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| United States Patent |
6,424,656
|
|
Hoebeke
|
July 23, 2002
|
Method to assign upstream timeslots to a network terminal and medium access
controller for performing such a method
Abstract
Upstream timeslots are assigned to a network terminal in a time division
multiplexed communications network, by means of queue grants, each of
these queue grants corresponding to a storage queue within said network
terminal and associated with a particular service category. The rate of
the queue grant bitstream composed of succeeding occurrences of these
queue grants is thereby determined from at least one parameter of a
parameter set associated to the corresponding storage queue and from at
least one other parameter of at least one other parameter set associated
to at least one other storage queue within any of the network terminals
within the communications network. The present invention relates as well
to a medium access controller adapted to perform the method, to a central
station including such a medium access controller and to a network
terminal including these storage queues.
| Inventors:
|
Hoebeke; Rudy (Deurne, BE)
|
| Assignee:
|
Alcatel (Paris, FR)
|
| Appl. No.:
|
304984 |
| Filed:
|
May 4, 1999 |
Foreign Application Priority Data
| Current U.S. Class: |
370/412; 370/468 |
| Intern'l Class: |
H04L 012/28; H04L 012/56 |
| Field of Search: |
370/229,230,230.1,231,232,235,395.1,395.7,395.71,395.72,412,389,428,429,468
|
References Cited [Referenced By]
U.S. Patent Documents
| 5631906 | May., 1997 | Liu | 370/455.
|
| 5926476 | Jul., 1999 | Ghaibeh | 370/395.
|
| 5936943 | Aug., 1999 | Sakagami et al. | 370/244.
|
| 5940369 | Aug., 1999 | Bhagavath et al. | 370/229.
|
| 5960000 | Sep., 1999 | Ruszczyk et al. | 370/447.
|
| 5966163 | Oct., 1999 | Lin et al. | 348/12.
|
| Foreign Patent Documents |
| 0 544 975 | Jun., 1993 | EP.
| |
| 0 544 975 | Jun., 1993 | EP.
| |
| 0 729 245 | Aug., 1996 | EP.
| |
| WO 97/15993 | May., 1997 | WO.
| |
Other References
Cheng, L.: "Quality of services based on both call admission and cell
scheduling" Computer Networks and ISDN Systems, vol. 29, No. 5, Apr. 1997,
pp. 555-567, XP000686166.
|
Primary Examiner: Patel; Ajit
Attorney, Agent or Firm: Sughrue Mion, PLLC
Claims
I claim:
1. Method to assign upstream timeslots to a network terminal (ONUi) of a
first plurality of network terminals (ONU1, . . . , ONUi, . . . , ONUn) in
a communications network wherein a central station (CS) is coupled to said
plurality of network terminals (ONU1, . . . , ONUi, . . . , ONUn) via the
cascade connection of a common transmission link (L) and respective
individual network terminal links (L1, . . . , Li, . . . , Ln) and wherein
said network terminals (ONU1, . . . , ONUi, . . . ONUn) are adapted to
transmit upstream data packets to said central station (CS) in a time
multiplexed way over said common transmission link (L) using said upstream
time slots, which are assigned to said network terminals by means of a
downstream bitstream (BSG) of network terminal grants, said downstream
bitstream being generated by a medium access controller (MAC) included
within said communications network,
characterised in that
within said network terminals (ONU1, . . . , ONUi, . . . , ONUn) said
upstream data packets are classified in accordance to their associated
service categories and temporarily stored in a second plurality of storage
queues, each respective storage queue of said second plurality being
related to a respective one of said service categories (1, . . . , i . . .
, m),
a grant (GONUi), associated to said network terminal (ONUi), includes a
third plurality of queue grants (GONUi1, . . . , GONUij, . . . , GONUim)
each associated to a respective storage queue (ONUiQ1, . . . , ONUiQj,
ONUiQj) within said network terminal (ONUi),
whereby a queue grant (GONUij) of said third plurality is enabling said
network terminal (ONUi) to transfer a predetermined amount of upstream
data packets from its corresponding storage queue (ONUiQj),
and whereby the rate (GRij) of the queue grant bitstream composed of
succeeding occurrences of said queue grants (GONUij), is determined from
at least one parameter (Pij) of a parameter set (Sij) associated to said
corresponding storage queue (ONUiQj), and from at least one other
parameter (P1m) of at least one other parameter set (S1m) associated to at
least one other storage queue (ONU1Qm) within any of said network
terminals within said communications network.
2. Method according to claim 1
characterised in that
said at least one other storage queue is included within said network
terminal (ONUi).
3. Method according to claim 1
characterised in that
said at least one other storage queue (ONU1Qm) is included in at least one
other network terminal (ONU1) of said plurality of network terminals.
4. Method according to claim 1
characterised in that
said parameter set (Sij) associated to said corresponding storage queue
(ONUiQj) includes traffic and connection parameters (TCPij) related to the
data packets stored in said corresponding storage queue (ONUiQj), and a
status parameter (STij) related to the status of said corresponding
storage queue,
said at least one parameter set (S1m) associated to said at least one other
storage queue (ONU1Qm) includes traffic and connection parameters (TCP1m)
related to data packets stored in said at least one other storage queue
(ONU1Qm) and at least one status parameter (ST1m) related to the status of
said at least one other storage queue.
5. Method according to claim 1
said at least one parameter (Pij) is upstream communicated to said medium
access controller (MAC) by said network terminal (ONUi) by means of a
corresponding upstream queue request message (QRMij).
said at least one other parameter (P1m) is upstream communicated to said
medium access controller (MAC) by the at least one other network terminal
(ONU1) including said at least one other storage queue (ONU1Qm), by means
of at least one other queue request message (QRM1m).
6. Method according to claim 5
characterised in that
for said corresponding storage queue (ONUiQj) and said at least one other
storage queue (ONU1Qm) constituting a group of storage queues, associated
to said corresponding storage queue (ONUiQj)
for said status parameter (STij) of said corresponding storage queue
(ONUiQj) and said at least one other status parameter (ST1m) of said at
least one other storage queue constituting a group of status parameters,
associated to said corresponding storage queue (ONUiQj),
said method includes a step of determining a subgroup of storage queues
within said group of storage queues, based on all status parameters of
said group of status parameters, said subgroup thereby comprising storage
queues of said group of storage queues for which said status parameters
respond to a predetermined criterion.
