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Networking 1 > Chapter 2 > Flashcards

Chapter 2 Flashcards

1
Q

– Fundamental network communications model.

A

Open Systems Interconnection (OSI) reference model

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2
Q

OSI model product of two standards organizations:

A

– International Organization for Standardization (ISO)
– American National Standards Institute (ANSI)

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3
Q

Is theoretical, not specific hardware or software.
Guidelines analogized to a grammar.

A

OSI

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4
Q

Accomplishments of the OSI model

A

– Enabling communications among LANs, MANs, WANs
– Standardizing network equipment
– Enabling backward compatibility to protect investments
– Enabling development of software and hardware with
common interfaces
– Making worldwide networks possible; e.g., the Internet

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5
Q

OSI model consists of seven distinct layers

A

Physical,
Data Link,
Network,
Transport,
Session,
Presentation,
Application

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6
Q

Set of layers in OSI model is called a

A

Stack

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7
Q

Called by actual name or placement in stack

A

Layers

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8
Q

Layers also divided into three groups

A

– Bottom: handles physical communications
– Middle: coordinates communication between nodes
– Top: involves data presentation

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9
Q

Contact between two network devices

A

– Communications traverse layered stack in each device
– Each layer handles specific tasks
– Each layer communicates with next layer using protocol

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10
Q

• Layer purpose: transmit and receive signals with data
•Network signals are either analog or digital
•Digital signal generates binary 1s or 0s

A

Physical Layer

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11
Q

– All data transfer mediums
• wire cable, fiber optics, radio waves, and microwaves
– Network connectors
– The network topology
– Signaling and encoding methods
– Data transmission devices
– Network interfaces
– Detection of signaling errors

A

Responsibilities of the Physical layer (Layer 1)

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12
Q

– Wave pattern with positive and negative voltages
– Examples: ordinary telephone or radio signal
– Used in WANs that employ analog modems

A

Analog signal

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13
Q

Physical network problems affect physical layer:

A

– Example 1: broken cable
– Example 2: electrical or magnetic interference

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14
Q

– Caused by magnetic force fields
– Generated by certain electrical devices
• Fans, electric motors, portable heaters, air-conditioners

A

Electromagnetic interference (EMI)

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15
Q

– Caused by electrical devices emitting radio waves
• Radio and television stations, radio operators, cable TV
– Problem when frequency matches network signal

A

Radio frequency interference (RFI)

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16
Q

• Layer purpose: format bits into frames
• Frame: discrete unit of information
– Contains control and address information
– Does not contain routing information

A

Data Link Layer

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17
Q

– Calculates size of information fields in frame
– Data Link layer at sender inserts value at end of frame
– Receiving Data Link layer checks value in frame

A

Cyclic redundancy check (CRC): monitor duplication

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18
Q

– Initiates communication link between two nodes
– Guards against interruptions to link
– Link to Network layer may be connection-oriented

A

Logical link control sublayer (LLC)

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19
Q

– Examines physical (device or _) address in frame
– Frame discarded if address does not match workstation
– Regulates communication sharing

A

Media access control sublayer (MAC)

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20
Q

MAC address burned into chip on network interface
– Coded as a hexadecimal number; e.g., 0004AC8428DE
• First half refers to _, second half _

A

•vendor
•unique to device

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21
Q

• Layer purpose: control passage of packets on network
– Physical routes: cable and wireless paths
– Logical routes: software paths

A

Network Layer

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22
Q

– Optimize physical and logical routes
– Permit routers to move packets between networks

A

Specific tasks of Network layer

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23
Q

: process of information gathering
– Obtain metrics about location of networks and nodes

A

Discovery

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24
Q

: logical communication paths
– Send and receive data
– Known only to Network layers between nodes
– Benefit: manage parallel data paths

A

Virtual circuits

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25
Q

– Checks (and corrects) packet sequence
– Addresses packets
– Resizes packets to match receiving network protocol
– Synchronizes flow of data between Network layers

A

Extra duties using virtual circuits

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26
Q

• Layer purpose: reliable data transmission
– Ensures data sent and received in same order
– Receiving node sends acknowledgement (“ack”)
Five reliability measures used by protocols
• _ mediates between different protocols

A

Transport Layer

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27
Q

Transport layer support of virtual circuits
– Tracks unique identification value assigned to circuit

A

• Value called a port or socket
• Port assigned by Session layer

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28
Q

• Half duplex communications

A

Session Layer

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29
Q

for dialog control
• Sets up node to separately send and receive
• Analogize to use of walkie-talkies

A

Two-way alternate mode (TWA)

