414Lecture4preview

414Lecture4preview - Lecture 4 Application Layer SMTP and...

Info iconThis preview shows pages 1–9. Sign up to view the full content.

View Full Document Right Arrow Icon
Lecture 4 Application Layer SMTP and Email protocols, DNS ECSE 414 – Fall 2010
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2010 Michael Rabbat ECSE 414, Lecture 4 2 Announcements Homework Assignment #1 Due next Thursday, Sep 23 Form project groups Email me (in WebCT) ASAP Project topics posted tonight Claim a topic by posting in WebCT “Project Topics” forum (can only claim if you already have a group)
Background image of page 2
2010 Michael Rabbat ECSE 414, Lecture 4 3 Problem Institutional Network connected to Internet Avg. object size requested = 100 000 bits Avg. request rate = 10 per second Access Link 2 Mbps Model access delay as D/(1-BD) D = avg. time to send object over access link (= average size/link rate) B = arrival rate of objects Avg. internet delay = 0.5 s (round-trip, from router/switch at other side of access link and back) What is total average response time T ? If we install a cache with hit rate 1/2 on the institutional side of the access link what is the new avg. response time T’ ? (Assume there is 0 delay if the object is in the cache).
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2010 Michael Rabbat ECSE 414, Lecture 4 5 Topics for Today Email Protocols DNS
Background image of page 4
2010 Michael Rabbat ECSE 414, Lecture 4 6 Electronic Mail: mail servers Mail Servers mailbox contains incoming messages (yet to be read) for user message queue of outgoing (to be sent) mail messages smtp protocol between mail servers to send email messages client: sending mail server “server”: receiving mail server mail server user agent user agent user agent mail server user agent user agent mail server user agent SMTP SMTP SMTP
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2010 Michael Rabbat ECSE 414, Lecture 4 7 Electronic Mail: smtp [RFC 821] Simple Mail Transfer Protocol uses tcp to reliably transfer email msg from client to server, port 25 direct transfer: sending server to receiving server three phases of transfer handshaking (greeting) transfer of messages closure command/response interaction commands: ASCII text response: status code and phrase messages in 7-bit ASCII
Background image of page 6
2010 Michael Rabbat ECSE 414, Lecture 4 8 smtp smtp uses persistent connections smtp requires message (header & body) to be in 7-bit ASCII Comparison with http: http: pull email: push both have ASCII command/ response interaction, status codes http: each object encapsulated in its own response msg smtp: multiple objects sent in multipart msg
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
ECSE 414, Lecture 4 9 Mail message format SMTP: protocol for exchanging email msgs RFC 822: standard for text message format: header lines, e.g.,
Background image of page 8
Image of page 9
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 26

414Lecture4preview - Lecture 4 Application Layer SMTP and...

This preview shows document pages 1 - 9. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online