Priority threaded message burst mechanism for TDMA communication

• US 4,319,353 A
• Filed: 02/29/1980
• Issued: 03/09/1982
• Est. Priority Date: 02/29/1980
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Krug, Robert W., Brennen, John F., Alvarez, Joseph A. III
• Primary Examiner(s): Britton, Howard
• Application Number:
  US06/126,080
• Time in Patent Office: 739 Days
• Field of Search: 370/104, 370/58, 370/60, 370/61, 370/93, 370/94, 370/77, 370/79, 455/12
• US Class Current: 370/321
• CPC Class Codes: H04B 7/18523 Satellite systems for providing broadcast service to terrestrial stations, i.e. broadcast satellite service arrangements specially adapted for satellite broadcast receiving H04H40/90; picture transmission via satellite H04N1/00103; television transmission via satellite H04N7/20
• CPC Class Codes: H04B 7/2121 Channels assignment to the different stations
• CPC Class Codes: H04B 7/2643 using time-division multiple access [TDMA] H04B7/2615, H04B7/2618 take precedence

Abstract

To make the most efficient use of the TDMA frame for a satellite communications network, the assignment of each local station'"'"'s TDMA burst duration is based on a statistical assessment of the demand by local voice and data ports. Occasionally the actual voice and data port demand at a local station exceeds that station'"'"'s assigned burst duration so that some of the messages which are ready for transmission cannot be transmitted and may be frozen-out. To avoid or minimize the effects of message freeze-out, the various types of messages are categorized into a hierarchy of priorities for transmission. Messages are divided into four basic types, control signaling messages which cannot be interrupted without loss of system control, high speed data messages whose flow cannot be interrupted without the destruction of data and the need to retransmit them, low speed data messages whose transmission can be deferred for short periods, and voice messages which can be frozen-out to a limited extent without destroying the meaning of the aggregate voice signals.

The subject invention deals with the architecture and operation of a digital switch at each local station which enables the messages in each priority level to be assembled in a separate respective threaded list for transmission, with the highest priority messages in the beginning of the burst and the lowest priority at the end of the burst. Thus, if a statistically greater number of messages occur than can be transmitted within the assigned burst period, only the lowest priority messages cannot be sent. A voice port prioritization mechanism is disclosed which increases the priority of voice ports as a function of the duration of their talkspurts, with those voice ports having talkspurts of longer duration being assigned to threaded lists which will be transmitted earlier in the TDMA burst.

Claims

1. In a satellite communications system including a plurality of ground stations which intercommunicate in TDMA mode via satellite transponder, each ground station having a radio frequency burst modem for transmitting a time divided sequence of information channels during an assigned burst period of a TDMA frame, said burst period duration being assigned based on a statistical assessment of demand at each ground station, a method for minimizing the effects of message freeze-out when the actual demand at a given ground station exceeds said assigned burst duration, comprising the steps of:

dividing a plurality of digital ports connected to terrestrial signal sources into a first subplurality for transferring information having a relatively high priority and a second plurality for transmitting information having a relatively lower priority;

storing said information from said first and second subpluralities of ports in a message memory having addressable storage locations;

storing the addresses of said information stored in said message memory corresponding to said first subplurality of ports, in a first threaded address memory;

storing the addresses of said information stored in said message memory corresponding to said second subplurality of ports in a second threaded address memory;

accessing said message memory during said burst period by initially accessing with said addresses stored in said first threaded address memory and subsequently accessing with said addresses stored in said second threaded address memory;

outputting said messages stored in said message memory in an output message stream, in the order of said accessing thereof;

whereby said relatively high priority messages are transmitted during an early portion of said burst period and said relatively lower priority messages are transmitted during a later portion of said burst period during which truncation of said output message stream may take place.

