[ColorForth] reinventing the internet?

[jeff@xxxxxxxxxxxxxxxxxx (Jeff Penn)]

The OSI reference model describes seven protcol layers to describe how
information is transferred between two devices. these are:

7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical

Writing software in well defined layers enables a protocol stack to change
from ethernet to token ring without a complete re-write.

Different network media & protocols will provide different levels of
service:

- Token ring provides reliable connection services at layer two where the
adapter card has the processing overhead.
- SPX (a Novell protocol) & TCP provide conncection services at layer 4
(TCP/IP pre-dates the OSI 7 layer model).
- The OSI protocol can specify that connection services are provided at
layer 3.  This means that each router must manage every connection through
it.

X.25 which was designed when copper wire was everywhere provides
connectiion management at layers 2 & 3 to provide a reliable service.  Frame
Relay is a moderm day replacement for X.25, & does not provides any
connection management, relying on the lower bit error rate of fibre networks
to enable it to reduce protocol overheads.

Each application will have different requirements for connectivity,
security, latency, recovery etc.  If the application is designed for a
specific enviroment it is straight-forward to provide the required level of
services using the minimum of resources - some of which may be inherent in
the network used.

To ensure that applications work effectively in any environment it can
either use the services provided by the data stack, or use its own
customised to specific requirements.

Jeff
-- 
 Jeff Penn - jeff@xxxxxxxxxxxxxxxxxx (Demon Internet Dial-Up)

 Connecting via Demon Internet Ltd
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