Unix System Administration Handbook 1997 October/usah_oct97.iso/rfc/1600s/rfc1680.txt

Text File | 1994-08-03 | 18KB | 396 lines

Network Working Group                                     C. Brazdziunas
Request for Comments: 1680                                      Bellcore
Category: Informational                                      August 1994


                     IPng Support for ATM Services

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

Abstract

   This document was submitted to the IETF IPng area in response to RFC
   1550.  Publication of this document does not imply acceptance by the
   IPng area of any ideas expressed within.  Comments should be
   submitted to the [e-mail] mailing list.

Executive Summary

   This white paper describes engineering considerations for IPng as
   solicited by RFC 1550 [1].  IPng should provide support for existing
   and emerging link technologies that it will be transported over. Link
   technologies like Ethernet simply multiplex traffic from upper layer
   protocols onto a single channel. "Sophisticated" link technologies
   like ATM are emerging in the marketplace allowing several virtual
   channels to be established over a single wire (or fiber) potentially
   based on an applications' network performance objectives.

   Support for both "sophisticated" (ATM) and existing link technologies
   needs to be considered in an IPng candidate. End-to-end applications
   will communicate through a network where IPng packets travel across
   subnetworks such as Ethernet and Hippi and also more "sophisticated"
   link levels such as ATM.  Though initial support for IPng over ATM
   subnetworks will not facilitate a virtual circuit per application,
   the hooks to provide such a mapping should be in place while also
   maintaining support for the transport of IPng packets across
   conventional subnetworks. Application support for QOS-based link
   level service requires that the  following types of ATM information
   be mappable (or derivable) from the higher level protocol(s) such as
   IPng: source and destination(s) addresses, connection quality of
   service parameters, connection state, and ATM virtual circuit
   identifier. Some of these mappings may be derivable from information
   provided by proposed resource reservation protocols supporting an
   integrated services Internet [4]. However, the ATM virtual circuit
   identifier should be efficiently derivable from IPng packet



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   information.

   An IPng candidate should provide evidence that the mapping from an
   applications' IPng packets to ATM virtual circuit(s) can be
   accomplished in a heterogeneous Internet architecture keeping in
   consideration the gigabit/sec rates that IPng/ATM subnetworks will
   eventually be operating at.

1.  Introduction

   This paper describes parameters that are needed to map IPng (or any
   protocol operating above the link level) to ATM services. ATM is a
   "sophisticated" link level technology which provides the potential
   capability for applications at the TCP/UDP level to map to a single
   ATM virtual circuit for transport across an ATM network(s) customized
   to the network performance and traffic requirements for that
   application. This is a step above many of today's existing link
   technologies which can only support a single level of network
   performance that must be shared by all applications operating on a
   single endpoint.

   The future Internet will be comprised of both conventional and
   "sophisticated" link technologies.  The "sophisticated" features of
   link layers like ATM need to be incorporated into an internet where
   data travels not only across an ATM network but also several other
   existing LAN and WAN technologies. Future networks are likely to be a
   combination of subnetworks providing best-effort link level service
   such as Ethernet and also sophisticated subnetworks that can support
   quality of service-based connections like ATM.  One can envision data
   originating from an Ethernet, passing through an ATM network, FDDI
   network, another ATM network, and finally arriving at its destination
   residing on a HIPPI network. IPng packets will travel through such a
   list of interconnected network technologies as ATM is incorporated as
   one of the components of the future Internet.

   To support per application customizable link level connections, four
   types of ATM information should be derivable from the higher level
   protocol(s) like IPng. This ATM information includes: source and
   destination ATM addresses, connection quality of service parameters,
   connection state, and an ATM virtual circuit identifier which maps to
   a single IPng application (i.e., single TCP/UDP application). Some of
   these mapping  could potentially be derivable through information
   provided by proposed resource reservation protocols supporting an
   integrated services Internet [4].  However, the ATM virtual circuit
   identifier needs to be efficiently mappable from IPng packet
   information.





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   Organization of this white paper is as follows. First the
   characteristics of ATM are described focusing on functions that are
   not provided in today's LAN technologies. This section provides
   background information necessary for the following section describing
   the parameters needed to map IPng services to ATM services.

2.  Terminology

   In this white paper, the term "application" refers to a process or
   set of collective processes operating at the TCP/UDP level or above
   in the protocol stack. For example, each instance of "telnet" or
   "ftp" session running on an end station is a distinct application.

