Rf Interface Support
Features and Terminology ▀
Cisco ASR 5x00 Packet Data Network Gateway Administration Guide ▄
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Timer Expiry Behavior
Upon establishing the Diameter connection, an accounting interim timer (AII) is used to indicate the expiration of a
Diameter accounting session, and is configurable at the CTF. The CTF indicates the timer value in the ACR-Start, in the
Acct-Interim-Interval AVP. The CDF responds with its own AII value (through the DRA), which must be used by the
CTF to start a timer upon whose expiration an ACR INTERIM message must be sent. An instance of the AII timer is
started in the CCF at the beginning of the accounting session, reset on the receipt of an ACR-Interim and stopped on the
receipt of the ACR-Stop. After expiration of the AII timer, ACR INTERIM message will be generated and the timer will
be reset and the accounting session will be continued.
Rf Interface Failures/Error Conditions
The current architecture allows for primary and secondary connections or Active-Active connections for each network
element with the CDF elements.
DRA/CCF Connection Failure
When the connection towards one of the primary/Active DRAs in CCF becomes unavailable, the CTF picks the
Secondary/Active IP address and begins to use that as a Primary.
If no DRA (and/or the CCF) is reachable, the network element must buffer the generated accounting data in non-volatile
memory. Once the DRA connection is up, all accounting messages must be pulled by the CDF through offline file
transfer.
No Reply from CCF
In case the CTF/DRA does not receive an ACA in response to an ACR, it may retransmit the ACR message. The
waiting time until a retransmission is sent, and the maximum number of repetitions are both configurable by the
operator. When the maximum number of retransmissions is reached and still no ACA reply has been received, the
CTF/DRA sends the ACRs to the secondary/alternate DRA/CCF.
Detection of Message Duplication
The Diameter client marks possible duplicate request messages (e.g. retransmission due to the link failover process)
with the T-flag as described in RFC 3588.
If the CDF receives a message that is marked as retransmitted and this message was already received, then it discards
the duplicate message. However, if the original of the re-transmitted message was not yet received, it is the information
in the marked message that is taken into account when generating the CDR. The CDRs are marked if information from
duplicated message(s) is used.
CCF Detected Failure
The CCF closes a CDR when it detects that expected Diameter ACRs for a particular session have not been received for
a period of time. The exact behavior of the CCF is operator configurable.