RFC1954 - Transmission of Flow Labelled IPv4 on ATM Data Links Ipsilon Version 1

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　　Network Working Group P. Newman, Ipsilon
Request for Comments: 1954 W. L. Edwards, Sprint
Category: Informational R. Hinden, Ipsilon
E. Hoffman, Ipsilon
F. Ching Liaw, Ipsilon
T. Lyon, Ipsilon
G. Minshall, Ipsilon

May 1996

Transmission of Flow Labelled IPv4 on ATM Data Links
Ipsilon Version 1.0

Status of this Memo

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

IESG Note:

This note documents a private protocol for IPv4-based flows. This
protocol is NOT the product of an IETF working group nor is it a
standards track document. It has not necessarily benefited from the
widespread and in depth community review that standards track
documents receive.

Abstract

This document specifies the manner for transmitting IPv4 datagrams
over an ATM data link, both in a default manner and in the presence
of flow labelling via Ipsilon Flow Management Protocol [IFMP].

Table of Contents

Introduction....................................................2
1. Labels.......................................................2
2. Default Encapsulation........................................2
3. Flow Type 0 Encapsulation....................................3
4. Flow Type 1 Encapsulation....................................4
5. Flow Type 2 Encapsulation....................................5
References......................................................7
Security Considerations.........................................7
Authors' Addresses..............................................7

Introduction

This document specifies the manner for transmitting IPv4 datagrams
over an ATM data link, both in a default manner and in the presence
of flow labelling via Ipsilon Flow Management Protocol [IFMP]. ATM
specific functions such as OAM cells, the CLP bit, and ABR RM cells
are not used. There are no reserved VCIs other than VPI = 0, VCI =
0, which indicates an unassigned cell; and VPI = 0, VCI = 15, which
is used for the default encapsulation. IFMP messages must be sent
using the default encapsulation.

1. Labels

Labels, as carried by IFMP, are realized on an ATM data link as
specific VPI/VCIs. The format of the Label field for ATM labels is:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Reservd| VPI | VCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The low order 16 bits of the label correspond to the VCI, with the
least significant bit of the Label field corresponding to the least
significant bit of the VCI. If the link cannot support a full 16 bit
VCI the unused bits of the VCI must be the most significant bits and
they must be set to zero.

The next 12 higher order bits of the label correspond to the VPI,
with the least significant of these bits corresponding to the least
significant bit of the VPI. If the link cannot support a full 12 bit
VPI, then the unused bits of the VPI must be the most significant
bits and they must be set to zero. The most significant four bits of
the label are reserved. They should be set to zero by the sender and
ignored by the receiver.

2. Default Encapsulation

The default encapsulation for IPv4 packets on ATM data links is the
LLC/SNAP encapsulation specified in section 4.1 "LLC encapsulation
for routed protocols" of RFC1483 [RFC1483]. Such frames begin with
the octets 0xAA 0xAA 0x03 0x00 0x00 0x00 0x08 0x00 (the LLC/SNAP
header for IPv4). The LLC/SNAP header is prefixed to the IP datagram
and the entire packet is encapsulated within the payload of an AAL-5
CPCS-PDU as specified in RFC1483 and illustrated below:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LLC (0xAA-AA-03) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| SNAP (0x00-00-00-08-00) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ IPv4 Datagram ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pad (0 - 47 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ AAL-5 CPCS-PDU Trailer (8 octets) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The maximum transmission unit (MTU) of an IPv4 datagram using the
default encapsulation is 1500 octets.

Frames using the default encapsulation are sent to: VPI = 0, VCI =
15.

3. Flow Type 0 Encapsulation

All IPv4 frames using Flow Type 0 are encapsulated within the payload
of an AAL-5 CPCS-PDU. This is the null encapsulation of section 5.1
"VC based multiplexing of routed protocols" from RFC1483 [RFC1483].
There is no LLC/SNAP header. The first octet of the frame
corresponds to the first octet of the IPv4 datagram (i.e., the octet
that contains the IP version number (4) and Internet Header Length
(IHL) ). The IP datagram is encapsulated within the payload of an
AAL-5 CPCS-PDU as specified in RFC1483 and illustrated below:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ IPv4 Datagram ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pad (0 - 47 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ AAL-5 CPCS-PDU Trailer (8 octets) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The MTU of an IPv4 datagram using Flow Type 0 encapsulation is 1500
octets.

Frames using Flow Type 0 encapsulation are sent to the VPI/VCI
specified in the Label field of the corresponding IFMP Flow Type 0
Redirect message element [IFMP].

