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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Mipshop WG T. Melia, Ed. 3 Internet-Draft Alcatel-Lucent 4 Intended status: Standards Track G. Bajko 5 Expires: July 17, 2009 Nokia 6 S. Das 7 Telcordia Technologies Inc. 8 N. Golmie 9 NIST 10 JC. Zuniga 11 InterDigital Communications, LLC 12 January 13, 2009 14 IEEE 802.21 Mobility Services Framework Design (MSFD) 15 draft-ietf-mipshop-mstp-solution-10 17 Status of this Memo 19 This Internet-Draft is submitted to IETF in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF), its areas, and its working groups. Note that 24 other groups may also distribute working documents as Internet- 25 Drafts. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 The list of current Internet-Drafts can be accessed at 33 http://www.ietf.org/ietf/1id-abstracts.txt. 35 The list of Internet-Draft Shadow Directories can be accessed at 36 http://www.ietf.org/shadow.html. 38 This Internet-Draft will expire on July 17, 2009. 40 Copyright Notice 42 Copyright (c) 2009 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. 52 Abstract 54 This document describes a mobility services framework design (MSFD) 55 for the IEEE 802.21 Media Independent Handover (MIH) protocol that 56 addresses identified issues associated with the transport of MIH 57 messages. The document also describes mechanisms for mobility 58 service (MoS) discovery and transport layer mechanisms for the 59 reliable delivery of MIH messages. 61 IESG Note 63 This document does not provide mechanisms for securing the 64 communication between a mobile node (MN) and the mobility service 65 (MoS). Instead, it is assumed that either lower layer (e.g., link 66 layer) security mechanisms, or overall system-specific proprietary 67 security solutions, are used. The details of such lower layer and/or 68 proprietary mechanisms are beyond the scope of this document. The 69 IESG recommends against using this protocol without careful analysis 70 that these mechanisms meet the desired requirements, and encourages 71 future standardization work in this area. The IEEE 802.21a Task 72 Group has recently started work on MIH security issues that may 73 provide some solution in this area. For further information, please 74 refer to Section 8. 76 Requirements Language 78 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 79 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 80 document are to be interpreted as described in RFC 2119 [RFC2119]. 82 Table of Contents 84 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 85 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 86 3. Deployment Scenarios . . . . . . . . . . . . . . . . . . . . . 7 87 3.1. Scenario S1: Home Network MoS . . . . . . . . . . . . . . 7 88 3.2. Scenario S2: Visited Network MoS . . . . . . . . . . . . . 8 89 3.3. Scenario S3: Third party MoS . . . . . . . . . . . . . . . 8 90 3.4. Scenario S4: Roaming MoS . . . . . . . . . . . . . . . . . 9 91 4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 10 92 4.1. Architecture . . . . . . . . . . . . . . . . . . . . . . . 11 93 4.2. MIHF Identifiers (FQDN, NAI) . . . . . . . . . . . . . . . 12 94 5. MoS Discovery . . . . . . . . . . . . . . . . . . . . . . . . 12 95 5.1. MoS Discovery when MN and MoSh are in the home network 96 (Scenario S1) . . . . . . . . . . . . . . . . . . . . . . 13 97 5.2. MoS Discovery when MN and MoSv both are in visited 98 network (Scenario S2) . . . . . . . . . . . . . . . . . . 14 99 5.3. MoS Discovery when MIH services are in a 3rd party 100 remote network (Scenario S3) . . . . . . . . . . . . . . . 14 101 5.4. MoS Discovery when the MN is in a visited Network and 102 Services are at the Home network . . . . . . . . . . . . . 15 103 6. MIH Transport Options . . . . . . . . . . . . . . . . . . . . 15 104 6.1. MIH Message size . . . . . . . . . . . . . . . . . . . . . 16 105 6.2. MIH Message rate . . . . . . . . . . . . . . . . . . . . . 17 106 6.3. Retransmission . . . . . . . . . . . . . . . . . . . . . . 17 107 6.4. NAT Traversal . . . . . . . . . . . . . . . . . . . . . . 18 108 6.5. General guidelines . . . . . . . . . . . . . . . . . . . . 18 109 7. Operation Flows . . . . . . . . . . . . . . . . . . . . . . . 18 110 8. Security Considerations . . . . . . . . . . . . . . . . . . . 20 111 8.1. Security Considerations for MoS Discovery . . . . . . . . 21 112 8.2. Security Considerations for MIH Transport . . . . . . . . 21 113 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 114 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22 115 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22 116 11.1. Normative References . . . . . . . . . . . . . . . . . . . 22 117 11.2. Informative References . . . . . . . . . . . . . . . . . . 23 118 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24 120 1. Introduction 122 This document proposes a solution to the issues identified in the 123 problem statement document [RFC5164] for the layer 3 transport of 124 IEEE 802.21 MIH protocols. 126 The MIH Layer 3 transport problem is divided into two main parts: the 127 discovery of a node that supports specific Mobility Services (MoS) 128 and the transport of the information between a mobile node (MN) and 129 the discovered node. The discovery process is required for the MN to 130 obtain the information needed for MIH protocol communication with a 131 peer node. The information includes the transport address (e.g., the 132 IP address) of the peer node and the types of MoS provided by the 133 peer node. 135 This document lists the major MoS deployment scenarios. It describes 136 the solution architecture, including the MSFD reference model and 137 MIHF identifiers. MoS discovery procedures explain how the MN 138 discovers MoS in its home network, in a visited network or in a third 139 party network. The remainder of this document describes the MIH 140 transport architecture, example message flows for several signaling 141 scenarios, and security issues. 