Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-01-26
2001-08-28
Vu, Huy D. (Department: 2664)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S398000, C370S412000, C370S418000, C370S230000, C370S232000
Reexamination Certificate
active
06282197
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ATM switching apparatus and an ATM communications network, which offers SVC (Switched Virtual Connection) services.
2. Description of the Related Art
Services offered in a B-ISDN (Broadband-Integrated Service Digital Network) constructed of ATM switching apparatuses are classified into connection-oriented services and connectionless services. The connection oriented services thereof are subdivided into a PVC (Permanent Virtual Connection) service in which a calling user and a bandwidth are semi-permanent, and an SVC (Switched Virtual Connection) service in which the communication connection is dynamically established according to the called user, the bandwidth and a quality of service that are declared from a calling user.
Standardization of signalling protocols at a user-network interface (UNI) and network-node interface (NNI) for actualizing the SVC service, is advanced stepwise (the way in which the functions are extended) by the ITU-T (International telecommunication Union-Telecommunication Standardization Sector) as a main organization. The signaling protocols at the UNI and NNI for B-ISDN are respectively known as DSS
2
(Digital Signalling System No. 2) and B-ISUP (B-ISDN User Part).
Hereinafter, an outline of the DSS
2
and B-ISUP will be explained. First, formats of DSS
2
, B-ISUP messages are explained.
DSS
2
message, as shown in
FIG. 11
, is composed of a protocol discriminator, a call reference length, a call reference, a message type, a message length, and some information elements.
The protocol discriminator is information identifying the specific protocol in which the message are to be interpreted, and is set to “00001001” for the DSS
2
message. The call reference length is information specifying the number of octets used for the call reference. The call reference is information identifying the connection to which the message pertains. Note that the call reference identifies the connection at the local UNI only, but has no end-to-end significance. That is, a connection is identified by two independent call references valid at the near-end and far-end UNIs.
The message type is information identifying the specific type of message, such as SETUP, CONNECT, and so on. The message length is information specifying the number of octets used for the information elements, and is set to 0000H when the message contains no information element. All DSS
2
messages must contain the protocol discriminator, the call reference length, the call reference, the message type and the message length, and so they are at least nine octets long.
Each of the information elements prepared for DSS
2
messages consists of an information element identifier, a coding standard, an information element instruction field, an information element content length and information element content.
The element identifier is information identifying the information element. The coding standard is information identifying the regulation with which the information element are coded, and is usually set to “00” for ITU-T coding. The information instruction field contains an action indicator indicating the receiving node how to act (clear call, discard and proceed, and so on) when the information element cannot be interpreted, and a flag bit indicating whether or not the action indicator is to be followed. The information element content length is information specifying the number of octets used for the information element content.
The set of DSS
2
messages is divided into call establishment messages, call clearing messages, messages used during the information phase of the connection, and a set of miscellaneous messages. Each DSS
2
message may contain multiple information elements, some are mandatory and some are optional, depending on the type and its use.
B-ISUP message, as shown in
FIG. 12
, is composed of MTP (Message Transfer Protocol)-3 header, a message type, a message length, a message compatibility information and some parameters.
The MTP-3 header is composed of a service information octet (SIO) indicating the specific protocol in which the message are to be interpreted, and a routing label. The routing label is used to route the message from one switching apparatus to another. It is composed of a destination point code (DPS), an originating point code (OPS), and a signalling link selection number (SLS). The DPS is the address of the switching apparatus to which the message must be delivered and the OPS is the address of the switching apparatus which originates the message. The SLS defines a virtual routes between the switching apparatuses. It is used assign the messages belonging to different transactions to separate routes.
The message type is information to identify the particular function carried out by the message. The message length specifies the number of octets used for the message compatibility information and the parameters. The message compatibility information indicates the receiving node how to act (disconnect call, ignore this message, and so on) in case that the message cannot be interpreted.
Each of the parameters prepared for B-ISUP messages is composed of a parameter name, a parameter length, parameter compatibility information and parameter contents. The parameter name is information identifying the parameter. The parameter length is information specifying the number of octets used for the parameter compatibility information and the parameter content. The parameter compatibility information is information indicating a node, which receives this parameter, how to act in case that the parameter cannot be interpreted.
The DSS
2
and the B-ISUP are separate protocols, however, their messages, information elements and parameters are closely associated with each other.
For example, as shown in
FIG. 13
, an IAM (Initial address message), which is a B-ISUP message corresponding to the DSS
2
SETUP message, may contain parameters corresponding to information elements used in the SETUP message. As shown in
FIG. 14
, an ANM (Answer message), which is a B-ISUP message corresponding to the DSS
2
CONNECT message, may contain parameters corresponding to information elements used in the CONNECT message.
Next, an outline of a call set up operation using the DSS
2
and B-ISUP will be explained by exemplifying a case of setting a call between two terminals (calling and called terminals) via two switching apparatuses (originating and destination switching apparatuses).
The call set up operation starts when the calling terminal sends to the originating switching apparatus (switching apparatus accommodating the calling terminal itself) the SETUP message containing pieces of information elements such as a called party number information element, an ATM traffic descriptor information element, a broadband bearer capability information element, a QOS (quality of service) parameter information element and so on.
The ATM traffic descriptor information element, as shown in
FIG. 15
, contains set of traffic parameters. The broadband bearer capability information element, as shown in
FIG. 16
, contains information indicating the broadband service to be offered. Note that the broadband bearer capability information element shown in
FIG. 16
is that defined in the recommendation Q.2931. In the new recommendation Q.2931.2, it is defined that octet
5
a
of the broadband bearer capability information element is used as an ATM transfer capability field as shown in FIG.
17
.
Upon receiving the SETUP message, the originating switching apparatus recognizes a destination switching apparatus from the called party number contained in the SETUP message. Then, it recognizes the virtual path connections (VPCs) provided between the destination switching apparatus and the originating switching apparatus itself.
Subsequently, it calculates a bandwidth value to be reserved for the call (connection) requested on the basis of the ATM traffic descriptor information element, a broadband bearer capability information element, a QOS (qual
Takahashi Satoshi
Ueki Kohei
Watanabe Yoshihiro
Fujitsu Limited
Helfgott & Karas, PC.
Phan M.
Vu Huy D.
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