Telephonic communications – Plural exchange network or interconnection
Reexamination Certificate
1997-02-27
2001-04-17
Marcelo, Melvin (Department: 2663)
Telephonic communications
Plural exchange network or interconnection
C379S229000, C379S230000
Reexamination Certificate
active
06219416
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for processing FISU frames carrying no data according to the Signalling System 7 protocol and more particularly to a method and an apparatus for discarding or generating FISU frames without interrupting the processor.
2. Background Discussion
Many telecommunication products are operating according to the Signalling System Number 7 (SS7) protocol. This protocol defines four layers among the seven layers of the OSI (open system interconnect) standard. The four layers are the signalling data link called MTP-1, the signalling link functions called MTP-2, the signalling network functions called MTP-3 and the signalling connection control part called SCCP.
MTP 1 which is a physical layer, defines three types of frames.
FIG. 1
a
shows the format of these SS7 frames also called Signalling Units (SU). MTP 2 uses these three types of SU: the Message Signalling Unit (MSU), the Link Status Signalling Unit (LSSU) and the Fill-In Signalling Unit (FISU).
The MSU, the LSSU and the FISU are respectively 278-byte, 7-byte and 5-byte long between flags. These three types of frames carry two specific data bytes BSN (backward sequence number) and FSN (forward sequence number) in common. The BSN and FSN bytes are respectively dedicated to the received and transmitted data frames and they are sequentially numbered. These numbers are modified according to the data traffic rate, and these bytes remain unchanged when no data are exchanged.
By referring to
FIG. 1-
a
, the other initials stand for:
F: flag
LI: Length Indicator
SF: Status Field
SIO: Service Information Octet
SIF: Signalling Informing Field
CRC: Cyclic Redundancy Check
The particularity of this protocol is: firstly, the format of the network link which is shown in
FIG. 1
b
. Two consecutive SS7 frames are separated by one flag and the ending flag of frame (n) is the starting flag of frame (n+1). Secondly, when no data frame has to be exchanged which corresponds to idle state, the network links carry FISU frames.
In case of no traffic, these FISU frames do not carry any information, and this occurs frequently. On the adapter side, an interrupt is raised to a processor each time a FISU is received or transmitted that is to say every 6 byte. This environment is applicable to the low speed SS7 network in which the present invention is implemented. A low speed network is operating at a speed of 56 Kbps in the U.S. and 64 Kbps in Europe. Hence, an interrupt occurs every 857 microseconds or 750 microseconds in both transmit and receive directions. These too many interrupts degrade the performance of the SS7 adapter. Therefore it is necessary to process the FISU frames externally from the adapter by suppressing useless FISU frames received from the network and then these interrupts, and by generating FISU frames when idle states (no data signals) are transmitted from the adapter to the network without interrupting the processor.
SUMMARY OF THE INVENTION
An object of the invention is to provide a method and an apparatus to avoid interruption of a processor located in the adapter when no data frames are transmitted nor received.
The Signalling System 7 (SS7) protocol uses particular types of frames. The apparatus according to the present invention is a FISU frame handler
50
which is connected between an adapter
60
and a SS7 low speed network
70
as shown in FIG.
2
. For each FISU frames transmitted or received in the adapter, an interrupt is generated to the processor
65
located in the adapter. Therefore, in order to diminish the number of processor interruptions, the FISU frames are externally processed by the FISU frame handler by discarding repeated FISU frames transmitted from the network
70
so as to generate idle state signals to the adapter
60
and by converting idle state signals received from the adapter
60
into repetitive FISU frames to transmit them to the network
70
without interrupting the processor. In order to perform both functions, the FISU frame handler comprises two dedicated hardware units which operate according to specific methods.
The FISU apparatus comprises first means for receiving FISU frames from the adapter and repeating FISU frames to transmit them to the network without interrupting the processor and second means for receiving FISU frames from the network and discarding repeated FISU frames without interrupting the processor of the system.
More specifically, the FISU apparatus comprises means for generating flags; repeated FISU frames and data frames received from the adapter to the network; multiplexing means for transmitting flags; repeated FISU frames or data frames received from the adapter to the network; and a logic circuit for controlling the generating means and the multiplexing means. Conversely the apparatus also comprises another generating means for discarding repeated FISU frames and data frames received from the network to the adapter; associated multiplexing means for transmitting idle pattern or data frames received from the network, and a logic circuit for controlling the generating and multiplexing means.
The method of processing the FISU frames comprises the following steps:
(a) Receiving, in transmission mode, a FISU frame from the adapter and repeating FISU frames when no data are received from the adapter to transmit them to the network without interrupting the processor; and
(b) Receiving, in reception mode, FISU frames from the network and discarding repeated FISU frames by transmitting idle state signals to the adapter without interrupting the processor.
REFERENCES:
patent: 5757895 (1998-05-01), Aridas et al.
Benayoun Alain
Le Pennec Jean-Francois
Michel Patrick
Pin Claude
Cisco Technology Inc.
Johnston A. Sidney
Marcelo Melvin
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