143 2. Terminology 145 The following acronyms and terminology are used in this document: 147 MIH Media Independent Handover: the handover support architecture 148 defined by the IEEE 802.21 working group that consists of the MIH 149 Function (MIHF), MIH Network Entities and MIH protocol messages. 151 MIHF Media Independent Handover Function: a switching function that 152 provides handover services including the Event Service (ES), 153 Information Service (IS), and Command Service (CS), through 154 service access points (SAPs) defined by the IEEE 802.21 working 155 group [IEEE80221]. 157 MIHF User An entity that uses the MIH SAPs to access MIHF services, 158 and which is responsible for initiating and terminating MIH 159 signaling. 161 MIHFID Media Independent Handover Function Identifier: an identifier 162 required to uniquely identify the MIHF endpoints for delivering 163 mobility services (MoS); it is implemented as either a FQDN or 164 NAI. 166 MoS Mobility Services: those services, as defined in the MIH problem 167 statement document [RFC5164] , which includes the MIH IS, CS, and 168 ES services defined by the IEEE 802.21 standard. 170 MoSh: Mobility Services assigned in the mobile node's Home Network. 172 MoSv: Mobility Services assigned in the Visited Network. 174 MoS3: Mobility Services assigned in a 3rd Party Network, which is a 175 network that is neither the Home Network nor the current Visited 176 Network. 178 MN Mobile Node: an Internet device whose location changes, along with 179 its point of connection to the network. 181 MSTP Mobility Services Transport Protocol: a protocol that is used 182 to deliver MIH protocol messages from an MIHF to other MIH-aware 183 nodes in a network. 185 IS Information Service: a MoS that originates at the lower or upper 186 layers of the protocol stack and sends information to the local or 187 remote upper or lower layers of the protocol stack. The purpose 188 of IS is to exchange information elements (IEs) relating to 189 various neighboring network information. 191 ES Event Service: a MoS that originates at a remote MIHF or the lower 192 layers of the local protocol stack and sends information to the 193 local MIHF or local higher layers. The purpose of the ES is to 194 report changes in link status (e.g., Link Going Down messages) and 195 various lower layer events. 197 CS Command Service: MoS that sends commands from the remote MIHF or 198 local upper layers to the remote or local lower layers of the 199 protocol stack to switch links or to get link status. 201 FQDN: Fully-Qualified Domain Name: a complete domain name for a host 202 on the Internet, showing (in reverse order) the full delegation 203 path from the DNS root and top level domain down to the host name 204 (e.g. myexample.example.org). 206 NAI Network Access Identifier: the user ID that a user submits 207 during network access authentication [RFC4282]. For mobile users, 208 the NAI identifies the user and helps to route the authentication 209 request message. 211 NAT Network Address Translator: A device that implements the Network 212 Address Translation function described in [RFC3022], in which 213 local or private network layer addresses are mapped to routable 214 (outside the NAT domain) network addresses and port numbers. 216 DHCP Dynamic Host Configuration Protocol: protocols described in 217 [RFC2131] and [RFC3315] that allow Internet devices to obtain 218 respectively IPv4 and IPv6 addresses, subnet masks, default 219 gateway addresses, and other IP configuration information from 220 DHCP servers. 222 DNS Domain Name System: a protocol described in [RFC1035] that 223 translates domain names to IP addresses. 225 AAA Authentication, Authorization and Accounting: a set of network 226 management services that respectively determine the validity of a 227 user's ID, determine whether a user is allowed to use network 228 resources, and track users' use of network resources. 230 Home AAA AAAh: an AAA server located on the MN's home network. 232 Visited AAA AAAv: an AAA server located in a visited network that is 233 not the MN's home network. 235 MIH ACK MIH Acknowledgement Message: a MIH signaling message that a 236 MIHF sends in response to an MIH message from a sending MIHF, when 237 UDP is used as the MSTP. 239 PoS Point of Service: a network-side MIHF instance that exchanges 240 MIH messages with a MN-based MIHF. 242 NAS Network Access Server: a server to which a MN initially connects 243 when it is trying to gain a connection to a network and which 244 determines whether the MN is allowed to connect to the NAS's 245 network. 247 UDP User Datagram Protocol: a connectionless transport layer 248 protocol used to send datagrams between a source and a destination 249 at a given port, defined in RFC 768. 251 TCP Transmission Control Protocol: a stream-oriented transport layer 252 protocol that provides a reliable delivery service with congestion 253 control, defined in RFC 793. 255 RTT Round-Trip Time: an estimation of the time required for a 256 segment to travel from a source to a destination and an 257 acknowledgement to return to the source that is used by TCP in 258 connection with timer expirations to determine when a segment is 259 considered lost and should be resent. 261 MTU Maximum Transmission Unit: the largest size of an IP packet that 262 can be sent on a network segment without requiring fragmentation 263 [RFC1191]. 