MULTINET4 MULTI-PORT SERIAL SERVER & MANAGED SWITCH – INSTRUCTION MANUAL
6–1
Multinet4 Multi-Port Serial Server
& Managed Switch
Chapter 6: Operational Guide
Digital Energy
Multilin
Operational Guide
6.1
Quality of Service
In the Multinet4 Multi-Port Serial Server & Managed Switch products, Quality of Service
(QoS) features exist at both layer 2 (Ethernet, frame relay) and layer 3 (IP) and is
implemented by a combination of tag analysis/marking and priority queuing.
At the IP layer, each packet header contains a Type of Service (ToS field). This field contains
a DiffServ code point that describes what sort of service routers should afford the packet
as it is forwarded through the network.
For IP-over-frame, packets are placed in one of four priority queues based on the DiffServ
marking found in the IP header.
For Serial-over-frame, packets are placed in one of four priority queues based on the
priority assigned to that particular serial-over-frame channel.
For Ethernet, in addition to the DiffServ marking in the IP header, each Ethernet header
may contain an IEEE 802.3ac tag containing IEEE 802.1p priority information. Using this
field, a priority of 0-7 may be assigned with priority 0 being the lowest priority and priority 7
being the highest. For received ethernet frames, the user may configure a port to assign
packets to a priority queue based on the IEEE 802.1p priority, the DiffServ marking, or the
ingress port.
6.1.1
QoS Model
The following block diagram depicts the QoS model used by Multinet4. Each block
represents a process or function that operates on a packet. The behavior of some blocks is
defined through user configuration, represented by text in an attached box with dashed
lines.
