OSI Layers Flashcards
OSI layer 1
Physical
Transmits binary over physical media between devices
OSI layer 2
Data link
Creates and address frames for host to host delivery on LANd and between WANs
OSI layer 3
Network
Creates and addresses packets for delivery between devices
OSI layer 4
Transport
Defines data segments and numbers them at the source, transfers the data, and reassembles the data at the destination.
OSI layer 5
Session
Manages sessions between users and synchronizes web sessions, video, etc.
OSI layer 6
Presentation
Provides data format info to the application
I.e. whether it is a jpg or encrypted etc.
OSI layer 7
Application
Performs services for applications used by the user
Acronym for remembering the OSI layers
All people seem to need data processing
What layer uses frames?
Layer 2 data link
What layer uses packets?
Layer 3 network
TCP/IP layer 1
Network access(OSI 1&2)
TCP/IP layer 2
Internet (OSI 3)
TCP/IP layer 3
Transport (OSI 4)
TCP/IP layer 4
Application (OSI 5-7)
What is used to identify an application at the transport layer?
Port #
2 transport layer protocols
TCP-uses segments, connection oriented
UDP-best effort, uses data grams
Well known ports
Reserved for services and applications
0-1023
Registered ports
Assigned to user processes or applications
1024-49151
Dynamic or private ports
Assigned dynamically to client applications when initiating a connection
49152-65535
FTP
TCP
Port 20/21
Telnet
TCP
Port 23
Smtp
Smtp
TCP
Port 25
TFTP
Trivial file transfer protocol
UDP
Port 69
HTTP
Hypertext transfer protocol
TCP
Port 80
POP3
Post office protocol
TCP
Port 110
IMAP
Internet message access protocol
Port 143
Port 993 w/ssl
TCP
HTTPS
Secure http
Port 443
Causes of physical layer problems
Power related Hardware faults Cabling faults Attenuation Noise Interface config errors Exceeding design limits CPU overload
Symptoms of data link problems
No functionality of network layer or above
Poor performance
Excessive broadcasts
Console messages
Causes of data link problems
Encapsulation errors
Address mapping errors
Framing errors
Stp failures or loops
TCP/IP application layer protocols
DNS, telnet, SMTP, POP3, IMAP, DHCP, HTTP, FTP, SNMP
TCP/IP transport protocols
TCP/IDP
TCP/IP Internet layer protocols
IP, ARP, ICMP
TCP/IP network access layer protocols
Ethernet, frame relay
Application layer PDU
Data
Transport layer PDU
Segment
Internetwork layer PDU
Packet
Network access layer PDU
Frame
What layer do client/server processes reside in?
Application
Primary responsibilities of transport layer
Tracking individual communications between applications on the source and destination hosts
Segmenting data and managing each piece
Reassembling the segments into streams of application data
Identifying different applications
Flow control between end users
Enabling error recovery
Initiating a session
3 key functions of physical layer
Physical components
Encoding
Signaling
Code group
A symbol that is a predefined small group of bits that represent a larger group of data bits at the physical layer
2 Ethernet data link sub layers
LLC logical link control
MAC media access control
LLC
Implemented on software
Adds control information to network layer packet
MAC
Implemented in hardware, typically the NIC
Data encapsulation
Placement of frames on media
MAC address
48 bit binary # expressed in hex
1st 3 bytes are vendor code
Last 3 bytes are unique #
Broadcast MAC address
FF-FF-FF-FF-FF-FF
48 1s in binary
ARP
Address resolution protocol
Uses a broadcast at layer 2 to discover the MAC address of the host when a layer 3 address is known
Maintains a cache of mapping
Multicast MAC address
Always beginning with 01-00-SE
