INTERNET DRAFT P. Mutaf C. Castelluccia Date: September, 2001 INRIA DPAC: Dynamic Paging Area Configuration Status of This Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026. Distribution of this memo is unlimited. This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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.'' The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This document defines dynamic paging area configuration extensions to IP paging. The motivation is three fold: First, paging areas are auto-configured, hence human effort is minimized. Second, paging area shapes adapt to host mobility characteristics, hence more efficient. Third, paging area sizes are variable, allowing future optimization. Dynamic paging area configuration can be regarded as the major advantage of having L3 paging areas. Mutaf, Castelluccia Expires February, 2001 [Page 1] INTERNET DRAFT DPAC September 2001 Table of contents 1.0 Introduction .................................................. 2 2.0 Paging area model ............................................. 2 3.0 Dynamic paging area configuration ............................. 3 3.1 Sampling ................................................... 3 3.2 Paging area composition .................................... 4 4.0 Convergence of paging areas ................................... 4 5.0 Model of operation with relevance to DMHA protocol ............ 5 6.0 How to support DPAC in current DMHA protocol proposals? ....... 6 7.0 Picking the paging area size .................................. 6 8.0 Security considerations ....................................... 7 9.0 Conclusion .................................................... 7 References ........................................................ 7 Authors' Addresses ................................................ 8 1.0 Introduction The DMHA (Dormant Mode Host Alerting) protocol offers IP paging services to dormant mode capable Internet hosts in order to reduce power and bandwidth consumption [PROB][REQ]. The flexibility of IP paging allows dynamic paging area configuration. Manual paging area configuration is difficult, prone to human error and not necessarily well adapted to user movement. This document defines extensions for Dynamic Paging Area Configuration (DPAC) for flexibility of administration and better paging performance. DPAC aims to be scalable, low-cost and adaptive: Paging areas should be available to millions of hosts regardless of their points of attachment in a cellular system comprising millions of cells (scalable). Furthermore, the cost of paging area configuration on mobile host operation and bandwith consumption should be negligible (low-cost). Finally, paging area shapes should adapt to hosts' mobility characteristics in order to efficiently reduce the rate of registrations. In addition, paging area shapes should adapt to the changes in the cellular topology, e.g., the addition of a new cell (adaptive). 2.0 Paging area model A dynamically configured paging area is a list of network prefixes (i.e. cells). The size of a paging area is the size of that list, hence the number of cells. These paging areas have the following properties: + Per-cell: There is a paging area corresponding (relative) to each cell. Naturally, paging areas overlap. + Loadable: A host requests the network a pre-configured paging area relative to its current cell. + Host-centered: A mobile host which obtains a new paging area is initially at the center of that paging area. Mutaf, Castelluccia Expires February, 2001 [Page 2] INTERNET DRAFT DPAC September 2001 3.0 Dynamic paging area configuration 3.1 Sampling A Cellular Sampling Agent (CSA) is a new function responsable for collecting samples sent by mobile hosts moving in its domain. A sample is an ordered pair of adjacent cells. Samples are generated randomly by mobile hosts. Upon location registration, a mobile host sends a sample to its current CSA with a very small probability (e.g. 1%, 2%) so that sampling has no impact on power consumption on mobile hosts nor bandwith consumption. The identity of the host which sends a given sample has no importance. This way DPAC captures the aggregated movement characteristics which are more or less common to each individual host. This sampling policy is at the heart of DPAC scalability. Then, the collected samples give the "aggregated host direction probabilities" in each cell of a CSA domain. In a given cell A, the probability of a given direction is the probability of moving to a corresponding cell in the neighborhood. For example, the samples [A|B], [A|C], [A|D], [A|B], ... will help extract the direction probabilities in cell A. This is illustrated in Figure 1. + + / \ / \ / \ / \ + + + | G | B | + + + / \ / \ / \ / \ / \ / \ + + + + | F | A | C | + + + + \ / \ / \ / \ / \ / \ / + + + | E | D | + + + \ / \ / \ / \ / + + Figure 1. Six possible directions that hosts may take in cell A (where P(B) + P(C) + P(D) + P(E) + P(F) + P(G) = 1) For example, on a two-way