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CROSS-REFERENCES TO RELATED APPLICATIONS
1. U.S. Pat. application Ser. No. 537,211, by H. G. Markey et al, entitled
"SWITCHING AND ACTIVITY COMPRESSION BETWEEN TELEPHONE LINES AND DIGITAL
COMMUNICATION CHANNELS," filed Dec. 30, 1974. 2. U.S. Pat. application
Ser. No. 537,502, by D. C. Flemming et al, entitled "MODULAR BRANCH
EXCHANGE AND NODAL ACCESS UNITS FOR MULTIPLE ACCESS SYSTEM," filed Dec.
30, 1974.
3. U.S. Pat. application Ser. No. 537,212, by D. C. Flemming, entitled
"INTER-RELATED SWITCHING, ACTIVITY COMPRESSION AND DEMAND ASSIGNMENT,"
filed Dec. 30, 1974.
4. U.S. Pat. application Ser. No. 537,281, by D. C. Flemming et al,
entitled "EXTERNAL MANAGEMENT OF SATELLITE LINKED EXCHANGE NETWORK," filed
Dec. 30, 1974.
BACKGROUND OF THE INVENTION
A problem in utilization of time division multiple access (TDMA) space
satellite communication facilities has been to strike an advantageous
balance between station costs and network performance; one factor of the
latter being the proportionate "throughput" of information bits to
non-information bits (e.g. bits used for time control, error control,
etc.).
Another problem has been to provide modular time division multiplex (TDM)
switching centers for such facilities, which can be conveniently assembled
into various station (access node) configurations without precise
foreknowledge of station traffic and geographic coverage.
Another problem has been to provide for efficient acquisition, timekeeping
and use of satellite time in such networks.
Another problem has been to provide multiple routing capability in modular
units relative to a TDMA facility.
Another problem has been to provide efficient terrestrial linkage of a
large geographic area to one station (access node) of a TDMA space
satellite facility.
Another problem has been to provide for efficient multiplex switching and
high speed transmission of diverse digital signal traffic--including
telephone (encoded voice), data and non-coded image (NCI) information--by
satellite and over point-to-point terrestrial links between physically
remote switching centers of one station.
An object of the present invention is to provide a method of communication
fulfilling requirements associated with eliminating the foregoing problems
and satisfying respective needs.
Another object is to provide an architecture for modular time domain
switching centers, and a related method of communication, which fulfill
the foregoing requirements.
Other objects are to provide modular "store and forward" digital switching
centers, for operating hierarchically in stations covering a variety of
"use-interface" areas relative to access nodes of a TDMA principal trunk
facility, and a method of operating a network of such stations.
Another object is to provide a method of TDMA satellite communication
characterized by use of modular unit terminals (representing small
increments of equipment and cost), to provide call switching, time
compression; activity compression and distributed demand assignment and
thereby provide a basis for achieving station and network efficiencies
relative to use of the satellite.
Another object is to provide a method of efficiently switching and handling
data and encoded sound (telephone) signals relative to a TDMA link.
A feature of the invention is the use of modular hierarchical switching and
activity compressing units in access stations interfacing with a TDMA
link, with units linked intranodally (within a station region) by
subsidiary digital trunks and with stations linked nodally by a principal
TDMA trunk; nodally associated centers operating to provide hierarchical
multiplexing, compression and switching of digital signal traffic relative
to associated access nodes of the TDMA link.
Another feature of the invention is the use of said units in reverse
hierarchical order to provide progressive decompression and demultiplexing
of composite signals received from the TDMA link.
Another feature is the use of plural digital trunks (such as leased high
speed public carrier lines), as TDM links between hierarchically
associated switching centers associated with a station having access to a
space satellite facility. A related feature is the use of individual
lowest level centers in the station hierarchy to control establishment and
release of local and toll (satellite) call connections and the use of
highest level centers to control acquisition, timekeeping and demand
assignment relative to the satellite.
Another feature is the use of land-linked multiplex switch modules to
administer time and space domain connections to time division transmission
facilities having fixed time capacity to handle a wide range of mixed
voice and data traffic in block multiplex relative to a satellite; the
extra cost of storage for block handling (over bit handling) being offset
by reductions in transmissions overhead relative to the land links and the
satellite.