7. Method according to claim 5
characterised in that
for said corresponding storage queue (ONUiQj) and said at least one other
storage queue (ONU1Qm) constituting a group of storage queues, associated
to said corresponding storage queue (ONUiQj)
for said status parameter (STij) of said corresponding storage queue
(ONUiQj) and said at least one other status parameter (ST1m) of said at
least one other storage queue constituting a group of status parameters,
associated to said corresponding storage queue (ONUiQj),
said method includes a step of determining, for all status parameters
within said group of status parameters, status related parameters, said
method further includes a next step of determining a subgroup of storage
queues within said group of storage queues, based on all of said status
related parameters, said subgroup thereby comprising storage queues of
said group of storage queues for which said status related parameters
respond to a predetermined criterion.
8. Method according to claim 6
characterised in that
said method includes a step of checking whether said corresponding storage
queue (ONUiQj) belongs to said subgroup, associated to said corresponding
storage queue (ONUiQj).
9. Method according to claim 8
characterised in that
in case said corresponding storage queue (ONUiQj) belongs to said subgroup,
said rate (GRij) of said queue grant bitstream is dependent on a
proportional part of an excess bandwidth.
10. Method according to claim 9
characterised in that
said excess bandwidth is determined from the values of said at least one of
the parameters of each parameter set associated to each storage queue of
said subgroup.
11. Method according to claim 10
characterised in that
said proportional part is determined from the values of said at least one
of the parameters of each parameter set associated to each storage queue
of said subgroup.
12. Method according to claim 11
characterised in that
said method is performed at predetermined instances.
13. Network terminal (ONUi) of a communications network wherein a central
station (CS) is coupled to a first plurality of network terminals (ONU1, .
. . , ONUi, . . . , ONUn) including said network terminal (QNUi), via the
cascade connection of a common transmission link (L) and respective
individual network terminal links(L1, . . . , Li, . . . , Ln)
said network terminal (ONUi) being adapted to detect an associated grant
(GONUi) within a downstream bitstream of network terminal grants (BSG)
transmitted from a medium access controller (MAC) included in said
communications network, to said network terminals (ONU1, . . . , QNUi, . .
. , QNUn)
said network terminal (QNUi) being further adapted to transmit a
predetermined amount of said upstream data packets to said central station
(CS) upon detecting of said associated grant (GONUi),
characterised in that
said network terminal (ONUi) includes sorting means (SMi) adapted to
classify said upstream data packets in accordance to their associated
service category, said sorting means (SMi) including a plurality of output
terminals, each of which is coupled to a respective storage queue of a
second plurality of storage queues (ONUiQ1, . . . , ONUiQj, . . . ,
ONUiQj) included within said network terminal (ONUi), each storage queue
of said second plurality being related to a respective one of said service
categories (1, . . . , j, . . . , m), and adapted to temporarily store
sorted data packets delivered by said sorting means (SMi)
said network terminal (ONUi) further includes detecting means (DMi) adapted
to discriminate within said bitstream of grants, respective queue grants
of a third plurality (GONUi1, . . . , GONUij, . . . , GONUim), each
respective queue grant being associated to a respective storage queue of
said second plurality (ONUiQ1, . . . , ONUiQj, . . . , ONUiQj), said
detecting means being further adapted to, upon detecting of a respective
queue grant (GONUij) of said third plurality, generate a respective
control signal to the corresponding storage queue (ONUiQj)
said corresponding storage queue (ONUiQj) is thereby adapted to transmit,
upon receipt of said respective control signal, a predetermined amount of
said upstream information packets, to said central station (CS).
14. Network terminal (ONUi) according to claim 13
characterised in that
said network terminal (ONUi) further includes request generating means (Ri)
which is adapted to determine, for at least one of said storage queues
(ONUiQj), at least one associated parameter (Pij) and to transmit said at
least one associated parameter to said medium access controller (MAC) by
means of a corresponding upstream queue request message (QRMij) being an
output signal of said request generating means (Ri).
15. Network terminal (ONUi) according to claim 14
characterised in that
said at least one associated parameter (Pij) associated to said at least
one storage queue (ONUiQj) consists of traffic and connection parameters
(TCPij) associated to the data packets stored within said at least one
storage queue (ONUiQj).
16. Network terminal according to claim 14
characterised in that
said at least one associated parameter (Pij) associated to a respective
storage queue (ONUiQj) consists of a status parameter (STij) related to
the status of said respective storage queue (ONUiQj).
17. Medium access controller (MAC) of a communications network wherein a
central station (CS) is coupled to a first plurality of network terminals
(ONU1, . . . , ONUi, . . . , ONUn) via the cascade connection of a common
transmission link (L) and respective individual network terminal links
(L1, . . . , Li, . . . , Ln) and wherein said network terminals (ONU1, . .
. , ONUi, . . . , ONUn) are adapted to transmit upstream data packets to
said central station (CS) in a time multiplexed way over said common
transmission link using time slots, said medium access controller (MAC)
including
grant generation means (GGM) adapted to determine a downstream bitstream of
network terminal grants (BSG) and to transmit said bitstream to said
network terminals of said first plurality,
characterised in that
said grant generation means (GGM) is further adapted to generate at least
one network terminal grant as a third plurality of queue grants (GONUi1, .
. . , GONUij, . . . , GONUim) each queue grant of said third plurality
being associated to a respective storage queue (ONUiQ1, . . . , ONUiQj, .
. . , ONUiQj) within at least one network terminal (ONUi) associated to
said at least one network terminal grant (GONUi),
said grant generation means (GGM) thereby includes calculating means (ARC)
adapted to determine the rate (GRij) of succeeding occurrences of a queue
grant (GONUij) of said third plurality, from at least one parameter (Pij)
of a parameter set (Sij) associated to a corresponding storage queue
(ONUiQj) to said queue grant (GONUij), and from at least one other
parameter (P1m) of at least one other parameter set (S1m) associated to at
least one other storage queue (ONU1Qm) within any of said network
terminals within said communications network .
18. Medium access controller according to claim 17
characterised in that
said medium access controller (MAC) further includes extraction means (EM)
adapted to extract, from at least one corresponding upstream queue request
message (QRMij), and respectively from at least one other upstream queue
request message (QRM1m), said at least one parameter (Pij) of said
parameter set (Sij) associated to said corresponding storage queue
(ONUiQj), and respectively said at least one other parameter (P1m) of said
at least one other parameter set (S1m) associated to said at least one
other storage queue (ONU1Qm), and to deliver said at least one parameter
(Pij), and respectively said at least one other parameter (P1m) as output
signals of said extraction means (EM).
