RFC 4830
Problem Statement for Network-Based Localized Mobility Management (NETLMM)
Problem Statement for Network-Based Localized Mobility Management (NETLMM) 🦋
okay bestie, this one is an Informational RFC from April 2007, written by J. Kempf, Ed. from DoCoMo USA Labs 💅 It's from the Network Working Group, and the header doesn't list anything it obsoletes or updates, so it's a standalone problem statement 🎀
Status of This Memo ✨
This memo gives information to the Internet community. It does not specify an Internet standard of any kind, and distribution of it is unlimited 💖
Copyright Notice 🌸
Copyright (C) The IETF Trust (2007).
Abstract 🧚
okay so localized mobility management is already a well-known concept at the IETF, and there are already solutions for it 🔥 This doc looks at the big problems with those existing solutions. Basically, they all make the host do the mobility work, and it argues for doing local mobility management in the network instead 👑
Table of Contents
1. Introduction ....................................................2
1.1. Terminology ................................................3
2. The Local Mobility Problem ......................................4
3. Scenarios for Localized Mobility Management .....................7
3.1. Large Campus ...............................................7
3.2. Advanced Cellular Network ..................................7
3.3. Picocellular Network with Small But Node-Dense Last
Hop Links ..................................................8
4. Problems with Existing Solutions ................................8
5. Advantages of Network-based Localized Mobility Management .......9
6. Security Considerations ........................................10
7. Informative References .........................................10
8. Acknowledgements ...............................................11
9. Contributors ...................................................121. Introduction 💖
Localized mobility management has been a hot topic in the IETF for a while 💅 Earlier work gave us Fast-Handovers for Mobile IPv6 (FMIPv6) [13] and Hierarchical Mobile IPv6 (HMIPv6) [18]. Both are experimental protocols, and both are host-based, meaning the host has to get involved at the IP layer, similar to or on top of what Mobile IPv6 [10] needs for global mobility management 😭
But a few recent things are giving "maybe it's time for a fresh look" energy ✨
First, there's new IETF work on global mobility management protocols that aren't Mobile IPv6, like Host Identity Protocol (HIP) [16] and IKEv2 Mobility and Multihoming (MOBIKE) [4]. So future wireless IP nodes might support a more varied mix of global mobility protocols 🦋 Existing localized protocols could be used with HIP and MOBIKE, but some would take extra work to implement, deploy, or in some cases even specify in a non-Mobile IPv6 mobile environment 🙈
Second, WLAN switches have been doing really well in the WLAN infrastructure market 🔥 They do localized management without touching the host's stack at all. That suggests a possible paradigm that could support other global mobility options on the mobile node while cutting host stack software complexity and letting more kinds of mobile nodes join the party 🌈
This document gives a quick overview of the general local mobility problem and the scenarios where localized mobility management would be useful 🧚 Then it briefly covers the problems with existing or proposed IETF localized mobility management protocols. It also presents the network-based mobility management architecture and explains how that architecture fixes those problems ✨ For a deeper dive into goals for a network-based localized mobility management protocol, and a gap analysis of existing protocols, check out [11] 🎀 Also, IPv6 and wireless links are the initial scope here, so the language reflects that. That said, the conclusions apply just as well to IPv4 and wired links where nodes disconnect and reconnect 💜
1.1. Terminology 🍓
Mobility terminology in this document follows RFC 3753 [14], plus a few new and revised terms defined below 💅
WLAN Switch
A WLAN switch is a multiport bridge Ethernet [8] switch that connects network segments. It also allows a physical and logical star topology, and it runs a protocol to control a bunch of 802.11 [6] access points 🔥 That access point control protocol lets the switch do radio resource management, like power control and terminal load balancing between the access points ✨ Most WLAN switches also have a proprietary protocol for inter-subnet IP mobility, usually involving some kind of inter-switch IP tunnel, which keeps sessions going when a terminal moves between subnets 💖
Access Network
