rfc2331.txt

<VC++网络游戏建摸与实现>源代码

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


bb_low_layer_information
   layer_2_id                       2
   user_information_layer          12       (lan_llc - ISO 8802/2)

qos_parameter
   qos_class_fwd                    0        (class 0)
   qos_class_bkw                    0        (class 0)

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

calling_party_number
   type_of_number                   (international number / unknown)
   addr_plan_ident                  (ISDN / ATM Endsystem Address)
   presentation_indic               (presentation allowed)
   spare                            0
   screening_indic                  (user_provided verified and passed)
   number                           (E.164 / ATM Endsystem Address)

+--------------------------------------------------------------------+

                               Figure 1.
                    Sample contents of SETUP message


























Maher                       Standards Track                    [Page 14]

RFC 2331        IP over ATM Signalling - SIG 4.0 Update       April 1998


Appendix B. ABR and VBR Signaling Guidelines for IP Routers

   When ATM is used to interconnect routers that are supporting a best
   effort service, the ATM connection typically carries an aggregation
   of IP flows, e.g., all best effort IP traffic between a pair of
   routers. With the efforts undertaken by ATM to be more "packet
   friendly" (e.g., frame discard), it is useful to examine ways that a
   VC can provide service comparable to or better than that of a
   dedicated or leased "link" in terms of performance and packet loss.

   For ATM connections used to interconnect routers, a non-zero
   bandwidth reservation may be required to achieve consistently
   adequate performance for the aggregate set of flows.  The support of
   bandwidth commitments for an ATM connection carrying IP traffic helps
   to assure that a certain fraction of each link's capacity is reserved
   for the total IP traffic between the routers.  Reserving bandwidth
   for the aggregation of best-effort traffic between a pair of routers
   is analogous to provisioning a particular link bandwidth between the
   routers. There are at least 3 service classes defined in the ATM
   Traffic Management specification that provide varying degrees of
   capability that are suitable for interconnecting IP routers: UBR, ABR
   and VBR non-real-time.  Although the use of best-effort service (UBR)
   at the ATM layer is the most straightforward and uncomplicated, it
   lacks the capability to enforce bandwidth commitments.

   Note that we are talking of providing a "virtual link" between
   routers, for the aggregate traffic. The provisioning is for the
   aggregate. It is therefore distinct from the per-flow bandwidth
   reservations that might be appropriate for Integrated Services.

   Even best-effort IP flows, when supported on an aggregate basis, have
   some broad service goals. The primary one is that of keeping packet
   loss rate reasonably small. A service class that strives to achieve
   this, keeping in mind the tradeoff between complexity and adequate
   service, is desirable. It has been recommended in this memo that UBR
   be the default service for this. UBR with (some form of) packet
   discard has the desirable goal of being simple in function, and it
   appears that vendors will be supporting it. However, when available,
   it may be quite worthwhile to consider ABR and VBR non-real-time
   service classes.

   Because AAL5 frames with missing cells are discarded by the receiver,
   ATM bandwidth commitments are most useful if supported in the form of
   a committed rate of cell delivery in complete, non-errored AAL5
   frames delivered to the receiver. In addition, it is desirable for
   the ATM connection to deliver additional complete frames, beyond this
   commitment, on a best-effort basis.




Maher                       Standards Track                    [Page 15]

RFC 2331        IP over ATM Signalling - SIG 4.0 Update       April 1998


   These characteristics can be achieved through the ABR service
   category through the use of a Minimum Cell Rate, if the ABR service
   is supported by the ATM endpoints and if efficient frame discard is
   supported at the ABR source. The mechanisms put in place for the ABR
   service strive to keep loss quite low within the ATM network.

   The parameters that should be specified by the end system are (i) the
   Peak Cell Rate (likely the link rate), (ii) the Minimum Cell Rate
   (the committed rate), and (iii) the Cumulative RM Fixed Round-Trip
   Time.  The remaining parameter values, if left unspecified by the
   calling party, are selected by the network or are chosen from the
   default values specified in the ATM Forum Traffic Management
   specification.