19. Medium access controller according to claim 17
characterised in that
said parameter set (Sij) associated to said corresponding storage queue
(ONUiQj) includes traffic and connection parameters (TCPij) related to
data packets stored in said corresponding storage queue (ONUiQj) and a
status parameter (STij) related to the status of said corresponding
storage queue,
said at least one other parameter set (S1m)) associated to said at least
one other storage queue (ONU1Qm) includes traffic and connection
parameters (TCP1m) related to data packets stored in said at least one
other storage queue (ONU1Qm) and at least one status parameter (ST1m)
related to the status of said at least one other storage queue (ONU1Qm).
20. Medium access controller according to claim 18
characterised in that
said at least one, respectively said at least one other, queue request
message includes said at least one, respectively said at least one other
status parameter,
for said corresponding storage queue (ONUiQj) and said at least one other
storage queue (ONU1Qm) constituting a group of storage queues, associated
to said corresponding storage queue (ONUiQj)
for said status parameter (STij) of said corresponding storage queue
(ONUiQj) and said at least one other status parameter (ST1m) of said at
least one other storage queue (ONU1Qm) constituting a group of status
parameters, associated to said corresponding storage queue
an input terminal of said calculation means (ARC) is coupled to an output
terminal of said extraction means (EM), said calculation means is thereby
adopted to receive all status parameters (Sij,S1m) of said group
(ONUiQj,ONU1Qm) and to determine therefrom a subgroup constituting of
storage queues within said group of storage queues for which said status
parameters respond to a predetermined criterion.
21. Medium access controller according to claim 18
characterised in that
said at least one, respectively said at least one other, queue request
message includes said at least one, respectively said at least one other
status parameter,
for said corresponding storage queue (ONUiQj) and said at least one other
storage queue (ONU1Qm) constituting a group of storage queues, associated
to said corresponding storage queue (ONUiQj)
for said status parameter (STij) of said corresponding storage queue
(ONUiQj) and said at least one other status parameter (ST1m) of said at
least one other storage queue (ONU1Qm) constituting a group of status
parameters, associated to said corresponding storage queue
an input terminal of said calculation means (ARC) is coupled to an output
terminal of said extraction means (EM), said calculation means is thereby
adapted to receive all status parameters (Sij,S1m) of said group
(ONUiQj,ONU1Qm), to determine therefrom status related parameters, and to
determine from said status related parameters a subgroup constituting of
storage queues within said group of storage queues for which said status
related parameters respond to a predetermined criterion.
22. Medium access controller according to claim 21
characterised in that
said calculation means (ARC) includes counter means (CM), adapted to
determine from said status parameters of said group, said status related
parameters of said group.
23. Medium access controller according to claim 20
characterised in that
said calculating means (ARC) is further adapted to determine whether said
corresponding storage queue (ONUiQj) belongs to said subgroup, associated
to said corresponding storage queue (ONUiQj).
24. Medium access controller according to claim 23
characterised in that
in case said corresponding storage queue belongs to said subgroup, said
calculating means (ARC) is further adapted to calculate said rate (GRij)
of said succeeding occurrences of said queue grant (GONUij) to be
dependent on a proportional part of an excess bandwidth.
25. Medium access controller according to claim 24
characterised in that
said calculating means (ARC) is further adapted to determine said excess
bandwidth from the values of said at least one of the parameters of each
parameter set associated to each storage queue of said subgroup.
26. Medium access controller according to claim 25
characterised in that
said calculating means is further adapted to determine said proportional
part of said excess bandwidth from the values of said at least one of the
parameters of each parameter set associated to each storage queue of said
subgroup.
27. Medium access controller according claim 17
characterised in that
said medium access controller is included in said central station (CS).
Description
BACKGROUND OF THE INVENTION
The present invention relates to a method to assign upstream timeslots to a
network terminal, as defined in the preamble of claim 1, a network
terminal adapted to perform this method, as defined in the preamble of
claim 13, and a medium access controller adapted to perform this method,
as defined in the preamble of claim 17.
Such a method, network terminal and medium access controller are already
known in the art, e.g. from the European patent specification EP 0 544 975
B1 "Time slot management system". Therein, a time slot management system
is described, being part of a communication system including a main
station coupled to each of a plurality of substations or user stations in
a point-to-multipoint way, via the cascade connection of a common
transmission link and an individual user link. The medium access
controller of the present invention thus corresponds to the time slot
management system of the prior art document, the network terminals to the
substations or user stations, and the central station to the main station
of this prior art document. The prior art time slot management system,
includes a conversion and transmission means which is adapted for
generating grants associated to the substations for downstream
transmission to them. Upon receipt of the associated grant by the
substations, these are then allowed to transmit a predetermined amount of
upstream data packets to the central station. The prior art conversion and
transmission means corresponds to the grant generation means of the
present invention. In the prior art system, the rate with which succeeding
occurrences of network terminal grants are generated is directly
proportional to bandwidth information earlier transmitted upstream by the
user stations, for instance the peak rate at which the user station
intends to perform upstream packet transfer.
A drawback of the prior art system however is that it does not
differentiate among different service categories pertaining to different
packet or bitstreams the network terminals want to transfer upstream to
the central station. Furthermore, to guarantee that each user station of
the prior art system, can transfer its upstream data, the information
related to the bandwidth requested by each user station or network
terminal, usually corresponds to a peak cell rate, being the maximum rate
at which this network terminal needs to upstream transfer its data
packets. This prior art system is therefore functioning properly as long
as the network terminals indeed have to transfer upstream bitstreams
pertaining to a service category for which only a peak cell rate is
specified, for instance the constant bit rate category as specified by the
ATM Forum specification AF-TM-0056.000 dated April 1996 in case the
bitstreams consist of ATM streams. In case however a network terminal
intends to send packets pertaining to another, for instance the so-called
"best effort" service category such as the unspecified bit rate service
category, described in the same ATM Forum specification, reserving a
maximum peak cell rate equivalent bandwidth during a certain time period,
while the packets are only to be transferred at irregular instances in
short bursts, seriously underutilises the capacity of the upstream link.
At the some time, this may result in a high call blocking probability
since the aggregate of the peak cell rates of the supported connections
cannot exceed the available upstream capacity of the common transmission
link, which was necessary to secure the correct operation of the prior art
time slot management system.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method, a network
terminal, and a medium access controller of the above known type but which
allows to differentiate amongst different types of service categories
pertaining to several bitstreams or connections to be upstream transmitted
from this network terminal to the central station, and which at the same
time, aims at a more efficient use of the capacity of the common upstream
transmission link.