An access network is a collection of fixed and mobile network components that give access to the Internet, all belonging to one operational domain 🦋 It can use multiple air interface technologies (for example, 802.16e [7], Universal Mobile Telecommunications System (UMTS) [1], and so on), interconnected with multiple types of backhaul (such as Synchronous Optical Network (SONET) [9], metro Ethernet [15] [8], and so on) 🌸
Local Mobility (revised)
Local Mobility is mobility over an access network. Heads up, though: the area of network topology the mobile node moves across might be restricted, but the actual geographic area could be pretty big 🌈 It all depends on how the network topology maps onto the wireless coverage area 🧚
Localized Mobility Management
Localized Mobility Management is a generic term for any protocol that keeps a mobile node's IP connectivity and reachability going, so sessions stay continuous when the mobile node moves, and whose signaling stays confined to an access network 👑
Localized Mobility Management Protocol
A protocol that supports localized mobility management 💅
Global Mobility Management Protocol
A Global Mobility Management Protocol is a mobility protocol the mobile node uses to change the global, end-to-end routing of packets, so sessions survive when movement causes a topology change that invalidates the mobile node's global unicast address 🔥 This could be Mobile IP [10] [17], but it could also be HIP [16] or MOBIKE [4] ✨
Global Mobility Anchor Point
A node in the network where the mobile node keeps a permanent address, plus a mapping from that permanent address to the local temporary address where the mobile node is currently located 💖 The Global Mobility Anchor Point may be used for rendezvous and possibly for traffic forwarding 🦋
Intra-Link Mobility
Intra-Link Mobility is mobility between wireless access points within a single link 🎀 It usually only involves Layer 2 mechanisms, which is why it's often called Layer 2 mobility 🙈 No IP subnet configuration is needed when the mobile node moves, since the link doesn't change 😭 Some IP signaling might still be needed so the mobile node can confirm whether switching access points also made the previous access routers unreachable 🌈 If the link is served by a single access point/router combination, this type of mobility is typically absent 💜 See Figure 1. ✨
2. The Local Mobility Problem ✨
okay so the local mobility problem is all about giving IP mobility management to mobile nodes inside one access network 🏠 the access network gateways act as aggregation routers 🛣️ and there's no fancy specialized routing protocol here (no GTP, no Cellular IP, no Hawaii, none of that) 🙅♀️ the routers just form a standard IP routed network with protocols like OSPF, Intermediate System to Intermediate System (IS-IS), RIP, etc. 💅 Figure 1 shows the access network gateway routers labeled "ANG" 🎀 and the important bit is that transitions between service providers in separate autonomous systems are excluded 🚫 same goes for crossing broader topological "boundaries" inside the same service provider 💀
Figure 1 is giving scope. It shows the local vs. global mobility vibe side by side 🦋 The Access Network Gateways (ANGs), GA1 and GB1, are the gateways to their access networks 🌸 The Access Routers (ARs), RA1 and RA2, live in access network A, and RB1 lives in access network B 🧚 It's totally possible to have extra aggregation routers between ANG GA1 and ANG GB1, plus more routers between the ANGs and the ARs if the access network is large 📈 Access Points (APs) PA1 through PA3 are in access network A, and PB1 and PB2 are in access network B 🍓 There can be other ANGs, ARs, and APs too, and other routers can separate the ARs from the ANGs 🫶 The figure implies a star topology for the access network deployment 🌟 star is the main focus because it's super common, BUT the same problems are equally relevant to ring or mesh topologies where ARs are directly connected through some part of the network 💜
Here's the diagram, bestie:
Access Network A Access Network B
+-------+ +-------+
|ANG GA1| (other ANGs) |ANG GB1| (other ANGs)
+-------+ +-------+
@ @ @
@ @ @
@ @ @ (other routers)
@ @ @
@ @ @
@ @ @
+------+ +------+ +------+
|AR RA1| |AR RA2|(other ARs) |AR RB1| (other ARs)
+------+ +------+ +------+
* * *
* * * * *
* * * * *
* * * * *
* * * * *
* * * (other APs) * * (other APs)
/\ /\ /\ /\ /\
/AP\ /AP\ /AP\ /AP\ /AP\
/PA1 \ /PA2 \ /PA3 \ /PB1 \ /PB2 \
------ ------ ------ ------ ------
+--+ +--+ +--+ +--+
|MN|----->|MN|----->|MN|-------->|MN|
+--+ +--+ +--+ +--+
Intra-link Local Global
(Layer 2) Mobility Mobility
Mobility
Figure 1. Scope of Local and Global Mobility Managementokay so as the figure shows, a global mobility protocol may be necessary when a mobile node (MN) moves between two access networks 🌍 exactly how big the access networks are depends on deployment stuff 🤷♀️ mobility between two APs under the same AR is intra-link (aka Layer 2) mobility ⚡ and it's usually handled by Layer 2 mobility protocols (if there's only one AP/cell per AR, then intra-link mobility might just be missing, lol) 🙈 and local mobility lives right in between those two. it happens when a mobile node moves between two APs connected to two different ARs 🦋
