CN8478 Datasheet, PDF (183/221 Pages) Conexant Systems, Inc – Multichannel Synchronous Communications Controller (MUSYCC)

CN8478/CN8474A/CN8472A/CN8471A
Multichannel Synchronous Communications Controller (MUSYCC™)
6.0 Basic Operation
6.5 Signaling System 7
6.5 Signaling System 7
6.5.1 SS7 Repeat Message Transmission
Signaling System 7 (SS7) requires the ability to continuously repeat a message
under certain circumstances. The Repeat Message Transmission section of this
document describes the repeat feature fully and is usable for an SS7 application.
6.5.2 Message Filtering
Message filtering is always enabled for a receive channel which is configured for
SS7-HDLC-CRC16 mode in Table 5-18, Channel Configuration Descriptor.
When receiving an unerrored message with a payload length of 3, 4, or 5
octets and the required 2-octet FCS, MUSYCC transfers the data into the memory
buffer as usual and then enters the message filtering mode. This mode does not
apply to messages with payloads greater than 5 octets.
In this mode, the next Message Descriptor is processed in the normal manner
(receive Buffer Status Descriptor is written, next pointer is used to read next
Message Descriptor, ONR and NP bits are checked, and so on). In this case, the
current memory buffer is not filled until MUSYCC exits the message filtering
mode.
The 3-, 4-, or 5-octet payload and the 2-octet FCS are stored inside MUSYCC
and are considered golden messages by being 3, 4, or 5 octets long. Subsequent
received messages are compared to this message.
Each bit of the subsequent message will be compared bit-wise to the contents
of the golden message. The following can occur:
• If a match occurs, the payload and FCS of the golden message match the
current message before a closing flag is received for the current message.
The maskable interrupt MSKSFILT is generated to the host. MUSYCC
remains in message filtering mode, and the golden message is retained.
• If a mismatch occurs, a bit-wise mismatch is detected between a bit in the
golden message and the corresponding bit in the current message before a
closing flag is received for the current message. MUSYCC immediately
exits the filter mode.
The treatment for the current message becomes a normal message treatment.
If the current message is unerrored and qualifies to become a golden message, it
is transferred to the current Receive Data Buffer and becomes the new golden
message internally to MUSYCC.
If the current message is unerrored and greater than 6 octets total, it cannot
become a golden message, and MUSYCC continues normal message treatment.
100660E
Conexant
6-49