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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'IESG' is mentioned on line 400, but not defined ** Obsolete normative reference: RFC 2460 (Obsoleted by RFC 8200) ** Obsolete normative reference: RFC 4960 (Obsoleted by RFC 9260) == Outdated reference: A later version (-09) exists of draft-ietf-behave-sctpnat-08 == Outdated reference: A later version (-23) exists of draft-ietf-tsvwg-natsupp-05 Summary: 2 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group M. Tuexen 3 Internet-Draft Muenster Univ. of Appl. Sciences 4 Intended status: Standards Track R. R. Stewart 5 Expires: September 20, 2013 Adara Networks 6 March 19, 2013 8 UDP Encapsulation of SCTP Packets for End-Host to End-Host Communication 9 draft-ietf-tsvwg-sctp-udp-encaps-14.txt 11 Abstract 13 This document describes a simple method of encapsulating SCTP Packets 14 into UDP packets and its limitations. This allows the usage of SCTP 15 in networks with legacy NAT not supporting SCTP. It can also be used 16 to implement SCTP on hosts without directly accessing the IP-layer, 17 for example implementing it as part of the application without 18 requiring special privileges. 20 Please note that this document only describes the functionality 21 required within an SCTP stack to add on UDP encapsulation, providing 22 only those mechanisms for two end-hosts to communicate with each 23 other over UDP ports. In particular, it does not provide mechanisms 24 to determine whether UDP encapsulation is being used by the peer, nor 25 the mechanisms for determining which remote UDP port number can be 26 used. These functions are are out of scope for this document. 28 This document covers only end-hosts and not tunneling (egress or 29 ingress) end-points. 31 Status of This Memo 33 This Internet-Draft is submitted in full conformance with the 34 provisions of BCP 78 and BCP 79. 36 Internet-Drafts are working documents of the Internet Engineering 37 Task Force (IETF). Note that other groups may also distribute 38 working documents as Internet-Drafts. The list of current Internet- 39 Drafts is at http://datatracker.ietf.org/drafts/current/. 41 Internet-Drafts are draft documents valid for a maximum of six months 42 and may be updated, replaced, or obsoleted by other documents at any 43 time. It is inappropriate to use Internet-Drafts as reference 44 material or to cite them other than as "work in progress." 46 This Internet-Draft will expire on September 20, 2013. 48 Copyright Notice 50 Copyright (c) 2013 IETF Trust and the persons identified as the 51 document authors. All rights reserved. 53 This document is subject to BCP 78 and the IETF Trust's Legal 54 Provisions Relating to IETF Documents 55 (http://trustee.ietf.org/license-info) in effect on the date of 56 publication of this document. Please review these documents 57 carefully, as they describe your rights and restrictions with respect 58 to this document. Code Components extracted from this document must 59 include Simplified BSD License text as described in Section 4.e of 60 the Trust Legal Provisions and are provided without warranty as 61 described in the Simplified BSD License. 63 Table of Contents 65 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 66 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3 67 3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3 68 3.1. Portable SCTP Implementations . . . . . . . . . . . . . . 3 69 3.2. Legacy NAT Traversal . . . . . . . . . . . . . . . . . . 4 70 4. Unilateral Self-Address Fixing (UNSAF) Considerations . . . . 4 71 5. SCTP over UDP . . . . . . . . . . . . . . . . . . . . . . . . 4 72 5.1. Architectural Considerations . . . . . . . . . . . . . . 4 73 5.2. Packet Format . . . . . . . . . . . . . . . . . . . . . . 5 74 5.3. Encapsulation Procedure . . . . . . . . . . . . . . . . . 6 75 5.4. Decapsulation Procedure . . . . . . . . . . . . . . . . . 7 76 5.5. ICMP Considerations . . . . . . . . . . . . . . . . . . . 7 77 5.6. Path MTU Considerations . . . . . . . . . . . . . . . . . 8 78 5.7. Handling of Embedded IP-addresses . . . . . . . . . . . . 8 79 5.8. ECN Considerations . . . . . . . . . . . . . . . . . . . 8 80 6. Socket API Considerations . . . . . . . . . . . . . . . . . . 8 81 6.1. Get or Set the Remote UDP Encapsulation Port Number 82 (SCTP_REMOTE_UDP_ENCAPS_PORT) . . . . . . . . . . . . . . 