Dynamically Switched Link Control Protocol
RFC 1307

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Network Working Group                                           J. Young
Request for Comments: 1307                                  A. Nicholson
                                                     Cray Research, Inc.
                                                              March 1992

               Dynamically Switched Link Control Protocol

Status of this Memo

   This memo defines an Experimental Protocol for the Internet
   community.  Discussion and suggestions for improvement are requested.
   Please refer to the current edition of the "IAB Official Protocol
   Standards" for the standardization state and status of this protocol.
   Distribution of this memo is unlimited.

Abstract

   This memo describes an experimental protocol developed by a project
   team at Cray Research, Inc., in implementing support for circuit-
   switched T3 services.  The protocol is used for the control of
   network connections external to a host, but known to the host.  It is
   documented here for the benefit of others who may wish to perform
   further research.

   While working with circuit-switched T3 networks, developers at Cray
   Research, Inc., defined a model wherein a host would generate control
   messages for a network switch.  This work is described in RFC 1306,
   "Experiences Supporting By-Request Circuit-Switched T3 Networks".  In
   order to simplify the model it was decided that the inconsistencies
   of switch control should be hidden from the host generating the
   control messages.  To that end, a protocol was defined and
   implemented.  This RFC documents the Dynamically Switched Link
   Control Protocol (DSLCP), which is used for creation and control of
   downstream network links by a host.

1.0  INTRODUCTION

   The Dynamically Switched Link Control Protocol (DSLCP) allows a host
   with knowledge of a special downstream network link to issue messages
   to control the status of that link.

   This document describes the functions of the DSLCP to control
   external network connections.

Young & Nicholson                                               [Page 1]
RFC 1307       Dynamically Switched Link Control Protocol     March 1992

1.1  Motivation

   Circuit Switched Networks are becoming available to the Internet
   community.  These networks are made available by requesting a
   connection through a switch.  Normally circuit switched network links
   are disconnected, and their prohibitive cost suggests that it is very
   costly to leave them connected at all times.

   Internet users and hosts wish to send data over a circuit switched
   networks, but only connect the network links when a transport
   connection is to be established.  While it would be possible to use
   packet routers to identify the need for switching a connection on and
   off, only the transport provider can positively identify the
   beginning and end of a transport session.  There must be a mechanism
   to activate and deactivate the link at the beginning and end of a
   transport session.

   The DSLCP assumes that a transport provider has knowledge of a
   downstream link which must be setup before data transfer may take
   place.  However, the details of link setup may vary by the type of
   link (circuit-switched or other), specific hardware, or
   administrative differences.  The DSLCP hides these details from the
   transport provider by offering a simple request/release model of link
   preparation.  The model assumes an entity in control of the link
   which handles the details of connection preparation while responding
   to the DSLCP commands of the transport provider.  This entity is
   called the link controller.

   The DSLCP allows internet hosts to dynamically change the fabric of
   the internet by sending messages through the internet in advance of
   data which is to travel across the newly created links.

1.2  Scope

   DSLCP is intended to provide an interface between transport providers
   and arbitrary network links requiring creation, control, setup, or
   conditioning before data communications may take place.

1.3  Interfaces

   There are no specific user level interfaces to DSLCP, although they
   are not precluded.  Link control is a function of the network layer,
   initiated by requests from the transport provider.

   A DSLCP transaction is defined as a transport provider communicating
   with a link controller for the duration of transport session.  A
   network path between the host providing transport services and the
   link controller must exist in advance of the DSLCP transaction.

Young & Nicholson                                               [Page 2]
RFC 1307       Dynamically Switched Link Control Protocol     March 1992

   Either party to an DSLCP transaction may asynchronously generate
   messages.

1.4  Operation

   The purpose of the DSLCP is to allow a transport provider to request
   the setup of a downstream network link so that data transfer may take