SPP(4P) SPP(4P) NAME spp - Xerox Sequenced Packet Protocol SYNOPSIS #include #include s = socket(AF_NS, SOCK_STREAM, 0); #include s = socket(AF_NS, SOCK_SEQPACKET, 0); DESCRIPTION The SPP protocol provides reliable, flow-controlled, two-way transmis‐ sion of data. It is a byte-stream protocol used to support the SOCK_STREAM abstraction. SPP uses the standard NS(tm) address formats. Sockets utilizing the SPP protocol are either “active” or “passive”. Active sockets initiate connections to passive sockets. By default SPP sockets are created active; to create a passive socket the _l_i_s_t_e_n(2) system call must be used after binding the socket with the _b_i_n_d(2) sys‐ tem call. Only passive sockets may use the _a_c_c_e_p_t(2) call to accept incoming connections. Only active sockets may use the _c_o_n_n_e_c_t(2) call to initiate connections. Passive sockets may “underspecify” their location to match incoming connection requests from multiple networks. This technique, termed “wildcard addressing”, allows a single server to provide service to clients on multiple networks. To create a socket which listens on all networks, the NS address of all zeroes must be bound. The SPP port may still be specified at this time; if the port is not specified the sys‐ tem will assign one. Once a connection has been established the socket’s address is fixed by the peer entity’s location. The address assigned the socket is the address associated with the network inter‐ face through which packets are being transmitted and received. Nor‐ mally this address corresponds to the peer entity’s network. If the SOCK_SEQPACKET socket type is specified, each packet received has the actual 12 byte sequenced packet header left for the user to inspect: struct sphdr { u_char sp_cc; /* _c_o_n_n_e_c_t_i_o_n _c_o_n_t_r_o_l */ #define SP_EM 0x10 /* _e_n_d _o_f _m_e_s_s_a_g_e */ u_char sp_dt; /* _d_a_t_a_s_t_r_e_a_m _t_y_p_e */ u_short sp_sid; u_short sp_did; u_short sp_seq; u_short sp_ack; u_short sp_alo; }; This facilitates the implementation of higher level Xerox protocols which make use of the data stream type field and the end of message bit. Conversely, the user is required to supply a 12 byte header, the only part of which inspected is the data stream type and end of message fields. For either socket type, packets received with the Attention bit sent are interpreted as out of band data. Data sent with send(..., ..., ..., MSG_OOB) cause the attention bit to be set. DIAGNOSTICS A socket operation may fail with one of the following errors returned: [EISCONN] when trying to establish a connection on a socket which already has one; [ENOBUFS] when the system runs out of memory for an internal data structure; [ETIMEDOUT] when a connection was dropped due to excessive retransmissions; [ECONNRESET] when the remote peer forces the connection to be closed; [ECONNREFUSED] when the remote peer actively refuses connection establishment (usually because no process is lis‐ tening to the port); [EADDRINUSE] when an attempt is made to create a socket with a port which has already been allocated; [EADDRNOTAVAIL] when an attempt is made to create a socket with a network address for which no network interface exists. SOCKET OPTIONS SO_DEFAULT_HEADERS when set, this determines the data stream type and whether the end of message bit is to be set on every ensuing packet. SO_MTU This specifies the maximum ammount of user data in a single packet. The default is 576 bytes - sizeof(struct spidp). This quantity affects win‐ dowing -- increasing it without increasing the amount of buffering in the socket will lower the number of unread packets accepted. Anything larger than the default will not be forwarded by a bona fide XEROX product internetwork router. The data argument for the setsockopt call must be an unsigned short. SEE ALSO intro(4N), ns(4F) BUGS There should be some way to reflect record boundaries in a stream. For stream mode, there should be an option to get the data stream type of the record the user process is about to receive. 4.3 Berkeley Distribution July 30, 1985 SPP(4P)