rfc2331.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

   enforce PCR.  In such environments, the user SHOULD specify 'no
   tagging' in the SETUP message (UBR.1).  Specifying 'no tagging'
   indicates to the network that cells should be dropped during periods
   of congestion instead of being randomly marked/tagged as low
   priority.  Cells of packets that the source itself has marked as low
   priority are dropped first, thereby preserving the source's
   characterization of the traffic.

   On the other hand, when the network applies PCR to the UPC function,
   meaning it enforces PCR, and traffic shaping is not enabled at the
   source, the source has the potential to violate the traffic contract
   and SHOULD therefore signal for tagging (UBR.2). Tagging allows the
   source's non-conforming cells to be tagged and forwarded instead of
   dropped.

5.3.2.  Traffic Parameter Negotiation

   SIG 4.0 allows certain traffic parameters to be negotiated during the
   call establishment phase Traffic parameters cannot be 'renegotiated'
   after the call is active. Two new IEs make negotiation possible:

     - the Minimum Acceptable ATM Traffic Descriptor IE allows
       negotiation of PCR parameters





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     - the Alternative ATM Traffic Descriptor IE allows negotiation of
       other traffic parameters

   A SETUP or CONNECT message may include ONLY one of the above IEs.
   That is, the calling party may only offer an 'alternative' or
   'minimum' to the requested traffic parameters. (See Section 8 of
   [SIG40].) IP over ATM entities SHOULD take advantage of this
   capability whenever possible. In order to do so, IP over ATM entities
   SHOULD specify PCR _equal_ to the link rate in the ATM Traffic
   Descriptor IE of the SETUP message and a minimum of zero PCR in the
   Minimum Acceptable ATM Traffic Descriptor IE.

5.3.3.  Broadband Bearer Capability

   A new field in UNI signalling 4.0 called, 'ATM Transfer Capability'
   (ATC), has been defined in the Broadband Bearer Capability IE for the
   purpose of explicitly specifying the desired ATM traffic category.
   The figure below shows the allowable ATC values.

       Format and field values of Broadband Bearer Capability IE

       -------------------------------------------------------------
       | bb_bearer_capability                                      |
       ------------------------------------------------------------|
       |  spare                       0                            |
       |  bearer_class                bcob-x,c,a or VP             |
       |  transfer_capability         cbr, rt-vbr, nrt-vbr, abr    |
       |  susceptibility_to_clipping  0     (not suscept)          |
       |  spare                       0                            |
       |  user_plane_configuration    pt-to-pt, pt-to-mpt          |
       -------------------------------------------------------------

5.3.4.  QoS Parameter

   Inclusion of the QoS Parameter IE is not mandatory in SIG 4.0.  It
   may be omitted from a SETUP message _if and only if_ the Extended QoS
   Parameters IE is included (see next section). This specification
   makes no explicit recommendation on the use of the QoS related IEs.

5.3.4.1.  Two IEs for Signalling of Individual QoS Parameters

   SIG 4.0 allows for signalling of individual QoS parameters for the
   purpose of giving the the network and called party a more exact
   description of the desired delay and cell loss characteristics. The
   two individual QoS related IEs, Extended QoS Parameters IE and End-
   to-End Transit Delay IE, can be used in the SETUP and CONNECT
   signaling messages in place of the 'generic' QoS Parameter IE. Note
   that inclusion of these two IEs depends on the type of ATM service



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   category requested (see Annex 9 in [SIG40]).

5.4.  ATM Addressing Information

   ATM addressing information is carried in the Called Party Number,
   Calling Party Number, and, under certain circumstance, Called Party
   Subaddress, and Calling Party Subaddress IE. The ATM Forum ILMI
   Specification 4.0 [ILMI40] provides the procedure for an ATM
   endsystem to learn its own ATM address from the ATM network, for use
   in populating the Calling Party Number IE.

