Browse Prior Art Database

Protocol for Isochronous Traffic over Fiber Channel Switching

IP.com Disclosure Number: IPCOM000112927D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 212K

Publishing Venue

IBM

Related People

Cieslak, RA: AUTHOR [+3]

Abstract

Disclosed is a protocol which can support isochronous traffic over a Fiber Channel Standard (FCS) switching fabric. This protocol provides an enhancement to the existing FCS standards. Furthermore, implementation of this protocol using fast circuit switching paradigm is also proposed.

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This is the abbreviated version, containing approximately 24% of the total text.

Protocol for Isochronous Traffic over Fiber Channel Switching

      Disclosed is a protocol which can support isochronous traffic
over a Fiber Channel Standard (FCS) switching fabric.  This protocol
provides an enhancement to the existing FCS standards.  Furthermore,
implementation of this protocol using fast circuit switching paradigm
is also proposed.

The FCS describes three classes of service:

o   Class 1:  full duplex connection service in which the bandwidth
    of the connection is the entire link bandwidth.

o   Class 2:  acknowledged connectionless packet service.

o   Class 3:  unacknowledged connectionless packet service.

      Many important applications for high-speed networks produce
connection-oriented isochronous traffic in which the required
bandwidth is less than the link bandwidth, such as voice and video.
These applications may use much less bandwidth than the link
bandwidth, so implementing these applications using a Class 1 service
leads to underutilization of the links.  Furthermore, using a Class 1
connection for connection-oriented service is inconvenient when
several isochronous channels need to:

o   be delivered to the same destination port,

o   share the same intermediate link between cascaded switches, or

o   be delivered out of the same source port.

On the other hand, implementing these applications using Class 2 or
Class 3 services is not attractive because these classes of service
provide no guarantee of bandwidth.  Thus, the quality of service will
degrade with increased network use.

      Previously, this problem has been resolved by using various
bandwidth reservation and flow control schemes such as leaky bucket,
virtual clock, and round robin proposed for Asynchronous Transfer
Mode (ATM) switching.  However, several issues remain unresolved when
these bandwidth reservation schemes are applied in a fast circuit
switching environment:

o   Nonzero cell loss rate, even for those connections whose peak
    rate does not exceed the prenegotiated value.  This is due to the
    fact that if the bandwidth is reserved using the nominal packet
    rate, short-term statistical fluctuation of the packet rate can
    result in buffer overflow.  On the other hand, if the bandwidth
    is reserved for the peak rate, inefficiency of bandwidth
    utilization is resulted.

o   Long buffering delay/Large jitter.  Even if the traffic is not
    congested, long buffering delay and thus large jitter is still
    unavoidable.  This is because the back pressure mechanism used by
    nearly all the flow control schemes is not precise and only deals
    with the sender at the packet level.

      In this invention, we propose an enhancement to the FCS
architecture and a switching architecture to implement it.  Briefly,
this enhancement is a new class of service, Class 1i, for isochronous
traffic.

      Assume that there is a bandwidth allocation table...