3Com CoreBuilder 7000, Operation Manual

Page: 120 / 264

120 C
HAPTER
5: E
STABLISHING
ATM C
HANNELS
UNI Signaling 4.0
Features
This section describes the features added in UNI Signaling 4.0 which are
supported by the CoreBuilder 7000 family ATM switch.
These include:
ATM Anycast Capability
Signaling of Individual QoS Parameters
Message Conversion Between Signaling Protocols
ATM Anycast
Capability
The anycast address in an ATM network provides redundancy and load
sharing in a network. The anycast addressing system works as follows: A
group of end-users, usually servers, each of which can provide an
equivalent service, identifies itself to the network via ILMI by a single
group address. A user that requires the service offered by the group
requests a connection to any one of the members of the group without
specifying which particular member. The network acts to connect the
requesting user to the nearest available group member in such a way that
the load on the group members is balanced. This arrangement also
provides redundancy: when a server in the group fails, the user is directed
to establish a connection with another server in group.
A calling user requests an ATM anycast capability by sending a SETUP
message that contains the desired ATM group address in the called party
number information element. When the network, receives the SETUP
message, it establishes a single point-to-point connection to a member of
the group identified by the ATM group address. The called member can
return its own individual ATM address or sub-address to the calling user
through the CONNECT message so that the calling party knows to whom
it was connected.
When a user initiates an anycast connection to a group it also includes
the ATM Address Organizational Scope, which specifies restrictions on
how to route a virtual path to the group. The purpose of the Connection
Scope Selection information element is to allow the calling user to
indicate to the network that the call/connection shall be processed and
progressed within the selected routing range. In this way, routing the
virtual path to the group can be more efficient. If the user does not
provide the Connection Scope, the default connection scope is the Local
Network.