According to the invention, this object is achieved due to the fact that
said method is further adapted as is described in the characteristic part
of the first claim, that said network terminal is further adapted as
described in the characteristic part of claim 13 and that said medium
access controller is further adopted as described in the characteristic
part of claim 17.
In this way, differentiation between different service categories is first
realised within said network terminal by sorting or classifying, and
temporarily storing the data packets to be upstream transmitted in
different storage queues, each respective storage queue corresponding to a
respective service category. This sorting is for instance based on header
information, as will be explained more into detail in a following
paragraph. Secondly, also the grant generation means is adapted to
generate differentiated grants with respect to each different service
category.
Furthermore, the grant rate associated to a particular storage queue is
thereby not only determined from the parameters associated to this storage
queue, but is also based upon at least one other parameter related to
another storage queue within any network terminal of the communications
network. This leads to a better partitioning of the available upstream
bandwidth of the common transmission link since the upstream packet
transmission rate will now be modulated, based on parameters associated to
two competing bitstreams of which the packets are stored in these two
storage queues.
These competing bitstreams can be upstream transmitted from the same
network terminal, in which case the storage queues are included within
this same network terminal as is stated in claim 2, or can be transmitted
from two different terminals, in which case the storage queues are also
belonging to two different network terminals as is stated in claim 3.
Another characteristic feature of the present invention is mentioned in
claims 4 and 18.
The respective sets of parameters, associated to the respective storage
queues, thereby include traffic and connection parameters associated to
the respective bitstreams of which the data packets are stored within
these queues, but also include a status parameter indicative of the status
of these queues. As was stated by the previous claims 1 and 17, the grant
rate associated to one queue, is then adapted based upon at least one
parameter from both queue parameter sets. This implies that this queue
grant rate may be solely dependent upon the status parameters, or solely
on one of the traffic and connection parameters associated to both queues,
or on a combination of both. In either case, the upstream data packet rate
can be more efficiently controlled for matching the common transmission
link capacity. Indeed, the traffic and connection parameters in general
represent boundaries within which the actual traffic rates must lie. If
the queue grant rate, which directly determines the corresponding upstream
data transmission rate, is now dependent both on the own traffic limits,
as well as on traffic limits of at least another, competing, bitstream, a
better fit to the capacity of the upstream transmission link is obtained
since a rate lying in between both boundaries will be the result.
In case only the status parameters are controlling the rate of the upstream
transmission of the data packets, a medium access control method
proportionally dividing the upstream link capacity amongst for instance
the active bitstreams, thus for which the corresponding storage queues are
not empty, is using that upstream link capacity in a much more efficient
way than for instance the prior art system, which only took the requested
bandwidth into account.
By combining the traffic and connection as well as the status parameters
for determining the queue grant rate, it is evident that even a more
optimal use of the upstream link capacity is obtained. Examples of such
algorithms will be described into detail in a following paragraph of this
document.
Yet a further characteristic feature of the present invention is mentioned
in claims 5, 14 and 19.
In this way, the parameters associated to the respective queues are
upstream transmitted by the network terminals themselves by means of
upstream queue request messages. This upstream transmission is mandatory
for the queue status parameters which can not be communicated to the
medium access controller in another way. The traffic and connection
parameters on the other hand can be incorporated within the same upstream
queue request messages, as is for instance stated in claim 15, but can
also be delivered to the medium access controller from for instance the
central station where this information is centrally stored during the
connection set-up phase.
Still another characteristic feature of the present invention is mentioned
in claims 6 to 11 and 20 to 26.
By this, the queue grant rate, being directly related to the upstream
associated packet transmission rate, is only adapted as long as the
corresponding storage queue status parameter is complying with a
predetermined criterion as is described by claims 6 and 20. In a previous
paragraph such a criterion was already mentioned, namely that the queue
should not be empty. Another criterion could be that at least a minimum
number of cells are buffered in the storage queue. The storage queues of
which the associated parameters are influencing the upstream packet
transmission rate of one particular storage queue together constitute one
group, whereas a subgroup of this group is formed by all storage queues
from the group for which the status parameters fulfil this predetermined
criterion. Claims 7 and 21 state that, in stead of using the status
parameters extracted from the upstream request messages as such, first
status related parameters are determined from them, after which step these
status related parameters are then further used for determining the
subgroup. The reason behind this latter solution is related to an eventual
long delay between the arrival of two successive queue request messages.
In this case downstream transmitted grants may already have caused a
particular storage queue to be empty, a long time before the next request
message with the indication of this new status has arrived. For these
networks, the status related parameters are derived from the latest
version of the received status parameters, but take already into account
recently generated grants to this same storage queue. The thereby
determined status related parameters thus aim at representing the actual
status of the storage queues. In case however upstream request messages
are arriving frequently enough to overcome this delay problem, there is no
need for determining these status related parameters.
From the parameters associated to the storage queues of the subgroup, an
excess bandwidth is then determined which will be proportionally divided
amongst the storage queues of the subgroup. In case the group consists of
the total of all storage queues within the network, and in case the grant
rates associated to the storage queues for which the status parameters do
not meet the predetermined criterion are set to zero, this excess
bandwidth may correspond to an upstream bandwidth remaining available on
the common transmission link when all bitstreams stored in the storage
queues are already using the part determined by their traffic parameters,
such as the peak cell rate or minimum cell rate. This excess bandwidth may
be determined according to different methods, more details will be given
in the descriptive part of this document. In addition, by proportionally
dividing this excess bandwidth amongst these bitstreams of the subgroup,
fairness amongst these competing bitstreams is obtained. This will also be
explained into more detail in this descriptive part.
Still a further characteristic feature of the present invention is
mentioned in claim 12.
Since the groups, the subgroups and the parameters may vary in time, the
method is performed at particular predetermined instances, resulting in an
adaptive method. These predetermined instances are for instance determined
by the sending, at regular intervals of so-called PLOAM (Physical Layer
Operation And Maintenance) cells, indicating to the network terminals that
these are allowed to transmit their upstream request messages, as was also
already the case for the prior art system.
The present invention relates as well to a central station including such a
medium access controller as described by the above mentioned claims 19 to
26, as well as to a communications network including such a medium access
controller and a network terminal as described in the above mentioned
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects and features of the invention will become more
apparent and the invention itself will be best understood by referring to
the following description of an embodiment taken in conjunction with the
accompanying drawings wherein:
FIG. 1 represents a scheme of a communications network wherein the present
invention is applied,
FIG. 2 represents a block scheme of network terminals ONUi and ONU1 of FIG.
