Data Communications And Networks I

Front 1

1 kilobyte

Back 1

1024 bytes

Front 2

1 byte

Back 2

8 bits

Front 3

Dedicated vs shared

Back 3

Dedicated serves one user
Shared serves multiple users

Front 4

Circuit-switched networks vs packet-switched networks

Back 4

Circuit-switched networks completely dedicate their end-to-end resources to the given task throughout communication between systems, so they have a guaranteed constant transmission rate. No sharing.

Packet-switched networks do not reserve their resources this way - they send data through the net in discrete "chunks," so delays might result.

Front 5

Circuit-switched network TDM vs FDM

Back 5

(time-division multiplexing) vs (frequency-division multiplexing)

Front 6

When sending a packet over a fixed route, what are the end-to-end delay components? (Name all 4)

Back 6

total nodal delay = processing delay + queuing delay + transmission delay + propagation delay

Front 7

Throughput for traffic in a network

Back 7

Equal to lowest link. If a path has 3 links of 500kbps, 2Mbps, and 1Mbps, the throughput is equal to 500kbps.

Front 8

Five layers of the internet protocol stack

Back 8

Application
Transport
Network
Link
Physical

Front 9

Application layer

Back 9

Hold network applications and many related protocols (HTTP for requesting and/or transferring files, SMTP for email, FTP for transferring files between two end systems, SSL, etc.) Another key application-layer protocol, DNS (Domain Name System), works to give Internet end systems more user-friendly names.

Front 10

Transport layer

Back 10

Data transfer between processes. Deliver messages from the application layer to the other endpoint(s). Uses either the TCP (connection-focused) or UDP (bandwidth-focused) protocols.

Front 11

Network layer

Back 11

Relays datagrams, or network-layer packets, between hosts. Follows the lone IP protocol to ensure that end systems and routers work to receive datagrams. However, also follows many available routing protocols to decide transport paths between sources. Provides logical communication between hosts.

Front 12

Link layer

Back 12

Helps the network layer transport a packet from one node to the next. These nodes can include hosts or routers, which are where the link layer takes over from the network layer. These different links may follow different protocols (Ethernet, Wifi, etc.)

Front 13

Physical layer

Back 13

Within the link layer, the physical layer works to deliver each bit of data across the link. Depending on the link, different protocols might come into play.

Front 14

Propagation delay

Back 14

distance / time
m / s

Front 15

Transmission delay

Back 15

length of packet / transmission rate
L / R

Front 16

UDP vs TCP

Back 16

UDP (User Datagram Protocol): No-frills and lightweight with minimal services. Connectionless, unreliable, and no handshaking.

TCP (Transmission Control Protocol): Connection-oriented service and reliable data transfer service. Connections limited in their sending rate and bandwidth.

Front 17

The ATNLP internet stack is missing two layers. What are they?

Back 17

Presentation: Allow applications to interpret meaning of data: encryption, compression, machine-specific conventions

Session: synchronization, checkpointing, recovery of data exchange

Front 18

Suppose Alice, with a Web-based e-mail account, sends a message to Bob, who accesses his email from his mail sever using POP3. How does the message gets from Alice's host to Bob's host?

Back 18

The message moves from Alice's host to her HTTP mail server. The server then uses SMTP to transmit the message to Bob's server. Finally, Bob's POP3 server delivers the message to his mail host.

Front 19

UDP vs TCP sockets

Back 19

UDP = only one socket
TCP = one socket for each new connection

Front 20

ACK vs NAK

Back 20

(Acknowledgement vs Negative Acknowledgement)
ACKs take more time and resources to send, but catch errors sooner

Front 21

IETF

Back 21

Internet Engineering Task Force - helps create internet standards, along with RFCs (Requests For Comments)

Front 22

What is in the network edge?

Back 22

Hosts (end systems) that run applications such as email

Front 23

What is in the network core?

Back 23

Interconnected networks: a network of networks

Front 24

Dial-up modem

Back 24

Use existing telephone infrastructure
Maximum of 56kbps
Dedicated

Front 25

Digital subscriber line (DSL)

Back 25

Use existing telephone infrastructure
Typically 256kbps upstream and 1 mbps downstream
Shared

Front 26

FTTH

Back 26

Fiber to the home: optical links from central office to home
2-10 Mbps upstream and 20 Mbps downstream
Dedicated

Front 27

Which two layers exist in a switch?

Back 27

link and physical

Front 28

Which three layers exist in a switch?

Back 28

network, link, and physical

Front 29

RTT

Back 29

Round-Trip delay Time, or time for a small packet to travel to client and back

One RTT to initiate TCP connection
One RTT for HTTP request and first few bytes of HTTP response to return

Front 30

Persistent HTTP

Non-persistent HTTP

Back 30

Persistent HTTP: multiple objects can be sent over single TCP connection between client, server.

Non-persistent HTTP: at most one object sent over TCP connection.