Connectionless communications system, its test method, and...

Details Connectionless communications system, its test method, and... Connectionless communications system, its test method, and...

1995-08-21

2001-12-25

Olms, Douglas (Department: 2661)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S253000, C370S351000, C370S360000, C370S377000, C370S432000, C370S471000

Reexamination Certificate

active

06333932

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a connectionless communications system for transmitting data at a high speed, to a method of testing the system, and to an intra-station control system of a switching station for transmitting data at a high speed.
2. Description of the Related Art
Recently, high-performance information processing devices such as work stations, personal computers, etc. have been developed to perform a distribution process in which a number of information processing devices are interconnected through a high speed local area network (LAN). The network connecting such LANs should also be provided with high speed processing capabilities.
One of the services to realize the above described high speed data communications is a switched multi-megabit data service (SMDS). The SMDS is a connectionless data switching service based on the transfer speed of 1.5 Mbps and 45 Mbps.
An asynchronous transfer mode (ATM) system is well known as a method of realizing a broadband ISDN, and the SMDS can be provided through an ATM network. In this case, an SMDS processing server (SMDS message handler) is supplied for a predetermined ATM switch, and a permanent virtual circuit or a permanent virtual channel (PVC) connects an SMDS subscriber with the SMDS processing server accommodating the SMDS subscriber. The connectionless data output from the SMDS subscriber is transferred to the SMDS processing server to perform a routing process, etc. at the server.
The connectionless data normally refers to a variable packet (data frame). However, since the above described PVC is a path to be established in a network, the connectionless data is transferred after being converted (decomposed) into an ATM cell format before it is input to the ATM switch. The cell is a 53-byte structure consisting of a 48-byte payload and a 5-byte header.
The ATM cell format data is temporarily structured as the layer-3 protocol data unit (L3-PDU) or in a data format of a higher-level layer in the SMDS processing server as shown in
FIG. 897
to analyze routing information, etc. according to a destination address DA, a source address SA, etc. stored in the L3-PDU. Then, the data is decomposed again into cells to route the data according to the analyzed information.
As described above, the conventional SMDS is limited in its speed because input cells are structured in a higher level layer data format (for example, in L3-PDUs) when the SMDS processing server performs a routing process through software of a microcomputer program, etc. Additionally, such processes as a data copying process performed when a group address is specified as a destination address DA, a traffic smoothing process, an action against no reception of an end-of-message cell (EOM: a cell storing the last portion of data when an L3-PDU is decomposed into a plurality of cells) have been processed through software by microcomputers, etc.
Thus, the conventional SMDS has been limited in its process speed because the processes in the SMDS processing server are performed through various software. Therefore, when connectionless communications data is transmitted using an SMDS, the operations of the transmission line and switch are sped up with the SMDS processing server processes interfering as a bottleneck, thereby preventing an actual high-speed process from being successfully realized. Furthermore, when the above described structuring process in the SMDS processing server, all cells forming each L3-PDU should be temporarily stored. Therefore, the necessary buffer capacity undesirably becomes very large.
In the SMDS, protocol performance is monitored when a service is offered as follows. That is, the formats of various parameters are checked in the data, and counted is the data which has been rejected by the check (the data which cannot be recognized as valid). A predetermined specific type of check is followed by a counting process performed on the rejected data based on a predetermined algorithm. If the resultant value exceeds a predetermined threshold, then output is a threshold crossing alert (TCA) indicating that the threshold is exceeded. Furthermore, an error log is collected each time data is rejected.
The following parameters are collected in the error log.
(1) Destination address DA
(2) Source address SA
(3) SNI number (subscriber network interface No.)
(4) Error type
In the PVC between the user (subscriber) and the SMDS processing server,
In the PVC between the user (subscriber) and an SMDS processing server, data is transferred in the cell format as described above (actually, the data is transmitted in the ATM cell format and processed in the L2-PDU in the SMDS processing server. The ATM cell and L2-PDU are based on the 53-byte configuration and simply referred to as cells. However, since the above described error log collection is mostly related to the layer 3, the data is received in the cell format and then reassembled into the L3-PDU in the SMDS processing server.
As described above, input cells are reassembled in the data format of the higher order layer (for example, L3-PDU) in the conventional SMDS. This prevents the processes from being performed at a high speed in the SMDS.
The above described services are based on the high reliability of the physical quality of the transmission lines forming the network. Therefore, it is important to test and evaluate the transmission quality of the network.
The test and evaluation of the transmission lines are activated from the OS center (operation center for managing the network) in the connectionless communications service network, and an inter-station loopback test is conducted to confirm the normality of any inter-station link (path between switches). The inter-station loopback test is described below by referring to FIG.
898
. In this embodiment, the test is conducted to check the link between SW station
3
and SW station
6
.
The test is started by issuing a test connectionless packet transmission request message (test start request) from the OS center
1
to SW station
3
. The request message contains an identification information ID indicating terminal SW station
6
. SW station
3
generates a test packet with the identification address of terminal SW station
6
set as its destination address DA and the identification address of its home station (SW station
3
) set as its source address SA. The test packet is output to terminal SW station
6
. In SW stations
4
and
5
, test packets are processed as normal packets and transferred to terminal SW station
6
. On receipt of the test packet, terminal SW station
6
outputs the packet with its DA and SA inverted. That is, the packet is returned from terminal SW station
6
to SW station
3
, and it is reported to the OS center
1
upon re-arrival of the packet at the source SW station
3
.
Thus, the OS center
1
checks whether or not the packet is normally transmitted in the network, that is, checks the normality of the transmission line (the link between SW station
3
and terminal SW station
6
in this embodiment). In the procedure, since the source SW station
3
and the terminal SW station
6
mark the time stamp onto the payload field of the packet, the OS center
1
is informed of the transmission time of packets according to the information.
However, in the above described test method, the information obtained by the test is to be provided for the OS center (operation center), and no method has been provided for the subscriber (terminal unit
2
in
FIG. 898
) to be autonomously informed of the transmission quality in the network (transmission delay time, etc.). Therefore, if a packet is not normally transmitted from a source subscriber to a destination subscriber, the subscribers cannot detect in which the factor of the fault resides, the subscriber terminal unit or the network transmission line. Thus, the OS center is invoked to recover from the fault, thereby requiring much time and cost.
FIG. 899
shows an embodiment of the SMDS. In
FIG. 899
, the SMDS support module analyz

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