INTERNET-DRAFT X. Zhang J. Castellanos A. Campbell Columbia University K. Sawada Fujitsu Limited, Japan M. Barry Broadcom, Eire July 2000 P-MIP: Minimal Paging Extensions for Mobile IP draft-zhang-pmip-00.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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 As the number of Mobile IP users grow so will the signaling overhead on the core IP network in support of mobility management. In cellular networks registration and paging techniques are used to minimize the signaling overhead and optimize the mobility management performance. Currently, Mobile IP supports registration but not paging. We believe that Mobile IP support for paging is important to improve the scalability of Mobile IP networks. Recently, a number of micro- mobility protocols [8] have been proposed that have built-in paging functions. These micro-mobility protocols are independent of the base Mobile IP protocol and interwork with Mobile IP [2] through mobile gateways. We take a different approach and propose a minimal set of paging extensions to the base Mobile IP called P-MIP. P-MIP is designed to reduce signaling load in the core Internet and power consumption of mobile nodes. In this draft, P-MIP, which assumes the use of foreign agents, is described and the construction of paging areas, movement detection, registration, paging and data handling are presented. Zhang, Sawada, Castellanos, Campbell, Barry Expires Jan 15,2001 [Page 1] INTERNET-DRAFT P-MIP July 2000 Table of Contents 1. Introduction 2 1.1 Goals. . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2 Assumption . . . . . . . . . . . . . . . . . . . . . . . . 3 1.3 Terminology. . . . . . . . . . . . . . . . . . . . . . . . 3 1.4 Protocol Overview. . . . . . . . . . . . . . . . . . . . . 4 1.5 Message Format and Protocol Extensibility. . . . . . . . . 5 1.5.1 New ICMP Router Discovery Message Extension . . . . 5 1.5.2 New Control Messages. . . . . . . . . . . . . . . . 5 1.5.3 New Extension in Mobile IP Control Message. . . . . 6 1.5.4 Modification to Registration Request Message in MIP 7 2. Protocol Description 7 2.1 Paging Areas . . . . . . . . . . . . . . . . . . . . . . . 7 2.2 Movement Detection . . . . . . . . . . . . . . . . . . . . 10 2.2.1 Movement Detection in within a Paging Area . . . . 10 2.2.2 Movemnet between paging Areas. . . . . . . . . . . 10 2.3 Registration . . . . . . . . . . . . . . . . . . . . . . . 11 2.4 Paging . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.5 Data Handling. . . . . . . . . . . . . . . . . . . . . . . 13 2.5.1 Incoming Data . . . . . . . . . . . . . . . . . . . 13 2.5.2 Outgoing Data . . . . . . . . . . . . . . . . . . . 14 3. Security Considerations . . . . . . . . . . . . . . . . . . . . 14 4. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 1. Introduction We envision a wireless Internet with many hundreds of millions of wireless subscribers. As the number of mobile subscribers grows so does the need to provide efficient location tracking that limits the signaling load introduced in the core IP network. The vast majority of wireless IP subscribers will not be actively communicating most of the time. Rather, mobile nodes will be in an idle state but passively connected to the network infrastructure. As a result, it will be sufficient for the wireless Internet only to know the approximate location of its population of idle users. The exact location of idle mobile nodes only becomes important when data needs to be forwarded to them in which case the network protocols need to be able to efficiently search and find these users in a scalable and timely manner. This process is called paging. While paging minimizes the need for mobiles to register their exact location it introduces paging overhead in terms of new signaling and delays. It is therefore important to balance paging and registration in order to optimize system performance. In this draft we provide an overview of P-MIP and discuss its implementation. For more details, see [1]. Zhang, Sawada, Castellanos, Campbell, Barry [Page 2] INTERNET-DRAFT P-MIP July 2000 1.1 Goals Reducing the signaling load in the core IP network and the power consumption of mobile nodes through the introduction a minimal set of paging extensions to the base Mobile IP protocol [2]. 1.2 Assumption Foreign agents are present on foreign networks and mobile nodes register through foreign agents. 1.3 Terminology Active Mode A mobile node is in active mode if it has recently sent or received data. A mobile node is considered to be active for an active time period starting from the instance the node sends or receives data. Active Mobile Node The mobile node in active mode. Active Time Period The number of seconds a mobile node is considered as active. It is implementation dependent. Active Timer The timer used to record the time when a mobile node is in active mode. Each time the mobile node sends or receives data the timer is reset. When the timer expires the mobile node enters idle state. Care of Address (CoA) As defined in [2]. Current Foreign Agent The foreign agent of the network which a mobile node is currently visiting. Foreign Agent As defined in [2]. Foreign Network As defined in [2]. Home Address As defined in [2]. Home Agent As defined in [2]. Home Network As defined in [2]. Zhang, Sawada, Castellanos, Campbell, Barry [Page 3] INTERNET-DRAFT P-MIP July 