CA1324204C - Communication system - Google Patents

Abstract

COMMUNICATION SYSTEM
A bidirectional broadband and telephony network controllable from the exchange end (15) An optical fibre 16 carries the services to customers premises(30, 31)via passive optical splitters(17, 18).
Telephony from block (10)is provided on one wavelength, broadcast TV
from block (11)on a second wavelength an bidirectional asynchronous time division information from block (40)on another wavelength using ATD (Asynchronous Time Division) techniques. Time-slots are allocated for information packets so they can travel without interference to and from receiving stations and the round trip delay between stations is adjusted to achieve this whilst maintaining minimum bandwidth requirements. Dynamic allocation of spare capacity is provided for bursty services.

Description

0021a 13242ii ~

CO~MUNI~ATION SYSTEM

Th~ inv~ntion relates to communication system9 and to such systems employing a passiv~ n~twork, for example a passiv~ optlcal network. Su~h passlve networks control th~ operstlon of th~ network a~ the lo~al exchange or head end for a num~r of customers.
For ~elephon~ companiss, optical flbres have the capacity to handle a range of services ~eyond telephony.
In the past, coaxlal cable ~V network~ have, in the main, been u~ed totally separately from the telephone network. It ls now becomlng clear that beyond the development of the swltched~star network and improved advanced optlcal fibre technology, there i9 a need for a more flex~ble telephony ba~ed ~ystem with additional ~rV~ ~A }~nvl ~
The present invent~on ls concerned w~th a confl~uration capable of produclng an enhanced serv~ce capabllit~ typlcally on a local fibre network using passive network~ ~mploying optical splitting to reduce and share costs.
According to the invention there is provided a bldlrectional broadband and telephony network controllabl~ from thQ ~xchange or head end of the network includlng means at th~ ~xchange or head end for allocatinq time 810ts for lnformation packets to travel without interference to and from a plurallty of recèivlng stations, whereln the allocating m~ans includea ~e~ns for determinlng the round-trip delay betw~en the exchange or head end and each of ~he recelvlng statlons and means for adjusting the round trlp delay to ensure correct spaclng of the lnformatlon packets during paBBa~e through the network, and includes means for interrogating ~tations and enforcing allocation thereto to ensure each stations mini~um bandwidt~ requirements are fulfllled, and mean~ for dynamically allocati~g spare capacity to each station for bursty services.
The inventlon will be described by way o$ example w1th reference to the accompanying drawing~ ln which:-~ iqure 1 shows a network configuration capable of handling telephony and broadband servicPs eg broadca~t TV).

0021a 132420~

Flgur~ 2 show~ on~ ~xample of the ~ram~ structure o the t~l~phony channel of Flgure 1.
~igure 3 sho~s an expanded configuration capabl~ of handllng broadband d1alogue s~rv~ces.
Fl~urB 4 shows the cu8~0mer end ~onflguration of the ATD
channel.
Figur~ 5 show~ the customer equipment of FlgurQ 4 in more d~ta~l~
F1gure 6 ShowB the exchange end block 40 ln more d~tallt Figur~ 7 ~hows the 'd' value controll~r of Figure 6 in more detall~
Fi9urR a shows a modified frame structure of the telephony channsl to accommodate the AT~ control lnformation) and ~igure g shows the cell structure of Flgure 3.
Flgure 1 shows a proposed conflguration for a passlve optical network. ~he ex~hang~ t~l~phony bloak 10 provlde~ telephony at a rate typically 20 Mbit/s on one wavelength (~1) and the TV block 11 provides broadcast TV on a second wavelength (~2) and the~e pass to the local exchange end 15.
A single mode optical ~ibre (16) is fanned out to a number of customers l~remlse~ (3V, 31) vl~ ~d~lv~ ~/yl.~ plll.~L-o (~7~ lel) located at the ca~inet (c) and street Dlst~lbutlon Point (~P) positlons respect1vely/ for example. An 8-way split is allowable at the cablnet and a 16-way split at the DP. However, the maximum a~ount of splltting is selected to be 32 to keep within the optical power budget available for broadband bit-rate~ in thl~ particular con~lguration.
For customers requirng telephony only, curr~nt system design views are favouring a network which features a max~mum optical split up to 128 ways and a highest bitrate of operation of 20 Mbit/s.
This bitra~etsplit combination allows an attractlve set of option8 ~or both business and residential customers. At the maxlmum split of 128 (120 custo~ers plU5 8 test portB)~ capacity would be available ~o feed each customer, if desired, with an ISD~ 144bit/s channel or equivalent capacity. For business districts, where multiple line customers are in the ma~ority, ~ lower optical split -132~2Qil would be employed, allowing higher capacities to be delivered per customer.
The advantages of a passive telephony network of this kind include low maintenance costs, reduced amounts of installed fibre, low fibre count cable requirements and sharing of exchange opto-electronic devices.
For broadband services the total number of customers can be increased to 128 by using 4 feeds from the head end to the cabinet. Each feed splits 32 ways. In addition, the single telephony-only feed can be split over the same fibre paths to all 128 customers because of its smaller bit-rate.
An example of the frame structure of the telephony channel for Figure 1 is shown in Figure 2.
Whilst the Figure 1 configuration can handle telephony and broadcast TV there is a need to provide broadband services in both directions for viewphone or high speed data handling.
Although these services could theoretically be provided (ignoring costs and other constraints) by employing separate wavelengths to and from each customer, however a different approaoh now proposed which could prove to be less costly and also capable of realisation much more readily is to carry such services by introducing two new channels, one for upstream ~i.e. customer to local exchange) and one for downstream connections (local exchange to customer).
Figure 3 shows the proposed configuration capable of handling the additional facilities. Individual connections are multiplexed within these channels using ATD (Asynchronous time division) and carried using a common new wavelength for the two directions of transmission.
To control the multiplexing of upstream information in one form of the embodiment, it is proposed to convey information via the telephony channel to update the exchange end on the condition of queues at each customer's end. The second form of the embodiment conveys all information on the condition of queues using the ATD channel.

