Note: Descriptions are shown in the official language in which they were submitted.
GR 99 P 1265
Description
CA 02371930 2001-08-21
Method for determining a communication path in a
communication network between two neighboring network
nodes.
The invention relates to a method according to
the preamble of patent claim 1.
Contemporary communication networks have a
plurality of network nodes which are intermeshed via
communication paths. These are formed from a number of
trunks which are combined to form trunk groups.
In contemporary communication networks,
different traffic mixtures are conducted via the
communication paths arranged between two or more
network nodes. Thus, for example, information can be
transmitted by means of a synchronous transfer mode
(STM) or asynchronous mode (ATM). In this context, the
information can have different bandwidths. Thus, as a
rule, a distinction is made between information which
is transmitted as narrowband signals and that which is
transmitted as wideband or broadband signals. Thus,
special significance is attached to setting up a
connection between two neighboring network nodes, i.e.
those connected to one another via one trunk group.
When setting up a connection, two decisions
must be made, in general, for determining a
communication path between two neighboring network
nodes . On the one hand, it must be decided on which of
the trunks of the trunk group connecting the network
nodes in question sufficient capacity is still free in
order to be able to establish a connection.
On the other hand, one of the communication
paths which are conceivable with regard to the
available capacity, must be selected in such a manner
that
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an optimum grade of service is obtained. This is
necessary in as much as a selected communication path
should ensure the lowest possible blocking probability
and an associated low connection loss probability for
subsequent connections.
A method by means of which both of these tasks
(search and selection) can be performed is called a
hunting strategy method or hunting strategy.
Hunting strategy methods are known from the
printed document "Probability of Loss of Data Traffics
with different Bit Rates Hunting One Common PCM
Channel", Proceedings of the 8th International
Teletraffic Congress (ITC 8), 1976, pp. 525.1 - 525.8,
Lothar Katzschner and Reinhard Scheller.
Accordingly, a first hunting strategy method is
described by means of which a sequential hunt is
performed from a fixed zero position. In this process,
the hunting always begins with the first trunk in the
trunk group. Which one of the trunks is to be
considered as the first one can be freely defined. The
hunt is terminated as soon as a trunk has been found
which meets the acceptance criteria. The acceptance
criterion used here is the transmission capacity still
available on the trunk in relation to the peak bit rate
of the connection to be accommodated. The new
connection to be accommodated will thus be accepted if
a trunk is found the free available transmission
capacity of which is greater than or equal to the peak
bit rate of this connection. If this is so, the hunt is
terminated. The next hunt is again started at the first
trunk. If no free transmission capacity is found by the
last trunk, the hunt
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is also terminated and the connection is question is
rejected.
The disadvantageous factor of such a procedure
is that~it results in a nonuniform load distribution on
the trunk group. The reason for this is that the hunt
is always started from the same position and is
terminated when a suitable trunk has been found. On
average, therefore, the trunks which have been hunted
first are used to high capacity whereas the remaining
trunks are used to low capacity ("unbalanced load").
According to this prior art, a second hunting
strategy method is described by means of which a
sequential hunt is performed from a variable zero
position. In this process, the hunting begins with a
specially marked trunk in the trunk group. The marking
has been performed by the immediately preceding hunt.
This defines the position at which the next hunt is to
be started. The new connection to be accepted is
accepted if a trunk is found, the freely available
transmission capacity of which is greater than or equal
to the peak bit rate of this connection. If this is so,
the hunt is terminated. At the same time as this, the
trunk immediately following is marked. The next hunt
thus begins at this trunk. If no free transmission
capacity is found by the last trunk, the connection in
. question will be rejected. The last trunk is defined as
the trunk which immediately precedes the marked trunk
after a cyclic rotation.
Although this prevents the disadvantage of the
first hunting strategy method (nonuniform load
distribution) because of the variable
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position which, on average, provides a more or less
uniform distribution on the trunk. The disadvantage of
such a procedure is, however, that, because of the
uniform load distribution, high-bit-rate connections
can no longer be accommodated it with greater
probability because of the lack of trunks with low
capacity utilization and a corresponding request for
connection setup must then be rejected.
These known methods were developed, in
particular, for a homogeneous traffic characteristic in
which each connection setup was associated with the
same capacity requirement of 64 kbit/s per connection.
However, this homogeneity of the traffic in connection
setup is often no longer given in contemporary
communication networks. Apart from the conventional
narrowband connections with 64 kbit/s,. for example,
wideband connections with. nx64 kbit/s occur (in the
case of STM-based connection-oriented multiple-rate
services) or even broadband connections with any bit
rate granularity in the case of ATM traffic.