2000 Idle Mode A mobile node is in idle mode if it has not recently sent or received data. Idle Mobile Node A mobile node in idle mode. Whenever an idle node sends or receives data, its mode is changed to active and its active timer started. In this case an idle mobile node becomes an active mobile node. Mobile Node State Mobile node state consists of a per-node tuple (operational mode, active timer). Operational mode can be active mode or idle mode. Mobile node state is kept in both mobile nodes and registered foreign agents. Mobility Binding As defined in [2]. Paging Area (PA) The area on which a registered foreign agent conducts paging. A PA consists of two or more networks. When an idle mobile node moves within a paging area, it does not register. Paging Request Message A message sent by a registered foreign agent in order to locate an idle mobile node. Paging Reply Message A message sent by a paged mobile node to the registered foreign agent to inform it of the paged mobile node's current location. Registered Foreign Agent The foreign agent of the network through which a mobile node has registered just before the mobile node receives a Paging Request. That is, the foreign agent through which a mobile node made its latest registeration with its home agent. Thus, the mobile node's care-of-address in its home agent's mobility binding is provided by the registered foreign agent. Note, a mobile node and its registered foreign agent may be in different networks. Security Parameter Index (SPI) As defined in [2]. 1.4 Protocol Overview An active mobile node behaves in exactly the same manner as in Mobile IP [2]. When it changes its point of attachment, it registers. For an idle mobile, when it moves within a paging area, it does not register. However, when an idle mobile node moves to a different paging area, it registers. When there are packets destined to a mobile node, its home agent Zhang, Sawada, Castellanos, Campbell, Barry [Page 4] INTERNET-DRAFT P-MIP July 2000 forwards data to its registered foreign agent. The registered foreign agent first checks if it has the mobile node's information on record. If it has a record, then it checks if the mobile node supports paging or not. If the mobile node supports paging, then the registered foreign agent checks the mobile node's state. If the mobile node is in active mode, the registered foreign agent decapsulates packets and sends them to the mobile node, just as in the case of Mobile IP [2]. If the mobile node is in idle mode, the registered foreign agent sends a Paging Request message to other foreign agents in the same paging area as well as to its own network. When the mobile node receives a Paging Request message, it registers through the current foreign agent to its home agent. After receiving a Registration Reply message, the mobile node sends a Paging Reply message back to its registered foreign agent through its current foreign agent to inform the registerd foreign agent of its current location. When the registered foreign agent receives a Paging Reply message, it forwards buffered packets to the mobile node through its current foreign agent. 1.5 Message Format and Protocol Extensibility 1.5.1 New ICMP Router Discovery Message Extension Paging area ID (PAI) extension: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | PAI | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ This PAI extension is used in non-overlapping paging area construction (see Section 2.1). It should be added in agent advertisement message and periocally broadcast on the network. 1.5.2 The New Control Messages Paging Request: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | length | reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | the home address of paged mobile node 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | the home address of paged mobile node 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extensions ... Zhang, Sawada, Castellanos, Campbell, Barry [Page 5] INTERNET-DRAFT P-MIP July 2000 +-+-+-+-+-+-+-+-+-+ length = 2 + 4 * N (bytes), where N is the number of mobile nodes paged. length does not cover the type, length and extensions fields. Paging response: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | length | reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | the home address of paged mobile node 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | the care-of address of paged mobile node 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extensions... +-+-+-+-+-+-+-+- length = 2 + 8 * N (bytes), where N is the number of responding mobile nodes. length does not cover the type, length, and extensions fields. 1.5.3 New Extension in Mobile IP Control Message Foreign-Foreign Authentication Extension: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | length | SPI... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... SPI (cont.) | Authenticator ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Paging Area ID Extension: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | length | reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IP address of FA1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IP address of FA2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IP address of FA3 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+- Paging Area ID extension is used for overlapping paging area construction. This extension represents a list of foreign agent IP Zhang, Sawada, Castellanos, Campbell, Barry [Page 6] INTERNET-DRAFT P-MIP July 2000 addresses in the same paging area. It should be inserted in the Registration Reply message. 