global mobility protocols let a mobile node stay reachable even when its globally routable IP address changes ✨ they do it by updating the address mapping between the permanent address and the temporary local address at the global mobility anchor point 📍 or even end to end, by changing the temporary local address directly at the node the mobile node is talking to 💬 so a global mobility management protocol can be used between ARs to handle local mobility 🙌 BUT (and this is a big but 😭) there are three well-known problems with using a global mobility protocol for every single movement between ARs. briefly, they are:
- Update latency. If the global mobility anchor point and/or correspondent node (for route-optimized traffic) is far away from the mobile node's access network, the global mobility update might take a considerable amount of time 🐢 during that time, packets keep getting routed to the old temporary local address and are basically dropped 💀
- Signaling overhead. When a mobile node moves from one last-hop link to another, the signaling can get extensive 🌪️ it includes everything needed to configure an IP address on the new link, plus global mobility protocol signaling back into the network to change the permanent-to-temporary local address mapping 🫠 that signaling volume can negatively impact wireless bandwidth usage and real-time service performance 📉
- Location privacy. Changing the temporary local address as the mobile node moves exposes its topological location to correspondents and possibly to eavesdroppers 👀 an attacker who can build a mapping between subnet prefixes in the mobile node's access network and geographical locations can figure out exactly where the mobile node is 😱 and that can expose the mobile node's user to threats on their location privacy 🚨 a more detailed discussion of location privacy for Mobile IPv6 is in [12] 📚
okay so these problems suggest that a protocol to localize the management of topologically small movements is way better than using a global mobility management protocol on every movement to a new link 🧠✨ on top of that, localized mobility management can give a measure of local control, so mobility management can be tuned for specialized local conditions 🎛️ also, if localized mobility management is provided, it is not strictly required for a mobile node to support a global mobility management protocol, since movement within a restricted IP access network can still be accommodated 🫶 without that global support though, a mobile node experiences a disruption in its traffic when it moves beyond the border of the localized mobility management domain 😭
3. Scenarios for Localized Mobility Management 🌈
there are a variety of scenarios where localized mobility management is useful 🙌
3.1. Large Campus 🏫
one scenario where localized mobility management would be attractive is a campus WLAN deployment 🎓 the geographical span of the campus, the distribution of buildings, the availability of wiring in buildings, etc. preclude deploying all WLAN access points as part of the same IP subnet 🧱 so WLAN Layer 2 mobility could not be used across the entire campus 💔
in this case, the campus is divided into separate last-hop links, each served by one or more access routers 🗺️ this kind of deployment is served today by WLAN switches that coordinate IP mobility between them, effectively providing localized mobility management at the link layer 🔗 since the protocols are proprietary and not interoperable, any deployments that require IP mobility necessarily require switches from the same vendor 🙃 very much a "stuck in one ecosystem" situation, ngl 💅
3.2. Advanced Cellular Network 📶
next-generation cellular protocols, such as 802.16e [7] and Super 3G/3.9G [2], have the potential to run IP deeper into the access network than current 3G cellular protocols, kinda like today's WLAN networks 🚀 this means the access network can become a routed IP network 🌐 interoperable localized mobility management can unify local mobility across a diverse set of wireless protocols, all served by IP 🫶 including advanced cellular, WLAN, and personal area wireless technologies like UltraWide Band (UWB) [5] and Bluetooth [3] 🦋
localized mobility management at the IP layer does not replace Layer 2 mobility (where it's available) but rather complements it ✨ a standardized, interoperable localized mobility management protocol for IP can remove the dependence on IP-layer localized mobility protocols that are specialized to specific link technologies or proprietary, which is the situation with today's 3G protocols 🙅♀️ the expected benefit is a reduction in maintenance cost and deployment complexity 💸 see [11] for a more detailed discussion of the goals for a network-based localized mobility management protocol 📖
