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What does Hop-by-Hop Id signify in a diameter header ?

+4 votes
What does Hop-by-Hop Id signify in a diameter header ?
posted Dec 25, 2014 by Harshita

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1 Answer

+2 votes

On behalf of Peeyush ( )

It is an identifier between two nodes to identify sequence of a message...similarly end to end identifier is used as an idenfier between source and destination where it can traverse multiple node

answer Dec 25, 2014 by Salil Agrawal
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+2 votes

The DRA is between e.g. MME and HSS or SGSN and HSS and maybe between HSS and IMS S-CSCF/I-CSCF. In the IETF Spec RFC3588 you can read the following: IETF - RFC3588

The Hop-by-Hop Identifier is an unsigned 32-bit integer field (in network byte order) and aids in matching requests and replies. The sender MUST ensure that the Hop-by-Hop identifier in a request is unique on a given connection at any given time, and MAY attempt to ensure that the number is unique across reboots. The sender of an Answer message MUST ensure that the Hop-by-Hop Identifier field contains the same value that was found in the corresponding request. The Hop-by-Hop identifier is normally a monotonically increasing number, whose start value was randomly generated. An answer message that is received with an unknown Hop-by-Hop Identifier MUST be discarded.

--> for me it sounds like that the HbHid must not jump in numbers but rather increase step by step sequential – is that also your experience?

Issue: I wonder if that Hop-by-Hop Identifier really increases the number sequentially as it seems to be a similar Parameter like the Local Reference in SS7 (DLR, SLR). I do not recall that in SS7 the Source/Destination Local Reference Numbers have to be increased sequentially.
If the Hop-by-Hop ID jumps too much, the other side may not be able to follow and Signalling errors occur? Have you seen problems on HSS or MME when that Hop-by-Hop Identifier increases in big steps rather than sequential?

0 votes

What is the use of keeping the same information in two places like Application-Id in the Diameter header and Application-Id as AVP ?

+3 votes

If we look into diameter header, fields like version, length, command flags, command code etc all are in a specific order. Is there any standard or concept is used to while defining a new protocol ?