MMS related Protocol structure & frame format

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Summary

 

 

Packet-based vs. stream-based:

COTP transports packets of data from one user to the other, so the receiver will get exactly the same data boundaries as the sender transmitted.

TCP transports a continuous stream of data to the receiver, so the protocol on top of TCP often has to add such boundaries itself (see the TPKT protocol for such a protocol).

 

TSAPs vs. ports:

 

To multiplex several conversations between two hosts, COTP uses TSAP's which are variable length binary blobs (often a meaningful string is used).

 

These TSAP's are matched at connection establishing phase, and replaced by the 2 byte (destination/source) references at data transfer.

 

TCP uses ports for this. One notable difference is that TSAP's are singletons - if a TSAP is used for a connection it cannot be used by another. XXX - Needs clarification. A single TSAP (Transport Service Access Point) may be used by multiple connections.

 

Tranport Layer:

 

Protocol                     Note

------------                   ---------------------------------------------------------------------------------------

COTP                          

TPKT                           = TPKT works on TCP port 102 to emulate COTP

TCP

----------------------------------------------------------------------------------------------------------------

 

 

1.  TPKT = RFC 1006

 

It start with \x03\X00.

 

TPKT is used to "emulate" ISO transport services COTP on top of TCP. The two major points missing in TCP (compared to COTP) are the TSAP addressing and the detection of packet boundaries on the receiving host.

Include Packet Header and TPDU, The format of the TPDU is defined in [ISO8073].  

Note that only TPDUs formatted for transport class 0 [TP0] are exchanged (different transport classes may use slightly different formats).

 

 

 

 

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      vrsn     |    reserved   |          packet length        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 

 

Header:version = always 3, 1 byte

 

TPDU = max. 65531. Based on the size of the data transfer (DT) TPDU, this permits a maximum TSDU size of 65524 octets.

 

 

2.  COTP = ISO 8073 / RFC983

 

Connection-oriented transport protocol

 

To support expedited data, a non-standard TPDU, for expedited data is permitted.  The format used for the ED TPDU is nearly identical to the format for the normal data, DT, TPDU.  The only difference is that the value used for the TPDU's code is ED, not DT:

 

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | header length | code  |credit |TPDU-NR and EOT|   user data   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      ...      |      ...      |      ...      |      ...      |
      |      ...      |      ...      |      ...      |      ...      |
      |      ...      |      ...      |      ...      |      ...      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 

 

 

 

 

TPDU Code

-------------------
CR = 0xE0, Connection Request

CC = 0xD0, Connection Confirm
DR = 0x80, Disconnection Request
DT = 0xF0, Data Transfer
ED = 0x70, Expected Data transfer

 

After the credit field (which is always ZERO on output and ignored on input), there is one additional field prior to the user data.

     

TPDU-NR and EOT = 8 bits

 Bit 7 (the high-order bit, bit mask 1000 0000) indicates the end of a TSDU.  All other bits should be ZERO on output and ignored on input.

 

  

The format of a CR or CC TPDU is:

       0                   1                   2                   3  
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | header length | code  | credit|     destination reference     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       source reference        | class |options| variable data |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    ...        |      ...      |      ...      |      ...      |
      |    ...        |      ...      |      ...      |      ...      |
      |    ...        |   user data   |      ...      |      ...      |
      |    ...        |      ...      |      ...      |      ...      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 

 

 

 

The format of a DR TPDU is:

       0                   1                   2                   3  
       0 1  2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | header length | code  | credit|     destination reference     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       source reference        |     reason    | variable data |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    ...        |      ...      |      ...      |      ...      |
      |    ...        |      ...      |      ...      |      ...      |
      |      ...      |   user data   |      ...      |      ...      |
      |    ...        |      ...      |      ...      |      ...      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 

The format of a DT or ED TPDU is:

       0                   1                   2                   3  
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+
      | header length | code  | credit|         TPDU-NR and EOT       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   user data   |      ...      |      ...      |      ...      |
      |    ...        |      ...      |      ...      |      ...      |
      |    ...        |      ...      |      ...      |      ...      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 

 

3.  ISO 8327-1

ISO Session Protocol

 

 

 

 

 

Format

-----------------------------------------------

SPDU Type  --  1 byte

Length  --  1 byte

Connect Accept Item  --  8 bytes

Session Requirement  --  4 bytes

Calling Session Selector  --  4 bytes

Called Session Selector  --  4 bytes

Session User Data  --  ...