1.5.4 Modification to Registration Request Message in Mobile IP the modified bit | 0 1 V 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type |S|B|D|M|G|V|P|r| Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Home Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Home Agent | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Care-of Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Identification + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extensions ... +-+-+-+-+-+-+-+- Change one of the reserved bits in the Registration Request message used in Mobile IP to the P bit which indicates if the mobile node supports the paging function or not. A P bit of '1' means that the mobile node supports paging and a P bit of '0' means that the mobile node does not support paging. 2. Protocol Description 2.1 Paging Areas A paging area consists of two or more networks and has a unique paging area ID (PAI). Paging areas can be configured based on a number of criteria (e.g., node mobility, traffic patterns, mobile density, etc.) so that most mobile nodes move within the same paging area. Paging areas can be configured manually by administrators setting parameters at each foreign agent or more automatically by having foreign agents interact with paging servers. The benefit of paging servers is that the administrator only needs to configure the server. In this case, each foreign agent acquires its paging area information directly orom the server. Foreign agents and mobile nodes are aware of their paging area based on the PAI. There are two types of paging area construction in P-MIP called non- overlapping and overlapping paging areas. In the case of non- overlapping paging areas, a network can only be associated with one paging area, as shown Figure 1. Zhang, Sawada, Castellanos, Campbell, Barry [Page 7] INTERNET-DRAFT P-MIP July 2000 Internet | | | | + --- | ------- | --+ +-- | ------- | ---+ | | | | | | | | | +--+--+ +--+--+| |+--+--+ +--+--+ | | | FA1 | | FA2 || || FA3 | | FA4 | | | +-----+ +-----+| |+-----+ +-----+ | | | | | +-------- PA1 ------+ +------ PA2 -------+ Figure 1: Non-overlapping Pagin Areas In the non-overlapping scheme, each paging area has a unique paging area ID. Paging area IDs can be reused in the same sense as spatial reuse, with adjacent paging areas having different IDs. Paging area ID assignment could follow the same lines as IP addresses, with authorized organizations managing their allocation and assignment. A paging table is maintained by each foreign agent and can be manually set or configured by a paging server or an administrator. In P-MIP, the agent advertisement message is extended to carry the paging area ID, as shown in the Section 1.5. The agent advertisement message must be broadcast periodically so that the paging area ID can be periodically distributed. Paging tables for the non-overlapping scheme have the following format: ------------------------- PAI | xxxx xxxx -----+------------------- FA1 | FA1's IP address FA2 | FA2's IP address FA3 | FA3's IP address . | . . | . . | . In the case of non-overlapping paging only the PAI value (0000-FFFFH) is transmitted in agent advertisement messages and not the list of FA IP addresses. In the case of overlapping paging areas, the paging area ID is made up of the entire list of foreign agent IP addresses in a paging area. This is different to the PAI for non-overlapping paging area where PAI is a two-byte value. The paging area ID in the overlapping scheme does not need to be broadcast periodically as is the case in non- overlapping paging IDs. Rather, the paging area ID is sent to mobile nodes using an extended registration reply message, as shown in Section 1.5. Each foreign agent maintains a paging table which is also the paging area ID in the case of the overlapping scheme. A paging table in the overlapping scheme can be manually configured and has the following format: Zhang, Sawada, Castellanos, Campbell, Barry [Page 8] INTERNET-DRAFT P-MIP July 2000 ------------------------- FA1 | FA1's IP address FA2 | FA2's IP address FA3 | FA3's IP address . | . . | . . | . Each paging scheme has a number of advantages and disadvantages. In the case of non-overlapping paging areas, a paging ID (i.e. two- octets value) is much shorter than overlapping paging IDs (i.e. multiple IP addresses). Therefore, the bandwidth and power consumed to manage paging IDs will be more efficient in the case of non- overlapping areas. However, this scheme can not take advantage of overlapping paging areas. As a result, there will be a disproportionate amount of registration traffic generated at paging area borders. With overlapping paging areas, the paging area ID could be rather large when there is a large number of foreign agents in a paging area. In this case, each mobile node must be aware of all the foreign agent IP addresses in the paging area. Mobile nodes need to be capable of maintaining this state information in order to detect if they have moved to a different paging area. Overlapping paging area information is not transmitted periodically so that the impact on radio resources and mobile node resources is limited. The maximum benefit of