Networks: Chapter 2

BItTorrent

Each torrent has an infrastructure node called a tracker. When a peer joins a torrent, it registers itself with the tracker and periodically informs the tracker that it is still in the torrent. In this manner, the tracker keeps track of the peers that are participating in the torrent. A given torrent may have fewer than ten or more than a thousand peers participating at any instant of time. TLDR: BitTorrent client starts sharing as soon as it downloads one chunk of the file (instead of waiting until the entire download has been completed).

host aliasing, mail server aliasing, load distribution (copy websites)

Important services DNS provides

distribution time

In a P2P file transfer among N peers the ____________ ____ is the time it takes to get a copy of the file to all N peers

DNS Caching

In order to improve DNS delay performance and to reduce the number of DNS messages this method is used... DNS server receives a DNS reply (containing, for example, a mapping from a hostname to an IP address), it can cache the mapping in its local memory. F

IP address

In the Internet, the host is identified by its _________

define the client and server process

In the context of a communication session between a pair of processes, the process that initiates the communication (that is, initially contacts the other process at the beginning of the session) is labeled as the client. The process that waits to be contacted to begin the session is the server.

P2P architecture

In this architecture there is minimal or no reliance on dedicated servers... exploits direct communication between pairs of intermittently connected hosts, called peers

client-server architecture

In this type of architecture there is an always-on host, called the server, which services requests from many other hosts, called clients.

Drawbacks of P2P

1. P2P video streaming and file distribution applications shift upstream traffic from servers to residential ISPs = significant stress on the ISPs 2. Security because of their highly distributed and open nature 3. Incentives. The success of future P2P applications also depends on convincing users to volunteer bandwidth, storage, and computation resources

UDP (User datagram protocol)

A no-frills, lightweight transport protocol, providing minimal services, DNS uses this protocol -connectionless -unreliable data transfer -no congestion control mechanism

FTP (file transfer protocol)

A simple file transfer protocol that uses two parallel TCP connections (a control connection and a data connection) to transfer a file.

socket

A software interface which messages are sent into and messages are received from in the network. Analogous to the doors of a house.

reliable data transfer

A type of protocal that provides a guaranteed data delivery services is said to provide RDT which stands for

proxy server

A web cache is also known as a ________ a network entity that satisfies HTTP requests on the behalf of an origin Web server. The Web cache has its own disk storage and keeps copies of recently requested objects in this storage

cookie

A web server identifies users by storing a file on the users computer using the set-cookie header in a server response. If a client already has a cookie it can notify the server of it using the cookie header

RTT

Abbreviation for round-trip time a.k.a time it takes for a small packet to travel from client to server and then back to the client

SSL (Secure Sockets Layer)

An enhancement for TCP providing security

HTTP is a pull protocol, SMTP is a push protocol, SMTP messages must be 7-bit ASCII, HTTP encapsulates images and other media types while SMTP places all objects into one message

Differences between HTTP and SMTP

GET, POST, HEAD, PUT, and DELETE

Different methods of HTTP request

HTTP vs FTP

The control connection is used for sending control information between the two hosts (user identification, password, commands to change remote directory, and commands to "put" and "get" files) & the data connection is used to actually send a file --> separate control connection, FTP sends control information out-of-band VS HTTP, sends request and response header lines into the same TCP connection that carries the transferred file itself --> HTTP sends its control information in-band.

A request line, header lines, and an entity body

The general format of an HTTP request message contains

A status line, six header lines, and then an entity body

The general format of an HTTP response message contains

conditional GET

The mechanism by which HTTP allows a cache to verify that its objects are up to date is called a

DNS

This protocol uses UDP and can be thought of as the "Internets Directory Service"

True

True or False: IMAP allows the user to view message instead of download them from a hierarchy on a remote server.

True of False: FTP must maintain state about the user

True: Server must associate the control connection with a specific user account, and the server must keep track of the user's current directory as the user wanders about the remote directory tree.