Another feature is the terrestrial connection of plural first level
switching modules with an access node of a TDMA space segment land-based
digital trunks and a common second level switching module; said first and
second level modules operating hierarchically to switch, buffer and
activity compress traffic signals passing between multiple independent
source/reception ports and the satellite.
Another feature is the linked association of a first level TDM switching
with plural second level TDM switching centers which in turn link to
different access nodes (stations) of a TDMA facility. A related feature is
the association of plural co-located second level TDM switching centers
with one or more access nodes of a TDMA facility. A variation is the
association of plural co-located second level TDM switching centers with
different TDMA carrier frequency bands (transponders) of a satellite
repeater and common timekeeping apparatus.
Another feature is the provision of a basic module structure which can be
adapted for first level switch operation, second level operation or both
(for co-location of station elements).
SUMMARY OF THE INVENTION
The invention concerns an access method and modular station apparatus for
switching voice and data signals relative to a TDMA link; especially a
satellite. The method is distinguished by use of long frame times (long by
comparison to the samapling period at a voice trunk), extensive block
storage per access station, (plural-stage) time and activity compression
of signals on a modularly structured block basis and demand assignment of
satellite time under collective station control.
Being modular in traffic capacity the subject apparatus can be variously
configured to adapt to changing traffic situations over the long term.
Being adaptive in respect to activity compression, demand assignment and
alternate path routing the apparatus adapts efficiently to short term
traffic fluctuations. Subject switch modules can be concentrated in a
combined center under one housing or dispersed over a region. The first
and second level centers can be constructed from a primitive module which
has attributes of both (individually and collectively).
Presently described first level switch modules (NCU's) connect with and
receive time base control from second level modules (NAU's). Each module
(switch center) is organized to provide varied local and toll call
connections, activity compression on a block basis and TDM digital signal
switching on a block (store and forward) basis. Each first level center
interfaces between respective input-output ports and one or more second
level centers via up to four terrestrial digital trunks.
Connection scheduling services typically include: detecting calling
("off-hook") conditions and "dial" signals at disconnected ports;
distinguishing between "local" and "toll" calls; making "local"
connections when available; testing for availability of a principal first
level path segment for toll (satellite) calls, as specified in a stored
"path locating directory"; communicating with second level centers (e.g.
via digital trunks) for determining availability of second level path
segments to extend toll connection from the calling port to the satellite
or from the satellite to a called port; providing "dial tone," "busy" and
"ringing" signals to called ports when appropriate; assigning call
connection paths when available by setting entries in connection
scheduling tables; time-stamping durations of calls initiated at
respective ports; providing management communications to external host
apparatus for high level connectivity control, call duration computation,
revenue billing and other purposes.
Activity compression and TDM handling services include: establishing (and
communicating) varying connection associations between use input/output
ports and buffer store locations representing virtual channels (VC) of
communication relative to digital trunks, the VC's associated with each
trunk being arranged in groups of 96; sampling (distributing) input/output
signals (voice or data) at each associated input/output port in repetition
intervals of short duration relative to a digital trunk frame; encoding
(decoding) samples (delta mod form); temporarily storing samples in
associated VC locations; accumulating up to 192 samples per location per
trunk frame; activity compressing (decompressing) the accumulated contents
of each VC group of 96 for handling over 46 real channels (per frame) of
the associated trunk; sending (receiving) an activity compression mask
signal in each trunk frame to indicate VC associations of VC contents sent
(received) in the same frame; grouping information signal transmissions
and associated mask signal bits relative to second-level down-link
destinations to simplify distribution handling on the down-link paths;
selecting mask and information channel assignments to adjust for over-runs
(less channels than active sample sets) and to block echo transmission;
conditioning over-run selections in a predetermined order of priority;
monitoring over-run rates; using the rate information to control setting
up of further connections relative to the associated digital trunk and
preserving the information as a communicatable statistic relative to high
level control of network (global) connectivity.