the overlapping scheme is achieved when each foreign agent is located at the center of its paging area. As shown in Figure 2, foreign agent FA2 is located at the center of paging area PA2, FA3 is located at the center of PA3, and so on. Whenever a mobile node registers, it will get a new paging area ID (i.e., the list of foreign agent IP addresses in the paging area). This allows the mobile node to position itself at the center of the new paging area when it has to register. In this case, registration initiated by crossing new paging area borders is reduced and it allows for an even distribution of registration traffic. This approach would further reduce the signaling associated with mobile nodes that move around paging area borders particularly in the case of non-overlapped paging areas. Internet | | | | | +--- | ------- | ------- | ---+ + --- | ---|--- | ------- | -- + | | | | | | | | | | | +--+--+ | +--+--+ +--+--+ | +--+--+ | | | FA1 | | | FA2 | | FA3 | | | FA4 | | | +-----+ | +-----+ +-----+ | +-----+ | | | | | +----------|---PA2-------------+ | +-------------PA3-------------+ Figure 2: Overlapping Paging Areas Zhang, Sawada, Castellanos, Campbell, Barry [Page 9] INTERNET-DRAFT P-MIP July 2000 Based on the paging area scheme selected, P-MIP operates differently such as in the case of movement detection. In this draft, we highlight these operational differences by referring to the two paging schemes discussed above. 2.2 Movement Detection 2.2.1 Movement within a Paging Area The algorithms used to detect if a mobile node has moved to a different network are the same for P-MIP as Mobile IP [2]. Two algorithms are used for movement detection in Mobile IP. In the first approach, mobile nodes detect movement using agent advertisement messages and the advertisement lifetime. When a mobile node receives an agent advertisement the lifetime of the advertisement is included in the message. If a mobile node does not receive another advertisement before the advertisement lifetime expires then the mobile node assumes that it has moved to a different network. In the second approach, a mobile node compares the network prefix obtained from newly received agent advertisement message with the current CoA. If they are different, the mobile will assume it has moved to a different network. If a mobile node is in active mode when it detects it has moved then a handoff is initiated which invokes the registration procedure. In this case, the mobile node's location will be updated at both the foreign and home agents. In contrast, if a mobile nodes is in idle state and it detects it has moved to a new network within the same paging area then no registration is necessary. However, if an idle mobile node does not have a valid foreign agent on record then it should locate one for further movement detection and registration. 2.2.2 Movement between Paging Areas The algorithms used to detect movement between paging areas are different based on the paging area scheme. In the case of non-overlapping paging areas, a mobile node records the lifetime received in agent advertisements until the lifetime expires. If a mobile node fails to receive another advertisement from the same agent within the specified lifetime then the mobile node assumes that is has lost contact with the foreign agent. If the mobile node has previously received an agent advertisement from another foreign agent for which the lifetime field has not yet expired then the mobile node should check if the paging area ID from the new agent is the same as its current paging ID. If the IDs are the same then the mobile node will do nothing except keep tracking the foreign agents identified in the advertisements. If the paging IDs are different then idle mobile nodes should immediately register with the new foreign agent. If the mobile node is not in contact with any foreign agent then it should send out an agent solicitation message. Upon reception of an agent advertisement message, the mobile node should check if the new paging area ID is the same as the old Zhang, Sawada, Castellanos, Campbell, Barry [Page 10] INTERNET-DRAFT P-MIP July 2000 one. It uses this test to determine whether it has moved to a different paging area. In the case of overlapping paging areas, a mobile node should record the lifetime received in agent advertisements until that lifetime expires. If a mobile node fails to receive another advertisement from the same agent within the specified lifetime then the mobile node assumes that it has lost contact with the agent. If the mobile node has previously received an agent advertisement from another foreign agent for which the lifetime field has not yet expired then the mobile node should check if the source IP address of the agent advertisement sent by the new foreign agent is in the current paging ID's foreign agent list. The current foreign agent list is obtained in the registration reply message. If the new foreign agent's IP address is not in the current foreign agent list then idle mobile node registers with the new foreign agent. If the mobile node is not in contact with a foreign agent then it should send out an agent solicitation message. Upon reception of a advertisement message, the mobile node should check if the new foreign agent's IP address is in the current foreign agent list or not. It uses this test to determine whether it has moved to a new paging area or