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/* PSTNFram.h
* * Copyright (c) 1993-1995 by DataBeam Corporation, Lexington, KY * * Abstract: * This function encodes and decodes functions according to the encoding * rules set by the T.123 communications standard for PSTN. The standard * states that a flag will precede each packet and a flag will be appended * to the end of each packet. Therefore no flags are permitted in the body * of the packet. Flags are replaced by an ESCAPE sequence. If an ESCAPE * byte is found in a packet, remove the ESCAPE, and negate the 6th bit of * the next byte. * * Caveats: * None * * Authors: * James W. Lawwill */
#ifndef _PSTN_FRAME_H_
#define _PSTN_FRAME_H_
#include "framer.h"
/*
** Commonly used definitions */#define FLAG 0x7e
#define ESCAPE 0x7d
#define COMPLEMENT_BIT 0x20
#define NEGATE_COMPLEMENT_BIT 0xdf
class PSTNFrame : public PacketFrame{public:
PSTNFrame(void); virtual ~PSTNFrame(void);
PacketFrameError PacketEncode ( PUChar source_address, UShort source_length, PUChar dest_address, UShort dest_length, DBBoolean prepend_flag, DBBoolean append_flag, PUShort packet_size); PacketFrameError PacketDecode ( PUChar source_address, UShort source_length, PUChar dest_address, UShort dest_length, PUShort bytes_accepted, PUShort packet_size, DBBoolean continue_packet); Void GetOverhead ( UShort original_packet_size, PUShort max_packet_size);
private: PUChar Source_Address; UShort Source_Length;
PUChar Dest_Address; UShort Dest_Length;
UShort Source_Byte_Count; UShort Dest_Byte_Count;
DBBoolean Escape_Found; DBBoolean First_Flag_Found;};typedef PSTNFrame * PPSTNFrame;
#endif
/*
* PSTNFrame::PSTNFrame ( * Void); * * Functional Description * This is the constructor for the PSTNFrame class. It initializes all * internal variables. * * Formal Parameters * None. * * Return Value * None * * Side Effects * None * * Caveats * None */
/*
* PSTNFrame::~PSTNFrame ( * Void); * * Functional Description * This is the destructor for the PSTNFrame class. It does nothing * * Formal Parameters * None. * * Return Value * None * * Side Effects * None * * Caveats * None */
/*
* PacketFrameError PSTNFrame::PacketEncode ( * PUChar source_address, * UShort source_length, * PUChar dest_address, * UShort dest_length, * DBBoolean prepend_flag, * DBBoolean append_flag, * PUShort packet_size); * * * Functional Description * This function encodes the passed in buffer to meet the T.123 standard. * * Formal Parameters * source_address (i) - Address of the buffer to encode * source_length (i) - Length of the buffer to encode * dest_address (i) - Address of the destination buffer * dest_length (i) - Length of the destination buffer * prepend_flag (i) - DBBoolean that tells us whether or not to put * a flag at the beginning of the packet * append_flag (i) - DBBoolean that tells us whether or not to put * a flag at the end of the packet * packet_size (o) - We return this to the user to tell them the new * size of the packet * * Return Value * PACKET_FRAME_NO_ERROR - No error occured * PACKET_FRAME_DEST_BUFFER_TOO_SMALL - The destination buffer passed * in was too small * * Side Effects * None * * Caveats * None */
/*
* PacketFrameError PSTNFrame::PacketDecode ( * PUChar source_address, * UShort source_length, * PUChar dest_address, * UShort dest_length, * PUShort bytes_accepted, * PUShort packet_size, * DBBoolean continue_packet); * * Functional Description * This function takes the input data and decodes it, looking for a * T123 packet. The user may have to call this function many times * before a packet is pieced together. If the user calls this function * and and sets either soure_address or dest_address to NULL, it uses * the addresses passed in, the last time this function was called. If * there is one source buffer to decode, the user can pass that address * in the first time and continue calling the function with NULL as the * source address until the buffer is exhausted. The user will know the * buffer is exhausted when the return code is simply PACKET_FRAME_NO_ERROR * rather than PACKET_FRAME_PACKET_DECODED. * * Formal Parameters * source_address (i) - Address of the buffer to decode * source_length (i) - Length of the buffer to decode * dest_address (i) - Address of the destination buffer * dest_length (i) - Length of the destination buffer * bytes_accepted (o) - We return the number of source bytes processed * packet_size (o) - We return the size of the packet. This is only * valid if the return code is * PACKET_FRAME_PACKET_DECODED. * continue_packet (i) - DBBoolean, tells us if we should start by * looking for the first flag. If the user wants * to abort the current search, use this flag. * * Return Value * PACKET_FRAME_NO_ERROR - No error occured, source buffer * exhausted * PACKET_FRAME_DEST_BUFFER_TOO_SMALL - The destination buffer passed * in was too small * PACKET_FRAME_PACKET_DECODED - Decoding stopped, packet decoded * * Side Effects * None * * Caveats * None */
/*
* Void PSTNFrame::GetOverhead ( * UShort original_packet_size, * PUShort max_packet_size); * * Functional Description * This function takes the original packet size and returns the maximum * size of the packet after it has been encoded. Worst case will be * twice as big as it was with two flags. * * Formal Parameters * original_packet_size (i) - Self-explanatory * max_packet_size (o) - Worst case size of the packet * * Return Value * None * * Side Effects * None * * Caveats * None */
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