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Connection oriented SCCP

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Connection oriented SCCP

How SLR and DLR helps in connection oriented SCCP ?

Miguel Nolasco
Miguel Nolasco's picture
never see them


They save signalling (less bytes sent and analyzed), when they are used properly. But since they do kind of action of TCAP, SLR and DLR are not used for example with MAP or CAP since they lies on TCAP. SLR and DLR are mostly used in direct conection links, for example A-interface, ISDN links, etc.

SLR(Source Local Reference)

SLR(Source Local Reference) and DLR(Destination Local Reference) are the fields that binds the messages to a connection.

Both ends of a connection generates its own SLR. When the SLR of the peer is known, that SLR is used as
the DLR in the messages exchanged. This is used by an endpoint to know which connection a received message belongs to.

Example connection between peers A and B
A---------------- B

------------------> CR msg , slr=4 A side chooses its SLR to be 4

------------------>CC msg, slr=9, dlr = 4 B side chooses its SLR to be 9, and responds to A with 4

------------------>DT1 msg, slr=4, dlr=9

<----------------- DT1 msg, slr=9, dlr=4


It is same as when we deliver any latter using the Post office.
We mentioned the TO Address to deliver it to destination and From Address to identifies we have delivered this message (Address of originator to receive the reply).

Same mechanism applies in connection oriented method,
To address is DLR (Destination Address) and FROM Address is SLR (Source Address).
For end to end connection SLR and DLR works for addressing of end points but it is temporary till the connection established.

hope this help, for more information on sccp follow the link: