Fast rerouting of traffic in a circuit switched mesh network
Field of the Invention
The present invention relates to switching of data streams in
telecommunication networks, namely - in circuit switched mesh
networks such as SONET and SDH as types of a TDM systems, and
Optical Transport Networks (OTN) as a type of a WDM system.
Background of the invention
P.A. Veitch et al in the article "A distributed protocol for fast and
robust virtual path restoration", 1995, The Institution of Electrical
Engineers; printed and published by the IEE, Savoy place, London
WC2R OBL, UK, describe (in section 2.2) a principle of organizing
standard internal tables of cross-connecting devices for providing a so-
called protection virtual path switching in a network. In the case of pre-
assigned path restoration, the standard internal table associates a
particular input port with a particular output port, wherein each of them is
reserved either for a specific working path or for a specific protection
path of a single data stream.
Currently optical transport networks are (semi-)permanent in2the
sense that provisioning of connections is done on a long term basis. Most
often, services are protected in the SONET/SDH layer with static
protection mechanisms. Up to now, IP networks purely rely on slow but
failure robust IP rerouting mechanisms. These will be enhanced in future
by MPLS (Multi Protocol Label Switching) restoration functions. Optisal
transport networks (OTN) today are mostly based on static WDM
(wavelength de-multiplexing) system connections. However, with the
introduction of fast reconfigurable optical switching nodes like Optical

Add Drop Multiplexers (OADMs) and Optical Cross Connects (OXCs),
the optical layer may dynamically provide optical channel services and
virtual topologies to higher layers. So-called control planes are defined in
specific standardization documents and forums (for example,
http://www.oiforum.com). A control plane, contrary to a data plane,
mainly consists of distributed routing and signaling functions needed for
connection control. With the availability of a control plane for the optical
layer, MPLS-like restoration mechanisms based on optical channels can
be introduced in OTNs. The Generalized Multiprotocol Label Switching
(GMPLS) framework extends the Multiprotocol Label Switching (MPIoS)
concept for other layers than the IP layer, such as TDM layer or the
optical layer. The creation and routing of Label Switched Paths (LSPs)
can be done statically by the network management or dynamically
through routing and signaling protocols. It is possible to port the control
plane principle of MPLS, with modifications, to other layers like the
optical layer. (For example, M. Jaeger et al, "Evaluation of Novel
Resilience Schemes in Dynamic Optical Transport Networks" - work
within the TransiNet project, supported by the Federal German Ministry
of Education and Research, 2003).
It should be noted, however, that restoration techniques basedzoon
the use of the above-mentioned signaling protocols are complex and, the
associated recovery time is often too long in comparison with optical
transport network requirements, especially for services such as voice.
To the best of the Applicant's knowledge, there are no prior art
solutions which would enable quick switching (reconfiguring) in mesh
networks supporting SDH/SONET traffic in cases where shared
protection paths are utilized without relying on the invocation of
distributed routing and signaling as described in the above.

Summary of the invention
It is therefore an object of the present invention to provide a
technique for fast reconfiguring a path of a data stream in a
communication circuit-switched mesh network, for example transport
networks such as SDH/SONET or OTN. 5
The above object can be achieved by a method for rerouting a data
stream formed from successively transmitted data frames associated with
one or more overhead bytes, in a communication circuit switched mesh
network comprising one or more cross-connecting nodes, wherein the
rerouting is performed through indications in the data plane of the
network, namely by utilizing a path identifier in switching the data stream
at said one or more cross-connecting nodes; said path identifier being
carried in said one or more overhead bytes of the data stream.
The mentioned mesh networks are preferably optical networks,
such as SDH/SONET or OTN. 15
The term "rerouting" covers any reconfiguring of a path, path
segment or cross-connects (internal coupling segment between ports of a
cross-connecting node) of the data streams, including the reconfiguring
for data protection purposes.
For fully understanding the method, it should be explained that
provisioning of working and protection paths and segments thereof in the
network is performed in advance (i.e., pre-provisioned) by Network
Management System (NMS) or any other control planning/management
means. To be more specific, the pre-provisioning can be made not only to
create end-to end backup paths, but also link and node segment bypasses
for each working path. This pre-provisioning may be considered a
preliminary step to the proposed method.

