The composing of Mac frame in computer network experiment

Practice One:

Practice One:

The sending interface of computer A of the sending end of practice one forgets.

Exercise two:

Exercise Three:

The composition of the Ethernet:

There are two standards for the MAC frame format of Ethernet, one is the Dix Ethernet V2 Standard and the other is the IEEE 802.3 standard. Both formats are judged by type/length. DIX Ethernet V2 The type/length of the frame that is greater than 1536,ieee 802.3 is less than 1518. For Dix Ethernet V2 frames, this field value represents the type of the high-level protocol, and for IEEE802.3, this field value represents the length of the data.

V2 frame length is not designed because: in Manchester code, there is a voltage conversion between each code source, when a frame is sent, no other code source is sent. The bottom fourth byte at the end is the end position of the data field.

Explanation of 1536 and 1518:1518=1500+4+2+6+6;1536~65535 is a reserved Type field value, 1518~1536 is not clear between them. It should be meaningless. After all, the type above 1536 is sufficient, and the difference between the 1536~1518, more convenient to distinguish/reduce errors. ( preamble not counted in)

V2 the format of the frame:

The difference between 802.3 and V2: type/length. When this value is greater than 1536, there is no difference between the frame data field of 802.3 when less than 1536 and the LLC Frame of the LLC Sublayer must be mounted above.

At present, most of them adopt V2 standard.

The presence of a Mac sublayer masks the difference between different physical link types, and the LLC Sublayer is responsible for providing services to its upper layers. --specific reference:http://blog.csdn.net/dadoneo/article/details/8315833

It is necessary to specify the minimum length: To facilitate detection and identification. As for why the 64, it is not much discussion significance, it should be tested by the best value of the test staff.

Add:

The maximum data length that can be loaded by the Ethernet V2 is 1500 bytes, while the maximum data that can be loaded by IEEE 802.3 is 1492 bytes (SNAP) or 1497 bytes; The Ethernet V2 does not provide the data-filling capabilities of the MAC layer, which is not only provided by IEEE 802.3, but also has service access points (SAP) and snap tiers that provide more efficient data link layer control and better transmission assurance. Then we can conclude that Ethernet V2 is more suitable for transmitting large amounts of data than IEEE802.3, but Ethernet V2 lacks the control of the data link layer, which is not conducive to the transmission of data that requires strict transmission control. This is also the advantage of IEEE802.3, the more the need for strict transmission control applications, the more need to use IEEE802.3 or snap to encapsulate, but IEEE802.3 also inevitably bring the loss of data load, so the format of the package is often used in less data load but also need strict control Transmitted in the application.

In practical applications, we will find that most applications of Ethernet packets are Ethernet V2 frames (such as HTTP, FTP, SMTP, POP3 and other applications), and the BPDUs between the switches (Bridge Protocol data Unit) packets are IEEE802.3 frames, VLAN Trunk protocols such as 802.1Q and Cisco's CDP (Cisco Discovery Protocol) are frames with IEEE802.3 snap.

Link:

Http://wenku.baidu.com/link?url=N5k5Hjk7XJw3dakscjWUeuWCxL8zT9NQ4dTdfdZPXD1kAWMDrA_ Vcfwexpz8wcosphihzqtji3i6qnvuyq_b3h7rceqdd24367zvtxsqa2i

The composing of Mac frame in computer network experiment