DICENTIS System installation design and planning | en 19
Bosch Security Systems B.V.
Hardware Installation Manual
2021.01 | V2.2 |
4.2 Hardware requirements
Switches
The following minimum requirements and recommendations apply to switches used in a
DICENTIS:
Requirement Standard Settings
Gbit Ethernet IEEE802.3 Switch latency is maximally 10µSec with Gbit.
Valid for both copper and/or fiber ports.
Packet forwarding in
HW per port
>1.2Mpps
n.a. If SW is responsible for packet switching, this would
result in variable latency which is unacceptable.
Quality of Service
With strict priority
DiffServ To make sure PTP synchronization packets and
audio packets get priority over control packets.
OMNEO uses QoS on IP level to avoid
synchronization and audio problems on busy
networks. Although the system does work without
problems on relatively quiet networks (< 10%
network load) it is important to configure your
network switches correctly.
The used QoS is Differentiated Services or DiffServ,
which is part of the Type of Services field (ToS) in
the IP header. For more details on DiffServ & IP
header, see Wikipedia.
Warning: IEEE802.1p is also used for QoS, but is limited to layer 2. Since OMNEO uses IP
communication, this mechanism is not suitable, so make sure the used equipment uses
DiffServ QoS!
The table below gives an overview of the used DSCP values which need to be configured in
the switch:
Data DSCP dec DSCP hex DSCP Label TOS byte
(hex)
Switch
Priority
queue
PTP sync,
delay req
56 0x38 CS7 0xE0 Highest
PTP follow-
up, delay
response,
audio
46 0x2E EF 0xB8 High
(reserved) 8 0x08 CS1 0x20 Low
Control 0 0x00 Best effort 0x00 None
Warning: Please check thoroughly if your switch’s highest priority queue is label as #1 or e.g.
#8, because this may differ per brand. Unfortunately this is not consistent over the different
brands. Setting it wrong is worse than not having priority.
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