265 PMTU Path MTU: the largest size of an IP packet that can be sent on 266 an end-to-end network path without requiring IP fragmentation. 268 TLS Transport Layer Security Protocol: an application layer protocol 269 that primarily assures privacy and data integrity between two 270 communicating network entities [RFC5246]. 272 SMSS Sender Maximum Segment Size: size of the largest segment that 273 the sender can transmit as per [RFC2581]. 275 3. Deployment Scenarios 277 This section describes the various possible deployment scenarios for 278 the MN and the MoS. The relative positioning of MN and MoS affects 279 MoS discovery as well as the performance of the MIH signaling 280 service. This document addresses the scenarios listed in [RFC5164] 281 and specifies transport options to carry the MIH protocol over IP. 283 3.1. Scenario S1: Home Network MoS 285 In this scenario, the MN and the services are located in the home 286 network. We refer to this set of services as MoSh as in Figure 1. 287 The MoSh can be located at the access network the MN uses to connect 288 to the home network, or it can be located elsewhere. 290 +--------------+ +====+ 291 | HOME NETWORK | |MoSh| 292 +--------------+ +====+ 293 /\ 294 || 295 \/ 296 +--------+ 297 | MN | 298 +--------+ 300 Figure 1: MoS in the home network 302 3.2. Scenario S2: Visited Network MoS 304 In this scenario, the MN is in the visited network and mobility 305 services are provided by the visited network. We refer to this as 306 MoSv as shown in Figure 2. 308 +--------------+ 309 | HOME NETWORK | 310 +--------------+ 311 /\ 312 || 313 \/ 314 +====+ +-----------------+ 315 |MoSv| | VISITED NETWORK | 316 +====+ +-----------------+ 317 /\ 318 || 319 \/ 320 +--------+ 321 | MN | 322 +--------+ 324 Figure 2: MoSv in the visited network 326 3.3. Scenario S3: Third party MoS 328 In this scenario, the MN is in its home network or in a visited 329 network and services are provided by a 3rd party network. We refer 330 to this situation as MoS3 as shown in Figure 3. (Note that MoS can 331 exist both in home and in visited networks). 333 +--------------+ 334 | HOME NETWORK | 335 +====+ +--------------+ +--------------+ 336 |MoS3| | THIRD PARTY | <===> /\ 337 +====+ +--------------+ || 338 \/ 339 +-----------------+ 340 | VISITED NETWORK | 341 +-----------------+ 342 /\ 343 || 344 \/ 345 +--------+ 346 | MN | 347 +--------+ 349 Figure 3: MoS from a third party 351 3.4. Scenario S4: Roaming MoS 353 In this scenario, the MN is located in the visited network and all 354 MIH services are provided by the home network, as shown in Figure 4. 356 +====+ +--------------+ 357 |MoSh| | HOME NETWORK | 358 +====+ +--------------+ 359 /\ 360 || 361 \/ 362 +-----------------+ 363 | VISITED NETWORK | 364 +-----------------+ 365 /\ 366 || 367 \/ 368 +--------+ 369 | MN | 370 +--------+ 372 Figure 4: MoS provided by the home while in visited 374 Different types of MoS can be provided independently of other types 375 and there is no strict relationship between ES, CS and IS, nor is 376 there a requirement that the entities that provide these services 377 should be co-located. However, while IS tends to involve a large 378 amount of static information, ES and CS are dynamic services and some 379 relationships between them can be expected, e.g., a handover command 380 (CS) could be issued upon reception of a link event (ES). This 381 document does not make any assumption on the location of the MoS 382 (although there might be some preferred configurations), and aims at 383 flexible MSFD to discover different services in different locations 384 to optimize handover performance. MoS discovery is discussed in more 385 detail in Section 5. 387 4. Solution Overview 389 As mentioned in Section 1, the solution space is being divided into 390 two functional domains: discovery and transport. The following 391 assumptions have been made: 393 o The solution is primarily aimed at supporting IEEE 802.21 MIH 394 services, namely Information Service (IS), Event Service (ES), and 395 Command Service (CS). 397 o If the MIHFID is available, FQDN or NAI's realm is used for 398 mobility service discovery. 400 o The solutions are chosen to cover all possible deployment 401 scenarios as described in Section 3. 403 o MoS discovery can be performed during initial network attachment 404 or at any time thereafter. 406 The MN may know the realm of the MoS to be discovered. The MN may 407 also be pre-configured with the address of the MoS to be used. In 408 case the MN does not know what realm/MoS to query, dynamic assignment 409 methods are described in Section 5. 411 The discovery of the MoS (and the related configuration at MIHF 412 level) is required to bind two MIHF peers (e.g. MN and MoS) with 413 their respective IP addresses. Discovery MUST be executed in the 414 following conditions: 416 o Bootstrapping: upon successful layer 2 network attachment the MN 417 MAY be required to use DHCP for address configuration. These 418 procedures can carry the required information for MoS 419 configuration in specific DHCP options. 421 o If the MN does not receive MoS information during network 422 attachment and the MN does not have a pre-configured MoS, it MUST 423 run a discovery procedure upon initial IP address configuration. 425 o If the MN changes its IP address (e.g. upon handover) it MUST 426 refresh MIHF peer bindings (i.e., MIHF registration process). In 427 case the MoS used is not suitable anymore (e.g. too large RTT 428 experienced) the MN MAY need to perform a new discovery procedure. 