X

~021a 132420 i Furth~rmore, ln ~lther form of the em~odlm~nt ~t th~ loc~l exchange thR ATD channel would be routed a6 shown via the ~Qrvice access 6wltch 42 (also based on ATD) and used a~ a very flexl~le integrated acce~s chann~l for any customer requiring a mix of broadband and narrowband ~ervlce~. Hence terminal A o~ th~ switch 42 could handle in~omlng and outgoing inf~rmatlon to/~rom the ATD
Broadband ne~work and terminal B will handl~ inc~ming and outgolng informatlon ~rom oth~r network~.
Th~ AT~ channels are handled by ATD blo~ (40) using wavelength 3 and for both outgoing and lncoming information which wlll pass vla the local exchange end 15 in optical form to be handled with other broadband or narrow band services. Thi~
wavelength carries two channels, one for the down~tream directions to the customers and one for th~ up~tream dlrection fro~ the customers end to th~ exchang~.
All ATD packets from the exchange end are received by all cu~tomers and the actions performed are determined by header infor~ation such that a customer will accept the packet and/or re-use ~he packet for upstream communication or lgnore the packet.
An ATD channel bit rate o~ about lS0 Nbit/s s~ared over 3~ -customers produces and average capacity of about 4 ~bit/s per cu6tomer. Giv~n that ATD dynamically assigns capacity, it i~
expected that cUBtomers Will ~suall~ be ~ble to obtaln much higher capacities on de~and ~eg a high probability of least 15 Mbit/s).
Also, ln either form of the embodiment ~lmost the entlre capacity of the link can be utllised by a slngle customer during tho~e ti~es when other customers are idle. Thus a gross bit rate of 150 Mblt/s for the ATD channel could be suitable for a wide ~ange of business customers having bursty data services and narrowband ~ervice~ to transmlt. In the longer term lt will al~o be suitable for resident~al custo~ers requ~rlng viewphone connections. At the moment lt is not foreseen whether constant bit rate or varia~le bit rate video code~s will be used ~or viewphone (the latter perhaps based on a mean bit-rate of 64 k~it/s and a peak bit rate of 384 kbit/s. However the ATD channel does not restrict the ~hoice since it would be capable of carrying either format.

0021a 1 3 2 4 2 0/~

~ ery large bit rate serYlce~ (broadcast TV) are carrled on separate wavelengths (ie on wavelength ~2). There~ore the bit rate required per cust~mer on the AT~ channel ls significantly ~aller ~h~ll w~uld ~e r~4uired i~ ~TD carrled a ~ull range o~
services.
The proposed ATD ~onfiguration lends itsel~ to being retro~ltt~d to the Flgure 1 arrangement or to a telephony only passlve optical networ~ of the type disclosed, wlthout replacing the entire network.
In elther form of thq embodlment shown, the ATD channel i9 provided with ~t~ own specific wavelength for the upstream and down6tream direction, and customers' ~qulpments are ~ltted with a wavelength filter ~20) to recelve this ch~nnel. custome~ 30 can have th~ capabillty of multiple services including AT~, telephony and broadcast TV. The cus~omer 31 still only needs the telephony servlc~ and ~herefore 18 50 restricted.
Th~ A~D channel carries a digital ~ltiplex with a gro~s bit rate of either 150 Mbit/B or 600 Mbit/s for exa~ple.
The ATD rhannel is handled at the customer's end as shown in Figure 4. a wavelength filter (20) is associated ~ith each channel and at optical/electrical interface~ (45, 46) data is buffered respectively to and from th~ local exchange end (via the distribution point and cabinet).
Block ~7 described in mor~ detail ~n Figure 5 will contain a phased-locked loop, loc~ed to the ATD transmisgi~n from the local exchange end, and used to control the frequency of tran0mission in the upstream direction. Addit~onally, each block 47 will contain an elastic buffer. The local exchange end adjusts the size of this buffer ~o that there is an equal number of bits in ea~h round-trip path ~exchange end to any customer and back). 8uitable signal~ to ~ontrol the size of the elastic bu~fers are sen~ over the ATD
channel to access control (47) from the local exchan~e end.

