Product manual

XStream-PKG-R™ RS-232/485 RF Modem – Product Manual v5.x00

5.1. Addressing

Each RF packet contains addressing information that is used to filter incoming RF data. Receiving

modems inspect the Hopping Channel (HP parameter), Vendor Identification Number (ID

parameter) and Destination Address (DT parameter) contained in each RF packet. Data that does

not pass through all three network security layers is discarded (Figure 5.1).

Figure 5.1. Filtration layers contained in the RF packet header

5.1.1. Address Recognition

Transmissions can be addressed to a specific modem or group of modems using the DT

(Destination Address) and MK (Address Mask) parameters. The transmitting modem dictates

whether the packet is intended for a specific modem (local address) or multiple modems (global

address) by comparing the packet’s DT parameter to its own MK parameter (Figure 5.2).

Figure 5.2. Local Packets vs. Global Packets (Transmitting Modem)

TX_DT = Transmitter Destination Address

TX_MK = Transmitter Address Mask

Note: When TX_DT = 0xFFFF (default), RF packets are global and are

received by all modems within range. (Receivers do not send ACKs.)

A receiving modem will only accept a packet if a packet is addressed to it (either as a global or

local packet). The RX modem makes this determination by inspecting the destination address of

the RF packet and comparing it to its own address and mask (Figure 5.3). The Destination

Address of the TX modem is logically “ANDed” with the Address Mask of the RX modem.

Figure 5.3. Address Recognition (Receiving Modem)

TX_DT = Transmitter Destination Address

RX_DT = Receiver Destination Address

RX_MY = Receiver Source Address

NOTE: For more information regarding addressing and masks, refer to Application Note “XST-

AN004b”. (Located on the Digi Support site at www.digi.com/support).