   Parameters (i) and (ii) are contained in the mandatory Traffic
   Descriptor IE, whereas parameter (iii) is contained in the mandatory
   ABR Setup Parameters IE. Other paramenters in the ABR Setup
   Parameters IE may be omitted. (Note that the third IE which pertains
   to ABR signalling, the ABR Additional Parameters IE, is an optional
   IE and therefore need not be included.) Parameter (iii) is dependent
   on the hardware of the end system, so that the default value
   specified for that hardware should be used. In the absense of such a
   default, a value of zero MAY be specified by the end system. Entities
   using ABR connections for IP over ATM SHOULD take advantage of
   parameter negotiation by specifying Peak Cell Rate equal to the link
   rate in the ATM Traffic Descriptor IE of the SETUP message. The value
   selected for the Minimum Cell Rate is implementation specific. Note
   that the MCR also MAY be negotiated if an MCR parameter is included
   by the end system in the Minimum Acceptable ATM Traffic Descriptor
   IE.  The use of MCR negotiation by the end system is implementation
   specific.  Also, note that Frame Discard MAY be requested for ABR
   connections as well as for UBR connections. Although the ABR service
   attempts to minimize cell loss, the use of Frame Discard may improve
   throughput when cell loss is not eliminated.

   ATM recognizes in addition to the service class (UBR, ABR, etc.), a
   notion of a QoS class. The QoS class specifies the type of guarantee
   requested of the network when the call is setup. This is distinct
   from the service class requested for the connection, and the
   specification of the traffic parameters (which specify what the
   source's traffic will look like).  QoS class 0 is the "simplest", and
   is called the Unspecified QoS class.  In the context of ABR (and VBR
   non-realtime below), we are only concerned with the QoS class
   providing an assurance of acceptable loss behavior for the
   connection.






Maher                       Standards Track                    [Page 16]

RFC 2331        IP over ATM Signalling - SIG 4.0 Update       April 1998


   The Unspecified QoS Class (QoS Class 0) MUST be requested for ABR
   connections. In this context, QoS Class 0 corresponds to a network-
   specific objective for the cell loss ratio.  Networks in general are
   expected to support a low Cell Loss Ratio for ABR sources that adjust
   cell flow in response to control information.

   The VBR-nrt service category provides an alternate means of achieving
   these characteristics.  These characteristics may be obtained with
   VBR-nrt connections for which (i) the VBR.3 conformance definition is
   used, (ii) a Sustainable Cell Rate (SCR) and Maximum Burst Size
   (MBS), and Peak Cell Rate (PCR) are specified, and (iii) both tagging
   and frame discard are requested.  A request for tagging indicates
   that best-effort delivery is desired for traffic offered in excess of
   the SCR and MBS.  A request for frame discard indicates to the
   network that the user desires allocations of committed and excess
   bandwidth to translate into corresponding throughputs at the frame
   level.

   As with UBR connections, entities using VBR-nrt connections for IP
   over ATM should take advantage of parameter negotiation by specifying
   PCR equal to the link rate in the ATM Traffic Descriptor IE of the
   SETUP message and PCR equal to SCR in the Minimum Acceptable Traffic
   descriptor. The selection of SCR, MBS, and CLR (cell loss ratio)
   should be implementation specific. However, for IP over ATM, an MBS
   value of N*(Maximum MTU) is RECOMMENDED, where N>=1 with a default of
   2 and where Maximum MTU is equal to 192 cells (consistent with an IP
   MTU size of 9180 bytes [RFC1626]).
























Maher                       Standards Track                    [Page 17]

RFC 2331        IP over ATM Signalling - SIG 4.0 Update       April 1998


Appendix C. Combinations of Traffic Related Parameters

   This appendix contains a copy of the five tables found in Annex 9 of
   [SIG40] which show the allowable combinations of traffic and QoS
   related parameters in a SIG 4.0 SETUP message.