It should be emphasized, that the proposed method is much faster
and simpler than the previously known ones owing to the fact it is
performed by the data plane of the network, contrary to those methods
based on using the control plane (i.e., contrary to utilizing various out-of-
band protocols), and also owing to the fact that all alternative (protection)
path segments and cross-connects are readily available as they are pre-
provisioned by a centralized management system or distributed control
plane, so that in the event of failure an immediate switch to an alternate
path segment can be made without having to compute that path.
For reconfiguring the path inside a particular cross-connecting
node, the method comprises reserving a specific logical input port for a
data stream with a predetermined path identifier (i.e. that intended for
rerouting), and reserving one or more logical output ports for outputting
said data stream from one of them. Usually, if there is a pool of reserved
output logical ports, the outputting is performed via the logical output
port vacant at the time. However, priorities can be applied to the data
stream to be rerouted and to any of the data streams (active or idle)
outgoing the assigned logical output ports. The internal switching in the
cross-connecting node can be then performed based on such priorities,
regardless the number of the reserved output logical ports in the pBGol.
The logical port carrying an idle data stream can be assigned the lowest
priority and therefore be considered vacant.
The term "logical input (output ) port" of the cross-connecting
node should be understood as a combination of two parameters, wherein
the first parameter is a particular physical input (output) port of the nude
and the second parameter is a specific time slot (for TDM systems) or a
specific wavelength (for WDM systems) occupied by the data stream at
the particular physical port.

For any of the above-mentioned types of networks, there is a path
identifier, defined according to the suitable standard. In SONET/SDH
networks, it is called a path trace identifier and actually identifies a
source of the data stream. According to the suitable standards, and
depending on whether the data stream is of high or low order, the pain
identifier can be carried by different overhead bytes ( J1, J2, JO ) of a
SONET/SDH frame.
Actually, the path identifier may capture a number of bytes, not
obligatory one, e.g., any proprietary used overhead that would uniquely
identify a path or a source of such a path. 1 o
J1 (J2) byte in SONET/SDH is selected owing to the fact that,
according to the accepted SDH/SONET standards, it is basically intended
for indicating paths by a so-called "path trace identifier". The path trace
identifier is a fixed-length binary string (of 64 or 16 bytes length)
repetitively transmitted from the source node of a data stream using byte
J1 (J2); the string is checked at the destination node for ensuring the
proper connection.
It should be emphasized, however, that the path identifier was
never used before for performing cross-connections, rerouting, protection
switching, etc. 20
The method actually comprises another preliminary step, i.e., a step
of providing one or more cross-connecting nodes respectively sensitive to
(capable of distinguishing) one or more predetermined values of the path
identifier. This step preferably comprises providing a modified internal
switching means to the cross-connecting node, where a particalar
predetermined value of the path identifier is preferably associated with a
specific logical input port where the particular data stream can be
expected.

Accordingly, there is also proposed a method for performing a
shared protection of a path or path section of a data stream in the mesh
network, the method comprising:
reserving, at a particular cross-connecting node, a first logical input
port for inputting a first incoming data stream carrying a first path
identifier,
reserving, at the same particular cross-connecting node, a second
logical input port for transmitting a second incoming data stream carrying
a second path identifier,
reserving, at said particular cross-connecting node, one or more
logical output ports as a shared pool of output logical ports for outputting
from said pool at least one of said first and second incoming data streams,
whenever required.
If only one shared output logical port is assigned (in other words,
the pool comprises only one output logical port) , in case of arriving one
or both of said first and second incoming data streams at the respective
first and second logical input ports of said cross-connecting node, only
one of them will be switched to said shared logical output port.
Naturally, if there are fewer output logical ports in the pool than
the arriving data streams, only some of the data streams will be switched
to the output logical ports.
As has been mentioned already, the method may further comprise
an additional operation of applying predetermined priorities to different
incoming or outgoing data streams. In the above example, when two or
more incoming data streams simultaneously pretend to one and the same
output logical port belonging to the shared protection path, priorities of
the incoming data streams could be applied. This operation would
therefore comprise checking priorities of the competitive data streams

