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AppleTalk API
Service Manual
34 pgs51.31 Kb0

Apple AppleTalk API Service Manual

____________________________________________________________________________ PREFACE ABOUT THIS REFERENCE ____________________________________________________________________________
This reference describes the AppleTalk application programming interface (API) specifications jointly developed by AT&T Computer Systems and Apple Computer, Inc. These API specifications define a standard interface to AppleTalk network protocols for AT&T's UNIX System V Release 4 operating system.
Software developers can create AppleTalk network application programs for UNIX systems that support both these API specifications and AppleTalk. Such applications are readily portable across various UNIX platforms.
APIs implemented according to these specifications provide interfaces to the AppleTalk family of protocols. AT&T's Transport Interface (TLI) provides the interface to the AppleTalk Data Stream Protocol (ADSP) and the Datagram Delivery Protocol (DDP).
ADSP resides in the session layer of the International Standards Organization's (ISO) Open System Interconnection (OSI) reference model. Protocols in the session layer guarantee reliable data delivery. ADSP provides bidirectional, sequential, duplicate-free byte-stream service between any two sockets on an AppleTalk internet. ADSP services allow client processes to establish socket connections, to send and receive data -- either as a continuous stream or as logical messages intelligible by the receiving client -- and to close socket connections. ADSP provides a flow-control mechanism to ensure that transmitted data does not exceed the capacity of the receiving client's buffer.
DDP corresponds to the network layer of the OSI model and provides best­effort data delivery service. DDP is an end-to-end data flow protocol that extends socket-to-socket datagram delivery to an AppleTalk internet consisting of one or more AppleTalk networks connected by routers. A datagram is a packet of data that carries its own routing information. DDP defines logical addresses for sockets on an internet.
The AppleTalk Session Protocol (ASP) resides in the session layer of the OSI model. ASP provides the transport services needed for higher-level interactions between workstations and servers. ASP uses the services of the AppleTalk Transaction Protocol to open, manage, and close sessions; and to sequence requests and replies. ASP services include sending commands to a server and returning replies to a workstation, writing blocks of data to a
server, and retrieving status information from a server. During a session -­that is, when a logical connection exists between a workstation and a server
-- ASP guarantees the delivery and execution of a sequence of transactions in the order sent.
The Name Binding Protocol (NBP) resides in the transport layer of the OSI model. NBP converts user-defined names for zones and devices, or entities, to internet socket addresses that AppleTalk protocols can use. Each node maintains name-to-address mapping for its sockets. NBP uses a names directory to provide services that include name registration, deletion, lookup, and confirmation.
The Printer Access Protocol (PAP) resides in the session layer of the OSI model. PAP manages transactions between workstations and servers -- including setting up, maintaining, and terminating connections; and transferring data. PAP allows multiple connections at both the workstation and the server. PAP uses NBP services to locate addresses and ATP services to transfer data. PAP can determine a server's status and filter duplicate requests.
The Routing Table Maintenance Protocol (RTMP) resides in the transport layer of the OSI model. Internet routers use RTMP to establish and maintain routing tables used in forwarding datagrams from any source socket to any destination socket on an internet. Each router on an internet periodically broadcasts RTMP data packets containing updated routing tables, allowing all other routers on the internet to update their own routing tables.
The Zone Information Protocol (ZIP) resides in the session layer of the OSI model. Routers use ZIP to maintain network-to-zone-name mapping on an internet. ZIP allows a node on an extended network to select its zone at startup. ZIP provides commands that allow nodes on a local area network to obtain zone information. NBP uses ZIP mapping to determine which networks contain nodes that belong to a zone.
What this reference contains This reference consists of three sections, which contain the following
information:
- Section 1, "ADSP TLI Specification," describes the Transport Interface to the AppleTalk Data Stream Protocol.
- Section 3, "AppleTalk Manual Pages," contains all AppleTalk Section 3N (Network Programming) manual pages for UNIX System V Release 4. These manual pages correspond to the following AppleTalk protocols: AppleTalk Session Protocol, AppleTalk Transaction Protocol, Routing Table Maintenance Protocol, Name Binding Protocol, Printer Access Protocol, and Zone Information Protocol.
Conventions used in this reference This reference uses the following typographic conventions to distinguish
elements of the text:
- The names of function calls, parameters, and fields in structures appear in italics in the text of the reference.
