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RFC 4907


Architectural Implications of Link Indications

Part 3 of 4, p. 28 to 40
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4.  Security Considerations

   Proposals for the utilization of link indications may introduce new
   security vulnerabilities.  These include:

      Indication validation
      Denial of service

4.1.  Spoofing

   Where link layer control frames are unprotected, they may be spoofed
   by an attacker.  For example, PPP does not protect LCP frames such as
   LCP-Terminate, and [IEEE-802.11] does not protect management frames
   such as Associate/Reassociate, Disassociate, or Deauthenticate.

   Spoofing of link layer control traffic may enable attackers to
   exploit weaknesses in link indication proposals.  For example,
   proposals that do not implement congestion avoidance can enable
   attackers to mount denial-of-service attacks.

   However, even where the link layer incorporates security, attacks may
   still be possible if the security model is not consistent.  For
   example, wireless LANs implementing [IEEE-802.11i] do not enable

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   stations to send or receive IP packets on the link until completion
   of an authenticated key exchange protocol known as the "4-way
   handshake".  As a result, a link implementing [IEEE-802.11i] cannot
   be considered usable at the Internet layer ("Link Up") until
   completion of the authenticated key exchange.

   However, while [IEEE-802.11i] requires sending of authenticated
   frames in order to obtain a "Link Up" indication, it does not support
   management frame authentication.  This weakness can be exploited by
   attackers to enable denial-of-service attacks on stations attached to
   distant Access Points (APs).

   In [IEEE-802.11F], "Link Up" is considered to occur when an AP sends
   a Reassociation Response.  At that point, the AP sends a spoofed
   frame with the station's source address to a multicast address,
   thereby causing switches within the Distribution System (DS) to learn
   the station's MAC address.  While this enables forwarding of frames
   to the station at the new point of attachment, it also permits an
   attacker to disassociate a station located anywhere within the ESS,
   by sending an unauthenticated Reassociation Request frame.

4.2.  Indication Validation

   "Fault Isolation and Recovery" [RFC816], Section 3, describes how
   hosts interact with routers for the purpose of fault recovery:

   Since the gateways always attempt to have a consistent and correct
   model of the internetwork topology, the host strategy for fault
   recovery is very simple.  Whenever the host feels that something is
   wrong, it asks the gateway for advice, and, assuming the advice is
   forthcoming, it believes the advice completely.  The advice will be
   wrong only during the transient period of negotiation, which
   immediately follows an outage, but will otherwise be reliably

   In fact, it is never necessary for a host to explicitly ask a gateway
   for advice, because the gateway will provide it as appropriate.  When
   a host sends a datagram to some distant net, the host should be
   prepared to receive back either of two advisory messages which the
   gateway may send.  The ICMP "redirect" message indicates that the
   gateway to which the host sent the datagram is no longer the best
   gateway to reach the net in question.  The gateway will have
   forwarded the datagram, but the host should revise its routing table
   to have a different immediate address for this net.  The ICMP
   "destination unreachable" message indicates that as a result of an
   outage, it is currently impossible to reach the addressed net or host

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   in any manner.  On receipt of this message, a host can either abandon
   the connection immediately without any further retransmission, or
   resend slowly to see if the fault is corrected in reasonable time.

   Given today's security environment, it is inadvisable for hosts to
   act on indications provided by routers without careful consideration.
   As noted in "ICMP attacks against TCP" [Gont], existing ICMP error
   messages may be exploited by attackers in order to abort connections
   in progress, prevent setup of new connections, or reduce throughput
   of ongoing connections.  Similar attacks may also be launched against
   the Internet layer via forging of ICMP redirects.

   Proposals for transported link indications need to demonstrate that
   they will not add a new set of similar vulnerabilities.  Since
   transported link indications are typically unauthenticated, hosts
   receiving them may not be able to determine whether they are
   authentic, or even plausible.

   Where link indication proposals may respond to unauthenticated link
   layer frames, they should utilize upper-layer security mechanisms,
   where possible.  For example, even though a host might utilize an
   unauthenticated link layer control frame to conclude that a link has
   become operational, it can use SEND [RFC3971] or authenticated DHCP
   [RFC3118] in order to obtain secure Internet layer configuration.