However, this results in completely new
requirements for the connection setup. For example, the
traffic handling capacity for all types of traffic must
be, at the same time, as high and as rugged as possible
with the least possible interaction. In the case of ATM
traffic, this results in the requirement for the most
even load distribution possible over all trunks of a
trunk group. Otherwise, connections on trunks with high
capacity utilization would be subject to greater delay
in the associated queues than on trunks with low
capacity utilization.
The invention is based on the object of
demonstrating an approach of how communication paths in
a communication network can also be determined with
inhomogeneous traffic.
_ -_ __ _._... ............_._.. _r
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The object is achieved by the features
specified in the characterizing clause on the basis of
the features specified in the preamble of patent
claim 1.
The advantageous factor of the invention is, in
particular, the provision of a bit rate threshold
value. According to this threshold value, a decision is
made as to which hunting strategy method is applied to
the trunks.
Advantageous further developments of the
invention are specified in the subclaims.
In the text which follows, the invention will
be explained in greater detail with reference to an
exemplary embodiment shown in the figures, in which:
Figure 1 shows the configuration in which the method
according to the invention is run,
Figure 2 shows the algorithm according to the
invention.
Figure 1 shows a communication network. In this
arrangement, only four network nodes N1 ... N4 are shown
for the sake of simplicity. Two network nodes, for
example network nodes N1, N4 are connected to one
another via a trunk TG. In the trunk group TG, a
plurality of trunks Tl ... Tn are arranged. Each of the
trunks Tl ... Tn has a specified transmission capacity Ca
as physical transmission parameter. The residual
transmission capacity Cr(T;,) (i=l...n) freely available
for further connections is obtained from the physical
connection capacity C$ minus the sum of the peak bit
rates Rp~ of the m connect ions ( j =1, 2..., m) current ly
conducted via this capacity.
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In the text which follows, it is assumed that a
connection V is to be set up from network node N1 to
network node N4. According to the invention, a
sequential hunt is now started from a bit-rate-
dependent starting position if a connection setup
request is present. The corresponding conditions are
shown in Figure 2.
For this purpose, the two known hunting
algorithms, called hunting strategy methods in the text
which follows, are combined. Firstly, a criterion is
established for when which one of the known hunting
strategy methods will be run. The criterion provided is
a bit rate threshold value which can be arbitrarily
predetermined but should usually be of the order of
magnitude 1/10 C8...1/5 C8. Firstly, it is decided in a
first step whether the peak bit rate Rp of the
connection newly to be accepted is greater than or less
than this bit rate threshold value.
If the peak bit rate RpV (j=V) of the connection
V newly to be accepted is greater than the bit rate
threshold value, the hunting strategy method of the
sequential hunt from the fixed zero position is used.
It must be assumed, therefore, that this connection is
a high-bit-rate connection.
The hunting process is thus started with the
first trunk in the trunk group. Which one of the trunks
is the first one can be freely defined. The new
connection V to be accommodated is accepted if a trunk
Ti is found, the freely available residual transmission
capacity Cr(Ti) of which is greater than or equal to the
peak bit rate Rp~ of this connection. In this process,
the trunks in the trunk group are checked successively
step by step. Once a suitable trunk has been found,
this trunk is taken and the hunting is terminated. If
no free transmission capacity is found by the last
trunk, the connection
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in question is rejected. If a further connection V' is
provided for acceptance at a later time, another hunt
is started. This will only be started again at the
first trunk if the peak bit rate Rp~. of the connection
to be newly accepted is greater than the bit rate
threshold value.
If the peak bit rate Rp~ of the connection V to
be newly accepted is less than or equal to the bit rate
threshold value, the hunting strategy method of the
sequential hunt from a variable zero position is used.
It must thus be assumed that this connection is a low-
bit-rate connection.
The hunting is thus started with a marked trunk
in the trunk group. The marking has been performed by
the immediately preceding hunt. The new connection to
be accommodated is accepted if a trunk Ti is found, the
freely available residual transmission capacity Cr(Ti)
of which is greater than or equal to the peak bit rate
of this connection. If this is so, the hunt is
terminated. At the same time as this, the trunk
immediately following this is marked. The next hunt is
started at this trunk. If no free transmission capacity
is found by the last trunk the connection in question
is rejected. In this context, the trunk which is
arranged immediately preceding the marked trunk after a
cyclic rotation is defined as the last trunk.
The present exemplary embodiment generally
discussed connections. These can be connections of any
type. Thus connections which transmit information in
accordance with a synchronous transfer method (STM) can
be set up in accordance with the method according to
the invention
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as can connections which transmit information in
accordance with asynchronous transfer method (ATM).