       Format and field values of Called Party Number IE

       ----------------------------------------------------------
       | called_party_number                                    |
       ----------------------------------------------------------
       |  type_of_number      (international number / unknown)  |
       |  addr_plan_ident     (ISDN / ATM Endsystem Address)    |
       |  addr_number         (E.164 / ATM Endsystem Address)   |
       ----------------------------------------------------------

6.  ABR Signaling In More Detail

   The IEs and procedures pertaining to ABR signalling are briefly
   described in this section. Nevertheless, this document makes no
   specific recommendation on when to use the ABR service category for
   IP VCCs or give suggestions on appropriate values for the various
   parameters in the ABR related IEs.

   Two new IEs have been defined for ABR signaling:

     o ABR Setup Parameters
     o ABR Additional Parameters

   These IEs may be optionally included in a SETUP or CONNECT message.
   The ABR Setup Parameters IE contains the following subfields:

     - Forward/Backward ABR Initial Cell Rate
     - Forward/Backward ABR Transient Buffer Exposure
     - Cumulative RM Fixed Round Trip Time
     - Forward/Backward Rate Increment Factor
     - Forward/Backward Rate Decrease Factor

   The ABR Additional Parameters IE contains one subfield:

     - Forward/Backward Additional Parameters Record





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   The Additional Parameters Record value is a compressed encoding of a
   set of ABR parameters (see [SIG40] and [ABRS]).

7.  Frame Discard Capability

   The frame discard capability in SIG 4.0 is primarily based on the
   'Partial and Early Packet Discard' strategy [ROM94]. Its use is
   defined for any of the ATM services, except for loss-less CBR.  Frame
   discard signaling MUST be supported by all IP over ATM entities and
   it is RECOMMENDED that frame discard be signaled for all IP SVCs
   because it has been proven to increase throughput under network
   congestion. Signaling for frame discard is done by setting the frame
   discard bit in the 'Traffic Management Options' subfield in the
   Traffic Descriptor IE.  It is possible that not all network entities
   in the SVC path support frame discard, but it is required that they
   all forward the signaling.

8.  Security Considerations

   The ATM Forum Security sub-working group is currently defining
   security mechanisms in ATM. The group has yet to produce a
   specification, therefore it is premature to begin defining IP over
   ATM signalling's use of ATM security.  The ATM Forum is working on
   authentication mechanisms for signalling and on mechanisms for
   providing data integrity and confidentiality (e.g encryption).  Lack
   of these ATM security mechanisms prevents the authentication of the
   originator of signalling messages, such as, connection setup request
   or connection teardown request. IP Security (RFC1825) can be applied
   to IP datagrams over ATM VCs to overcome the lack of security at the
   ATM layer.

9.  Acknowledgements

   The authors would like to thank the members of the ION working group
   for their input. Special thanks to K.K. Ramakrishnan and Kerry
   Fendick who contributed Appendix B of this document.

REFERENCES

   [ABRS] ATM Forum, "Addendum to UNI Signalling v4.0 for ABR Parameter
   Negotiation", af-sig-0076.000; available at
   ftp://ftp.atmforum.com/pub.

   [ABRT] ATM Forum, "Addendum to Traffic Management v4.0 for ABR
   Parameter Negotiation", af-tm-0077.000; available at
   ftp://ftp.atmforum.com/pub.





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

   [RFC1633] Braden, R., Clark, D., and S. Shenker, "Integrated Service
   in the Internet Architecture: An Overview", RFC 1633, June 1994.

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

   [RFC1483] Heinanen, J., "Multiprotocol Encapsulation over ATM
   Adaptation Layer 5", RFC 1483, July 1993.

   [ILMI40] ATM Forum, "Integrated Local Management Interface (ILMI)
   Specification Version 4.0", af-ilmi-0065.000, finalized September
   1996; available at ftp://ftp.atmforum.com/pub.

   [ISO8473] ISO/IEC 8473, Information processing systems - Data
   communications - Protocol for providing the connectionless-mode
   network service, 1988.