Second level centers are organized to interface between up to four first
level centers (via TDM digital trunks if not co-located) and rf station
apparatus which links to the space segment.
Services provided include:
Acquiring and maintaining time synchronization relative to the satellite
(after receiving initial high level control -- program initialization and
activation ordering -- from host management apparatus externally linked to
all first and second level centers); maintaining buffer storage addressing
in time correspondence with path delay variations to the satellite;
communicating time base control information to associated first level
centers; scheduling and maintaining second level segments of toll
connection paths between associated first level centers and the space
segment; scheduling (including carrying out necessary communication for)
assignments of traffic burst lengths relative to the satellite in
accordance with demand (demand relative to demand at other stations);
providing additional temporary storage and time compression/decompression
of communicated signals between associated first level centers and the
space segment; separating out associated information from the interleaved
space composite; temporarily storing the separated information;
rearranging the information and associated activity compression mask
elements into a unified recompressed structure for efficient passage
down-link over associated digital trunks; handling transmission over-runs
relative to down-link trunks by a selective blocking technique similar to
the technique used in first level up-link handling.
By providing down-link activity compression in the second level modules the
system avoids compounding origin station inefficiencies in the down-link
paths. For example many "low traffic" stations can transmit inefficiently
(allowing idle channels) over the satellite to a common trunk path of a
high traffic down-link station and the inefficiencies (idle channels) of
the transmitting stations need not be carried along in the down-link path.
With the above-mentioned demand assignment capability the wasteful
transmission of vacant channels is minimized. The stations continually
adjust for global traffic conditions (e.g. due to time differences). Thus,
burst length assignments of "east coast" centers in a continental United
States network, can be progressively shortened with the approach of
regional "sleeping" hours (11 P.M. - 6 A.M., EST), while assignments of
"mid-west" and "west coast" centers are progressively lengthened.
First level centers are configurable to link to one or more second level
centers and to carry on concurrent TDM signalling relative to up to four
digital trunks.
Second level centers are capable of linking to and accommodating aggregate
traffic of plural first level centers. Plural second level centers can be
"co-located" to operate under common time base control through common rf
equipment into different time channels or even different frequency
(transponder) bands of the space segment.
First and second level centers can be co-located in a combined center
constructed from a primitive or basic module structure arranged to receive
personalization for first and/or second level application.
All level centers utilize "large" capacity solid state random access buffer
storage facilities for ordering, queueing, compressing and multiplexing
the information traffic in "molecular" sample sets of substantial bit
length (192 bits per set). This affords transmission overhead efficiencies
by reducing the per frame proportion of control signals (signals used for
timekeeping and source tagging purposes) to information (traffic) signals;
in comparison to "atomic" (single sample) systems.
Second level centers cooperatively track satellite path length variations
due to doppler and differential doppler perturbations associated with
short-term satellite motion. Information thereby acquired is carried over
into buffer storage addressing functions in second and first level
handling, and thereby maintain correspondence between storage addresses
used for traffic storage and TDM channels used for transmission. This
simplifies the programming of traffic handling operations and high level
network functions incidental to diagnostics, reconfiguration, etc.
The foregoing and other features, objects and advantages of our invention
will be further appreciated from the following detailed description.
DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically illustrates an exemplary geographic organization of a
network according to the invention for explanatory purposes;
FIG. 2 schematically illustrates a station configuration of first and
second level switching centers linked by land-based digital trunks, for
interfacing hierarchically between the satellite and first level use ports
in accordance with one aspect of the invention;
FIG. 3 schematically illustrates the modular organization of the second
level centers;
FIG. 4 schematically illustrates various land-linked station
configurations, according to the invention, for providing time, space and
frequency domain "toll" switching relative to the satellite and first
level use ports;
FIGS. 5 and 6 indicate TDM frame timing and usage relative to the
satellite;
FIG. 7 indicates the form and content of station bursts relative to the
satellite;
FIG. 8 indicates the form and timing of the TDM signal frame employed on
digital trunks between first and second levels;
FIG. 9 indicates the form of the activity compression mask (exclusive of
transmission redundancy) used to indicate virtual-to-real channel
assignment associations of compressed information block transmissions;
FIGS. 10-12 indicate network inter-communication and operational sequencing
for call processing;
FIG. 13 provides a network configuration overview for explaining certain
connection path capabilities of the subject system;
FIG. 14 shows the system organization of the NCU;
FIG. 15 schematically shows utilization of the NCU to establish local
connection paths;
FIG. 16 shows the use of NCU's in tandem to establish connection paths
which do not utilize the satellite;
FIG. 17 shows toll connection paths utilizing the satellite transponder
path;
FIG. 18 shows the call processing facility (CPF) section of the NCU;
FIG. 18A shows the control clock sequence timing of the CPF;
FIG. 19 shows the voice processing unit (VPU) section of the NCU;
FIGS. 20.1 and 20.2 together show the digital switch section of the NCU;
FIGS. 21-61 are utilized to describe the NCU;
FIG. 21 shows the A/D card layout;
FIG. 22 shows the A/D conversion logic;
FIG. 23 shows the path of local call switching through the VPU and SIM
elements of the NCU;
FIG. 24 shows the modulation demodulation logic interconnection in the VPU;
FIG. 25 shows the delta modulation algorithm logic;
FIG. 26 shows the correlation between the algorithm function and the
control signals in FIG. 25;
FIGS. 27 and 28 are utilized to explain the relationship between the delta
modulation algorithm parameters R1, R2 and Md;
FIG. 29 describes the voice activity detection logic;
FIG. 30 describes the analog to digital conversion and algorithm timing;
FIG. 31 describes the algorithm logic and the algorithm memory timing;
FIG. 32 is a sequencer block diagram;
FIG. 33 indicates sequence timing;
FIG. 34 indicates the NCU path for ringing and busy tones;
FIG. 35 indicates the D/A interface memories;
FIGS. 36 and 37 indicate the D/A interface memory timing;
FIG. 38 provides a simplified block diagram view of the digital switch;
FIG. 39 indicates trunk interfaces between the NCU and NAU;
FIG. 40 indicates trunk interface signal timing;
FIG. 41 indicates trunk frame format;
FIG. 42 indicates the elastic buffer utilized for NCU bit synchronization;
FIG. 43 indicates the byte correct and frame synchronization circuits;
FIGS. 44, 45A, 45B and 46 indicate frame structure and timing;
FIG. 47 indicates clock generation circuits of the NCU;
FIG. 48 indicates clock timing;
FIG. 49 indicates frame timing structure for multiple NCU's sharing a
common 3705 control unit;
FIGS. 50 and 51 indicate the trunk buffer memory;
FIG. 52 indicates trunk-in uncorrected and corrected handling;
FIG. 53 indicates trunk to TGIM/TGIM to SIM handling;
FIG. 54 indicates SIM to TGOM/TGOM to trunk handling;
FIG. 55 indicates VAC Freezeout handling;
FIG. 56 indicates VAC encoding and decoding with forward error correction
(FEC);
FIG. 57 indicates SIM memory organization;
FIG. 58 indicates ICM memory organization;
FIG. 59 indicates SIM/ICM timing;
FIG. 60 indicates LGIM/LGOM in block diagramatic form;
FIG. 61 indicates the 3705/NCU interface;
FIG. 62 indicates system multi-path routing via NCU and NAU modules;
FIGS. 63-116 are utilized to explain the structure and operation of the NAU
module;
FIG. 63 indicates the general layout of parts in the NAU;
FIG. 64 indicates the NAU Receive Chain;
FIG. 65 indicates the NAU IF interface;
FIG. 66 indicates the MAU TICSW unit;
