Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
2000-04-05
2004-05-25
Pham, Chi (Department: 2667)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
Reexamination Certificate
active
06741597
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an Asynchronous Transfer Mode (ATM) switching system, and more particularly, to an apparatus and method for managing traffic of an ATM switching system, and to its method.
2. Background of the Related Art
An ATM switching system has a limited amount of bandwidth. Accordingly, only a predetermined amount of information per unit time can be transferred through a network. In order to allocate usable bandwidth in the network, a system provider and a system user should agree on a ‘traffic contract’ that defines ‘traffic parameters’, a source traffic descriptor, and a connection traffic descriptor at an initial stage of a system, that is, when a call is established.
Normally, traffic parameters are variables representing traffic characteristics of a terminal that generates traffic, which include four elements as shown in Table 1.
TABLE 1
Traffic parameter
Formula
Unit
Content
PCR (Peak cell rate)
1/T
Cell/sec
T: time of minimal
interval of cells
SCR (Sustainable cell rate)
MBS/T
Cell/sec
Maximum average
transfer rate of ON-OFF
burst traffic
MBS (Maximum burst size
MBS
Cell
Number of maximum
transfer cell in PCR
MCR (Minimum cell rate)
Cell/sec
As used herein, ‘T’ indicates a maximum burst interval time.
The source traffic descriptor defines traffic characteristics of a terminal when a call is established, in order to satisfy a quality of service (QoS, i.e., delay, cell loss and throughput) of a cell to be established.
The source traffic descriptor is constructed using a combination of the traffic parameters and the cell delay variation tolerance (CDVT) of Table 1.
FIGS. 1A and 1B
respectively show constant bit rate (CBR) traffic parameters (PCR and CDVT), and variable bit rate (VBR) traffic parameters (PCR, CDVT, SCR and MBS).
The connection traffic descriptor represents traffic characteristics of an ATM connection, including the source traffic descriptor, CDVT, and elements defining a conformance of a cell.
When the ATM connection is made after the system provider and the user agree on the communication ‘traffic contract,’ a generic cell rate algorithm (GCRA) having a traffic policing function in a network interface determines whether input cells comply with the traffic contract. That is, it identifies whether the cells inputted from the terminal match the traffic parameters stipulated in the initial traffic contract, and then performs the operations of tagging, discarding, and monitoring depending on whether the cells break the contract or not.
The GCRA is implemented by a Virtual Scheduling Algorithm (VSA) or a Leaky Bucket Algorithm (LBA) described in a CCITT Recommendation 1.371 Document, Geneva 1999, and normally defined using an ‘Increment (I)’ parameter and a ‘Limit (L)’ parameter.
FIG. 2
illustrates a GCRA implemented by the VSA.
As shown in
FIG. 2
, when a cell is received in step S
10
, the VSA checks whether the arrival time t
a
(k) of kth cell is greater than a theoretical arrival time (TAT) in step S
11
. If the arrival time t
a
(k) of the cell is greater than the TAT, that is, if the cell arrives after the TAT, the VSA regards the corresponding cell as a conforming cell and updates the TAT to an added value of the arrival time t
a
(k) of the cell and an Increment (I) in steps S
12
and S
13
. If, however, the arrival time T
a
(k) of the kth cell is not greater than the TAT, that is, if the cell arrives before the theoretical arrival time TAT, the VSA determines whether the kth cell arrives beyond the Limit (L) value before the theoretical arrival time TAT, in step S
14
. Upon making that determination, if the kth cell arrives beyond the Limit (L), that is, the arrival time of the kth cell is smaller than the TAT-L, the VSA regards the corresponding cell as a non-conforming cell and does not modify the TAT in step S
15
.
FIG. 3
illustrates cell conformance checking by the VSA having an Increment (I=5) and a Limit (L=9).
In step S
11
(FIG.
2
), since the arrival time T
a
(
3
)=11 of the third cell is greater than the TAT(
3
)=10, the VSA updates the TAT(
3
) of the third cell to ‘11’ rather than ‘10’ in step S
12
. The VSA then updates the TAT(
4
) of the fourth cell to ‘16’ by increasing by Increment (I=5) over the previous value in step S
13
.
Though arrival times t
a
(k) of the remaining cells, except for the seventh and the tenth cells, are not all greater than the TAT, since they are not smaller than the TAT in steps S
11
and S
14
, the VSA regards the corresponding cells as conforming, and increases the TAT as much as the Increment (I=5) than before in the step S
13
.
In this respect, since the arrival times t
a
(
7
) and t
a
(
10
) of the seventh and the tenth cells are each smaller beyond the Limit (L=9) than the TAT(
7
) and the TAT(
10
) in steps S
11
and S
14
, the VSA regards the seventh and the tenth cells as non-conforming cells and thus does not increase the TAT(
7
) and the TAT(
10
) in step S
15
.
FIG. 4
illustrates the GCRA implemented by LBA.
The Leaky Bucket Algorithm is a model in which a constant amount of traffic cells come in and go out, of which an input cell overflowing the bucket is tagged or discarded according to the resource environment of the system. Thus, if the content of the bucket is not overflowing, incoming cells are conforming. Otherwise, the cells are non-conforming.
Referring to
FIG. 4
, when the cell is received in step S
20
, the LBA first computes the temporary bucket counter value X′ in step S
21
. The temporary bucket counter X′ is defined as a value obtained by subtracting the arrival time t
a
(k) of the cell from an addition value (X+LCT) of a leaky bucket counter value X and a last compliance time (LCT) representing an input time of a last conforming cell, and the leaky bucket counter value X is decreased by 1 at every unit time.
After the temporary bucket counter value X′ is computed, the LBA checks whether the computed temporary bucket counter value X′ is smaller than ‘0’ in step S
22
, and if the value X′ is smaller than 0, the LBA sets the corresponding temporary bucket counter X′ to 0 in step S
23
.
Accordingly, the LBA regards the input cell as a conforming cell and updates the leaky bucket counter value X to the sum of the temporary bucket counter X′ and the Increment (I), and updates the LCT to the arrival time t
a
(k) of the cell in step S
24
.
If, however, the temporary bucket counter value X′ is not smaller than 0 in step S
22
, the LBA checks whether the corresponding temporary bucket counter X′ exceeds the Limit (L) of the bucket in step S
25
. If the temporary bucket counter X′ exceeds the Limit (L) of the bucket, the LBA regards the input cell as a non-conforming cell, and does not modify the leaky bucket counter value X and the LCT in step S
26
. If, on the other hand, the temporary bucket counter X′ does not exceed the Limit (L) of the bucket, it regards the input cell as a conforming cell and increases the bucket counter, as shown in step S
24
.
FIG. 5
illustrates cell conformance checking by the LBA using an Increment (I=5) and a Limit (L=9).
If the arrival time t
a
(
2
) of the second cell is 5, the temporary bucket counter value X′ in the step S
21
is −5. That is, the temporary bucket counter value X′ is determined by a value obtained by subtracting the difference (5−0=5) of the LCT of the first cell and the arrival time t
a
(
2
) of the second cell, from the count value (X=0) of the leaky bucket counter of the first cell. In this respect, upon checking in step S
22
, since the temporary bucket counter (X′ =−5) is smaller than 0, the temporary bucket counter X′ of the second cell in steps S
23
and S
24
is set as 0, and the leaky bucket counter value X and the LCT are respectively set as 5.
If the arrival time t
a
(
3
) of the third cell is
11
, the temporary bucket counter X′ in the step S
21
is &min
Boakye Alexander O.
Fleshner & Kim LLP
LG Information & Communications Ltd.
Pham Chi
LandOfFree
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