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DATA (FINAL) > Chapter 1: Introduction > Flashcards

Chapter 1: Introduction Flashcards

1
Q

What are the communication links?

A
  1. Fiber.
  2. Copper.
  3. Radio.
  4. Satellite.
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2
Q

Transmission rate:

A

Bandwidth.

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3
Q

What are packet switches?

A

Forward packets (chunk of data).

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4
Q

What is the internet?

A
  1. “networks of networks”.

2. Interconnected ISPs.

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5
Q

What are the protocols of sending and receiving of messages?

A
  1. TCP.
  2. IP.
  3. HTTP.
  4. Skype.
  5. 802.11 home.
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6
Q

Internet standards:

A
  1. RFC (Request for comment).

2. IETF (Internet Engineering Task Force).

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7
Q

What’s the Internet? (A service view)

A
  1. Infrastructure that provides services to application:
    (i) Web,
    (ii) VoIP,
    (iii) email,
    (iv) games,
    (v) e-commerce,
    (vi) social nets.
  2. Provide programming interface to apps:
    (i) hooks that allow sending
    and receiving app
    programs to “connect” to
    Internet.
    (ii) provides services
    options, analogous to
    postal service.
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8
Q

What’s a network protocol?

A

All communication activity in Internet governed by protocols.

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9
Q

Protocols define (determine):

A

Format, order of messages sent and received among network entities, and actions taken on message transmission, receipt.

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10
Q

Computer network protocol (diagram):

A

Refer to the final folder in DCI file.

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11
Q

What is the network edge?

A

Clients and servers (Hosts).

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12
Q

What is the access network, physical media?

A
  1. Wired.

2. Wireless communication link.

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13
Q

What is network core?

A
  1. Interconnected routers.

2. Network of networks.

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14
Q

How to connect end system to edge router?

A
  1. Residential access nets.
  2. Institutional access networks (school, company).
  3. Mobile access network.

Keep in mind:

  1. bandwidth (bits per second) of access network?
  2. shared or dedicated?
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15
Q

Access Network: Digital Subscriber Line (DSL)

A
  1. Use existing telephone line to central office DSLAM.
  2. Data over DSL phone line goes to internet.
  3. Voice over DSL phone line goes to telephone net.,
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16
Q

What is frequency division multiplexing?

A

Different channels transmitted in different frequency band.

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17
Q

What is Hybrid Fiber Coax (HFC)?

A

Asymmetric: up to 30Mbps downstream transmission rate, 2Mbps upstream transmission rate.

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18
Q

Access Network: Cable Network?

A
  1. Network of cable, fiber attaches homes to ISP router.
  2. Home share access network to cable headend.
  3. Unlike DSL, which has a dedicated access to central office.
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19
Q

What is enterprise access networks (ETHERNET)?

A
  1. Typically used in companies, universities, etc,
  2. Transmission rates: 10Mbps, 100Mbps, 1Gbps.
  3. Today, end system typically connect into Ethernet switch.
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20
Q

Wireless Access Network:

A
  1. Shared wireless access network connects end system to router.
  2. This connection is via base station aka “access point”.
  3. Hosts send packets of data.
  4. Host sending function:
    (i) takes application message.
    (ii) breaks into smaller chunks, known as packets, of length L bits.
    (iii) Transmit packet into access network at transmission rate R.
    – link transmission rate, aka
    link capacity, aka link
    bandwidth–
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21
Q

What are the two types of wireless access network?

A
  1. Wireless LANs.

2. Wide-area wireless access.

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22
Q

Wireless LAN:

A
  1. Within building (100ft. or 30m).

2. 802.11 b/g/n (Wi-Fi): 11, 54, 450Mbps transmission rate.

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23
Q

Wide are wireless access:

A
  1. Provided by telco (cellular) operator: 10’s km.
  2. Between 1 and 10Mbps.
  3. 3G, 4G: (LTE).
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24
Q

Packet transmission delay formula:

A

packet transmission delay formula = time needed to transmit L-bit packet into link = L (bits)/R (bits/sec).

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25
Q

What is physical media?

A
  1. Bit.
  2. Physical link.
  3. Guided media.
  4. Unguided media.
  5. Twisted pair (TP).
26
Q

[Physical media] bit:

A

Propagates between transmitter/receiver pairs.

27
Q

[Physical media] physical link:

A

What lies between transmitter and receiver.

