Introduction - Essay Questions PDF

Introduction – Essay Questions 1. Define Client and server ? a client is any computer hardware or software device that requests access to a service provided by a server A server is a computer program or device that provides a service to another computer program and its...

Introduction – Essay Questions 1. Define Client and server ? a client is any computer hardware or software device that requests access to a service provided by a server A server is a computer program or device that provides a service to another computer program and its user, also known as the client. 2. Define both switch and router? Switch is a network device whose responsibility is to Connect Network devices Router is a device which directs the packets or data to their destination 3. Define Simplex, half-duplex, full-duplex connection type. In the simplex mode of communication, only one node can send data. Example Television channels In half-duplex, both devices (nodes) can send data but one at a time. In full-duplex, both devices can send data at a time. 4. Define Mesh Topology and mention its disadvantages Mesh Topology A fully connected mesh network, therefore, has [n (n-1) / 2] physical channels to link it devices disadvantages of a mesh topology are: Difficult installation and reconfiguration because every device must be connected to every other device. The bulk of the wiring can be greater than the available space can accommodate. The hardware required to connect each link can be expensive 5. Mention adv. And disadvantages of start topology The advantages of star topology are: 1. Less expensive than a mesh topology. 2. Easy to install. 3. Robustness. 4. Easy fault identification and fault isolation. The disadvantages of the star topology are: 1. Any fault occur to the central controller will drop down the entire network. 2. Although the star needs less cabling than mesh, it still needs more cables than ring and tree topology. 6. Define Bus Topology and mention its adv. And disadv. One long cable acts as a backbone to link all the devices in the network. Nodes are connected to the bus cable by drop lines and taps. A drop line is a connection that runs between the device and the main cable, a tap is a connector that splices into the main. The advantages of a bus topology are: Ease of installation. Backbone cables can be laid along the most efficient path, then connected to the nodes by drop lines of various lengths. Use less cabling than mesh, star, and tree topologies disadvantages are: Difficult reconfiguration and fault isolation. A fault or break in the bus cable stops all transmission, even between devices on the same side of the problem. 7. Define ring topology and mention its adv. And disadvantages Ring Topology In a ring topology, each device has a dedicated point-to-point line configuration only with the two devices on either side of it. A signal is passed along the ring in one direction, from device to device, until it reaches its destination. The advantages of ring topology are: 1. Relatively easy to install and reconfigure. 2. Addition or deletion of a device requires moving only two connections.  3. Fault isolation is simplified. The disadvantage of the ring topology is that a break in the ring (such as a disabled station) can disable the entire network, and it is a one-way data flow. 8. Define a tree topology network Tree Topology A Tree topology is a type of network topology that resembles a tree. In a tree topology, there is one central node (the “trunk”), and each node is connected to the central node through a single path 9. Define PAN and LAN 1- PAN A PAN provides data transmission among personal devices such as computers, smartphones, tablets , and personal digital or for connecting to a higher-level network and the Internet where one master device takes up the role of a gateway 2- LAN A local area network is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building.  Chapter One – Essay Questions What is the Internet from a “service” view? ▪ Infrastructure that provides services to applications: Web, streaming video, multimedia teleconferencing, email, games, e-commerce, social media, inter-connected appliances, … provides programming interface to distributed applications Define network protocol? Protocols define the format, order of messages sent and received among network entities, and actions taken on msg transmission, receipt What are components of network edge and network core? Network edge: ▪ hosts: clients and servers ▪ servers often in data centers Network core: ▪ interconnected routers ▪ network of networks How to connect end systems to edge router? ▪ residential access nets ▪ institutional access networks (school, company) ▪ mobile access networks (WiFi, 4G/5G) Describe wireless local area networks and wide area cellular network? Wireless local area networks (WLANs) ▪ typically within or around building (~100 ft) ▪ 802.11b/g/n (WiFi): 11, 54, 450 Mbps transmission rate Wide-area cellular access networks ▪ provided by mobile, cellular network operator (10’s km) ▪ 10’s Mbps ▪ 4G cellular networks (5G coming) Describe how host sends packets of data and how to compute transmission delay? host sending function: ▪ takes application message ▪ breaks into smaller chunks, known as packets, of length L bits ▪ transmits packet into access network at transmission rate R link transmission rate, aka link capacity, aka link bandwidth Packet transmission delay = time needed to transmit L-bits = L/R bits Define physical link, guided media and unguided media? physical link: what lies between transmitter & receiver guided media: signals propagate in solid media: copper, fiber, coax unguided media: signals propagate freely, e.g., radio Define wireless radio? signal carried in electromagnetic spectrum with