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Unformatted text preview: x ones can for example, WWW (HTTP) is layered over TCP over IP (and uses for DNS, ARP, DHCP, RIP, OSPF, BGP, PPP, ICMP) Abstraction of implementation details Abstraction
separation of implementation and speciﬁcation separation can change implementation as long as service interface is can maintained Can reuse functionality, allow mix-and-match Can
upper layers can share lower layer functionality. Example: Both upper TCP and UDP (transport layer protocols) can share the service of IP (network layer protocol) Same upper layer protocol can run over different lower layer Same protocols. Example: IP can run over different link technologies such as ethernet, ﬁber, telephone lines or even wireless link. How many versions of “networking software” do we need to support How all the functions supported by the current set of Internet protocols? Problems with layering
Layering hides information Layering
if it didn t then changes to one layer could require changes if then everywhere layering violation layering But sometimes hidden information can be used to improve But performance
for example, ﬂow control protocol may think packet loss is always for because of network congestion if it is, instead, due to a lossy link, the ﬂow control breaks if this is because we hid information about reason of packet loss from this ﬂow control protocol Layering
There is a tension between information-hiding (abstraction) and There achieving good performance Art of protocol design is to leak e...
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This note was uploaded on 12/08/2010 for the course IEG IEG3310 taught by Professor Wingc.lau during the Spring '10 term at CUHK.
- Spring '10