e Figure 6.27). This ensures that no two cards will be using the same address in any network. Note that although these addresses are globally unique, they have only local importance. They are never transmitted to other networks. If all stations in a LAN should receive the same message, all destination address bits are set to one. This is called a broadcast address and used, for example, by the address resolution protocol discussed in Section 6.6. Data Communications The length-of-data field indicates how many bytes there are in the data field, from 0 to the maximum of 1,500 (Hex 0000-05DC). If this number is higher than 1,500 in a frame, it cannot be an 802.3 frame. In this case the frame is a DIX Ethernet frame and a receiver interprets these two bytes as a protocol type information that defines a higher layer protocol. Here are some examples of type field hexadecimal values and corresponding higher layer protocols: 0800: the Internet Protocol (IP) packet; 0806: Address Resolution Protocol (ARP); 8137: Novell IPX; 0000-05DC:LLC, that is, the 802.3 frame. The data field is where the PDU of the upper LLC sublayer of the data link layer is carried. In the case of DIX Ethernet (type field higher than 05DC hex.), the data field contains user data for the protocol identified by the type number. For collision detection the minimum length of the frame is defined to be 64 bytes from the destination address to the checksum. If the data field is very short, the PAD field contains random data to extend the frame length to the minimum of 64 bytes. The frame check sequence (FCS) is added to the end of the frame and with the help of this 32-bit check code the receiver is able to determine if errors have occurred. The 32-bit cyclic redundancy check (CRC-32) code is used for error detection. [The FCS is actually the remainder of the division when a binary number from the destination address to PAD (included) is divided by the specified binary number (in hex.: 10411DB7). The receiver divides the whole frame including the FCS by t