design principles of internet - nus computing - homeooiwt/cs5229/archives/0708s1/slides/... · b....
Post on 23-Mar-2018
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Why ?
The networks to be integrated arepacket switched network. Packet
switch is natural choice for theapplications at the time (remote
login).
More GoalsRobust - work despite failure of networks or gatewaysVersatile - support a variety of services and networksPermit distributed management of resourcesCost effectiveEasy to add new hostsPermit accounting of resources
Top Goal“Survivability in the Face of Failure”
Communication between two entities shouldcontinue after temporary disruption without
needing to reestablish connection states.
Or
Mask transient failure
Why ?
Easier to implement thanreplication. Replication only
protects against finite numberof node failures.
Services
Remote login - low delay, reliableFile transfer - delay not important,
reliableTeleconferencing - reliability not
important, low delay
Protocols
IP - datagram-based, best effortTCP - reliable service over IPUDP - unreliable service over IP
Not assuming
ReliabilityOrdered delivery
Packet prioritizationBroadcast/multicast
Knowledge of network stats
GoalsRobust - work despite failure of networks or gatewaysVersatile - support a variety of services and networksPermit distributed management of resourcesCost effectiveEasy to add new hostsPermit accounting of resources
Steps
1. A reads file from disk2. A transmits file as packets3. Network delivers packets4. B receives packets5. B write data to disk
Possible Errors
1. Disk failure2. Software bugs3. Packet loss4. Processor/Memory errors5. OS crashes
Choices
A. Make sure every step isreliable
B. End-to-end check andretry (compare checksum,resend if error)
The Argument
To achieve careful file transfer,the transfer application must
apply application-specific, end-to-end reliability guarantee.
”“
The Argument
The end-to-end check of the filetransfer application must still be
implemented no matter howreliable the communication
system becomes.
To implement atlow-level?
Additional cost for applications thatdo not require the feature.
Less information than the “end”, lessefficient.
The Argument
Any attempt by the computerdesigner to anticipate the client’srequirements will probably missthe target and the client will endup re-implementing it anyway.
”
“E2E Argument
The function in question can completely andcorrectly be implemented only with theknowledge and help of the application standingat the endpoints of the communication system.Therefore, providing the questioned function asa feature of the communication system itself isnot possible. (Sometimes an incomplete versionof the function provided by the communicationsystem may be useful as a performanceenhancement)
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