4.3.  Denial of Service

   Link indication proposals need to be particularly careful to avoid
   enabling denial-of-service attacks that can be mounted at a distance.
   While wireless links are naturally vulnerable to interference, such
   attacks can only be perpetrated by an attacker capable of
   establishing radio contact with the target network.  However, attacks
   that can be mounted from a distance, either by an attacker on another
   point of attachment within the same network or by an off-link
   attacker, expand the level of vulnerability.

   The transport of link indications can increase risk by enabling
   vulnerabilities exploitable only by attackers on the local link to be
   executed across the Internet.  Similarly, by integrating link
   indications with upper layers, proposals may enable a spoofed link
   layer frame to consume more resources on the host than might
   otherwise be the case.  As a result, while it is important for upper
   layers to validate link indications, they should not expend excessive
   resources in doing so.

   Congestion control is not only a transport issue, it is also a
   security issue.  In order to not provide leverage to an attacker, a
   single forged link layer frame should not elicit a magnified response

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   from one or more hosts, by generating either multiple responses or a
   single larger response.  For example, proposals should not enable
   multiple hosts to respond to a frame with a multicast destination

5.  References

5.1.  Normative References

   [RFC2119]      Bradner, S., "Key words for use in RFCs to Indicate
                  Requirement Levels", BCP 14, RFC 2119, March 1997.

5.2.  Informative References

   [RFC816]       Clark, D., "Fault Isolation and Recovery", RFC 816,
                  July 1982.

   [RFC1058]      Hedrick, C., "Routing Information Protocol", RFC 1058,
                  June 1988.

   [RFC1122]      Braden, R., "Requirements for Internet Hosts --
                  Communication Layers", STD 3, RFC 1122, October 1989.

   [RFC1131]      Moy, J., "The OSPF Specification", RFC 1131, October

   [RFC1191]      Mogul, J. and S. Deering, "Path MTU discovery", RFC
                  1191, November 1990.

   [RFC1256]      Deering, S., "ICMP Router Discovery Messages", RFC
                  1256, September 1991.

   [RFC1305]      Mills, D., "Network Time Protocol (Version 3)
                  Specification, Implementation and Analysis", RFC 1305,
                  March 1992.

   [RFC1307]      Young, J. and A. Nicholson, "Dynamically Switched Link
                  Control Protocol", RFC 1307, March 1992.

   [RFC1661]      Simpson, W., "The Point-to-Point Protocol (PPP)", STD
                  51, RFC 1661, July 1994.

   [RFC1812]      Baker, F., "Requirements for IP Version 4 Routers",
                  RFC 1812, June 1995.

   [RFC1918]      Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot,
                  D., and E. Lear, "Address Allocation for Private
                  Internets", BCP 5, RFC 1918, February 1996.

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   [RFC1981]      McCann, J., Deering, S. and J. Mogul, "Path MTU
                  Discovery for IP version 6", RFC 1981, June 1996.

   [RFC2131]      Droms, R., "Dynamic Host Configuration Protocol", RFC
                  2131, March 1997.

   [RFC2328]      Moy, J., "OSPF Version 2", STD 54, RFC 2328, April

   [RFC2461]      Narten, T., Nordmark, E., and W. Simpson, "Neighbor
                  Discovery for IP Version 6 (IPv6)", RFC 2461, December

   [RFC2778]      Day, M., Rosenberg, J., and H. Sugano, "A Model for
                  Presence and Instant Messaging", RFC 2778, February

   [RFC2861]      Handley, M., Padhye, J., and S. Floyd, "TCP Congestion
                  Window Validation", RFC 2861, June 2000.

   [RFC2914]      Floyd, S., "Congestion Control Principles", RFC 2914,
                  BCP 41, September 2000.

   [RFC2923]      Lahey, K., "TCP Problems with Path MTU Discovery", RFC
                  2923, September 2000.

   [RFC2960]      Stewart, R., Xie, Q., Morneault, K., Sharp, C.,
                  Schwarzbauer, H. Taylor, T., Rytina, I., Kalla, M.,
                  Zhang, L., and V. Paxson, "Stream Control Transmission
                  Protocol" RFC 2960, October 2000.

   [RFC3118]      Droms, R. and B. Arbaugh, "Authentication for DHCP
                  Messages", RFC 3118, June 2001.