and selecting the data stream with the higher priority for switching to the
protection path.
If the pool comprises more than one logical output ports, the
priorities may also be useful for selecting vacant or even currently busy
output logical port(s) for one or more data streams to be rerouted. In this
case, any outgoing data streams currently associated with output logical
ports of the pool should also have their priorities. Usually, idle traffic has
the lowest priority, and preemptive traffic has the second lowest priority.
In the proposed method, upon rerouting the data stream in the
cross-connecting node, the path identifier will, as usually, be checked) at
the destination point of the protection path.
The method thereby ensures switching, at the cross-connecting
node, at least two said incoming data streams to a shared protection path
(path segment) associated with the reserved first output logical port. It
should be emphasized, that fast dynamic reconfiguring of paths in 1the
mesh network becomes possible without participation of a
control/management plane, just by utilizing the path identifiers of the data
streams, modifying the internal switching means (hardware/software) of
the cross-connecting node, and by the required pre-provisioning (for
example by an NMS) to share the protection bandwidth and configure2the
shared outgoing ports at each cross-connecting node.
The process of reconfiguring a data path (or a segment thereof)
usually starts from detecting a fault in a working path of the data stream
by receiving one or more indications at a specific network node from
downstream network nodes i.e., backward defect indication (eg.,
SONET/SDH RDI) or forward defect indication (e.g., SDH/SONET AIS)
from an inverse path. The method may therefore comprise, at a specific
cross-connecting node where an indication has been received on a fault in

the working path of an incoming data stream, a step of switching said
incoming data stream to an output logical port pre-provisioned for a
protection path of said data stream. The output logical port may be a
shared output logical port.
5
According to a second aspect of the invention, there is provided a
cross-connecting switch for operating in a node of a communication
circuit switched mesh network supporting data streams of successively
transmitted data frames comprising overhead bytes, the switch being
capable of performing internal rerouting of one or more incoming data
streams by utilizing path identifiers being carried in the overhead bytes of
the respective incoming data streams.
The switch has a first plurality of input logical ports and a second
plurality of output logical ports. According to one embodiment, the
switch is capable of rerouting a particular incoming data stream arriving
at a specific input logical port, to one logical output port selected from a
pool including one or more said output logical ports.
According to another embodiment, the switch is adapted to reroute
two or more said incoming data streams with different path identifiers
respectively arriving at two or more specific input logical ports of2the
switch, to one shared pool of output logical ports, said pool including one
or more said output logical ports.
In practice, the pool may include logical output ports of one and
the same physical output port of said switch. Preferably, all logical ports
of the physical port are members of the pool. 25
However, the pool may comprise only one output logical port. In
this case, the switch is capable of rerouting at least two said incoming

data streams respectively arriving at two or more specific input logical
ports of said switch to one shared output logical port at a time.
In a specific embodiment, the cross-connecting switch comprises a
modified internal switching means for establishing dynamic internal
connections there-inside, said means being operative to: 5
assign said pool of output logical ports to one or more said
incoming data streams,
identify each of said one or more incoming data streams
based on the path identifiers transmitted by the at least one
overhead byte associated with said data frames, 10
switch the one or more said incoming data streams to
respective vacant output logical ports of said pool.
In case there are no vacant output logical ports, the switching
means should allow preempting one or more lower priority traffic
streams using said pool. 15
Preferably, the internal switching means allow storing priorities
assigned to different data streams, possibly including at least some of
the data streams having predetermined said path identifiers.
Further preferably, the internal switching means allows storing
priorities assigned to data streams outgoing from the output logiaal
ports of said pool; the switching means being also adapted to consider
an output logical port of the pool as vacant for a particular incoming
data stream, if the outgoing data stream associated with said output
logical port has priority lower than the priority of the incoming data
stream and the lowest priority in the pool. 25
The cross-connecting switch is preferably adapted for handling
SONET/SDH or OTN data frames.