1 as well of as the central station CS of this same figure, this central
station including a medium access controller according to the invention
DETAILED DESCRIPTION OF THE INVENTION
The communications network of FIG. 1 is composed of a central station CS
and network terminals ONU1, . . . , ONUi, . . . to ONUn. the central
station is coupled to these optical network units via the cascade
connection of a common transmission link L, for instance an optical fibre
link, and respective individual network terminal links L1, . . . ,Li, . .
. ,Ln, also for instance consisting of optical fibres. The network hence
has a point-to-multipoint architecture in the downstream direction, which
is the direction from the central station CS to the network terminals ONU1
to ONUn, and a multipoint-to-point architecture in the upstream direction,
i.e. the direction from the network terminals ONU1 to ONUn towards the
central station CS.
In the downstream direction, the central station CS broadcasts information
to all network terminals ONU1 to ONUn. The information is empacked in
so-called downstream frames. In the opposite direction, the network
terminals ONU1 to ONUn commonly share the link L in a time-multiplexed
way. This means that different network terminals transmit information to
the central station CS in different timeslots. Each network terminal thus
sends upstream information in short bursts to the central station. The
upstream timeslots constitute so-called upstream frames.
To be allowed to send a burst in an upstream timeslot, a network terminal,
for instance ONUi, has to receive a permission or grant from medium access
controller MAC, usually included within the central station CS, as is also
drawn in FIG. 1.
At regular time intervals such permissions are downstream broadcasted by
the medium access controller by means of a so-called PLOAM (Physical Layer
Operation And Maintenance) cell wherein the contents of grant fields
precisely define which network terminal is allowed to occupy which
upstream timeslot.
In a multi-service network, network terminals are adapted to transmit
several bitstreams, pertaining to several connections. In case of ATM
bitstreams, pertaining to different ATM connections, these are associated
with a set of traffic and connection parameters, related to the ATM
service category associated with the connection, and which parameters are
declared to the network by the user connected to the network terminal,
during the connection-set-up, by means of signalling parameters. These
traffic and connection parameters are for instance a peak cell rate,
abbreviated with PCR, a minimum cell rate, abbreviated with MCR, a
sustainable cell rate, abbreviated with SCR, etc. These parameters are
standardised by the ATM Forum by specification AF-TM-0056.000 dated April
1996.
A network terminal, such as ONUi of FIGS. 1 and 2, adapted to transmit
several bitstreams associated to several service categories, therefore
includes for each service category one associated storage queue, in which
subsequent cells or packets of the bitstreams associated with this service
category, are stored. Thus in case four service categories are supported
by this network terminal, four respective storage queues are included.
These service categories may for instance comprise the constant bit rate,
abbreviated with CBR, the variable bit rate, abbreviated with VBR, the
available bit rate, abbreviated with ABR and the unspecified bit rate,
abbreviated with UBR, service categories, again specified by the
aforementioned ATM forum specification.
These storage queues included within network terminal ONUi are
schematically depicted in FIG. 2 with ONUiQ1, . . . , ONUiQj, to ONUiQm,
for the general case of m service categories. In order to classify
incoming data packets from one incoming bitstream, in FIG. 2 denoted BSi,
and composed of m individual bitstreams BSi1 to BSim, each individual
bitstream pertaining to a respective one of the m service categories, the
network terminal ONUi includes a sorting means SMi, adapted to classify
incoming data packets from bitstream BSi, in accordance to their
associated service category. SMi then includes m output terminals, one for
each respective service category, which are coupled to the m respective
storage queues. SMi is thereby adapted to extract the m individual
bitstreams BSi1, . . . , BSij . . . ,BSim, succeeding packets of which are
then stored in the respective associated storage queues ONUiQ1 to ONUiQm.
For ATM networks, the sorting may be performed by examining the header of
each ATM cell or packet. This header information includes the VPI/VCI
identifier, which is during connection set-up uniquely linked to a
particular service category. SMi then is adapted to extract this header
information, compare this to connection set-up information previously
captured and stored during the connection set-up phase, and to accordingly
determine the associated service category. SMi is further adapted to
forward these packets to one of the appropriate output terminals, which
are further coupled to an appropriate storage queue. Since such sorting
means are further known to a person skilled in the art, these will not be
further described within this document.
For multi-service networks, it is clear that the grants transmitted to each
network terminal, now not only have to include an identifier for the
network terminal itself, but also an identifier concerning the service
category of the bitstream for which transmission is allowed. Since per
service category one storage queue is associated, the service category
identifier thus also corresponds to the storage queue identifier.
The present invention therefore concerns a method for determining the
grants associated per network terminal and per storage queue, as well as a
medium access controller, which is adapted for executing this method.
According to the subject method, the queue grant rate GRij for an
individual storage queue, for instance ONUiQj, is determined from at least
one parameter of a parameter set associated to the corresponding queue
ONUiQj, and from at least one other parameter of at least one other
parameter set associated to another storage queue. This other storage
queue may be included in the same network terminal ONUi as the one
comprising storage queue ONUiQj, but may also be located in another
network terminal, for instance network terminal ONU1. For the latter case,
parameters associated to for instance storage queue ONU1Qm, may be used
for determining the queue grant rate GRij. The parameter set associated to
each of the storage queues within the network, and for instance denoted
Sij for storage queue ONUiQj, includes the traffic and connection
parameters, denoted TCPij associated to the bitstream of which the data
packets are stored in ONUiQj, and furthermore contains a parameter
reflecting the status STij of this storage queue. This latter parameter
may be simply indicating whether the queue is empty or not, or whether a
minimum number of cells is available in the storage queue, but, in more
sophisticated variants, may also indicate the amount of packets stored at
a particular moment in time, within this storage queue.
Suppose that, besides one of the parameters associated to storage queue
ONUiQj, at least one of the parameters of storage queue ONU1Qm is
influencing the rate GRij. GRij is thus a function of a parameter Pij of
the set Sij, and of a parameter P1m of the set Sim. Several options are
then possible. Pij as well as P1m may correspond to the respective traffic
and connection parameters, respectively denoted TCPij and TCP1m. For this
variant of the method, these traffic and connection parameters may be
explicitly communicated by the respective network terminals ONUi and ONU1
to the medium access controller MAC, by means of upstream queue request
messages. Since these traffic and connection parameters were however
already assigned to the individual bitstreams by the connection admission
control function centrally residing within the network, these may
therefore already have been communicated to the central station during
this assignment phase. The central station CS in that case includes a
central memory denoted CACM on FIG. 2 and adapted to store the traffic and
connection parameters associated to all bitstreams or storage queues
within the network and for which such a traffic a connection parameter was
assigned. Since the medium access controller is also residing in this
central station, this medium access controller can easily access this
central memory, for getting the desired parameters such as TCPij and TCP1m
in order to determine the grant rate GRij.