430 o If the MN is a multi-homed device and it communicates with the 431 same MoS via different IP addresses it MAY run discovery 432 procedures if one of the IP addresses changes. 434 Once the MIHF peer has been discovered, MIH information can be 435 exchanged between MIH peers over a transport protocol such as UDP or 436 TCP. The usage of transport protocols is described in Section 6 and 437 packing of the MIH messages does not require extra framing since the 438 MIH protocol defined in [IEEE80221] already contains a length field. 440 4.1. Architecture 442 Figure 5 depicts the MSFD reference model and its components within a 443 node. The topmost layer is the MIHF user. This set of applications 444 consists of one or more MIH clients that are responsible for 445 operations such as generating query and response, processing Layer 2 446 triggers as part of the ES, and initiating and carrying out handover 447 operations as part of the CS. Beneath the MIHF user is the MIHF 448 itself. This function is responsible for MoS discovery, as well as 449 creating, maintaining, modifying, and destroying MIH signaling 450 associations with other MIHFs located in MIH peer nodes. Below the 451 MIHF are various transport layer protocols as well as address 452 discovery functions. 454 +--------------------------+ 455 | MIHF User | 456 +--------------------------+ 457 || 458 +--------------------------+ 459 | MIHF | 460 +--------------------------+ 461 || || || 462 || +------+ +-----+ 463 || | DHCP | | DNS | 464 || +------+ +-----+ 465 || || || 466 +--------------------------+ 467 | TCP/UDP | 468 +--------------------------+ 470 Figure 5: MN stack 472 The MIHF relies on the services provided by TCP and UDP for 473 transporting MIH messages, and relies on DHCP and DNS for peer 474 discovery. In cases where the peer MIHF IP address is not pre- 475 configured, the source MIHF needs to discover it either via DHCP or 476 DNS as described in Section 5. Once the peer MIHF is discovered, the 477 MIHF must exchange messages with its peer over either UDP or TCP. 478 Specific recommendations regarding the choice of transport protocols 479 are provided in Section 6. 481 There are no security features currently defined as part of the MIH 482 protocol level. However, security can be provided either at the 483 transport or IP layer where it is necessary. Section 8 provides 484 guidelines and recommendations for security. 486 4.2. MIHF Identifiers (FQDN, NAI) 488 MIHFID is an identifier required to uniquely identify the MIHF end 489 points for delivering the mobility services (MoS). Thus an MIHF 490 identifier needs to be unique within a domain where mobility services 491 are provided and independent of the configured IP addresse(s). An 492 MIHFID MUST be represented either in the form of an FQDN [RFC2181] or 493 NAI [RFC4282]. An MIHFID can be pre-configured or discovered through 494 the discovery methods described in Section 5. 496 5. MoS Discovery 498 The MoS discovery method depends on whether the MN attempts to 499 discover an MoS in the home network, in the visited network, or in a 500 3rd party remote network that is neither the home network nor the 501 visited network. In the case the MN has already a MoS address pre- 502 configured it is not necessary to run the discovery procedure. If 503 the MN does not have pre-configured MoS the following procedure 504 applies. 506 In the case where MoS is provided locally (scenarios S1 and S2) , the 507 discovery techniques described in [I-D.ietf-mipshop-mos-dhcp-options] 508 and [I-D.ietf-mipshop-mos-dns-discovery] are both applicable as 509 described in Section 5.1 and Section 5.2. 511 In the case where MoS is provided in the home network while the MN is 512 in the visited network (scenario S4), the DNS based discovery 513 described in [I-D.ietf-mipshop-mos-dns-discovery] is applicable. 515 In the case where MoS is provided by a third party network which is 516 different from the current visited network (scenario S3), only the 517 DNS based discovery method described in 518 [I-D.ietf-mipshop-mos-dns-discovery] is applicable. 520 It should be noted that authorization of a MN to use a specific MoS 521 server is neither in scope of this document nor is currently 522 specified in [IEEE80221]. We further assume all devices can access 523 discovered MoS. In case future deployments will implement 524 authorization policies the mobile nodes should fall back to other 525 learned MoS if authorization is denied. 527 5.1. MoS Discovery when MN and MoSh are in the home network (Scenario 528 S1) 530 To discover an MoS in the home network, the MN SHOULD use the DNS 531 based MoS discovery method described in 532 [I-D.ietf-mipshop-mos-dns-discovery]. In order to use that 533 mechanism, the MN MUST have its home domain pre-configured (i.e., 534 subscription is tied to a network). The DNS query option is shown in 535 Figure 6a. Alternatively, the MN MAY use the DHCP options for MoS 536 discovery [I-D.ietf-mipshop-mos-dhcp-options] as shown in Figure 6b 537 (in some deployments, a DHCP relay may not be present). 539 (a) +-------+ 540 +----+ |Domain | 541 | MN |-------->|Name | 542 +----+ |Server | 543 MN@example.org +-------+ 545 (b) 546 +-----+ +------+ 547 +----+ | | |DHCP | 548 | MN |<----->| DHCP|<---->|Server| 549 +----+ |Relay| | | 550 +-----+ +------+ 552 Figure 6: MOS Discovery (a) using DNS query, (b) using DHCP option 554 5.2. MoS Discovery when MN and MoSv both are in visited network 555 (Scenario S2) 557 To discover an MoS in the visited network, the MN SHOULD attempt to 558 use the DHCP options for MoS discovery 559 [I-D.ietf-mipshop-mos-dhcp-options] as shown in Figure 7. 