Network Models Flashcards
ISO
International Organization of Standardization
OSI
Open Systems Interconnection
importance of models in networking
provides standardization across networks of different manufacturers
OSI 7 layer model encourages [blank]
modular design
limited integration between layers
layers of OSI 7-layer model
1) Physical
2) Data Link
3) Network
4) Transport
5) Session
6) Presentation
7) Application
PDNTSPA: Please Do Not Think Saruman Proved Allegiance
OSI layer 1
anything that moves data between machines
copper cabling, fiber-optics, radio waves, etc.
central box, NIC, hub
UTP
unshielded twisted pair
number of wires in UTP cable
8 wires - 4 pairs
type of wire in UTP cable
copper
central box
device that handles flow of information from every computer to each other computer
each system on network has its own cable running to central box
NIC
Network Interface Card
interface between PC (device) & network
contains host firmware & MAC address
creates / sends & reads / receives frames
MAC address
media access control address
48-bit value
never shared
OUI
organizationally unique identifier
1st 6 digits (24 bits) of MAC address
NIC manufacturer number
device ID
last 6 digits (24 bits) of MAC address
serial number for NIC
Windows command to view MAC address
ipconfig /all
other names for MAC address
MAC-48 & EUI-48 > IEEE
physical address
IEEE
Institute of Electrical & Electronic Engineers
defines industry-wide standards that promote the use & implementation of technology
order of generic frame
recipient’s MAC address
sender’s MAC address
Type
Data
FCS
binary electrical transmission
1 - charge on the wire
0 - no charge on the wire
frame
container for discrete amount of data moving across a network
frame type
specific network technology of the frame
all NICs on network must use the same frame type
FCS
frame check sequence
uses cyclic redundancy check (CRC) - binary math - to verify data arrived intact
sending system generates key used by receiving system
most only 4 bytes long > check up to 1500 bytes
MAC addressing
use of MAC addresses to get frames to the recipient
usually not configured - Ethernet uses MAC assigned by manufacturer
frame size limitations
most frames hold 1500 bytes of data
sent data exceeding frame size - broken into frame-sized chunks
hub
essentially just a repeater (early networks)
made copies of frame - sent to every other system on the network
only NIC to which frame was addressed would process that frame
all other NICs erase frame
switch
filters traffic by MAC address
sends frame only to recipient MAC address
recipient MAC not already known/cached
NIC sends broadcast on network to request MAC
every NIC on network processes the frame
address request contained in frame data
IP address used to isolate target computer
desired system reads request - responds with MAC address
broadcast MAC address
FF-FF-FF-FF-FF-FF
complete frame movement
1 - sending system OS hands data to its NIC
2 - NIC builds frame
3 - NIC adds FCS & data to frame
4 - NIC adds destination & its own MAC address
5 - NIC waits for cable to be free - sends frame on cable through network
6 - Frame moves to central box (hub/switch)
7 - Receiving NIC applies FCS - strips off all framing information-sends to OS
OSI layer 2
any device that deals with a MAC address
provides DLC
NIC, switch
only later with sub-layers
DLC
data link control
LLC
logical link control
aspect of NIC that talks to OS - handles multiple network protocols & provides flow control
drivers
sub-layer
MAC
media access control
creates & addresses frame
adds or checks FCS
sub-layer
NIC in OSI layers 1 & 2
1 - puts frame on cable
2 - assembles frame
go with 2 if asked to pick 1 answer
TCP
Transmission Control Protocol
IP
Internet Protocol
range of each 8-bit number in IP address
0 - 255
[blank] make logical addressing powerful
routers
TCP/IP data encapsulation
packet inside a frame
frame header - packet header - data - FCS
packet enters router
router removes incoming frame
determines destination via IP address
creates new frame
sends packet
new frame will match technology of of that attached to receiving router
packet reaches destination subnet router
router removes frame
replaces with frame containing destination MAC address that matches destination IP address
OSI layer 3 hardware
router
last layer that deals directly with hardware
OSI layer 4
assembly & disassembly
initiates requests to resend problematic packets
TCP/IP transport - sending data
serving computer receives request
must break up data to fit within a packet
organize packets for receiving system
hand packets to NIC for sending
TCP/IP transport - receiving data
receiving computer must be able to recognize a series of incoming packets
correctly reassemble packets based on information from sending system
verify all data arrived intact
transport protocol breaks data into [blank]
segments - get sequence number (TCP)
datagrams - no sequence number (UDP)
sequencing number
allows receiving system to know the total number of packets & their arrangement
OSI layer 5
connecting applications to applications
limited time of communication between 2 systems
client/server or computer/computer
initiates, accepts, opens/closes sessions
Windows command to display all running sessions
netstat
OSI layer 6
translation
translates data from lower layers into a format usable by the Application layer & vice versa
OSI layer 7
network applications
web browsers, Office, Quicktime, etc.
code built into every OS to enable network-aware apps
API
application programming interface
used by programmers to make apps network-aware
encapsulation
entire process of preparing data to go onto a network
OSI layers 2 - 7
de-encapsulation
process of removing all extra header information as data travels up the stack
layers of TCP/IP model
1 - link / network interface
2 - Internet
3 - transport
4 - application
LITA: Legolas Is Trained Archer
OSI layers 5-7 linked together*
TCP/IP link layer
“network interface layer”
all physical components (minus router)
any part of network that deals with complete frames
TCP/IP Internet layer
“IP packet” layer
any device or protocol that deals with pure IP packets - getting packet to destination
creation of IP packets
IP addressing
router
TCP/IP transport layer
assembly & disassembly of packets
defines connection-oriented vs. connectionless communication
OSI layers 5 - 7
connection-oriented communication
connection verified before data is sent (TCP)
connectionless communication
data sent without verifying receiving system is ready (UDP)
UDP
user datagram protocol
TCP segment
remaining data after removing IP address from packet
fields ensure connection-oriented communication works properly & data arrives intact
TCP segment fields
checksum
flags
acknowledgement
TCP creation
data received from application layer
transport layer:
breaks data into discrete sections - adds port number & sequence number (creates TCP segment)
hands TCP segment to Internet layer to create IP packet
UDP creation
receives data from application layer
adds port & length numbers + checksum
missing fields > doesn’t care about data integrity
TCP/IP application layer
every application must know how to initiate, control, & disconnect from a remote system
no application requires any particular form of presentation as in OSI model
all TCP/IP apps are network-aware by definition
TCP/IP data structures per layer
link - frame
internet - IP packet
transport - TCP segment / UDP datagram
application - data
flow control
provides mean for receiver to govern the amount of data sent by sender
TCP using windowing by default - decrease window to slow down transmitting host - receiving host does not overflow buffers
