ards and protocols. The logical architecture of wireless networks will be described in this chapter with reference to the OSI model. The OSI Network Model The Open Systems Interconnect (OSI) model was developed by the International Standards Organisation (ISO) to provide a guideline for the development of standards for interconnecting computing devices. The OSI model is a framework for developing these standards rather than a standard itself - the task of networking is too complex to be handled by a single standard. The OSI model breaks down device to device connection, or more correctly application to application connection, into seven so-called "layers" of logically related tasks (see Table 2-1). An example will show Chapter Two Table 2-1: The Seven Layers of the OSI Model Layer Description Standards and Protocols 7 - Application layer Standards to define the provision HTTP, FTP, SNMP, of services to applications - such POP3, SMTP as checking resource availability, authenticating users, etc. 6 - Presentation layer Standards to control the translation of incoming and outgoing data from one presentation format to another. 5 - Session layer Standards to manage the ASAP, SMB communication between the presentation layers of the sending and receiving computers. This communication is achieved by establishing, managing and terminating "sessions". 4 - Transport layer Standards to ensure reliable TCP, UDP completion of data transfers, covering error recovery, data flow control, etc. Makes sure all data packets have arrived. 3 - Network layer Standards to define the IPv4, IPv6, ARP management of network connections - routing, relaying and terminating connections between nodes in the network. 2 - Data link layer Standards to specify the way in which devices access and share Ethernet the transmission medium (IEEE 802.3), Wi-Fi (known as Media Access Control (IEEE 802.11), or MAC) and to ensure reliability Bluetooth (802.15.1) of the physical connection (known as Logical Link Control or LLC). 1 - Physical layer Standards to 