packet sizes

Gerard K. Newman (GKN%SDSC.Bitnet@WISCVM.WISC.EDU)
Fri, 29 AUG 1986 22:17 GMT

        From: lzaz!jmc@seismo.CSS.GOV
        Subject: X.25 Negotiation
        Date: Mon, 25 Aug 86 10:45:51 EDT

        There is some disagreement, at our particular site, over what OSI
        layer is responsible for packet size negotiation.

The transport layer is the first layer which is responsible for determining
frame size, and provides segmenting and blocking to meet the restrictions
imposed by station/network management.

The network layer also provides blocking and segmenting to meet network
frame size requirements. Generally the link layer does not do blocking
or segmentation. So, typically the network layer provides "efficient"
frame sizes to the link layer. If the link layer has adjustable frame
sizes the network layer and station/network management would be responsible
for them.

X.25 can be considered both as a network and a transport level service.
In the context of most full-service networks X.25 provides only link
level services, hiding intermediate X.25 nodes from the larger network's
routing tables.

In lieu of a "strong" station/network management layer the network layer
would be responsible for selecting the link layer frame size.


USPS: Gerard K. Newman
        San Diego Supercomputer Center
        P.O. Box 85608
        San Diego, CA 92138
AT&T: 619.534.5076

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