Application Layer

Terms in this set (34)

Application Architectures
Client Server
P2P
Hybrid
Client Server- The Client
Communicate with server
May be intermittently connected
May have dynamic IP_ADDR
Do not communicate directly to each other
Client Server- The Server
Always-on host
Permanent IP Address
Server Farms for Scaling
P2P Architecture
No always on server
Arbitrary end systems
Peers change IP_ADDR and are intermittently connected

Highly scalable but hard to manage
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Components of file distribution
Tracker: tracks peers participating in torrent

Torrent: Group of peers exchanging chunks of a file
Explain P2P File Distribution
New peer joining torrent registers with tracker to get list of peers and joins a subset of peers
Tit for Tat
Evaluates top senders and receivers
Distributed Hash Table
A hash
Circular DHT
Circular DHT with Shortcuts
Each peer now knows its predecessor, successor, and short cuts
Peer Churn
Each peer know its next 2 successors and pings them to see if they're there, if one leaves search for that new succssor
Hybrid of Client Server and P2P
Skype and Instant messaging

Knows when users are online via Client Server but sends data P2P
App-Layer
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Do
Many processes can be run on the same host
Identifier
Includes IP_ADDR and Host
App-Layer Protocol Defines
Types of messages exchanged eg. request, response

Message Syntax

Message Semantics

Rules for how and when to processes send and respond to messages
Public Domain protocols
HTTP, FTP, SMTP
Proprietary Protocols
Skype
Which transport service do apps need?
Data loss prevention eg. file transfer
Timing eg. phone calls
Throughput eg. streaming
Security
HTTP
Uses TCP on port 80
It is stateless
Nonpersistent HTTP
Only one object sent over a TCP connection

+2 RTTs for each referenced object
Persistent HTTP
Multiple objects sent over one TCP connection
Round Trip Time (RTT)
The time it takes for client to server and back. Total RTT = 2RTT + Transmit Time
Explain Persistent with Pipelining and without Pipelining
With:
1. Client sends Req as soon as it encounters referenced object
2. As little as one RTT for all referenced objects

Without:
Client sends new Req only when previous response received
One RTT per referenced object
Method Types
GET
POST
PUT
DELETE
HEAD
Status Codes
200 OK
301 Moved Permanently
400 Bad Req
404 Not found
505 HTTP Version not Supported
Web Caches (Proxy Server)
Get from cache if object exists there or go to origin server
Conditional Get
Send object if cache has up-to-date object
SMTP
User send messages to mail server which sends messages to receiver's mail server which the receiver agent can read;
Domain Name SystemDNS
Host name to IP_ADDR aliasing
Top Level Domain (TLD Servers)
Responsible for com, org, edu...
Authoritative DNS Servers
Organization's DNS server, providing authoritative hostname to IP mappings for organization's servers
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