gtpc1m1b | Transmission Control Protocol/Internet Protocol |
One link layer in the TPF system is the IP over channel data link control (CDLC) protocol.
The 3745 and 3746 IP routers have the following configuration characteristics:
The link layer protocol that is used to communicate between the IP router and host processor is IP over CDLC, which is very similar to the SNA over CDLC protocol that TPF host processors use to connect to SNA networks.
The exchange identification (XID) process that is used to activate the connection between the IP router and the TPF system is the same as activating a SNA PU 2.1 link connection. Although the process is the same, the information exchanged is different. Instead of SNA information (for example, control point (CP) name and transmission group (TG) number), IP information (for example, IP addresses) is exchanged.
After the connection is activated, data is transferred using separate read and write channel programs. Multiple packets can be sent or received in a single channel program.
I/O interrupts from IP routers are enabled on all I-streams in the TPF host processor. This allows the interrupt to be processed faster and allows you to take full advantage of TPF tightly coupled support.
Figure 13 shows a uniprocessor TPF system connected to three IP routers. The IP routers are then connected to the remainder of the IP network.
In this example, there is only one IP address needed for the TPF host (9.123.145.111). Every remote client that wants to connect to the TPF system specifies that IP address on its connect request. A Domain Name System (DNS) round-robin of IP addresses or other load balancing methods are not needed for this. The same is true for loosely coupled TPF systems that have only one TPF host processor connected to the IP network.
If the connection to an IP router fails, no sockets are lost because other paths still exist from the TPF host to the remote clients. IP routers are not single points of failures in this example.
Figure 13. One TPF Host Connected to One IP Network
Figure 14 shows a three-way loosely coupled TPF complex connected to two separate IP networks: one being a private intranet and the other the Internet. IP routers 1 and 2 are connected to the intranet. IP routers 3 and 4 are connected to the Internet.
Each TPF host processor must have a unique IP address for each IP network to which it connects. For example, host TPFA uses IP address 25.111.222.82 when connecting to the intranet and IP address 9.123.145.201 when connecting to the Internet. The IP addresses of hosts TPFA, TPFB, and TPFC must all be unique.
When a remote client wants to connect to the TPF system, a DNS round-robin of IP addresses or other load balancing method is needed. For example, if a remote client in the Internet wants to connect to the TPF system and does not care which TPF host is selected, you can select IP address 9.123.145.201 (TPFA), 9.123.145.205 (TPFB), or 9.123.145.210 (TPFC). The decision of which IP address to use is done at the client end before the first packet flows into the TPF system.