FIG. 67 indicates the TICSW interface;
FIG. 68 indicates the INTIC data flow;
FIG. 69 indicates the INTIC interface;
FIG. 70 indicates the OUTIC data flow;
FIG. 71 indicates traffic buffer partitions;
FIGS. 72-74 indicate traffic buffer in/out timing;
FIG. 75 indicates TOUT interface;
FIG. 76 indicates BOUT interface;
FIGS. 77 and 78 indicate the elastic buffer of the MAU;
FIGS. 79-81 indicate traffic buffer interfaces;
FIGS. 82-85 indicate MAU sequencer organization and interfaces;
FIG. 86 indicates transmit side clock generation;
FIG. 87 indicates receive side clock generation;
FIG. 88 (parts A, B, C and D) indicates receive acquisition;
FIG. 89 (parts A, B and C) indicates transmit acquisition;
FIG. 90 indicates a status register;
FIG. 91 indicates a control register;
FIG. 92 (parts A and B) indicates MAU data flow details; FIG. 93 indicates
BSU initialization procedure;
FIG. 94 indicates MAU initialization procedure;
FIG. 95 indicates acquisition procedure;
FIG. 96 indicates connectivity control processing;
FIG. 97 indicates interrupt organization;
FIG. 98 provides an overview of the BSUM process;
FIGS. 99-105 indicate information formats;
FIG. 106 indicates order wire supervisor processing;
FIG. 107 indicates sequencer start times map;
FIG. 108 indicates traffic buffer partition functions;
FIGS. 109-112 indicate MAU sequencer processes;
FIGS. 113 and 114 indicate the IOS (I/O Supervisor) process;
FIGS. 115 and 116 indicate satellite path control procedures; and
FIG. 117 indicates the network manager in relation to the other system
elements.
DETAILED DESCRIPTION
Table of Contents
I. introduction
A. network Configurations
B. nodal (Station) Organizations
Ii. network Signaling
A. space Segment Signaling
B. digital Trunk Signaling
C. signaling At First Level Input/Output Ports
D. compression-Multiplex
E. network Sequence For Connection Path Preparation
F. call Timing and Termination
Iii. exchange Center Apparatus/Operation
A. introduction
B. ncu (first Level)
1.0 NCU General Description
2.0 Call Processing
3.0 Voice Processing
4.0 Digital Switch
5.0 NCU/3705 Interface
6.0 Summary of NCU Operation
C. nau (second Level)
1.0 Introduction
2.0 MAU System
3.0 Functional Principles (Timing Structure)
4.0 Input/Output
5.0 Programming
Iv. (high Level) Network Control
A. initialization
B. ipl
c. nmf "control" After IPL
I. INTRODUCTION
The invention concerns a modular hierarchical approach to TDM switching
relative to TDMA facilities; particularly earth satellite TDMA facilities.
Presently described exchange modules/centers are used for connection
scheduling and time compression handling of TDM voice and data information
signals relative to a principal TDMA link; in particular a time divided
frequency channel (transponder) of a satellite space segment. Also of
interest are particular activity compression and demand assignment control
techniques presently described.
The invention contemplates time-compressed use of multiple subsidiary
digital trunks (e.g. leased high speed public carrier lines) in space and
time domain associations with each of a plurality of "regional" access
nodes (rf ground stations) of the space segment. The digital trunks are
installed as point-to-point links between regionally associated first
level and second level switching exchange centers constructed from basic
modules. These cooperatively provide switching and activity compression
handling between use access ports of the first level centers and
respective access nodes.
A. Network Configuration
An illustrative geographic configuration of regional stations is shown in
FIG. 1. The number of regions (three) is for simplified illustration only
and not limiting. Each station encompasses a land area or region of use
"access ports" at which information bit signaling speeds (or effective
speeds for analog voice trunks) are quite low in comparison to the
signaling capability of rf apparatus 10 relative to satellite 12.
The rf stations 10 transmit up-link to the satellite 12, in time divided
bursts, on carrier frequency f1 (e.g. 6 gigahertz) and receive "down-link"
in time-divided composite bursts on carrier frequency f2 (e.g. 4
gigahertz). The up-link information (traffic) bursts have varied lengths
assigned according to station demand. The bursts of all participating
stations are timed to span a TDM frame and to reach the satellite in
juxtaposed or close succession without overlap. The satellite apparatus
thereby acts as a repeater, broadcasting the composite of all bursts at
the new carrier frequency f2.
