Defined Architecture: Junctions
Original instructions
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Introduction
A Quantum EIO network can support both remote I/O devices (including 140CRP31200 remote I/O head modules and •••CRA312•0 adapter modules) and Connexium extended managed switches.
Both remote I/O devices and Connexium extended managed switches constitute a network junction, as follows:
Each junction presents the queueing point, which can add delay — or jitter — to the system. If 2 packets simultaneously arrive at a junction, only 1 can be immediately transmitted. The other waits for a period referred to as “one delay time” before it is transmitted.
Because remote I/O packets are granted priority by the Quantum EIO network, the longest a remote I/O packet can wait at a junction is 1 delay time before it is transmitted by the device or switch.
The following scenarios depict how different junction types handle packets that arrive simultaneously.
Remote I/O Device
In the following example, a remote I/O device originates packets for transmission, and forwards packets it receives on the ring:
The remote I/O device handles remote I/O packets in the following sequence:
Time
Ring In
Remote I/O Packet
Ring Out
Comment
T0
1 (started)
a
–
packet “a” arrived after transmission of packet “1” begins
T1
2
–
1
packet “2” arrived after packet “a”
T2
3
–
a
packet “3” arrived after packet “2”
T3
4
–
2
packet “4” arrived after packet “3”
T4
5
–
3
packet “5” arrived after packet “4”
Switch
In the following example, a switch receives a steady flow of packets from both the remote I/O main ring and a remote I/O sub-ring:
The switch handles remote I/O packets in the following sequence:
Time
Ring In
Sub-ring
Ring Out
Comment
T0
1 (started)
a
–
packet “a” arrived after transmission of packet “1” begins
T1
2
b
1
packets “2” and “b” arrive simultaneously
T2
3
c
a
packets “3” and “c” arrive simultaneously
T3
4
d
2
packets “4” and “d” arrive simultaneously
T4
5
e
b
packets “5” and “e” arrive simultaneously
Switch with Sub-ring Cable Break
In the following example, a switch receives a steady flow of packets from the remote I/O main ring and also from both segments of a remote I/O sub-ring with a cable break:
The switch handles remote I/O packets in the following sequence:
Time
Ring In
Sub-ring A
Sub-ring B
Ring Out
Comment
T0
1 (started)
a
p
–
packets “a” and “p” arrive after transmission of packet “1” begins
T1
2
b
q
1
packets “2” , “b” and “q” arrive simultaneously
T2
3
c
r
a
packets “3”, “c” and “r” arrive simultaneously
T3
4
d
s
p
packets “4”, “d” and “s” arrive simultaneously
T4
5
e
t
2
packets “5”, “e” and “t” arrive simultaneously