Interprocess message formats overview

Interprocess Message Formats

Version 0.2
March 21, 2011

PathMATE Technical Notes

Pathfinder Solutions

www.pathfindermdd.com
+1 508-568-0068

Copyright 1995-2011 Pathfinder Solutions LLC – all rights reserved

Table Of Contents
1 Introduction .......................................................................................... 1

2 Overview............................................................................................... 1
2.1 Terminology.................................................................................. 1
2.1.1 The TCP/IP Network model ....................................................... 1
2.1.2 Ethernet Link Protocol - Layer 1 ................................................ 1
2.1.3 Internet Protocol(IP)- Layer 2 ................................................... 2
2.1.4 TCP Transport Protocol - Layer 3 ............................................... 3
2.1.5 PathMATE Application Protocol - Layer 4 ..................................... 3

3 PathMATE Application Messaging Protocol ............................................ 5
3.1 Incident Message Type ................................................................... 5
3.1.1 Service Handle Incident Type.................................................... 5
3.1.1.1 32bit Signed Integer(INTEGER_VALUE) ...................................... 6
3.1.1.2 64bit Signed Integer(LONG_LONG_VALUE) ................................. 6
3.1.1.3 64bit Floating Point Value(REAL_VALUE)..................................... 6
3.1.1.4 32bit/64bit Pointer Value(POINTER_VALUE) ................................ 7
3.1.1.5 String Value(STRING_VALUE) ................................................... 7
3.1.1.6 Service Handle(SVCHANDLE_VALUE) ......................................... 7
3.1.1.7 Fine Grained Time Value(TIME_VALUE) ...................................... 7
3.1.1.8 Groups and External Serialized Types (SERIAL_VALUE or
RC_SERIAL_VALUE) ............................................................................... 8
3.2 Init Connection Message Type ......................................................... 9
3.3 External Realized Message Type......................................................10
3.4 Shutdown Notification Message Type ...............................................10

A. Appendix - References ........................................................................ 10

Table Of Figures
Figure 1 - Ethernet Protocol............................................................................. 1
Figure 2 - IP Header and Data within an Ethernet Packet ..................................... 2
Figure 3 - IP Header Definition ......................................................................... 2
Figure 4 - TCP Header and Data within an IP Packet............................................ 3
Figure 5 - TCP Header Definition ...................................................................... 3
Figure 6 - PathMATE Application Message Definition ............................................ 3
Figure 7 - Depiction PathMATE messages transmitted over Ethernet packets .......... 5

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1 Introduction
This Technical Note describes the Message formats used in PathMATE Multi-Process
deployments when communicating between any two process instances.
Section 2 provides an overview of the different message protocol layers involved during
transmission defining basic terminology and the basic concepts.
Section 3 describes in the detail the PathMATE Application Messaging Protocol and all
supported message formats, as defined for the CPP Transformation Maps in 8.2.0 software
releases.
Appendix A lists sources for referenced information for Ethernet and TCPIP protocols.

2 Overview
2.1 Terminology
In the document we first present the various network protocol layers used in sending
PathMATE messages using the TCPIP protocol suite and over an Ethernet based network.
2.1.1 The TCP/IP Network model
The TCP/IP Network model defines four layers to define the combination of protocols used for
communication:
 Layer 1 - Link - The Link layer defines the device driver and network hardware(network interface
card). Ethernet/IEEE 802.3 is handles the link layer.
 Layer 2 - Internet(aka Network) - The Internet layer handles basic communication,
addressing and routing. IP, ICMP, ARP and IGMP protocols are at the network layer.
 Layer 3 - Transport Layer - The Transport layer handles flow of data among applications. It
segments data into packets for transport over the network. TCP and UDP operate at the transport
layer.
 Layer 4 - Application - The Application layer handles details of the particular end-user
applications. Commonly used TCP/IP applications include Telnet, FTP, SMTP, SNMP, DNS, RIP,
NFS, NTP, Traceroute. In this document we will define the PathMATE application layer message
protocol in detail.