TCP

connection-oriented service -TCP has the client and server exchange transport layer control information with each other before the application-level messages begin to flow "handshaking procedure" alerts the client and server reliable data transfer service TCP congestion-control mechanism throttles a sending process and limits respective bandwidth

Web page

consists of objects(files), base HTML file, referenced object

1024^2 B

convert a MB to a B

1024 bps

convert a kbps to bps

One DNS is bad bc

single point failure, traffic volume, distance, maintenance --> DNS server doesn't scale therefore needs hierarchy

API (Application Programming Interface)

sockets are the ___ between the application and the network

Time from the browser's request of an object until its receipt of the object

sum of the LAN delay, the access delay (the delay between the two routers), and the Internet delay

HTTP (HyperText Transfer Protocol)

the Web's application-layer protocol HTTP is implemented in two programs: a client program and a server program. HTTP defines the structure of these messages and how the client and server exchange the messages.

data center

Often in a client-server application, a single-server host is incapable of keeping up with all the requests from clients so for this reason a ____ ______, housing a large number of hosts, is often used to create a powerful virtual server.

self-scalability

One of the most compelling features of P2P architectures is their _______________. Although each peer generates workload by requesting files, each peer also adds service capacity to the system by distributing files to other peers.

canonical hostname

The book describes relay1.west-coast.eneterprise.com (a hostname which contains the IP) as a

max{F/u,F/dmin,NF/(u+sum of rate of peers)}

What is the minimum total distribution time for P2P?

NF/u

in P2P what is the formula for the client-server time to distribute the file, where N is the number of peers, F is the number of bits in the file, and u is the upload rate of the server.

F/dmin

in P2P what is the formula for the minimum distribution, where F is the number of bits in the file.

client-server architecture

-there is an always-on host, called the server, which services requests from many other hosts, called clients -server has a fixed, well-known address, called an IP address -client can always contact the server by sending a packet to the server's IP address

DNS task's

1) a distributed database implemented in a hierarchy of DNS servers, and (2) an application-layer protocol that allows hosts to query the distributed database

Content Distributed Network

A CDN is a company that installs many geographically distributed caches throughout the Internet, thereby localizing much of the traffic. What does the abbreviation stand for?

(Name, Value, Type, TTL)

A DNS resource record (RR) is a four-tuple record that contains what fields?

2

A TCP connection between a client and a server requires a minimum of how many RTTs?

Web cache function

A cache is both a server and a client at the same time. When it receives requests from and sends responses to a browser, it is a server. When it sends requests to and receives responses from an origin server, it is a client.

Socket IRL analogy

Aprocess is analogous to a house and its socket is analogous to its door. When a process wants to send a message to another process on another host, it shoves the message out its door (socket). This sending process assumes that there is a transportation infrastructure on the other side of its door that will transport the message to the door of the destination process. Once the message arrives at the destination host, the message passes through the receiving process's door (socket), and the receiving process then acts on the message

port number

Because a host could be running many network applications, a destination ____ ______ is needed.

torrent

BitTorrent is a popular P2P protocol for file distribution, the collection of all peers participating in the distribution of a particular file is called a ______

RRs

DNS distributed database store resource records (RRs), including RRs that provide hostname-to-IP address mappings. Each DNS reply message carries one or more resource records

Domain name system

DNS is the abbreviation for

user agents, mail servers, and SMTP

Electronic mail in the internet has three major components, these are

True or False: an HTTP server is stateless

HTTP server maintains no information about the clients, HTTP is said to be a stateless protocol

It does so in 3 phases: authenticate phase, retrieve phase, update phase

How doess Post Office Protocol--Version 3 (POP3) access mail?

13 Root DNS servers to top level DNS servers to authoritative DNS servers

How is the DNS hierarchical database broken down?

8

How many bits are typically in a byte

ICMP and POP3

Name the two popular mail access protocols

P2P equations

Pg 146

TCP (Transmission control protocol)

Protocol is the underlying layer of HTTP and is said to be a connection-oriented service

Application-layer protocol

TCP an UDP are forms of transport layer protocols, HTTP and SMTP are forms of what protocol (protocol sends messages between end systems) ALP defines -types of messages exchanges, syntax of various message types, semantics, rules for when and how response

SMTP (Simple mail transfer protocol)

The principle application-layer protocol for electronic mail is

Date, Server, Last-Modified, Content-Length, Content-Type

The six header lines of an HTTP response message

non-persistent connections

type of HTTP connections that closes after each request from the client ... brand-new connection must be established and maintained for each requested object

persistent connections

type of HTTP connections that keeps connections open after a request to the server the server leaves the TCP connection open after sending a response. Subsequent requests and responses between the same client and server can be sent over the same connection.. multiple Web pages residing on the same server can be sent from the server to the same client over a single persistent TCP connection. These requests for objects can be made back-to-back, without waiting for replies to pending requests (pipe-lining).