From: Ivan Centeno (icenteno2001@yahoo.com)
Date: Sat Aug 02 2003 - 14:15:12 GMT-3
I think that a good analogy is between selector and
the tcp/udp ports. Both type fields solve the problem
of identify which process/software components in the
receiving machine is the objective of the information
carried in the payload. In ATM without the selector
field there would not be a mechanism to answer this
question.
Usually how the field is used depends a lot of the
applications involved and if they are multiplexing a
PVC/SVC to carry different information interchanges (
in this case you HAVE to use the selector byte ) or
they assign one PVC/SVC per information interchange.
Ivan Centeno
CCIE #10746 R&S.
--- "Amer Mdanat (amdanat)" <amdanat@cisco.com> wrote:
> Guys here is a good explanation of the different
> fields of an ATM NSAP
> [E.164] address:
>
> 1. Authority and format identifier (AFI) -
> identifies the type and the
> format of the address [E.164, ICD or DCC this is a
> common field]
>
> 2. Data Country Code (DCC) - Identifies the country
>
> 3. High-Order Domain Specific Part (HO-DSP) - a
> combination of the
> routing domain (RD) and the area identifier (AREA)
> of the NSAP address.
> The ATM forum combined both together to support a
> flexible multilevel
> addressing hierarchy for prefix based routing
> protocols (let me know if
> you need information on this but I would not worry
> about it if I were
> you).
>
> 4. End System Identifier (ESI) - specifies a 48-bit
> MAC address (note
> that this does not have to be the MAC address [it
> defaults to it in most
> vendor implementations] You can actually set any
> value if you want to
> configure this manually but it is a very hectic job
> to do so and
> extremely confusing!
>
> 5. Selector (SEL) - used by end stations (for local
> multiplexing) and
> has no network significance (remember that this has
> nothing to do with
> Cisco or non Cisco (should have nothing to do with
> the interface but I
> think it is a good practice and if needed I can only
> see this important
> for LANE implementations.
>
> 6. International code designator (ICD) - Identifies
> particular
> international organisations.
>
> 7. E.164 - Indicates the BISDN E.164 address.
>
> The order within the NSAP [E.164 format
> representation] address is as
> follows:
>
>
>
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