2.1.2 Ethernet Link Protocol - Layer 1
Ethernet protocols refer to the family of local-area network (LAN) covered by the IEEE 802.3.
Below is the basic IEEE 802.e Ethernet MAC Data Frame for 10/100Mbps Ethernet:

6 4
7 1 6
byte 2 bytes 46-1500 bytes byte
bytes bytes Bytes
s s

Pre SFD DA SA Length Type Data unit + pad FCS
Figure 1 - Ethernet Protocol

 Preamble (PRE)- 7 bytes. The PRE is an alternating pattern of ones and zeros that
tells receiving stations that a frame is coming, and that provides a means to

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synchronize the frame-reception portions of receiving physical layers with the incoming
bit stream.
 Start-of-frame delimiter (SFD)- 1 byte. The SOF is an alternating pattern of ones
and zeros, ending with two consecutive 1-bits indicating that the next bit is the left-
most bit in the left-most byte of the destination address.
 Destination address (DA)- 6 bytes. The DA field identifies which station(s) should
receive the frame..
 Source addresses (SA)- 6 bytes. The SA field identifies the sending station.
 Length/Type- 2 bytes. This field indicates either the number of MAC-client data bytes
that are contained in the data field of the frame, or the frame type ID if the frame is
assembled using an optional format.
 Data- Is a sequence of n bytes (46=< n =<1500) of any value. (The total frame
minimum is 64bytes.)
 Frame check sequence (FCS)- 4 bytes. This sequence contains a 32-bit cyclic
redundancy check (CRC) value, which is created by the sending MAC and is recalculated
by the receiving MAC to check for damaged frames.

2.1.3 Internet Protocol(IP)- Layer 2
The Internet Protocol (IP) is the principal communications protocol used for
relaying datagrams (packets) across an internetwork using the Internet Protocol Suite.
Responsible for routing packets across network boundaries, it is the primary protocol that establishes
the Internet.

MAC MAC
IP Header IP Data
Header FCS
Figure 2 - IP Header and Data within an Ethernet Packet

00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Version IHL Differentiated Services Total length
Identification Flags Fragment offset
TTL Protocol Header checksum
Source IP address
Destination IP address
Options and padding :::
Figure 3 - IP Header Definition

Specific field information is as follows:
Version - Set to 4 for IP Protocol
Protocol - Set to 6 when the next encapsulated protocol is TCP
Padding - used to ensure that the IP Data starts at a 32-bit boundary.

For more detailed IP Header information refer to the following link:
http://www.networksorcery.com/enp/protocol/ip.htm

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2.1.4 TCP Transport Protocol - Layer 3
TCP is a transport layer protocol used by applications that require guaranteed delivery. It is a
sliding window protocol that provides handling for both timeouts and retransmissions.
TCP establishes a full duplex virtual connection between two endpoints. Each endpoint is
defined by an IP address and a TCP port number. The operation of TCP is implemented as a
finite state machine.
The byte stream is transferred in segments. The window size determines the number of bytes
of data that can be sent before an acknowledgement from the receiver is necessary.

MAC IP MAC
TCP Header TCP Byte Stream Data
Header Header FCS
Figure 4 - TCP Header and Data within an IP Packet

00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Source Port Destination Port
Sequence Number
Acknowledgment Number
Data Offset reserved ECN Control Bits Window
Checksum Urgent Pointer
Options and padding :::
Figure 5 - TCP Header Definition

For more detailed TCP Header information refer to the following link:
http://www.networksorcery.com/enp/protocol/tcp.htm

2.1.5 PathMATE Application Protocol - Layer 4
All PathMATE messages conform to format specified in the following figure.

1-2147483639 bytes
(The actual Message Size Dependent on Type and will
4 bytes 4 bytes
be limited to heap memory allocation restrictions on
each process)

Message Length Message Type Message Data
Figure 6 - PathMATE Application Message Definition

 Message Length - 4 bytes. Indicates the number of bytes for the next message in the
byte stream, including the Message Type (4 bytes) and the Message Data.

