US 6222848 Gigabit ethernet interface to synchronous optical network (SONET) ring
ABSTRACT – A method and apparatus for routing data packets via a synchronous optical (SONET) network from devices connected to a local area network to devices connected to other local area networks. At each transport node in the SONET network the data packets are unloaded from SONET payloads and requeued for transmission on an output path. This allows for easy resolution of contention between devices transmitting at the same time and avoids pre-assigning SONET channels. Source and destination address information from the data packets can be used to route the data packets through the SONET network. A time-to-live indicator can be used to find the shortest path to a destination address in a SONET ring network or any bidirectional ring network.
FIELD OF INVENTION
This invention is concerned with an apparatus and method by which packetized data from a local area network can be transmitted over a synchronous optical (SONET) network. This invention is also concerned with a method for selecting the shortest path to a destination address in a bidirectional ring network.
BACKGROUND OF THE INVENTION
Local area networks, or LANS, are used to transmit packetized data. One type of LAN is known as the Ethernet which conforms to a family of IEEE standards, IEEE 802.3. Although Ethernet LANs have been produced for over 20 years, recent technological advances have increased the speed at which devices connected to the ethernet LAN can transmit and receive data. In IEEE draft standard 802.3z an Ethernet LAN capable of gigabit per second transmission rates is proposed. However, one limitation of current ethernet LANs is that they must limit the distance between devices to about 2 km, in order to allow their carrier-sense multiple-access collision-detection (CSMA/CD) contention management systems to function effectively. A description of local area networks is found in the textbook Basic Data Communications: A Comprehensive Overview by W. J. Beyda which is hereby incorporated by reference for all purposes.
Data transmitted over a LAN is packetized or subdivided into a stream of segments of varying length. Packet flow is often described as “bursty”. Packets may flow intensely between two devices connected to the LAN and then flow may suddenly drop to zero. When packets flow intensely from a number of different devices simultaneously, contention problems may arise and it is necessary to share the bandwidth on the LAN between contending devices.
It would be desirable for devices connected to an ethernet LAN to be able to transmit data to or receive data from devices connected to separate ethernet LANS. In this regard, it is known to use expensive special purpose wide area network (WAN) routers interposed between LANs.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and apparatus by which devices connected to a local area network can send packetized data through a SONET network to devices connected to other local area networks.
It is a further object of the present invention to allow the capacity on SONET payloads between specified transport nodes to remain unassigned if the capacity is not needed for carrying data packets between those transport nodes.
It is another object of the present invention to rationally share bandwidth dynamically on a SONET network between contending packetized devices.
It is another object of the present invention to provide a method to find the shortest route to a destination address on a bi-directional ring network.
In one aspect there is provided a method for routing data packets at a transport node of a SONET network comprising: receiving SONET payloads having data packet at said transport node; removing said data packets from said SONET payloads; for each data packet of said data packets: determining a destination address; determining if an entry exists in a table associated with said transport node matching said destination address; and if a matching entry does not exist, queuing said each data packet on a first queue for a first output path and a copy of said each data packet on a second queue for a second output path; transmitting selected data packets from said first queue onto said first output path; and transmitting selected data packets from said second queue onto said second output path.
another aspect, there is provided a method for routing data packets at a transport node of a SONET network comprising: receiving SONET payloads having data packets at said transport node; removing said data packets from said SONET payloads; for each data packet of said data packets: determining whether a current time-to-live “TTL” indicator having a current value has been appended to said each data packet; if said current TTL indicator has been appended to said each data packet, adjusting said current value of said current TTL indicator and where any said current value bears a pre-defined relationship to a threshold, outputting said each data packet.
Apparatus is also provided to achieve these methods.