HP Mainframe Connectivity Design Guide

FCIP gateways support:
• Ethernet connections of 10 to 100 Mb/s, and 1 Gb/s. Select the network connection that
matches the amount of data to be transferred and the time allowed for that transfer.
• FICON at 1 Gb/s, 2 Gb/s, 4 Gb/s, and 8 Gb/s. Not all FCIP gateways support all FICON
speeds.
FCIP bandwidth considerations
When sites are located several kilometers apart, there can be unacceptable delays in the completion
of an I/O transaction. Increasing the available bandwidth does not solve this problem. Network
latency is a constant value of approximately 1 ms for each 200 km (125 miles), regardless of the
bandwidth connection. Round-trip latency is approximately 2 ms for each 200 km.
NOTE: These latency figures are for direct circuit distances. The circuit distance can be significantly
greater than the physical distance between two data centers. Switching equipment can significantly
increase network latency. Consider the circuit distance and latency when planning an extension
solution.
Increasing the bandwidth reduces the time required to clock a data packet onto the circuit and
therefore, speed up the data transmission. However, it does not reduce round-trip latency.
Table 88 (page 140) lists the transmit times of various circuit types for a 2 KB FICON frame in a
161 km (100 mile) circuit.
Table 88 Sample transmit times
Throughput
2
Transmit time
1
Circuit type
0.61 GB/hr13.23 msT1 (1.544 Mb/s)
0.80 GB/hr10.26 msE1 (2.048 Mb/s)
32.57 GB/hr1.28 ms
OC-3/STM-1
(155.52 Mb/s)
50.98 GB/hr1.20 ms
OC-12/STM-4
(622.08 Mb/s)
1
Based on the circuit data transmission rate (raw bandwidth minus circuit overhead); this does not take into account
latency caused by switching and other equipment. Round-trip latency is approximately twice this value, plus any CU
delay.
2
This is under ideal conditions, with no additional latency or retransmissions due to dropped packets or bits.
NOTE: Do not use T1 or E1 circuits for FICON long-distance extension because of the slow
clocking speed.
Recommendations for managing bandwidth with FCIP
To manage bandwidth in a FICON long-distance implementation with FCIP:
• When calculating the circuit bandwidth required for disk replication, consider the following:
For synchronous replication, ensure that the bandwidth can support the peak write
workload. Insufficient bandwidth causes delays when writes queue for the remote site.
◦
◦ For asynchronous replication, ensure that the bandwidth can support the average write
workload. The bandwidth must be sufficient to prevent the replication cache from filling.
140 FICON and FICON SAN extension