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 Message Type - 4 bytes. The message type indicates the specific contents of the
Message Data. Currently there are four defined message types:
1. SW_SOCK_MSG_INIT_CONN = 18 - Message sent to remote process after a
new connection is established.
2. SW_SOCK_MSG_INTERPROCESS_INCIDENT_HANDLE = 353 - Message
used to send messages containing an incident, which currently can only be a
service incident type (used to send domain service handles and class service
handles).
3. SW_SOCK_MSG_INTERPROCESS_SHUTDOWN = 355 - When a process is
shutdown, it send this message to remote processes on all active connections to
notify that it is shutting down.
4. SW_SOCK_MSG_REALIZED_EXTERNAL = 777 - Message type used to allow
sharing of PathMATE socket connections with external realized code. This allows
communications between realized code integrated with PathMATE and external
processes executing realized code developed independently of PathMATE.
 Message Data - Contains the message type specific data. See section 3 for more detail
regarding each message type.

As with all TCPIP standard based protocols, PathMATE adheres to serializing and
transmitting all multi-byte data types in Network Byte Order (which is also the same as Big
Endian). That is, the Most Significant Byte is transmitted first. For example, the Message
Length is sent as a 32-bit word, byte offset 0 contains the most significant byte and byte
offset 3 contains the least significant byte. On a 0x86 PC data is stored natively in Little
Endian format, where the Least Significant Byte(LSB) is stored in offset 0, and the Most
Significant Byte(MSB) is stored in byte offset 3. When transmitting a message from a little
endian based processor, all multi-byte data types are converted to match Network Byte
Order. Vice-Versa, when receiving data the data is converted to the native little endian
format. On Big Endian based processors no conversion is necessary.

PathMATE messages are sent on an established TCP/IP based socket, which is a guaranteed
delivery based protocol. A PathMATE message is inserted into the socket byte stream. A
TCP packet can contain a single or multiple PathMATE messages, and on the Process
receiving the byte stream the PathMATE messages are distinguished with the following
procedure:

1. After a socket is established, the Transmitting process sends the complete
PathMATE message over the socket. The number of bytes transmitted MUST
match the number of bytes comprising the message length (4 bytes) + the
message type (4 bytes) + the message data (the actual message data length +
the message type MUST match exactly the length indicated in the message
length field. Any deviation from this will prevent the receiver process to achieve
message synchronization.
2. The receiving process will first read ONLY 4 bytes, which contain the message
length of the remaining bytes to read. Once the Message length is read, it then
can read the remaining message using the received message length.
3. Subsequent messages can be read following the previous step.

As TCP sends data as a byte stream, each TCP packet can contain multiple PathMATE
messages or a portion of a single large PathMATE message. The figure on the next page
shows a depiction of how messages can appear on TCP/IP packets over Ethernet. The

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number within the TCP Data field indicates distinct PathMATE messages. The figure shows
3 complete messages and a partial message (the 4th message).

Data Packet 1

MAC IP TCP TCP Byte Stream Data MAC
Header Header Header 1 1 2 2 FCS

Data Packet 2

Header Header Header 2 3 3 FCS

Data Packet 3

Header Header Header 3 FCS

Data Packet 4

Header Header Header 3 4 4 FCS

Figure 7 - Depiction PathMATE messages transmitted over Ethernet packets

3 PathMATE Application Messaging Protocol
The following sections describe more detail for each PathMATE message types.

3.1 Incident Message Type
3.1.1 Service Handle Incident Type
The following figure shows the fixed portion of service handle incident message.
Relative Byte Size Data Name Data Values
Offset (bytes)
(in Hex)
00 4 Message Length Length of Message Type +
Message Data
04 4 Message Type 00 00 01 61 (353)
08 4 Incident Type 00 00 00 00 (0)
0C 4 Process Type Deployment value index for
Process Type
10 4 Sentinel Value DE AD FA CE
14 4 Message Version 00 00 00 01
18 4 Process ID Unique Process Identifier
1C 4 Domain Index Deployment value index for
Domain
20 4 Service Index Deployment value index for
Domain or Class Service
24 4 Task Index Deployment value index for Task
ID
28 2 Destination(not used) 2 byte string -> "0,"
2A 4 Priority (not set) 00 00 00 00
2E 4 Sender Process (not set) 00 00 00 00