561 +-----+ +------+ 562 +----+ | | |DHCP | 563 | MN |<----->| DHCP|<---->|Server| 564 +----+ |Relay| | | 565 +-----+ +------+ 567 Figure 7: MoS Discovery using DHCP options 569 5.3. MoS Discovery when MIH services are in a 3rd party remote network 570 (Scenario S3) 572 To discover an MoS in a remote network other than home network, the 573 MN MUST use the DNS based MoS discovery method described in 574 [I-D.ietf-mipshop-mos-dns-discovery]. The MN MUST first learn the 575 domain name of the network containing the MoS it is searching for. 576 The MN can query its current MoS to find out the domain name of a 577 specific network or the domain name of a network at a specific 578 location (as in Figure 8a, IEEE 802.21 defines information elements 579 such as OPERATOR ID and SERVICE PROVIDER ID which can be a domain 580 name. An IS query can provide this information, see [IEEE80221]). 582 Alternatively, the MN MAY query a MoS previously known to learn the 583 domain name of the desired network . Finally, the MN MUST use DNS 584 based discovery mechanisms to find MoS in the remote network as in 585 Figure 8b. It should be noted that step b can only be performed upon 586 obtaining the domain name of the remote network. 588 (a) 589 +------------+ 590 +----+ | | 591 | | |Information | 592 | MN |-------->| Server | 593 | | |(previously | 594 +----+ |discovered) | 595 +------------+ 597 (b) 598 +-------+ 599 +----+ |Domain | 600 | MN |-------->|Name | 601 +----+ |Server | 602 MN@example.org +-------+ 604 Figure 8: MOS Discovery using (a) IS Query to a known IS Server, (b) 605 DNS Query 607 5.4. MoS Discovery when the MN is in a visited Network and Services are 608 at the Home network 610 To discover an MoS in the visited network when MIH services are 611 provided by the home network, the DNS based discovery method 612 described in [I-D.ietf-mipshop-mos-dns-discovery] is applicable. To 613 discover the MoS at home while in a visited network using DNS, the MN 614 SHOULD use the procedures described in Section 5.1. 616 6. MIH Transport Options 618 Once the Mobility Services have been discovered, MIH peers run a 619 capability discovery and subscription procedure as specified in 620 [IEEE80221]. MIH peers MAY exchange information over TCP, UDP or any 621 other transport supported by both the server and the client. The 622 client MAY use the DNS discovery mechanism to discover which 623 transport protocols are supported by the server in addition to TCP 624 and UDP that are recommended in this document. While either protocol 625 can provide the basic transport functionality required, there are 626 performance trade-offs and unique characteristics associated with 627 each that need to be considered in the context of the MIH services 628 for different network loss and congestion conditions. The objectives 629 of this section are to discuss these trade-offs for different MIH 630 settings such as the MIH message size and rate, and the 631 retransmission parameters. In addition, factors such as NAT 632 traversal are also discussed. Given the reliability requirements for 633 the MIH transport, it is assumed in this discussion that the MIH ACK 634 mechanism is to be used in conjunction with UDP, while it MUST NOT be 635 used with TCP since TCP includes acknowledgement and retransmission 636 functionality. 638 6.1. MIH Message size 640 Although the MIH message size varies widely from about 30 bytes (for 641 a capability discovery request) to around 65000 bytes (for an IS 642 MIH_Get_Information response primitive), a typical MIH message size 643 for the ES/CS service ranges between 50 to 100 bytes [IEEE80221]. 644 Thus, considering the effects of the MIH message size on the 645 performance of the transport protocol brings us to discussing two 646 main issues, related to fragmentation of long messages in the context 647 of UDP and the concatenation of short messages in the context of TCP. 649 Since transporting long MIH messages may require fragmentation that 650 is not available in UDP, if MIH is using UDP a limit MUST be set on 651 the size of the MIH message based on the path MTU to destination (or 652 the Minimum MTU where PMTU is not implemented). The Minimum MTU 653 depends on the IP version used for transmission, and is the lesser of 654 the first hop MTU, and 576 or 1280 bytes for IPv4 [RFC1122] or for 655 IPv6 [RFC2460], respectively, although applications may reduce these 656 values to guard against the presence of tunnels. 658 According to[IEEE80221] when MIH message is sent using an L3 or 659 higher layer transport, L3 takes care of any fragmentation issue and 660 the MIH protocol does not handle fragmentation in such cases. Thus, 661 MIH layer fragmentation MUST NOT be used together with IP layer 662 framentation. 664 The loss of an IP fragment leads to the retransmission of an entire 665 MIH message, which in turn leads to poor end-to-end delay performance 666 in addition to wasted bandwidth. Additional recommendations in 667 [RFC5405] apply for limiting the size of the MIH message when using 668 UDP and assuming IP layer fragmentation. In terms of dealing with 669 short messages, TCP has the capability to concatenate very short 670 messages in order to reduce the overall bandwidth overhead. However, 671 this reduced overhead comes at the cost of additional delay to 672 complete an MIH transaction, which may not be acceptable for CS and 673 ES services. Note also that TCP is a stream oriented protocol and 674 measures data flow in terms of bytes, not messages. Thus it is 675 possible to split messages across multiple TCP segments if they are 676 long enough. Even short messages can be split across two segments. 