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RFC 2615                  PPP over SONET/SDH                   June 1999


5.  Configuration Details

   Other than the FCS length (see below), the standard LCP sync
   configuration defaults apply to SONET/SDH links.

   The following Configuration Options are RECOMMENDED for STS-3c-
   SPE/VC-4:

      Magic Number
      No Address and Control Field Compression
      No Protocol Field Compression

   For operation at STS-12c-SPE/VC-4-4c and above, Address and Control
   Field Compression and Protocol Field Compression are NOT RECOMMENDED.
   The Magic Number option remains RECOMMENDED.

   Regarding the FCS length, with one exception, the 32-bit FCS MUST be
   used for all SONET/SDH rates. For STS-3c-SPE/VC-4 only, the 16-bit
   FCS MAY be used, although the 32-bit FCS is RECOMMENDED.  The FCS
   length is set by provisioning and is not negotiated.

6.  Security Considerations

   The major change from RFC 1619 is the addition of payload scrambling
   when inserting the HDLC-like framed PPP packets into the SONET STS-
   SPE/SDH Higher Order VC.  RFC 1619 was operationally found to permit
   malicious users to generate packets with bit patterns that could
   create SONET/SDH-layer low-transition-density synchronization
   problems, emulation of the SDH set-reset scrambler pattern, and
   replication of the STM-N frame alignment word.

   The use of the x^43 + 1 self-synchronous scrambler was introduced to
   alleviate these potential security problems.  Predicting the output
   of the scrambler requires knowledge of the 43-bit state of the
   transmitter as the scrambling of a known input is begun.  This
   requires knowledge of both the initial 43-bit state of the scrambler
   when it started and every byte of data scrambled by the device since
   it was started.  The odds of guessing correctly are 1/2**43, with the
   additional probability of 1/127 that a correct guess will leave the
   frame properly aligned in the SONET/SDH payload, which results in a
   probability of 9e-16 against being able to deliberately cause
   SONET/SDH-layer problems.  This seems reasonably secure for this
   application.

   This scrambler is also used when transmitting ATM over SONET/SDH, and
   public network carriers have considerable experience with its use.





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   A known security issue is bandwidth reduction by intentional
   transmission of characters or sequences requiring transparency
   processing by including flag and/or escape characters in user data. A
   user may cause up to a 100% increase in the bandwidth required for
   transmitting his or her packets by filling the packet with flag
   and/or escape characters.

7.  Changes from RFC 1619

   As mentioned in the previous section, the major change from RFC 1619
   was the addition of payload scrambling when inserting the HDLC-like
   framed PPP packets into the SONET STS-SPE/SDH Higher Order VC.  Other
   changes were:

   The terminology was updated to better match that used by ANSI and
   ITU-T.

   The specification's applicability is now specifically restricted to:

       SONET                   SDH
   ----------------------------------------
   STS-3c-SPE                  VC-4
   STS-12c-SPE                 VC-4-4c
   STS-48c-SPE                 VC-4-16c
   STS-192c-SPE                VC-4-64c

   The Path Signal Label (C2) is set to 22 (16 hex) when using X^43 + 1
   scrambling.

   The 32-bit FCS is required except for operation with STS-3c-SPE/VC-4,
   in which case the 16-bit FCS is allowed (but the 32-bit FCS is still
   recommended).

   The Security Considerations section was added.

8.  Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11.  Copies of
   claims of rights made available for publication and any assurances of
   licenses to be made available, or the result of an attempt made to
   obtain a general license or permission for the use of such



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RFC 2615                  PPP over SONET/SDH                   June 1999


   proprietary rights by implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF Executive
   Director.

9.  Acknowledgments

   The scrambler description was provided by J. Manchester, S. Davida,
   B. Doshi, and J. Anderson of Lucent Technologies, R. Broberg of Cisco
   Systems, and Peter Lothberg of Sprint Corporation.  The security
   analysis was provided by Iain Verigin of PMC-Sierra and Larry McAdams
   of Cisco Systems.  The authors would also like to thank the members
   of the IETF's Point-to-Point Protocol Extensions Working Group for
   their many suggestions and improvements to the text.

10.  References

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

   [2]   Simpson, W., Editor, "PPP in HDLC-like Framing", STD 51, RFC
         1662, Daydreamer, July 1994.

   [3]   American National Standards Institute, "Synchronous Optical
         Network (SONET) - Basic Description including Multiplex
         Structure, Rates and Formats," ANSI T1.105-1995.

   [4]   American National Standards Institute, "Synchronous Optical
         Network (SONET)--Payload Mappings," T1.105.02-1998.

   [5]   ITU Recommendation G.707, "Network Node Interface For The
         Synchronous Digital Hierarchy", 1996.

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












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11.  Authors' Addresses

   Andrew G. Malis
   Ascend Communications, Inc.
   1 Robbins Road
   Westford, MA 01810 USA

   Phone: [phone]
   EMail: [e-mail]


   William Allen Simpson
   DayDreamer
   Computer Systems Consulting Services
   1384 Fontaine
   Madison Heights, Michigan  48071

   EMail: [e-mail]

































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12.  Full Copyright Statement

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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