Internet DRAFT - draft-demaria-dmm-dimensioning-considerations

draft-demaria-dmm-dimensioning-considerations






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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   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
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
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   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



























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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].






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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:



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                      +----------------------+
                      |                      |
                      |       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),



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   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:


























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                      +----------------------+
                      |                      |
                      |       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.



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   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



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   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.



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   [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
























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