2. In a satellite communications system including a plurality of ground stations which intercommunicate in TDMA mode via satellite transponder, each ground station having a radio frequency burst modem for transmitting a time divided sequence of information channels during an assigned burst period of a TDMA frame, a given ground station having a plurality of digital ports connected to terrestrial signal sources divided into a first subplurality for transferring information having a relatively high priority and a second plurality for transmitting information having a relatively lower priority, said burst period duration being assigned based on a statistical assessment of demand at each ground station, an apparatus for minimizing the effects of message freeze-out when the actual demand at a given ground station exceeds said assigned burst duration, comprising:

means connected to said ports for storing said information from said first and second subpluralities of ports in a message memory having addressable storage locations;

means connected to said message memory for storing the addresses of said information stored in said message memory corresponding to said first subplurality of ports, in a first threaded address memory;

means connected to said message memory for storing the addresses of said information stored in said message memory corresponding to said second subplurality of ports in a second threaded address memory;

means connected to said message memory and said first and second threaded memories for accessing said message memory during said burst period by initially accessing with said addresses stored in said first threaded address memory and subsequently accessing with said addresses stored in said second threaded address memory;

means connected to said message memory for outputting said messages stored in said message memory in an output message stream, in the order of said accessing thereof;

whereby said relatively high priority messages are transmitted during an early portion of said burst period and said relatively lower priority messages are transmitted during a later portion of said burst period during which truncation of said output message stream may take place.

3. In a satellite communications system including a plurality of ground stations which intercommunicate in TDMA mode via a satellite transponder, each ground station having a radio frequency burst modem for transmitting a time divided sequence of information channels during an assigned burst period of a TDMA frame, said burst period duration being based on a statistical assessment of the demand by terrestrial signal sources connected to the ports of a given ground station, means for minimizing the effects of message freeze-out when the actual demand at a given station exceeds said assigned burst period duration, comprising:

a first plurality of digital ports, each having a transmission register gatably connected to a transmit bus, for transferring information having a higher relative priority type;

a second plurality of digital ports, each having a transmission register gatably connected to said transmit bus, for transferring information having a low relative priority type;

a transmit burst buffer having a plurality of addressable storage locations, each selectively connectable to said transmit bus;

a switch control memory connected to an address input of said transmit burst buffer, having a plurality of addressable storage locations, each of a first subplurality of which corresponds to one of said ports in said first plurality of ports and each of a second subplurality of which corresponds to one of said ports in said second plurality of ports, and stores an SCM word containing the identity and type of said corresponding port and the storage address of one of said locations in said transmit burst buffer assigned to said corresponding port;

a port scanning means connected to an address input of said switch control memory for sequentially accessing each of said locations in said switch control memory and accessing the SCM word stored therein, said switch control memory having an output connected to gate inputs of said transmission registers for sequentially gating during a port scan period, each of said port transmission registers onto said transmit bus, there being an integral multiple of said port scan period in each of said TDMA frame periods;

said switch control memory outputting in the accessed SCM word, the storage address of said location in said transmit burst buffer assigned to said port synchronously scanned by said scanning means in response to said accessing by said port scanning means;

said transmission register gated by said port scanning means, transmitting said information over said transmit bus to said correspondingly accessed location in said transmit burst buffer;

a scan cycle counter connected to said port scanner, for counting said port scan periods and outputting first and second signals after predetermined first and second number of said scan periods have been counted, respectively;

a comparator means having a control input connected to said first output of said scan cycle counter, a data input connected to said switch control memory and a control output, for comparing said port type stored in said SCM word addressed from said switch control memory with said first priority type, and outputting a control signal when the comparison is satisfied;

said comparator means having a control input connected to said second output of said scan cycle counter, and a second control output, for comparing said port type stored in said SCM word accessed from said switch control memory with said second priority type, and outputting a second control signal when the comparison is satisfied;

a first threaded memory having a data input connected, through a gate controlled by the first output of said comparator means to said switch control memory, for storing in a first threaded list said transmit burst buffer address in said SCM word accessed from said switch control memory, when said port type stored in said SCM word is said first priority type and having an output connected to an address input of said transmit burst buffer;