3.3. Picocellular Network with Small But Node-Dense Last-Hop Links 🍭
future radio link protocols at very high frequencies may be constrained to very short, line-of-sight operation 📡 even some existing protocols, like UWB [5] and Bluetooth [3], are designed for low transmit power, short-range operation 🔋 for protocols like these, extremely small picocells become more practical 🔬 although picocells do not necessarily imply "pico subnets", wireless sensors and other advanced applications may end up making picocellular type networks node-dense 🌡️ which means they might require subnets that cover small geographical areas, such as a single room 🛋️ the ability to aggregate many subnets under a localized mobility management scheme can help reduce the amount of IP signaling required on link movement 💖
4. Problems with Existing Solutions ✨
okay so existing localized mobility management solutions come in two big classes 💅
- Interoperable IP-level protocols that require changes to the mobile node's IP stack and handle localized mobility management as a service provided to the mobile node by the access network.
- Link specific or proprietary protocols that handle localized mobility for any mobile node but only for a specific type of link layer, for example, 802.11 [6].
The dedicated localized mobility management IETF protocols for Solution 1 aren't widely deployed yet, but standardization work is still going 🛠️ Some Mobile IPv4 deployments use localized mobility management. For Solution 1, these are the specific problems:
- The host stack software requirement limits broad usage even if the modifications are small. The success of WLAN switches shows that network operators and users prefer no host stack software modifications. This preference doesn't depend on the lack of widespread Mobile IPv4 deployment, since it's way easier to deploy and use the network 🙄
- Future mobile nodes may choose other global mobility management protocols, such as HIP or MOBIKE. The existing localized mobility management solutions all depend on Mobile IP or derivatives.
- Existing localized mobility management solutions don't support both IPv4 and IPv6.
- Existing host-based localized mobility management solutions require setting up additional security associations with network elements in the access domain.
Market acceptance of WLAN switches has been huge, so Solution 2 is widely deployed and still growing 📈 Solution 2 has these problems:
- Existing solutions only support WLAN networks with Ethernet backhaul, so they aren't available for advanced cellular networks, picocellular protocols, or other types of wired backhaul.
- Each WLAN switch vendor has its own proprietary protocol that doesn't interoperate with other vendors' equipment. 😤
- Because these solutions are based on Layer 2 routing, they may not scale up to a metropolitan area or local province, especially when multiple kinds of link technologies are used in the backbone.
5. Advantages of Network-based Localized Mobility Management 🦋
Having an interoperable, standardized localized mobility management protocol that scales to topologically large networks, but doesn't need any host stack involvement for localized mobility management, is a highly desirable solution. Honestly, it's the main character 👑 Here's how it beats Solutions 1 and 2 above:
- Compared with Solution 1, a network-based solution requires no localized mobility management support on the mobile node and is independent of the global mobility management protocol. That means it can be used with any of the existing global mobility management protocols, or none at all. The result is a more modular mobility management architecture that better handles changing technology and market requirements 🧚
- Compared with Solution 2, an IP-level network-based localized mobility management solution works for link protocols other than Ethernet, and for wide area networks 🌈
RFC 4831 [11] discusses a reference architecture for a network-based, localized mobility protocol and the goals of the protocol design. Go read it if you want the full picture 🫶
6. Security Considerations 🔐
Localized mobility management has certain security considerations. One of them, the need for security from access network to mobile node, was discussed in this document. Host-based localized mobility management protocols have all the security problems involved with providing a service to a host. Network-based localized mobility management requires security among network elements that is equivalent to what is needed for routing information security, and security between the host and network that is equivalent to what is needed for network access, but no more. A more complete discussion of the security goals for network-based localized mobility management can be found in [11].