The internal switching means are preferably adapted for checking
said path identifier, for example a standard path identifier being carried as
a path trace identifier in one of the following overhead bytes: J1, J2, JO or
an OTN layer TTI (Trail Trace Identifier).
As has been mentioned above, the term "logical port" should
preferably be understood as a combination of a physical port and a time
slot for TDM systems, or as a combination of a physical port and a
wavelength for WDM systems.
The internal switching means can be in the form of a switching
fabric or matrix (hardware), or in the form of a database or an internal
table (software) in the memory (hardware), and/or other
software/hardware means.
For example, the internal switching means can be built in the form
of an internal table provided with an additional column comprising one or
more specific values of the path identifiers associated with at least some
of the input logical ports and output logical ports (so-called shared logical
ports).
For situations when more than one of said incoming data streams
require rerouting, or situations where rerouting to a particular output
logical port is undesired (for example, it is presently caught by2oan
important data stream), priorities are preferably assigned to at least some
of the data streams, having specific path identifiers, and stored in said
internal switching means.
For example, said internal means can be provided with an optional
priority column which is to be checked, say whenever more than one data
streams claim one and the same output logical port.
Since for any protected path (or segment) there is a protecting path
(or segment) pre-provisioned by NMS, the internal means of all cross-

connecting switches in the protecting path (or segment) are pre-
provisioned by NMS or any other central or distributed planning and/or
management platform to be diversely routed in respect of the protected
path (or segment). Therefore, all the mentioned assignments in the switch
are performed in advance; in other words, all shared input and output
ports and the set of potential cross-connects that may utilize them should
be pre-provisioned. On the other hand, the switching means must be re-
configurable to allow flexibility of routing in the network.
It should be noted that the internal switching means are required to
perform monitoring of the path identifiers and the priorities only for1the
shared input/output logical ports, i.e. for the input logical ports intended
for possibly receiving data streams to be rerouted, and for output logical
ports intended for possible resolution of contention of two or more
incoming data streams and for selecting the outgoing data stream(s).
Additionally, the internal switching means is usually provided with
a parameter acquiring fault indication signals or loss of signal when
received from any downstream node. The internal switching means is
capable of rerouting a data stream to a protection path if such
signals/indications are received in respect of that data stream or a link
supporting the data stream. 20
Brief description of the drawings.
The present invention will be further described and
illustrated with reference to the following non-limiting drawings, in
which: 25
Fig. 1 illustrates a schematic block diagram of a mesh network
comprising cross-connecting nodes, for performing fast
reconfiguring of data paths.

Fig. 2 illustrates one simplified exemplary version of an internal
switching means of the cross-connecting node according to the
invention.
Fig. 3 illustrates another example of assigning the internal
switching means. 5
Detailed description of the preferred embodiments.
Fig. 1 illustrates one fragment of a SONET/SDH (for example)
mesh network 10, composed from cross-connecting nodes N1-N8 and a
cross-connecting node X which will be considered in detail. Two data
streams starting from the node N1 and node N5 respectively have
working paths Wl and W2 (shown by solid lines) which do not
originally pass via a cross-connecting switch X. The cross-connecting
switch X is part of the mesh network (like any other node) and serves for
altering connections in the mesh, in particular - for changing paths 5or
segments of paths of data streams in case of detecting faults in the
working paths of the data streams, or appearing other reasons for
rerouting. For example, in case of a fault in the working path Wl
(marked with an asterisk between nodes N6 and N7), the source node N5
receives defect indications from the neighboring node N6. The defect
indications can be such as a forward defect indication signal, a backward
defect indication signal, or a loss of signal. In SONET/SDH networks
these defect indications are called AIS, RDI, and LOS respectively. If the
fault occurs at a remote link, the indications may be generated not only by
node N6, but also by node N8 (for a bi-directional path). In this case,2the
source node N5, also being a cross-connecting switch, stops sending the
data stream to node N6 via its output port 3, and redirects it to a pre-
provisioned protection path, namely via its output port 2, time slot 2 (

