Automatic channel switching from fallback channels to regular channels

• US 5,138,609 A
• Filed: 12/20/1989
• Issued: 08/11/1992
• Est. Priority Date: 12/20/1988
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Hashimoto, Akira
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): Jung, Min
• Application Number:
  US07/453,891
• Time in Patent Office: 965 Days
• Field of Search: 370/16, 370/13, 370/17, 371/8.2, 371/20.3
• US Class Current: 370/228
• CPC Class Codes: H04L 69/40 for recovering from a failure of a protocol instance or entity, e.g. service redundancy protocols, protocol state redundancy or protocol service redirection management of faults, events, alarms or notifications in data switching networks H04L41/06
• CPC Class Codes: H04Q 11/04 for time-division multiplexing H04Q11/0001 takes precedence

Abstract

In a channel switching system, first and second stations are normally interconnected through first and second regular channels and switched to fallback channels established by a public switched network in the event of a fault in the regular channels. In the event of a fault in the regular channels, a tone generator at the first station transmits a tone signal to the second station through the first regular channel. A signal-to-noise (S/N) ratio detector at the second station receives it and derives a S/N ratio of the first regular channel, and transmits a S/N ratio indicating signal to the first station. A switching controller at the first station receives it to detect when the S/N ratio of the first regular channel is higher than a reference to interpret that the first regular channel has been recovered. Upon recovery of the first channel, a tone generator at the second station returns a tone signal to the first station through the second channel. A S/N ratio detector at the first station receives it and derives a S/N ratio of the second regular channel. The switching controller at the first station detects when the S/N ratio of the second regular channel is higher than the reference and switches the first station from the fallback to the regular channels and notifies the second station of this fact to allow it to be switched from the fallback to the regular channels.

Claims

1. A channel switching system for normally interconnecting first and second stations through first and second regular channels and interconnecting said stations through fallback channels established by a public switched telecommunications network in the event of a fault in said regular channels, comprising:

first tone generator means for transmitting a first tone signal from said first station to said second station through said first regular channel in the event of said fault;

first signal-to-noise detector means for receiving said first tone signal at said second station, deriving a signal-to-noise ratio of said first regular channel from the received tone signal, and transmitting a quality signal indicative of the signal-to-noise ratio of the first regular channel to said first station;

first switching control means for receiving said quality signal at said first station and determining whether the signal-to-noise ratio of said first regular channel represented by the received quality signal is higher than a reference value, and switching the first station from said fallback channels to said regular channels if said signal-to-noise ratio is higher than the reference value;

second tone generator means for transmitting a second tone signal from said second station to said first station through said second regular channel when the signal-to-noise ratio is determined by the first switching control means as being higher than said reference value;

second signal-to-noise detector means for receiving said second tone signal at said first station and deriving a signal-to-noise ratio of said second regular channel from the received tone signal; and

second switching control means for determining whether the signal-to-noise ratio of said second regular channel is higher than said reference value and switching said second station from said fallback channels to said regular channels if the signal-to-noise ratio of the second regular channel is higher than the reference value.

2. A channel switching system for a communications system including first and second stations each including a modulator/demodulator (modem), said first and second modems being normally interconnected through first and second regular channels and interconnected through fallback channels established by a public switched telecommunications network in the event of a fault in said regular channels, said first station comprising:

first tone generator means for transmitting a tone signal to said first regular channel in the event of said fault to said second station;

first signal-to-noise detector means for receiving a tone signal transmitted through said second regular channel from said second station and deriving a signal-to-noise ratio of said second regular channel from the received tone signal;

first switching means programmed to perform the steps of (a) receiving a quality signal indicative of a signal-to-noise ratio of said first channel transmitted from said second station, (b) detecting when the signal-to-noise ratio of said first regular channel represented by the received quality signal is higher than a reference value to interpret that said first regular channel has been recovered, (c) transmitting a tone request signal upon recovery of said first regular channel to said second station, (d) detecting when the signal-to-noise ratio of said second regular channel is higher than said reference value to interpret that said second regular channel has been recovered, (e) switching said first modem from said fallback channels to said regular channels, and (f) transmitting a recovery signal, said second station comprising;

second signal-to-noise detector means for receiving said tone signal transmitted by said first tone generator means through said first regular channel, deriving a signal-to-noise ratio of said first regular channel from the received tone signal to generate said quality signal, and transmitting said quality signal to said first station;

second tone generator means for transmitting a tone signal to said first station through said second regular channel upon receipt of said tone request signal; and

second switching control means for switching said second modem from said fallback channels to said regular channels upon receipt of said recovery signal.

3. A method for switching a communications system from a public switched telecommunications network to first and second regular channels upon recovery of the regular channels, said communications system including first and second stations which are normally interconnected by said first and second regular channels and interconnected by fallback channels established by said public switched telecommunications network in the event of a fault in said regular channels, comprising the steps of:

a) transmitting a tone signal from said first station to said second station through said first regular channel in the event of said fault;

b) receiving said tone signal at said second station, deriving a signal-to-noise ratio of said first regular channel from the received tone signal, and transmitting a quality signal indicative of the derived signal-to-noise ratio to said first station;

c) receiving said quality signal at said first station and detecting when the signal-to-noise ratio of said first regular channel represented by the received quality signal is higher than a reference value to interpret that said first regular channel has been recovered;

d) transmitting a tone request signal from said first station to said second station upon recovery of said first regular channel;

e) receiving said tone request signal at said second station and transmitting a tone signal to said first station through said second regular channel;

f) receiving said tone signal at said first station and deriving a signal-to-noise ratio of said second regular channel from the received tone signal;

g) detecting when the signal-to-noise ratio of said second regular channel is higher than said reference value to interpret that said second regular channel has been recovered;

h) switching said first station to said first and second regular channels from said fallback channels and transmitting a recovery signal to said second station; and

i) switching said second station to said first and second regular channels from said fallback channels upon receipt of said recovery signal at said second station.

4. A channel switching system for normally interconnecting first and second stations through a regular channel and interconnecting said stations through a fallback channel established by a public switched telecommunications network in the event of a fault in said regular channel, comprising:

tone generator means for transmitting a tone signal from said first station to said second station through said regular channel in the event of said fault;

signal-to-noise detector means for receiving said tone signal at said second station, deriving a signal-to-noise ratio of said regular channel from the received tone signal, and transmitting a quality signal indicative of the signal-to-noise ratio of the regular channel to said first station; and

switching control means for receiving said quality signal at said first station and switching said first and second stations from said fallback channel to said regular channel when the signal-to-noise ratio of said regular channel represented by the received quality signal is higher than a reference value.

5. A method for switching a communications system from a fallback channel established through a public switched telecommunications network to a regular channel upon recovery of the regular channel, said communications system including first and second stations which are normally interconnected by said regular channel and interconnected by said fallback channel in the event of a fault in said regular channel, comprising the steps of:

a) transmitting a tone signal from said first station to said second station through said regular channel in the event of said fault;

b) receiving said tone signal at said second station, deriving a signal-to-noise ratio of said regular channel from the received tone signal, and transmitting a quality signal indicative of the derived signal-to-noise ratio to said first station;

c) receiving said quality signal at said first station and comparing the signal-to-noise ratio of said regular channel represented by the received quality signal with a reference value;

d) if the signal-to-noise ratio is determined as being higher than said reference value by the step (c), switching said first station to said regular channel from said fallback channel and transmitting a recovery signal from the first station to said second station; and

e) switching said second station to said regular channel from said fallback channel upon receipt of said recovery signal at said second station.