TP(4P)

NAME
TP - ISO Transport Protocol

SYNOPSIS
#include <sys/socket.h>
#include <netargo/iso_errno.h>
#include <netargo/tp_param.h>
#include <netargo/tp_user.h>

s = socket( [ AF_INET, AF_ISO ] , SOCK_SEQPACKET, 0);

DESCRIPTION

The ISO Transport Protocol implemented for AOS R2 at the University of Wisconsin - Madison includes classes 0 and 4 of the ISO transport protocols as specified in the September 1984 version of DIS 8073. Class 4 of the protocol provides reliable, sequenced, flow-controlled, two-way transmission of data packets with an alternate stop-and-wait data path called the "expedited data" service. Class 0 is essentially a null transport protocol, which is used when the underlying network service provides reliable, sequenced, flow-controlled, two-way data transmission. Class 0 does not provide the expedited data service. The protocols are implemented as a single transport layer entity that coexists with the Internet protocol suite. Class 0 may be used only in the ISO domain. Class 4 may be used in the Internet domain as well as in the ISO domain.

The user interface to this protocol is the Berkeley interprocess communication interface (see socket(2).) Two new system calls for sending and receiving were added to this interface to to permit the support the end-of-transport-service-data-unit (EOTSDU) indication. See sendv(2) and recvv(2). If the EOTSDU is not needed, the Berkeley 4.3BSD interface can be used. See send(2) and recv(2).

Through the getsockopt and setsockopt system calls, TP supports several options to control such things as negotiable options in the protocol and protocol strategies. The options are defined in <netargo/tp_user.h>, and are described below.

In the tables below, the options marked with a pound sign ( # ) may be used with setsockopt() after a connection is established. Others must be used before the connection is established, in other words, before calling connect() or accept(). All options may be used with getsockopt() before or after a connection is established.

Name
    Value [default]

    Description

TPOPT_MY_TSEL
    1-64 bytes.

    An "extended" transport selector (tsel) for this socket. This option is used to set or get the local tsel. When this option is used to set a tsel, the default the 2-byte tsel that may have been allocated by bind() is retained, but this "extended" tsel is the tsel that is transmitted in a connection request When this option is used to get a tsel, it will return whatever transport tsel exists; if no "extended" tsel was given to this socket, the 2-byte tsel is returned.

TPOPT_PEER_TSEL
    1-64 bytes.

    An "extended" transport selector (tsel) for the peer transport entity. This option is used to get the peer's tsel after a connection is established. When used before a connection is established, this option can set the tsel that will be transmitted as the "called" tsel in a connection request.

TPOPT_PERF_MEAS #
    Boolean.

    When true, performance measurements will be kept for this connection. When set before a connection is established, the active side will use a locally defined parameter on the connect request packet; if the peer is another ARGO implementation, this will cause performance measurement to be turned on on the passive side as well. See tpperf(8).

TPOPT_PSTATISTICS
    No associated value on input. On output, struct tp_pmeas.

    This command is used to read the performance statistics accumulated during a connection's lifetime. It can only be used with getsockopt(). The structure it returns is described in <netargo/tp_stat.h>. See tpperf(8).

TPOPT_FLAGS
    unsigned integer. [ 0x0 ]

    This command can only be used with getsockopt(). See the description of the flags below.

TPOPT_PARAMS
    struct tp_conn_param.

    Used to get or set a group parameters for a connection. The struct tp_conn_param is the argument used with the getsockopt() or setsockopt() system call. It is described in <netargo/tp_user.h>.

The fields of the tp_conn_param structure are described below.

Values for TPOPT_PARAMS:

Field
    Value [default]

    Description

p_Nretrans
    nonzero short integer [ 1 ]

    Number of times a TPDU will be retransmitted before the local TP entity closes a connection.

p_dr_ticks
    nonzero short integer [ various ]

    Number of clock ticks between retransmissions of disconnect request TPDUs.

p_dt_ticks
    nonzero short integer [ various ]

    Number of clock ticks between retransmissions of data TPDUs. This parameter applies only to class 4.

p_cr_ticks
    nonzero short integer [ various ]

    Number of clock ticks between retransmissions of connection request TPDUs.

p_cc_ticks
    nonzero short integer [ various ]

    Number of clock ticks between retransmissions of connection confirm TPDUs. This parameter applies only to class 4.

p_x_ticks
    nonzero short integer [ various ]

    Number of clock ticks between retransmissions of expedited data TPDUs. This parameter applies only to class 4.

p_sendack_ticks
    nonzero short integer [ various ]

