Internet-Draft Daniele Giordano
Expires: 5 May 2008 2 November 2007
Ethernet preamble variation - Use Ethernet preamble to perform
frame's classification and a switching optimization
draft-giordano-ethpre-class-opt-01
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
Ethernet, standardized as IEEE802.3, is a family of frame-based
networking technologies for local area networks. It's the most
widespread wired LAN technology.
This document proposes a variation of the original frame's structure
to perform a frame's classification and a switching optimization
(fundamental steps for QoS mechanism).
Daniele Giordano [Page 1]
Internet-Draft Ethernet preamble variation Oct 2007
Table of Contents
1. Conventions Used In This Document . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Implementation and Operations . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . . . 7
Daniele Giordano [Page 2]
Internet-Draft Ethernet preamble variation Oct 2007
1. Conventions Used In This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Introduction
Ethernet, standardized as [IEEE] [802.3], (now Ethernet or 802.3) is
a family of frame-based networking technologies for local area
networks (LAN). It's the most widespread wired LAN technology.
This document proposes a variation of the frame's structure to
perform a frame's classification and a switching optimization
(fundamental steps for QoS mechanism).
Actual 802.3 frame
-----------------------------------------
field |PRE |SFD |DA |SA |LT |Payload |FCS |
-----------------------------------------
byte |7 |1 |6 |6 |2 |46 - 1500|4 |
-----------------------------------------
Acronyms:
PRE - The preamble field consists of seven bytes of alternating ones
and zeros and It's used for synchronization.
SFD - Start Frame Delimiter is the 8-bit sequence 10101011 and It's
the same as the eighth byte of the Ethernet preamble.
DA - The destination address specifies the station or stations to
which a frame should be sent.
SA - The source address field contains the unique address of the
transmitter station.
LT - The length field.
FCS - Frame check sequence is an error checking field. It's generated
using the Cyclic Redundancy Check (CRC) on the destination address,
source address, length, and payload fields.
In this frame there isn't information about the type or the
priority of data carried.
Now a days IEEE [802.1q] standard (the evolution of 802.3) has a
classification mechanism implemented with [802.1p] or CoS but this
type of frame is not large supported from all LAN devices.
Daniele Giordano [Page 3]
Internet-Draft Ethernet preamble variation Oct 2007
Actual 802.1q frame
----------------------------------------------
field |PRE |SFD |DA |SA |TAG |LT |Payload |FCS |
----------------------------------------------
| \
| \
--------------------
|TPID|PRI |CFI |VID|
--------------------
bit |16 |3 |1 |12 |
--------------------
Acronyms:
PRE, SFD, DA, SA, LT and FCS fields are similar to corresponding
fields in the 802.3 frame.
TPID - The Tag Protocol Identifier identifies the frame as an
IEEE 802.1q tagged frame.
PRI - Priority, this field refers to the IEEE 802.1p 8 levels
priority (CoS).
CFI - The Canonical Format Indicator specifies if the MAC address is
in canonical or non canonical format.
VID - The VLAN Identifier identifies the VLAN to which the frame
belongs.
This type of classification can also be defined as best-effort
Layer 2 QoS. It is implemented in network adapters and switches.
The traffic is simply classified and sent to the destination.
No type of resources reservation are established.
e.g. 1) A switch which supports both types of protocols (802.3 and
802.1q) receives traffic in a 802.3 frame from a PC;
2) It converts the original frame in a 802.1q frame;
3) the switch performs an IP packet inspection to read [DSCP]
value writing from the PC in the IP header;
4) It writes this value in the PRI field of the 802.1q frame;
5) the frame is sent in a specific output queue in function of
CoS value;
6) when the queue is served the switch converts the frame in a
802.3 format and It sends that in a UART output interface.
THE NEW FRAME DOESN'T HAVE ANY INFORMATION OF PRIORITY.
7) The process restarts for any switch encountered.
Daniele Giordano [Page 4]
Internet-Draft Ethernet preamble variation Oct 2007
3. Implementation and Operations
New Ethernet preamble format
----------------------------------------------
field |PRE |SFD+PRI |DA |SA |LT |Payload |FCS |
----------------------------------------------
byte |7 |1 |6 |6 |2 |46 - 1500|4 |
----------------------------------------------
| \
| \
-----------
|SFD |PRI |
-----------
bit |5 |3 |
-----------
Acronyms:
PRE - The preamble field consists of seven bytes of alternating ones
and zeros and It's used for synchronization.
SFD - Start Frame Delimiter is the 5-bit sequence 10111 and it
identifies the start of the frame.
PRI - Priority, It is a 3-bit field similar to the IEEE 802.1p
levels priority.
DA, SA, LT and FCS are similar to corresponding fields in the 802.3
frame.
Using preamble's bits a switch can know the frame's priority before
of the switching process. It doesn't use resources to perform IP
packet inspection to read the IP DSCP. It doesn't convert 802.3 frame
in other format. The frame maintains its information of priority.
Another advantage is represented by the fact that the switch MUST
change its switching modality (if supported) according to priority
value:
preamble priority < 5 ---> switch engine: store & forward
preamble priority >= 5 ---> switch engine: cut through
In cut through modality the switch starts forwarding a frame before
the whole frame has been received. This technique reduces latency
through the switch and delay of critical applications.
Daniele Giordano [Page 5]
Internet-Draft Ethernet preamble variation Oct 2007
4. IANA Considerations
None.
5. Security Considerations
This document is not directly concerned with security.
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
6.2. Informative References
[802.3] "IEEE Standard for Information technology Telecommunications
and information exchange between systems Local and metropolitan
area networks", IEEE 802.3-2005/Cor 1-2006
[802.1q] "IEEE Standard for Local and metropolitan area networks /
Virtual Bridged Local Area Networks", IEEE 802.1Q-2005, 19 May
2006.
[802.1p] "Traffic Class Expediting and Dynamic Multicast Filtering",
IEEE 802.1d-1998
[IEEE] Institute of Electrical and Electronics Engineers
<http://www.ieee.org>.
[DSCP] K. Nichols, S. Blake, F. Baker, D. Black, "Definition of the
Differentiated Services Field (DS Field) in the IPv4 and IPv6
Headers", RFC 2474,December 1998.
Daniele Giordano [Page 6]
Internet-Draft Ethernet preamble variation Oct 2007
Author's Address
Daniele Giordano
Email: d.giordano@fastpiu.it
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
Daniele Giordano Expires: 5 May 2008 [Page 7]