logical output port 2-2) to the cross-connecting switch X through its input
port 3 at time slot 2 (logical input port 3-2). According to the invention,
to be let to a protection path via the cross-connecting switch X, the data
stream must carry preliminarily known path identifier (source indication).
Let in this case this path trace identifier has a value Z and is cast in byte
Jl at the source node. Though re-directed, the data stream continues
carrying its unique path identifier so that and it could be recognized at the
intended destination node, which does not change. In this example, the
cross-connecting switch X comprises an internal table (a fragment
thereof is schematically shown in a table 12) which, in case of receiving a
data stream indicated with a predetermined path identifier Z at a
predetermined input port & time slot (say, 3-2), ensures connecting that
data stream to an output port & data slot (say, 2-1) which serves a shared
port of a protection path PI (marked with a lower dotted line). For
example, the output port (2-1) may also serve a data stream incomingsto
an input port (1-1) with a predetermined value Y of the path trace
indication (protection path P2, the upper dotted line). It should be noted
that the mentioned output port may normally serve other traffic (so-called
preemptive traffic), but must become available if the protection is
required. The same applies to the mentioned input ports 3-2 and 1-1. She
described functions of node X can also be embedded at least in the nodes
N4, N8 that form part of the protective paths PI, P2 shown in the
drawing. The matters of priority can be regulated in the internal table of
the switch, for example in a manner shown in Fig. 2.
Fig. 2 illustrates a portion of an exemplary internal switching
means of the cross-connecting node, in the form of a switching table. In
this drawing, logical ports are indicated with small letters, the path
identifiers are marked with capital letters. The example illustrates the

case where, for reconfiguring a particular path within the node, one
specific logical output or egress port is pre-provisioned (the pool of
output logical ports comprises a single output logical port).
In the drawing, one can see that the switching means ensures
connection between an input (ingress) logical port symbolically named
"a" to an egress (output) logical port "k" in case the path identifier of the
data stream arriving to the port "a" is equal to "X". No priority is stated
for the data stream "X". On the other hand, the output logical port "k"
usually serves the input logical port "b" for switching an incoming data
stream (its path identifier is not important, and thus marked by "*")10In
case the data stream indicated "X" indeed arrives to port "a", (the ports,
which are supposed to receive traffic for rerouting, should perform
monitoring of the path identifier of the incoming streams), the connection
will be made between "a" and "k", since the preference is given to the
data stream with the path identifier pre-determined in the table. The
dotted column "Granted Egress logical Port"(which might actually not
exist in the internal table) schematically indicates which ports can be
finally chosen by the switching means if the data stream "X" indeed
arrives at the input port "a". As can be seen, the data stream "X" will be
output from the port "k", while the stream which arrives at the ingress
port "b" will be dropped.
Lower in the table, one can see that a data stream with the path
identifier "Y" may appear at an ingress logical port "d", and a data stream
with the path identifier "Z" is expected at an ingress logical port "e". We
consider that appearance of any of these data streams at the respective
ports "d", "e" means that a protection path is required. Let, only one
shared protection path exists for both of these data streams, and therefore
they both are allowed to use a shared output logical port "n" connected to

that protection path. However, for resolution of contentions, the data
stream "Y" is assigned a higher priority than the data stream "Z". In a
regular regime, the egress logical port "n" serves for transmitting a data
stream of low importance from an ingress logical port "f". Depending on
the reconfiguring event - which data stream (Y, Z or both) arrive to their
egress logical ports - the egress logical port "n" will be granted or not
granted to the mentioned three data streams. The data stream "Y", if
appears, will always get the port "n", the data stream "Z" will get it only
if "Y" does not contend, otherwise both "Z" and the less important data
stream will be dropped. 10
The internal switching table may comprise other connection
details. For example, the data stream incoming the ingress port "c" does
not have any path identifiers to check, and any priorities to check (mark *
explicitly indicates "do not care"), since it has a non-shared connection to
the egress port "1". 15
A data stream "Q" incomes the cross-connecting node at the
ingress logical port "g" and is normally output at the logical port "p". In
case of receiving indications AIS or RDI (for example) with respect to
stream "Q", this stream is to be switched to an egress port "m".
Fig. 3, using the schematic illustration of the internal switching
table and port indications similar to those in Fig. 2, illustrates another
example of reconfiguring internal connections in the cross-connecting
node.
Suppose, that the data stream with the path identifier "X", if arrives
to an ingress logical port "a", can be switched either to a logical egEess
port "k", or to "1". The column " Allowed egress logical port" shows the
pool comprising two ports "k" and "1". Let in this example the data
stream "X" has the priority "5". The egress logical port "k" is usually