28
Q

[Physical media] guided media:

A

Signals propagate in solid media:

  1. copper
  2. fiber
  3. coax
29
Q

[Physical media] unguided media:

A

Signals propagate freely:

1. radio

30
Q

[Physical media] twisted pair (TP)

A

Two insulated copper wires:

  1. Category 5: 100Mbps, 1Gbps Ethernet
  2. Category 6: 10Gbps
31
Q

Physical media: Coax

A 
Coaxial cable:
1. Two concentric copper conductors.
2. Bidirectional.
3. Broadband: 
 (i) multiple channels on
      cable
 (ii) HFC
32
Q

Physical media: Fiber

A

Fiber optic cable:

  1. Glass fiber carrying light pulses, each pulse a bit
  2. High speed operation:
    (i) high-speed point-to-point transmission (eg 10’s - 100’s Gbps transmission rate).
  3. Low error rate:
    (i) repeaters spaced far apart.
    (ii) immune to electromagnetic noise.
33
Q

Physical media: Radio

A
  1. Signal carried in electromagnetic spectrum.
  2. No physical wire.
  3. Bidirectional.
  4. Propagation environment effects:
    (i) reflection.
    (ii) obstruction by objects.
    (iii) interference.
34
Q

Radio link types:

A 
1. Terrestrial microwave
(up to 45Mbps channels)
2. LAN (e.g. Wi-Fi)
(54Mbps).
3. Wide-area (e.g. cellular)
(4G cellular: ~10Mbps)
4. Satellite
(kbps to 45Mbps channel
--or multiple smaller channels--).
(270msec end-end delay).
(geosynchronous versus low altitude).
35
Q

The network core:

A
  1. Mesh of interconnected routers.
  2. Packet-switching: hosts break application-layer into packets.
    (i) Forward packets from one router to the next, across links on path from source to destination.
    (ii) each packet transmitted at full link capacity.
36
Q

Packet switching: store-and-forward

A
  1. Takes L/R seconds to transmit (push out) L-bit packet into link at R bps, where
    L = length of packets (bit)
    R = transmission rate (bps).
  2. Store and forward: entire packet must arrive at router before it can be transmitted on the next link.
  3. End-end delay = 2L/R (assuming 0 propagation delay).
37
Q

Packet Switching: queueing delay, loss

A

queueing and loss:

  1. If arrival rate (in bits) to link exceeds transmission rate of link for a period of time:
    (i) packets will queue, wait to be transmitted on link.
    (ii) packets can be dropped (lost) if memory (buffer) fills up.
38
Q

Two key network-core functions:

A
  1. Routing: determines the route taken to forward the packets from source to destination.
  2. Forwarding: move packets from router’s input to appropriate router’s output.
39
Q

End-end resources allocated to, reserved for call between source and destination:

A
  1. In diagram (refer to final folder), each link has four circuits.
    - - call gets 2nd circuit top link and 1st circuit in right link.
  2. Dedicated resources: no sharing.
    - - circuit-like (guaranteed) performance.
  3. Circuit segment idle ifnot used by call (no sharing).
  4. Commonly used in traditional telephone networks.
40
Q

Circuit switching: FDM vs TDM:

A

Refer to the final folder in DCI file.

41
Q

Packet switching vs. Circuit switching

A

== Packets switching allows more users to use the network==
¿¿ Is packet switching a slam dunk winner ??
1. Great for busty data
(i) resource sharing.
(ii) simpler, no call setup.
2. Excessive congestion possible: packet delay and loss
(i) protocols needed for reliable data transfer, congestion control.

42
Q

How to provide circuit-like behaviour?

A
  1. Bandwidth guarantees needed for audio/video apps.

2. Still an unsolved problem.

43
Q

Internet structure: network of networks:

A
  1. End systems connect to Internet via access
    ISPs (Internet Service Providers)
    (i) residential,
    (ii) company and
    (iii) university ISPs.
  2. Access ISPs in turn must be interconnected
    (i) so that any two hosts can send packets to each other.
  3. Resulting network of networks is very complex
    (i) evolution was driven by economics and national policies.
44
Q

Given millions of access ISPs, how to connect them together?

A

((Refer to the final folder in DCI file.))
Option:
1. Connect each ISP to every other ISP.
2. Connect each access ISP to one global transit ISP.
2.1. Customer and provider ISPs have economic agreement.
2.2. But if one global ISP is viable business, there will be competitors
2.2.1. which must be interconnected
2.2.2. and regional networks may arise to access nets to ISPs
2.2.3. and content provider networks (e.g. Google, Microsoft, Akamai) may run their own network, to bring services, content close to end users.

45
Q

At center: small number of well-connected large networks:

A

((Refer to the final folder in DCI file.))