0021a ~2~20~

~ h~ con~lguratlon o~ Figur~ 4 is shown in mor~ detail ln ~igure 5. The wavelength fllters 20 of Figure 4 cooperate wlth the down~tream and upstream opto-electronlc lnterfaces 46, 45. The electric~l output of interface 46 is received by reqister/~f~er block 50. The output Of block 50 is availa~le to interfac~ 45. The block so al~o contalns the pha~ locked loop locked to the ATD
transmisslon fro~ the local exchange end. The elastic bu~fer within blo~k 50 ensure~ correct ad~ustment of the round trip delay.
Control block 52 conne~ted to blOCk S0 Will control upstream access a~ well as aownstream control, The do~nstream buffer 54 handles received packets passed vla control 52 and the data is passed to the appropriate service buffers 57, 58. 3uffer 57 may handle viqwphone ar voice informatlon and buffer 5g may deal wlth bursty data for exa~ple. The recei~ed packets are then available for conversion in standard depacketisers for receipt by the customer as voice or other data. Vlewphone or data f~r transmission back to the exchange end for example would ~e recelved (after conversion ln to digital form as necessary and packetised) by buffers 55 and 59. Buffer 55 could handle viewphone or voice ~ervices for exa~ple and buffer 59 could handle other data. Data from the~e buffers can be made available for transmisslon depend~nt on polling block 49 which wlll operate under the control of allocation control 5~. This polling and allocatlon will depend on the priority given to services associated with buffers 55 and 59 and the allocation allowance provided from the 'd' counters within block 56. In one embodlment addltional info~mat1on concerning packet arrivals in buffers 55 and 59 ~waiting to be sent) is detected in monitoring block 48 and sent via the telephony channel tas represented ~y the broken line in ~igure 5 from queue monitoring block 48).
The packet infor~ation made available from buffers 61 and 62 pa~es to upstream packet buffer 53 to control 52 which will add information to the header to indicate ~d~ allocatlon requirement~
(as described in ~ore detail below) and thence to reglster/buffer 50 to interface 45 to pass along the optical medium to the exchanqe end.

, .....

` -0021a 132420~

~ n the downstream direction, the local exchange end transmits a ~ontinuous series of ~T~ cells, whlch may be full or empt~.
Typically each customer's ~quipment w111 extract cell synchron1~ation ~rom eith~r specially recognisabl~ ~ynchronisatlon c~lls in~cted r~guldrly by the local exchange Qnd, o~ from racoqnising the known informatlon content and header content of empty cells.
In the upstream direction, succQssive ~ustomer transmissions may differ in phd~e but should not dlffe~ ln ~requency. Therefore to ensure the loc~l exchange receiver can maintain bit synchronisation with r~poct to Upstream trans~ls~ions, each cell will b~gin with suff1ci~nt ~lts so that the recelv~r can re-synchron~se to any change of phase. A suitabl~ line code, eg coded mark inversion ~CNI), will be used in both direc~ions of tran~misslon.
~ xcluding the synchronisatlon field (whlch is not cons1dered t~ add mor~ than a few per cent to the overall cell len~th, the cell size ls arouhd 3fi o~tets, with a format a~ described below. The same cell si~e i5 used for upstream and downstream transmissions.
The downstream ATD block at the exchange end is shown in more detail in ~igure 6~ The informatlon from the service ac~ess switch 42 19 received by packst bu~f~r 60. Customer identification is taken ~are of by connection number transla~or 61. ~he assembly block 67 assembles the packet ~n the format required to meet cell size and synchronising field requlrements and this is made a~ailable to the customer via the opto-electroni~ interface 74. Ranging control 70 can also have acce~s ~o assembler 6~ to determLne and set round-trip de~ay. ~he ranging parameters can be set via a man-machine interface for example. The connection number translator 64 detects ~ncoming ranging control cells and passes this to block 7~ to facilitate ~easurement of round trip delay. Ranging control can then if required send out further control cells via bloc~s G7 and 74 to the customer end to ad~ust the sl~e of the ela~tic buffer within block 50 to ensure the round trip delay is ldentical with other customers. ~dditionally translator 64 holds connection nu~ber information identlfying customers.

0021a - 8 - 132~20~

Asse~blHr 68 provides the access and control fleld in~ormation respectfully to accompanylnq the pack~t informatlon to identi~y customer~ and al~o identlfy the type of lnSormatlon being sent ~eg ran~lnq lndication or normal data). Controller 66 has th~ stored 'd~ value applicable to th~ amount of access available and extracts information from the headers of packets receiv~d from the customers vla bloc~s 73 and 63 to d~termine the late~t Id~ allocatlon requirements.
The controller 66 is shown ln more detall in Flgure 7. ~he change allocation control 76 receives the ~hange allocatlon header subfield (as descri~ed below) from up~tr~am packet buffer 6~.
Current 'd' values are stored fo~ all cu~tomers in store 7g. Thi~
is connected to poller 71 to allow loading of current îd' values t~
the poller or to receive from the poller 71 a request for all current ~d' values. Th~ poller ~1 also provides a message to bloc~
76 to reset rates or to inltiate conflrmation of the latest received "change allocatlon~ ~nformatlon from a eustomer. Regi~ter~ 78 have lnformatlon on e~ch customer concerning requests, modlflcation or checks on any customer 'd~ value. The latest allocation requests for all ~ustomers are held ln ~tore 77.
Returning to Flgure 6, additlonal received information from the customers is available Via opto-electronl~ interfac~ 73 and thls passes to packe~ buffer 63. This buffer provide~ an output to the service access switch 42. The buffer 63 also i9 accessed by the translator 64 WhiCh translates customers connec~ion numbers.
Polling block 71 may make use of 'd' allocation information provided on the AT~ channol~ and (ln one embodiment) use the telephony channel (as represented by the broken llnes) for polling customers who have indicated that packets are walting. The telephony channel of Figure 2 showed 17 subframe periods wlth a ranging capabllity within a single 2ms frame and Figure 8 is ~tructured so that each customer has access to separate parts of the subframe (in this example sub~rame part 1) to ena~le both telephony and ATD users access to the telephony and A~ users access to the telephony channel tin one of the embodiménts~. As 6hown, the configuration is of 70 sectors each of 32 bits for ATD control or telephony plU9 18 blts spare to give the 225~ channels of size 1 bi~.