677 This can also cause unacceptable delays, especially if the link 678 quality is severely degraded as is likely to happen when the MN is 679 exiting a wireless access coverage area. The use of the TCP_NODELAY 680 option can alleviate this problem by triggering transmission of a 681 segment less than the SMSS. (It should be noted that [RFC4960] 682 addresses both of these problems, but discussion of it is omitted 683 here due to the lack of running code). 685 6.2. MIH Message rate 687 The frequency of MIH messages varies according to the MIH service 688 type. It is expected that CS/ES message arrive at a rate of one in 689 hundreds of milliseconds in order to capture quick changes in the 690 environment and/ or process handover commands. On the other hand, IS 691 messages are exchanged mainly every time a new network is visited 692 which may be in order of hours or days. Therefore a burst of either 693 short CS/ES messages or long IS message exchanges (in the case where 694 multiple MIH nodes request information) may lead to network 695 congestion. While the built-in rate-limiting controls available in 696 TCP may be well suited for dealing with these congestion conditions, 697 this may result in large transmission delays that may be unacceptable 698 for the timely delivery of ES/CS messages. On the other hand, if UDP 699 is used, a rate-limiting effect similar to the one obtained with TCP 700 SHOULD be obtained by adequately adjusting the parameters of a token 701 bucket regulator as defined in the MIH specifications [IEEE80221]. 702 Recommendations for token bucket parameter settings are as follow: 704 o If the MIHF knows the RTT (e.g., based on the request/response MIH 705 protocol exchange between two MIH peers), the rate can be based 706 upon this as specified in [IEEE80221]. 708 o If not, then on average it SHOULD NOT send more than one UDP 709 message every 3 seconds. 711 6.3. Retransmission 713 For TCP, the retransmission timeout is adjusted according to the 714 measured RTT. However due to the exponential backoff mechanism, the 715 delay associated with retransmission timeouts may increase 716 significantly with increased packet loss. 718 If UDP is being used to carry MIH messages, MIH MUST use MIH ACKs. 719 An MIH message is retransmitted if its corresponding MIH ACK is not 720 received by the generating node within a timeout interval set by the 721 MIHF. The maximum number of retransmissions is configurable and the 722 value of the retransmission timer is computed according to the 723 algorithm defined in [RFC2988]. The default maximum number of 724 retransmissions is set to 2 and the initial retransmission timer 725 (TMO) is set to 3s when RTT is not known. The maximum TMO is set to 726 30s. 728 6.4. NAT Traversal 730 There are no known issues for NAT traversal when using TCP. The 731 default connection timeout of 2 hours 4 minutes [RFC5382] (assuming a 732 2 hours TCP keep-alive) is considered adequate for MIH transport 733 purposes. However, issues with NAT traversal using UDP are 734 documented in [RFC5405]. Communication failures are experienced when 735 middleboxes destroy the per-flow state associated with an application 736 session during periods when the application does not exchange any UDP 737 traffic. Hence, communication between the MN and the MoS SHOULD be 738 able to gracefully handle such failures and implement mechanisms to 739 re-establish their UDP sessions. In addition and in order to avoid 740 such failures, MIH messages MAY be sent periodically, similarly to 741 keep-alive messages, in an attempt to refresh middlebox state. As 742 [RFC4787] requires a minimum state timeout of two minutes or more, 743 MIH messages using UDP as transport SHOULD be sent once every two 744 minutes. Re-registration or Event indication messages as defined in 745 [IEEE80221] MAY be used for this purpose. 747 6.5. General guidelines 749 Since ES and CS messages are small in nature and have tight latency 750 requirements, UDP in combination with MIH acknowledgement SHOULD be 751 used for transporting ES and CS messages. On the other hand, IS 752 messages are more resilient in terms of latency constraints and some 753 long IS messages could exceed the MTU of the path to the destination. 754 TCP SHOULD be used to transport IS messages. 756 For both UDP and TCP cases, if a port number is not explicitly 757 assigned (e.g. by the DNS SRV), MIH messages sent over UDP, TCP or 758 other supported transport MUST use the default port number defined in 759 Section 9 for that particular transport. 761 A MoS server MUST support both UDP and TCP for MIH transport and the 762 MN MUST support TCP. Additionally, the server and MN MAY support 763 additional transport mechanisms. The MN MAY use the procedures 764 defined in [I-D.ietf-mipshop-mos-dns-discovery] to discover 765 additional transport protocols supported by the server (e.g. SCTP). 767 7. Operation Flows 769 Figure 9 gives an example operation flow between MIHF peers when a 770 MIH user requests an IS service and both the MN and the MoS are in 771 the MN's home network. DHCP is used for MoS discovery and TCP is 772 used for establishing a transport connection to carry the IS 773 messages. When MoS is not pre-configured, the MIH user needs to 774 discover the IP address of MoS to communicate with the remote MIHF. 776 Therefore the MIH user sends a discovery request message to the local 777 MIHF as defined in [IEEE80221]. 