For another variant of the method Pij as well as P1m consist of the status
parameters, STij and ST1m, of the respective storage queues ONUiQj and
ONU1Qm. This information is however to be explicitly communicated in the
upstream direction by the corresponding network terminals ONUi and ONU1
towards the medium access controller. This upstream communication occurs
by means of upstream queue request messages, respectively denoted QRMij
for the storage queue ONUiQj, and QRM1m for storage queue ONU1Qm. In this
case the respective terminals ONUi and ONU1 include respective queue
request generating means, respectively denoted Ri for ONUi and R1 for
ONU1. These respective queue request generating means are adapted for
determining the respective status parameters STij and ST1m, to incorporate
them into respective upstream queue request messages, QRMij and QRM1m, and
to further transmit these messages at regular instances upstream to the
medium access controller MAC. The status parameters are determined at
regular times, by means of the bi-directional links depicted on FIG. 2
between for instance Ri and the respective storage queues ONUiQ1 to
ONUiQj. For R1 only one bi-directional link is shown between R1 and
ONU1Qm, in order to not overload the drawing. The status parameters may
consist of a simple indication of the queue being empty or not, whether or
not a minimum number of cells are available in the queue or may consist of
the real amount of cells, contained in this queue at a particular instance
in time. The predetermined instances at which these queue request messages
are generated and upstream transmitted are determined by the medium access
controller itself, which regularly transmits downstream grants specially
dedicated to the upstream transmission of this kind of request information
from one or from a multiple of network terminals.
Such queue request messages, for instance QRMij including the status
parameter STij of storage queue ONUiQj, and QRM1m including the status
parameter ST1m of storage queue ONU1Qm, are regularly transmitted from the
respective network terminals ONUi and ONU1 towards the medium access
controller MAC. The latter further includes an extraction means, denoted
EM in FIG. 2, which is adapted to receive from all network terminals their
queue request messages, and to extract therefrom the parameters associated
to their respective storage queues. These associated parameters are
further transmitted by the extraction means EM to a memory means denoted
MM in FIG. 2. This memory means includes, per storage queue, a memory
location for storing the upstream communicated parameters associated to
this storage queue. How to realise embodiments of such an extraction means
and such a memory means is known by a person skilled in the art and this
will therefore not be further described in this document. By means of an
example, in FIG. 2 two output signals from the extraction means, serving
as input signals to the memory means are depicted, namely the status
parameters ST1m and STij.
The storage queues, of which the parameters, at a particular moment in
time, are influencing the queue grant rate associated to a particular
storage queue, for instance ONUiQj, are forming a so-called group of
storage queues associated to that particular storage queue. For the
previously mentioned example, ONUiQj and ONU1Qm are forming the group
associated to storage queue ONUiQj.
Several algorithms are of course possible for determining the grant rate
GRij. As already mentioned, GRij may be solely determined based on the
status parameters STij and ST1m of the storage queues of the group
mentioned by the previous example, these status parameters thereby also
constituting a group of status parameters associated to storage queue
ONUiQj. In this case, in general a method for calculating GRij first
includes a step of checking the values of these status parameters of all
storage queues of this group against a predetermined criterion. In a
variant method, first status related parameters are derived from these
status parameters by for instance already taking into account already
generated grants, as will be described in a further paragraph of this
document. These status related parameters aim at representing as close as
possible the actual status of the queues within the medium access
controller. They are introduced since it may take some time for an
upstream queue request message to arrive at the central station, whereas
at the same moment the already arrived grants may have caused the
corresponding storage queue to be empty.
The thus determined status related parameters are then also used for
determining the subgroup, by comparing them also against the same
predetermined criterion as in the case merely the status parameters are
used for determining the subgroup.
This predetermined criterion may for instance consist of comparing all
status or status related parameters of the group with a predetermined
value. Only these status or status related parameters exceeding this
predetermined value are then further used by the method for calculating
GRij, these storage queues thereby constituting a subgroup of storage
queues associated to storage queue ONUiQj. Besides this, it also needs to
be checked whether ONUiQj belongs to its own subgroup, by checking the own
status or status related parameter STij against this predetermined
criterion. In case the own status or status related parameter STij is not
conform to this predetermined criterion, the corresponding queue grant
rate may be put to zero, or to a low predetermined value, or even left
unchanged. For the case where the predetermined criterion consists of
checking whether the queues are empty or not, for one variant of the
method the queue grant rate for empty queues is set to zero, since no data
packets are to be transmitted. For a non-empty storage queue, the
corresponding queue grant rate is then further determined by partitioning
an excess bandwidth amongst the bitstreams of the subgroup. This excess
bandwidth may for instance correspond to a predetermined capacity of the
common upstream transmission link, whereby this is for instance
distributed amongst the active bitstreams taking into account the amount
of cells in their storage queue as proportionality factor.
However a lot of other variant methods for determining the queue grant
rates are possible.
In case only traffic and connection parameters are used for determining a
queue grant rate, without using the status parameters, again an excess
bandwidth may as well be proportionally distributed over the different
input bistreams of the group. In this case no subgroups are determined.
The proportionality factor as well as the excess bandwidth may thereby be
determined based upon the traffic and connection parameters of the
individual storage queues of the group.
In the most general case however, the queue grant rate of a particular
storage queue is determined from both status parameters and traffic and
connection parameters associated to all storage queues of the group
associated to this particular storage queue this group thereby thus also
including the particular storage queue itself. In one particular variant
of the method, used in for instance asynchronous passive optical networks,
hereafter abbreviated with APON, a queue grant rate GRij is determined
from the total of all traffic and connection parameters and all status
parameters associated to all storage queues within the network. The group
associated to storage queue ONUiQj is thus consisting of the whole
plurality of all storage queues within the network.
