Data communication process:
1. Data encapsulation process: convert data to binary numbers (0 and 1)
2. Data transmission process: forwarding through media and network equipment
3. Data unpacking process: convert binary numbers into data
1. Data encapsulation process: convert data into binary numbers
Reference model: TCP / IP reference model
osi reference model
OSI reference model:
Application layer: generate data ———– PDU protocol data unit
Http: Hypertext Transfer Protocol ——— 80 TCP
FTP: File Transfer Protocol ———— 20 21tcp
DNS: domain name resolution protocol ————- 53tcp or UDP
DHCP: Dynamic Host Configuration Protocol —— 67 68udp
Telnet: remote login protocol ————- 23tcp
SSH: Secure Remote Login Protocol ——— 22tcp
POP3: post office protocol ————————– 110tcp
SMTP protocol: Simple Mail Transfer Protocol —- 25tcp
Qicq: QQ protocol ———————– UDP member 4000 UDP non member 8000 tcp443
Port:
Because different applications will produce different data and different data have different requirements during transmission, different protocols should be encapsulated in the transmission layer.
Function of port number: used to identify the application layer protocol
Port number: 65536 0 — 65536
Well known port number: 0 — 1023 reserved for the network
Registered port number: commercial 1024 — 49151
Random port number: 49152 — 65535
Layer 4: —————- data segment
Function: data segmentation. 1500 bytes by default
Encapsulate TCP or UDP header message
TCP: Transmission Control Protocol
TCP 49155—->80|http-date
Advantages: reliable transmission; disadvantages: slow transmission
How does TCP ensure reliable transmission?
Front: TCP three handshakes
Medium: packet loss retransmission (confirm retransmission number)
Window size: same as sending and receiving
After: TCP Quad breakup (full duplex)
Connection oriented: a connection needs to be established before transmission
TCP working process:
1. Establish TCP connection (before): three handshakes
2. Transmission process (in process): packet loss retransmission
3. Close TCP connection (after): four Breakups
UDP: User Datagram Protocol
Advantages: fast disadvantages: unreliable transmission
Why can’t UDP guarantee reliability?
There is no reliable confirmation mechanism in the message
Why is UDP fast?
The header message has only 8 bytes
Under what circumstances will UDP encapsulation be used?
Flow for time delay
Layer 3: network layer
Role: IP addressing routing forwarding
Packet fragmentation ——- MTU maximum transmission unit (1500b) — data packet
IP: Internet Protocol (Internet Interconnection Protocol)
ARP: Address Resolution Protocol
Find MAC address through IP address
ARP send request is sent in the form of broadcast
ARP response (replay) is sent in unicast form
Layer 2: — data link layer — data frame
Role: connect physical layer and network layer
Connect frame header and end
MAC address globally unique
It consists of two parts, namely supplier code and serial number, of which the first 24 represent supplier code,
Managed and assigned by IEEE (Internet task force)
communication mode
Unicast: it is the MAC address of your own computer, one-to-one
The 8th bit of the first byte of unicast MAC address is “0”
Broadcast: one to many
Broadcast MAC address: full FF (111111111111)
Multicast: one to many Tencent News
Multicast MAC address: the 8th bit of the first byte is “1”
Expression: usually expressed in hexadecimal numbers
Layer 1: ——- physical layer —— bitstream
Convert data frames into bitstreams for transmission