A data format of
this data framing layer, and the flow control.
A data format of a MAC frame:
head comprising a fixed :( 18 bytes)
sender (source address, six bytes) of
the recipient (the destination address, six bytes)
of data type (6 bytes) = 2 word type + section frame check sequence FCS (CRC test) 4-byte
data byte 46 comprising :( minimum, maximum 1500 bytes)
packets details
head length + the shortest length = 64 data bytes, up to 1518 bytes , exceeds the maximum limit on the transmitted fragment.
There are 8 bytes before the MAC frame: 7 bytes + 1 byte frame synchronization pattern before the start delimiter
Second, the function
of data transfer between two hosts, is always transmitted on a section of the link, which requires using a special protocol link layer. Physical shielding layer, a data link provides a connection for the network layer, it is possible to go wrong in a physical connection, for virtually error-free data transmission (error control). This layer specifies addressing topology and provide the hardware. Each data frame is divided into: a header and a data head data of two parts.
Between two adjacent nodes to transmit data, the data link layer, network layer IP datagram delivery down drive assembly frame, the transmission frame on the link between two adjacent nodes. Each frame comprising data and control information necessary (e.g., synchronization information, address information, error control, etc.).
When receiving data, the control information so that the receiving end can know which bit of a frame to which the bits from the beginning and the end. Thus, after receiving the data link layer frame, which can be made part of the data, to the network layer.
Control information further enable the receiving end can detect the received frame has an error fault. If the error detection, the data link layer is simply discards the frame went wrong, in order to avoid further down in the network transmission network resources wasted. If you need to correct errors in the data link layer transmission (that is to say, not only to the data link layer error detection, but also error correction), then it must use reliable transmission protocol to correct errors occur. This method will make the link layer protocol is complicated.
Third, the common equipment
cards, bridge, switch;
adapters: contains the data link layer and physical layer of the two layers
Hub:
twisted-pair Ethernet hubs always used in conjunction with each station needs two pairs of unshielded twisted pair, respectively for transmission and reception. Both ends of the twisted pair using RJ-45. Send data and receive data by radio, all ports share a collision domain, speed is the same for each port.
Bridge:
expanding the scope of physics. Increase the amount of network reliability. Mac connect different layers and rate without
the bridge receiving a frame to be forwarded according to the destination address stored in the MAC frame, the delay has
a transparent bridging and source routing bridge
When too easily lead frame when the broadcast storm
Switch (multi-interface bridges)
virtual local area network (VLAN)