a second threaded memory having a data input connected, through a gate controlled by the second output of said comparator means to said switch control memory, for storing in a second threaded list said transmit burst buffer address in said SCM word accessed from said switch control memory, when said port type stored in said SCM word in said second priority type, and having an output connected to said address input of said transmit burst buffer;

a burst scanner means having a control input connected to said scan cycle counter, an output connected to an address input of said first and second threaded memories, for sequentially gating the transmission of said transmit burst buffer addresses stored in said first threaded memory and then next, those stored in said second threaded memory, to said address input of said transmit burst buffer, after said frame period has expired;

a system output bus connected to the data output of said transmit burst buffer, and connected to a satellite communications link, for outputting in burst form in the next TDMA frame said information stored in said locations of said transmit burst buffer accessed by said first and second threaded memories, with information originating from said first ports with said higher priority preceding information originating from said second ports with said lower priority.

4. In a satellite communications system including a plurality of ground stations which intercommunicate in TDMA mode via a satellite transponder, each ground station having a radio frequency burst modem for transmitting a time divided sequence of information channels during an assigned burst period for a TDMA frame, said burst period duration being based on a statistical assessment of the demand by terrestrial signal sources connected to the ports of a given ground station, means for minimizing the effects of a message freeze-out when the actual demand at a given station exceeds said assigned burst period duration, comprising:

a first plurality of digital ports, each having a transmission register gatably connected to a transmit bus, for transferring information having a higher relative priority type;

a second plurality of digital ports, each having a transmission register gatably connected to said transmit bus, for transferring information having a low relative priority type;

a transmit burst buffer having a plurality of addressable storage locations, each selectively connectable to said transmit bus;

a switch control memory connected to an address input of said transmit burst buffer, having N sequentially addressable storage locations, N-p of which forming a first plurality of addressable storage locations, each of a first subplurality of which corresponds to one of said ports in said first plurality of ports and each of a second subplurality of which corresponds to one of said ports in said second plurality of ports, and stores an SCM word containing the identity and type of said corresponding port and storage address of one of said locations in said transmit burst buffer assigned to said corresponding port;

said switch control memory having a second plurality of p addressable storage locations mutually equally separated in the order of increasing address, where N divided by p is a whole number;

said transmit burst buffer having first and second halves, with said first half having a data input connected to said transmit bus and an address input sequentially connected to successive ones of said first plurality of addressable storage locations in said switch control memory, for storing information from said first and second plurality of digital ports, said second half of said transmit burst buffer having been loaded with information from said first and second plurality of digital ports during a preceding TDMA frame and having a data output connected to said burst modem;

a burst priority memory having a first half and a second half, with said first half having a data input sequentially connected to each of said first plurality of addressable storage locations in said switch control memory for forming a first threaded list of addresses to locations in said first half of said transmit burst buffer corresponding to selected ones of said ports in said first plurality of digital ports and for forming a second threaded list of addresses to said first half of said transmit burst buffer corresponding to selected ones of said ports in said second plurality of digital ports, said second half of said burst priority memory having an address input accessed in synchronism with said sequential accessing of each of said second plurality of addressable storage locations in said switch control memory for accessing first and second threaded lists of addresses to said second half of said transmit burst buffer corresponding to information respectively loaded from selected ones of said first plurality and second plurality of digital ports in said preceding TDMA frame, said second burst priority memory having a data output connected to the address input of said second half of said transmit burst buffer;

whereby said first half of said transmit burst buffer may be loaded with information from said digital ports and said first half of said burst priority memory may form said first and second threaded lists when storage locations in said first plurality of addressable storage locations in said switch control memory are being accessed and said first and second threaded lists in said second half of said burst priority memory can access storage locations in said second half of said transmit burst buffer transmitting information stored therein during said preceding TDMA frame to said burst modem when storage locations in said second plurality of addressable storage locations in said switch control memory are being accessed.

