International Business Machines Corporation

Guy Platel

Claude R Galand

Pierre Secondo

Gerard Marmigere

James P Gray

Denis Chevalier

Eric Lebrun

Jeffrey G Knauth

Paul Raymond Callens

Robert Vermot-Gauchy

Lawrence Edward Troan

James L Ashton

Michel Geneste

Michael F Gierlach

Andre Cretegny

Robert T Gibbs

Patrick Massi

Jean Gallian

Alain Rey

Jean-jacques Chartreux

Stuart W Pretzman

Anne Chabanet

Lionel Bustini

Sylvain Wiest

Communication controller allowing communication between application programs running in at least one host computer and DTEs attached to a X25 packet switched network and communicating through virtual circuits (VC), the communication being provided through the X25 network and a Systems Network Architecture (SNA) network. The controller includes tables and logic for establishing predetermined SNA sessions between the application programs and the communication controller, and tables and logic for linking at least one virtual circuit on a predetermined SNA session. The controller further includes memory for storing a set of alternate session tables defining, for each of said established predetermined SNA sessions, a prioritized list of alternate backup sessions, logic for detecting the occurrence of one failure on one SNA session, and logic for switching the virtual circuits linked to said session being subject of a failure to one backup session defined in the corresponding alternate session table. The alternate sessions being pre-established, the virtual circuits can be immediately connected to one alternate session without requiring further delay. A quick end-user reconnection is then allowed.

Communication controller allowing continued communication through an X25

A communication controller CCP includes line adapters (104-i) each having a storage which is loaded with a general application program during an initialization phase. The line adapters allow the attachment and the communication of different telecommunication entities, e.g. a LAN, a teleprocessing line etc. . . The CCP is connected by means of a control adapter to a local control terminal (100) which is associated with a storage for storing the different general application programs which are likely to be required by the different line adapters. A storage contains an access key comprising data relative to the types and the number of line adapters of any type which are authorized to be loaded with the general application program stored in the storage controlled by the control terminal. The CCP also has logic for checking whether a loading request received from one adapter complies with the contents of the stored access key in order to prevent the loading of an unauthorized line adapter. A method is disclosed for performing the loading of a line adapter card which is attached to a communication controller product CCP, the line adapter card being loadable with a general application program during an initialization phase. The method includes the steps of receiving a request from a determined line adapter to be loaded with the corresponding general application program which is loaded in its said storage, and of checking whether the requesting line adapter is included in a list of line adapters which are authorized to be loaded with their corresponding general program application. The method further includes checking whether the number of already defined line adapters which are of the same type as the one which requests the loading operations does not exceed a predetermined value, and of eventually preventing the loading of the requesting line adapter in the case when one of the preceding conditions is not satisfied.

Programmable communication controller line adapter and method for

A method of operating a communication system which includes a number of host systems each communicating via sessions with other devices over different connections and in which the sessions assigned to a failed connection are suspended for a first and second time period and non-destructively moved to an alternate connection when a unique command is issued by one of the host systems and received by a control unit involved in the failed connection.

Non-disruptive session recovery

In a packet switching network, voice packets are made to include an EC field whose contents indicates whether the corresponding packet is eligible for clipping if required in a node queue within the network. Should clipping of a non eligible packet be required, then another bit field would be set in the following packet on same link to limit any possible clipping of successive packets on same link.

Digital packet switching networks

A method of reconstructing, at the receiving end, digital data defining an encoded voice signal segment lost in transmission between the transmitter and the receiver in a transmission system wherein a low-frequency signal such as a residual baseband signal is derived at the transmitting end from the signal to be encoded and is then distributed among several sub-bands whose sampled contents are quantized separately. The reconstruction method includes a step of analyzing the received signal to detect any missing segment thereof and, as the case may be, to initiate an analysis, within each sub-band, of the segment(s) adjacent to the lost segment, so as to generate a term relating to the period T.sub.(k) of the signal so analyzed and to reconstruct a segment of signal of period T.sub.(k) intended to be substituted for the lost segment. Cyclic redundancy is used to detect errors, and modulo sequence numbering identification is used to detect loss of packet.

Method of reconstructing lost data in a digital voice transmission

In a voice transmission network having an echo canceler including a flat delay line in series with an adaptive digital filter, a process is provided for adjusting the flat delay line length, thus enabling limiting the filter length to minimal value. The method is based on intercorrelation operations. It includes first intercorrelating sequences of energy values of blocks or consecutive samples, to derive a rough flat delay estimation therefrom; then intercorrelating sequences of signal samples with one of the sequences being roughly delayed, to derive therefrom an accurate flat delay estimation.

Process for determining an echo path flat delay and echo canceler using

This process enables cancelling residual echo signals in a transmission system wherein echo signals are partially cancelled through use of a filter generating an echo replica, and substracting said replica from the signal in the echo path. The process involves measuring energies of incoming and outgoing signals, comparing the ratio of said energies to a predetermined threshold value to generate a flag information, which flag is used to control a switch on the echo path. The threshold is determined, for instance by using the information provided by the echo path impulse response not considered for the generation of the echo replica.

Process and system for improving echo cancellation within a transmission

A buffer device for a digital transmission network transmitting voice signals, by packets, including so-called purging means for eliminating a number x.sub.(t) of the oldest packets stored in the buffer to prevent saturation thereof. The number of packets received at the input of the buffer within a given time interval is used to address a storage that supplies two pre-stored digital values, namely, x.sub.(t) and L.sub.(t). When the contents of the buffer are equal to L.sub.(t), a number x.sub.(t) of the oldest packets contained in the buffer are dropped.

Buffer device for a voice transmission network

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La Gaude, France

Guy Platel