", ",, ~21a 1324%0 1 The two multiple-user ATD channels on wav~length ~3 will typically have the cell format shown in Figurc 3. Each packet 80 will be carried in the tlme slot structure ln the system in either directlon and ~ill include an information field portion 81 and a header portlon 82.
The header is provlded with thr~ sub-fields 82a - 82~
relating to th~ sub-fields of CONTROL, ACCES8, and CON~E~T~ON ID
respectively.
The ~ACCESS' sub-~i~ld 82b ~ontains cu~tomer address information, to be used to control transmi~sion~ ln thé upstream direction. As the downstream AT~ cells are sent from the local exchange end, each with a Sp~CifiC ~ettlng of the A~C~ fleld provlded by block 6~ of Figure 6, 8 customer's equipment wlth matchLng address has the rlght to transmit one ATD cell ln the upstream dlrectlon. The addres~ value is ~et by thé local exchange end ~a~ed on lnformatlon recelved about actlve ter~inals aB
descrlbed ~elow. Thu~ this sUb-fi~ld determines which cu~tomer i9 allowQd to ~ransmit neXt.
The Connector I.D. (CONN ID) 82a sub-field of the header contains a Connection number (typically 16 bits) which ls examined by the receiving circultary of each customer~s equlpment (ie ~lock 52) to deter~ine ~hether the downstream cells should be ~ept or discarded. There is additionally a requirement to include some ~its for ~abel error detection/correction (e.g. 4-8 bits). Thus the CONN
ID ~ub-fleld determines which customer receives a downstream cell.
The information field 81 has a slze typically around 32 octets.
A sui~able method of downstream mul~tplexlng can employ a time slot configuration described in European Patent Publication 0168265 for example, where 'd~ package~ ~an be a~gned to u~ers to prevent monopolising the network.
The control (CTRL) ~ub-field 82c of the header contains the following control information:

, 0021~
13242~ 1 - full/empty lndica~lon.
- reset¦transmlt indlcatlon.
- broad~ast in~catio~.
- ranging lndicatlon.
- priority lndicatl~n.
- change allocatlon.
On the ATD channel ~he local exchange end equlpment can measure the round-trip delaY to any customer and back. ~uch measurement periods are lnitl~ted by the local exchange end ~ending ~pecially recognlsed ~ranging' cells, wlth the upstr~am AC~ESS field (~pstream rlght to transmit) set to th~ ~ustomer to bè measured.
continuous train of such cells are s~nt from b~ock 70 of Flg~re 6 from the exchange ~nd throughout the measur~ment perlod. Thlfi mode of operation is required so that the local exchànge ènd can ad~ust the delay in the round trip path to ensure that upstream ~ells from different ~ustomerc are correctly ~nterleaved. However, ranglng ls considered to be only o~casionally requir~d and may be intlated vla a man-machine inter~ace as described above in relat~on to Figure 6.
Y
ta) 1st embodiment ~n the first form of the e~bodiment the telephone channel i5 used to pro~ide the local e~change with information about ac~i~e ter~lnal~.
Because the original telephony channel is occassionally unavailable through ranging operations for telephony-only customers, as shown ln the example frame structure of Fig~res 2 or 7, control of upstream polllng i9 via two mechanisms:
- infor~ation from this telephony channel on pac~et arr~vals - polllng ~recently' actlve users for thelr whole 'd~ value.
On this channel, see Figure 8, (originally only for telephony) each multiservice cu~tomer is as~lgned 70 bits per frame. Thls i8 ~urther s~bdivided into 64 bits which are set according to packet arrivals, and a further 6 blts lndicatlng the su~ of all packet ~rri~als in the last frame period.

-0021~ - 11 - 132 4 2 ~ ~

The 70 blts ar~ dlsper~ed regularly throughout the ~rame such ~hat any ad~acent yroup of 32 ~its on thi~ chann~l carrles I bit from each of the ~roadband customers. If an A~D cell arrlves for upstream tran~ml~slon on a cu~tomer~ equlpment, thl~ is indica~ed to the local ~xchange end by -qetting one blt, le ~hat cu5tomer's next asslgned bit in the currènt frame. Further packet arrlvals wil} be likewise indicated. In this way, the local exchange end receives updated information about waiting CellB on each ~u~tomer's equlpment approximately ~very 1.5 microsecondB ~apart from the ranging pe~iod of the telephony channel).
(b) 2nd embodiment In the second fo~ of the embodiment, which does no~ roquire the use of the tel~phony ~hannel the upstream multiplexlng ls controlled from the local exchange and ba~ed on two mechanisms.
- polling on each customer' con~rol channel exactly once every 4 milliseconds - polllng all active customers at least on~e every 125 microseconds for their permitted alloca~ion (le their ~d~
value - see ~elow) The polling is effected by blocks ~1 and 6~ of Figur~ 6. For the purpose~ of polling, the local exchan~e access controller ~8 re~ards each customer~ access equipm~nt as two devlces. At the cusSo~er~s end these two ~devices~ are the separate responses of the ac~ess equipment to two different AC~ESS addresses which it will match with.
The first ~device' is the allocation control (Control 56 and block 52 of Figure 5) which ls responsible ~or sending all 'change allocation~ messages to the controller at the local exchange, via appropriate settings o~ the header. As stated above, lt has a guaranteed access rate of one cell every 4 milllseconds. User data (eg signalling in~or~ation) can be incl~ded in the information fie~d provided the he~der is also set to 'full'. In this case the data part is treated a~ belonging to the connection whose ldentity i~
~iven by CONN ID.