   [ISO9577] Information Technology - Telecommunication and information
   exchange between systems - Protocol identification in the network
   layer ISO/IEC TR9577 (International Standards Organization: Geneva,
   1990)

   [LAUB98] Laubach, M., and J. Halpern, "Classical IP and ARP over
   ATM", RFC 2225, April 1998.

   [LUC98] Luciani, J., Katz, D., Piscitello, D., Cole, B., and N.
   Doraswamy, "NBMA Next Hop Resolution Protocol (NHRP)", RFC 2332,
   April 1998.

   [RFC1755] Perez*, M., et. al., "ATM Signaling Support for IP over
   ATM", RFC 1755, February 1995. (* see author's information below)

   [ROM94] Romanow, A., and Floyd, S., Dynamics of TCP Traffic over ATM
   Networks.  IEEE JSAC, V. 13 N. 4, May 1995, p. 633-641. Abstract.  An
   earlier version appeared in SIGCOMM '94, August 1994, pp. 79-88.

   [RFC2205] Braden, R., Zhang, L., Berson, S., Herzog, S., and S.
   Jamin, "Resource ReSerVation Protocol (RSVP) - Version 1 Functional
   Specification", RFC 2205, September 1997.

   [SIG40] ATM Forum, "ATM User-Network Interface (UNI) Signalling
   Specification Version 4.0", af-sig-0061.000, finalized July 1996;
   available at ftp://ftp.atmforum.com/pub.





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   [TMGT40] ATM Forum, "Traffic Management Specification Version 4.0",
   af-tm-0056.000, finalized April 1996; available at
   ftp://ftp.atmforum.com/pub.

   [UNI95] ATM Forum, "ATM User-Network Interface Specification Version
   3.1", Prentice Hall, Upper Saddle River, NJ, 1995.

Author's Address

   Maryann P. Maher (formerly Maryann Perez)
   USC/ISI
   4350 N. Fairfax Drive, Suite 620
   Arlington VA 22203

   EMail: [e-mail]




































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RFC 2331        IP over ATM Signalling - SIG 4.0 Update       April 1998


Appendix A. A Sample SIG 4.0 SETUP Message

+--------------------------------------------------------------------+
                             SETUP

 Information Elements/
   Fields                         Value/(Meaning)
 --------------------             ---------------

aal_parameters
   aal_type                         5        (AAL 5)
   fwd_max_sdu_size_ident         140
   fwd_max_sdu_size               (xmit IP MTU value)
   bkw_max_sdu_size_ident         129
   bkw_max_sdu_size      (recv IP MTU, 0 for disallowing return traffic)
   sscs_type identifier           132
   sscs_type                        0        (null SSCS)

traffic_descriptor
   fwd_peak_cell_rate_0_1_ident   132
   fwd_peak_cell_rate_0_1         (link rate)
   bkw_peak_cell_rate_0_1_ident   133
   bkw_peak_cell_rate_0_1         (link rate)
   traff_mngt_options_ident       191
   fwd_frame_discard                1   (on)
   bkw_frame_discard                1   (on if return traffic indicated)
   spare                            0
   tagging_bkw                      1   (on)
   tagging_fwd                      1   (on if return traffic indicated)
   best_effort_indication         190   (on)

minimum_acceptable_traffic_descriptor
   fwd_peak_cell_rate_0_1_ident   132
   fwd_peak_cell_rate_0_1           0
   bkw_peak_cell_rate_0_1_ident   133
   bkw_peak_cell_rate_0_1           0

bb_bearer_capability     /* a coding for specifying UBR like service */
   spare                            0
   bearer_class                    16      (BCOC-X)
   spare                            0
   atm_transfer_capability         10      (nrt-vbr)
   susceptibility_to_clipping       0      (not susceptible to clipping)
   spare                            0
   user_plane_configuration         0      (point_to_point)






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