ations with the SIP Toolkit Control of Networked Appliances Currently, the number of home devices with a network interface is rela- tively small: a desktop computer, perhaps a laptop, a printer, and SO on. This situation is expected to change dramatically in the next few years. When everyday appliances such as the refrigerator or the alarm clock include a network interface, they become networked appliances. The main advantage of networked appliances is their capability to interact with one another and with any other networked device. Thus, when the refrigerator is running out of mayonnaise, it can order a fresh supply through the supermarket's Web page. The bedside clock can get information about traffic conditions and reset the alarm accordingly. If Bob forgets to turn off the porch light when he leaves home in the morning, he can always turn it off from his office. A number of protocols are already designed to control networked appli- ances within a home. However, no solution is available for the inter-domain communication of network appliances [draft-tsang-appliances-reqs]. SIP, suitably extended, is a candidate to perform this role. Figure 7-20 shows how various SIP extensions work together to control the appliances inside a house. Say that a technician is scheduled to fix Bob's washing machine in the morning when Bob is at work. Bob simply SUBSCRIBES to his doorbell. When the technician rings the bell, he automatically causes a NOTIFY to go to Bob. Bob then establishes a video session with the camera on his door, and checks that the person ringing is the technician. He also establishes an audio session with the audio system on his door and informs the technician that no one is home. Bob explains the trouble he's been having with the washing machine and gives the go-ahead for repairs. At this point, Bob sends a DO to his door in order to unlock it. Now the technician can do his work while Bob observes him through cameras installed in his place. When the technician finishes the job and leaves the apartment, Bo