+--------------------------------------------------------------------+
|ATM Service Category|                     CBR                       |
|--------------------|---------------|---------------|---------------|
| Conformance        |CBR.1 (note 10)|   (note 4)    |   (note 4)    |
|--------------------|---------------|---------------|---------------|
| Bearer Capability  |               |               |               |
|--------------------|---------------|---------------|---------------|
| BB Bearer Class    |  A |  X  | VP |  A |  X  | VP^|  A |  X  | VP^|
|--------------------|---------------|----|-----|----|----|-----|----|
| ATM Transfer       |               |    | 4,5,|    |    | 4,5,|    |
| Capability (note 1)|       7       | abs| or 6|  5 | abs| or 6|  5 |
|--------------------|---------------|---------------|---------------|
| Traffic Descriptor |               |               |               |
|  for a given dir.  |               |               |               |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0)        |               |               |       S       |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0+1)      |       S       |       S       |       S       |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0)   |               |               |               |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0+1) |               |               |               |
|--------------------|---------------|---------------|---------------|
| Best Effort        |               |               |               |
|--------------------|---------------|---------------|---------------|
| Tagging            |       N       |       N       |      Y/N      |
|--------------------|---------------|---------------|---------------|
| Frame Discard      |      Y/N      |      Y/N      |      Y/N      |
|--------------------|---------------|---------------|---------------|
| QoS Classes        |       *       |       *       |       *       |
|--------------------|---------------|---------------|---------------|
| Transit Delay      |       O       |       O       |       O       |
|--------------------|---------------|---------------|---------------|
| Peak-to-Peak CDV   |       O       |       O       |       O       |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0)~       |               |       O       |       O       |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0+1)~     |       O       |               |               |
+--------------------------------------------------------------------+






Maher                       Standards Track                    [Page 18]

RFC 2331        IP over ATM Signalling - SIG 4.0 Update       April 1998


+--------------------------------------------------------------------+
|ATM Service Category|                 Real Time VBR                 |
|--------------------|---------------|---------------|---------------|
| Conformance        |VBR.1 (note 10)|     VBR.2     |     VBR.3     |
|--------------------|---------------|---------------|---------------|
| Bearer Capability  |               |               |               |
|--------------------|---------------|---------------|---------------|
| BB Bearer Class    |  C |  X  | VP |  C |  X  | VP |  C |  X  | VP |
|--------------------|---------------|----|-----|----|----|-----|----|
| ATM Transfer       |               |    |  1  |    |    |  1  |    |
| Capability         |      19       |  9 | or 9|  9 |  9 | or 9|  9 |
|--------------------|---------------|---------------|---------------|
| Traffic Descriptor |               |               |               |
|  for a given dir.  |               |               |               |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0)        |               |               |               |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0+1)      |       S       |       S       |       S       |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0)   |               |       S       |       S       |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0+1) |      S        |               |               |
|--------------------|---------------|---------------|---------------|
| Best Effort        |               |               |               |
|--------------------|---------------|---------------|---------------|
| Tagging            |       N       |       N       |      Y/N      |
|--------------------|---------------|---------------|---------------|
| Frame Discard      |      Y/N      |      Y/N      |      Y/N      |
|--------------------|---------------|---------------|---------------|
| QoS Classes        |       *       |       *       |       *       |
|--------------------|---------------|---------------|---------------|
| Transit Delay(nt.2)|       O       |       O       |       O       |
|--------------------|---------------|---------------|---------------|
| Peak-to-Peak CDV   |       O       |       O       |       O       |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0)~       |               |       O       |       O       |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0+1)~     |       O       |               |               |
+--------------------------------------------------------------------+












Maher                       Standards Track                    [Page 19]

RFC 2331        IP over ATM Signalling - SIG 4.0 Update       April 1998


+--------------------------------------------------------------------+
|ATM Service Category|                 Real Time VBR                 |
|--------------------|---------------|---------------|---------------|
| Conformance        |  (note 4,7)   |   (note 4,8)  |    (note 4)   |
|--------------------|---------------|---------------|---------------|
| Bearer Capability  |               |               |               |
|--------------------|---------------|---------------|---------------|
| BB Bearer Class    |       X       |       X       |   X | C or VP^|
|--------------------|---------------|---------------|-----|---------|
| ATM Transfer       |               |               |     |         |
| Capability         |    1 or 9     |     1 or 9    | 1or9|    9    |
|--------------------|---------------|---------------|---------------|
| Traffic Descriptor |               |               |               |
|  for a given dir.  |               |               |               |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0)        |       S       |               |               |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0+1)      |       S       |       S       |       S       |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0)   |               |               |               |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0+1) |               |               |       S       |
|--------------------|---------------|---------------|---------------|
| Best Effort        |               |               |               |
|--------------------|---------------|---------------|---------------|