9 83 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 84 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 85 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 86 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 87 10.1. Normative References . . . . . . . . . . . . . . . . . . 10 88 10.2. Informative References . . . . . . . . . . . . . . . . . 11 89 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 91 1. Introduction 93 This document describes a simple method of encapsulating SCTP packets 94 into UDP packets. SCTP as defined in [RFC4960] runs directly over 95 IPv4 or IPv6. There are two main reasons for encapsulating SCTP 96 packets: 98 o Allow SCTP traffic to pass through legacy NATs, which do not 99 provide native SCTP support as specified in 100 [I-D.ietf-behave-sctpnat] and [I-D.ietf-tsvwg-natsupp]. 102 o Allow SCTP to be implemented on hosts which do not provide direct 103 access to the IP-layer. In particular, applications can use their 104 own SCTP implementation if the operating system does not provide 105 one. 107 SCTP provides the necessary congestion control and reliability 108 service that UDP does not perform. 110 2. Conventions 112 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 113 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 114 document are to be interpreted as described in [RFC2119]. 116 3. Use Cases 118 This section discusses two important use cases for encapsulating SCTP 119 into UDP. 121 3.1. Portable SCTP Implementations 123 Some operating systems support SCTP natively. For other operating 124 systems implementations are available, but require special privileges 125 to install and/or use them. In some cases no kernel implementation 126 might be available at all. When providing an SCTP implementation as 127 part of a user process, most operating systems require special 128 privileges to access the IP layer directly. 130 Using UDP encapsulation makes it possible to provide an SCTP 131 implementation as part of a user process which does not require any 132 special privileges. 134 A crucial point for implementing SCTP in user space is that the 135 source address of outgoing packets needs to be controlled. This is 136 not an issue if the SCTP stack can use all addresses configured at 137 the IP-layer as source addresses. However, it is an issue when also 138 using the address management required for NAT traversal, described in 139 Section 5.7. 141 3.2. Legacy NAT Traversal 143 Using UDP encapsulation allows SCTP communication when traversing 144 legacy NATs (i.e those NATs not supporting SCTP as described in 145 [I-D.ietf-behave-sctpnat] and [I-D.ietf-tsvwg-natsupp]). For single- 146 homed associations IP addresses MUST NOT be listed in the INIT and 147 INIT-ACK chunks. To use multiple addresses, the dynamic address 148 reconfiguration extension described in [RFC5061] MUST be used only 149 with wildcard addresses in the ASCONF chunks in combination with 150 [RFC4895]. 152 For multi-homed SCTP association the address management as described 153 in Section 5.7 MUST be performed. 155 SCTP sends periodic HEARTBEAT chunks on all idle paths. These can 156 keep the NAT state alive. 158 4. Unilateral Self-Address Fixing (UNSAF) Considerations 160 As [RFC3424] requires a limited scope, this document only covers SCTP 161 end-points dealing with legacy constraints as described in Section 3. 162 It doesn't cover generic tunneling end-points. 164 Obviously, the exit strategy is to use hosts supporting SCTP natively 165 and middleboxes supporting SCTP as specified in 166 [I-D.ietf-behave-sctpnat] and [I-D.ietf-tsvwg-natsupp]). 168 5. SCTP over UDP 170 5.1. Architectural Considerations 172 UDP encapsulated SCTP is normally communicated between SCTP stacks 173 using the IANA-assigned UDP port number 9899 (sctp-tunneling) on both 174 ends. There are circumstances where other ports may be used on 175 either end: As stated earlier, implementations in the application 176 space might be required to use other than the registered port. Since 177 NAT boxes might change UDP port numbers, the receiver might observe 178 other UDP port numbers than were used by the sender. Discovery of 179 alternate ports is outside of the scope of this document, but this 180 section describes considerations for SCTP stack design in light of 181 their potential use. 183 Each SCTP stack uses a single local UDP encapsulation port number as 184 the destination port for all its incoming SCTP packets. While the 185 uniqueness of the local UDP encapsulation port number is not 186 necessarily required for the protocol, this greatly simplifies 187 implementation design, since different ports for each address would 188 require a sender implementation to choose the appropriate port while 189 doing source address selection. Using a single local UDP 190 encapsulation port number per host is not possible if the SCTP stack 191 is implemented as part of each application, there are multiple 192 applications, and some of the applications want to use the same IP- 193 address. 