3.  Characteristics of ATM Service

   ATM has several characteristics which differentiates it from current
   link level technologies.  First of all, ATM has the capability of
   providing many virtual channels to transmit information over a single
   wire (or fiber). This is very similar to X.25, where many logical
   channels can be established over a single physical media. But unlike
   X.25, ATM allows for each of these channels or circuits to have a
   customizable set of performance and quality of service
   characteristics. Link level technologies like Ethernet provide a
   single channel with a single performance and quality of service
   characteristic. In a sense,  a single ATM link level media appears
   like an array of of link level technologies each with customizable
   characteristics.

   ATM virtual circuits can be established dynamically utilizing its
   signaling protocol. ATM signaling is a source initiated negotiation
   process for connection establishment. This protocol informs elements
   in the network of the characteristics for the desired connection. ATM
   signaling does not provide any guidelines for how network elements
   decide whether it can accept a call or where a signaling request
   should be forwarded if the end destination (from the link level
   perspective) has not been reached. In short, ATM signaling does not
   support any routing functionality of network admission control.

   ATM signaling establishes a "hard state" in the network for a call.
   "Hard state" implies that the state of a connection in intermediate
   switching equipment can be set and once established it will be
   maintained until a message is received by one of the ends of the call
   requesting a change in state for the connection [2]. As a result, an
   ATM end system (this could be a workstation with an ATM adapter or a
   router with an ATM interface) receives guaranteed service from the
   ATM network. The ATM network is responsible for maintaining the
   connection state. The price the ATM termination points pay for this
   guarantee is the responsibility of changing the state of the



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   connection, specifically informing the ATM network to establish,
   alter, or tear-down the connection.

   Each ATM end point in a network has an ATM address associated with it
   to support dynamic connection establishment via signaling. These
   addresses are hierarchical in structure and globally unique [3]. As a
   result, these addresses are routable. This allows ATM networks to
   eventually support a large number of ATM endpoints once a routing
   architecture and protocols to support it become available.

   The ATM User-Network Interface (UNI) signaling protocol based on
   ITU-TS Q.93B  allows many different service parameters to be
   specified for describing connection characteristics. [3] These
   parameters can be grouped into several categories: ATM adaptation
   layer (AAL) information, network QOS objectives, connection traffic
   descriptor, and transit network selector. The AAL information
   specifies negotiable parameters such as AAL type and maximum packet
   sizes. The network QOS objectives describe the service that the ATM
   user expects from the network. Q.93B allows for one of five service
   classes to be selected by the ATM user. The service classes are
   defined as general traffic types such as circuit emulation (class A),
   variable bit rate audio and video (class B), connection-oriented data
   transfer (class C), connectionless data transfer (class D), best
   effort service (class X), and unspecified [3]. Each of these
   categories are further specified through network provider objectives
   for various ATM performance parameters. These parameters may include
   cell transfer delay, cell delay variation, and cell loss ratio. The
   connection traffic descriptor specifies characteristics of the data
   generated by the user of the connection. This information allows the
   ATM network to commit the resources necessary to support the traffic
   flow with the quality of service the user expects. Characteristics
   defined in the ATM Forum UNI specification include peak cell rate,
   sustainable cell rate, and maximum and minimum burst sizes [3].
   Lastly, the transit network selection parameter allows an ATM user to
   select a preferred network provider to service the connection [3].

4.  Parameters Required to Map IPng to ATM

   There are several parameters required to map ATM services from a
   higher level service like IPng. These ATM parameters can be
   categorized in the following manner: addressing parameters,
   connection QOS-related parameters, connection management information,
   and ATM virtual circuit identifier. The first three categories
   provide support for ATM signaling. The last parameter, a connection
   identifier that maps IPng packets to ATM virtual circuits, provides
   support for an ATM virtual circuit per application when the end-to-
   end connection travels across an ATM subnetwork(s) (this does not
   assume that ATM is the only type of subnetwork that this connection



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   travels across). Below, mapping issues for each of these parameters
   will be described.

4.1.  Addressing

   ATM supports routable addresses to each ATM endpoint to facilitate
   the dynamic establishment of connections. These addresses need to be
   derived from a higher level address such as an IPng address and IPng
   routing information.  This type of mapping is not novel. It is a
   mapping that is currently done for support of current IP over link
   technologies such as Ethernet.  An IP over ATM address resolution
   protocol (ARP) has been described in the Internet Standard,
   "Classical IP over ATM" [5]. In addition, support for IP routing over
   large ATM networks is being worked in the IETF's "Routing over Large
   Clouds" working group.

