Virtual line switching ring

Details Virtual line switching ring Virtual line switching ring

1999-10-19

2003-11-25

Rao, Seema S. (Department: 2666)

Multiplex communications

Fault recovery

C370S228000, C370S907000

Reexamination Certificate

active

06654341

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a method and system for implementing a virtual line-switched ring network; such as a line switched ring network carrying optical signals in accordance with a synchronous optical network (SONET) standard.
SONET networks often have a ring configuration including a collection of nodes forming a closed loop.
FIG. 1
illustrates an example of a conventional SONET bidirectional ring
100
whereby information may flow in either a clockwise or counterclockwise in the figure, as indicated by arrows labeled “working” and “protect”. Add-drop multiplexers (A/D mux)
110
,
120
,
130
and
140
add and/or drop signals to switch data from one span (SP
1
to SP
7
) to another. Ring
100
is thus termed a “bidirectional line switched ring” or BLSR, and data transmitted in such a ring typically must conform to a particular protocol.
As further shown in
FIG. 1
, each of spans SP
1
to SP
7
includes one working line and a corresponding protection line. For example, spans SP
1
and SP
5
interconnect A/D muxes
110
and
120
and include working lines carrying data in opposite directions. The working lines within each of these spans further include respective protection lines for transmitting data in the event the associated working line fails.
The SONET ring provides protection for transmission of data in two way. First if a working lines fails, the corresponding protection lines may be used. In the alternative, if working lines fail between two A/D muxes, any communication route directed through the failed line may be rerouted through the A/D muxes through a process known as span switching. For example, if the working lines between A/D mux
110
and A/D mux
120
fail, instead of using the corresponding protection lines, communications may be sent from A/D mux
110
to A/D mux
120
via A/D mux
140
and
130
.
Typically, the working and protect lines are provided in a fiber optic bundle. Accordingly, if the working line fails, due to a fiber cut, for example, the corresponding protect line often will also fail. Span switching is thus often preferred to simply switching data from the faulty working line to the protect line. Both schemes may be used in conjunction with each other, however, whereby an attempt is first made to use the protect line when the associated working line fails, and then, if the protection line is itself faulty, span switching is used to redirect communications.
The SONET standard has a plurality of optical levels and logical levels that represent the amount of optical information a line is capable of carrying at a given time. These different optical levels are referred to as OC-n, where n is indicative of the bandwidth or capacity associated with the line. Current SONET bidirectional rings require that all spans carry data at the same optical rate because A/D muxes can only direct communications from one line to another having the same OC-n level. Therefore, BLSR requires that all lines in the network are of the same type and that each span between A/D muxes has the same number of lines.
In accordance with the SONET standard, spans transfer units of information called Synchronous Transport Signals (STS). For the different optical carrier levels OC-n (such as OC-1, OC-3 and OC-12), there is a corresponding STS-n, where n is the number of STS-1 segments or time slots. Typical spans are composed of 1, 3, 12, 48, or 192 STS-1's. All SONET spans transmit 8,000 frames per second, where each frame is composed of an integer number of STS-1 segments, such as 1, 3, 12, 48 or 192.
Each STS-1 segment includes a payload section and an overhead section. The overhead includes K-bytes that communicate error conditions between spans in a network and allow for link recovery after network failure. K-byte signaling takes place over the protection lines. In a series of STS segments, only K-bytes from the first STS-1 segment are used to carry error data. Current SONET networks make no use of the framing overhead of the remaining STS-1 segments. The series of STS-1 segments only carries K-byte error information for a single ring.
FIG. 2
illustrates an example of a connection between two rings
200
and
210
using four SONET A/D multiplexors. Specifically, A/D mux
202
of ring
200
is coupled to A/D mux
212
of ring
210
, while A/D mux
206
of ring
200
is coupled to A/D mux
216
of ring
210
. Data is transmitted on these connections at a slower rate than through rings
200
and
210
. Thus, a total of four “matched” A/D mux nodes are often required to connect two rings. Typically, each such pair of A/D muxes is dedicated to providing ring-to-ring connections, and are not configured to pass information around a ring and forward information to another ring at the same time.
In the SONET network ring environment, there currently does not exist a ring configuration that allows for spans within a single ring to have different bandwidth or for a different number of lines to exist between nodes. In addition, no current SONET network ring allows for sharing protection lines between different rings. Finally, current SONET network rings do not allow for connecting rings using a single node.
SUMMARY OF THE INVENTION
Systems and methods consistent with this invention allow for sharing a ring using a single node by using switches at the nodes in place of A/D multiplexors. Systems and methods consistent with this invention allow for sharing a protection line between different rings by utilizing unused overhead in frames sent between switches. Systems and methods consistent with this invention allow for using a different number and type of fibers or lines between switches in the same ring network by using switches and an algorithm to control changing lines in the ring.
Systems and methods consistent with this invention include structure and steps for connecting optical ring networks using a first ring network including a plurality of optical network switches and a second ring network including a plurality of optical network switches. At least one of the optical network switches is a member of both ring networks and passes information between the first and second ring networks.
In another embodiment consistent with the present invention structure and steps are provided that connect two optical ring networks with two switches where a protection line between the two switches is shared by both ring networks.
In another embodiment consistent with the invention, structure and steps are provided that add and/or remove optical carrier lines from a network, where the network includes a plurality of switches having one or more optical carrier lines between each pair of switches. A request for changing a line between two switches is received from a system administrator at one of the switches. The switch determines whether the change results in a total line bandwidth between the two switches in the network. The switch executes the line change when the change results in a total line bandwidth between the two switches being equal to a total line bandwidth between other switches in the network.


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Ching et al, SONET Implementation, IEEE, pp. 34-40, Sep. 1993.

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