MIS365 9 - Internet Protocols - General Architecture

MIS365 9 - Internet Protocols - General Architecture -...

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MIS365 Data Communications & Networking Jerry Malcolm Internet Protocols – General Architecture
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Internet Communications Two basic design points of internet communications: Request / Response Stateless
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Internet Communications Request / Response The client sends a request The server sends a response The response can often generate a second request Not supported: “Give me some info now and some more later”
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Internet Communications Stateless At the basic TCPIP level The server has no memory of the request The server does not track ‘sessions’ A request is received The request is serviced A second request is received It’s a new sunrise…
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Internet Communications How does this correlate with web sessions? Once I log in, the server knows me It tracks my shopping cart, etc.
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Web Sessions “Web Sessions” are an artificial abstraction Added on top of the TCPIP protocol Server generates a ‘session key’ Typically just a long string of characters Session key is returned with first response to the client Browser sends the key back in on subsequent requests Server will use the session key to remember what it chooses
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Web Sessions Are there problems that need to be addressed with sessions? eBay does not have “one server” They have a huge server farm A ‘ sprayer ’ server sits in front of the farm and routes requests Each request will likely go to a different server based on load balancing of the server farm (We’ll discuss clustering in a couple of weeks…) Server 1 generated and sent a key back on a response Next request from the client (with the key) comes to Server 2 Server 2 does not recognize the key
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Web Sessions Two possible solutions 1) The sprayer needs to send all requests from a particular IP address to the same server 2) Servers need to store session information in a common database Slow performance
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Multiple Concurrent Requests When a request is sent, there is an understandable wait time for the response Wait time can vary But it won’t go to zero We need to be able to send out multiple concurrent requests Much more efficient Even to the same server “Fill up all the pipes”… minimize dead time
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Multiple Concurrent Requests Web page example
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