Multiplex communications – Diagnostic testing – Determination of communication parameters
Reexamination Certificate
1998-03-20
2001-07-24
Chin, Wellington (Department: 2664)
Multiplex communications
Diagnostic testing
Determination of communication parameters
C370S230000
Reexamination Certificate
active
06266327
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to communications and, more particularly, to a packet communications system.
BACKGROUND OF THE INVENTION
Existing ATM (Asynchronous Transfer Mode) services are mainly geared towards native cell-based applications, at least in regard to their Quality of Service (QoS) commitments. In contrast, the Guaranteed Frame Rate service (GFR) is a new proposed Service Category in the ATM Forum, or ATM Transfer Capability (ATC) in ITUT-T, that is a specialize call transport mechanism for packet-based or frame-based applications (e.g., se ITU-T Recommendation I.371 Living List: Perth, Australia, Rapporteur Meeting, 1998). Generally speaking, the GFR service is expected to deliver a minimum bandwidth guarantee to a user with respect to the user's frame traffic that conforms to a set of predefined conditions (also referred to herein as a traffic set, or traffic descriptors). (This minimum bandwidth guarantee, typically expressed in terms of a low cell loss, is also referred to herein as one example of a GFR QoS commitment). The minimum bandwidth guarantee can be determined at subscription time, or negotiated during call setup.
GFR is intended to support non-real time applications. Higher-layer protocol data units (PDUs) or frames, are segmented into one or more user-generated cells prior to their transmission over the standardized network interface. Multiple frames are not expected to straddle a single ATM cell, nor are cells from multiple frames expected to be interleaved unless a suitable de-multiplexing mechanism is provided (e.g., the MID (message identification) field in ATM Adaptation Layer (AAL) 3/4 or a Virtual Path Identifier (VPI)/Virtual Connection Identifier (VCI) fields in other AALs (e.g., see ITU-T Recommendation I.363.3 BISDN ATM Adaptation Layer Specification (AAL 3/4), (1996)). In addition, a mechanism to identify frame boundaries at the ATM layer is required (e.g., the User-to-User Indication (UUI) bit in AAL5). Although, theoretically, a GFR service may be implemented with any AAL providing a frame delineation mechanisms, the initial implementation of the GFR service is geared towards the use of AAL5.
As part of providing the GFR service, a conformance algorithm is used to identify that portion of the user generated traffic that meets the requirements of the above-mentioned traffic set. Illustratively, the traffic set includes a set of parameters such as (but not limited to): peak cell rate (PCR) (instantaneous cell rate); minimum cell rate (MCR) (a maximum number of cells over a period of time, T, to which a QoS commitment applies); maximum burst size (MBS) (which can be interpreted as the maximum number of cells allowed in a data burst at rate PCR); and a maximum frame size (MFS) (a maximum number of cells permitted in a frame). The conformance algorithm evaluates, in real time, a received data stream from a user against the user's predefined traffic set, where the received data stream is partitioned into frames that are further made up of ATM cells. This is shown in FIG.
1
. An illustrative received data stream comprises data burst
51
, occurring over a time interval T. Each data burst comprises a plurality of cells. The cells are further partitioned into frames
61
and
62
(denoted by the dashed boxes). The conformance algorithm measures the above described PCR, MCR, MBS, and MFS values for this received data stream. For example, assume that the permitted MFS value of the traffic set is equal to 6 (it should be noted that these numbers are used for illustrative purposes only). The conformance algorithm counts each received cell for frame
61
. Upon reaching the seventh cell, the conformance algorithm declares frame
61
to be in non-conformance, and, as such, frame
61
does not receive the committed QoS. (It should be noted that frame
61
, albeit non-conforming, may still be transmitted by the network.) In the context of frame
61
, the first six cells from frame
61
are referred to conforming and the two excess cells
71
are referred to as non-conforming. However, even through frame
61
has been declared non-conforming with respect to the MFS, those six conforming cells from frame
61
are still used in determining conformance to the other traffic set parameters. In particular, the six conforming cells from frame
61
are used to determine whether data burst
51
conforms to the MBS. Illustratively, assume that the MBS is equal to a value of 10 cells. In this instance, data burst
51
is non-conforming since frame
62
comprises six cells, which when added to the six conforming cells from frame
61
exceeds the MBS requirement. As such, frame
62
is also declared as non-conforming notwithstanding the fact that frame
62
meets the MFS requirement. As such, in this conformance technique, cells from a prior non-conforming frame are also applied to the next frame for use in determining if that (future) frame can receive the committed QoS.
SUMMARY OF THE INVENTION
I have observed that the above-described GFR service conformance definitions do not intend to specify the disposition by a network of non-conforming cells or non-conforming frames to allow for vendor and service differentiation. In other words, cells from a non-conforming frame may be forwarded by the ingress network interface (e.g., edge network element (NE)) to the downstream NEs. However, the downstream NEs are not able to differentiate cells from non-conforming frames from cells in conforming frames. This aspect makes it harder for a downstream NE to fulfill its QoS commitments since these non-conforming cells are in fact in excess of the GFR traffic set and, as such, potentially consume unallocated NE resources.
Therefore, and in accordance with the invention, a frame-level conformance indication code is defined for each frame. As a result, each NE is able to determine whether a frame, and its constituent cells, are conforming or non-conforming by inspecting values of the conformance indication code.
In an embodiment of the invention, the Payload Type Indicator (PTI) of an ATM cell header is used to indicate whether that cell belongs to a non-conforming frame or a conforming frame. In particular, if a frame is determined to be non-conforming, a NE sets the PTI field, of at least the end-of-frame cell (i.e., the cell with the UUI bit set in one in AAL5), to a predefined code representative of non-conformance (hereafter referred to as an NCF code). As a result, downstream NEs are able to determine which of the currently buffered cells belong to a non-conforming frame by looking at both the PTI field and the frame boundary market (UUI bit). For instance, if a downstream NE determines that the end-of-frame cell belongs to a non-conforming frame, any of the cells from that frame may be discarded from a buffer irrespective of the PTI field status of the other user data cells for that frame. (Whether or not a subset of cells of a non-conforming frame, or all of the cells of a non-conforming frame, are discarded is a matter of local NE policy or global GFR service policy.)
REFERENCES:
patent: 5406550 (1995-04-01), McTiffin
patent: 5666353 (1997-09-01), Klausmeier et al.
patent: 5926476 (1999-07-01), Ghaibeh
patent: 6049530 (2000-04-01), Petersen et al.
Fabrice Guillemin et al., “Cell conformance testing with respect to the peak cell rate in ATM networks” Computer Networks and ISDN Systems, vol. 27, Issue: 5, pp. 703-725, Mar. 1995.*
The ATM Forum Technical Committee, Traffic Management Specification, Version 4.0, Apr. 1996.*
Rohit Goyal et al., “Simulation Experiments with Guaranteed Frame Rate for TCP/IP Traffic”, ATM Forum, pp. 1-12, Jul. 1997.
Chin Wellington
Jones Prenell
Lucent Technologies - Inc.
Opalach Joseph J.
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