5. The apparatus of claim 4 which further comprises:

activity detection means connected between said first and second digital ports and said first half of said burst priority memory, for preventing the inclusion of addresses in said first half of said transmit burst buffer corresponding with selected ones of said ports from being included in said first or second lists being formed therein if no port activity is detected.

6. In a TDMA communications system, means for minimizing the effects of a message freeze-out when the actual demand at a given station exceeds the assigned burst period duration, comprising:

a first plurality of high priority input ports, gatably connected to a transmit bus;

a second plurality of low priority input ports, gatably connected to said transmit bus;

a transmit burst buffer having a plurality of addressable storage locations, each selectively connectable to said transmit bus;

a switch control memory connected to an address input of said transmit burst buffer, having N sequentially sequentially addressable storage locations, N-p of which forming a first plurality of addressable storage locations, each of a first subplurality of which corresponds to one of said first plurality of ports and each of a second subplurality of which corresponds to one of said second plurality of ports, and stores an SCM word containing the identity and type of said corresponding port and the storage address of one of said locations in said transmit burst buffer assigned to said corresponding port;

said switch control memory having a second plurality of p addressable storage locations mutually equally separated in the order of increasing address, where N divided by p is a whole number;

said transmit burst buffer having first and second halves, with said first half having a data input connected to said transmit bus and an address input sequentially connected to successive ones of said first plurality of addressable storage locations in said switch control memory, for storing information from said first and second plurality of ports, said second half of said transmit burst buffer having been loaded with information from said first and second plurality of ports during a preceding TDMA frame and having a data output connected to a TDMA system output;

a burst priority memory having a first half and a second half, with said first half having a data input sequentially connected to each of said first plurality of addressable storage locations in said switch control memory for forming a first threaded list of addresses to locations in said first half of said transmit burst buffer corresponding to selected ones of said first plurality of ports and for forming a second threaded list of addresses to said first half of said transmit burst buffer corresponding to selected ones of said second plurality of digital ports;

accessing means connected to said switch control memory and said second half of said burst priority memory for simultaneously accessing said second plurality of addressable storage locations and accessing said second half of said burst priority memory for first and second threaded lists of addresses to said second half of said transmit burst buffer corresponding to information respectively loaded from selected ones of said first plurality and second plurality of ports in said preceding TDMA frame, said second burst priority memory having a data output connected to the address input of said second half of said transmit burst buffer;

whereby said first half of said transmit burst buffer may be loaded with information from said ports and said first half of said burst priority memory may form said first and second threaded lists when storage locations in said first plurality of addressable storage locations in said switch control memory are being accessed and said first and second threaded lists in said second half of said burst priority memory can access storage locations in said second half of said transmit burst buffer transmitting information stored therein during said preceding TDMA frame to said TDMA output when storage locations in said second plurality of addressable storage locations in said switch control memory are being accessed.

7. In a TDMA communications system, means for minimizing the effects of message freeze-out when the actual demand at a given station exceeds the assigned burst period duration, comprising:

a first plurality of high priority input ports, gatably connected to a transmit bus;

a second plurality of low priority input ports, gatably connected to said transmit bus;

a transmit burst buffer having a plurality of addressable storage locations, each selectively connectable to said transmit bus;

a switch control memory connected to an address input of said transmit burst buffer, having a plurality of addressable storage locations, each of a first subplurality of which corresponds to one of said first plurality of ports and each of a second subplurality of which corresponds to one of said ports second plurality of ports, said first and second subpluralities storing an SCM word containing the identity and type of said corresponding port and the storage address of one of said locations in said transmit burst buffer assigned to said corresponding port;

a port scanning means connected to an address input of said switch control memory for sequentially accessing each of said locations and accessing the SCM word stored therein, said switch control memory having an output connected to said ports for sequentially gating during a port scan period, each of said ports onto said transmit bus, there being an integral multiple of said port scan periods in each TDMA frame period;

said switch control memory, in response to said accessing by said port scanning means, outputting in the accessed SCM word, the storage address of said location in said transmit burst buffer assigned to said sequentially gated port;

