CCNA ITN: Module 3

message source

origin of the communication in a network

message destination

target device or system for network communication

channel

medium through which a message is transmitted

protocol

agreed set of rules for communication covering source, destination, encoding, formatting, timing, and delivery

bit conversion

process of converting messages into bits for transmission

IP

main protocol for sending data across multiple networks from source to destination

frame

smaller piece of a message with addressing info

must be within size limits

flow control

controls data rate and amount of data sent

response timeout

sets wait time for replies and action if none is received

access method

rules that determine when a device can send data

unicast

message sent to one specific device

multicast

message sent to multiple specified devices

broadcast

message sent to all devices on a network

protocol necessity

all communicating devices must follow the same protocols to exchange data

network communication protocols

examples include IP, TCP, HTTP

network security protocols

SSH, SSL, TLS used for encryption, authentication, and integrity

routing protocols

OSPF and BGP, used by routers to share and select best routes

service discovery protocols

DHCP and DNS for automatic device or service detection

protocol functions

addressing, reliability, flow control, sequencing, error detection, and application interfacing

protocol suite

collection of related protocols needed for communication

TCP/IP model

4-layer open standard protocol suite: application, transport, internet, network access

protocol stack

each layer supports the one above it and provides services to higher layers

higher-level protocols

handle message content

lower-level protocols

handle data transmission and network service

application layer (TCP/IP)

includes protocols like DNS, FTP, HTTPS

transport layer (TCP/IP)

includes TCP and UDP

internet layer (TCP/IP)

includes IPv4, ICMPv4, OSPF

network access layer (TCP/IP)

includes ARP, Ethernet, WLAN

open standards

promote competition, compatibility, and innovation

IEEE

standards body for Ethernet, WLAN, and related tech

IETF

maintains TCP/IP and publishes RFCs

ICANN/IANA

manages IP address and domain name allocation

layered model

breaks network functions into layers for standardization

OSI model

7 layers: application, presentation, session, transport, network, data link, physical

OSI layer 7

application layer for user interaction and processes

OSI layer 6

presentation layer for data representation and formatting

OSI layer 5

session layer for managing sessions and dialogs

OSI layer 4

transport layer for segmentation, reliability, and flow

OSI layer 3

network layer for logical addressing and routing

OSI layer 2

data link layer for framing and physical addressing

OSI layer 1

physical layer for transmission of bits

OSI to TCP/IP correlation

OSI layers 7-5 map to TCP/IP application layer, layer 4 to transport, 3 to internet, 2-1 to network access

encapsulation

wrapping data with protocol headers at each layer

de-encapsulation

removing protocol headers as data moves up the stack

PDU

protocol data unit, form of data at each layer

application layer PDU

data

transport layer PDU

segment (TCP) or datagram (UDP)

network layer PDU

packet

data link layer PDU

frame

physical layer PDU

bits

multiplexing

supports multiple simultaneous data streams across a network

local resource access

requires IP (layer 3) and MAC (layer 2) addresses

IP address

structure includes network/prefix and host/interface parts

same network communication

uses direct MAC address of destination device

different network communication

IP addresses differ in network portion, MAC address is that of default gateway

MAC address

layer 2 address used within local network, changes as packet travels across routers

hexadecimal notation

format used to display MAC addresses