- Code samples appear in Courier type -- for example: This is 10-point Courier type.
- The manual pages in Section 3 appear in the standard UNIX man page format. For more information The following documents provide information about either the AppleTalk
network system or the UNIX System V Release 4 operating system:
- AT&T, UNIX System V Release 4 Programmer's Guide: STREAMS. Englewood Cliffs, N.J.: Prentice-Hall, 1990. Provides detailed information about STREAMS.
- Jacobson, Van. "Congestion Avoidance and Control." Proceedings of the ACM, SIGCOM '88, Palo Alto, Calif., August 1988. Describes algorithms developed for the TCP/IP protocol that improve performance over slow or congested data links.
____________________________________________________________________________ SECTION 1: ADSP TLI INTERFACE SPECIFICATION ____________________________________________________________________________
Summary of ADSP data structures This section describes a Transport Interface (TLI) to the AppleTalk Data
Stream Protocol (ADSP) and consists of several subsections:
- "General Concepts" explains STREAMS and TLI concepts relevant to this document.
- "Implementation Issues" describes several important implementation issues.
- "ADSP TLI Library Calls and Parameters" describes each ADSP function call and its parameters.
- "A Client/Server Example" presents a sample client/server program.
- "Summary of ADSP Data Structures" presents ADSP constants and data structures.
Some portions of this document are taken from The External Reference Specification for ADSP 1.5/2.0, version 0.14.
General concepts The services of ADSP map closely to the TLI connection-mode calls. TLI's
Error handling Failures are indicated by a return value of -1. An external integer, t_errno,
holds the specific error numbers. When a function sets t_errno to [TSYSERR] it indicates an operating system error, the specifics about which can be accessed through the external variable errno. When a function sets t_errno to [TLOOK], it indicates that an asynchronous event has happened. The user can call t_look(3N) to determine what event has occured.
Synchronous and asynchronous modes In the synchronous mode, the user has to wait for a specific event to happen
TLI functions supported for ADSP The following TLI functions, which correspond to connection-oriented
services, are supported: t_accept(3N) t_bind(3N) t_close(3N) t_connect(3N) t_listen(3N)
t_look(3N) t_open(3N) t_rcv(3N) t_rcvconnect(3N) t_rcvdis(3N) t_snd(3N) t_snddis(3N) t_unbind(3N) The following general TLI functions are also supported: t_alloc(3N) t_error(3N) t_free(3N) t_getinfo(3N) t_getstate(3N) t_optmgmt(3N) t_sync(3N) The following functions are not supported and upon calling will return -1,
with t_errno set to [TNOTSUPPORT]: t_rcvrel(3N) t_rcvudata(3N) t_rcvuderr(3N) t_sndrel(3N) t_sndudata(3N) Key for parameter arrays For each function, an array is presented that summarizes the content of the
input and output parameters. The key for the parameter arrays is as follows: The parameter value is meaningful. (The input parameter must be set before
the call and the output parameter may be read after the call.) (x) The content of the object to which the x pointer points is
meaningful. The parameter value is meaningful but the parameter is optional.
-- The parameter value is meaningless. The parameter keeps the same value after the call as before the call. Implementation issues Options and management parameters There are two user-selectable options: filter_addr, which supports
Connection-opening filters The ADSP client may need to be selective about establishing connections with
remote clients, because the addresses of some remote clients that make open­connection requests may not be acceptable to the local client. In order to establish a selection criterion, the client can provide ADSP with a filter of valid network addresses with which it is willing to establish connections. This filter could be as simple as specifying "open a connection only with the socket to which you are sending the open-connection request" or "open a connection only with a socket on a particular node." If ADSP receives an open-connection request from an address that does not match the filter, it sends back an open-connection denial and ignores the packet. In the case of a connection-listening socket, the end could conceivably become established with a different network address than the one to which the original open request was sent. The original requester can provide ADSP with a filter of network addresses with which it is willing to establish a connection.
Filter_addr is defined in adsp_opt structure. (See "Summary of ADSP Data Structures" later in Section 1.) It can be set when calling t_connect(3N) or before a t_listen(3N) by calling t_optmgmt(3N). A zero in the network number, node identifier, or socket number of filter_addr means that a connection can be established with any connection end on any network, node, or socket, respectively. Setting filter_addr to be the same as remote address means that a connection will be established only with a connection end on the specified remote address.