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30
Q

– Establish and maintain link between two nodes
– Provide for orderly transmission between nodes
– Determine how long node can transmit
– Determine how to recover from transmission errors
– Link unique address to each node (like a zip code)

A

Multiple goals

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31
Q

– Two-way simultaneous (TWS) for dialog control
• Devices configured to send and receive at same time
– Increases efficiency two-fold
– Made possible by buffering at network interface

A

Full duplex communications

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32
Q

– Signal can travel in only one direction in a medium
– Not as desirable as either half or full duplex

A

Simplex alternative

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33
Q
  • Primary purpose: manages data formatting
    – Acts like a syntax checker
    – Ensures data is readable to receiving
A

Presentation Layer

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34
Q

• 8-bit coding method for 256-character set
• Used mainly by IBM computers

A

EBCDIC (Extended Binary Coded Decimal Interchange Code)

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35
Q

• 8-bit character coding method for 128 characters
• Used by workstations running Windows XP, Fedora, Linux

A

ASCII (American Standard Code for Information
Interchange)

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36
Q

: scrambling data to foil unauthorized users
• Example 1: account password encrypted on LAN
• Example 2: credit card encrypted on a LAN

A

Encryption

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37
Q

• Encryption tool:

A

Secure Sockets Layer (SSL)

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38
Q

: compact data to conserve space
• Presentation layer at receiving node decompresses data

A

Data compression

39
Q

• Connecting workstations to network services
– Link application into electronic mail
– Providing database access over the network

A

Application Layer

40
Q

– File transfer, file management, remote access to files
– Remote access to printers
– Message handling for electronic mail
– Terminal emulation

A

• Services managed by Application layer

41
Q

– Makes computer visible to another for network access
– Example: access shared folder using redirector

A

Microsoft Windows redirector

42
Q

• OSI model enables two computers to communicate

A

Communicating Between Stacks

43
Q

Standards provided by OSI models

A

– Communicating on a LAN
– Communicating between LANs
– Internetworking between WANs and LANs (and WANs)

44
Q

Constructing a message at the sending node

A

– Message created at Application layer
– Message travels down stack to Physical layer
– Information at each layer added to message
• Layer information is encapsulated
– Message sent out to network form Physical layer

45
Q

term for transferred data

A

Protocol data unit (PDU)

46
Q

Control data added to PDU as it traverses stack

A

– Next layer gets transfer instructions from previous layer
– Peer protocols used to communicate with companion layer

47
Q

• remains after data stripped

A

Service data unit (SDU)

48
Q

Key points

A

– Each layer forms a PDU (from an SDU)
– Each PDU is communicated to counterpart PDU

49
Q

• Example: workstation accesses shared drive
– Redirector at Application layer locates shared drive
– Presentation layer ensures data format is ASCII
– Session layer establishes and maintains link
– Transport layer monitors transmission/reception errors
– Network layer routes packet along shortest path
– Data Link layer formats frames, verifies address
– Physical layer converts data to electrical signal
• OSI model also applied to network hardware and software communications

A

Applying the OSI Model

50
Q

basis for standards and conventions

A

Request for Comment (RFC)

51
Q

RFCs managed by

A

IETF (Internet Engineering Task Force)

52
Q

RFCs evaluated by

A

IESG (Internet Engineering Steering Group) within IETF

53
Q

Two kinds of RFC documents

A

– Universal Protocol for transferring data on Internet
– Informational RFCs (RFC 2555 provides RFC history)

54
Q

Two main LAN transmission methods

A

– Ethernet: defined in IEEE 802.3 specifications
– Token ring: defined in IEEE 802.5 specifications

55
Q

Ethernet is more widespread than token ring
– Has more high-speed and expansion options

A

LAN Transmission Methods

56
Q

High-speed variation of token ring

A

Fiber Distributed Data Interface (FDDI)

57
Q

• Leverages bus and star topologies
• Collision occurs if two nodes transmit simultaneously

A

Ethernet

58
Q

Control method: of ethernet
Algorithm that transmits and decodes formatted frames

A

Carrier Sense Multiple Access with
Collision Detection (CSMA/CD)

59
Q

Frames find destination through physical addressing
– Node has unique MAC address associated with NIC
• Functions performed with network drivers
– Network access, data encapsulation, addressing
• Data transmitted in Ethernet encapsulated in frames

A

Ethernet

60
Q

Frame composed of six predefined fields
Of ethernet

A

– Preamble
– Start of frame delimiter (SFD or SOF):
– Destination address (DA) and source address (SA):
– Length (Len)
– Data and pad
– Frame check sequence or frame checksum (FCS)