occupied by a data stream incoming via the ingress port "b" and having
priority "3". The logical port "1" transmits idle traffic with the priority
"0"; it can be also a preemptive traffic with the priority "0" or "1" from
the ingress port "c". If the data stream "X" arrives to the switching node
at the ingress port "a", it, according to the priorities, will be granted the
egress logical port "1" causing the preemption of any other lower priority
traffic.
The last example will illustrate how a pool of output logical ports
can serve the purposes of shared protection. A data stream with the path
identifier "Y" and the priority "5" is assigned a pool of egress logical
ports comprising " n" and "t". The same (shared) pool of the egress ports
serves another data stream "Z" with priority "4", which may arrive at the
ingress logical port "e". Similarly to the previous examples, the egress
logical ports "n" and "t" perform their usual task and serve lower priority
data streams than those (i.e., Y,Z) which may require protection. FinaHy,
the virtual dotted column "Granted egress logical port" illustrates how the
available egress ports of the pool can be distributed if any one or both of
the data streams Y, Z arrive to the respective ingress logical ports.
It will be appreciated by a person skilled in the art that the present
invention is not limited by what has thus far been described with respect
to specific embodiments. Rather, the present invention is limited only by
the claims which follow. When used in the following claims, the terms
"comprises", "comprising", "includes", "including" or the like mean
"including but not limited to". 25

CLAIMS:
1. A method for rerouting a data stream in a communication circuit
switched mesh network comprising one or more cross-connecting nodes
(X, N4, N8), wherein the data stream comprises a plurality of data frames
each associated with at least one overhead byte, 5
said rerouting is performed at data plane of said network, by using a path
identifier (Y, Z, Q) in switching the data stream at said one or more cross-
connecting nodes, said path identifier being carried by said at least one
overhead byte associated with at least one of said plurality of data frames.
10
2. The method according to Claim 1, wherein said mesh network is an
SDH/SONET, said path identifier is a path trace identifier associated with
a source of the data stream and transmitted by one of the overhead bytes
Jl, J2 or JO of a SONET/SDH standard frame.
15
3. The method according to Claim 1, wherein said mesh network is an
OTN optical network, and wherein the path identifier is transmitted by
OTN TTI (Trail Trace Identifier).
4. The method according to any one of the preceding claims,
comprising a preliminary step of pre-provisioning, for said data stream, of
working (Wl, W2) and protection paths (PI, P2) and segments thereof in
the network; said pre-provisioning comprises reserving, at a particular
cross-connecting node (X), a specific logical input port (3-2) for a data
stream with a predetermined path identifier (Z), and reserving one25or
more logical output ports for outputting said data stream from one (2-1)
of said one or more logical output ports.

5. The method according to any one of the preceding claims, further
comprising a preliminary step of providing one or more said cross-
connecting nodes (N4, N8) capable of distinguishing one or more
predetermined values (Y, Z) of said path identifier.
5
6. The method according to any one of the preceding claims,
comprising providing internal switching means in said respective one or
more cross-connecting nodes, the switching means being responsive to
predetermined values of the path identifier.
10
7. The method according to any one of the preceding claims, adapted
for performing a shared protection of paths or path segments of the data
streams in the mesh network, the method comprising:
reserving, at a particular cross-connecting node (X), a first logical
input port (1-1) for inputting a first incoming data stream carrying a first
path identifier (Y),
reserving, at the same particular cross-connecting node (X), a
second logical input port (3-2) for transmitting a second incoming data
stream carrying a second path identifier (Z),
reserving, at the same particular cross-connecting node (X), oneoor
more logical output ports (2-1) as a shared output logical port pool for
outputting there-from at least one of said first or second incoming data
streams, whenever required.
8. The method according to any one of Claims 4 to 7, wherein said
logical input/output port (1-1, 3-2, 2-1) of the cross-connecting node (X)
is a combination of two parameters, wherein the first parameter is a
particular physical input/output port of the node, and the second