    Number of clock ticks that the local TP entity will wait before sending an acknowledgment for normal data (not applicable if the acknowlegement strategy is TPACK_EACH). This parameter applies only to class 4.

p_ref_ticks
    nonzero short integer [ various ]

    Number of clock ticks for which a reference will be considered frozen after the connection to which it applied is closed. This parameter applies to classes 4 and 0 in the ARGO implementation, despite the fact that the frozen reference function is required only for class 4.

p_inact_ticks
    nonzero short integer [ various ]

    Number of clock ticks without an incoming packet from the peer after which TP close the connection. This parameter applies only to class 4.

p_keepalive_ticks
    nonzero short integer [ various ]

    nonzero short integer [ various ] Number of clock ticks between acknowledgments that are sent to keep an inactive connection open (to prevent the peer's inactivity control function from closing the connection). This parameter applies only to class 4.

p_winsize
    short integer between 128 and 16384. [4096 bytes]

    The buffer space limits in bytes for incoming and outgoing data. There is no way to specify different limits for incoming and outgoing paths. The actual window size at any time during the lifetime of a connection is a function of the buffer size limit, the negotiated maximum TPDU size, and the rate at which the user program receives data. This parameter applies only to class 4.

p_tpdusize
    unsigned char between 0x7 and 0xd. [ 0xc for class 4 ] [ 0xb for class 0 ]

    Log 2 of the maximum TPDU size to be negotiated. The TP standard (ISO 8473) gives an upper bound of 0xd for class 4 and 0xb for class 0. The ARGO implementation places upper bounds of 0xc on class 4 and 0xb on class 0.

p_ack_strat
    TPACK_EACH or TPACK_WINDOW. [ TPACK_WINDOW ]

    This parameter applies only to class 4. Two acknowledgment strategies are supported:

    TPACK_EACH means that each data TPDU is acknowledged with an AK TPDU.

    TPACK_WINDOW means that upon receipt of the packet that represents the high edge of the last window advertised, and AK TPDU is generated.

p_rx_strat
    4 bit mask [ TPRX_USE_CW | TPRX_FASTSTART over connectionless network protocols ] [ TPRX_USE_CW over connection-oriented network protocols ]

    This parameter applies only to class 4. The bit mask may include the following values:

    TPRX_EACH: When a retransmission timer expires, retransmit each packet in the send window rather than just the first unacknowledged packet.

    TPRX_USE_CW: Use a "congestion window" strategy borrowed from Van Jacobson's congestion window strategy for TCP. The congestion window size is set to one whenever a retransmission occurs.

    TPRX_FASTSTART: Begin sending the maximum amount of data permitted by the peer (subject to availability). The alternative is to start sending slowly by pretending the peer's window is smaller than it is, and letting it slowly grow up to the real peer's window size. This is to smooth the effect of new connections on a congested network by preventing a transport connection from suddenly overloading the network with a burst of packets. This strategy is also due to Van Jacobson.

p_class
    5 bit mask [ TP_CLASS_4 | TP_CLASS_0 ]

    Bit mask including one or both of the values TP_CLASS_4 and TP_CLASS_0. The higher class indicated is the preferred class. If only one class is indicated, negotiation will not occur during connection establishment.

p_xtd_format
    Boolean. [ false ]

    Boolean indicating that extended format shall be negotiated. This parameter applies only to class 4.

p_xpd_service
    Boolean. [ true ]

    Boolean indicating that the expedited data transport service will be negotiated. This parameter applies only to class 4.

p_use_checksum
    Boolean. [ true ]

    Boolean indicating the use of checksums will be negotiated. This parameter applies only to class 4.

p_use_nxpd
    Reserved for future use.

p_use_rcc
    Reserved for future use.

p_use_efc
    Reserved for future use.

p_no_disc_indications
    Boolean. [ false ]

    Boolean indicating that the local TP entity shall not issue indications (signals) when a TP connection is disconnected.

p_dont_change_params
    Boolean. [ false ]

    If true the TP entity will not override any of the other values given in this structure. If the values cannot be used, the TP entity will drop, disconnect, or refuse to establish the connection to which this structure pertains.

p_netservice
    One of { ISO_CLNS, ISO_CONS, ISO_COSNS, IN_CLNS }. [ ISO_CLNS ]

    Indicates which network service is to be used.

    ISO_CLNS indicates the connectionless network service provided by CLNP (ISO 8473).

    ISO_CONS indicates the connection-oriented network service provided by X.25 (ISO 8208) and ISO 8878.