B. Nodal (Station) Organizations
As shown in FIG. 2 the TDM switching apparatus of a region includes at
least one first level TDM switching module-center, also termed NCU for
Network Control Unit, and at least one second level TDM switching
module/center, also called NAU for Network Access Unit. First and second
level centers, when not co-located as discussed later, are linked
bidirectionally by subsidiary digital trunks (e.g. high speed leased
public carrier lines) each capable of supporting time-compressed time
division multiplex signaling at information rates intermediate the high
rate of the space segment (49.4 Megabits per sec.) and the low rates at
individual input/output ports (e.g. effectively 32 kilobits per sec. per
connected voice trunk). Certain NCU ports are connected to not-shown voice
signaling facilities (e.g. PBX analog voice trunks) and others are
connected to data sources and receivers (or modems).
FIG. 3 indicates that a NAU unit contains up to four MAU (Multiple Access
Unit) basic switching modules having common program storage BSU (for "Base
Support Unit"). FIG. 4 indicates that several NAU's may share common rf
equipment, and that an NCU can link to the satellite via plural digital
trunks and NAU's (or MAU's) over a variety of switched paths having space,
time and frequency domain elements or segments. This figure is intended to
illustrate further that one rf station can be adapted to communicate over
more than one transponder band (f1/f2 and f3/f4) of one or more
satellites. In the latter configuration one or more MAU's of a NAU may use
different transponder bands of one satellite and economize on timing
synchronization by sharing timing acquisition controls. This will be more
fully explained later in the discussion of satellite tracking.
II. NETWORK SIGNALING
A. Space Segment
FIGS. 5-7 illustrate TDM frame usage for signaling over a transponder
channel of the space segment. Frames (FIG. 6) are of 6 millisecond
duration. Fifty-six successive frames constitute a superframe (FIG. 5) of
336 milliseconds duration. Nine successive superframes form a masterframe.
Initial "fixed length" burst segments of the frames of a superframe (FIG.
5 are assigned uniquely to different stations or earth access nodes (56
stations thereby being the maximum number of stations supportable on one
time divided transponder channel) for control signaling usage. The
aggregate of these control burst segments is termed the "Order Wire" (or
OW).
The OW segments are used by respective stations for timekeeping (synch
acquisition, satellite tracking, doppler-differential doppler correction,
etc.), call connection scheduling and demand assignment communications.
After initial acquisition the OW segments of acquired (active) stations
(top line FIG. 7) have fixed equal lengths and uniform formats. The OW
segments of inactive and initially acquiring stations (second line FIG. 7)
are of fixed durations shorter than those of acquired stations. The OW
segments of inactive (not transmitting and not receiving) stations are
quiescent but always available for use.
The remainder of each frame is reserved for the traffic (information)
bursts of all acquired ground stations (see FIG. 6 illustrating two
acquired stations). These bursts have various lengths, selected according
to a demand assignment procedure discussed later, and are sequenced in the
numerical ordering sequence of the stations (i.e. 1, 2, . . . 56; assuming
56 stations, all acquired and having traffic burst assignments). The
control (OW) and traffic bursts in each frame are timed by the source
stations to interleave without overlap at the satellite. A small "guard"
interval is maintained between bursts to avoid overlap.
Each type of burst (FIG. 7) carries bit timing (clock recovery) information
and "unique word" information distinguishing the burst type. OW bursts are
distinguishable by a unique work number 1 or number 2. Word number 1 is
associated uniquely with a "reference" station determined at system
initialization. It is the first station to acquire and its OW bursts
provide a time/distance reference to other stations for superframe and
masterframe timing, and for doppler shift correction relative to the
satellite as discussed later. The reference station sends word number 1 in
the first superframe of each masterframe. In other superframes the
reference station sends word number 2. The other stations send word number
2 only (in their OW slots). Traffic bursts are distinguished by unique
word number 3.
OW bursts carry control message information. The control message
information of an initially acquiring station is used only to distinguish
the burst as an initial transmission. The acquired stations follow the
control message portion of their OW bursts with station identity
information and satellite range information. Thus, OW bursts of acquired
stations are longer than those of transitionally acquiring or inactive
stations.
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