TOP (ISO) addressing

4 Feb 86 09:43:00 PST

ubject: RE: TOP (ISO) addressing
To: "hedrick" <To: "hedrick" <hedrick@rutgers>
cc: cc: tcp-ip@sri-nic

> Apparently a few people on this group are interested in the ISO
> protocols. At least there has been enough interest to post some
> of the standards as RFC's (for which I am grateful). So I hope
> there may be someone who can answer a question:
> I have been looking at the specifications for TOP.

         [deleted text]

> If I undestand all of the
> verbiage correctly (and the probability is high that I do not),
> it looks like TOP is likely to run out of address space. As I
> read the spec, an address contains two major parts: a two-byte
> subnetwork number and a variable component which for most of us
> will turn out to be the host's Ethernet address. It seems to
> me that 16 bits is not very much for the subnetwork number.
> As I understand it, the subnetwork number will have to be
> globally unique (i.e. no other subnetwork in the world can
> have the same subnetwork number). Even if that is not said in
> the spec, it seems clear that it is going to have to be the
> case if we are going to allow for the possibility that subnetworks
> will communicate with each other over common-carrier X.25 networks
> or the Arpanet. Furthermore, it is said that routing through
> gateways is to be based entirely on the subnetwok number. This
> seems to imply that places like Rutgers that are class B
> Internet sites will need to use a separate TOP subnetwork number
> for each of our internal subnets. So in practice, it seems
> like we are going to need roughly one subnetwork number for
> every Ethernet that runs TOP. I find it hard to believe that
> 16 bits will be enough.

The Top spec is very early in its development (at V1.0). TOP
is intended to interoperate with MAP at the Network, Transport
and Session layers. For interoperation at the Network layer,
both MAP and TOP will have to use the same addressing formats.
The MAP 2.1 spec calls out three Network address formats allowed
by the ISO address rules. One of these formats has a CCITT
administered Initial Domain Identifier (IDI), and the other two
formats are for locally administered addresses. The address
format in the V1.0 TOP spec is not compatible with any of these.
The TOP spec appears to call out the address format that was
chosen for the Autofact show and I believe is also the NBS OSINET
format. Also, routing protocols are not currently defined.
Routing and congestion control will be absolutely necessary
before ISO protocols could be used in the DoD community.
MAP 3.0 is supposed to include network routing and management

There is a recently established distribution list for ISO protocol
discussion: <>.



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