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335 lines
9.6 KiB
335 lines
9.6 KiB
/*++
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Copyright (c) 1996 Microsoft Corporation
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Module Name:
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PROTOCOL.H
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Abstract:
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Another Reliable Protocol - CPP implementation
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Author:
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Aaron Ogus (aarono)
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Environment:
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Win32/COM
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Revision History:
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Date Author Description
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====== ====== ============================================================
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12/10/96 aarono Original
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2/11/97 aarono Removed channel from header, now rides in body of 1st packet.
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along with the length field.
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3/12/97 aarono channel is gone, not relevant to transport protocol, can be
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prepended to messages that want it. Length field is gone,
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not required.
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6/6/98 aarono Turn on throttling and windowing - fix some definitions
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--*/
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#ifndef _PROTOCOL_H_
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#define _PROTOCOL_H_
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#pragma pack(push,1)
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typedef unsigned char byte;
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typedef unsigned short word;
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typedef unsigned int dword;
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//
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// ARP - Another Reliable Protocol - Packet Definitions
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//
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// Terminology
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//
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// message - an arbitrary sized chunk of data
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// to be sent from one computer to a another over
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// the available media.
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//
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// packet - a piece of a message broken down
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// for the media, including protocol information
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// to allow the message to be reconstructed at
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// the other end.
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//
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// frame - an instance of a packet.
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//
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// Assumptions:
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//
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// All values on the wire are little endian.
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//
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// This protocol allows packets to arrive out of
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// order but is optimized for the in-order case.
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//
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#define EXT 0x80 /* EXTENSION BIT */
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#define BIG 0x40 /* BIG HEADERS (FAST MEDIA) */
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#define CMD 0x20 /* COMMAND FRAME */
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#define STA 0x10
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#define EOM 0x08 /* END OF MESSAGE */
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#define SAK 0x04 /* SEND ME AN ACK */
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#define ACK 0x02 /* ACKNOWLEDGE FRAME */
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#define RLY 0x01 /* RELIABLE FRAME */
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// Shifts used in small extended fields.
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#define nNACK_MSK 0x60
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#define nNACK_SHIFT 5
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#define CMD_MSK 0x1F
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#define IDMSK (pCmdInfo->IDMSK)
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#define SEQMSK (pCmdInfo->SEQMSK)
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// Note: abort packets contain serial numbers but no sequence numbers.
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// the nACK field can be used to abort many messages at the same
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// time. (using ABORT2 or ABORT3). Also just the messageid is
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// provided in the abort case.
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typedef struct _Packet1 { // simple small -I- frame
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byte flags;
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byte messageid;
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byte sequence;
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byte serial;
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byte data[0];
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} Packet1, *pPacket1;
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typedef struct _Packet2 { // simple large -I- frame
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byte flags;
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word messageid;
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word sequence;
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byte serial;
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byte data[0];
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} Packet2, *pPacket2;
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typedef struct {
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byte flag1; // header flags
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byte flag2; // extended flags for small hdr/command for lrg
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byte flag3; // nNACK for large hdr.
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byte pad; // make it a dword.
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} FLAGS, *pFLAGS;
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// different frame components that may be part of any
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// frame. type 1 - small frames, type 2 - large frames
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//
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// ACKNOWLEDGE information
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//
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typedef struct _ACK1 {
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byte messageid;
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byte sequence;
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byte serial;
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dword bytes; // bytes received from remote
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dword time; // time when bytes received was this value
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} ACK1, *pACK1;
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typedef struct _ACK2 {
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word messageid;
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word sequence;
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byte serial;
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dword bytes; // bytes received from remote
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dword time; // remote time when bytes receive was this value
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} ACK2, *pACK2;
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//
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// ABORT
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//
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typedef struct _ABT1 {
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byte messageid;
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byte sequence;
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} ABT1, *pABT1;
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typedef struct _ABT2 {
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word messageid;
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word sequence;
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} ABT2, *pABT2;
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//
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// MISSING packet information
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//
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typedef struct _NACK1 {
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byte messageid;
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byte sequence;
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dword bytes; // bytes received from remote
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dword time; // remote time when bytes received was this value
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byte mask[0];
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} NACK1, *pNACK1;
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typedef struct _NACK2 {
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word messageid;
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word sequence;
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dword bytes; // bytes received from remote
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dword time; // remote time when bytes received was this value
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byte mask[0];
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} NACK2, *pNACK2;
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//
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// COMMAND information (including -I- frames)
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//
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typedef struct _CMD1 {
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byte messageid;
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byte sequence;
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byte serial;
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byte data[0];
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} CMD1, *pCMD1;
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typedef struct _CMD2 {
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word messageid;
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word sequence;
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byte serial;
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byte data[0];
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} CMD2, *pCMD2;
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#pragma pack(pop)
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#endif
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/*==============================================================================
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Protocol Operational description
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================================
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Characteristics:
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----------------
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The ARP protocol provides for reliable and non-reliable packet delivery
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over an existing non-reliable (datagram) protocol. It is assumed that
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packet length information and addressing information is carried by the
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datagram protocol and these fields are therefore ambiguous and excluded
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from ARP.