  1. “tier-1” commercial ISPs (e.g., Level 3, Sprint, AT&T, NTT), national & international coverage.
  2. Content provider network (e.g. Google): private network that connects it data centers to Internet, often bypassing tier-1, regional ISPs.
46
Q

Tier-1 ISP: e.g. Sprint

A

Refer to the final folder in DCI file.

47
Q

How do loss and delay occur?

A
  1. Packet queue in router buffers.
    1.1. packet arrival rate to link exceeds output link capacity.
    1.2. packets queue, wait for turn.
    ((Refer to the final folder in DCI file))
48
Q

Four sources of packet delay:

A
  1. dproc: nodal processing.
    (i) check bit errors
    (ii) determine output links
    (iii) typically < msec.
  2. dqueue: queueing delay.
    (i) time waiting at output link for transmission.
    (ii) depends on congestion level of router.
  3. dtrans: transmission delay.
    (i) L: packet length (bits).
    (ii) R: link bandwidth (bps).
    (iii) dtrans = L/R.
  4. dprop: propagation delay.
    (i) d: length of physical link.
    (ii) s: propagation speed (~2x10^8m/sec).
    (iii) dprop = d/s.
49
Q

Real internet delays and routes

A
  1. Traceroute program: provides delay measurement from source to router along
    end-end Internet path towards destination.
  2. For all i:
    (i) sends three packets that will reach router i on path towards destination.
    (ii) router i will return packets to sender.
    (iii) sender times interval between transmission and reply.
50
Q

Packet loss:

A
  1. queue preceding link in buffer has finite capacity.
  2. packet arriving to full queue drop.
  3. lost packet may be retransmitted by previous node, by source end system, or not at all.
51
Q

Throughput:

A

Rate (bits/time unit) at which bits transferred between sender/receiver

(i) instantaneous: rate at given point in time.
(ii) average: rate over longer period of time.

52
Q

Throughput: Internet scenario

A
  1. per-connection end-end throughput:
    (i) min (Rc, Rs/10)
  2. in practice: Rc or Rs is often bottleneck.
53
Q

Protocol layers:

A

Networks are complex with many pieces:

(i) hosts
(ii) routers
(iii) links of various media
(iv) applications
(v) protocols
(vi) hardware, software

54
Q

Why layering?

A
  1. explicit structure allows identification, relationship of complex system’s pieces
    (i) layered reference model for discussion .
  2. modularization eases maintenance, updating of system
    (i) change of implementation of layer’s service transparent to rest of system.
    (ii) e.g., change in gate procedure doesn’t affect rest of system.
55
Q

Internet protocol stack:

A
  1. Application: supporting network applications
    ((FTP, SMTP, HTTP))
  2. Transport: process-process data transfer
    ((TCP, UDP))
  3. Network: routing of datagrams from source to
    destination
    ((IP, routing protocols))
  4. Link: data transfer between neighboring network elements
    ((Ethernet, 802.11 (WiFi), PPP))
  5. Physical: bits “on the wire”.
56
Q

ISO/OSI reference model

A
  1. presentation: allow applications to interpret
    meaning of data, e.g., encryption, compression,
    machine-specific conventions.
  2. session: synchronization, checkpointing, recovery of data exchange.
57
Q

Network security:

A
  1. Field of network security:
    (i) how bad guys can attack computer networks.
    (ii) how we can defend network against attacks
    (iii) how to design architectures that are immune to attacks.
58
Q

Bad guys: put malware into host via internet:

A
  1. Malware can get in host from:
    (i) virus: self-replicating infection by receiving/executing object (e.g., e-mail attachment).
    (ii) worm: self-replicating infection by passively receiving object that gets itself executed.
  2. Spyware malware can record keystrokes,
    web sites visited, upload info to collection site.
  3. Infected host can be enrolled in botnet, used for spam. DDoS attack.
59
Q

Bad guys: attack server, network infrastructure:

A

Denial of Service (DoS): attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic.

Ways:
1. Select target
2. Break into hosts around the network (see
botnet)
3. Send packets to target from compromised
hosts

60
Q

Bad guys can sniff packets:

A
  1. Packet “sniffing”:
    1.1. Broadcast media (shared Ethernet, wireless)
    1.2. Promiscuous (indiscriminate) network interface reads/records
    all packets (e.g., including passwords!) passing by.
  2. IP spoofing:
    2.1. Send packet with false source address.
61
Q

Internet history:

A

Refer Shur’s note page 12

DATA (FINAL) (2 decks)

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