 Two applied in wired networks, which provides an introduction to the more complex solutions required for media access control in wireless networks. MAC Addressing A receiving device needs to be able to identify those data packets transmitted on the network medium that are intended for it - this is achieved using MAC addresses. Every network adapter, whether it is an adapter for Ethernet, wireless or some other network technology, is assigned a unique serial number called its MAC address when it is manufactured. The Ethernet address is the most common form of MAC address and consists of six bytes, usually displayed in hexadecimal, such as 00-D0-59- FE-CD-38. The first three bytes are the manufacturer's code (00-D0-59 in this case is Intel) and the remaining three are the unique serial number of the adapter. The MAC address of a network adapter on a Windows PC can be found in Windows 95, 98 or Me by clicking Start, Run, and then typing "winipcfg", and selecting the adapter, or in Windows NT, 2000, and XP by opening a DOS Window (click Start, Programs, Accessories, Command Prompt) and typing "ipconfig/all". When an application such as a web browser sends a request for data onto the network, the Application layer request comes down to the MAC SAP as an MSDU. The MSDU is extended with a MAC header that includes the MAC address of the source device's network adapter. When the requested data is transmitted back onto the network, the original source address becomes the new destination address and the network adapter of the original requesting device will detect packets with its MAC address in the header, completing the round trip. As an example, the overall structure of the IEEE 802.11 MAC frame, or MAC Protocol Data Unit (MPDU) is shown in Figure 2-5. The elements of the MPDU are as shown in Table 2-6. Media Access Control in Wired Networks If two devices transmit at the same time on a network's shared medium, whether wired or wireless, the two signals will interfere and the result will be unusable to both devices. Acc