Hi folks-

The discussion below makes me think we need to explicit about the difference between the "user data payload" and the "framing protocol". The former is the information that is to be transported [unmodified] from the source to the destination within a circuit, the latter is that information placed on a link in addition to or surrounding the user data that allows the user data to be recovered or routed. The User Data Payload should always be delivered at the egress point just as it was accepted at the ingress point. But the network is free to do whatever it has to within the network to transport it (e.g. segmentation and reassembly, transport protocol adaptations, etc.)

I think this explicit terminology will allow us to be clear about what is the user data payload at any point in the circuit, and what is the outer layer of transport framing protocol.

I would also define two other terms: "access" framing protocol, and the "transport" framing protocol. The former defines framing protocol that delivers the user data payload to the ingress point of a circuit (or how it is delivered at the egress point), where the latter defines the framing protocol(s) used within the network to transport the user data (and of course, the latter may be different along different segments of the circuit).

These terms I think will help us be clear as we discuss things like tunneling and when we encapsulate ot de-encapsulate circuit segments and protocols.

Jerry

John Vollbrecht wrote:

Jeroen van der Ham wrote:

- layers come and go. We got rid of the ATM layer, and some people try
to get rid of the SONET layer(s). However, just the same, we add
(sub)layers for Ethernet and OTN.
- The order can not be fixed: it is getting common to see network
tunnels, e.g. Ethernet over IP over Ethernet, or simply Ethernet over
Ethernet (think Q-in-Q).

I am wondering if layers are different if they are Q-in-Q or Ethernet over IP. Seems there needs to be an adaptation between these, but the client info stays the same. It seems to me that collapsing layers where the client info stays the same and only the characteristic info changes can be useful.

Where adaptations do not exist between specific layers it seems silly (at least to me) to flatten the topology.
Where adaptations are not possible between layers - one cannot adapt a VLAN portion of a fiber, at least not without another adaptation (e.g. SONEHi folks-T) between them.

I would agree that an Ethernet frame carried Q-in-Q would need to be adapted somehow to the EoIP environment. The router does this but you need to tell it whether to encapsulate the whole inbound ethernet frame into IP packets, or to strip the inbound [outter] ethernet frame off, and simply forawrad the Q-in-Q frame over the IP link.

I think we should distinguish between the link layer protocol which is the protocol that actually carries data on a physical link, from what I call the "access" protocol - the protocol that is used to present data at the ingress or egress points of a circuit. (There maybe other terms used for these...these are what I use). The di

My concern about layer collapsing is how it handles multiplexing and
inverse multiplexing. A SONET circuit in the GLIF community may carry
multiple Ethernet connections. At my work, we have an immediate problem
that we must describe the relations between these connections -- if the
SONET circuit goes does, so will the Ethernet circuits, and our software
must know this relations or we will not inform the correct customers.
Therefor, we need a network description that is able to describe this
relation. I have doubts that this can still work for collapsed topologies.

I think this is probably a valid concern. However I don't completely understand it. Is this the case where lower layers are carrying multiplexed upper layer connections and one needs to know which upper layer connections are being carried at the lower layer so that if it fails the upper layer can be notified?

If so it seems that the lower layer is a Link which carries segments of the upper layer and if it goes down the upper layer link goes down. It is then the upper layer's job to notify its users that the link is down.

Regards,
Freek
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