said port transmitting said information over said transmit bus to said correspondingly accessed location in said transmit burst buffer;

a scan cycle counter connected to said port scanner, for counting said port scan periods and outputting first and second signals after predetermined first and second number of said scan periods have been counted, respectively;

a comparator means having a control input connected to said first output of said scan cycle counter, a data input connected to said switch control memory and a control output, for comparing said port type stored in said SCM word accessed from said switch control memory with said first priority type, and outputting a control signal when the comparison is satisfied;

said comparator means having a control input connected to said second output of said scan cycle counter, and a second control output, for comparing said port type stored in said SCM word accessed from said switch control memory with said second priority type, and outputting a second control signal when the comparison is satisfied;

a threaded memory having a data input connected to said switch control memory, for storing in a first threaded list, in response to said first output from said comparator means connected thereto, said transmit burst buffer address in said SCM word accessed from said switch control memory, when said port type stored in said SCM word is said first priority type, said threaded memory having an output connected to an address input of said transmit burst buffer;

said threaded memory storing in a second threaded list, in response to said second output from said comparator means connected thereto, said transmit burst buffer address in said SCM word accessed from said switch control memory, when said port type stored in said SCM word is said second priority type, and having an output connected to said address input of said transmit burst buffer;

a burst scanner means having a control input connected to said scan cycle counter, an output connected to an address input of said threaded memory, for sequentially gating the transmission of said transmit burst buffer addresses stored in said first list and then next, in said second list stored in said threaded memory, to said address input of said transmit burst buffer, after said frame period has expired;

a system output bus connected to the data output of said transmit burst buffer, and connected to a TDMA output, for outputting in burst form in the next TDMA frame said information stored in said locations of said transmit burst buffer accessed by said threaded memory, with information originating from said first ports with said higher priority preceding information originating from said second ports with said lower priority.

8. In a TDMA Satellite Communications Controller having voice ports input thereto, a voice control mechanism for increasing the priority of voice messages as a function of the duration of their talkspurts, comprising:

a voice history control memory for storing the code corresponding to each voice port representing the duration of the talkspurt for that port;

activity detection means connected to each of said voice ports, for detecting voice port activity;

voice history code incrementing means having an input connected to said voice history code memory and a second input connected to said activity detection means, for incrementing each voice history code accessed from said memory when said voice activity detector indicates the corresponding voice port is active, said voice history code incrementing means having an output connected to an input to said memory to store the updated voice history code for each active voice port;

a threaded list memory means having an input connected to said voice history code memory, for forming a first threaded list of the identities of those voice ports having a talkspurt in excess of a first duration and for forming a second threaded list of the identities of those voice ports having a talkspurt duration in excess of a second duration which is greater than said first duration;

a TDMA burst means having an input connected to said threaded list memory means and a second input connected to said voice ports, for bursting information from those voice ports whose identities are stored in said second threaded list before bursting information from those voice ports having identities stored in said first threaded list;

whereby those voice ports with longer duration talkspurts are transmitted first.

9. In a TDMA Communications Controller having voice ports input thereto, a voice control mechanism for increasing the priority of voice messages as a function of the duration of their talkspurts, comprising:

a voice history control memory for storing the code corresponding to each voice port representing the duration of the talkspurt for that port;

activity detection means connected to each of said voice ports, for detecting voice port activity;

voice history code incrementing means having an input connected to said voice history code memory and a second input connected to said activity detection means, for cyclically incrementing each voice history code accessed from said memory when said voice activity detector indicates the corresponding voice port is active, said voice history code incrementing means having an output connected to an input to said memory to store the updated voice history code for each active voice port;

a memory means having an input connected to said voice history code memory, for storing the identities of said voice ports in a sequential order in accordance with said voice history code;

a TDMA burst means having an input connected to said memory means and a second input connected to said voice ports, for bursting information from the voice ports in said sequential order stored in said memory means;

whereby those voice ports with longer duration talkspurts are transmitted first.