 

 

ISO Session Protocol (ISO-SP) Messages:

Functional unit	SPDU code	SPDU name
Kernel	CN OA CDO AC RF FN DN AB AA DT PR	CONNECT OVERFLOW ACCEPT CONNECT DATA OVERFLOW ACCEPT REFUSE FINISH DISCONNECT ABORT ABORT ACCEPT DATA TRANSFER PREPARE
Negotiated release	NF GT PT	NOT FINISHED GIVE TOKENS PLEASE TOKENS
Half-duplex	GT PT	GIVE TOKENS PLEASE TOKENS
Duplex		No additional associated SPDUs
Expedited data	EX	EXPEDITED DATA
Typed data	TD	TYPED DATA
Capability data exchange	CD CDA	CAPABILITY DATA CAPABILITY DATA ACK
Minor synchronize	MIP MIA GT PT	MINOR SYNC POINT MINOR SYNC ACK GIVE TOKENS PLEASE TOKENS
Symmetric synchronize	MIP MIA	MINOR SYNC POINT MINOR SYNC ACK
Data separation		No additional associated SPDUs
Major synchronize	MAP MAA PR GT PT	MAJOR SYNC POINT MAJOR SYNC ACK PREPARE GIVE TOKENS PLEASE TOKENS
Resynchronize	RS RA PR	RESYNCHRONIZE RESYNCHRONIZE ACK PREPARE
Exceptions	ER ED	EXCEPTION REPORT EXCEPTION DATA
Activity management	AS AR AI AIA AD ADA AE AEA PR GT PT GTC GTA	ACTIVITY START ACTIVITY RESUME ACTIVITY INTERRUPT ACTIVITY INTERRUPT ACK ACTIVITY DISCARD ACTIVITY DISCARD ACK ACTIVITY END ACTIVITY END ACK PREPARE GIVE TOKENS PLEASE TOKENS GIVE TOKENS CONFIRM GIVE TOKENS ACK

 

  

 

4.  ISO 8823

ISO Presentation Protocol, on top of ASN.1, BER.

 

Frame format

-------------------------------------------------------------------------

Mode-selector  --  3 bytes

Normal-mode-parameters

Padding  --  1 byte

Protocol-version  --  1 byte, 80 = version-1

calling-presentation-selector  --  4 bytes

called-presentation-selector  --  4 bytes

presentation-contex-definition-list  --  ??

Padding --  1 byte

Presentation- requirement  --  1 byte

User-data  --  ...

 

 

Protocol Structure - ISO-PP: OSI Presentation Layer Protocol (X.226, X.216, ISO 8823, 8822)

 

Connection Release Primitive	Token Handling Primitive
P-RELEASE request P-RELEASE indication P-RELEASE response P-RELEASE confirm	P-TOKEN-GIVE request P-TOKEN-GIVE indication P-TOKEN-PLEASE request P-TOKEN-PLEASE indication P-CONTROL-GIVE request P-CONTROL-GIVE indication

Presentation Exception Reporting Primitive	Activity Management Primitive
P-P-EXCEPTION-REPORT indication P-U-EXCEPTION-REPORT request P-U-EXCEPTION-REPORT indication	P-ACTIVITY-START request P-ACTIVITY-START indication P-ACTIVITY-RESUME request P-ACTIVITY-RESUME indication P-ACTIVITY-INTERRUPT request P-ACTIVITY-INTERRUPT indication P-ACTIVITY-NTERRUPT response P-ACTIVITY-INTERRUPT confirm P-ACTIVITY-DISCARD request P-ACTIVITY-DISCARD indication P-ACTIVITY-DISCARD response P-ACTIVITY-DISCARD confirm P-ACTIVITY-END request P-ACTIVITY-END indication P-ACTIVITY-END response P-ACTIVITY-END confirm
Synchronization Services Primitive
P-SYNC-MINOR request P-SYNC-MINOR indication P-SYNC-MINOR response P-SYNC-MINOR confirm P-SYNC-MAJOR request P-SYNC-MAJOR indication P-SYNC-MAJOR response P-SYNC-MAJOR confirm

 

 

5.  ISO 8650-1, ACSE-1

ISO Association Control Service Element (Layer 7)

 

The OSI method for establishing a call between two application programs. ACSE checks the identities and contexts of the application entities, and could apply an authentication security check.

 

ICCP uses the ISO Association Control Service element (ACSE) to establish logical associations. Multiple associations may be established from a client to multiple, different control center servers.

 

Application Association & network connection are different.

 

 

 

6.  MMS

ISO 9506-2