5


Offset (bytes)
(in Hex)
32 4 Sender Task (not set) 00 00 00 00
36 4 Parameter Count # of parameters for domain or
class service
3A 4 Provided Parameter Count # of of provided parameters for
domain or class service
The following Parameter fields are provided for each parameter value specified for
this service handle.
3E 4 Parameter "name" index Deployment value index for
parameter name
42 4 Parameter native data type value index for native data type
46 Based on Parameter Value Based on data type
native data
type

The following sub sections describes the various PathMATE native data types.

3.1.1.1 32bit Signed Integer(INTEGER_VALUE)

Offset (bytes)
(in Hex)
00 4 INTEGER_VALUE 00 00 00 01
04 4 32bit Signed Integer Value -2147483648 (80 00 00 00) to
2147483647(7F FF FF FF)

3.1.1.2 64bit Signed Integer(LONG_LONG_VALUE)

Offset (bytes)
(in Hex)
00 4 LONG_LONG_VALUE 00 00 00 0A
04 8 64bit Signed Integer Value -9223372036854775808
(80 00 00 00 00 00 00 00) to
9223372036854775807
(7F FF FF FF FF FF FF FF)

3.1.1.3 64bit Floating Point Value(REAL_VALUE)

Offset (bytes)
(in Hex)
00 4 REAL_VALUE 00 00 00 02
04 8 64bit IEEE-754 Floating BIT63: Sign Bit
Point Value BITS[62-52]:Exponent
BITS[51-0]:Fraction

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3.1.1.4 32bit/64bit Pointer Value(POINTER_VALUE)

Offset (bytes)
(in Hex)
00 4 POINTER_VALUE 00 00 00 04
04 8 Native Host Pointer Value. Any Pointer Value
Warning: Only relevant on
Source Process or Shared
Memory Map Address. On
32 bit processors the
pointer is stored in the first
most significant 32 bits.

3.1.1.5 String Value(STRING_VALUE)

Offset (bytes)
(in Hex)
00 4 STRING_VALUE 00 00 00 03
04 String Length Null Terminated String The last byte is a NULL character.
+1

3.1.1.6 Service Handle(SVCHANDLE_VALUE)

Offset (bytes)
(in Hex)
00 4 SVCHANDLE_VALUE 00 00 00 05
The rest of the message is exactly as shown in
section 3.1.1 - Service Handle Incident Type.
04 4 Incident Type 00 00 00 00 (0)
08 4 Process Type Deployment value index for
Process Type
0C 4 Sentinel Value DE AD FA CE
10 4 Message Version 00 00 00 01
...

3.1.1.7 Fine Grained Time Value(TIME_VALUE)
NOTE: Currently Fine Grained time is not implemented. If an attempt to send a Fine Grain
Time is attempted it will first be converted into a double floating point variable, then into a
string representation of the value. The receiving process will have no way of knowing that it is
a time variable. The current serialized output is shown here:
Offset (bytes)
(in Hex)
00 4 STRING_VALUE 00 00 00 03
04 String Length Null Terminated String The last byte is a NULL character.
+1 representing the fine Examples:
grained time in "1259009.0023" <- (in
milliseconds. milliseconds)

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In the future we may represent it natively as follows:
Offset (bytes)
(in Hex)
00 4 TIME_VALUE 00 00 00 09
04 4 Seconds Number of seconds since the
process started
08 4 Nanoseconds Number of fractional nano-
seconds in the current second

3.1.1.8 Groups and External Serialized Types (SERIAL_VALUE or RC_SERIAL_VALUE)
PathMATE provides the ability to serialize/de-serialize externally defined types; to learn more
about how to do this please refer to the advanced realized types technical note. There are two
types of serialized data types: SERIAL_VALUE & RC_SERIAL_VALUE. They are serialized/de-
serialized exactly the same, the difference being that the RC_SERIAL_VALUE provides an
indication to the receiving process that the data type container class needs to have pointer
reference counting.

