Shulou(Shulou.com)06/01 Report--

PPP Protocol:

PPP point-to-point protocol is a link layer protocol designed for simple links such as transmitting packets between peer units. This link provides full-duplex operation and delivers packets sequentially. It is designed primarily to send data over dial-up or dedicated point-to-point connections, making it a common solution for simple connectivity between various hosts, bridges, and routers.

The PPP protocol defines an encapsulation method for datagrams transmitted over serial links based on the High Level Data Link Control (HDLC) standard.

Frame Format: Flag Field--Address Field--Control Field--Protocol--Data--FCS--Flag Field

Ethernet II Protocol:

Ethernet Type II Ethernet frames have a minimum length of 64 bytes (6+6+2+46+4) and a maximum length of 1518 bytes (6+6+2+1500+4). The first 12 bytes identify the MAC address of the source node sending the data frame and the MAC address of the target node receiving the data frame respectively.

The next two bytes identify the upper layer data type carried by the Ethernet frame, for example, hexadecimal number 0x0800 represents IP protocol data, hexadecimal number 0x86dd represents IPv6 protocol data, hexadecimal number 0x809B represents AppleTalk protocol data, hexadecimal number 0x8138 represents Novell type protocol data, etc.

After the variable-length data field is a 4-byte frame check sequence (Frame. Check Sequence (FCS), which uses a 32-bit CRC cyclic redundancy check to check data from the Destination MAC Address field to the Data field.

Ethernet minimum transmission frame length is 64 bytes, according to the standard, 10Mbps Ethernet using repeaters, the maximum length of the connection is 2500 meters, a maximum of 4 repeaters, so the minimum transmission time for a 10Mbps Ethernet frame is 51.2 microseconds. The amount of data that can be transmitted during this time is 512 bits, so it is also called 512 bits. This time is defined as Ethernet time slots, or collision time slots. 512 bits =64 bytes, which is why Ethernet frames are 64 bytes minimum. Now basically are switches or routers directly connected to computers, hub connections rarely exist, in the switch or router directly connected to computers between each computer and the device is an independent collision domain, is not a collision, therefore, at this time to send a frame length of less than 64 bytes is theoretically OK, but in order to comply with the original standard, considering that some concentrator equipment is still in use, so keep the minimum frame length of 64 bytes unchanged.

HDLC protocol:

SDLC/HDLC frame information consists of the following fields, all fields are transmitted from the least significant bit.

SDLC/HDLC flag character

SDLC/HDLC protocol stipulates that all information transmission must start with a flag character and end with the same character. This flag character is 0111110 and is called the flag field (F). From the start mark to the end mark, a complete unit of information is formed, which is called a frame. All information is transmitted in frames, and flag characters provide the boundaries of each frame. The receiver can establish frame synchronization by searching for "0111110" to find out the beginning and end of the frame

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.