195 An SCTP implementation supporting UDP encapsulation MUST maintain a 196 remote UDP encapsulation port number per destination address for each 197 SCTP association. Again, because the remote stack may be using other 198 than the well-known port, each port may be different from each stack, 199 but because of remapping of ports by NATs, the remote ports 200 associated with different remote IP addresses may not be identical, 201 even if they are associated with the same stack. 203 Implementation note: Because the well-known port might not be used, 204 implementations need allow other port numbers to be specified as a 205 local or remote UDP encapsulation port number through APIs. 207 5.2. Packet Format 209 To encapsulate an SCTP packet, a UDP header as defined in [RFC0768] 210 is inserted between the IP header as defined in [RFC0791] and the 211 SCTP common header as defined in [RFC4960]. 213 Figure 1 shows the packet format of an encapsulated SCTP packet when 214 IPv4 is used. 216 0 1 2 3 217 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 1 218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 219 | IPv4 Header | 220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 221 | UDP Header | 222 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 223 | SCTP Common Header | 224 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 225 | SCTP Chunk #1 | 226 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 227 | ... | 228 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 229 | SCTP Chunk #n | 230 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 231 Figure 1: An SCTP/UDP/IPv4 packet 233 The packet format for an encapsulated SCTP packet when using IPv6 as 234 defined in [RFC2460] is shown in Figure 2. Please note the the 235 number m of IPv6 extension headers can be 0. 237 0 1 2 3 238 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 1 239 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 240 | IPv6 Base Header | 241 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 242 | IPv6 Extension Header #1 | 243 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 244 | ... | 245 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 246 | IPv6 Extension Header #m | 247 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 248 | UDP Header | 249 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 250 | SCTP Common Header | 251 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 252 | SCTP Chunk #1 | 253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 254 | ... | 255 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 256 | SCTP Chunk #n | 257 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 259 Figure 2: An SCTP/UDP/IPv6 packet 261 5.3. Encapsulation Procedure 263 Within the UDP header, the source port MUST be the local UDP 264 encapsulation port number of the SCTP stack, the destination port 265 MUST be the remote UDP encapsulation port number maintained for the 266 association and the destination address to which the packet is sent 267 (see Section 5.1). 269 Because the SCTP packet is the UDP payload, the length of the UDP 270 packet MUST be the length of the SCTP packet plus the size of the UDP 271 header. 273 The SCTP checksum MUST be computed and the UDP checksum SHOULD be 274 computed for IPv4 (see [RFC0768]) and IPv6 (see [RFC2460] and 275 [I-D.ietf-6man-udpzero]). Although UDP with a zero checksum over 276 IPv6 is allowed under certain constraints [I-D.ietf-6man-udpzero], 277 this document does not specify mechanisms for this mode. Deployed 278 support may be limited and at the time of writing, the use of a zero 279 UDP checksum would also be counter to the goal of legacy NAT 280 traversal. 282 5.4. Decapsulation Procedure 284 When an encapsulated packet is received, the UDP header is removed. 285 Then the generic lookup is performed, as done by an SCTP stack 286 whenever a packet is received, to find the association for the 287 received SCTP packet. After finding the SCTP association (which 288 includes checking the verification tag), the UDP source port MUST be 289 stored as the encapsulation port for the destination address the SCTP 290 packet is received from (see Section 5.1). 