    ISO_COSNS indicates the connectionless network service running over a connection-oriented subnetwork service : CLNP (ISO 8473) over X.25 (ISO 8208).

    IN_CLNS indicates the DARPA Internet connectionless network service provided by IP (RFC 791).

p_dummy
    Reserved for future use.

The TPOPT_FLAGS option is used for obtaining various boolean-valued options. Its meaning is as follows. The bit numbering used is that of the PC/RT, which means that bit 0 is the most significant bit, while bit 8 is the least significant bit.

Values for TPOPT_FLAGS:

Bits
    Description [Default]

0   TPFLAG_NLQOS_PDN : set when the quality of the network service is similar to that of a public data network.

1   TPFLAG_PEER_ON_SAMENET : set when the peer TP entity is considered to be on the same network as the local TP entity.

2   Not used.

3   TPFLAG_XPD_PRES : set when expedited data are present [ 0 ]

4..7
    Reserved.

LIBRARIES

The new system calls recvv and sendv are supported by a library, libtp.a (rather than a modified C library). Also in this library are new optional interfaces to the connect and accept system calls. See LIBTP(3).

FILES

The following files in have entries necessary for the correct operation of the TP utilities.

	/etc/isodir
	/etc/protocols

The symbolic link is needed for users to write programs using IPC with TP:

	/usr/include/netargo@  ->  /sys/netargo

The following utilities have changed:
	netstat
	ifconfig
	config

The following are new utilities and daemons:
	isoroute
	rlogin.iso, rcp.iso, rsh.iso, isod, rlogind
	tpdiscard
	tpping
	tppt (for maintenance and debugging)
	bark (for maintenance and debugging)
	tpfileget, tpfileput (for debugging)
	tpstat, tpmon
	tpset
	tppkt
	viid

In the kernel source, many files have changed or been added. For a list of these, see the installation guide, "Installing Wisconsin ARGO 1.0 on Academic Operating System 4.3 Release 2".

ERROR VALUES

The TP entity returns errno error values as defined in <sys/errno.h> and <netargo/iso_errno.h>. User programs may print messages associated with these value by using an expanded version of perror() found in the ISO library, libisodir.a.

If the TP entity encounters asynchronous events that will cause a transport connection to be closed, such as timing out while retransmitting a connect request TPDU, or receiving a DR TPDU, the TP entity issues a SIGURG signal, indicating that disconnection has occurred. If the signal is issued during a a system call, the system call may be interrupted, in which case the errno value upon return from the system call is EINTR. If the signal SIGURG is being handled by reading from the socket, and it was a accept() that timed out, the read may result in ENOTSOCK, because the accept() call had not yet returned a legitimate socket descriptor when the signal was handled. ETIMEDOUT (or a some other errno value appropriate to the type of error) is returned if SIGURG is blocked for the duration of the system call. A user program should take one of the following approaches:

Block SIGURG.
    If the program is servicing only one connection, it can block or ignore SIGURG during connection establishment. The advantage of this is that the errno value returned is somewhat meaningful. The disadvantage of this is that if ignored, disconnection and expedited data indications could be missed. For some programs this is not a problem.

Handle SIGURG.
    If the program is servicing more than one connection at a time or expedited data may arrive or both, the program must service SIGURG. It can use the getsockopt(...TPOPT_FLAGS...) system call to see if the signal was due to the arrival of expedited data or due to a disconnection. In the latter case, getsockopt() will return ENOTCONN.

BUGS

When running TP over the token ring, if checksumming is NOT used, the TP entity sents packets to the lan driver faster than the driver can reasonably handle them. A bug in the lan driver causes it to reorder the packets in this situation, causing an overall degradation of TP performance. In general, this is not a problem because very few applications will actually be able to send packets this fast. Nevertheless, in order to prevent this reordering, one may induce a delay in the TP entity by setting the 1-byte value tp_delay to 1 using the debugger. Hit the <pause> key, then type /b tp_delay followed by the <enter key>. The debugger will print the value 00. You then type 1 followed by the <enter key>. Then type end <enter key>. Then type go <enter key>.

SEE ALSO

tcp(4P), sendv(2), recvv(2), libtp(3), isodir(3), isodir(5), netstat(1), iso(4F), clnp(4P), viid(8) tppt(8), tpstat(8), bark(8), tppkt(8), tpset(8), tpperf(8) isoroute(8), ifconfig(8), isod(8), rlogin.iso(1), "Installing Wisconsin ARGO 1.0 on Academic Operating System 4.3 Release 2", "ARGO 1.0 Kernel Programmer's Manual"