   [RFC3315]      Droms, R., Bound, J., Volz, B., Lemon, T., Perkins,
                  C., and M. Carney, "Dynamic Host Configuration
                  Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC3366]      Fairhurst, G. and L. Wood, "Advice to link designers
                  on link Automatic Repeat reQuest (ARQ)", BCP 62, RFC
                  3366, August 2002.

   [RFC3428]      Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema,
                  C., and D. Gurle, "Session Initiation Protocol (SIP)
                  Extension for Instant Messaging", RFC 3428, December

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   [RFC3748]      Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and
                  H. Levkowetz, "Extensible Authentication Protocol
                  (EAP)", RFC 3748, June 2004.

   [RFC3775]      Johnson, D., Perkins, C., and J. Arkko, "Mobility
                  Support in IPv6", RFC 3775, June 2004.

   [RFC3921]      Saint-Andre, P., "Extensible Messaging and Presence
                  protocol (XMPP):  Instant Messaging and Presence", RFC
                  3921, October 2004.

   [RFC3927]      Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
                  Configuration of Link-Local IPv4 Addresses", RFC 3927,
                  May 2005.

   [RFC3971]      Arkko, J., Kempf, J., Zill, B., and P. Nikander,
                  "SEcure Neighbor Discovery (SEND)", RFC 3971, March

   [RFC4340]      Kohler, E., Handley, M., and S. Floyd, "Datagram
                  Congestion Control Protocol (DCCP)", RFC 4340, March

   [RFC4423]      Moskowitz, R. and P. Nikander, "Host Identity Protocol
                  (HIP) Architecture", RFC 4423, May 2006.

   [RFC4429]      Moore, N., "Optimistic Duplicate Address Detection
                  (DAD) for IPv6", RFC 4429, April 2006.

   [RFC4436]      Aboba, B., Carlson, J., and S. Cheshire, "Detecting
                  Network Attachment in IPv4 (DNAv4)", RFC 4436, March

   [RFC4821]      Mathis, M. and J. Heffner, "Packetization Layer Path
                  MTU Discovery", RFC 4821, March 2007.

   [Alimian]      Alimian, A., "Roaming Interval Measurements",
                  11-04-0378-00-roaming-intervals-measurements.ppt, IEEE
                  802.11 submission (work in progress), March 2004.

   [Aguayo]       Aguayo, D., Bicket, J., Biswas, S., Judd, G., and R.
                  Morris, "Link-level Measurements from an 802.11b Mesh
                  Network", SIGCOMM '04, September 2004, Portland,

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   [Bakshi]       Bakshi, B., Krishna, P., Vadiya, N., and D.Pradhan,
                  "Improving Performance of TCP over Wireless Networks",
                  Proceedings of the 1997 International Conference on
                  Distributed Computer Systems, Baltimore, May 1997.

   [BFD]          Katz, D. and D. Ward, "Bidirectional Forwarding
                  Detection", Work in Progress, March 2007.

   [Biaz]         Biaz, S. and N. Vaidya, "Discriminating Congestion
                  Losses from Wireless Losses Using Interarrival Times
                  at the Receiver", Proceedings of the IEEE Symposium on
                  Application-Specific Systems and Software Engineering
                  and Technology, Richardson, TX, Mar 1999.

   [CARA]         Kim, J., Kim, S., and S. Choi, "CARA: Collision-Aware
                  Rate Adaptation for IEEE 802.11 WLANs", Korean
                  Institute of Communication Sciences (KICS) Journal,
                  Feb. 2006

   [Chandran]     Chandran, K., Raghunathan, S., Venkatesan, S., and R.
                  Prakash, "A Feedback-Based Scheme for Improving TCP
                  Performance in Ad-Hoc Wireless Networks", Proceedings
                  of the 18th International Conference on Distributed
                  Computing Systems (ICDCS), Amsterdam, May 1998.

   [DNAv6]        Narayanan, S., "Detecting Network Attachment in IPv6
                  (DNAv6)", Work in Progress, March 2007.

   [E2ELinkup]    Dawkins, S. and C. Williams, "End-to-end, Implicit
                  'Link-Up' Notification", Work in Progress, October

   [EAPIKEv2]     Tschofenig, H., Kroeselberg, D., Pashalidis, A., Ohba,
                  Y., and F. Bersani, "EAP IKEv2 Method", Work in
                  Progress, March 2007.

   [Eckhardt]     Eckhardt, D. and P. Steenkiste, "Measurement and
                  Analysis of the Error Characteristics of an In-
                  Building Wireless Network", SIGCOMM '96, August 1996,
                  Stanford, CA.

