The Transmission of IP Datagrams over the SMDS Service
RFC 1209

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Network Working Group                                      D. Piscitello
Request for Comments: 1209                                   J. Lawrence
                                            Bell Communications Research
                                                              March 1991

         The Transmission of IP Datagrams over the SMDS Service

Status of this Memo

   This memo defines a protocol for the transmission of IP and ARP
   packets over a Switched Multi-megabit Data Service Network configured
   as a logical IP subnetwork.  This RFC specifies an IAB standards
   track protocol for the Internet community, and requests discussion
   and suggestions for improvements.  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 initial use of IP and ARP in an SMDS service
   environment configured as a logical IP subnetwork, LIS (described
   below).  The encapsulation method used is described, as well as
   various service-specific issues.  This memo does not preclude
   subsequent treatment of the SMDS Service in configurations other than
   LIS; specifically, public or inter-company, inter-enterprise
   configurations may be treated differently and will be described in
   future documents.  This document considers only directly connected IP
   end-stations or routers; issues raised by MAC level bridging are
   beyond the scope of this paper.

Acknowledgment

   This memo draws heavily in both concept and text from [4], written by
   Jon Postel and Joyce K. Reynolds of ISI and [5], written by David
   Katz of Merit, Inc.  The authors would also like to acknowledge the
   contributions of the IP Over SMDS Service working group of the
   Internet Engineering Task Force.

Conventions

   The following language conventions are used in the items of
   specification in this document:

      o MUST, SHALL, or MANDATORY -- the item is an absolute
        requirement of the specification.

IP over SMDS Working Group                                      [Page 1]
RFC 1209            IP and ARP over the SMDS Service          March 1991

      o SHOULD or RECOMMENDED -- the item should generally be followed
        for all but exceptional circumstances.

      o MAY or OPTIONAL -- the item is truly optional and may be
        followed or ignored according to the needs of the implementor.

Introduction

   The goal of this specification is to allow compatible and
   interoperable implementations for transmitting IP datagrams and ARP
   requests and replies.

   The characteristics of the SMDS Service and the SMDS Interface
   Protocol (SIP) are presented in [3], [6], and in [7].  Briefly, the
   SMDS Service is a connectionless, public, packet-switched data
   service.  The operation and features of the SMDS Service are similar
   to those found in high-speed data networks such as LANs:

      o The SMDS Service provides a datagram packet transfer, where each
        data unit is handled and switched separately without the prior
        establishment of a network connection.

      o The SMDS Service exhibits high throughput and low delay, and
        provides the transparent transport and delivery of up to 9188
        octets of user information in a single transmission.

      o No explicit flow control mechanisms are provided; instead, the
        rate of information transfer on the access paths is controlled
        both in the subscriber-to-network direction and in the network-
        to-subscriber direction through the use of an access class
        enforcement mechanism.

      o Both individually and group-addressed (multicast) packets can
        be transferred.

      o In addition to these LAN-like features, a set of addressing-
        related service features (source address validation, source and
        destination address screening) are provided to enable a
        subscriber or set of subscribers to create a logical private
        network, or closed user group, over the SMDS Service.  The
        access control provided by the closed user group mechanism is
        supplied by the SMDS provider according to the specifications
        stated in [3].

      o SMDS addresses are 60 bits plus a 4 bit Address Type.  The
        Address Type subfield occupies the 4 most significant bits of
        the destination and source address fields of the SIP Level 3
        Protocol Data Unit (PDU).  It contains the value 1100 to

IP over SMDS Working Group                                      [Page 2]
RFC 1209            IP and ARP over the SMDS Service          March 1991

        indicate an individual address and the value 1110 for a 60-bit
        group address.

   The SMDS Interface Protocol is based on the IEEE Standard 802.6,
   Distributed Queue Dual Bus (DQDB) Connectionless MAC protocol [8].
   The SMDS service layer corresponds to the IEEE 802 MAC sublayer.  The