Inside Macintosh: Networking /

Chapter 7 - Datagram Delivery Protocol (DDP)

Summary of DDP

Pascal Summary

Constants

CONST
   {.MPP driver unit and reference numbers}
   mppUnitNum     =        9;                {MPP unit number}
   mppRefNum      =      -10;                {MPP reference number}
   
   {csCodes}
   writeDDP       =      246;                {write out DDP packet, csCode}
   closeSkt       =      247;                {close DDP socket, csCode}
   openSkt        =      248;                {open DDP socket, csCode}

Data Types

The Write-Data Structure

TYPE  WDSElement = 
   RECORD
      entryLength:   Integer;
      entryPtr:      Ptr;
   END;

The Address Block Record

TYPE AddrBlock = 
   PACKED RECORD
      aNet:          Integer;    {network number}
      aNode:         Byte;       {node ID}
      aSocket:       Byte;       {socket number}
   END;

MPP Parameter Block

MPPParmType = (...OpenSktParm,CloseSktParm,WriteDDPParm ...)
TYPE MPPParamBlock = 
   PACKED RECORD
      qLink:               QElemPtr;   {reserved}
      qType:               Integer;    {reserved}
      ioTrap:              Integer;    {reserved}
      ioCmdAddr:           Ptr;        {reserved}
      ioCompletion:        ProcPtr;    {completion routine}
      ioResult:            OSErr;      {result code}
      ioNamePtr:           StringPtr;  {reserved}
      ioVRefNum:           Integer;    {reserved}
      ioRefNum:            Integer;    {driver reference number}
      csCode:              Integer;    {command code}
      CASE MPPParmType OF
         OpenSktParm,
         CloseSktParm,
         WriteDDPParm:
         (
            socket:        Byte;       {socket number}
            checksumFlag:  Byte;       {checksum flag}
            listener:      Ptr;        {For POpenSkt, pointer to socket }
                                       { listener routine. For PWriteDDP, }
                                       { pointer to write-data structure.}
         )
   END;
MPPPBPtr = ^MPPParamBlock;

Routines

Opening and Closing DDP Sockets

FUNCTION POpenSkt(thePBptr: MPPPBPtr; async: Boolean): OSErr;
FUNCTION PCloseSkt (thePBptr: MPPPBPtr; async: Boolean): OSErr;

Sending DDP Datagrams

FUNCTION PWriteDDP (thePBptr: MPPPBPtr; async: Boolean): OSErr;
PROCEDURE BuildDDPwds (wdsPtr,headerPtr,dataPtr: Ptr; 
destAddress: AddrBlock; DDPType: Integer; 
dataLen: Integer);

C Summary

Constants

/*DDP parameter constants*/
#define MPPioCompletion MPP.ioCompletion
#define MPPioResult MPP.ioResult
#define MPPioRefNum MPP.ioRefNum
#define MPPcsCode MPP.csCode
#define DDPsocket DDP.socket
#define DDPchecksumFlag DDP.checksumFlag
#define DDPwdsPointer DDP.DDPptrs.wdsPointer
#define DDPlistener DDP.DDPptrs.listener
/*.MPP driver unit and reference number*/
enum { 
   mppUnitNum     =        9,          /*MPP unit number*/
   mppRefNum      =      -10           /*MPP reference number*/
};

/*DDP csCodes*/
enum {
   writeDDP       =        246,        /*send DDP packet*/
   closeSkt       =        247,        /*close DDP socket*/
   openSkt        =        248         /*open DDP socket*/
};

Data Types

The Write-Data Structure

struct   WDSElement { 
   short    entryLength;
   Ptr      entryPtr;
} WDSElement;

The Address Block Record

struct AddrBlock { 
      short                aNet;                /*network number*/
      unsigned char        aNode;               /*node ID*/
      unsigned char        aSocket;             /*socket number*/
};

typedef struct AddrBlock AddrBlock;