parameter is a specific time slot or a specific wavelength occupied by the
data stream at the particular physical port.
9. The method according to any one of the preceding claims, further
comprising an additional operation of applying predetermined priorities
to different data streams incoming and/or outgoing the cross-connecting
node.
10. A cross-connecting switch for operating in a node (X, N4, N8) of a
communication circuit switched mesh network supporting data streams
comprising a plurality of data frames each associated with at least one
overhead byte, the switch being capable of performing internal rerouting
of one or more incoming data streams by utilizing path identifiers
(Y,Z,Q) being transmitted by the overhead bytes associated with the data
frames of the respective one or more incoming data streams. 15
11. The cross-connecting switch according to Claim 10, having a first
plurality of input logical ports (1-1, 3-2) and a second plurality of output
logical ports (2-1),
the cross-connecting switch being capable of rerouting a particular
incoming said data stream carrying said path identifier (Y,Z) and arri>2rng
at a specific input logical port, to one logical output port (2-1) selected
from a pool including one or more said output logical ports.
12. The switch according to Claim 10 or 11, having a first plurality of
input logical ports (a,b,c,d,e,f,g) and a second plurality of output logical
ports (k,l,n,m,p), and capable of rerouting at least two said incoming data
streams(Y,Z,) respectively arriving at two or more specific input logical
ports of said switch, to one shared pool of output logical ports, wherein
said pool includes one or more said output logical ports (n).

13. The cross-connecting switch according to Claim 11 or 12,
comprising internal switching means for establishing dynamic internal
connections there-inside, said means being operative to:
assign said pool of output logical ports to one or more said
incoming data streams, 5
identify each of said one or more incoming data streams
based on the path identifiers transmitted by the overhead
bytes of said data frames,
switch the one or more said incoming data streams to
respective vacant output logical ports of said pool. 10
14. The cross-connecting switch according to Claim 13, wherein said
switching means allows assigning priorities to different incoming and/or
outgoing data streams.
15. The cross-connecting switch according to Claim 14, wherein, in
case there are no vacant output logical ports in said pool, the switching
means ensures preempting one or more lower priority traffic streams
using said pool.
16. The cross-connecting switch according to any one of Claims 11 to
15, wherein said logical port (1-1, 3-2, 2-1, 2-2) is either a combination of
a physical port and a time slot occupied by said data stream, a
combination of a physical port and a wavelength occupied by said data
stream.
17. The cross-connecting switch according to any one of Claims 10 to
16, adapted for handling SONET/SDH or OTN data frames and for
checking said path identifier being carried as a path trace identifier in one
of the following overhead bytes: J1, J2, JO, or at OTN layer Trail Trace
Identifier TTI.

18. The cross-connecting switch according to any one of Claims 11 to
17, adapted for monitoring said path identifiers at least at the input logical
ports intended for possibly receiving data streams to be rerouted.
19. The cross-connecting switch according to any one of Claim 13 to
18, designed to allow pre-configuring and re-configuring said internal
switching means for pre-provisioning of working and alternative paths
and/or segments of paths of the data streams.
20. The cross-connecting switch according to Claim 10, capable of
rerouting the data stream to a protection path if indications of fault or loss
of signal are received in respect of that data stream or a link supporting
the data stream.
ECIP/F055/EP

Technology for rerouting a data stream in a communication circuit
switched mesh network comprising one or more cross-connecting nodes,
the data stream comprises a plurality of data frames each associated with
at least one overhead byte, and the rerouting is performed by using a path
identifier while switching the data stream at one or more cross-connecting
nodes; the path identifier is carried by at least one overhead byte
associated with at least one of the data frames.