One particular algorithm used for adapting the grant rate GRij within these
APON networks will now be further described. This algorithm is performed
by the calculating means ARC included within the medium access controller
MAC. This medium access controller, as depicted in FIG. 2, includes the
already mentioned extraction means EM and memory means MM, in which the
respective status parameters of all storage queues within the network are
first extracted and then temporarily stored. In order to not overload the
drawing, only two status parameters STij and ST1m are depicted in this
FIG. 2, as well as two network terminals having transmitted one of their
upstream queue request messages. It is however evident that for the
embodiment of the medium access controller MAC, used in for instance the
APON network all network terminals are sending upstream queue request
messages for each of their incorporated storage queues.
Within the embodiment of the medium access controller depicted in FIG. 2,
the memory means MM is coupled to a counter means denoted CM, also
included in the medium access controller. This counter means CM is
composed of a plurality of individual counters, one counter assigned to
each respective storage queue within the network. Each of these individual
counters, such as for instance counter Cij receives as input parameters on
one hand the status parameters STij of the corresponding storage queue
ONUiQj, from the memory means MM, on the other hand a control signal CSij,
generated by a grant generator GGij. The latter device will be described
more extensively in a further paragraph. In the embodiment of the medium
access controller used in the APON network, the respective status
parameters STij are indicating the amount of cells or packets residing
within the corresponding storage queue ONUiQj. This status parameter
output signal is transmitted at regular time intervals from the memory
location towards the counter means, and serves to reset the counters to
this value. Upon receipt of the respective control signals from the
respective grant generators, each counter decreases its output value with
one, or with a predetermined value in case this same predetermined amount
of cells is to be transmitted upstream from the corresponding storage
queue ONUiQj upon receipt of a grant GONUiQj.
Upon receipt of a new queue request message, the thereby included updated
value of the status parameter STij will however reset the counter to this
new updated value. By this mechanism the corresponding counter output
value always aims at reflecting the actual amount of cells within the
queue ONUiQj, and thus the actual value of the status parameters at any
point in time. This counter output value is therefore to be considered as
a status related parameter for its corresponding storage queue.
It however needs to be remarked, that, dependent upon the frequency with
which the request signals are transmitted by the individual network
terminals, and read out by the extraction means, also embodiments of the
medium access controller without such counter means are possible. In these
embodiments the memory means is then directly coupled to the grant rate
determining means GRCM which will be described in the following paragraph,
whereby in this case no status related parameters are determined. In case
the counter means is included in the MAC, this device may also directly be
coupled to the extraction means EM, in which case the MAC does not include
the memory means MM. A person skilled in the art is adapted in any of
these cases how to realise different embodiments for these three devices,
taken into account the frequency with which the request signals are
arriving at the MAC.
In order to calculate an individual grant rate GRij, a grant rate
calculating means GRCM is included within the medium access controller
MAC, adapted for performing the method. This grant rate calculating means
forms part of a calculating means ARC, which is coupled to the extraction
means, and which, in some embodiments such as the one depicted in FIG. 2,
may also include the aforementioned counter means CM. The grant rate
calculating means is thereby adapted to receive the output signals from
the corresponding counters, these signals thus constituting status related
parameters, or in case this counter means is not present in the
embodiment, output signals from the corresponding memory locations, these
signals thus constituting status parameters. With these status or status
related parameters as input parameters, the grant rate calculating means
is adapted to check whether the associated storage queue ONUiQj is not
empty. This grant rate calculating means is thereby adapted to compare the
corresponding counter output value, denoted CVij in FIG. 2, with zero. In
the case the storage queue was empty, the grant rate GRij, being an output
signal of this grant rate calculating means, is set to zero. In case the
counter value CVij is larger than zero, the grant rate calculating means
will then further determine the subgroup associated to the storage queue
ONUiQj, by comparing all counter values of all counters with zero. This is
schematically depicted in FIG. 2 by the connection between the counter C1m
towards the GRCM, whereby counter C1m transmits its output signal CV1m
towards the grant rate calculating means GRCM. In order to not overload
the drawing control signals from the calculating means towards the counter
means for requesting these output values are not drawn.
For a non-empty storage queue ONUiQj the grant rate calculating means next
determines an excess bandwidth which is to be proportionally distributed
amongst the active storage queues of the subgroup. To this purpose, first
the traffic and connection parameters, associated to the bitstreams of
which packets are stored within storage queues of the subgroup, are to be
converted into internal parameters used by the method. For the bitstream
BSij, of which the packets are temporarily stored in storage queue ONUiQj,
the following internal parameters are used as internal variables: a
minimum service rate, abbreviated with MSRij, and a peak service rate,
abbreviated with PSRij. A conversion between the presently standardised
traffic and connection parameters as given by the aforementioned ATM Forum
document is given in the following table:
standardized Standard standard
ATM service parameters for the parameter parameter
category ATM service category used for MSRij used for PSRij
CBR PCRij PCRij PCRij
VBR PCRij,SCRij,BTij SCRij PCRij
ABR PCRij,MCRij MCRij PCRij
UBR PCRij,MCRij MCRij PCRij
Conversion table between standardized ATM-Forum traffic and connection
parameters, and the parameters MSRij and PSRij used by the algorithm.
Following abbreviations are used:
CBR: constant bit rate service category
VBR variable bit rate service category
ABR: available bit rate service category
UBR: unspecified bit rate service category
PCRij: peak cell rate associated to bitstream BSij
SCRij: sustainable cell rate associated to bitstream BSij
MCRij minimum cell rate associated to bitstream BSij
BTij: burst tolerance associated to bitstream BSij
MSRij: minimum service rate parameter for bitstream BSij
PSRij: peak service rate parameter for bitstream BSij
Remark that this table represents only one example of conversion between
standardised parameters and the internal parameters used by the algorithm.
Other conversion methods are possible as well. This conversion is
performed by a conversion device denoted CD and included in the
calculating means ARC. The conversion device is adapted to receive from
the connection admission control memory denoted CACM and residing within
the central station CS of which also the medium access controller MAC
forms part, the values of the standardized traffic and connection
parameters. These are by way of example represented by the traffic and
connection parameters TCP1m associated to storage queue ONU1Qm, and the
traffic and connection parameters TCPij associated to the storage queue
ONUiQj. These traffic and connection parameters thereby thus include the
peak cell rates PCR1m, resp. PCRij, the minimum cell rates MCR1m, resp.
MCRij, the sustainable cell rates SCR1m, resp, SCRij, and others which are
currently not used by the method, and which are therefore also not
represented in FIG. 2.
These converted parameters, denoted MSR1m, PSR1m, MSRij and PSRij, are then
delivered to the grant rate calculating means GRCM included within the
calculating means ARC.
