Token ring, Ethernet, and fiber distributed data interconnect (FDDI) connections use the IEEE 802.2 DLC protocol to connect to the host. In a mainframe environment, SNA Server usually connects to a front-end processor (FEP) or a communications controller, such as an IBM 3174. Occasionally, a connection to an adapter within a mainframe may be possible. With an AS/400 system, the connection goes directly to a network adapter in the AS/400 itself.
Token ring connections are typically limited to 4 or 16 megabits per second. Token ring solutions are commonplace in established mainframe environments. In many scenarios, a token ring connection provides good performance at a reasonable cost in equipment.
Ethernet connections can reach a maximum of 10 megabits per second, but actual throughput can decrease dramatically with increased network traffic. Ethernet is a common connection type for LANs with workstations or PCs. This connection type is also common in peer-type networks. Ethernet connections are among the cheapest available, but performance is sacrificed as network congestion increases.
FDDI connections use fiber cabling to achieve connections reaching 100 megabits per second or greater. The FDDI line communicates through an FEP that is channel-attached to the mainframe. This may limit the overall speed of communications. In many cases, this kind of connection can provide a reasonably cost-effective solution if higher throughput is required and a channel solution is not possible.
DLC connections are well-suited for the centralized and distributed deployment models, as both strategies implement SNA Server computers close to the host. DLC can also be deployed in a branch model using routers or bridges that can route traffic between the branch offices and the central host system.
SNA Server supports DLC connections over any network adapter supported by Windows NT using the Windows NT DLC network transport driver.