- . .
';' .
.

.

- 12~ 132a~2 The frequen~y of these transmis6ion~ from all cus~omers~
e~uipments ma~ be used to provide a minimum level of monitoring of the round-trip delay so as to ~ompute any nece~sary fine tunlng to conveyed to ~h~ customer~ equlpment.
The second ~devicol eomprlses the control 52 and b~ffer 53 and iB always considered to be active by the controller ae th~ local exchange, and i~ given a permit~ed upstream allocation - which may include zero. Changin~ the allocation o~ this device ls the method by which the customer~s equipment gains an appropriate upstream access rate for lts queues.
Whenever a customer is polled on elther 'devi~e~ it must return either a ~ull~ cell or ~empty' cell and repeat the value in the ACCESS field. For all upstream transmissions the t~ansmittlng source ls identified at the local exchange through th~ setting of ACCESS.
To service waiting queues at the customer's end, any downstream cell with either of the two matching value~ of ACCE8S
causes the next waiting cell to be trans~itted up~tream. This upstream cell will then ~e set to be tr~n~mitted ~pstream. This upstream cell will then be set to 'full' and the ~ONN ID value wlll ~e s~t to the appropriate connection number, In addition, if the ACC~99 field matches the control channel then the '~hange allocation' part o~ tho header is appropriately set.
The 6 ~ettlngs of the ~change allocation' field are:
- increase 'd' by 1/ repeat ln~rease 'd' by 1 - no change/ repeas no change - decrease 'd' by l/repeat decrease 'd~ by 1 - 'd~ equals zero/ repeat ~d~ equals zero Whenever a 'change allocation' ~essage i6 sent from the customer~s end the lnformation ~s repeated by the controller at the local exchange. It ~s inserted in the 'change allocation' ~ield of the next poll request sent down~tream on the same ACCES~ channel numbe~ via block~ 7~ and 77 of Figure 7. This allows the cu~tomer'~
access equipment to check ~hat the information it sent last time was correctly received. I~ there ls any error the cuqtomer's end sends a ~repeat~ type settin~ (see the above settings) and recordQ the 0021a - 13 - 13242~'i error. (The repeat typs setting is not used ln the fir~t embodiment cas~).
To en~ure t~lat any repeat-type ~ch~nge alloatlon' me~Ba9es ar~ correctly responded to, the local ~xchang~ controlle~ (bloc~ 66) maintains 3 regis~rs 7B for sach customer, le dREQ, dCHECK, and d~OD as ~hown in ~lg~re 7. The reglster dR~Q d~termln~fi the current allocation (as de~crlbed in the next section), th~ other two re~isters contain lntermediat~ ~alues. The rul~ governlng the use of these 3 reglsters are set out in Ta~le 1.
,.... , ~
C~STONER FOLLOWED ~Y REaISTER CHAN~S
SENDS (~ ~9 later) IN LOCAL EXCHANGS ~ON~ROLLER

OPERATION OPERATION' dCHECK flrst load~d ln~o dRE~
(eg INCREASE perfor~ OP' on dREQ and load (eg NO CHA~GE) d aY 1) result in dCHE~K
_.... .. , . _ ~

OP~RATION REPEAT perfor~ 0P' on dR~Q and load OPERATION' result ln d~OD
l _ . ~
REP~AT OPERATION' dMOD flrst loaded into dR~Q
OPERATION perform OP' on d~EQ and load result in dCHECK
. _ -.