7. Informative References 📚
- [1] 3GPP, "UTRAN Iu interface: General aspects and principles", 3GPP TS 25.410, 2002,
http://www.3gpp.org/ftp/Specs/html-info/25410.htm. - [2] 3GPP, "3GPP System Architecture Evolution: Report on Technical Options and Conclusions", TR 23.882, 2005,
http://www.3gpp.org/ftp/Specs/html-info/23882.htm. - [3] Bluetooth SIG, "Specification of the Bluetooth System", November, 2004, available at
http://www.bluetooth.com. - [4] Eronen, P., "IKEv2 Mobility and Multihoming Protocol (MOBIKE)", RFC 4555, June 2006.
- [5] IEEE 802.15 WPAN High Rate Alternative PHY Task Group 3a (TG3a),
http://www.ieee802.org/15/pub/TG3a.html. - [6] IEEE, "Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications", IEEE Std. 802.11, 1999.
- [7] IEEE, "Amendment to IEEE Standard for Local and Metropolitan Area Networks - Part 16: Air Interface for Fixed Broadband Wireless Access Systems - Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands", IEEE Std. 802.16e-2005, 2005.
- [8] IEEE, "Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specifications", IEEE Std. 802.3-2005, 2005.
- [9] ITU-T, "Architecture of Transport Networks Based on the Synchronous Digital Hierarchy (SDH)", ITU-T G.803, March, 2000.
- [10] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in IPv6", RFC 3775, June 2004.
- [11] Kempf, J., Ed., "Goals for Network-Based Localized Mobility Management (NETLMM)", RFC 4831, April 2007.
- [12] Koodli, R., "IP Address Location Privacy and Mobile IPv6: Problem Statement", Work in Progress, February 2007.
- [13] Koodli, R., "Fast Handovers for Mobile IPv6", RFC 4068, July 2005.
- [14] Manner, J. and M. Kojo, "Mobility Related Terminology", RFC 3753, June 2004.
- [15] Metro Ethernet Forum, "Metro Ethernet Network Architecture Framework - Part 1: Generic Framework", MEF 4, May, 2004.
- [16] Moskowitz, R. and P. Nikander, "Host Identity Protocol (HIP) Architecture", RFC 4423, May 2006.
- [17] Perkins, C., "IP Mobility Support for IPv4", RFC 3344, August 2002.
- [18] Soliman, H., Castelluccia, C., El Malki, K., and L. Bellier, "Hierarchical Mobile IPv6 Mobility Management (HMIPv6)", RFC 4140, August 2005.
8. Acknowledgements 🙏
The authors want to shout out the following folks for their particularly diligent reviewing: Vijay Devarapalli, Peter McCann, Gabriel Montenegro, Vidya Narayanan, Pekka Savola, and Fred Templin. Absolute legends 🫶
9. Contributors 💜
Here are the contributors, with their details exactly as listed:
Kent Leung
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
USA
EMail: kleung@cisco.com
Phil Roberts
Motorola Labs
Schaumberg, IL
USA
EMail: phil.roberts@motorola.com
Katsutoshi Nishida
NTT DoCoMo Inc.
3-5 Hikarino-oka, Yokosuka-shi
Kanagawa,
Japan
Phone: +81 46 840 3545
EMail: nishidak@nttdocomo.co.jp
Gerardo Giaretta
Telecom Italia Lab
via G. Reiss Romoli, 274
10148 Torino
Italy
Phone: +39 011 2286904
EMail: gerardo.giaretta@tilab.com
Marco Liebsch
NEC Network Laboratories
Kurfuersten-Anlage 36
69115 Heidelberg
Germany
Phone: +49 6221-90511-46
EMail: marco.liebsch@ccrle.nec.deEditor's Address 🎀
James Kempf
DoCoMo USA Labs
181 Metro Drive, Suite 300
San Jose, CA 95110
USA
Phone: +1 408 451 4711
EMail: kempf@docomolabs-usa.comFull Copyright Statement ⭐
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