>At 11:55 AM 6/13/01, Howard C. Berkowitz wrote:
>
>>Lots of books are indeed wrong, when judged against the ISO Internal
>>Organization of the Network Layer document. Stripping to a minimum
>>of OSI speak, what we think of the network layer actually has three
>>sublayers, one of which arguably extends into the data link layer or
>>at least overlaps it.
>>
>>The Subnetwork Independent Convergence Layer is the truly
>>link-independent part such as IP or CLNP.
>>
>>The Subnetwork Access Protocol is the interface to intelligent layer
>>2 protocols that have payload identification -- X.25, ATM, LLC, etc.
>
>Same SNAP that we have come to love and know on LANs? It seems to do
>nothing except payload identification. It has five bytes: 3-byte
>vendor code and 2 byte Type. Protocols with an Ethernet history put
>their EtherType in the Type field.
>
>I'm just checking my understanding. Thanks.
>
>Priscilla
Not quite. It's an abstract service, and, if I went back to the
original document, would probably find it called the Subnetwork
Access Convergence Facility.
802.2 certainly is one example, but it can also be a static mapping
(as in X.25), or even a recursive mapping (802.2 over 802.3 over LANE
using Q.2931).
You may want to go to the IETF page and start tracking the Sub-IP
Temporary Area, which is dealing with lots of these issues.
>
>>The Subnetwork Dependent Convergence Facility maps between the
>>Subnetwork Independent and Subnetwork Access parts. ARP goes here.
>>
>>Going a step farther, it's also worth considering the functional as
>>well as layering models of B-ISDN/ATM, which identify the U(ser),
>>C(ontrol)/signaling and M(anagement) planes at each layer. ARP is a
>>C plane protocol between the end host and the ingress relay, much as
>>is Q.931 and Q.2931. IP routing protocols, PNNI and SS7 are
>>relay-to-relay M plane protocols.
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=8577&t=8335
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