   [Eddy]         Eddy, W. and Y. Swami, "Adapting End Host Congestion
                  Control for Mobility", Technical Report CR-2005-
                  213838, NASA Glenn Research Center, July 2005.

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                  Gunaratne, C. and K. Christensen, "Ethernet Adaptive
                  Link Rate: System Design and Performance Evaluation",
                  Proceedings of the IEEE Conference on Local Computer
                  Networks, pp. 28-35, November 2006.

   [Eggert]       Eggert, L., Schuetz, S., and S. Schmid, "TCP
                  Extensions for Immediate Retransmissions", Work in
                  Progress, June 2005.

   [Eggert2]      Eggert, L. and W. Eddy, "Towards More Expressive
                  Transport-Layer Interfaces", MobiArch '06, San
                  Francisco, CA.

   [ETX]          Douglas S. J. De Couto, Daniel Aguayo, John Bicket,
                  and Robert Morris, "A High-Throughput Path Metric for
                  Multi-Hop Wireless Routing", Proceedings of the 9th
                  ACM International Conference on Mobile Computing and
                  Networking (MobiCom '03), San Diego, California,
                  September 2003.

   [ETX-Rate]     Padhye, J., Draves, R. and B. Zill, "Routing in
                  multi-radio, multi-hop wireless mesh networks",
                  Proceedings of ACM MobiCom Conference, September 2003.

   [ETX-Radio]    Kulkarni, G., Nandan, A., Gerla, M., and M.
                  Srivastava, "A Radio Aware Routing Protocol for
                  Wireless Mesh Networks", UCLA Computer Science
                  Department, Los Angeles, CA.

   [GenTrig]      Gupta, V. and D. Johnston, "A Generalized Model for
                  Link Layer Triggers", submission to IEEE 802.21 (work
                  in progress), March 2004, available at:

   [Goel]         Goel, S. and D. Sanghi, "Improving TCP Performance
                  over Wireless Links", Proceedings of TENCON'98, pages
                  332-335.  IEEE, December 1998.

   [Gont]         Gont, F., "ICMP attacks against TCP", Work in
                  Progress, October 2006.

   [Gurtov]       Gurtov, A. and J. Korhonen, "Effect of Vertical
                  Handovers on Performance of TCP-Friendly Rate
                  Control", to appear in ACM MCCR, 2004.

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   [GurtovFloyd]  Gurtov, A. and S. Floyd, "Modeling Wireless Links for
                  Transport Protocols", Computer Communications Review
                  (CCR) 34, 2 (2003).

   [Haratcherev]  Haratcherev, I., Lagendijk, R., Langendoen, K., and H.
                  Sips, "Hybrid Rate Control for IEEE 802.11", MobiWac
                  '04, October 1, 2004, Philadelphia, Pennsylvania, USA.

   [Haratcherev2] Haratcherev, I., "Application-oriented Link Adaptation
                  for IEEE 802.11", Ph.D. Thesis, Technical University
                  of Delft, Netherlands, ISBN-10:90-9020513-6, ISBN-
                  13:978-90-9020513-7, March 2006.

   [HMP]          Lee, S., Cho, J., and A. Campbell, "Hotspot Mitigation
                  Protocol (HMP)", Work in Progress, October 2003.

   [Holland]      Holland, G. and N. Vaidya, "Analysis of TCP
                  Performance over Mobile Ad Hoc Networks", Proceedings
                  of the Fifth International Conference on Mobile
                  Computing and Networking, pages 219-230.  ACM/IEEE,
                  Seattle, August 1999.

   [Iannaccone]   Iannaccone, G., Chuah, C., Mortier, R., Bhattacharyya,
                  S., and C. Diot, "Analysis of link failures in an IP
                  backbone", Proc. of ACM Sigcomm Internet Measurement
                  Workshop, November, 2002.

   [IEEE-802.1X]  Institute of Electrical and Electronics Engineers,
                  "Local and Metropolitan Area Networks: Port-Based
                  Network Access Control", IEEE Standard 802.1X,
                  December 2004.