292 When a non-encapsulated SCTP packet is received by the SCTP stack, 293 the encapsulation of outgoing packets belonging to the same 294 association and the corresponding destination address MUST be 295 disabled. 297 5.5. ICMP Considerations 299 When receiving ICMP or ICMPv6 response packets, there might not be 300 enough bytes in the payload to identify the SCTP association which 301 the SCTP packet triggering the ICMP or ICMPv6 packet belongs to. If 302 a received ICMP or ICMPv6 packet can not be related to a specific 303 SCTP association or the verification tag can't be verified, it MUST 304 be discarded silently. This means in particular that the SCTP stack 305 MUST NOT rely on receiving ICMP or ICMPv6 messages. Implementation 306 constraints could prevent processing received ICMP or ICMPv6 307 messages. 309 If received ICMP or ICMPv6 messages are processed, the following 310 mapping SHOULD apply: 312 1. ICMP messages with type 'Destination Unreachable' and code 'Port 313 Unreachable' SHOULD be treated as ICMP messages with type 314 'Protocol Unreachable' and code 'Destination Port unreachable. 315 See [RFC0792] for more details. 317 2. ICMPv6 messages with type 'Destination Unreachable' and code 318 'Port unreachable' SHOULD be treated as ICMPv6 messages with type 319 'Parameter Problem' and code 'Unrecognized Next Header type 320 encountered'. See [RFC4443] for more details. 322 5.6. Path MTU Considerations 324 If an SCTP endpoint starts to encapsulate the packets of a path, it 325 MUST decrease the Path MTU of that path by the size of the UDP 326 header. If it stops encapsulating them, the Path MTU SHOULD be 327 increased by the size of the UDP header. 329 When performing Path MTU discovery as described in [RFC4820] and 330 [RFC4821] it MUST be taken into account that one cannot rely on the 331 feedback provided by ICMP or ICMPv6 due to the limitation laid out in 332 Section 5.5. 334 If the implementation does not allow control of the don't fragment 335 (DF)-bit contained in the IPv4 header, then Path MTU discovery can't 336 be used. In this case, an implementation specific value should be 337 used instead. 339 5.7. Handling of Embedded IP-addresses 341 When using UDP encapsulation for legacy NAT traversal, IP addresses 342 that might require translation MUST NOT be put into any SCTP packet. 344 This means that a multi homed SCTP association is setup initially as 345 a singled homed one and the protocol extension [RFC5061] in 346 combination with [RFC4895] is used to add the other addresses. Only 347 wildcard addresses are put into the SCTP packet. 349 When addresses are changed during the lifetime of an association 350 [RFC5061] MUST be used with wildcard addresses only. If an SCTP end- 351 point receives an ABORT with the T-bit set, it MAY use this as an 352 indication that the addresses seen by the peer might have changed. 354 5.8. ECN Considerations 356 If the implementation supports the sending and receiving of the ECN 357 bits for the IP protocols being used by an SCTP association, the ECN 358 bits MUST NOT be changed during sending and receiving. 360 6. Socket API Considerations 362 This section describes how the socket API defined in [RFC6458] needs 363 to be extended to provide a way for the application to control the 364 UDP encapsulation. 366 Please note that this section is informational only. 368 A socket API implementation based on [RFC6458] is extended by 369 supporting one new read/write socket option. 371 6.1. Get or Set the Remote UDP Encapsulation Port Number 372 (SCTP_REMOTE_UDP_ENCAPS_PORT) 374 This socket option can be used to set and retrieve the UDP 375 encapsulation port number. This allows an endpoint to encapsulate 376 initial packets. 378 struct sctp_udpencaps { 379 sctp_assoc_t sue_assoc_id; 380 struct sockaddr_storage sue_address; 381 uint16_t sue_port; 382 }; 384 sue_assoc_id: This parameter is ignored for one-to-one style 385 sockets. For one-to-many style sockets the application may fill 386 in an association identifier or SCTP_FUTURE_ASSOC for this query. 387 It is an error to use SCTP_{CURRENT|ALL}_ASSOC in sue_assoc_id. 389 sue_address: This specifies which address is of interest. If a 390 wildcard address is provided it applies only to future paths. 392 sue_port: The UDP port number in network byte order used as the 393 destination port number for UDP encapsulation. Providing a value 394 of 0 disables UDP encapsulation. 