Computer Networks Quiz 2

DNS consists of two parts:

1. Distributed database implemented in a hierarchy of DNS servers 2. Application layer protocol that allows hosts to query distributed database

Root DNS servers

13, each server is a network of replicated servers for security and reliability.

If the object has not been modified, the server sends an empty message with "_____"

304 not modified

_____ ______ HTTP request mitigates the stale objects issue.

Conditional GET

Network Application != Application-layer Protocol

Ex: World Wide Web application vs HTTP protocol

(T/F) Layers on different machines can't process the same message.

False, layers on different machines

Web pages consists of objects. Give examples

HTML file, JPEG image, Java applet, video clip

What two pieces of information are needed to identify a process?

IP address of the host, port number of the process.

HTTP provides two types of connections:

Non-persistent and persistent

Local DNS servers

Not part of hierarchy, local cache of recent name-to-address translation pairs. Acts as proxy, forwards query into hierarchy

The Pre-Internet 7-layer model is used in ____ architecture.

OSI (Open Systems Interconnection)

There are two addition layers in the OSI Model. What are they and what do they do?

Presentation Layer: interprets the meaning of the exchanged data. Used in compression and encryption. Session Layer: delimiting and synchronization of data exchange.

Link Layer

Protocols: Ehternet, Wi-Fi, DOCSIS Unit: Frame

Application Layer

Protocols: HTTP, SMTP, DNS, FTP Unit: Message

Network Layer

Protocols: IP Unit: datagram

Transport Layer

Protocols: TCP, UDP Unit: segment

Physical Layer

Protocols: copper wire Unit: bits

Three classes of DNS servers

Root, top-level domain, authoritative

What are the two transport layer protocols that provide services to applications?

Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)

DNS is used by other application-layer protocols, it's not something you use. (T/F)

True, DNS

Messages send from one process to another must go through underlying network. (T/F)

True, underlying network

(T/F) Web caches reduce traffic in internet as a whole, improving the performance for ALL applications

True, web caches

Application-layer protocols define:

Type of messages exchanged, syntax of various messages, semantics of the message fields, and rules on how process sends/responds re messages.

Objects are addressable by ____.

URL

The process is controlled by the ___ ___ while the TCP is controlled by ___ ___.

application developer, operating system

Application programming interface (API) is located between the ____ and the ____.

application, network

non-persistent connection

at most one object sent over TCP connection then connection is closed. Using this, multiple objects requires multiple TCP connections.

Web browser is the ___ side of HTTP. Web servers is the ___ side of HTTP. (server/client)

client, server

Name the 2 main network application architectures

client-server architecture and peer-to-peer (P2P) architecture

Protocol Stack

collective protocols of various layers

Describe TCP.

connection-oriented, reliable data transfer, flow control, congestion control.

Network application

consists of pairs of processes that send messages to each other

Request messages

contains a request line and header line. Most important part is the host.

Response messages

contains status line, header line, and entity body (data).

Four main components of cookies

cookie header line in response cookie header line is request cookie file on client, managed by browser back-end database at Web site

HyperText Transfer Protocol (HTTP)

defines how Web clients request Web pages from Web servers and how Web servers transfer Web pages to clients

DNS(Domain name Service)

directory service that translates hostnames (latech.edu) into IP addresses (138.47.18.212).

DNS is implemented as ___ ___ ___.

distributed hierarchical database

load distribution

distributes the load among replication web servers.

Communication for a network application takes place between ____ ____ at the _____ layer.

end systems, application

Syntax

fields in messages and how they are delineated

IP protocol is a ___ ___. It defined a common method for exchanging packets among a wide collection of networks.

focal point

Each lower level protocol wraps message with its own ____.

header

Identifier

header contains this. It encodes which protocol a particular message belongs to.

____ level messages are encapsulated in ____ level messages. (low/high)

high, low

Port number

identifier that specifies the process on the host

Main Computer network protocol stacks (2)

internet(TCP/IP) and Open Systems Interconnection (OSI)

Computer network architectures are organized in _____.

layers

Describe UDP.

lightweight, connection-less, unreliable data transfer. Can lose packets and still work.

Host Aliasing

maps additional hostnames (alias) to canonical hostname

semantics

meaning of the information in the fields

Persistent connection

multiple objects can be sent over single TCP connection between client and server. This is the default.

Web cache (proxy server)

network entity that satisfies HTTP requests on behalf of an origin web server

Stale objects

object house in web server that might have been modified since the last copy was cached

Authoritative DNS servers

organization's own DNS servers that provide authoritative hostname to IP mappings for organizations named hosts

Process

part of a program that is running within the end system

On the physical layer, messages contain multiple headers and a ____. (message body)

payload

Protocol passes message down to the ____ layer. Why? Only this layer can send messages directly.

physical. There's no direct layer-to-layer communication.

Client

process that initiates the communication

server

process that waits to be contacted

Each layer is composed of ____. And each ____ belongs to a single layer. (same word)

protocol(s)

Protocols at each level serve to main functions:

provide commucation services between layers. Provide common functionality within the layer.

mail server aliasing

provides canonical hostname for supplied alias hostnames in mail applications

Application Layer

provides process-to-process communication by allowing messages exchange.

Advantages of web cache:

reduces the response time for a client request Reduces traffic on access link to the internet

Web browsers do what?

request, receive, and interpret web objects

What are the two types of messages exchanged?

request/response

Top level domain DNS servers

responsible for top-level domains (com, net, edu, gov)

Cache is a ___ and a client at the same time

server

Header

small data structure attached to the front of the message.

Socket

software interface that is used by process to send message into and receive message from network

Cache introduces the problem of ___ objects.

stale

HTTP is _____ protocol. What does this mean?

stateless. Server maintains no information about past client requests.

Web servers do what?

store and send Web objects

Cookies

used by websites to keep track of users. Controversial because they can potentially invade privacy.

pipe-lining

when requests for objects are made back to back.