no physical “wire” Mention radio link types? ▪ terrestrial microwave ▪ Wireless LAN (WiFi) ▪ wide-area (e.g., cellular) ▪ satellite What are the propoagation effects for radio signals? propagation environment effects: reflection obstruction by objects interference Define network core? mesh of interconnected routers What is the main concept of packet switching hosts break application-layer messages into packets forward packets from one router to the next, across links on path from source to destination each packet transmitted at full link capacity Define Packet queuing and loss in packet switching? If arrival rate (in bps) to link exceeds transmission rate (bps) of link for a period of time: ▪ packets will queue, waiting to be transmitted on output link ▪ packets can be dropped (lost) if memory (buffer) in router fills up What are the core-network functions? Forwarding: local action: move arriving packets from router’s input link to appropriate router output link Routing: global action: determine source-destination paths taken by packets routing algorithms Define the concept of circuit switching? end-end resources allocated to, reserved for “call” between source and destination commonly used in traditional telephone networks Mention and define two approaches of circuit switching ? Frequency Division Multiplexing (FDM) ▪ optical, electromagnetic frequencies divided into (narrow) frequency bands ▪ each call allocated its own band, can transmit at max rate of that narrow band Time Division Multiplexing (TDM) ▪ time divided into slots ▪ each call allocated periodic slot(s), can transmit at maximum rate of (wider) frequency band, but only during its time slot(s) Sketch and describe modern Internet structure? Tier-1 ISPs are global transit ISP. There are approximately a dozen tier-1 ISPs, including Level 3 Communications, AT&T, Sprint, and NTT. Do not pay anyone as they are at the top of the hierarchy. A hierarchy of multiple competing regional ISPs in a region pay to reginal ISP which they connect. Each regional ISP pays the tier-1 ISP to which it connects. The amount that a customer ISP pays a provider ISP reflects the amount of traffic it exchanges with the provider. To reduce costs, a pair of nearby ISPs at the same level of the hierarchy can peer through IXP. Define Internet Exchange Points (IXP). What are benefits of it ? An Internet Exchange Points (IXP) (typically in a standalone building with its own switches) is a meeting point where multiple ISPs can connect and/or peer together. An IXP earns its money by charging each of the the ISPs that connect to the IXP a relatively small fee, which may depend on the amount of traffic sent to or received from the IXP. There are over 400 IXPs in the Internet today Describe google as a content-provider networks Google is currently one of the leading examples of such a content-provider network. Google has over 50–100 data centers distributed across North America, Europe, Asia, South America, and Australia. The Google data centers are all interconnected via Google’s private TCP/IP network, The Google private network attempts to “bypass” the upper tiers of the Internet by peering (settlement free) with lower-tier ISPs, either by directly connecting with them or by connecting with them at IXPs. Mention and define the four sources of packet delay dnodal = dproc + dqueue + dtrans + dprop dproc: nodal processing check bit errors , determine output link, typically < msec dqueue: queueing delay time waiting at output link for transmission , depends on congestion level of router dtrans: transmission delay: L: packet length (bits) , R: link transmission rate (bps) → dtrans = L/R dprop: propagation delay: d: length of physical link , s: propagation speed (~2x108 m/sec) → dprop = d/s Define Throughput, what are ways of computing throughput how to compute ? Throughput: rate (bits/time unit) at which bits are being sent from sender to receiver instantaneous: rate at given point in time average: rate over longer period of time per-connection end-end throughput is the minimum rate How can malware get in host ? virus: self-replicating infection by receiving/executing object (e.g., e-mail attachment) worm: self-replicating infection by passively receiving object that gets itself executed What is spyware malware? spyware malware can record keystrokes, web sites visited, upload info to collection site infected host can be enrolled in botnet, used for spam or distributed denial of service (DDoS) attacks What is the denial of service attack? Denial of Service (DoS): attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic What is packet “sniffing” attack? Is a packet interception, attacker reads, records all packets passing by What is IP spoofing? Fake identity, attackers send packet with false source address Define Internet protocol stack TCP/IP, give examples? Application: supporting network applications e.g. IMAP, SMTP, HTTP transport: process-process data transfer e.g TCP, UDP network: routing of datagrams from source to destination e.g. IP, routing protocols link: data transfer between neighboring network elements e.g. Ethernet, 802.11 (WiFi), PPP physical: bits “on the wire” What are benefits of layering? dealing with complex systems explicit structure allows identification, relationship of complex system’s pieces modularization eases maintenance, updating of system change in layer's service implementation: transparent to rest of system  Chapter 2- Essay Questions Part 1 Describe both server and client in Client-Server paradigm? server: always-on , has permanent IP address , often in data centers, for scaling issues clients: contact, communicate with server, may be intermittently connected, may have dynamic IP addresses do not communicate directly with each other examples: HTTP, IMAP, FTP Describe Peer-peer