highway the direction probabilities will be approximately 0.5 and 0.5 in each cell along that highway. Mutaf, Castelluccia Expires February, 2001 [Page 3] INTERNET DRAFT DPAC September 2001 3.2 Paging area composition A paging area PA relative to a given cell A and of a given size S, can be composed as follows: PA={A}; \\initially the paging area contains \\only one cell. i=1; while (i A,B,C,D / A paging agent ----------+ +----> R1\ A,C,D / C +---------+ +---> R2\ C,D / +------+ R3\ D +---> Figure 2. Illustration of paging a DMH on a paging area comprising the nets A,B,C,D. 6.0 How to support DPAC in current DMHA protocol proposals? In MIPv6HP [HP] dormant mode state is hold by a MAP [HMIP]. MAPs can be augmented with CSA functionality for sampling and paging area composition. The MAP will be responsable for sampling and composing the paging areas relative to the cells in its domain. Samples can be sent along with dormant mode registrations (in a Binding Update sub-option). Paging area request and reply messages can be also defined as Binding Update sub-options. In LH-DMHA [LH], the last contacted access router holds the dormant mode state. The CSA function can be implemented on a MAP or a dedicated machine. Then, LH-DMHA can be augmented with a message exchange between the CSA and each access router in its domain. In this case, the CSA will configure paging areas as described above and send each access router in its domain the paging area relative to the cell served by that access router. The access router will cache this information, and periodically (once per week for example) update it by requesting the CSA a new one in order to adapt to some changes in paging area shape. Paging area request and reply messages can be defined in TLV formatted LH-DMHA messages. 7.0 Picking the paging area size Manual configuration of paging area sizes is considered difficult. A cellular operator faces an impossible decision: 1. If I choose large paging areas, then I'll increase the cost of paging, 2. If I choose small paging areas, then I'll increase the rate of registrations and battery consumption. What do to? In current systems, cellular operators choose fixed paging area sizes. This is by no means optimal. DPAC will support adaptive schemes with per-host and time-varying paging area sizes (picked by each individual host) [ADAPT]. This scheme minimizes the costs of location tracking and provides better Mutaf, Castelluccia Expires February, 2001 [Page 6] INTERNET DRAFT DPAC September 2001 power savings. The idea is quite simple: If a host moves slowly, then the paging area for that host can be small since the cost of registrations will be small. On the other hand, if a host rarely receives incoming sessions, the paging area for that host can be large since the cost of paging will be small. If the DMHA protocol is DPAC compatible (as described in Section 5), a host can request its paging agent a paging area of a personally defined size which adapts well to its mobility and incoming session rate characteristics. This way paging area sizes can be also auto-configured. 8.0 Security considerations Security issues with relevance to paging area auto-configuration, are not discussed in this document. 9.0 Conclusion The flexibility of IP paging allows dynamic paging area configuration. With auto-configured, adaptive paging area shapes and flexible paging area sizes, this can be regarded as the major advantage of having L3 paging areas. In this document we proposed dynamic paging area configuration extensions to IP paging. References [PROB] J. Kempf, "Dormant Mode Host Alerting ("IP Paging") Problem Statement", RFC 3132, June 2001. [REQ] J. Kempf, et al., "Requirements and Functional Architecture for an IP Host Alerting Protocol", RFC 3154, August 2001. [SGM] R. Boivie, et al., "Small Group Multicast", draft-boivie-sgm-02.txt, February 2001, Work in Progress. [HMIP] H. Soliman, et al. "Hierarchical MIPv6 Mobility Management", draft-ietf-mobileip-hmipv6-04.txt, July 2001, Work in Progress. [LH] Y. Ohba, et al., "LH-DMHA - Last Hop DMHA (Dormant Mode Host Alerting) Protocol", draft-ohba-seamoby-last-hop-dmha-01.txt, August 2001, Work in Progress. [RP] B. Sarikaya, et al., "Mobile IPv6 Hierarchical Paging", draft-sarikaya-mobileip-mipv6hp-00.txt, July 2001, Work in Progress. [ADAPT] C. Castelluccia, "Extending Mobile IP with Adaptive Individual Paging: A Performance Analysis", ACM Mobile Computing and Communications Review (MC2R), April 2001. Mutaf, Castelluccia Expires February, 2001 [Page 7] INTERNET DRAFT DPAC September 2001 Authors' Addresses Pars Mutaf INRIA Rhone-Alpes 655 avenue de l'Europe 38330 Montbonnot Saint-Martin FRANCE email: pars.mutaf@inria.fr phone: +33 4 76 61 55 07 fax: +33 4 76 61 52 52 Claude Castelluccia INRIA Rhone-Alpes 655 avenue de l'Europe 38330 Montbonnot Saint-Martin FRANCE email: claude.castelluccia@inria.fr phone: +33 4 76 61 52 15 fax: +33 4 76 61 52 52 Mutaf, Castelluccia Expires February, 2001 [Page 8] INTERNET DRAFT DPAC September 2001