Siemens SCALANCE X-300 - Page 376

Appendix C
C.1 Tagging frames
SCALANCE X-300 / X-400
376 Configuration Manual, 10/2014, C79000-G8976-C187-22
Tag control information field
The 2 bytes of the Tag Control Information field (TCI) contain the following information:
CoS prioritization
The tagged frame has 3 bits for the priority that is also known as
C
lass
o
f
S
ervice (CoS). The
priority according to IEEE 802.1p is as follows:
CoS bits
Type of data
000
Non time-critical data traffic (less then best effort [basic setting])
001
Normal data traffic (best effort [background])
010
Reserved (standard)
011 Reserved ( excellent effort )
100
Data transfer with max. 100 ms delay
101
Guaranteed service, interactive multimedia
110
Guaranteed service, interactive voice transmission
111
Reserved
The prioritization of the data packets is possible only if there is a queue in the components in
which they can buffer data packets with lower priority.
An IE switch has four parallel queues in which the frames with different priorities can be
processed. First, the frames with the highest priority ("Strict Priority" method) are processed.
This method ensures that the frames with the highest priority are sent even if there is heavy
data traffic.
Canonical format identifier
The TR bit is used as an identifier for a
T
oken
R
ing encapsulation process.
VLAN–ID
With the remaining 12 bits, up to 4095 VLAN-IDs can be formed (VLAN ID 4095 is not
permitted). The following conventions apply:
VLAN-ID
Meaning
0 The frame contains only priority information (priority tagged frames) and no valid
VLAN identifier.
1 - 4094 Valid VLAN identifier, the frame is assigned to a VLAN and can also include priori-
ty information.