61
Q

transport method
– Uses physical star topology and logic of ring topology
– Data transmission up to 100 Mbps

A

Token ring

62
Q

hub ensures packet circulated

A

Multistation access unit (MAU)

63
Q

Token: specialized packet continuously transmitted

A

– Size: 24 bits
– Structure: three 8-bit fields
• Starting delimiter (SD)
• Access control (AC)
• Ending delimiter (ED)

64
Q

– Node must capture token to transmit
– Node builds frame using token fields
– Resulting frame sent around ring to target node
– Target node acknowledges frame received and read
– Target node sends frame back to transmitting node
– Transmitting node reuses token or returns it to ring

A

Using a token

65
Q

Node sends frame to indicate problem
– Ring tries to self-correct problem

A

Beaconing

66
Q

– Broadcast storms and interference are rare

A

Token ring networks reliable

67
Q

– Standard for high-capacity data throughput 100 Mbps
Uses fiber-optic cable communications medium.

A

Fiber Distributed Data Interface (FDDI)

68
Q

uses timed token access method
– Send frames during target token rotation time (TTRT)
– Allows for parallel frame transmission

A

FDDI

69
Q

uses timed token access method
– Send frames during target token rotation time (TTRT)
– Allows for parallel frame transmission

A

FDDI

70
Q

Two types of packets

A

– Synchronous communications (time-sensitive traffic)
– Asynchronous communications (normal traffic)

71
Q

• Two classes of nodes connect to FDDI network

A

– Class A: nodes attached to both rings (hubs)
– Class B: node (workstation) attached via Class A node

72
Q

•built on topologies and network transmission
– Similar to LAN structure, with greater complexity
– Providers do not provide detailed specifications

A

WAN Network Communications

73
Q

WAN network service providers

A

– Telecommunications companies
• Especially regional telephone companies (telcos or
RBOCs (regional bell operating companies))
– Cable television companies (cablecos)
– Satellite TV companies

74
Q

Plain old telephone service (POTS)
– Carry most basic WAN communications
– 56-Kbps dial-up access, Integrated Service Digital
Network (ISDN), Digital Subscriber Line (DSL)

A

Telecommunications WANs

75
Q

• Topology between RBOCs and long distance carrier

A

– RBOC provides local access and transport area (LATA)
– IXC lines join RBOC and long distance carrier
• Point of presence (POP) is term for junction

76
Q

dedicated telephone line for data link
– Example: states use to connect offices to capitol

A

T-carrier lines

77
Q

synchronous 56-Kbps service

A

Alternative to T-carrier

78
Q

• Architecture consists of star-shaped locations
• Headend is the focal point in the star
• Grouping of antennas, cable connections, satellite dishes, microwave towers
• Distribution centers transfer signals to feeder cables
• Cable modems convert signals for computer use

A

Cable TV WANs

79
Q

use of radio, microwaves, satellites

A

Wireless WANS

80
Q

– Connect wireless LAN to wireless bridge or switch
– Connect bridge or switch to antenna
– Antenna transmits wave to distant antenna

A

Topology of radio communications

81
Q

– Connect microwave dish to LAN
– Dish transmits to microwave dish at remote location

A

Topology of microwave communication

82
Q

– Satellite dish transmits to satellite in space
– Satellite relays signal to satellite dish at remote location

A

Topology of satellite communications

83
Q

• Switching techniques creating data paths (channels)

A

WAN Transmission Methods

84
Q

divides the channels into frequencies instead of time slots

A

Frequency Division Multiple Access (FDMA)

85
Q

bandwidth of cable dynamically allocated based on application need

A

Statistical multiple access

86
Q

involves creating a dedicated physical
circuit between the sending and receiving nodes

A

Circuit switching

87
Q

uses store-and-forward method to
transmit data from sending to receiving node

A

Message switching

88
Q

establishes a dedicated logical circuit between the two transmitting nodes

A

Packet switching

89
Q

Scenario: new campus needs new network
Ethernet appropriate for all areas of new campus

A

Designing an Ethernet Network

90
Q

– Ethernet enjoys widespread vendor/technical support
– Compatible with star-bus topology popular with LANs
– Network upgrades easily to higher bandwidths
– Standards exist for cable and wireless versions
– Ethernet network scales well, adapts well to WANs
– Network devices on old campus may be used
– Many options for Internet connections

A

Reasons for choosing Ethernet technology

91
Q

Message travels up stack from

A

Physical layer

92
Q

checks address of frame
uses CRC to check frame integrity

A

Data Link layer

93
Q

Receives valid frame and sends up stack

A

Network layer

Networking 1 (2 decks)

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