System administration parameters There are several parameters tunable by the system administrator. These are:
- Max Receive buffer
- open connection request retries
- initial round-trip time Dynamically set parameters Many of the ADSP variables are dynamically determined based on algorithms
that have been successful in the TCP/IP community. A researcher at the Lawrence Berkeley Labs, Van Jacobson, has done significant work to improve the performance of the TCP/IP protocol over slow or congested data links. Since ADSP is very similar in design to TCP/IP, several of the techniques developed can and will be used for ADSP.
One of the techniques used involves dynamically determining round-trip times between two connection ends, through which ADSP will dynamically determine the values to use for retry intervals.
ADSP TLI protocol address There are two ways to view the TLI protocol address for ADSP. Primitives like
t_bind(3N) and t_connect(3N) accept an NBP entity name (object:type@zone) as their protocol address. The name registration, in t_bind(3N), or name resolution, in t_connect(3N), is done by the transport provider, transparent to the applications. This eliminates the need for NBP primitives in applications. The elimination of NBP primitives and use of the Name-to­Address Mapping provided by System V Release 4 are necessary to allow the development of protocol-independent applications. Since AppleTalk nodes are not required to have network names, NBP entity names are not available in some cases. Sometimes all that is available is the internet socket address. This is the case with t_listen(3N). When a connection request arrives, t_listen(3N) returns the protocol address of the requesting user. All that is available for return is the internet socket address. An application is likely to respond with a t_accept(3N) and use the address returned by t_listen(3N) as the destination address.
The transport provider must be able to distinguish between NBP entity names and internet socket addresses, so that it knows how to process the address field. The convention adopted involves using NULL-terminated strings for NBP entity names and using a leading NULL in the first character position, followed by an at_inet_t structure to identify an internet socket address. The t-bind(3N), t-connect(3N),
t-rcvconnect(3N), and t-listen(3N) calls return an internet socket address. See "Summary of ADSP Data Structures" later in Section 1.
The object and type fields of the NBP entity names cannot contain wildcards. The zone name field may be set to an asterik (*). Using an illegal NBP entity name or a name that cannot be resolved causes t-bind(3N) or t-connect(3N) to return a -1 and set t-errno to [TBADADDR]
Names that are transparently registered with a t_bind(3N) are transparently deregistered with t_unbind(3N) or upon the closing of the corresponding file descriptor.
ADSP features not supported The following ADSP features are outside the scope of TLI and are not
supported:
- connection opening outside of ADSP
- accepting connections on alternate nodes Non-TLI calls In addition to the TLI calls mentioned in "TLI Functions Supported for ADSP"
earlier in Section 1 the following nonstandard call is also supported: adsp_fwdreset(3) ADSP TLI library calls and parameters
Several of the ADSP TLI library function calls are described here. For a more detailed description of these calls refer to the UNIX System V Release 4 Programmer's Guide: Networking Interfaces.
fd = t_open (path, oflag, info) T_open(3N) is called as the first step in the initialization of a transport
endpoint. This function returns various default characteristics of the underlying transport protocol by setting fields in the t_info structure.
The following should be the values returned by the call to t_open(3N) and t_getinfo(3N) with ADSP as the transport provider:
Parameters Before call After call path ADSP_DEV -­oflag x -­info->addr -- 99 info->options -- 64 info->tsdu -- -1 info->etsdu -- 572 info->connect -- -2 info->discon -- -2 info->servtype -- T_COTS The argument path points to the ADSP device identifier, such as, /dev/adsp,
normally extracted from /etc/netconfig (see netconfig(4) and getnetpath(3N)). Oflag may be constructed from O_NDELAY or O_NONBLOCK OR-ed with O_RDWR. T_open returns a file descriptor that identifies the local ADSP endpoint. The default characteristics of ADSP are returned in info. The maximum size of the ADSP address, addr, is 99 bytes. There is no limit to the size of the Transport Service Data Unit (TSDU). The maximum size of the Expedited Transport Service Data Unit (ETSDU), the attention packet, is 572 bytes. The attention packet is composed of 2 bytes of attention code followed by up to 570 bytes of attention data. No data can be sent with connection-request or disconnect calls. The only service type supported is T_COTS, the connection­oriented mode.
t_bind (fd, req, ret) This function associates a protocol address with the transport endpoint
specified by fd and activates that transport endpoint. The transport provider can then begin accepting or requesting connections. The req and ret arguments point to a t_bind structure. Qlen is used to indicate the maximum number of outstanding connection indications.