REPEAT REP~T perform 0P' on dCHECK and PERATIo~ 0QE~AIION~ 1 d r~ult i- D

TABLE 1: CHANGE ALLOCATI0N MES~AGES - RESPON8E BT LOCAL E~CHANGE

' 0021a - 14 - 1 3 2 ~ 2 ~

Thls -~cheme fully correets any isolated case of an incorrectly recelved control mes4age~ in either the upstream or downstream direction. In combinatlon wi~h a limlted error correc~ion field in all ATD headers (eg correcting any single blt error)l the number of cases whree ~he allocation is lncorrectly set is expe~ted to bs extremely ~mall.
Entr~ lhto the state where the allocatlon ls ~ero ls always performed by the use of the 'd' equals zero operation, rather than decrease 'd' by 1. Thi~ absolute settlng provldes an addltional safeguard agalnst th~ local exchange dREQ reglster ~e~ng in long term misalignment with the valu~ held a~ ~he customer end.
As wQll as knowlng where cells are waitlng, the exchange end also operat~s a s~hem~ which provldes yuaranteed a~ce~s to each customer every 125 microseconds. The exchang~ end block 73 store6 an intege~ ~alu~, known as ~d~ value, for each cus~o~r WhiCh iB the number of cells the customer rèquire~ to be ~ûaranteed to be transmitted upstream every 125 microseconds. Every time a customer is polled by ~lock 71 an associa~ed ~ounter in Plock 71 18 decremented, starting from the value 'd~. wmen the counter reache6 zero, the customer cannot be polled even lf he has furthe~ ~ells w~ltlng. Polliny of that customer can only begln again after the local exchange end control block 66 via block 7~ has 'reset' all counter~ within poller 71. In the caxe of the first embodiment, this condition is reached when the local exchange end ha~ no ~ore customers which it may validly pol~ (either becau~e no more cells a~e waiting or all custom~rs have exhausted thelr 'd' values).
In the second embodi~ent each customer ls polled until hi~ ~d' counter in poller 71 reaches zero, regardless of whether he has p~kets waiting. When his counter reaches zero, the customer ~annot be polled until the polling of all other customers has been completed. This includes any allocation control devices whlch are due to be polled (nb. assuming 32 customers, one such control device is due to be polled every 125 microseconds). When no further cu~to~ers can be polled the controller 66 via block 7~ resets all counter6.

~021~ - 15 - 1 3 2 ~ 2 ~ '1 Similarly, in th~ flrst embodlment during the ran~ing periods o~ the telephony cllannel, tho local exchan~e end will poll (via blo~k 71) all cu~tomers who have been a~tive during tne last frame.
Polling will contrinue to the level of each custo~er's 'd' value regardless of wh~ther th~y have c~119 waltlng or no~. Then the local exchange end ~6 wlll reset all its counters and blo~k 71 begin polling again accordlng to the same pattern.
Whenever ~he local excha~ge end perform~ a reset of the counter~, lt 1ndicat~s thls to all cu~tomers~ equipment~ by setting the control fleld of a downstream cell to lndicate 'reset'. This lnfor~ation ls used by each customer~s equipment to re~et different service queues o~ waltlng cells to control the amount of cells which any one servlc~ q~ue can submit for up~tream transmls6ion.
In the first embodiment, every customer 15 given an lnltial 'd~ value o~ 1, and this guarantee of ac~ess i~ ~alntalned. For cell6 with an lnfor~ation field of 32 octets, a 'd' of 1 i9 equivalent to primary rate acces~ to all 32 customer~ on demand.
In the second em~odiment, an idle customer will have a ~d~
value of zero to prevent unnecessary polling, but every ~u~tomer i~
guaranteed a 'd' value of 1 on demand ~via blocks 56, 52, 50 and 45 to th~ sxchange end block~ 73, 63 and ~6), ~herefore no cus~omer may increa~e his ~uaranteed access rate to a level where other customers could be refused a minimum 'd~ of 1.
The controller 66 at the local exchange may receive requests from ~lock 56 to increase a customer's Id~ value via the Ichange allocation~ setting. It will comply with thl~ reque6t provided the current level of ~uaranteed acce~s is not already e~ual to the availahle capacity (ie approximately 65 cells every lZ5 m~croseconds, qiven a gross bit rate of around 150 Nbit/s).
For example, to determine the correct allocation for the variable bit rate services (data, VBR video), the customers equip~ent b~ock 56 via block ~0 will measure the number of cell arrival~, say every 4 mill1se~ond~. If the number o~ arr~val~
exceeds the current ~d~ lor part of 'd~ assigned to these services) ths customer~s equipment a~ ~ust de~cribed w111 signal to the local exchange end for an increase ln its 'd' allocatlon. As already 0021a 1 3 2 4 2 ~!1 stated, th~ local exchange end will comply wlth this request if possible, but will no~ allow already allocat~d bandwidth to be used.
In ~he ~ase of the flrst em~odimHnt, c~ange allocation lnformation is supplied whenever the customer 1~ next polled having first lndlcated that a packet i8 waiting via the telephony channel.
A~ain ln the case of the flrst embodlment occasionally the cuqtomers~ equip~ent wlll qenerate a slgnalllng call to verlfy its current 'd' requirements and ensure that the local exchange end remains in ~tep wlth all rocent changes. The frequen~y of the~e transmis~ions ~ro~ all customers' equipments may be u~ed to pro~lde a minimum level o~ monitoring o~ t~e round-trip d~lay so as to compute any necessary fine tunin~ to be convey~d to the cu~tomers~
~ equlpment via the ordinary telephong channel.
`. To signal to the local exchange end ~he customer~ equipment~ends an ~increase d~ setting on lts next up~trQam control cell.
In the ~ase of the second embodimQnt, the local exchanqe end ~' block 66 malntalns both a copy of each cu~tomer~s ideal requi~ments in the dREQ regi~ter and also holds the per~itted 'd' value ln ~, another register ln blo~k 66. Normally ~d~ 1B set equal to dR~Q.
However ~d~ may be held less than dREQ until additional ~apaclty be~omes free. ~hen thi~ happens, any customer ~d~ valu~ whlch i~
less than it~ dR~Q can be increased by 1 via block 76 (and no 'd' can b~ increased by ~ until all other such ~ustomers have received an increase of 1).
The delay experienced by a cell wlll depend upon i~s service priority and the allocation of the to~al ~d~ value (for a given cu~tomer) wh~ch has been assign~d to its service queue. In the case ~ of the first embodiment, the delay is composed of two parts:
`2 - a round-trip delay to indicate the cell arrival to the ~ exchange end and receive permission to transmit from the s exchange end.
- a random waiting period. Thi~ would be typlcally le89 than 10 microsecpnds (and would never be more than 12S micro~econds for those cells requlrlng guaranteed ~rress).

