IBM eServer zSeries 900 Technical Guide

Chapter 3. Connectivity 113

򐂰 Intermixing of CU types with different channel usage characteristics on the same channel

is possible.

Input for the selection of ESCON channel candidates for aggregation to FICON channels is

provided by measurement data, the number of FICON Bridge channels required to satisfy

connectivity, and a “best fit” judgement by the user of the FICON Channel Aggregation Tool.

Mixed channel attachment to one control unit

A configuration of mixed channels is not recommended for the long term. Nevertheless,

knowing all the supported combinations (CNC, FCV, FC) from one system to one control unit

may help during migration phases.

Figure 3-20 shows that from one system, a single control unit can be attached through a mix

of channel path types and topologies. Any ESCON topologies (CNC point-to-point and

switched point-to-point), FICON types (FCV, FC) and topologies (FC point-to-point and

switched point-to-point) can be combined to ease migration.

Figure 3-20 Mixing channel path types to one control unit

3.4.4 FICON distance solutions

Distance support

The distance supported by the z900 server FICON features is dependent upon the

transceiver (LX or SX), the fiber being used (9 micron single-mode, or 50 micron or 62.5

micron multimode), and the speed at which the feature is operating. A FICON Express feature

supports a link data rate of 1 Gbps or 2 Gbps. A FICON feature supports a link data rate of

1 Gbps. Table 3-8 on page 114 shows the distance impacts and the link budget impacts of

high data rates.

In Table 3-8, a link is a physical connection over a transmission medium (fiber) used between

an optical transmitter and an optical receiver. The Maximum Allowable Link Loss, or link

budget, is the maximum amount of link attenuation (loss of light), expressed in decibels (dB),

that can occur without causing a possible failure condition (bit errors). Note that as the link

data rate increases, the unrepeated distance and link budget decreases when using

multimode fiber.

CU

F

I

C

O

N

b

r

i

d

g

e

p

o

r

t

LP 1

EMIF

E

S

C

D

9

0

3

2

-

0

0

5

FC Link

F

C

S

w

i

t

c

h

F

C

FCV

C

N

C

E

S

C

O

N

L

i

n

k

LP 2

LP 3

F

C

C

N

C

FC Links

FC Link

F

C

L

i

n

k

E

S

C

O

N

L

i

n

k

E

S

C

O

N

L

i

n

k

E

S

C

O

N

L

i

n

k

114 IBM eServer zSeries 900 Technical Guide

These numbers reflect the Fibre Channel Physical Interface specification. The link budget is

derived from combining the channel insertion loss budget with the unallocated link margin

budget. The link budget numbers have been rounded to the nearest 10th of a dB.

For more information, see

Planning for Fiber Optic Links (ESCON, FICON, Coupling Links,

and Open Systems Adapters)

, GA23-0367.

Table 3-8 Fibre Channel distance specifications

For all FICON features using repeaters, the end-to-end distance between the FICON channel

and the FICON Director port can be up to 100 km. The same end-to-end distance is also

available between the FICON Director port and the control unit port. However, the overall

end-to-end distance between the FICON channel and control unit should not exceed 100 km.

Data rate performance droop

For ESCON links, significant data rate performance droop occurs at extended distances over

9 km. For FICON channels in FICON native (CHPID type FC) mode, the channel-to-control

unit end-to-end distance can be increased up to 100 km before data rate performance droop

starts to occur.

FICON’s distance capability is becoming increasingly important as movement occurs towards

remote I/O, vaulting for disaster recovery, and Geographically Dispersed Parallel Sysplexes

(GDPS) for availability.

FICON Express and FICON LX

Using 9 micron single-mode fiber, FICON Express and FICON LX features support an

unrepeated distance of 10 km. This can be increased to 20 km via an RPQ; see Figure 3-21.

1 Gbps link 2 Gbps link

Fiber type Light source

(nanometers)

Unrepeated

Distance

Link

Budget

Unrepeated

Distance

Link

Budget

9 micron

single mode

LX laser

(1300 nm)

10 km

(6.2 miles)

7.8 dB 10 km

(6.2 miles)

7.8 dB

50 micron

multimode

SX laser

(850 nm)

500 meters

(1640 feet)

3.9 dB 300 meters

(984 feet)

2.8 dB

62.5 micron

multimode

SX laser

(850 nm)

250 meters

(820 feet)

2.8 dB 120 meters

(394 feet)

2.2 dB