The present invention relates to network communications, and in particular, to methods and systems for bandwidth reservation in communications networks.
A conventional telecommunication network comprises a plurality of devices represented by “nodes” and a plurality of configurable communication links for communicating data (e.g., communication messages) among the nodes.
Networks may be configured according to any one of various types of network topologies. The multi-hop (or “mesh”) network is one topology that has gained keen interest in the last several years. One reason for the heightened interest relates to the recent introduction of WiMAX (Worldwide Interoperability for Microwave Access). WiMAX is a wireless technology based on the IEEE 802.16 standard that contemplates use of mesh networks to provide last-mile wireless broadband access as an alternative to cable and DSL.
A major challenge in implementing a mesh network involves managing and controlling traffic through the network. The network must be capable of determining the best path between source and destination nodes; must be able to simultaneously handle multiple messages; and must be capable of coordinating traffic flow in situations where a node must lend itself as a hop point for multiple messages carried along different paths of the network. Because the transmission capacity between link nodes is finite, bandwidth reservation schemes must be used to ensure that bandwidth is fairly distributed and that all messages are properly communicated from their respective sources to their intended destinations.
One bandwidth reservation technique used in conventional mesh networks that employ time-division multiplexing (TDM) is to typically perform a Layer 3 packet flow on a link-by-link basis. Master nodes along an end-to-end path between a source and destination node allocate bandwidth by reserving time slots in a fixed manner, one link after another along the path.
As used in
Unfortunately, particularly when the network is large, success in achieving an end-to-end allocation is not fully guaranteed. When a bandwidth allocation is insufficient to allow a message to be communicated end-to-end, all fixed allocations made prior to the failure point must be released, for example, by sending an allocation release message to master nodes controlling the bandwidth allocation along the path. Before the fixed allocations can be released, however, there is a high probability that other nodes (e.g., nodes S3 and S6 in
The hole may be purged by moving it to the tail of the allocations, as shown in
It would be desirable, therefore, to have a system and method for allocating bandwidth in mesh networks, and other types of networks, which avoids the need for processing resources to purge allocated but unused bandwidth reservations.
Methods and systems for reserving bandwidth in communications networks (e.g., time-division multiplexed (TDM) networks) are disclosed. According to an exemplary aspect of the invention, a bandwidth request on a forward path of a communications network is temporarily held without any fixed slot timings. The bandwidth request is held for a time long enough for the request to travel the forward path end-to-end. Once the request reaches the destination of the forward path, the temporary bandwidth is confirmed by sending a bandwidth confirmation message back from destination to the source of the path. Each slave node along the path performs an allocation confirm with its associated master node, which responds by converting the temporary holds to full allocations by fixing slot timings.
Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to accompanying drawings, in which like reference numbers are used to indicate identical or functionally similar elements.
Referring first to
As used in
The bandwidth reservation scheme described in
Referring now to
In
As steps 602-606 of the method 600 are being performed, and up until the time the bandwidth allocation is finally released, newer bandwidth times may have been allocated to other stations, e.g., stations S3 and S6 in
After the bandwidth reservations are confirmed to time slots according to one of the techniques described above, for example, the wireless system may have to adapt to link variations (e.g., signal quality variations), by reducing the rate during times when the signal quality degrades and increasing the rate when the signal quality improves. Because transmit time is inversely proportional to the transmit rate, the time slots have to be constantly readjusted according to the rate changes.
As used in
Instead of moving the “bubble in” and “bubble out” in stages, as described above, the following process may be performed, according to an embodiment of the present invention. When a slave node (e.g., station S5) requests a master node in its cluster to adjust its bandwidth (i.e., increase or decrease), the cluster master node broadcasts a cluster-wide bandwidth adjustment announcement to all slave nodes that will be immediately affected by the adjustment (in this example stations S3 and S6). The announcement may be broadcast more than once to ensure that the affected nodes receive the announcement. According to an exemplary embodiment, the announcement is sent two times. Each slave node is required to receive only one announcement out of 2N announcements made (N represents the number of slave nodes immediately affected by the adjustment (e.g., stations S3 and S6 in the above example).
The affected slave nodes respond to the bandwidth adjustment announcement by sending a bandwidth adjustment request acknowledgment signal back to the master node. After receiving the acknowledgment signals from the slave nodes, the cluster master node sends a positive acknowledgment signal to the slave node which requested the bandwidth adjustment, and to notify the slave node of the created hole next to its slot allocation (as in
While the bandwidth adjustment process can be performed in various ways, according to one embodiment of the invention, a two-stage countdown process is employed. The first countdown stage is employed to allow time for the slave nodes affected by the bandwidth adjustment request to become aware of the bandwidth being adjusted and send bandwidth adjust acknowledgment signals back to the cluster master node. According to one aspect of the invention, each of the slave nodes starts a countdown on its own, based on the beacon periods (as each announcement takes exactly one beacon period), and positive acknowledgment signals in the form of a checksum of the message are sent back to the master nodes as a validation token. If the master node does not receive acknowledgments from all affected slave nodes at the expiration of the first countdown period, the first countdown may be repeated a predetermined number of additional times. If after the predetermined number of additional attempts the master node has still not received all of the acknowledgment signals, a negative acknowledge signal is sent to the slave node that requested the bandwidth adjustment and the connection(s) for the non-responding slave node(s) is/are terminated.
The second countdown stage commences after the master node receives all of the acknowledgment signals. At the end of the second countdown, the master node instructs the slave nodes to adjust their slot timings all at once.
While the above is a complete description of the preferred embodiments of the invention sufficiently detailed to enable those skilled in the art to build and implement the system, it should be understood that various additions, modifications, and equivalents may be made to the invention without departing from the spirit and scope of the invention, which is defined by the appended claims. For example, while the exemplary embodiments described herein are applicable to mesh networks, they are also applicable to other communication network topologies requiring bandwidth reservation techniques. Further, whereas the exemplary embodiments are well suited to wireless networks, the inventions embodied by the exemplary embodiments are also applicable to wired networks. Accordingly, for these and other reasons, various modifications or changes to the specifically disclosed exemplary embodiments will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims.
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