| Technical Summary of the SWAP Specification, March 1998
Introduction
The HomeRF Shared Wireless Access Protocol (SWAP) system is designed to carry both
voice and data traffic and to interoperate with the Public Switched Telephone Network (PSTN)
and the Internet; it operates in the 2400MHz band and uses a digital frequency hopping spread
spectrum radio. The SWAP technology was derived from extensions of existing cordless
telephone (Digital Enhanced Cordless Telephone or DECT) and wireless LAN technology to
enable a new class of home cordless services. It supports both a TDMA (Time Division Multiple
Access) service to provide delivery of interactive voice and other time-critical services, and a
CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) service for delivery of high
speed packet data.
Main System Parameters
- Frequency hopping network: 50 hops/second
- Frequency range: 2400MHz ISM band
- Transmission power: 100mW
- Data Rate: 1 Mbps using 2FSK modulation; 2 Mbps using 4FSK modulation
- Range: Covers typical home and yard
- Supported stations: Up to 127 devices per network
- Voice connections: Up to 6 full duplex conversations
- Data security: Blowfish encryption algorithm (over 1 trillion codes)
- Data compression: LZRW3-A algorithm
- 48-bit Network ID: Enables concurrent operation of multiple co-located
networks.
Network Topology
The SWAP system can operate either as an ad-hoc network or as a managed network
under the control of a Connection Point. In an ad-hoc network, where only data communication
is supported, all stations are equal and control of the network is distributed between the stations.
For time critical communications such as interactive voice, a Connection Point is required to
coordinate the system. The Connection Point, which provides the gateway to the PSTN, can be
connected to a PC via a standard interface such as USB that will enable enhanced voice and data
services. The SWAP system also can use the Connection Point to support power management for
prolonged battery life by scheduling device wakeup and polling.
The network can accommodate a maximum of 127 nodes. These nodes can be a mixture of
these 4 basic types:
- Connection Point that supports voice and data services.
- Voice Terminal that only uses the TDMA service to communicate with a base station.
- Data Node that uses the CSMA/CA service to communicate with a base station and other
data nodes.
- Voice and Data Node which can use both types of services
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