not. 2.3 Registration Registration follows the same procedure as Mobile IP [2]. However, after receiving a registration reply message both the foreign agent and the mobile node update the mobile node state by setting the the operational mode to active state and starting the active timer. In the case of the overlapping paging areas scheme, the registration reply message includes the paging area ID. The mobile node records the paging area ID. The list of foreign agents in the paging area that represents the paging ID is inserted by the foreign agent in the registration reply message returned to the mobile node. An important performance difference between Mobile IP and P-MIP relates to the number of registration generated. P-MIP reduces signaling in comparison to the base Mobile IP protocol because idle mobile nodes do not register when moving between networks in the same paging area. For an evaluation Of P-MIP see [1]. In Mobile IP, a mobile node registers when: o a mobile node changes its point of attachment; o a mobile node's registration lifetime is near expiration (we call this registration refresh); and o a mobile node detects that its current foreign agent has rebooted. In P-MIP, a mobile node registers when: o a mobile detects it has moved to a new paging area; o a mobile node's registration lifetime is near expiration; o a mobile nodes detects that its current foreign agent has rebooted; o a mobile node is paged and is not on the same network as the paging Zhang, Sawada, Castellanos, Campbell, Barry [Page 11] INTERNET-DRAFT P-MIP July 2000 foreign agent; and o an idle mobile node is about to transmit data. 2.4 Paging When a foreign agent needs to locate an idle mobile node, it broadcasts a paging request message in its network, and at the same time, unicasts the message to all other foreign agents in its paging area. These foreign agents then broadcast the page within their own wireless networks. The paging request message lists the home addresses of all paged mobile nodes, as shown in the Section 1.5. P- MIP supports the optimization that a foreign agent may have a number of paging request to make at any one moment. In this case P-MIP can aggregate all mobile nodes paging requests into a single paging request message. This helps to minimize the paging overhead as the number of paged mobile nodes grow. When a foreign agent receives a paging request, it first conducts an authentication check if the foreign agents share a mobility security association. If authentication is passed, the foreign agent broadcasts the paging message on its own network. When a mobile node finds its home address in the paging request and the message is directly from its registered foreign agent then the mobile node is still located in the same network. In this case, the mobile node sends a paging reply back to its registered foreign agent without registering, and then sets its operational mode to active and restarts its active timer. Otherwise, the mobile node will first start the registration procedure to make sure that the binding between its home address and new CoA from its current foreign agent is valid. Following this the mobile node responds to the paging request by sending a paging reply. The mobile node will insert its CoA in the paging reply. To avoid potential collisions between signaling messages (i.e., registrations and paging reply messages) from multiple paged mobiles in the same network, the transmission time for each registration and paging reply (to a foreign agent) is randomized. A foreign agent conducts authentication checks on paging reply messages received from paged mobile nodes if the foreign agent and the mobile nodes share a secure association. If a foreign agent is not the registered foreign agent, then it will forward the paging reply message to the registered foreign agent which initiated paging. It does this after appending the foreign agent to foreign agent authentication extension in the message. If the foreign agent is the mobile node's registered foreign agent, then it updates the mobile node state by setting the operational mode to active and starting the active timer. The registered foreign agent originating paging removes the mobile node ``record'' associated with all paged mobile nodes that are not located in its network after receiving a paging reply. The registered foreign agent takes this action because it assumes that these mobile nodes have initiated new registrations. The term ``record'' used in this draft refers to Mobile IP mobility management related Zhang, Sawada, Castellanos, Campbell, Barry [Page 12] INTERNET-DRAFT P-MIP July 2000 information maintained by a home agent, foreign agent and mobile node. A record comprises transient state information that includes the mobile nodes home address, home agent address, CoA and various timer related information associated with control messages (e.g., registration lifetime, etc.). The registered foreign agent will retransmit the paging request after a paging period if no response is received to an earlier paging request. The paging period is implementation dependent. If a mobile node's registration lifetime expires during paging then the registered foreign agent stops paging the mobile node. Each successive paging period should be at least twice the previous duration. After sending three successive paging request the foreign agent assumes that the mobile is not in the paging area and removes the record associated with this mobile. Once a paging reply is received by the registered foreign agent then any buffered data for the paged mobile node is forwarded toward the mobile node. 2.5 Data Handling When a mobile node is on a foreign network incoming and outgoing data to and from the mobile, respectively, are handled as follows. 