Brocade Communications Systems, Inc.

Andy Dooley

Isaac Larson

Siva Adiraju

Ryan Hegland

Maulik Patel

Amr Sabaa

Poulo Kuriakose

Hiren Desai

Amar Vutukuru

The SACK scoreboard is used in slow recovery and the SACK scoreboard and an application programmed timeout are used to determine the initial CWND in slow recovery. The CWND is calculated so that all packets will be recovered before the application times out. A new socket option is provided for an application to program an application timeout (say APP_TO). This value is used in conjunction with the RTT (round trip time) to determine the initial CWND value to insure completion before timeout. Along with the timeout, the application can also set the mode as 'soft,' where the CWND value is set to '1' as conventional but when that packet is ACKed, the CWND value is increased immediately to a modified calculated value to allow timely recovery.

Application timeout aware TCP loss recovery

In a network where there are two local area networks (LANs) connected over a wide area network (WAN) by paralleled LAN to WAN devices at each end of the WAN, Transmission Control Protocol (TCP) connections may be requested by a first near end LAN to WAN device and received at a first far end LAN to WAN device but the acknowledgement may be returned to a second far end LAN to WAN device. The second far end LAN to WAN device contacts the first far end LAN to WAN device and the TCP connection is moved to the second far end LAN to WAN device, which provides the acknowledgement to the first near end LAN to WAN device to complete the TCP connection. Similar operations occur during active TCP connection operation but with certain queued data being flushed during the TCP connection transfer.

TCP connection relocation

After sending M consecutive DUP ACKs, M generally being three, the TCP receiver generates DUP ACKs every N packets, with N greater than one, with the eventually transmitted DUP ACK containing SACK information. After receiving the third DUP ACK the TCP transmitter uses the positive acknowledgements provided in the SACK information in the TCP header to inflate the congestion window. With the reduced DUP ACKs from the TCP receiver to the TCP transmitter, the impact of TCP DUP ACKs on the data rate from the TCP receiver to the TCP transmitter is substantially reduced.

Bandwidth optimization using coalesced DUP ACKs

A system and method for sharing a WAN TCP tunnel between multiple flows without having head of the line blocking problem is disclosed. When a complete but out of order PDU is stuck behind an incomplete PDU in a TCP tunnel, the complete but out of order PDU is removed from the tunnel. To do that, first the boundaries of the PDUs of the different flows are preserved and the TCP receive window advertisement is increased. The receive window is opened when initially receiving out-of-order data. As out-of-order complete PDUs are pulled out of the receive queue, to address double counting, place holders are used in the receive queue to indicate data that was in the queue. As out-of-order data PDUs are pulled out of the queue the window advertisement is increased. This keeps the sending side from running out of TX window and stopping transmission of new data.

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Rogers, MN, United States of America

Andy Dooley