MPP Parameter Block

#define MPPATPHeader\ 
   QElem          *qLink;        /*reserved*/\
   short          qType;         /*reserved*/\
   short          ioTrap;        /*reserved */\
   Ptr            ioCmdAddr;     /*reserved*/\
   ProcPtr        ioCompletion;  /*completion routine*/\
   OSErr          ioResult;      /*result code*/\
   long           ioNameptr;     /*command result (ATP user bytes)*/\
   short          ioVRefNum;     /*request transaction ID*/\
   short          ioRefNum;      /*driver reference number*/\
   short          csCode;        /*command code*/

typedef struct {
   MPPATPHeader 
}MPPparms;

union ParamBlockRec {
   MPPparms    MPP;              /*general MPP parms*/
   DDPparms    DDP;              /*DDP calls*/
};
typedef MPPParamBlock   *MPPPBtr;

typedef struct {
MPPATPHeader 
   char socket;                  /*socket number*/
   char checksumFlag;            /*checksum flag*/
   union {
   Ptr wdsPointer;               /*pointer to write-data structure*/
   Ptr listener;                 /*pointer to write-data structure or */
                                 /* pointer to socket listener*/
} DDPptrs;
}DDPparms;

Routines

Opening and Closing DDP Sockets

pascal OSErr POpenSkt (MPPPBPtr the PBptr, Boolean async);
pascal OSErr PCloseSkt (MPPPBPtr thePBptr, Boolean async); 

Sending DDP Datagrams

pascal OSErr PWriteDDP (MPPPBPtr the PBptr, Boolean async);
pascal void BuildDDPwds(Ptr wdsPtr, header Ptr, Ptr dataPtr, 
const AddrBlock netAddr, short ddpType, 
short dataLen); 

Assembly-Language Summary

Constants

mppUnitNum     EQU      9        ;MPP unit number
;csCodes for DDP
writeDDP       EQU      246      ;write out DDP packet
closeSkt       EQU      247      ;close DDP socket
openSkt        EQU      248      ;open DDP socket
;long DDP packet header
ddpHopCnt      EQU      0        ;hop count (byte)
ddpLength      EQU      0        ;packet length (word)
ddpChecksum    EQU      2        ;checksum (word)
ddpDstNet      EQU      4        ;destination network number (word)
ddpSrcNet      EQU      6        ;source network number (word)
ddpDstNode     EQU      8        ;destination node address (byte)
ddpSrcNode     EQU      9        ;source node address (byte)
ddpDstSkt      EQU      10       ;destination socket number (byte)
ddpSrcSkt      EQU      11       ;source socket number (byte)
ddpType        EQU      12       ;DDP protocol type field (byte)
;short DDP packet header
sddpDstSkt     EQU      2        ;destination socket number (byte)
sddpSrcSkt     EQU      3        ;source socket number (byte)
sddpType       EQU      4        ;DDP protocol type field (byte)
;DDP long header size
ddphSzLong     EQU      13       ;size of extended DDP header

DDP short header size
ddphSzShort    EQU      5        ;size of short DDP header

shortDDP       EQU      $01      ;LAP type code for DDP (short header)
longDDP        EQU      $02      ;LAP type code for DDP (long header)
;DDP miscellaneous
ddpMaxWKS      EQU      $7F      ;highest valid well-known socket
ddpMaxData     EQU      586      ;maximum DDP data size
ddpLenMask     EQU      $03FF    ;mask for DDP length
rhaSize        EQU      $18      ;size of read-header area
toRHA          EQU      1        ;top of the read-header area
wdsEntrySz     EQU      6        ;size of a write-data structure entry
DDPHopsMask    EQU      $3C00    ;mask hop count bits from field in DDP
                                 ; header
;command codes (csCodes)
writeDDP       EQU      246      ;write out DDP packet
closeSkt       EQU      247      ;close DDP socket
openSkt        EQU      248      ;open DDP socket

Data Structures

MPP Parameter Block Common Fields for DDP Routines

0	qLink	long	reserved
4	qType	word	reserved
6	ioTrap	word	reserved
8	ioCmdAddr	long	reserved
12	ioCompletion	long	address of completion routine
16	ioResult	word	result code
18	ioNamePtr	long	reserved
22	ioVRefNum	word	reserved
24	ioRefNum	word	driver reference number

OpenSkt

26	csCode	word	command code; always openSkt
28	socket	byte	socket number
30	listener	long	pointer to socket listener

Parameter Variant

CloseSkt

26	csCode	word	command code; always closeSkt
28	socket	byte	number of socket to be closed

Parameter Variant

WriteDDP

26	csCode	word	command code; always writeDDP
28	socket	byte	number of socket to write from
30	listener	long	pointer to write-data structure

Parameter Variant

Result Codes

noErr	0	No error
ddpSktErr	-91	Bad socket number or socket table is full
ddpLenErr	-92	Datagram data exceeds 586 bytes
noBridgeErr	-93	Could not find router to forward packet