RFC 1209 (rfc1209) - Page 2 of 11

Transmission of IP datagrams over the SMDS Service

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