4.2.  Quality of Service

   As described in section 3, an ATM virtual circuit is established
   based upon a user's traffic characteristics and network performance
   objectives. These characteristics which include delay and throughput
   requirements can only be defined by the application level (at the
   transport level or above) as opposed to the internetworking (IPng)
   level. For instance, a file transfer application transferring a 100
   MB file has very different link level performance requirements than a
   network time application. The former requires a high throughput and
   low error rate connection whereas the latter could perhaps be
   adequately serviced utilizing a best-effort service. Current IP does
   not provide much support for a quality of service specification and
   provides no support for the specification of link level performance
   needs by an application directly. This is due to the fact that only a
   single type of link level performance is available with link
   technologies like Ethernet.  As a result, all applications over IP
   today receive the same level of link service.

   IPng packets need not explicitly contain information parameters
   describing an application's traffic characteristics and network
   performance objectives (e.g., delay = low, throughput = 10 Mb/s).
   This information could potentially be mapped from resource
   reservation protocols that operate at the IP (and potentially IPng)
   level [4].

4.3.  Connection Management

   The establishment and release of ATM connections should ultimately be
   controlled by the applications utilizing the circuits. As described
   in section 3, ATM signaling establishes a "hard state" in the network
   which is controlled by the ATM termination points [2]. Currently, IP



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   provides no explicit mechanism for link level connection management.
   Future support for link level connection management could be
   accomplished through resource reservation protocols and need not
   necessarily be supported directly via information contained in the
   IPng protocol.

4.4.  Connection Identifier

   A mapping function needs to exist between IPng packets and ATM so
   that application flows map one-to-one to ATM virtual circuits.
   Currently, application traffic flows are identified at the transport
   level by UDP/TCP source and destination ports and IP protocol
   identifiers.  This level of identification should also be available
   at the IPng level so that information in the IPng packets identify an
   application's flow and map to an ATM virtual circuit supporting that
   flow when the IPng packets travels across an ATM subnetwork(s).

   Using the current IP protocol, identifying an application's traffic
   flow requires the combination of the following five parameters:
   source and destination IP addresses, source and destination UDP/TCP
   ports, and IP protocol identifier. This application connection
   identifier for IP is complex and could potentially be costly to
   implement in IP end stations and routers.  The IPng connection
   identifier should be large enough so that all application level
   traffic from an IPng end point can be mapped into the IPng packet.
   Currently, ATM provides 24 bits for virtual circuit identification
   (VPI and VCI). This provides sufficient capacity for 2^24
   (16,777,216) connections [6]. The actual number of bits that are used
   for the ATM virtual circuit however is established through
   negotiation between the ATM endpoint and ATM network. This number is
   useful as an upper bound for the number of mappings that are needed
   to be supported by IPng.

   An IPng candidate should be able to identify how IPng packets from an
   application can map to an ATM  virtual circuit. In addition, this
   mapping should be large enough to support a mapping for every IPng
   application on an end system to an ATM virtual circuit. Careful
   consideration should be given to complexity of this mapping for IPng
   to ATM since it needs to eventually support gigabit/sec rates.












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References

   [1] Bradner, S., and A. Mankin, "IP: Next Generation (IPng) White
       Paper Solicitation", RFC 1550, Harvard University, NRL, December
       1993.

   [2] Clark, D., "The Design Philosophy of the DARPA Internet
       Protocols", Proc.  ATM SIGCOMM '88, August 1988.

   [3] "ATM User-Network Interface Specification, Version 3.0", ATM
       Forum, September 10, 1993.

   [4] Zhang, L., Estrin, D., Herzog, S., and S. Jamin, "Resource
       ReSerVation Protocol (RSVP) - Version 1 Functional
       Specification", Work in Progress, October 1993.

   [5] Laubach, M., "Classical IP and ARP over ATM", RFC 1577, Hewlett-
       Packard Laboratories, January 1994.

   [6] "Asynchronous Transfer Mode (ATM) and ATM Adaptation Layer (AAL)
       Protocols Generic Requirements", Bellcore Technical Advisory TA-
       NWT-001113, Issue 1, June 1993.

Security Considerations

   Security issues are not discussed in this memo.

Author's Address

   Christina Brazdziunas
   Bellcore
   445 South Street
   Morristown, NJ 07960

   Phone: [phone]
   EMail: [e-mail]















Brazdziunas                                                     [Page 7]