Browse Prior Art Database

Virtual Connection-Based Packet Transfer for Network Adapters

IP.com Disclosure Number: IPCOM000103950D
Original Publication Date: 1993-Feb-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 4 page(s) / 140K

Publishing Venue

IBM

Related People

Patel, B: AUTHOR [+3]

Abstract

Disclosed is a virtual connection packet transfer mechanism for a bus based communication adapter architecture which minimizes the packet processing overhead and increases the adapter capacity to handle multiple attachments to very high speed networks (e.g., FDDI).

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Virtual Connection-Based Packet Transfer for Network Adapters

      Disclosed is a virtual connection packet transfer mechanism for
a bus based communication adapter architecture which minimizes the
packet processing overhead and increases the adapter capacity to
handle multiple attachments to very high speed networks (e.g., FDDI).

      This applies to any bus based Network Adapters (NA) of the type
illustrated in Fig. 1.  The main component in the design is the
centralized Packet Memory Manager (PMM).  All aspects of the memory
management are performed by the PMM, including the queue structures
and the buffer allocation in the Packet Memory (PM).  These functions
are kept transparent to the Attachment Interface Modules (AIMs).  By
relieving the AIMs of these functions their complexity is reduced and
packet transfer operations are streamlined.  The AIMs do not have
direct access to the Packet Memory, instead, they operate at a higher
level based on packet identifiers.  This also simplifies/reduces the
number of signals that the bus has to support: a Connection ID (CID)
(4/5 bits) and a few control signals (5 bits) rather than the address
signals (24 bits).

      Transfers to and from packet memory are performed by
establishing a virtual connection between an AIM and the PMM.  The
PMM establishes the connection at the time of a transfer request by
assigning a Connection ID (CID) to the transfer.  A unique CID is
assigned to each packet transfer.  The states of all virtual
connections are maintained in the PMM's Write and Read Connection
Tables, WCT and RCT, respectively (see Fig. 2).  A CID is freed to
establish a new connection once a transfer is complete.

      Although multiple virtual connections may exist at any instant,
only one is being serviced by the PMM at a time, due to the fact that
all transfers pass through the bus.  A distinction is made between
READ requests (reading from the PM) and WRITE requests (writing to
the PM), since different state information is maintained for each
(the WRITE CID and the READ CID are represented as WCID and RCID,
respectively).

      The PMM always anticipates that a bus request is a WRITE_PM
request and responds accordingly.  If this is not the case, and in
fact the AIM requests a READ_PM, the AIM will respond to the bus
grant by placing a QID on the bus.  Upon detecting the QID the PMM
recognizes that the AIM desires to READ_PM and responds accordingly.

      Packet WRITE to PM.  When an AIM obtains a packet to be written
to the PM, it issues a bus request.  The PMM responds with a bus
grant and provides a new WCID.  If the PM_WRITE request is the
resumption of a previous request to which a WCID has already been
assigned, then the AIM will ignore the new WCID, otherwise it will
use it for the dura...