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TCAP dialogue portion

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TCAP dialogue portion

Hi All,

I have a question regarding the Dialogue portion(request), When do I need to send it? I'm talking about SMS operation by the way. It seems that the dialogue request is sent after if the message reaches certain length, like for example if the message length is more that 130 byte then send only the dialogue portion, if less then that then send only the dialogue portion with the component portion in one packet.

Re:Dialogue portion is optional

Dialogue portion is optional with in the TCAP message.
If the message length exceeds 140 bytes (160 characters for GSM7 bit)
then u can send the dialogue portion in TCAP-BEGIN and send the actual content in multiple TCAP-CONTINUE messages without dialogue portion. This is nothing but the TCAP segmentation.
This is because there is a size limitation for TCAP message.
I hope this clarifies ur doubt.

Thanks for the info, I'm not

Thanks for the info, I'm not sure how accurate is this, I have a trace with a message length of 130 and the TCAP was segmented, is there a specific number that I need to segment the message if the length exceeded it?

Just to avoid

Just to avoid misunderstanding - dialogue portion is mandatory part of TCAP message. Here is what 3GPP TS 29.002 says about use of TCAP handshake(TC_BEGIN goes without any payload or without any component portion):

the capacity of a message signal unit in the lower layers of the protocol is enough to carry the content of the MAP_OPEN request and the content of the MAP_MO_FORWARD_SHORT_MESSAGE request in a single TC message and
b) the Interworking MSC operator and the serving node (MSC or SGSN) operator agreed not to use the TCAP handshake countermeasure against SMS fraud for messages exchanged between their networks (see 3GPP TS 33.204 [34a]) then the TCAP handshake may be omitted.

In other words you shall use TC-Handshake if:

  • payload does not fit with max MSU length on signalling links between SC and MSC/SGSN
  • link between SC and MSC/SGSN always uses TC-Handshake for security reasons
Dialogue portion is optional ref:Q series of Q771e-Q774e


Dialogue portion in a TCAP message is optional and its not mandatory.
Please refer to Q series doc (Q771e-Q774e)
Especially in case of concatenated messages dialogue portion can be optional.

If dialogue is established with plane BEGIN which carried dialogue portion already, not required to send in further CONTINUE messages which carry your actual message (In case of concatenated).

To --->dev-bag

I am not sure about your trace which is segmented for 130 characters.
Max TCAP signaling message size is limited to around 270 bytes so it can carry up to 160 GSM-7 bit characters(User data header + actual user data) (140 bytes) of user data.

Since 5 years i stopped working on ss7 i forgot lot of things.
If you need trace related to concatenated message with or without dialogue portion i can forward it to you.

Thank you both, I found out

Thank you both,
I found out how to handle this actually, it's related to the SCCP connectionless packet, where the packet has to be < 273.