ATM time stamped queuing

Details ATM time stamped queuing ATM time stamped queuing

1998-11-09

2004-05-18

Luther, William A. (Department: 2664)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S412000, C370S429000

Reexamination Certificate

active

06738381

ABSTRACT:

BACKGROUND
1. Field of the Invention
The present invention pertains to communications systems, and particularly to communications systems which employ ATM technology.
2. Related Art and Other Considerations
Asynchronous Transfer Mode (ATM) is becoming increasingly used in communication networks. ATM is a packet-oriented transfer mode which uses asynchronous time division multiplexing techniques. Packets are called cells and have a fixed size.
As shown in
FIG. 1
, an ATM cell consists of 53 octets, five of which form a header and forty eight of which constitute a “payload” or information portion of the cell. The header of the ATM cell includes two quantities which are used to identify a connection in an ATM network over which the cell is to travel, particularly the VPI (Virtual Path Identifier) and VCI (Virtual Channel Identifier). In general, the virtual path is a principal path defined between two switching nodes of the network; the virtual channel is one specific connection on the respective principal path.
Between termination points of an ATM network a plurality of nodes are typically situated, such as switching nodes having ports which are connected together by physical transmission paths or links. The switching nodes each typically have several functional parts, a primary of which is a switch core. The switch core essentially functions like a cross-connect between ports of the switch. Paths internal to the switch core are selectively controlled so that particular ports of the switch are connected together to allow a cells ultimately to travel from an ingress side of the switch to an egress side of the switch.
A protocol reference model has been developed for illustrating layering of ATM. The protocol reference model layers include (from lower to higher layers) a physical layer (including both a physical medium sublayer and a transmission convergence sublayer), an ATM layer, and an ATM adaptation layer (AAL), and higher layers. The basic purpose of the AAL layer is to isolate the higher layers from specific characteristics of the ATM layer by mapping the higher-layer protocol data units (PDU) into the information field of the ATM cell and vise versa. There are several differing AAL types or categories, including AAL
0
, AAL
1
, AAL
2
, AAL
3
/
4
, and AAL
5
.
AAL
2
is a standard defined by ITU recommendation I.363.2. An AAL
2
packet is shown in
FIG. 2
as comprising a three octet packet header, as well as a packet payload. The AAL
2
packet header includes an eight bit channel identifier (CID), a six bit length indicator (LI), a five bit User-to-User indicator (UUI), and five bits of header error control (HEC). The AAL
2
packet payload, which carries user data, can vary from one to forty-five octets
FIG. 3
shows how plural AAL
2
packets can be inserted into a standard ATM cell. In particular,
FIG. 3
shows a first ATM cell
20
1
, and a second ATM cell
20
2
. Each ATM cell
20
has a header
22
(e.g., cell
20
1
, has header
22
1
and cell
20
2
has header
22
2
). The payload of the ATM cells
20
begin with a start field
24
(e.g., cell
20
1
has start field
24
1
and cell
20
2
has start field
24
2
). After each start field
24
, the ATM cell payload contains AAL
2
packets. For example, the payload of ATM cell
20
1
contains AAL
2
packets
26
1
and
26
2
in their entirety, as well as a portion of AAL
2
packet
26
3
. The payload of cell
20
2
contains the rest of AAL
2
packet
26
3
, and AAL
2
packets
26
4
and
26
5
in their entirety. In addition, the payload of cell
20
2
has padding
28
.
The start field
24
, shown in
FIG. 3A
, facilitates one AAL
2
packet bridging two ATM cells. Start field
24
includes a six bit offset field (OSF), a one bit sequence number (SN), and one parity bit (P). The six bit offset field (OSF) contains a value, represented by offset displacement
29
in
FIG. 3
, indicative of the octet in the payload whereat the first full AAL
2
packet begins. For ATM cell
22
1
, the value of the offset field (OSF) is one, since AAL
2
packet starts just after start field
24
1
. For ATM cell
22
2
, the value of the offset field (OSF) is the sum of one (in view of start field
24
1
) and the number of octets of AAL
2
packet
26
3
protruding into cell
22
2
.
AAL
2
advantageously allows multiplexing of data from many users within a single ATM VCC. In such multiplexing scheme, each user's data is carried in a separate AAL
2
packet, but AAL
2
packets of differing users are carried in the same ATM cells or cells borne on the same ATM VC. Thus, assuming each user has a different channel identifier (CID) value, as many as
248
user channels can be multiplexed onto one ATM VC. AAL
2
thus allows more efficient utilization of low speed links than standard ATM while still maintaining low delay properties.
A problem with using AAL
2
arises when terminating AAL
2
channels at different nodes or different addresses in the same node. Since the individual AAL
2
channels may be multiplexed into one ATM-VCC, it is not possible to direct the individual AAL
2
channels (e.g., the AAL
2
packets on which the channel data is carried) to different destinations using conventional ATM switches.
One approach for switching AAL
2
packets is set forth by Mauger and Rosenberg, “QoS Guarantees for Multimedia Services on TDMA-Based Satellite Network”, IEEE Communications Magazine July 1997). In that approach, fixed-cell ATM switches work in conjunction with separate variable-cell ATM switches for handling AAL
2
packets.
BRIEF SUMMARY OF THE INVENTION
A queuing system stores a package derived from an ATM cell, the package including an internal interface header and either an ATM cell payload or an AAL
2
packet. The queuing system comprises a queue for storing the package, as well as a processor which executes plural functions. A time stamping function applies a time stamp upon storage of the package in the queue. The time stamping function can apply the time stamp to a package as replacement of the internal interface header. A time stamp checking function uses the time stamp to make a determination whether the tenure of the package in the queue is longer than permissible. The time stamp checking function can make the tenure determination in conjunction with a potential readout of the package from the queue. Alternatively, time stamp checking function can make the tenure determination when invoked by a queue monitoring function which monitors a fill level of the queue (e.g., when a queue fill level exceeds a threshold). A discard function is provided for discarding the package if the tenure of the package in the queue is longer than permissible.


REFERENCES:
patent: 5224099 (1993-06-01), Corbalis et al.
patent: 5276681 (1994-01-01), Tobagi et al.
patent: 5467347 (1995-11-01), Petersen
patent: 5537400 (1996-07-01), Diaz et al.
patent: 5825773 (1998-10-01), Shutoh et al.
patent: 5946309 (1999-08-01), Westberg et al.
patent: 5963564 (1999-10-01), Petersen et al.
patent: 6032205 (2000-02-01), Ogimoto et al.
patent: 95/11557 (1995-04-01), None
US 5,361,257, 11/1994, Petersen (withdrawn)

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