Implementing Filters to Route Inbound Communications Data

Implementing Filters to Route Inbound Communications Data

      A programmable method for routing incoming data
communications frames is disclosed.  This invention uses existing
standards, such as those from CCITT and IEEE, to provide a
generalized solution, which can be used by any protocol using these
standards for the physical, data link and network layers.  This
filtering is performed within the network layer in the ISO model, as
shown in Fig. 1.  This invention is extendable to any architected
data link protocol.

      To solve the generalized data routing problem, a 'filter' was
invented, and communications support was added to perform the
'filtering' function which routes the data to the appropriate
protocol application.

      The filter is data structure, based on architected or
standardized formats of the incoming data frames.  Existing
implementations using this method route Unacknowledged Information
(UI) frames over IEEE 802.3 and 802.5, Ethernet Version 2 data, and
CCITT X.25 Call Request packets.

      Several types for filters are defined in the filter data
structure for each of the data link controls supported. Multiple
filter types exist to allow applications the ability to have generic
as well as specific filters. Generic filters would allow data from
multiple end systems, and possibly multiple high-level protocols to
be routed to one application.  Specific filters allow data from
specific high-level protocols and specific end systems to be routed
to an application.

      Fig. 2 shows conceptual view of these filters.

      A filter describes the information which can be extracted from
the incoming frame.  This information is then used by the
communications support to route the frame.  For LANs, this
information includes DSAP, SSAP, MAC values and Ethernet TYPE field
for Ethernet and bridged- Ethernet data. For X.25, this information
includes protocol ID, DTE address, and some facility codes (fast
select and reverse charging).  At some point, the application passes
the information to be used as the filter to the communications
support through an application programming interface.  In doing this,
a filter is activated for the application.

      For each different data link protocol (X.25 and 802.2 LAN),
there are varying degrees in which an application can filter its
inbound data.  There is one core element which is always used
(protocol ID for X.25,...