Translating the concepts behind gateways.

Abstract

The intention of this installment of IT World is to bring the various aspects of gateways into view. You can see how loosely the gateway term is used and how the meaning of the term has changed over time. Keep concepts of gateways in order by considering their main function. The main function for gateways is to convert from one set of communication protocols to some other set of communication protocols-thus allowing access to otherwise incompatible networks. These functions include: Protocol Conversion--When a message is prepared for transmission, each layer adds control information unique to the protocol used at that layer (see Figure 1). The gateway must be able to convert control information to the format the receiving network expects. Services affected may include message segmentation and reassembly, data flow control, and error detection and recovery. Protocol converters connect networks that use different communication protocols. Address Translation--Different networks may employ different network addressing schemes, mechanisms, and network address structures. The gateway must be able to interpret network addresses in one network and convert them into appropriate network addresses for the other network while holding the validity of the address resolution. Examples that include both protocol conversion and address translation are when a gateway converts a TCP/IP packet to a NetWare IPX packet and vice versa or from AppleTalk to DECnet, and so on. Message Format Conversion--Different networks can employ different message formats, maximum message sizes, or character codes. The gateway must be able to convert messages to an appropriate format, size, and coding for the receiving network. Examples are CGI and an email gateway (which is a layer 7-application layer-gateway). Keep these main concepts in mind while surfing the web trying to find out more information about what your gateways are up to!