Why is the OSI model not the dominant one?
•unclear what layers 5,6, & 7 should do
•layers 1, 2, & 3 have had to be split into sublayers, so the original layering was unrealistic
•several functions (e.g. error control, flow control) can occur in more than one layer
•with 7 layers, long processing delays are possible
•de facto standards (such as the Internet protocols, which were already widely used) don’t fit very well with the OSI model
•the OSI model was devised before the protocols were invented
•associated OSI service definitions and protocols are complex, difficult to implement, and relatively inefficient in operation
•However:unlike the Internet protocols, the OSI model distinguishes between services, interfaces, and protocols, and has proved to be a useful “textbook” introduction to layered networking
•OSI terminology is widely used in describing other models
Why do we need standards standards?
So that there can be open systems available
So that complex problems can be tackled by divide and conquer techniques
To give a fixed quality and product to the customer
To allow the same product to be re used again elsewhere
To aid the design and implementation of ideas
Is there a question of over standardising?
Legal Standards
ITU, International Telecommunications Union formerly the (CCITT)
ISO, International Standards Organisation
IEC, International ElectrotechnicalCommission
FCC, Federal Communications Commission
Loads more as well. ETSI, CEPT, CCIR ...
Informal Standards
IEEE, LAN's WAN's
ATM Forum, X Consortium
Xerox, IBM, Dec, Eircomm, BT, AT& T
•unclear what layers 5,6, & 7 should do
•layers 1, 2, & 3 have had to be split into sublayers, so the original layering was unrealistic
•several functions (e.g. error control, flow control) can occur in more than one layer
•with 7 layers, long processing delays are possible
•de facto standards (such as the Internet protocols, which were already widely used) don’t fit very well with the OSI model
•the OSI model was devised before the protocols were invented
•associated OSI service definitions and protocols are complex, difficult to implement, and relatively inefficient in operation
•However:unlike the Internet protocols, the OSI model distinguishes between services, interfaces, and protocols, and has proved to be a useful “textbook” introduction to layered networking
•OSI terminology is widely used in describing other models
Why do we need standards standards?
So that there can be open systems available
So that complex problems can be tackled by divide and conquer techniques
To give a fixed quality and product to the customer
To allow the same product to be re used again elsewhere
To aid the design and implementation of ideas
Is there a question of over standardising?
Legal Standards
ITU, International Telecommunications Union formerly the (CCITT)
ISO, International Standards Organisation
IEC, International ElectrotechnicalCommission
FCC, Federal Communications Commission
Loads more as well. ETSI, CEPT, CCIR ...
Informal Standards
IEEE, LAN's WAN's
ATM Forum, X Consortium
Xerox, IBM, Dec, Eircomm, BT, AT& T
No comments:
Post a Comment