779 In this example (one could draw similar mechanisms with DHCPv6), we 780 assume that MoS discovery is performed before a transport connection 781 is established with the remote MIHF, and the DHCP client process is 782 invoked via some internal APIs. The DHCP Client sends a DHCP INFORM 783 message according to standard DHCP and with the MoS option as defined 784 in [I-D.ietf-mipshop-mos-dhcp-options]. The DHCP server replies via 785 a DHCP ACK message with the IP address of the MoS. The MoS address 786 is then passed to the MIHF locally via some internal APIs. The MIHF 787 generates the discovery response message and passes it on to the 788 corresponding MIH user. The MIH user generates an IS query addressed 789 to the remote MoS. The MIHF invokes the underlying TCP client which 790 establishes a transport connection with the remote peer. Once the 791 transport connection is established, the MIHF sends the IS query via 792 a MIH protocol REQUEST message. The message and query arrive at the 793 destination MIHF and MIH user respectively. The MoS MIH user 794 responds to the corresponding IS query and the MoS MIHF sends the IS 795 response via a MIH protocol RESPONSE message. The message arrives at 796 the source MIHF which passes the IS response on to the corresponding 797 MIH user. 799 MN MoS 800 |===================================| |======| |===================| 801 + ---------+ + ---------+ 802 | MIH USER | +------+ +------+ +------+ +------+ | MIH USER | 803 | +------+ | | TCP | |DHCP | |DHCP | | TCP | | +------+ | 804 | | MIHF | | |Client| |Client| |Server| |Server| | | MIHF | | 805 +----------+ +------+ +------+ +------+ +------+ +----------+ 806 | | | | | | 807 MIH Discovery | | | | | 808 Request | | | | | 809 | | | | | | 810 |Invoke DHCP Client | | | | 811 |(Internal process with MoS)|DHCP INFORM| | | 812 |==========================>|==========>| | | 813 | | | | | | 814 | | | DHCP ACK | | | 815 | | |<==========| | | 816 | Inform MoS address | | | | 817 |<==========================| | | | 818 | (internal process) | | | | 819 | | | | | | 820 MIH Discovery | | | | | 821 Response | | | | | 822 | | | | | | 823 IS Query | | | | | 824 MIH User-> MIHF | | | | | 825 | | | | | | 826 |Invoke TCP Client| | | | | 827 |================>| | | | | 828 Internal process | | | | | 829 | | TCP connection established | | 830 | |<=============================>| | 831 | | | | | | 832 | IS QUERY REQUEST (via MIH protocol) | 833 |===========================================================>| 834 | | | | | | 835 | | | | | IS QUERY| 836 | | | | | REQUEST| 837 | | | | MIHF-> MIH User | 838 | | | | | | 839 | | | | | QUERY| 840 | | | | | RESPONSE| 841 | | | | MIHF <-MIH User | 842 | | | | | | 843 | | IS QUERY RESPONSE (via MIH protocol) | 844 |<===========================================================| 845 | | | | | | 846 IS RESPONSE | | | | | 847 MIH User <-MIHF | | | | | 848 | | | | | | 850 Figure 9: Example Flow of Operation Involving MIH User 852 8. Security Considerations 854 There are two components to the security considerations: MoS 855 Discovery and MIH Transport. For MoS Discovery, DHCP and DNS 856 recommendations are hereby provided per IETF guidelines. For MIH 857 Transport, we describe the security threats and expect that the 858 system deployment will have means to mitigate such threats when 859 sensitive information is being exchanged between the mobile node and 860 MoS. Since IEEE 802.21 base specification does not provide MIH 861 protocol level security, it is assumed that either lower layer 862 security (e.g., link layer), or overall system specific (e.g. 863 proprietary) security solutions are available. The present document 864 does not provide any guidelines in this regard. It is should be 865 stressed that the IEEE 802.21a Task Group has recently started work 866 on MIH security issues that may provide some solution in this area. 868 8.1. Security Considerations for MoS Discovery 870 There are a number of security issues that need to be taken into 871 account during node discovery. In the case where DHCP is used for 872 node discovery and authentication of the source and content of DHCP 873 messages is required, network administrators SHOULD use the DHCP 874 authentication option described in [RFC3118], where available, or 875 rely upon link layer security. [RFC3118] provides mechanisms for 876 both entity authentication and message authentication. In case where 877 the DHCP authentication mechanism is not available administrators may 878 need to rely upon the underlying link layer security. In such cases 879 the link between DHCP client and layer-2 termination point may be 880 protected but the DHCP message source and its messages can not be 881 authenticated or the integrity of the latter checked unless there 882 exits a security binding between link layer and DHCP layer. 884 In the case where DNS is used for discovering MoS, fake DNS requests 885 and responses may cause DoS and the inability of the MN to perform a 886 proper handover, respectively. Where networks are exposed to such 887 DoS, it is RECOMMENDED that DNS service providers use the Domain Name 888 System Security Extensions (DNSSEC) as described in [RFC4033]. 889 Readers may also refer to [RFC4641] to consider the aspects of DNSSEC 890 Operational Practices. 892 8.2. Security Considerations for MIH Transport 894 The communication between an MN and an MoS is exposed to a number of 895 security threads: 897 o MoS Identity spoofing. A fake MoS could provide the MNs with 898 bogus data and force them to select the wrong network or to make a 899 wrong handover decision. 