Here we will show the format for groups of specific native data types.
Relative Size Data Name Data Values
Byte Offset (bytes)
(in Hex)
00 4 SERIAL_VALUE 00 00 00 07
RC_SERIAL_VALUE 00 00 00 08
04 4 SERIAL_TYPE_[groupname] Deployment value index for the
Group of Integer Example: group data type. This will not
SERIAL_TYPE_GroupListInteger vary on the same deployment
The remainder of the information provided for realized types is specified within the
type’s serialization code itself. Generally this is a combination of PathMATE native
data types specified in sections 3.1.1.1 through 3.1.1.7.

The format for groups of generic data types is as follows:
Offset (bytes)
(in Hex)
00 4 SERIAL_VALUE 00 00 00 07
RC_SERIAL_VALUE 00 00 00 08
04 4 One of the following: Deployment value index
SERIAL_TYPE_ListGroupGeneric for the generic group
SERIAL_TYPE_ArrayGroupGeneric type. This will not vary
SERIAL_TYPE_HashGroupGeneric on the same deployment
08 4 Number of Items(N) 1 or higher
0C 4 Native Data Type for value 1 One of the following:
INTEGER_VALUE,
LONG_LONG_VALUE,
REAL_VALUE,
POINTER_VALUE
SVCHANDLE_VALUE,
STRING_VALUE,

8


Offset (bytes)
(in Hex)
SERIAL_VALUE,
RC_SERIAL_VALUE
10 Datasize_item1 Value 1 Dependent on native
data type
10 + 4 Native Data Type for value 2 One of the following:
datasize_item1 INTEGER_VALUE,
LONG_LONG_VALUE,
REAL_VALUE,
POINTER_VALUE
SVCHANDLE_VALUE,
STRING_VALUE,
SERIAL_VALUE,
RC_SERIAL_VALUE
10 + Datasize_item2 Value 2 Dependent on native
datasize_item1 data type
+ 04
...
0C + 4 Native Data Type for value N One of the following:
SUM[N-1] INTEGER_VALUE,
(04 + LONG_LONG_VALUE,
datasize_itemx) REAL_VALUE,
POINTER_VALUE
SVCHANDLE_VALUE,
STRING_VALUE,
SERIAL_VALUE,
RC_SERIAL_VALUE
0C + Datasize_itemN Value N Dependent on native
SUM[N-1] data type
(04 +
datasize_itemx)
+ 04

3.2 Init Connection Message Type
The following message is sent on the transmit socket after the Sender process establishes a
socket with a process listening on a port. All of the provided data is from the Sender process.
Offset (bytes)
(in Hex)
00 4 Message Length 00 00 00 14 (20)
04 4 Message Type 00 00 01 12 (18)
08 4 Process Type Deployment index value for
process type
0C 4 OS Process Id Runtime and OS dependent
10 4 Process ID Unique Process Identifier
14 4 Connection Count prior to 0 and higher
this connection.

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3.3 External Realized Message Type
External realized message types are simply defined by setting the message type field to 777,
which over the network will be sent (shown in hex) as 00 00 03 09. The message data
contents are user defined based on the external realized code
Offset (bytes)
(in Hex)
00 4 Message Length Length of Message Type + user
defined size
04 4 Message Type 00 00 03 09 (777)
08 User defined User Data Contains data defined by external
size software

3.4 Shutdown Notification Message Type
This message is sent to all connected remote processes to notify when the local process will
close all connections and shut down.
Offset (bytes)
(in Hex)
00 4 Message Length 00 00 00 04 ( 4)
04 4 Message Type 00 00 01 63 (355)

A. Appendix - References
The following references where used in creating this document

1. PathMATE CPP Mechanisms 8.2.0 source code
2. http://en.wikipedia.org/wiki/IP_Protocol
3. http://en.wikipedia.org/wiki/IP
4. http://www.networksorcery.com/enp/protocol/ip.htm
5. http://www.networksorcery.com/enp/protocol/tcp.htm
6. http://www.speedguide.net/articles/the-tcpip-and-osi-network-models-120

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