IP Introduction
IP is the TCP / IP protocol suite, the core of the agreement. All TCP, UDP, ICMP, IGMP data is transmitted in IP datagrams format.
IP provides an unreliable, connectionless datagram delivery service.
Unreliable (unreliable) it does not guarantee an IP datagram can successfully reach the destination. IP provides only the best transport service. If some error occurs, such as a router runs out of buffer temporarily, the IP has a simple error processing algorithm: discard the packet and send an ICMP message packet to the source terminal. Any required reliability must be provided by an upper layer (e.g., TCP).
No connection (connectionless) IP does not maintain any state information about the subsequent datagrams. Processing of each packet are independent. IP datagrams may not receive the transmitted sequence. If two successive transmission source to sink the same data packet (first A, then B), each datagram is routed independently, may choose a different route, so B may arrive first before reaching the A .
This chapter first minister of the IP total of 20 bytes projections diverged
A projected source tutorial way: Tutorial Address: https://www.bilibili.com/video/av59638344/?p=3 period: 10: 20--11: 30
According to 1111 in terms of four 4-bit header length binary maximum length of 15 decimal, said 15 where 1 represents 4 bytes of 32 bits, followed barabara affect determination.
Now converted into a decimal so also do a binary comparison is reasonable?
Disagreement points: 15 in which 1 represents a 4-byte 32-bit who is defined?
My own understanding is:
Wherein the data of the first row of the four versions of Ministers headed +4 + +16 8 bit type of service is equal to the total length of 16 + 16 = 32
32bit = 4Byte
4 bytes per line to the head of the 32-bit destination IP address is a total of 20 bytes of row 5
Byte unit conversion:
"1" is represented. 1 'bit
"1 byte" indicates. 1 Byte
"1 byte" = "8" ie. 1 Byte S =. 8 ' bit