CSCI 4500: Chapter 2 Application Layer | QUESTIONS AND
ANSWERS
1. What are some network apps?: social networking, web, text messaging, e-mail, multi-user network games,
streaming stored video(YouTube, Hulu, Netflix), P2P file sharing, voice over IP(Skype), real time video conferencing,
internet search, remote login, Dropbox
2. when creating a network app, write programs that:: run on (different) end systems, communicate over network,
e.g., web server software communicates with browser software
3. what you don't need to do when writing a network app: don't need to write software for network-core
devices(they don't run user applications, applications on end systems allows for rapid app development, propagation
4. application architectures: client-server(including data centers/cloud comput- ing), peer-to-peer(P2P), hybrid of
client-server and P2P
5. client-server paradigm: the server must be running all the time but the client needs to be running only when it is
needed, only one way request
6. What are hybrids of C-S and P2P(client-server and peer-to-peer): skype, instant messaging, zoom
7. server: always-on host, permanent IP address, often in data centers, for scaling
8. clients: contact, communicate w server, may be intermittently connected, may have dynamic IP addresses, do not
communicate directly with each other, Ex: HTTP, IMAP, FTP
9. peer-peer architecture: no always-on server, request and provide service to other peers, god at self-scalability bc
new papers bring new service capacity and new service demands
10.process: program running within host
11.how to processes commmunicate: inter-process communication(defined by OS) and exchanging messages
12.client process: process that initiates communication
13.server process: process that waits to be contacted
14.applications with P2P architectures have client processes server
processes: AND
15.socket: process sends/receives message to/from its
, CSCI 4500: Chapter 2 Application Layer | QUESTIONS AND
16.A socket is analogous to a ANSWERS : door, sending process shoves message out door, sending
process relies on transport infrastructure on other s ide of door
to one on
deliver message to socket at receiving process, two sockets involved, side
each
17.How do we identify a process?: Tasklist(Windows, Ps-ax or top(Mac/Linux)
, CSCI 4500: Chapter 2 Application Layer | QUESTIONS AND
ANSWERS
18.Identifies of addressing processes: IP address identifies the device/ma- chine(street address) and also the
port number(process id-unit number)
19.example port numbers: HTTP server: 80 mail server: 25
20.application-layer protocol defines:: types of messages exchanged(request, response), message syntax(what fields
in messages & how fields are delineated), message semantics(meaning of information in fields), rules(for when/how
process- es send&respond to messages), open protocols(defined in RFCs, everyone has access to protocol definition,
allows for interoperability, HTTP, SMTP), proprietary protocols(Skype)
21.transport services: data loss, timing, throughput, security
22.data loss: Some apps (e.g. audio) can tolerate some loss
Other apps (e.g. file transfer, telnet) require 100% reliable data transfer
23.timing: some apps(e.g., Internet, telephony, interactive games) require low de- lay to be "effective"
24.throughput: some apps("elastic apps") make use of whatever throughput they get, while some apps(multimedia)
require minimum amount of throughput to be effective
25.security: encryption, data integrity
26.transport service requirements:
27.TCP: Transmission control protocol
28.TCP service: reliable transport, flow control, congestion control, does not pro- vide timing, min throughput
guarantee, security, connection-oriented
29.UDP: User datagram protocol
30.UDP service: unreliable data transfer, does not provide reliability, flow control, congestion control, timing,
throughput, guarantee, security, or connection setup
31.internet transport protocols services:
32.traditional TCP & UDP sockets: no encryption, clear text passwords sent into socket traverse Internet in cleartext
ANSWERS
1. What are some network apps?: social networking, web, text messaging, e-mail, multi-user network games,
streaming stored video(YouTube, Hulu, Netflix), P2P file sharing, voice over IP(Skype), real time video conferencing,
internet search, remote login, Dropbox
2. when creating a network app, write programs that:: run on (different) end systems, communicate over network,
e.g., web server software communicates with browser software
3. what you don't need to do when writing a network app: don't need to write software for network-core
devices(they don't run user applications, applications on end systems allows for rapid app development, propagation
4. application architectures: client-server(including data centers/cloud comput- ing), peer-to-peer(P2P), hybrid of
client-server and P2P
5. client-server paradigm: the server must be running all the time but the client needs to be running only when it is
needed, only one way request
6. What are hybrids of C-S and P2P(client-server and peer-to-peer): skype, instant messaging, zoom
7. server: always-on host, permanent IP address, often in data centers, for scaling
8. clients: contact, communicate w server, may be intermittently connected, may have dynamic IP addresses, do not
communicate directly with each other, Ex: HTTP, IMAP, FTP
9. peer-peer architecture: no always-on server, request and provide service to other peers, god at self-scalability bc
new papers bring new service capacity and new service demands
10.process: program running within host
11.how to processes commmunicate: inter-process communication(defined by OS) and exchanging messages
12.client process: process that initiates communication
13.server process: process that waits to be contacted
14.applications with P2P architectures have client processes server
processes: AND
15.socket: process sends/receives message to/from its
, CSCI 4500: Chapter 2 Application Layer | QUESTIONS AND
16.A socket is analogous to a ANSWERS : door, sending process shoves message out door, sending
process relies on transport infrastructure on other s ide of door
to one on
deliver message to socket at receiving process, two sockets involved, side
each
17.How do we identify a process?: Tasklist(Windows, Ps-ax or top(Mac/Linux)
, CSCI 4500: Chapter 2 Application Layer | QUESTIONS AND
ANSWERS
18.Identifies of addressing processes: IP address identifies the device/ma- chine(street address) and also the
port number(process id-unit number)
19.example port numbers: HTTP server: 80 mail server: 25
20.application-layer protocol defines:: types of messages exchanged(request, response), message syntax(what fields
in messages & how fields are delineated), message semantics(meaning of information in fields), rules(for when/how
process- es send&respond to messages), open protocols(defined in RFCs, everyone has access to protocol definition,
allows for interoperability, HTTP, SMTP), proprietary protocols(Skype)
21.transport services: data loss, timing, throughput, security
22.data loss: Some apps (e.g. audio) can tolerate some loss
Other apps (e.g. file transfer, telnet) require 100% reliable data transfer
23.timing: some apps(e.g., Internet, telephony, interactive games) require low de- lay to be "effective"
24.throughput: some apps("elastic apps") make use of whatever throughput they get, while some apps(multimedia)
require minimum amount of throughput to be effective
25.security: encryption, data integrity
26.transport service requirements:
27.TCP: Transmission control protocol
28.TCP service: reliable transport, flow control, congestion control, does not pro- vide timing, min throughput
guarantee, security, connection-oriented
29.UDP: User datagram protocol
30.UDP service: unreliable data transfer, does not provide reliability, flow control, congestion control, timing,
throughput, guarantee, security, or connection setup
31.internet transport protocols services:
32.traditional TCP & UDP sockets: no encryption, clear text passwords sent into socket traverse Internet in cleartext