4. Flow Type 1 Encapsulation

All IPv4 frames using Flow Type 1 are encapsulated directly in the
payload of an AAL-5 CPCS-PDU. This is the null encapsulation of
section 5.1 "VC based multiplexing of routed protocols" from RFC1483
[RFC1483]. There is no LLC/SNAP header. Also, the following fields
of the IP header are not transmitted: Version, Internet Header Length
(IHL), Type of Service (TOS), Time to Live (TTL), Protocol, Source
Address, and Destination Address. In addition, the first 4 octets
immediately following the IP header (as determined by the IHL field)
are not transmitted. (These 4 octets correspond to the source and
destination ports for TCP and UDP datagrams.) The value of the Total
Length field is not changed; it remains the total length of the IP
datagram before the above fields were removed. The transmitted value
of the Checksum field is the checksum value that would have been
computed for the entire IP header if the TTL field had been set to
zero (i.e., the actual value of the TTL field is "subtracted", using
one's-complement arithmetic, from the Checksum before transmission).

The IP datagram is encapsulated within the payload of an AAL-5 CPCS-
PDU as specified in RFC1483 and illustrated below:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Total Length | Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Flags| Fragment Offset | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Data ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pad (0 - 47 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ AAL-5 CPCS-PDU Trailer (8 octets) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The MTU of the IPv4 datagram using Flow Type 1 encapsulation is 1484
octets (1500 octets minus the 16 octets specified above).

Frames using Flow Type 1 encapsulation are sent to the VPI/VCI
specified in the Label field of the corresponding IFMP Flow Type 1
redirect message element [IFMP].

5. Flow Type 2 Encapsulation

All IPv4 frames using Flow Type 2 are encapsulated directly in the
payload of an AAL-5 CPCS-PDU. This is the null encapsulation of
section 5.1 "VC based multiplexing of routed protocols" from RFC1483
[RFC1483]. There is no LLC/SNAP header. Also, the following fields
of the IP header are not transmitted: Version, Internet Header Length
(IHL), Time to Live (TTL), Source Address, and Destination Address.
The first 4 octets immediately following the IP header (as determined
by the IHL field) are transmitted. (These 4 octets correspond to the
source and destination ports for TCP and UDP datagrams.) The value of
the Total Length field is not changed; it remains the total length of
the IP datagram before the above fields were removed. The
transmitted value of the Checksum field is the checksum value that
would have been computed for the entire IP header if the TTL field
had been set to zero (i.e., the actual value of the TTL field is
"subtracted", using one's-complement arithmetic, from the Checksum
before transmission).

The IP datagram is encapsulated within the payload of an AAL-5 CPCS-
PDU as specified in RFC1483 and illustrated below:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |Type of Service| Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |Flags| Fragment Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Protocol | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Data ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pad (0 - 47 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ AAL-5 CPCS-PDU Trailer (8 octets) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The Reserved fields are not used and should be set to zero by the
sender and ignored by the receiver.

The MTU of the IPv4 datagram using Flow Type 2 encapsulation is 1492
octets (1500 octets minus the 8 octets specified above).

Frames using Flow Type 2 encapsulation are sent to the VPI/VCI
specified in the Label field of the corresponding IFMP Flow Type 2
redirect message element [IFMP].

References

[IFMP] Newman, P., et. al., "Ipsilon Flow Management Protocol
Specification for IPv Version 1.0", Ipsilon Networks
Inc., RFC1953, May 1996.

[RFC1483] Heinanen, J., "Multiprotocol Encapsulation over ATM
Adaptation Layer 5", RFC1483, July 1993.

SECURITY CONSIDERATIONS

Security issues are not discussed in this document.

AUTHORS' ADDRESSES

Peter Newman Phone: +1 (415) 846-4603
Ipsilon Networks, Inc. EMail: pn@ipsilon.com

W. L. Edwards, Chief Scientist Phone: +1 (913) 534 5334
Sprint EMail: texas@sprintcorp.com

Robert M. Hinden Phone: +1 (415) 846-4604
Ipsilon Networks, Inc. EMail: hinden@ipsilon.com

Eric Hoffman Phone: +1 (415) 846-4610
Ipsilon Networks, Inc. EMail: hoffman@ipsilon.com

Fong Ching Liaw Phone: +1 (415) 846-4607
Ipsilon Networks, Inc. EMail: fong@ipsilon.com

Tom Lyon Phone: +1 (415) 846-4601
Ipsilon Networks, Inc. EMail: pugs@ipsilon.com

Greg Minshall Phone: +1 (415) 846-4605
Ipsilon Networks, Inc. EMail: minshall@ipsilon.com

Ipsilon Networks, Inc. is located at:

2191 East Bayshore Road
Suite 100
Palo Alto, CA 94303
USA

Sprint is located at:

Sprint
Sprint Technology Services - Long Distance Division
9300 Metcalf Avenue
Mailstop KSOPKB0802
Overland Park, KS 66212-6333
USA

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