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TPDUTransport Protocol Data Unit
TPDUTerminal Power Distribution Unit
TPDUTranscranial Pulsed Doppler Ultrasound
TPDUTropical Parasitic Diseases Unit (Northwick Park Institute for Medical Research; UK)
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A third approach requires a minimum amount of time before a connection between the same two transport entities can be reestablished, and enforces a maximum lifetime of any TPDU to be less than that minimum.
A TPDU may be acknowledged without granting the transport sender additional credit to send new TPDUs, and additional credit can be given without acknowledging a TPDU.
The silly window syndrome can start either because the transport receiver advertises a very small window, or the transport sender sends a very small TPDU. Clark [1982] describes how this can degenerate into a vicious cycle where the average TPDU size ends up being much smaller than the optimal case, and throughput suffers as a result.
When the network layer provides no support for explicit access control, the transport protocol may operate on the assumption that any TPDU loss indicates network congestion -- a reasonable assumption when the underlying network links are highly reliable.
Blocking combines several TSDUs into a single TPDU (see Figure 7(a)), thereby reducing the number of transport layer encapsulations and the number of NSDUs submitted to the network layer.
Sender-independent N/A Sender-independent Error Control Error detection Sequence no; Optional Checksum on checksum on header and header and data data Error reporting No No Error recovery PAR No Flow/Congestion Control End-to-end flow control Window No Window allocation Byte-oriented N/A Rate control parameters N/A N/A Congestion control Implicit No access control TPDU Format TPDU numbering Byte-oriented No Min TPDU header/trailer 20-byte header 8-byte header Multiplexing/Demultiplexing Yes Yes Splitting/Recombining No No Concatenation/Separation Yes(7) No Blocking/Deblocking Yes(8) No Segmentation/Reassembly Yes No Protocol Features TP4 (OSI) TP0 (OSI) CO vs CL Protocol CO CO Transaction-oriented No No CO Protocol In-band vs.
(2) While data may be sent in TCP connection opening TPDU, it cannot be delivered to user receiver until 3-way-handshake is complete.
(7) Data and ACK TPDU is concatenated in the case of piggybacking.
N/A(4) Sender-independent Error control Error detection No(7) Sequence No Error reporting No(7) Error recovery No(7) PAR Flow/Congestion control End-to-end flow control N/A9 Window Window scheme N/A(9) TPDU(segment) -oriented Rate control parameters N/A(9) N/A Congestion control N/A(9) Explicit access control TPDU format TPDU numbering TPDU-oriented TPDU-oriented Min TPDU header/trailer 9-byte header Multiplexing/Demultiplexing No No Splitting/Recombining No No Concatenation/Separation No Yes(11) Blocking/Deblocking No No Segmentation/Reassembly Yes Yes Protocol Features XTP SSCOP/AAL5 (ATM) CO vs.
Connection is established via a 2-way-handshake during which buffer, TPDU and burst sizes are negotiated.
First, after an initial transaction is handled using a 3-way-handshake connection, subsequent transactions streamline connection establishment through the use of a 32-bit incarnation number, called a "connection count" (CC) carried in each TPDU. T/TCP uses the monotonically increasing CC values in initial CR-TPDUs to bypass the 3-way-handshake, using a mechanism called TCP Accelerated Open.
Originally XTP was designed to be implemented in VLSI; hence it has a 64-bit alignment, a fixed-size header, and fields likely to control a TPDU's initial processing located early in the header.