architecture? ▪ End systems directly communicate, peers request service from other peers, provide service in return to other peers. ▪ Provide self scalability – new peers bring new service capacity, as well as new service demands ▪ peers are intermittently connected and change IP addresses ▪ complex management ▪ example: P2P file sharing Define Process, Describe how processes communicate within same hosts and in different hosts? process: program running within a host. within same host, two processes communicate using inter-process communication (defined by OS) processes in different hosts communicate by exchanging messages what is the benefit of sockets? process sends/receives messages to/from its socket What an application-layer protocol defines? ▪ types of messages exchanged, e.g., request, response ▪ message syntax: what fields in messages & how fields are delineated ▪ message semantics meaning of information in fields ▪ rules for when and how processes send & respond to messages ▪ open protocols: defined in RFCs, everyone has access to protocol definition allows for interoperability e.g., HTTP, SMTP ▪ proprietary protocols: e.g., Skype What transport services does an app need? data integrity ▪ some apps (e.g., file transfer, web transactions) require 100% reliable data transfer ▪ other apps (e.g., audio) can tolerate some loss timing ▪ some apps (e.g., Internet telephony, interactive games) require low delay to be “effective” throughput ▪ some apps (e.g., multimedia) require minimum amount of throughput to be “effective” ▪ other apps (“elastic apps”) make use of whatever throughput they get security ▪ encryption, data integrity, … What are the internet transport protocol services? differentiate between them? TCP service: ▪ reliable transport between sending and receiving process ▪ flow control: sender won’t overwhelm receiver ▪ congestion control: throttle sender when network overloaded ▪ does not provide: timing, minimum throughput guarantee, security ▪ connection-oriented: setup required between client and server processes UDP service: ▪ unreliable data transfer between sending and receiving process ▪ does not provide: reliability, flow control, congestion control, throughput guarantee, security, or connection setup. What are the two types of HTTP Connections? Define each? Non-persistent HTTP 1. TCP connection opened 2. at most one object sent over TCP connection 3. TCP connection closed downloading multiple objects required multiple connections Persistent HTTP TCP connection opened to a server multiple objects can be sent over single TCP connection between client, and that server TCP connection closed What is HTTP response time per object transferred in non-persistent Http? one RTT to initiate TCP connection one RTT for HTTP request and first few bytes of HTTP response to return object/file transmission time Non-persistent HTTP response time = 2RTT+ file transmission time Mention and define HTTP request types? POST method: ▪ web page often includes form input ▪ user input sent from client to server in entity body of HTTP POST request message GET method (for sending data to server): ▪ include user data in URL field of HTTP GET request message (following a ‘?’): HEAD method:  ▪ requests headers (only) that would be returned if specified URL were requested with an HTTP GET method. PUT method: ▪ uploads new file (object) to server ▪ completely replaces file that exists at specified URL with content in entity body of POST HTTP request message Mention some of HTTP response status codes? 200 OK request succeeded, requested object later in this message 301 Moved Permanently requested object moved, new location specified later in this message (in Location: field) 400 Bad Request request msg not understood by server 404 Not Found requested document not found on this server 505 HTTP Version Not Supported Define cookies and what it is used for? Web sites and client browser use cookies to maintain some state between transactions cookies can be used for: authorization shopping carts recommendations user session state (Web e-mail) What is the goal of web cache ? describe how it can work as server and client? And why web caching? ▪ Goal: satisfy client request without involving origin server Web cache acts as both client and server, server for original requesting client, reduce response time for client request cache is closer to client reduce traffic on an institution’s access link Internet is dense with caches enables “poor” content providers to more effectively deliver content How is conditional get work? ▪ don’t send object if cache has up-to-date cached version no object transmission delay lower link utilization ▪ cache: specify date of cached copy in HTTP request If-modified-since: server: response contains no object if cached copy is up-to-date: HTTP/1.0 304 Not Modified Describe how HTTP1.1 work with multiple object pipeline? ▪ introduced multiple, pipelined GETs over single TCP connection ▪ server responds in-order (FCFS: first-come-first-served scheduling) to GET requests ▪ with FCFS, small object may have to wait for transmission (head-of-line (HOL) blocking) behind large object(s) ▪ loss recovery (retransmitting lost TCP segments) stalls object transmission Define HTTP2 goal? How it works to mitigate HOL blocking Key goal: decreased delay in multi-object HTTP requests HTTP/2: [RFC 7540, 2015] increased flexibility at server in sending objects to client: methods, status codes, most header fields unchanged from HTTP 1.1 transmission order of requested objects based on client-specified object priority (not necessarily FCFS) push unrequested objects to client divide objects into frames, schedule frames to mitigate HOL blocking What are three major components of email? user agents mail servers simple mail transfer protocol: SMTP