INTERNET-DRAFT Subrata Goswami Expires February 10, 2003 Independent Consultant Sept 09, 2002 Simultaneous Handoff in Mobile-IPv4 and 802.11 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. 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 RFC 2119 [RFC 2119]. Abstract This document describes a way to perform simultaneous Mobile-IPv4 handoff and 802.11 Access Point Association/Reassociation. This is an attempt to seek comments and critique on this approach. 1. Overview and Rationale In the 802.11 wireless lan [WiFi] network an 802.11 client connects to an 802.11 Access Point (AP) at the link level. 802.11 provides a mechanism to achieve handoffs between AP's and the client. A 802.11 client first authenticates and then associates with one AP. When the 802.11 client decides that it is better to move to a second AP, it can do a pre-authentication and re-association with the second AP. Similarly when a Mobile-IPv4 (MIP4) client move from subnet to subnet it seeks a Foreign Agent (FA) situated in the subnet and registers with the FA. The IP packet sent in Registration Message has the Home IP address as the source, and the destination address can be the FA's IP address or the "All Mobility Agents" multicast address (224.0.0.11). The FA then responds with Registration Reply message. The Registration Message also includes Authentication Extensions. There is no obvious reason why the Mobile Node (MN) has to go through the authentication and association/registration twice. It would be beneficial to subsume the authentication and registration of MIPv4 to be completed during the 802.11 Authentication and Association exchanges. 2. 802.11 Network Architecture. A hypothetical IP over 802.11 network is shown in the following figure. The mobile client MN can move from subnet X1 to X2 and from AP2 to AP3. [FA1] | ... [AP1]-------[X1]--| [MN]... | | [AP2]---- |----[X]-----> [HA] | [AP3/FA3]---[X2]--| [MN] - Mobile Node [FA] - Foreign Agent [HA] - Home Agent [AP] - Access Point [X] - IP Router ... - 802.11 link --- - 802.3 link Figure 1: 802.11 Network 3. Message Sequence The following figure shows the what happens when MN move from AP1 to AP2 to AP3. During the AP1 to AP2 handoff, the MN is in same subnet, hence MIPv4 registration is not required. The MN has no good way to figure that it is still within the same subnet, hence it sends a MIPv4 Registration Message element in the 802.11 Association Message. The FA responds with MIPv4 reply which can be generated without doing a FA to HA message sequence. MN AP1 AP2 AP3 ------ Authentication Request------> <------Authentication Response----- -------Authentication Response-----> <------Authentication Response----- -------Reassociation Request -----> (MIPv4 Registration included but not reqd.) <------Reassociation Response----- (MIPv4 Reply included) . . ------ Reassociation Request--------------------------> (MIPv4 Registration included) <------Reassociation Response------------------------- (MIPv4 Reply included) Figure 2. 802.11/MIPv4 Message Sequence 4. Additional Information Elements in 802.11 Management Frames The 802.11 Association/Reassociation frames are shown in the following figure. The Association/Reassociation frames carry an optional MIPv4 information element. The MIPv4 Registration Request message is contained in the 802.11 Association/Reassociation Request messages. The MIPv4 Registration Reply message is contained in the 802.11 Association/Reassociation Response messages. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Frame Control | Duration | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Destination Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Source Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Basic Service Set ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Sequence Control | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Capability Information | Listen Interval | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Current AP Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Current AP Address | SSID (2-34 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Supported Rates (3-7 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . + MIPv4-802.11 Registration Request + . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Frame Check Sequence | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3. 802.11 (Re) Association Request Frame In Figure 3., 802.11 Association Reassociation frames differ primarily in the absence of the Current AP address field from the first. The MIPv4-802.11 element is an 802.11 Information Element (IE) with a unique Element ID (say 128) (see page 55 of [WiFi]). The 802.11 Information Element consists of the following fields: Element ID, Length ID, and Information. The length field is 1 octet long and specifies the length of the Information field in number of octets. Thus the MIPv4-802.11 can be at most 255 octets, and as such it would be a waste to put the full IP and UDP header. Hence a psuedo-IP and psuedo-UDP header is used. The pseudo-IP header is composed of Source and Destination IP addresses. The destination address can be the FA's IP address or the "All Mobility Agents" multicast address (224.0.0.11). The Source IP address is the Home Address of the MN. The pseudo-UDP header is composed of Source Port and Destination Port. The rest of the MIPv4-802.11 is the MIPv4 fields. Figure 4 below shows the MIPv4-802.11 Information Element. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Element ID | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source IP Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Destination IP Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | UDP Source Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | UDP Destination Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type |S|B|D|M|G|V|rsv| Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Home Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Home Agent | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Care-of Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Identification + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extensions ... +-+-+-+-+-+-+-+- Figure 4. MIPv4-802.11 Registration Request Information Element Similarly a MIPv4-802.11 Registration Reply IE is defined which has the same format as Request IE's. The Source IP Address is the unicast IP address of the FA. The Destination IP Address is copied from the IP Source Address of the corresponding Registration Request IE. The UDP ports are also copied from the Registration Request IE, with the destination and source exchanged. 5. Acknowledgments All the RFC's, freely available 802.11 standards, and Linux web-sites. 6. References [WiFi] IEEE, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications", 1999. [MIPv4] Bradner, S., "IP Mobility Support", RFC 2002, October 1996. 7. Author's Address Dr. Subrata Goswami Independent Consultant Newark, CA 94560 sgoswami@umich.edu This document expires February 10, 2003.