901 o Tampering. Tampering with the information provided by an MoS may 902 result in the MN making wrong network selection or handover 903 decisions 905 o Replay attack. Since MoSs as defined in [IEEE80221] support a 906 'PUSH model', they can send bulk of data to the MNs whenever the 907 MoSs think that the data is relevant for the MN. An attacker may 908 intercept the data sent my the MoSs to the MNs and replay it at a 909 later time, causing the MNs to make network selection or handover 910 decisions which are not valid at that point in time. 912 o Eavesdropping. By snooping the communication between an MN and an 913 MoS, an attacker may be able to trace a user's movement between 914 networks or cells, or predict future movements, by inspecting 915 handover service messages. 917 There are many deployment specific system security solutions 918 available and can be used to countermeasure the above mentioned 919 threats. For example, for the MoSh and MoSv scenarios (including 920 roaming scenarios), link layer security may be sufficient to protect 921 the communication between MN and MoS. This is a typical mobile 922 operator environment where link layer security provides 923 authentication, data confidentiality and integrity. In other 924 scenarios, such as the third party MoS, link layer security solutions 925 may not be sufficient to protect the communication path between the 926 MN and the MoS. The communication channel between MN and MoS needs 927 to be secured by other means. 929 The present document does not provide any specific guidelines about 930 the way these security solutions should be deployed. However, if in 931 future the IEEE 802.21 Working Group amends the specification with 932 MIH protocol level security or recommends the deployment scenarios, 933 IETF may revisit the security considerations and recommend specific 934 transport layer security as appropriate. 936 9. IANA Considerations 938 This document registers the following TCP and UDP port(s) with IANA: 940 Keyword Decimal Description 941 -------- --------------- ------------ 942 ieee-mih TBD_BY_IANA/tcp MIH Services 943 ieee-mih TBD_BY_IANA/udp MIH Services 945 10. Acknowledgements 947 The authors would like to thank Yoshihiro Ohba, David Griffith, Kevin 948 Noll, Vijay Devarapalli, Patrick Stupar and Sam Xia for their 949 valuable comments, reviews and fruitful discussions. 951 11. References 953 11.1. Normative References 955 [I-D.ietf-mipshop-mos-dhcp-options] 956 Bajko, G. and S. Das, "Dynamic Host Configuration Protocol 957 (DHCPv4 and DHCPv6) Options for IEEE 802.21 Mobility 958 Server (MoS) discovery", 959 draft-ietf-mipshop-mos-dhcp-options-10 (work in progress), 960 January 2009. 962 [I-D.ietf-mipshop-mos-dns-discovery] 963 Bajko, G., "Locating IEEE 802.21 Mobility Servers using 964 DNS", draft-ietf-mipshop-mos-dns-discovery-04 (work in 965 progress), October 2008. 967 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 968 Requirement Levels", BCP 14, RFC 2119, March 1997. 970 [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS 971 Specification", RFC 2181, July 1997. 973 [RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP 974 Messages", RFC 3118, June 2001. 976 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 977 and M. Carney, "Dynamic Host Configuration Protocol for 978 IPv6 (DHCPv6)", RFC 3315, July 2003. 980 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 981 Rose, "DNS Security Introduction and Requirements", 982 RFC 4033, March 2005. 984 [RFC4282] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The 985 Network Access Identifier", RFC 4282, December 2005. 987 11.2. Informative References 989 [IEEE80221] 990 "Draft IEEE Standard for Local and Metropolitan Area 991 Networks: Media Independent Handover Services", IEEE LAN/ 992 MAN Draft IEEE P802.21/D13.00, August 2008. 994 [RFC1035] Mockapetris, P., "Domain names - implementation and 995 specification", STD 13, RFC 1035, November 1987. 997 [RFC1122] Braden, R., "Requirements for Internet Hosts - 998 Communication Layers", STD 3, RFC 1122, October 1989. 1000 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 1001 November 1990. 1003 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 1004 RFC 2131, March 1997. 1006 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1007 (IPv6) Specification", RFC 2460, December 1998. 1009 [RFC2581] Allman, M., Paxson, V., and W. Stevens, "TCP Congestion 1010 Control", RFC 2581, April 1999. 1012 [RFC2988] Paxson, V. and M. Allman, "Computing TCP's Retransmission 1013 Timer", RFC 2988, November 2000. 1015 [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network 1016 Address Translator (Traditional NAT)", RFC 3022, 1017 January 2001. 1019 [RFC4641] Kolkman, O. and R. Gieben, "DNSSEC Operational Practices", 1020 RFC 4641, September 2006. 1022 [RFC4787] Audet, F. and C. Jennings, "Network Address Translation 1023 (NAT) Behavioral Requirements for Unicast UDP", BCP 127, 1024 RFC 4787, January 2007. 1026 [RFC4960] Stewart, R., "Stream Control Transmission Protocol", 1027 RFC 4960, September 2007. 1029 [RFC5164] Melia, T., "Mobility Services Transport: Problem 1030 Statement", RFC 5164, March 2008. 1032 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 1033 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 1035 [RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P. 1036 Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142, 1037 RFC 5382, October 2008. 1039 [RFC5405] Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines 1040 for Application Designers", BCP 145, RFC 5405, 1041 November 2008. 1043 Authors' Addresses 1045 Telemaco Melia (editor) 1046 Alcatel-Lucent 1047 Route de Villejust 1048 Nozay 91620 1049 France 1051 Email: telemaco.melia@alcatel-lucent.com 1052 Gabor Bajko 1053 Nokia 1055 Email: Gabor.Bajko@nokia.com 1057 Subir Das 1058 Telcordia Technologies Inc. 1060 Email: subir@research.telcordia.com 1062 Nada Golmie 1063 NIST 1065 Email: nada.golmie@nist.gov 1067 Juan Carlos Zuniga 1068 InterDigital Communications, LLC 1070 Email: j.c.zuniga@ieee.org