The grant rate calculating means is further adapted to calculate 3 global
parameters during the execution of the algorithm: an active peak service
rate, abbreviated with APSR, an active minimum service rate, abbreviated
with AMSR, and an allowed service rate, abbreviated with ASR. The ASR is
initialised at the start of the operation of the medium access controller
to a predetermined value ASR0, in general ASR0 corresponding to the
upstream capacity of the common transmission link. AMSR and APRS are
initialised as zero.
The algorithm uses the following rules
1. APSR=.SIGMA. PSRkl
2. AMSR=.SIGMA. MSRkl
3. ASR=ASRO-.SIGMA. MSRkl
with PSRkl,MSRkl representing the peak service rate, respectively the
minimum service rate of an arbitrary storage queue ONUkQl (not shown in
FIG. 2) of the subgroup associated to storage queue ONUiQj. The summations
are performed over all storage queues of the subgroup.
##EQU1##
with .DELTA.ij=PSRij-MSRij
.DELTA.=APSR-AMSR
with PSRij, MSRij respectively representing the peak service rate and the
minimum service rate associated to the bitstream of which the packets are
temporarily stored within storage queue ONUiQj.
Rule 4 thus implies that the grant rate GRij is determined as the minimum
of two values, a first value being the associated peak service rate PSRij,
a second value being a proportional division of the allowed service rate
ASR amongst all bitstreams of the subgroup. An excess bandwidth,
corresponding to this allowed service rate, is thus determined as the
difference between the initialised value ASRO, which in general
corresponds to the capacity of the common transmission link, and the sum
of all minimum service rates of all bitstreams of the subgroup, in this
case consisting of all active bitstreams. The thus determined value of ASR
corresponds to an excess bandwidth remaining available at the common
transmission link after all minimum service rates of all active bitstreams
are used. This excess bandwidth is then proportionally divided amongst all
active bitstreams or storage queues, based on their negotiated traffic
contract parameters related to PSRij and MSRij, while non of the storage
queues is arbitrarily discriminated or favoured. Fairness is thus
obtained.
It further needs to be remarked that when the counters are updated, the
global parameters APSR, AMSR and ASR need also to be updated. The
algorithm is executed at predetermined instances, in order to closely
follow the latest version of the status related parameters. This algorithm
can thus be considered as an adaptive algorithm, following as closely as
possible the status of the queues within the network terminals.
Other implementations exist whereby incremental differences between
successive values of the status related parameters are used for
determining the variables used by the algorithm. A lot of other algorithms
are of course also possible.
Although not drawn in FIG. 2 for simplicity reasons, circuitry for the
control and synchronisation between the calculating means ARC and the
connection admission control memory CACM as well as between the counters
of CM and the calculating means is necessary, for proper operation of the
method. A person skilled in the art is capable of realising such
circuitry. Since these control circuits are however not relevant to the
invention they will not be further discussed in this document.
The grant rates for each of the active storage queues are determined using
the same algorithm. The calculations may be performed in parallel or
sequentially by the calculating means, depending upon the processing
capacity of such means. Nevertheless, from the formula's of the algorithm
it is clear that a lot of calculations can be shared.
The grant rate calculating means is further adapted to deliver these
respective grant rates, by way of example represented by GR1m for the
grant rate associated to storage queue ONU1Qm and GRij for the grant rate
associated to storage queue ONUiQj, as input signals to a grant generator
denoted GG. This grant generator consists of a plurality of individual
grant generation devices, such as GG1m and GGij. An individual grant
generation device, for instance GGij, is adapted to generate a succession
of respective queue grant messages, such that the rate of the bitstream
composed of successive occurrences of these queue grant messages
corresponds to GRij. The principles for converting these rates to such a
bitstream of grants is commonly known to a person skilled in the art, and
will therefore not be further described into detail in this document.
Furthermore, upon generation of each grant GONUij by the grant generation
device GGij, a control signal denoted CSij is generated by this grant
generation device GGij and supplied on a control output terminal of the
grant generation device to the corresponding counter Cij. Therefore, each
of the grant generating devices, includes a control output terminal which
is coupled to a control input terminal of a corresponding counter,
associated to the same storage queue. Each time a grant is generated, the
value of the control signal delivered to the counter equals the amount of
cells which are allowed to be upstream transmitted by the corresponding
storage queues, after receipt of an associated downstream grant. In case
one cell is to be transmitted upstream, this value is thus one, and the
corresponding counter will decrease its output value with one. In order to
not overload the drawing on FIG. 2, only control signal CSij is shown.
The thus determined individual queue grant bitstreams are further scheduled
by a scheduler device, denoted SD in FIG. 2, which is adapted to generate
from these nxm individual bitstreams one downstream bitstream. The
simplest implementation of such a scheduler device may consist of a
multiplexer, but also more sophisticated scheduler devices can be used,
whereby more complex scheduling or work conserving service discipline
methods are realised. These are for instance described in the article
"Service Disciplines for Guaranteed Performance Service in
Packet-Switching Networks" by H. Zhang, Proceedings of the IEEE, 83 (10),
October 1995. Therein on the pages 5 to 9 a series of these
work-conserving service disciplines is discussed. These scheduler means
furthermore may consist of several stages, first including a scheduler
device to schedule the nxm queue grant bitstreams into m queues, one queue
per service category, and to further multiplex then the bitstreams from
these m queues into one global downstream bitstream BSG of grants.
It further is to be remarked that since the downstream bitstream of grants
BSG now includes succeeding occurrences of queue grants, each network
terminal also is further adapted to determine from the bitstream of
grants, the respective queue grants associated to the storage queues which
are included within this network terminal. To this purpose a detecting
means is included in each of these network terminals, denoted DMi for
network terminal ONUi in FIG. 2. In order to not overload this figure,
neither the input nor the output signals of this detecting means are
drawn. This detecting means is adapted to receive the bitstream of grants,
to extract therefrom the queue grants associated to the respective storage
queues within ONUi, and, upon detection of such a queue grant, to generate
a corresponding control signal towards the corresponding storage queue,
allowing this storage queue to upstream transmit this predetermined amount
of packets towards the central station CS. Since also such detecting means
are known to persons skilled in the art, more detailed embodiments will
not be described in this document.
Although the medium access control method and controller have been
described for APON networks, they may as well be used for any network
based on time division multiplexing, such as hybrid fiber coax networks,
satellite networks and so on.
While the principles of the invention have been described above in
connection with specific apparatus, it is to be clearly understood that
this description is made only by way of example and not as a limitation on
the scope of the invention, as defined in the appended claims.
* * * * *
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