0021a 132~2~

In th~ case o~ the second ~mbodlment b0cause the local exchange snd does not wait for an arrlvlng call lndication before polling, the random component of delay ls the only component arising in thls case.
Thu~ the ATD chann~l is capable 1~ carrying a wlde mlx of service~, so~ bursty and some requlrlng guaranteed bandwidth. It may be used ln an envlronment where there are ~om~ telephony-only customers on th~ orl~lnal chann~l mlxed with oth~r customers who~e servl~es have migrated onto the ATD channel.
~ he propose channels would allow the flexlble use of bandwidth to carry d~alogue 6ervices as they evolve. ~he mlgration from narrow band to broadband to the AT~ situation ~ould be effected ln stages a0 requlred.
Although the passive network has been descrlbed in terms of optical fibre, other con~lgurations e.g. copper cable or wire-les6 transml~ion coulld be envi~aged.
Although end lS of Figure 3 has been de6cribed as the exchang~
end, this term 19 meant to encompass a location where multiple packet handling is arranged for a number of remote users (60metime~
called a head end).

.

Claims (49)

1. A bidirectional broadband and telephony network controllable from the exchange or head end of the network including means (67) at the exchange or head end for allocating time slots for information packets to travel without interference to and from a plurality of receiving stations, wherein the allocating means includes means (70) for determining the round-trip delay between the exchange or head end and each of the receiving stations and means (70) for adjusting the round trip delay to ensure correct spacing of the information packets during passage through the network and includes means (71, 66) for interrogating stations and enforcing allocation thereto to ensure each stations minimum bandwidth requirements are fulfilled, and, means (71) for dynamically allocating spare capacity to each station for bursty services.

2. A network as claimed in Claim 1 wherein the means for allocating time slots including means (67) at the exchange or head end for generating a continuous series of cells, means (74) for transmitting said cells, means (61) for routing information to be carried to receiving stations in selected cells and means (68) for generating information within a header portion of a cell to allow a designated station access to transmit an information packet using that cell or retain an information packet from that cell.

3. A network as claimed in Claim 2 wherein the means for generating information includes means (61) for generating station identification information in the cell header indicative of a receiving station and means (61) for generating a connection number for receipt by each station.

4. A network as claimed in Claim 1, wherein the allocating means includes means (68) for generating control information indicative of the presence and type of information contained in each cell for receipt by receiving stations.

5. A network as claimed in Claim 4 wherein the means for generating control information includes means (68) for generating a cell full/empty indicator, means (68, 71) for generating a reset/transmit indicator for service access, and means (61, 67) for generating a broadcast indicator to allow all customers to retain the received packet.

6. A network as claimed in Claim 4 or 5 wherein the means for generating control information includes means (61, 67) for generating a priority indicator.

7. A network as claimed in Claim 4 or 5 wherein the means for generating control information includes means for (66) for generating a change in allowed allocation.

8. A network as claimed in any one of claims 1, 2 or 3, wherein each station includes means (56, 52) for requesting an alteration in its amount of access for transmission determined by the exchange end.

9 A network as claimed in claim 1, wherein at the exchange or head end, polling means (71) are provided for repeatedly polling each station to determine current user requirements.

10. A network as claimed in Claim 9 wherein each station includes means (56, 52) for requesting a change in transmission access and the exchange or head end includes means (66) for responding to the request to change allocation or to maintain or decrease allocation and generator means (66, 71) are provided for generating information to the requesting station indicative of any change.

11. A network as claimed in claim 9, wherein the requesting means includes detector means (77, 76, 52) for checking the received allocation changes and means (52) for generating a further request if an error is detected.

12. A network as claimed in any one of claims 9, 10 or 11, wherein the requesting means includes an allocation request store (78), an allocation check store (78) and an allocation modification store (78).

13. A network as claimed m any one of claims 9, 10 or 11, where m the polling means (71) includes counter means (71) for decrementing the allocation of each station on handling each cell until its allocation is exhausted and means (66, 71) for resetting the counter means when no further stations have allocation remaining and/or no further cells from or for any station are waiting to be transmitted.

14. A network as claimed in any one of claims 9, 10 or 11, wherein the polling means (71) is configured to effect access via the telephony channel.

15. A network as claimed in any one of claims 9, 10 or 11,- where m the means for determining the round trip delay includes means (70, 67) for transmitting ranging signals during a measuring period.

16. A network as claimed in any one of claims 9, 10 or 11, wherein the means for adjusting the round trip delay includes a phased locked loop (50) at each station locked to the local exchange to ensure synchronism and an elastic buffer (50) controllable by the exchange to ensure an equal number of bits in each round trip path from any station.

17. A network as claimed in any one v. Claims 1, 2 or 3, wherein a telephony channel is provided and interface means (48) are provided thereto to convey information on the transmission requirement of a station.

18. a network as claimed in Claim 17 wherein the interface includes means (48, 71) for determining packet arrivals at respective stations, and means (71) for polling stations for their allocation requirements dependent on information queuing therein.

19. A network as claimed in any one of claims 1, 2 or 3, wherein information on the transmission requirements of a station are sent in the header of information packets.

