Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1999-11-12
2004-04-13
Pham, Chi (Department: 2667)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S389000, C370S392000, C370S474000
Reexamination Certificate
active
06721335
ABSTRACT:
FIELD OF THE INVENTION
This invention generally deals with increasing the efficiency of message communications occurring at high volume and high speed among nodes in a network, in which the nodes may be central electronic computer complexes (CECs). The invention segments the transmission of packets in messages, wherein each segment is transmitted as high speed bursts of digital packets on a link in a network. This invention can significantly enable a communication cache to reduce castout thrashing in port packet control caches. In networks containing a common link switch to enable single port per node operation, this invention can increase overall network communication speed by maintaining transmitted segments within a network link switch, which is lost in conventional network link switches due to their failure to maintain segment contiguity when forwarding switch received packets to destination nodes.
INCORPORATION BY REFERENCE
Incorporated by reference herein is the entire specification, including all text disclosure and all drawings, having USPTO Ser. No. 09/439,011 filed on the same day as the present application and entitled “Segment-Controlled Process for Controlling Castouts from a Communication Cache in a Port in any of Multiple Nodes in a Communications Network” by the inventor of the present application.
BACKGROUND OF THE INVENTION
Communication networks contain N number of nodes in which each node may be a computer system, often called a Central Electronic Complex (CEC). Messages are communicated on links between the nodes of the network, and any node in the network may both send and receive messages. A node may be considered a message sender when it generates and sends a message, generally starting with a command. A node may be considered a message receiver if it receives the message. The command part of a message is followed by a response part of the message for informing the message sender of the status of the message received at the message receiver. A data part of the message is optional, and the data part may be included between the command part and the response part. The data part may be read data or write data, which are transmitted in either direction between the message sender and message receiver.
Each message is transmitted as a sequence of packets on one or more links connected between the message sender and message receiver in the network. Each packet header contains a source node ID and a destination node ID. Generally, each message starts with one or more command packets, which travel on the links in the direction from the message sender (generating the message) to the message receiver (receiving the message). After the command part of the message is transmitted, it is followed with any optionally data part of the message as a sequence of one or more data packets, which may travel in either direction on the network links according to whether “read” data or “write” data is indicated in the command part of the message. “Write data” travels from the message sender (commanding node) to the message receiver (commanded node). “Read data” travels in the opposite direction from the message receiver to the message sender. The message ends when its response part is sent by the message receiver to the message sender. The response part of the message follows any optional data part of the message, but the response part follows the command part if the message has no data part. Thus, the response part is transmitted on the links in the opposite direction from the command part.
A link switch may or may not be used in a network to connect the nodes in a network. A link switch may contain a plurality of switch receivers and switch transmitters, which may be respectively connected to bi-directional communication links to/from the nodes in the network, such as when a respective switch receiver and switch transmitter pair are connected to the link to one of the nodes in the network. Each of the receiver/transmitter pairs may be permanently assigned to a link connected node, the receiver receiving packets from the node when the node is acting as a source node and the transmitter sending packets to the node when the node is acting as a destination node. Each node has a unique identifier (ID) in the network, and each packet has a header containing the source node ID (source ID) and destination node ID (destination ID) of its message.
In a network switch, each of a plurality of switch receivers may be concurrently receiving packets from different source nodes, and each of the switch transmitters may be concurrently sending packets to different destination nodes. Thus, each receiver then always receives packets from same source node (to which it is connected), so that all packets received by each receiver have the same source ID, but may have different destination node IDs.
Further, each transmitter in the switch searches the headers of newly received packets at all of the switch receivers looking for a packet header having a destination ID matching the destination ID assigned to the respective transmitter. Then the packet is forwarded from the receiver to the transmitter having the destination ID in a received packet, and the transmitter sends the packet from the switch to the identified destination node.
During a receiver search, a transmitter may find multiple concurrently received packets at different receivers matching the transmitter's assigned destination ID, in which all such concurrently received packets have different source IDs, but all have the same destination ID which identifies the node connected to the transmitter. The transmitter may use a packet priority control to determine which of these concurrently received packets from different nodes should be selected next and sent to the transmitter's assigned destination node. Generally in the prior art, the switch priority control uses a round-robin selection among the receivers having concurrently received packets, so that the concurrent received packets are sequentially sent by the transmitter to its connected destination node, which at the destination node interleaves this sequence of link-communicated packets into different messages from different source nodes.
When sequences of packets are provided to a link, they comprise a burst of signals. If these packets are received by a network link switch, the speed of the packets in a given message may be slowed by the priority controls in the internal operations in prior art switches, because of the internal priority schemes used in the switches. This signal slow-down may be caused by a “fairness” priority protocol often used in link switches to select among concurrently received packets for transmission to the packet's indicated destination node. Generally, the prior art “fairness” priority selects for next transmission to an assigned destination node, either: the oldest waiting packet currently received by the switch, or the it may poll the receivers in the switch in a predetermined order (such as “round-robin”) and select the first receiver found to have a waiting packet.
These prior types of “fairness” prioritization's schemes in a link switch tend to lose the transmission continuity of fast transmitted bursts of packets. A sequence of packets may be considered a burst when they are transmitted very fast on a link without any significant pause occurring between the packets in a burst. A loss in packet transmission continuity within a burst (such as due to packet interleaving by switch prioritization) may result in a slow-down in the ultimate speed of packet communication seen by the destination nodes. This slow-down therefore may be caused by the prior art “fairness” prioritization selection process in the prior art when it selects for next transmission by a transmitter the longest waiting packet in another message to the same destination node, or selects the next transmitted packet by a round-robin selection among the receivers.
Hence, while the prior art “fairness” prioritization schemes may appear to be the desirable thing to do, they have
Goldman Bernard M.
Gonzalez Floyd A.
International Business Machines - Corporation
Pham Chi
Qureshi Afsar M.
LandOfFree
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