Internet interconnection and OSI seven-layer model

Sp2ak.W

=============================================
Physical layer
Role: define some appliances, machinery, processes and specifications, such as hubs;
PDU (Protocol Data Unit): bit / bit
Equipment: Hub HUB;
Note: there is no concept of addressing;
==============================================
data link layer
Role: Define how to format data and support error detection;
Typical protocols: Ethernet, Frame Relay (antique VPN)
PDU: frame (frame) equipment: Ethernet switch;
Remarks: The switch forwards data through MAC addresses, and logical link control;
===============================================
Network layer
Role: Define a logical addressing, select the best path for transmission, and route data packets;
Typical protocols: IP, IPX, ICMP, ARP (IP-> MAC), IARP;
PDU: packet / data packet;
Device: Router
Note: Addressing
================================================
Transport layer:
Role: Provide reliable and best-effort transmission;
Typical protocols: TCP, UDP, SPX, port (65535 ports), EIGRP, OSPF,
PDU: fragment segment;
No typical equipment
Remarks: responsible for network transmission and session establishment;
=================================================
Session layer:
Role: control the session, establish management and terminate the application session;
Typical protocols: NFS, SQL, ASP, PHP, JSP, RSVP (resource source reservation protocol), windows,
Remarks: responsible for session establishment;
===================================================
Presentation layer:
Role: Format the data;
Typical protocols: ASCII, JPEG. PNG, MP3. WAV, AVI,
Note: Can provide encryption services;
===================================================
Application layer:
Role: control application;
Typical protocols: telnet, ssh, http, ftp, smtp, rip, BGP, (to be continued)
Note: Provide network services for applications;
====================================================