20. A network as claimed in claim 1, wherein switching means (42) at the exchange or head end are provided for handling incoming and outgoing information on a multiplexed basis.

21. A network as claimed in Claim 20, wherein the switching means (42) is configured to handle information on an asynchronous time division basis on a single common wavelength.

22. A network as claimed in any one of claims 1, 2 or 3, wherein each station includes wavelength filter means (20) to permit receipt of broadband packet information.

23. A network as claimed in any one of claims 1, 2 or 3, wherein each station includes buffer means (50, 53, 54) for temporarily holding information sent or received via the exchange end and means (52) for arranging said information into the cell format required.

24. A network as claimed in any claim 1, where m the network is configured using an optical medium and an optical/electrical interface (45, 46) is provided at each station.

25. A network as claimed in Claim 24 wherein the exchange end includes an optical/electrical interface (73, 74).

26. A network as claimed m any one of claims 1, 2 or 3, wherein the means (71, 66) for enforcing allocation includes means (66) for providing at least a minimum access on request by a station and means (66, 71) for maintaining at least such allocation till it is no longer required thereby and means (66) for providing at least a minimum access to further stations to ensure all requesting stations some access regardless of bandwidth constraints.

27. A network as claimed in any one of claims 1, 2 or 3, including means (61, 64) at the exchange or head end for translating a connection number of an incoming/outgoing packet to/from the associated station.

28. A networks claimed in any ale of claims 1, 2 or 3, wherein each station includes means (56) for calculating the access requirements from current traffic information to determine if an increased allocation is required.

29. A network as claimed in any one of claims 1, 2 or 3, wherein generator means (64, 63) at the exchange end are configured to generate cells in the form of ATD cells complete with an information header portion.

30. A method of controlling a bidirectional broadband and telephony network from the exchange or head end of the network including allocating at the exchange or head end time slots for information packets to travel without interference to and from a plurality of receiving stations, the allocation including determining the round-trip delay between the exchange or head end and each of the receiving stations;
adjusting the round trip delay to ensure correct spacing of the information packets during passage through the network;
interrogating stations and enforcing allocation thereto to ensure each stations minimum bandwidth requirements are fulfilled; and, dynamically allocating spare capacity to each station for bursty services.

31. A method as claimed in Claim 30 including generating at the exchange or head end a continuous series of cells, transmitting said cells, routing information to be carried to receiving stations in selected cells and generating information within a header portion of a cell to allow a designated station access to transmit an information packet using that cell or retain an information packet from that cell.

32. A method as claimed in Claim 31 including generating station identification information in the cell header indicative of a receiving station and generating a connection number for receipt by each station.

33. A method as claimed in Claim 30 wherein the allocation includes generating control information indicative of the presence and type of information contained in each cell for receipt by receiving stations.

34. a method as claimed in Claim 33 wherein the control information generation step includes generating a cell full/empty indicator, generating a reset/transmit indicator for service access, or generating a broadcast indicator to allow all customers to retain the received packet.

35. A method as claimed in either claim 33 or 34, wherein the generating control information step includes generating a priority indicator.

36. A method as claimed in either claim 33 or 34, wherein the control information step includes generating a change in allowed allocation.

37. a method as claimed in any one of claims 1, 2 or 3, including at any station the step of requesting an alteration in its amount of access for transmission determined by the exchange end.

38. A method as claimed in claim 30, including repeatedly polling each station to determine current user requirements from the exchange or head end.

39. A method as claimed in Claim 38 including requesting from any station a change in transmission access and responding from the exchange or head end to the request to change allocation or to maintain or decrease allocation and generating information to the requesting station indicative of any change.

40. A method as claimed in claim 38, wherein the requesting step includes checking the received allocation changes and for generating a further request if an error is detected.

41. A method as claimed in any one of claims 30, 31 or 32, including the polling step includes decrementing the allocation of each station on handling each cell until its allocation is exhausted and reallocating the stations when no further stations have allocation remaining and/or no further cells from or for any station are waiting to be transmitted.

42. A method as claimed in any one of claims 30, 31 or 32 including transmitting ranging signals during a measuring period to determine the round trip delay, and generating a signal to adjust an elastic buffer at any station to equalize the round trip delay of all stations.

43. A method as claimed in any one of claims 30, 31 or 32 wherein information on the transmission requirements of a station are sent in the header of information packets.

44. A method as claimed in any one of claims 30, 31 or 32, including multiplexing incoming and outgoing information at the exchange or head end on an asynchronous time division basis on a single common wavelength.

45. A method a claimed in any one of claims 30, 31 or 32 including providing an optical transmission medium and interfacing electrical signals thereto at both the exchange or head end and each station.

46. A method as claimed in any onf of claims 30, 31 or 32, including providing at least a minimum access on request by a station and maintaining at least such allocation till it is no longer required thereby and providing at least a minimum access to further stations to ensure all requesting stations some access regardless of bandwidth constraints.

47. A method as claimed in any one of claims 30, 31 or 32, including translating at the exchange or head end a connection number of an incoming/outgoing packet to/from the associated station.

48. A method as claimed in any one of claims 30, 31 or 32, including calculating each at any station the access requirements from current traffic information to determine if an increased allocation is required.

49. A method as claimed in any one of claims 30, 31 or 32, including generating cells at the exchange or head end in the form of ATD cells complete with an information header portion.