[LINK] Story: FBI seeking more interception
Fri, 23 Nov 2001 23:15:35 +1100
Sorry Adam, but you have this the wrong way round. Routered IP services
can and do transmit packets along multiple paths and they can arrive
mis-ordered and need to be reassembled (see RFC 815 etc). ATM circuits
are connection oriented and an end to end path needs to be established
before the cells will flow. ATM Cells must arrive in the same order as
they are transmitted along a unique virtual path. To simplify the 5 byte
ATM header, there's no cell sequence number that facilitates reassembly
(unlike the IP datagram header). The receiving ATM AAL just counts the
53 bytes to identify the unique cells. (Unlike Frame Relay where there
are specific frame start and frame end flags).
There's a couple of other statements that are wrong but this'll do.
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From: email@example.com [mailto:firstname.lastname@example.org] On
Behalf Of Adam Todd
Sent: Friday, 23 November 2001 7:38 PM
To: Chirgwin, Richard; 'email@example.com'
Subject: Re: [LINK] Story: FBI seeking more interception
> >The bulk of the FBI's new requests, however, apply to technologies
>rely on so-called "packet-switched"
> >networks, where communications data is broken up into digital bits
>being sent and reassembled at the
> >receiving end.
>Hmm. The author is clearly suffering huge gaps in his technical
>he doesn't understand that Internet services are packet based. He also
>doesn't understand that all digital communications fit the description
>"communications data is broken up into digital bits" (except that the
>description itself is that of a simpleton).
Actually no, the author isn't wrong, just badly stating. Although IP is
packets, they normally follow the same path. However the Author is
referring to ATM which by design breaks even an IP packet into 53 byte
chunks and sends it via any and EVERY path that is available where it is
reconstructed at the other end. (Roughly speaking.)
> >But packet switching makes it difficult to monitor a single
>seamlessly as it travels across different
> >communications platforms, routes and services, and the FBI wants
>to implement changes that would make
> >such services more reliable and easier to track.
>Well. A single communication can easily enough be monitored at its
>ingress to the network - for example, the customer-facing access
Packet switching is what ATM does, not what IP routers do.
Yes, you are correct that it can be monitored at the ingress point, or
egress point. But that's not always in a jurisdiction that is suitable
FBI activities :)
Think of the amount of traffic that passes THROUGH the USA network as
pretty much the "center" of the Internet routing world.
>This matters: inaccurate reporting compromises the quality of any
>based on that reporting.
I do agree.