2.5.1 Incoming Data When there are incoming packets destined to a mobile node, the mobile node's home agent forwards data to its CoA which belongs to the mobile node's registered foreign agent. When the registered foreign agent receives the data, it first determines whether it has a record for the mobile node. If it has a record, then it checks if the mobile node supports a paging function which is determined based on the P bit in Registration Request message (see Section 1.5). If P bit is set to '1', then it means the mobile node supports paging function. In contrast, if the P bit is set to '0', then it means the mobile node does not support a paging function or does not need a paging function (e.g., when the mobile node stays in a network for a long period of time). If the mobile node supports paging then the registered foreign agent checks the mobile node state. If the mobile node is in an active state then it is likely that the mobile node is located on the same network. In this case, the foreign agent decapsulates packets and forwards them to the mobile node. As discussed above, the originating foreign agent sends a paging request if the mobile node is in idle state, and at the same time, buffers the data for the mobile node. When the originating foreign agent receives a paging reply it forwards any buffered data to the mobile node. If the mobile node is not in the registered foreign agent's network any more then the registered foreign agent removes the mobile node's record. In the case that a mobile node does not respond to multiple page requests the registered foreign agent removes the mobile node's Zhang, Sawada, Castellanos, Campbell, Barry [Page 13] INTERNET-DRAFT P-MIP July 2000 record and send an ICMP message ``node not found'' to the home agent. 2.5.2 Outgoing Data In active mode a mobile node can simply send data. If the mobile node is idle it first determines if it is still located on the same network where it is currently registered by checking agent advertisement lifetime or by sending an agent solicitation message. If the mobile node resides on the same network then it sets the operational mode to active and starts the active timer before transmitting data. If a mobile node is on a different network then it initiates a registration procedure to update its location record in its home agent and foreign agent. It is very likely that a mobile that is sending out going data will also receive data in return. Therefore, the home agent and foreign agent bindings need to be updated to facilitate the delivery of incoming data to the mobile node. In order for a foreign agent to track a mobile node's operational state, both outgoing and incoming data should be routed through the current foreign agent. Therefore, the foreign agent should act as a routing point for outgoing data as well as decapsulating and forwarding incoming data. 3. Security Considerations The authentication method used in P-MIP is the same as in Mobile IP [2]. If a mobility security associations exist among foreign agents in a paging area then the foreign agent to foreign agent authentication extension should be attached at the end of the paging request and reply messages. If a mobility security association exists between a foreign agent and a mobile node then the mobile node to foreign agent authentication extension should be attached at the end of the paging request and reply messages. 4. References [1] X. Zhang, K. Sawada, J. Castellanos, A. Campbell, "P-MIP: Minimal Paging Extensions for Mobile IP," In submission to WMCSA 2000 - Third IEEE workshop on Mobile Computing Systems and Application, June, 2000. http://comet.columbia.edu/pmip. [2] C. Perkins, "IP Mobility Support," RFC 2002, IETF, Oct. 1996. [3] A. Campbell, J. Gomez, C-Y. Wan, Z. Turanyi, and A. Valko, "Cellular IP," Internet Draft, IETF, 1999. [4] R. Ramjee, T. La Porta, S. Thuel, K. Varadhan, and L. Salgarelli, "IP Micro-mobility support using HAWAII," Internet Draft, IETF, Dec. 1999. [5] R. Ramjee, T. La Porta, and L. Li, "Paging support for IP mobility using HAWAII," Internet Draft, IETF, Mar. 2000. Zhang, Sawada, Castellanos, Campbell, Barry [Page 14] INTERNET-DRAFT P-MIP July 2000 [6] E. Gustafsson, A. Jonsson, and C. Perkins, "Mobile IP Regional Registration," Internet Draft, IETF, Mar. 2000 [7] C. Castelluccia, "Extending Mobile IP with Adaptive Individual Paging: A Performance Analysis," INRIA, Nov. 1999. http://www.inrialpes.fr/planete/people/ccastel/Welcome.html#PUB [8] A. Campbell, J. Gomez, S. Kim, C-Y Wan, Z. Turanyi, and A. Valko, "Comparison of Micro-mobility Protocols," Internet Draft, IETF, July 2000. Authors' Addresses Xiaowei Zhang, Javier Castellanos, Andrew Campbell, Kentaro Sawada, Micheal Barry Department of Electrical Engineering, Columbia University Rm. 807 Schapiro Research Building 530 W. 120th Street, New York, NY 10027 Phone: (212) 939-7157 email: {xzhang, sawaken, javierg, campbell}@comet.columbia.edU Zhang, Sawada, Castellanos, Campbell, Barry Expires Jan 15,2001 [Page 15]