Computer Networking: Application Layer Vocabulary

Vocabulary flashcards generated from Chapter 2 (Application Layer) notes of Computer Networking: A Top-Down Approach.

Client-Server Paradigm

An application architecture where an always-on host with a permanent IP address (server) services requests from intermittently connected hosts with dynamic IP addresses (clients).

Peer-to-Peer Architecture

An application architecture with no always-on server, where arbitrary end systems directly communicate, requesting and providing services to each other with self-scalability.

Client Process

The process that initiates communication in a network application exchange.

Server Process

The process that waits to be contacted to initiate communication in a network application exchange.

Socket

The software interface or door between an application process and the underlying transport-layer protocol within a host.

Open Protocols

Network protocols defined in Requests for Comments (RFCs) that are publicly accessible to ensure interoperability between different systems (such as HTTP and SMTP).

Proprietary Protocols

Network protocols whose specifications are privately owned and controlled by a specific entity rather than publicly defined in RFCs (such as Skype and Zoom).

Elastic Applications

Applications that can adjust to whatever network throughput is available rather than requiring a guaranteed minimum bit rate.

TCP Service

An Internet transport service providing reliable data transfer, flow control, congestion control, and connection-oriented setup between sending and receiving processes.

UDP Service

A lightweight, connectionless Internet transport service that provides unreliable data transfer without flow control, congestion control, or timing guarantees.

Transport Layer Security (TLS)

An application-layer library enhancement to TCP that provides encrypted connections, data integrity, and end-point authentication.

Hypertext Transfer Protocol (HTTP)

The Web's application-layer protocol that defines how client browsers request Web objects from Web servers and how servers respond.

Stateless Protocol

A protocol in which the server maintains no information about past client requests.

Non-persistent HTTP

An HTTP connection model where a TCP connection is opened for at most one object transmission and then closed.

Persistent HTTP

An HTTP connection model where a single TCP connection remains open after sending a response, allowing multiple objects to be transferred between the same client and server.

Round Trip Time (RTT)

The time required for a small packet to travel from client to server and back.

Cookies

A mechanism used by Web sites and client browsers to maintain user/server state across transactions via HTTP header lines, a local browser file, and a backend database.

Web Cache

A network entity (proxy server) that satisfies HTTP requests on behalf of an origin Web server by storing and serving recently requested objects closer to the client.

Conditional GET

An HTTP request mechanism using the If-modified-since header line that allows a server to return status 304 Not Modified without retransmitting the object if it has not changed.

Head-of-Line (HOL) Blocking

A performance bottleneck where small objects must wait in queue behind large objects being transmitted over a single ordered connection.

HTTP/2

A version of HTTP that reduces delay by introducing frame-based interleaving of objects, client-specified object prioritization, and server push over a single TCP connection.

HTTP/3

A version of HTTP that adds security and per-object error and congestion control over UDP transport to prevent TCP loss recovery stalling.

User Agent (E-mail)

A software program (mail reader) that allows users to compose, edit, read, and manage e-mail messages.

Mail Server

An infrastructure component of e-mail that stores incoming user mailboxes, manages an outgoing message queue, and communicates via SMTP.

Simple Mail Transfer Protocol (SMTP)

The primary application-layer protocol for reliably transferring e-mail messages directly between mail servers using TCP on port 25.

Internet Mail Access Protocol (IMAP)

An e-mail access protocol that allows a user agent to retrieve, organize into folders, and manage e-mail messages stored on a remote server.

Domain Name System (DNS)

A distributed hierarchical database and application-layer protocol that translates human-readable hostnames into 32-bit IP addresses.

Top-Level Domain (TLD) Servers

DNS servers responsible for generic top-level domains (such as .com, .org, .edu) and country-code domains.

Authoritative DNS Servers

An organization's own DNS servers that maintain official hostname-to-IP address mappings for its named hosts.

Local DNS Name Server

An ISP name server that acts as a proxy for client queries, caching recent translation pairs and forwarding unresolved requests into the DNS hierarchy.

Iterated Query

A DNS resolution method where a contacted name server responds with the address of the next DNS server the client should contact if it cannot resolve the name itself.

Recursive Query

A DNS resolution method where a contacted name server takes on the burden of contacting other DNS servers on behalf of the requesting client to obtain the final IP address.

BitTorrent Torrent

A group of peer end systems actively exchanging and distributing chunks of a specific file.

BitTorrent Tracker

An infrastructure node in a BitTorrent network that tracks and maintains the list of peers participating in a torrent.

Optimistically Unchoke

A BitTorrent tit-for-tat strategy where a peer randomly selects a new neighbor every 30 seconds to send chunks to, allowing new peers to obtain data and find higher-rate trading partners.

Constant Bit Rate (CBR)

A video encoding approach where the output video bit rate remains fixed throughout transmission.

Variable Bit Rate (VBR)

A video encoding approach where the video bit rate dynamically changes based on spatial and temporal image complexity.

Dynamic, Adaptive Streaming over HTTP (DASH)

A video streaming protocol where video is divided into multi-bit-rate chunks, enabling the client to dynamically select chunk quality based on current network bandwidth.

Manifest File

A file provided by a streaming server that contains URLs and encoding bit-rate details for available video chunks.

Content Distribution Network (CDN)

A system of geographically distributed servers that stores and serves copies of Web content or video close to users to improve performance and scale capacity.