Present day, the Internet telephony growth is much faster than previous. Now the authors are familiar with digitized packet of voice stream. So, authors have required VOIP communication. SIP is one type of VOIP protocol. This one has a SIP proxy. There have one of the important communication environment Wireless LAN (WLAN). WLAN have different radio link standard. Here author comparing SIP protocol in two radio link standard 802.11a and 802.11b environment. The first one have maximum transmission rate of 54 Mbps and second one have maximum transmission rate of 11 Mbps. In this paper author want to show the results in a comparative plot. These comparisons include server /client throughput, packet drops, end to end delay etc.