 each Mbps for the link considered (cost_link), multiplied by the 222 traffic of the PoP considered (Local_Traffic_PoP_i) in Gbps, 223 multiplied by 2^10 to consider that the cost is expresses in euros/ 224 Mbps and the traffic in Gbps, multiplied by 2*2 since we consider the 225 need to reserve a backup link for redundancy and that the local 226 traffic goes to PGW and back to the PoP. 228 The third term calculates the cost of the centralized PGW needed to 229 manage the traffic of all PoPs. Given the total traffic for all 230 PoPs, the function returns the costs of the PGWs to allocate. This 231 is a nonlinear function. 233 4.2. Distributed scenario 235 Different distributed scenarios may exist but we consider the one in 236 which each PoP is equipped with a PGW as depicted in the following 237 figure: 239 +----------------------+ 240 | | 241 | Backbone | 242 | | 243 | | 244 +----------------------+ 245 | | | 246 | | +-----------+ 247 +--------+ | | 248 +-------|-----+-+----|------ + +-------|-----+ 249 | | | | | | | | | | 250 | | | | | | 251 | PoP1 | | PoP2 | | PoPn | 252 | | | | | | 253 | | | | | | 254 | +------+ | | +------+ | | +------+ | 255 | | PGW1 | | | | PGW2 | | | | PGWn | | 256 | +------+ | | +------+ | | +------+ | 257 +-------------+ +------------+ +-------------+ 258 | 259 | 260 +---------------------------+ 261 | Internet Exchange Point | 262 +---------------------------+ 264 Figure 3: Distributed scenario network topology 266 In the current draft we assume that the traffic generated by each PoP 267 may be directed to the Internet or it is local to the PoP. We do not 268 consider inter-PoP traffic scenario. 270 In this scenario the cost is given by the cost of the transport to 271 the exchange point for the quota of traffic directed to the internet 272 plus the cost of the PGWs in each PoP properly dimensioned to manage 273 the traffic of that PoP. The first term is calculated for all PoPs 274 except the one hosting the Internet exchange point. 276 In this case the result is the following formula: 278 sum_{i=1}^{n-1}(2*2^10*cost_link*Internet_Traffic_PoP_i)+ 280 sum_{i=1}^{n}(cost_PGW(traffic_PoP_i)) 282 where the first term calculates the cost of the transport of the 283 traffic of each PoP to the internet exchange point. In this term we 284 only consider the traffic quota directed to the internet since each 285 PoP is equipped with a PGW. The other factors are the same of the 286 centralized case. 288 The second term calculates the cost of the PGWs distributed in each 289 PoP dimensioned to manage all the traffic of the PoP considered. 290 Given the total traffic of each PoP, the function returns the costs 291 of the PGW to allocate. This term is considered for all PoPs. 293 5. Comparison and Analysis based on traffic distribution 295 The analysis made in the previous chapters allows each operator to 296 calculate costs of different scenarios based on their own costs for 297 transport and PGWs and on traffic distribution. A general result 298 cannot be achieved since costs and traffic distribution may vary a 299 lot. What we can try to do is to understand which is the condition 300 that makes one scenario more convenient than the other. 302 If we observe the formulas we can see that the cost of the transport 303 differs in the two cases: in the centralized scenario we have to 304 consider all the traffic of each PoP, both local and internet, while 305 in the distributed one we only consider the quota of traffic directed 306 to the internet (since the local traffic must not be transported to 307 the internet exchange point). 309 The second term, instead, that calculates the cost of the PGWs is 310 always based on the total traffic of each PoP (local and directed to 311 the internet) since all the traffic must reach a PGW anyway. 313 Based on our simulations we observed that there is a quota of traffic 314 local to the PoP over which the distributed scenario becomes more 315 convenient in terms of costs with respect to the centralized one. 317 6. Security Considerations 319 This document does not raise any new security concern. 321 7. IANA Considerations 323 This document has no requests to IANA. 325 8. Conclusions 327 What can be earned from this analysis is that there is not an always- 328 valid model but, based on traffic distribution, one model can be more 329 convenient than the other. 331 In particular it is interesting to observe that what makes the 332 difference is the percentage of traffic directed to the Internet or, 333 which is the same, the percentage of traffic local to the PoP. If 334 sufficient traffic is exchanged internally to the PoP there is no 335 need to transport it to the exchange point so that the distributed 336 scenario becomes more convenient. 338 On the opposite side, if all the traffic generated by the customers 339 is directed to the internet the difference between the two scenarios 340 reduces and there is no convenience to have a local PGW when the 341 traffic must however be transported to the exchange point. 343 In addition, there are some technologies which, if introduced in the 344 single PoPs, may increment the local traffic quota. One example, 345 significant if we consider the amount of video in current networks, 346 is the use/distribution of CDNs in the PoPs. Moreover, in the long 347 term, also VoIP calls could bring to an increase of local traffic 348 since most of voice calls are terminated in the same region. 350 It is then clear that the exact quota that makes the distributed 351 scenario more convenient depends on the network topology, link and 352 equipment costs of each operator and cannot be generalized. 354 However, the proposed cost model, properly extended and adapted to 355 different situations, may provide an useful method to calculate costs 356 in order to derive an indication of the most convenient scenario. 358 9. Acknowledgments 360 The research leading to these results has received funding from the 361 European Community's Seventh Framework Programme (FP7-ICT-2009-5) 362 under grant agreement n. 258053 (MEDIEVAL project). 364 10. References 366 10.1. Normative References 368 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 369 Requirement Levels", BCP 14, RFC 2119, March 1997. 371 10.2. Informative References 373 [I-D.liu-distributed-mobility-traffic-analysis] 374 Liu, D., Luo, W., and J. Song, "Distributed Mobility 375 Management Traffic analysis", 376 draft-liu-distributed-mobility-traffic-analysis-00 (work 377 in progress), March 2011. 379 [I-D.yokota-dmm-scenario] 380 Yokota, H., Seite, P., Demaria, E., and Z. Cao, "Use case 381 scenarios for Distributed Mobility Management", 382 draft-yokota-dmm-scenario-00 (work in progress), 383 October 2010. 385 Authors' Addresses 387 Elena Demaria 388 Telecom Italia 389 Via Reiss Romoli 274 390 Torino 10148 391 Italy 393 Phone: +390112285403 394 Email: elena.demaria@telecomitalia.it 396 Loris Marchetti 397 Telecom Italia 398 Via Reiss Romoli 274 399 Torino 10148 400 Italy 402 Phone: +390112285031 403 Email: loris.marchetti@telecomitalia.it