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CROSS-REFERENCES TO RELATED APPLICATIONS
1. u.s. patent 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.
2. U.S. patent application Ser. No. 537,212, by D. C. Flemming, entitled
"INTER-RELATED SWITCHING, ACTIVITY COMPRESSION AND DEMAND ASSIGNMENT",
filed Dec. 30, 1974.
3. U.S. patent application Ser. No. 537,501, by B. E. Parker et al.,
entitled "DISTRIBUTIONAL ACTIVITY COMPRESSION", filed Dec. 30, 1974.
4. U.S. patent application Ser. No. 537,281, by D. C. Flemming et al.,
entitled "EXTERNAL MANAGEMENT OF SATELLITE LINKED EXCHANGE NETWORK", filed
Dec. 30, 1974.
5. U.S. patent application Ser. No. 590,547, by H. G. Blasbalg, entitled
"MODULAR SLOT INTERCHANGE DIGITAL EXCHANGE" filed June 26, 1975.
6. U.S. patent application Ser. No. 560,422, by U. Appel, entitled "LOSS
SIGNAL GENERATION FOR DELTA-MODULATED SIGNALS" filed Mar. 20, 1975.
7. U.S. patent application Ser. No. 560,423, by P. Abramson et al. entitled
"DIGITAL VOICE SIGNALING WITH DIGITAL ECHO DETECTION AND VOICE ACTIVITY
COMPRESSION USED TO CANCEL ECHO", filed Mar. 20, 1975.
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.
Another need has been to provide digital switching service to voice users
of satellites with echo suppression taken care of in the switch.
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 digital switching coordinated over all access
nodes, time multiplexing and activity compression of switched virtual
channels into system transmission channels to achieve 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 is the use of land-linked time and space domain digital switch
modules 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 transmission overhead relative to the land links and the
satellite.
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 sampling period at a voice trunk), extensive block
storage of switched traffic per access station, and time compression and
activity compression of traffic signals on a modularly structured block
basis.
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 geographically.
Switching, activity compression and TDM handling services include:
establishing (and communicating) varying connection associations between
input/output ports and buffer store locations representing virtual
channels (VC) of communication relative to potentially "outnumbered" real
channels on associated digital trunks, the VC's associated with each trunk
being arranged in ordered 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 VC
location per trunk frame; activity compressing (decompressing) the
accumulated contents of each group of 96 outbound VC's for handling over
46 real channels (per frame) of the associated trunk; sending (receiving)
an activity compression mask signal per VC group in each trunk frame to
indicate VC to real channel assignment associations in the group in the
same frame; rearranging received information signal transmissions and
associated mask signal bits from origin-ordered form to
destination-ordered form for output distribution handling in ordered VC
groups; selecting mask and information channel assignments to adjust for
over-runs (fewer real channels than active VC's) and to block echo
transmission; selecting active VC's over-run eliminations 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 relative to the satellite 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 station processing 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 segments of "toll" connection paths
between virtual path switching 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 virtual path switching 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 for output
distributional handling relative to ports in virtual channel groups;
handling transmission over-runs relative to virtual channel groups by a
selective blocking technique similar to the technique used in
origin-ordered activity compression handling relative to the satellite.
By providing selective activity compression in the distribution handling
the system avoids compounding origin station inefficiencies in receiving
stations. For example many "low traffic" stations can transmit
inefficiently (allowing idle channels) over the satellite to a common
virtual channel receiving group of a high traffic station and the
inefficiencies (idle channels) of the transmitting stations need not be
carried along in the virtual usage at the receiving station.
All stations 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.
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 enters 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 word 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.
Traffic bursts (illustratively that of station J in the lower part of FIG.
7) carry user message information and control (activity compression mask)
information relating to activity compression. Each burst contains one or
more parts associated with respective source MAU's of the origin station.
Each part is further subdivided into pieces associated with source trunks
(e.g. J21, J22 . . . ) of the respective MAU. The compression mask
information consists of 192 bits containing "two for one" information
redundancy for error correction. With redundancy eliminated the
compression information constitutes a 96-bit ordered mask having bits
arranged in a predetermined order. The mask bits are associated with up to
96 correspondingly ordered first level virtual channels of the origin
station. The association extends in varied order to origin ports by virtue
of the slot interchange connection process described later and is
pre-communicated among the stations by a technique described later.
The compression mask information occupies a time channel of 192 bit slots.
Traffic information channels follow the associated compression information
channel. The traffic information is arranged in ordered sets (or blocks)
of 192 bits, each set associated with a variably positioned port of the
origin station and an NCU storage area representing a virtual channel.
Each set occupies a separate time channel of 192 consecutive bit slots in
the transmission frame. The non-redundant mask bits having binary "1"
value (always restricted to less than 48 of the 96 bits for reasons
explained later) serve to indicate source associations of individual user
message blocks.
The bit slots of a satellite frame are highly time compressed to
accommodate a digital signaling rate of about 49.4 .times. 10.sup.6 bits
per second (contrasted with the analog to digital voice sampling rate, at
any first level voice trunk/PBX interface, of 32 .times. 10.sup.3 bits per
sec.) The information content and timing of bursts within a frame is
determined at associated source NAU's (or MAU's for the more primitive
second level access interfaces).
Received composites (of interleaved station bursts) are partially
decomposed at receiving NAU's, according to connection association
information (prepared by techniques described later), and temporarily
stored. Each MAU re-structures the activity compression mask elements
(bits) and associated user message (traffic) information sets scheduled
for its station to optimize down-link use of associated digital trunks.
The activity compression mask thereby defines the interpolative
(virtual-to-real channel assignment) handling of traffic relative to
virtual channels of origin stations (source NCU up-link; destination MAU
down-link). This type of handling is related to time assignment speech
interpolation (TASI) techniques dealt with in earlier patents (for
instance in U.S. Pat. No. 3,644,680).). It differs in several significant
respects: (1) the compressively handled user message information is
accumulated and transmitted in multi-sample blocks (192-bit sets) rather
than single sample units (hence proportionately fewer mask bits need be
sent); (2) the compression is applied to modular fixed size ordered groups
of virtual channels and extended to ports in arbitrary order through
switching between ports and satellite access station nodes which is
controllable relative to activity at other access | | |