   [IEEE-802.11]  Institute of Electrical and Electronics Engineers,
                  "Wireless LAN Medium Access Control (MAC) and Physical
                  Layer (PHY) Specifications", IEEE Standard 802.11,

   [IEEE-802.11e] Institute of Electrical and Electronics Engineers,
                  "Standard for Telecommunications and Information
                  Exchange Between Systems - LAN/MAN Specific
                  Requirements - Part 11: Wireless LAN Medium Access
                  Control (MAC) and Physical Layer (PHY) Specifications
                  - Amendment 8: Medium Access Control (MAC) Quality of
                  Service Enhancements", IEEE 802.11e, November 2005.

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   [IEEE-802.11F] Institute of Electrical and Electronics Engineers,
                  "IEEE Trial-Use Recommended Practice for Multi-Vendor
                  Access Point Interoperability via an Inter-Access
                  Point Protocol Across Distribution Systems Supporting
                  IEEE 802.11 Operation", IEEE 802.11F, June 2003 (now

   [IEEE-802.11i] Institute of Electrical and Electronics Engineers,
                  "Supplement to Standard for Telecommunications and
                  Information Exchange Between Systems - LAN/MAN
                  Specific Requirements - Part 11:  Wireless LAN Medium
                  Access Control (MAC) and Physical Layer (PHY)
                  Specifications: Specification for Enhanced Security",
                  IEEE 802.11i, July 2004.

   [IEEE-802.11k] Institute of Electrical and Electronics Engineers,
                  "Draft Amendment to Telecommunications and Information
                  Exchange Between Systems - LAN/MAN Specific
                  Requirements - Part 11:  Wireless LAN Medium Access
                  Control (MAC) and Physical Layer (PHY) Specifications
                  - Amendment 7: Radio Resource Management", IEEE
                  802.11k/D7.0, January 2007.

   [IEEE-802.21]  Institute of Electrical and Electronics Engineers,
                  "Draft Standard for Telecommunications and Information
                  Exchange Between Systems - LAN/MAN Specific
                  Requirements - Part 21:  Media Independent Handover",
                  IEEE 802.21D0, June 2005.

   [Kamerman]     Kamerman, A. and L. Monteban, "WaveLAN II: A High-
                  Performance Wireless LAN for the Unlicensed Band",
                  Bell Labs Technical Journal, Summer 1997.

   [Kim]          Kim, K., Park, Y., Suh, K., and Y. Park, "The BU-
                  trigger method for improving TCP performance over
                  Mobile IPv6", Work in Progress, August 2004.

   [Kotz]         Kotz, D., Newport, C., and C. Elliot, "The mistaken
                  axioms of wireless-network research", Dartmouth
                  College Computer Science Technical Report TR2003-467,
                  July 2003.

   [Krishnan]     Krishnan, R., Sterbenz, J., Eddy, W., Partridge, C.,
                  and M. Allman, "Explicit Transport Error Notification
                  (ETEN) for Error-Prone Wireless and Satellite
                  Networks", Computer Networks, 46 (3), October 2004.

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   [Lacage]       Lacage, M., Manshaei, M., and T. Turletti, "IEEE
                  802.11 Rate Adaptation: A Practical Approach", MSWiM
                  '04, October 4-6, 2004, Venezia, Italy.

   [Lee]          Park, S., Lee, M., and J. Korhonen, "Link
                  Characteristics Information for Mobile IP", Work in
                  Progress, January 2007.

   [Ludwig]       Ludwig, R. and B. Rathonyi, "Link-layer Enhancements
                  for TCP/IP over GSM", Proceedings of IEEE Infocom '99,
                  March 1999.

   [MIPEAP]       Giaretta, C., Guardini, I., Demaria, E., Bournelle,
                  J., and M. Laurent-Maknavicius, "MIPv6 Authorization
                  and Configuration based on EAP", Work in Progress,
                  October 2006.

   [Mishra]       Mitra, A., Shin, M., and W. Arbaugh, "An Empirical
                  Analysis of the IEEE 802.11 MAC Layer Handoff
                  Process", CS-TR-4395, University of Maryland
                  Department of Computer Science, September 2002.

   [Morgan]       Morgan, S. and S. Keshav, "Packet-Pair Rate Control -
                  Buffer Requirements and Overload Performance",
                  Technical Memorandum, AT&T Bell Laboratories, October

   [Mun]          Mun, Y. and J. Park, "Layer 2 Handoff for Mobile-IPv4
                  with 802.11", Work in Progress, March 2004.

