draft-brownlee-acct-req

Last Version:	draft-brownlee-acct-req-00.txt		Tracker Entry
Date:	25-Jun-2002
Disposition:	expired

INTERNET DRAFT
						Nevil Brownlee
						The University of Auckland
						31 March 1994
							
		Accounting Requirements for IPng
              <draft-brownlee-ipng-acct-req-00.txt>

   This document was submitted to the IETF IPng area in response to
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Summary

This white paper discusses accounting requirements for IPng. It recommends 
that all IPng packets carry accounting tags, which would vary in size. In 
the simplest case a tag would simply be a voucher identifying the party 
responsible for the packet. At other times tags should also carry other 
higher-level accounting information.


Background

The Internet Accounting Model - described in RFC 1272 - specifies how 
accounting information is structured, and how it is collected for use by 
accounting aplications.  The model is very general, with accounting 
variables being defined for various layers of a protocol stack.  The group's 
work has so far concentrated on the lower layers, but the model can be 
extended simply by defining the variables required, e.g. for session and 
application layers. 

Brian Carpenter's White Paper on 'transition and other considerations', 21 
Mar 94, suggests that IPng packets should carry authenticated (source, 
destination, transaction) triplets, which could be used for policy-based 
routing and accounting. The following sections explain how the transaction 
field - hereafter called an 'accounting tag' - could be used. 

Lower-layer (Transport) Accounting

At the lower (network) layers the tag would simply be a voucher. This
means it is an arbitrary string which identifies the party
responsible, i.e. willing to pay for, a packet. It would initially be
set by the host which originates the packet, hence at that stage the
tag would identify the user who sent it.

A tag could be changed at various points along a packet's pat. This could 
be done as part of the routing policy processing so as to reflect changes 
of the party responsible over each section of the path. For example: 

	user - provider		  tag identifies user
	provider A - provider B	  tag identifies provider A

The tag could be used by accounting meters to identify the party 
responsible for a traffic flow, without having to deduce this using tables 
of rules. This should considerably simplify accounting for transit traffic 
across intermediate networks. 


Higher-layer (Session and Application) Accounting

At higher layers there is a clear need to measure accounting variables and 
communicate them to various points along a packet's path, for example an
application server may wish to inform a client about its usage of 
resources. A tag containing this information could be read by meters at any 
point along the packet's path for charging purposes, and could also be used 
by the client to inform the user of charges incurred.  

It would make the collection of accounting data much simpler if this 
information was carried in a standard tag within each packet, rather than 
having different protocols provide this service in differing ways.

For 'old' applications which remain unaware of the tag field, a meter could 
be placed at a gateway for the application's host. This 'gateway' meter could 
determine what the application is by watching its streams of packets, then 
set an appropriate value in thir tag fields. 


Structure of the accounting tag

The two uses of tags outlined above must be able to coexist. Since
many - indeed most - of the packets will only carry a voucher, it
seems simplest to keep this as part of the routing tuple (see below).

For the application variables, a separate tag seems sensible. This would 
simply contain a list of the variables.  Having two tags in this way 
would keep separate the management of routers and meters.

If the encryption/digital signature overhead of the second tag proves
to be too high, it should be possible to combine this with the
voucher.

The fine detail of this, or at least the way variables are packed into the 
tags, could be standardised by the Accounting Working Group in due course. 
For the purpose of IPng all that is required is the ability to carry one 
or two variable-size objects in every packet.


Security Considerations

For IPng to provide reliable transport in a hostile environment, routing 
and accounting information, i.e. the (source, dest, network-tag) and 
(application-tag) tuples, must be tamper-proof. Routers and meters which 
need to use the tuples will need to hold appropriate keys for them. Network 
operators will have to plan for this, for example by determining which 
routers need which sets of keys. This will be neccessary in any case for 
reliable policy-based routing, so the extra work required to set up 
accounting meters should be acceptable.