396 7. IANA Considerations 398 This document refers to the already assigned UDP port 9899 (sctp- 399 tunneling). IANA is requested to update this assignment to refer to 400 this document. As per [RFC6335] the Assignee should be [IESG] and 401 the Contact should be [IETF_Chair]. 403 Please note that the TCP port 9899 (sctp-tunneling) assignment is not 404 needed anymore and IANA is asked to remove this TCP port number 405 assignment. 407 8. Security Considerations 409 Encapsulating SCTP into UDP does not add any additional security 410 considerations to the ones given in [RFC4960] and [RFC5061]. 412 Firewalls inspecting SCTP packets must also be aware of the 413 encapsulation and apply corresponding rules to the encapsulated 414 packets. 416 An attacker might send a malicious UDP packet towards an SCTP end- 417 point to change the encapsulation port for a single remote address of 418 a particular SCTP association. However, as specified in Section 5.4, 419 this requires the usage of one the two negotiated verification tags. 420 This protects against blind attackers the same way as described in 421 [RFC4960] for SCTP over IPv4 or IPv6. Non-blind attackers can affect 422 SCTP association using the UDP encapsulation described in this 423 document in the same way as SCTP associations not using the UDP 424 encapsulation of SCTP described here. 426 9. Acknowledgments 428 The authors wish to thank Stewart Bryant, Dave Crocker, Gorry 429 Fairhurst, Tero Kivinen, Barry Leiba, Pete Resnick, Martin 430 Stiemerling, Irene Ruengeler, and Dan Wing for their invaluable 431 comments. 433 10. References 435 10.1. Normative References 437 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 438 August 1980. 440 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 441 1981. 443 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 444 RFC 792, September 1981. 446 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 447 Requirement Levels", BCP 14, RFC 2119, March 1997. 449 [RFC2460] Deering, S.E. and R.M. Hinden, "Internet Protocol, Version 450 6 (IPv6) Specification", RFC 2460, December 1998. 452 [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control 453 Message Protocol (ICMPv6) for the Internet Protocol 454 Version 6 (IPv6) Specification", RFC 4443, March 2006. 456 [RFC4820] Tuexen, M., Stewart, R., and P. Lei, "Padding Chunk and 457 Parameter for the Stream Control Transmission Protocol 458 (SCTP)", RFC 4820, March 2007. 460 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 461 Discovery", RFC 4821, March 2007. 463 [RFC4895] Tuexen, M., Stewart, R., Lei, P., and E. Rescorla, 464 "Authenticated Chunks for the Stream Control Transmission 465 Protocol (SCTP)", RFC 4895, August 2007. 467 [RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC 468 4960, September 2007. 470 [RFC5061] Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M. 471 Kozuka, "Stream Control Transmission Protocol (SCTP) 472 Dynamic Address Reconfiguration", RFC 5061, September 473 2007. 475 10.2. Informative References 477 [RFC3424] Daigle, L. IAB, "IAB Considerations for UNilateral Self- 478 Address Fixing (UNSAF) Across Network Address 479 Translation", RFC 3424, November 2002. 481 [RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S. 482 Cheshire, "Internet Assigned Numbers Authority (IANA) 483 Procedures for the Management of the Service Name and 484 Transport Protocol Port Number Registry", BCP 165, RFC 485 6335, August 2011. 487 [RFC6458] Stewart, R., Tuexen, M., Poon, K., Lei, P., and V. 488 Yasevich, "Sockets API Extensions for the Stream Control 489 Transmission Protocol (SCTP)", RFC 6458, December 2011. 491 [I-D.ietf-6man-udpzero] 492 Fairhurst, G. and M. Westerlund, "Applicability Statement 493 for the use of IPv6 UDP Datagrams with Zero Checksums", 494 draft-ietf-6man-udpzero-12 (work in progress), February 495 2013. 497 [I-D.ietf-behave-sctpnat] 498 Stewart, R., Tuexen, M., and I. Ruengeler, "Stream Control 499 Transmission Protocol (SCTP) Network Address Translation", 500 draft-ietf-behave-sctpnat-08 (work in progress), February 501 2013. 503 [I-D.ietf-tsvwg-natsupp] 504 Stewart, R., Tuexen, M., and I. Ruengeler, "Stream Control 505 Transmission Protocol (SCTP) Network Address Translation 506 Support", draft-ietf-tsvwg-natsupp-05 (work in progress), 507 February 2013. 509 Authors' Addresses 510 Michael Tuexen 511 Muenster University of Applied Sciences 512 Stegerwaldstrasse 39 513 48565 Steinfurt 514 DE 516 Email: tuexen@fh-muenster.de 518 Randall R. Stewart 519 Adara Networks 520 Chapin, SC 29036 521 US 523 Email: randall@lakerest.net