Parameters Before call After call req->addr.maxlen -- --
req->addr.len x>=0 -­req->addr.buf x(x) -­req->qlen x>=0 -­ret->addr.maxlen x -­ret->addr.len -- x ret->addr.buf x (x) req->qlen -- x>=0 req->addr.buf is a pointer to an NBP name (a NULL-terminated C string). The
transport provider will allocate a dynamic socket and register that name on this socket.
If req is set to NULL or req->addr.len is zero, the transport provider will assign a dynamic socket and return the internet address of this socket in ret->addr.buf in a format described in "ADSP TLI Protocol Address," earlier in Section 1.
t_unbind (fd) This function disables the transport endpoint specified by fd, which was
previously bound by t_bind(3N). On completion of this call, no further data or events destined for this transport endpoint will be accepted by the transport provider.
Parameters Before call After call fd x -­The NBP name that was transparently registered by the transport provider
during t_bind(3N) will be deregistered. t_connect (fd, sndcall, rcvcall) This function enables a user to request a connection to a specified
destination. Fd identifies the local connection endpoint. Sndcall and rcvcall point to a t_call structure.
Parameters Before call After call fd x -­sndcall->addr.maxlen -- -­sndcall->addr.len x>0 -­sndcall->addr.buf x(x) -­sndcall->opt.maxlen -- -­sndcall->opt.len x>0 -­sndcall->opt.buf x(x) --
sndcall->udata.maxlen -- -­sndcall->udata.len 0 -­sndcall->udata.buf -- -­sndcall->sequence -- -­rcvcall->addr.maxlen x -­rcvcall->addr.len -- x rcvcall->addr.buf x (x) rcvcall->opt.maxlen x -­rcvcall->opt.len -- x rcvcall->opt.buf x (x) rcvcall->udata.maxlen -- -­rcvcall->udata.len -- -­rcvcall->udata.buf -- -­rcvcall->sequence -- -­In sndcall, addr specifies the protocol address of the destination transport
In sndcall, opt points to an adsp_opt structure that is used to set ADSP address filters or turn on/off DDP checksum. The user can set the filter_addr field in the adsp_opt to filter connection ends responding to this connection request. A zero in the network number, node identifier, or socket number of filter_addr means that a connection can be established with any connection end on any network, node, or socket, respectively. Setting filter_addr to be the same as remote address means that a connection will be established only with a connection end on the specified remote address.
t_rcvconnect (fd, call) This function enables a user to determine the status of a previously sent
connection request and is used in conjunction with t_connect(3N) to establish a connection in asynchronous mode. The connection will be established on successful completion of this function. Fd identifies the endpoint and call contains information associated with the newly established connection.
Parameters Before call After call fd x -­call->addr.maxlen x --
call->addr.len -- x call->addr.buf x (x) call->opt.maxlen x -­call->opt.len -- x call->opt.buf x (x) call->udata.maxlen 0 -­call->udata.len -- -­call->udata.buf -- -­call->sequence -- -­Since data cannot be sent with a connection request, call->udata.maxlen must
be set to 0 before calling t_rcvconnect(3N). On return, the call->addr structure contains the protocol address of the responding endpoint.
t_optmgmt (fd, req, ret) This function enables a transport user to retrieve, verify, or negotiate
Parameters Before call After call fd x -­req->opt.maxlen -- -­req->opt.len x -­req->opt.buf x(x) -­req->flags x -­ret->opt.maxlen x -­ret->opt.len -- x ret->opt.buf x (x) req->flags -- x The req->opt.buf points to an adsp_opt structure. The user can set the
filter_addr field in the adsp_opt. A zero in the network number, node identifier, or socket number of filter_addr means that a connection can be established with any connection end on any network, node, or socket, respectively. Setting filter_addr to be the same as remote address means that a connection will be established only with a connection end on the specified remote address. The user can also change the default value of checksum.
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