   [ONOE]         Onoe Rate Control,

   [Park]         Park, S., Njedjou, E., and N. Montavont, "L2 Triggers
                  Optimized Mobile IPv6 Vertical Handover: The
                  802.11/GPRS Example", Work in Progress, July 2004.

   [Pavon]        Pavon, J. and S. Choi, "Link adaptation strategy for
                  IEEE802.11 WLAN via received signal strength
                  measurement", IEEE International Conference on
                  Communications, 2003 (ICC '03), volume 2, pages 1108-
                  1113, Anchorage, Alaska, USA, May 2003.

   [PEAP]         Palekar, A., Simon, D., Salowey, J., Zhou, H., Zorn,
                  G., and S. Josefsson, "Protected EAP Protocol (PEAP)
                  Version 2", Work in Progress, October 2004.

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   [PRNET]        Jubin, J. and J. Tornow, "The DARPA packet radio
                  network protocols", Proceedings of the IEEE, 75(1),
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   [Qiao]         Qiao D., Choi, S., Jain, A., and Kang G. Shin, "MiSer:
                  An Optimal Low-Energy Transmission Strategy for IEEE
                  802.11 a/h", in Proc. ACM MobiCom'03, San Diego, CA,
                  September 2003.

   [RBAR]         Holland, G., Vaidya, N., and P. Bahl, "A Rate-Adaptive
                  MAC Protocol for Multi-Hop Wireless Networks",
                  Proceedings ACM MOBICOM, July 2001.

   [Ramani]       Ramani, I. and S. Savage, "SyncScan: Practical Fast
                  Handoff for 802.11 Infrastructure Networks",
                  Proceedings of the IEEE InfoCon 2005, March 2005.

   [Robust]       Wong, S., Yang, H ., Lu, S., and V. Bharghavan,
                  "Robust Rate Adaptation for 802.11 Wireless Networks",
                  ACM MobiCom'06, Los Angeles, CA, September 2006.

   [SampleRate]   Bicket, J., "Bit-rate Selection in Wireless networks",
                  MIT Master's Thesis, 2005.

   [Scott]        Scott, J., Mapp, G., "Link Layer Based TCP
                  Optimisation for Disconnecting Networks", ACM SIGCOMM
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   [Schuetz]      Schutz, S., Eggert, L., Schmid, S., and M. Brunner,
                  "Protocol Enhancements for Intermittently Connected
                  Hosts", ACM SIGCOMM Computer Communications Review,
                  Volume 35, Number 2, July 2005.

   [Shortest]     Douglas S. J. De Couto, Daniel Aguayo, Benjamin A.
                  Chambers and Robert Morris, "Performance of Multihop
                  Wireless Networks: Shortest Path is Not Enough",
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                  Networking (HotNets-I), Princeton, New Jersey, October

   [TRIGTRAN]     Dawkins, S., Williams, C., and A. Yegin, "Framework
                  and Requirements for TRIGTRAN", Work in Progress,
                  August 2003.

   [Vatn]         Vatn, J., "An experimental study of IEEE 802.11b
                  handover performance and its effect on voice traffic",
                  TRITA-IMIT-TSLAB R 03:01, KTH Royal Institute of
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   [Velayos]      Velayos, H. and G. Karlsson, "Techniques to Reduce
                  IEEE 802.11b MAC Layer Handover Time", TRITA-IMIT-LCN
                  R 03:02, KTH Royal Institute of Technology, Stockholm,
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   [Vertical]     Zhang, Q., Guo, C., Guo, Z., and W. Zhu, "Efficient
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                  and WLAN", IEEE Communications Magazine, November

   [Villamizar]   Villamizar, C., "OSPF Optimized Multipath (OSPF-OMP)",
                  Work in Progress, February 1999.

   [Xylomenos]    Xylomenos, G., "Multi Service Link Layers: An Approach
                  to Enhancing Internet Performance over Wireless
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   [Yegin]        Yegin, A., "Link-layer Triggers Protocol", Work in
                  Progress, June 2002.

6.  Acknowledgments

   The authors would like to acknowledge James Kempf, Phil Roberts,
   Gorry Fairhurst, John Wroclawski, Aaron Falk, Sally Floyd, Pekka
   Savola, Pekka Nikander, Dave Thaler, Yogesh Swami, Wesley Eddy, and
   Janne Peisa for contributions to this document.

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