zl50405 Zarlink Semiconductor, zl50405 Datasheet - Page 42

• Manufacturer Part Number: zl50405
• Description: Managed5-port 10/100 M Ethernet Switch
• Manufacturer: Zarlink Semiconductor

6.2.5
The port control module calculates the SRAM read address for the frame currently being transmitted. It also writes
start of frame information and an end of frame flag to the MAC TxFIFO. When transmission is done, the port control
module requests that the buffer be released.
6.2.6
The TxDMA multiplexes data and address from port control, and arbitrates among buffer release requests from the
port control modules.
7.0
7.1
Quality of service is an all-encompassing term for which different people have different interpretations. In general,
the approach to quality of service described here assumes that we do not know the offered traffic pattern. We also
assume that the incoming traffic is not policed or shaped. Furthermore, we assume that the network manager
knows his applications, such as voice, file transfer, or web browsing, and their relative importance. The manager
can then subdivide the applications into classes and set up a service contract with each. The contract may consist
of bandwidth or latency assurances per class. Sometimes it may even reflect an estimate of the traffic mix offered to
the switch. As an added bonus, although we do not assume anything about the arrival pattern, if the incoming traffic
is policed or shaped, we may be able to provide additional assurances about our switch’s performance.
Table 8 shows examples of QoS applications with three transmission priorities, but best effort (P0) traffic may form
a fourth class with no bandwidth or latency assurances. MMAC port actually has four total transmission priorities.
A class is capable of offering traffic that exceeds the contracted bandwidth. A well-behaved class offers traffic at a
rate no greater than the agreed-upon rate. By contrast, a misbehaving class offers traffic that exceeds the
agreed-upon rate. A misbehaving class is formed from an aggregation of misbehaving microflows. To achieve high
Highest
transmission
priority, P3
Middle
transmission
priority, P2
Low transmission
priority, P1
Total
Model
Quality of Service and Flow Control
Port Control
TxDMA
Goals
50 Mbps
37.5 Mbps
12.5 Mbps
100 Mbps
(user defined)
TotalAssured
Bandwidth
Table 8 - Two-dimensional World Traffic
Apps: phone calls, circuit
emulation.
Latency: < 1 ms.
Drop: No drop if P3 not
oversubscribed.
Apps: interactive apps, Web
business.
Latency: < 4-5 ms.
Drop: No drop if P2 not
oversubscribed.
Apps: emails, file backups.
Latency: < 16 ms desired, but
not critical.
Drop: No drop if P1 not
oversubscribed.
Zarlink Semiconductor Inc.
Low Drop Probability
ZL50405
(low-drop)
42
Apps: training video.
Latency: < 1 ms.
Drop: No drop if P3 not
oversubscribed; first P3 to drop
otherwise.
Apps: non-critical interactive apps.
Latency: < 4-5 ms.
Drop: No drop if P2 not
oversubscribed; firstP2 to drop
otherwise.
Apps: casual web browsing.
Latency: < 16 ms desired, but not
critical.
Drop: No drop if P1 not
oversubscribed; first to drop
otherwise.
High Drop Probability
(high-drop)
Data Sheet