ghput. CTS to self The CTS to self option dispenses with the exchange of RTS/CTS messages and just relies on the 802.11b station to check that the channel is clear before transmitting. Although this does not provide the same degree of collision avoidance, it can increase throughput significantly when there are fewer stations competing for medium access. Backoff time 802.11g backoff timing is based on the 802.11a specification (up to a maximum of 15x9 uS slots) but in mixed-mode an 802.11g network will adopt 802.11b backoff parameters (maximum 31 X 20 uS slots). The longer 802.11b backoff results in reduced network throughput. The impact of mixed mode operation on the throughput of an 802.11g network is shown in Table 6-10. A number of hardware manufacturers have introduced proprietary extensions to the 802.11g specification to boost the data rate above 54 Mbps. An example is D-Link's proprietary "108G" which uses packet bursting and channel bonding to achieve a PHY layer data rate of 108 Mbps. Packet bursting, also known as frame bursting, bundles short data packets into fewer but larger packet to reduce the impact of gaps between transmitted packets. Packet bursting as a data rate enhancement strategy runs counter to packet fragmentation as a strategy for improving transmission robustness, SO packet bursting will only be effective when interference or high levels of contention between stations are absent. Chapter Six Channel bonding is a method where multiple network interfaces in a single machine are used together to transmit a single data stream. In the 108G example, two non-overlapping channels in the 2.4 GHz ISM band are used simultaneously to transmit data frames. Data Rates at the PHY and MAC Layer In considering the technical requirements for a WLAN implementation in Chapter 7, it will be important to recognise the difference between the headline data rate of a wireless networking standard and the true effective data rate as seen by the higher OSI layers when passing data packets down to the MAC layer. Ea