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ARP is optimized to provide a minimum of overhead in the case of low
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bandwidth links. The overhead per-packet is 3 bytes.
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ARP's default command is the delivery of I frames. This avoids the need
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for a command field in the protocol header for the most common frame type.
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ARP does segmentation and reassembly on large datagram messages. This
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allows for datagram delivery of messages larger than 1 packet.
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ARP does a hybrid of windowing with selective NACK of missing packets,
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allowing optimal operation on both good and weak links, regardless
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of latency.
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ARP assigns each frame a serial number that is used in the ACK responses.
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This allows the protocol to keep up to date latency information as well
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as recognize which packet is being responded to in a retry situation.
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The serial number allows the protocol to adjust timeouts reliably.
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ARP allows multiple messages to be sent concurrently. Having multiple
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messages prevents the system from blocking on retry from a single packet
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transmission failure. It also allows better use of available bandwidth
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since the protocol does not wait for the ACK from one message before
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sending the next.
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{FUTURE: What about packet sub-allocation? Bandwidth allocation?}
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Header Description:
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-------------------
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Flags:
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+-----+-----+-----+-----+-----+-----+-----+-----+
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| EXT | BIG | CMD | STA | EOM | SAK | ACK | RLY |
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+-----+-----+-----+-----+-----+-----+-----+-----+
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Extended Flags:
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Small:
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+-----+-----+-----+-----+-----+-----+-----+-----+
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| EXT | nNACK | COMMAND |
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+-----+-----+-----+-----+-----+-----+-----+-----+
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Big:
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+-----+-----------------------------------------+
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| EXT | COMMAND | (only if CMD & BIG set)
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+-----+-----------------------------------------+
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| EXT | nNACK |
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+-----+-----------------------------------------+
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Flags:
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STA - start of a message.
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EOM - this bit is set when the packet is the last packet of a message
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ACK - used to signify that this is an ACK packet, otherwise a COMMAND
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- if nACK != 0, the ACK is informative only. i.e - tells client
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last ACKed frame that instigated the nACK to update latency
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information. An ACK without nACK indicates all frames up
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to the ACK frame were successfully received. Any bit set
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in the nACK mask indicates a missing frame, any 0 bit indicates
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a frame that was successfully received.
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SAK - when this bit is set, the receiver must send an ACK packet
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for this packet.
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RLY - indicates that this message is being delivered reliably.
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BIG - when this bit is set, the packets are in large format TYPE 3.
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CMD - command frame. When this bit is set, the packet contains a
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command. If there is no COMMAND field it is an I frame.
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EXT - when the BIG bit is not set, indicates extended flags are present.
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Extended Flags:
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nNACK - if non-zero indicates presence of nNACK byte masks. The NACK
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field consists of a sequence number followed by nNACK byte masks.
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Each bit in the mask represents a packet after the packet specified
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in the sequence number. The packet in the sequence number is also
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being NACKed.
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Command:
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The command field is used to specify protocol subcommands. The following
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are defined. Commands larger than 15 require BIG packets. Commands that
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require responses include the response in the ACK packet. All protocol
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commands are unreliable. Each command has its own messageid sequence and
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serial. This means commands can be of arbitrary length. The Response
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to a command is also a command.
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0000 0 - Default - I Frame or ACK/NACK (nACK != 0)
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0001 1 - ABORT
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0010 2 - Ping - send packet back to sender.
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0011 3 - Ping Response - a message being returned.
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0100 4 - GetTime - Get the tick count.
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0101 5 - Get Time Response - Response to the Get Time request.
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0110 6 - SetTime - Set the tick count.
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0111 7 - Set Time Response - Response to the Set Time request.
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Rule for processing EXT bits. If a byte in the flags has the high
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bit set, there is one more byte. Ignore any bits beyond what you know
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how to process.
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Sample Packets:
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===============
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Time setting algorithm?
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Bandwidth Calculations?
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Scheduling?
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Window Size?
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Interpacket wait?
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Send Queue Management?
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Command for selective NACK.
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RLY bit separates 2 streams - reliable/datagram. For piggyback
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ACK this means reliable piggyback ACKs are only on reliable streams
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and datagram piggyback ACKs are only on non-reliable streams.
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==============================================================================*/
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#ifdef __DPMESS_INCLUDED__
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#define MAX_SEND_HEADER (sizeof(Packet2)+sizeof(MSG_PROTOCOL))
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// leave space for a 128 bit NACK message, this is the maximum window we ever allow
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#define MAX_SYS_HEADER (sizeof(NACK2)+(128/8)+sizeof(MSG_PROTOCOL))
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#endif
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