Multi-Thresholding Packet Discard Mechanism for Data Traffic in Asynchronous Transfer Mode Network
Original Publication Date: 1996-Apr-01
Included in the Prior Art Database: 2005-Mar-31
Aznar, A: AUTHOR [+6]
Disclosed is an enhanced packet discard mechanism in an Asynchronous Transfer Mode (ATM) network, improving the network efficiency for classical Transmission Control Protocol/Internet Protocol (TCP/IP) traffic.
Multi-Thresholding Packet Discard Mechanism for Data
Traffic in Asynchronous
Transfer Mode Network
an enhanced packet discard mechanism in an
Asynchronous Transfer Mode (ATM) network, improving the network
efficiency for classical Transmission Control Protocol/Internet
Protocol (TCP/IP) traffic.
well-known technique of Early Packet Discard (EPD), a
congested ATM switch discards new incoming packets entirely. This is
an improvement if compared to the previous method consisting in
randomly discarding incoming cells with the inherent risk of
corrupting every packet going through the switch as described in (*).
In the same
document (*), it appears that the EPD mechanism
leads to a network global synchronization, packets from every
connection being discarded when the EPD threshold is reached, and
that EPD has a bias against connections with shorter packets, more
likely to be 'caught' by the discarding mechanism in the context of
short epoch congestion.
Principle - In
the disclosed mechanism, a multiple threshold
scheme is added to the existing EPD mechanism, in order to reduce the
previously mentioned drawbacks. The principle which operates in a
single FIFO queue environment consists in defining several thresholds
and to associate a counter to each threshold. The lower the
threshold is, the larger the counter. The highest threshold has no
associated counter and corresponds to the well-known threshold TH-n.
CNT_i associated to the treshold Th_i is
incremented each time a cell is received and the queue count exceeds
threshold Th_i. When an incoming cell makes one or several counter
wrap arounds, the connection the cell belongs to is marked, causing
the next incoming packet of this connection to be discarded. The
mechanism is summarized in the Figure. Th_A in the Figure is the
upper threshold at which all incoming cells have to be dropped.
The benefits of these inventions are:
1. Lower thresholds allow to start discarding packets sooner in
regard to congestion and randomly, thus avoiding the drawback
global synchronization. Sources for which one or several
have been dropped at this early stage are warned that