In many implementations of CS CDPD, a chief component is a modem bank functioning as a data link layer relay between a CM-ES and a Circuit Switched Mobile Data Intermediate System (CMD-IS). This Part specifies a set of protocols and procedures designed to enable a modem bank to interoperate with a CMD-IS in a CS CDPD environment.

Note—The CS-MB to CMD-IS interface is within a single service provider and therefore is not part of the I interface. Service providers may choose to implement this interface in various manners, and optionally may use the TCP/IP based protocol specified in the following parts.

The interface between the modem bank and the CMD-IS utilizes TCP/IP technology across either a LAN or WAN environment. The modem bank operates as a data link layer relay between the CM-ES and the CMD-IS.

Once a connection is established between the CM-ES and the CMD-IS via the modem bank, data can flow between the CM-ES and the CMDIS. A physical view of such a CS CDPD environment can be seen in Figure 100-1.