DART 200 CDPD Modem User’s Guide | 5 DART Supported Protocols |
TCP
Transmission Control Protocol (TCP) is an advanced transmission protocol that adds substantial functionality to the underlying Internet Protocol it is built on. Because of this structure it is often referred to as TCP/IP. The advantage of TCP is reliability of data transmission; achieved by using positive acknowledgments with retransmission if required. The main disadvantage is the overhead needed to provide this reliability under any and all conditions.
Unlike UDP, TCP offers both reliable and connected data transmission service. Lost, delayed, duplicated, or out of sequence packets are detected and automatically corrected. A logical point-to-point connection is established and maintained throughout the communications session. TCP is ideally suited for applications where speed of development is critical, or for applications where the MAS is low on compute power, available memory, or both. It requires very little other than session establishment, sending data over the serial port, and session termination to get a basic application operational.
The price for this reliability is the number of extra data packets used and the time required to process them. Both need to be considered when selecting an application protocol.
DART TCP capabilities
The DART software stack offers industry standard client-server capability where the client originates communications and the server waits for incoming requests. In server mode it includes auto answer capability and an optional Friends Only mode. Friends Only mode restricts the devices the server can receive calls from to help prevent unauthorized access to applications or devices.
Friends Only mode operation
Friends Only mode permits communication with the modem to be restricted (for security reasons) to a predefined group of addresses (friends). Friends Only mode is controlled by S-Register 82, that enables and disables the comparison of packet source addresses against a list stored in the DART 200’s destination dial directory. Refer to the Modem dial directory, p. 8-24 AT&Z command in Appendix F, DART AT Command Set, for details. Only the IP Address portion of the addresses in the dial directory is used with this feature. Bit 0 of S-Register 82 controls this mode. The default is to accept all incoming datagrams (bit 0 = 0).
Sierra Wireless, Inc. | 5-14 |
