Enterprise QoS Solution Reference Network Design Guide

Chapter 2 Campus QoS Design
Version 3.3
Enterprise QoS Solution Reference Network Design Guide
QoS Design Overview
Note In this context, “Softphone” can be used to refer to any PC-Based IP Telephony application, including
Cisco IP Communicator and similar products.
The logic of such an access edge policer marking Cisco Softphone traffic from an untrusted PC endpoint
is shown in Figure 2-4.
Figure 2-4 Untrusted Endpoint Policing —PC + SoftPhone + Scavenger Model
Start
The syntax for implementing such a policer may vary slightly from platform to platform, as is detailed
in the subsequent platform-specific sections.
Untrusted Server with Scavenger-Class QoS
UDP
16384 to
32767
No
TCP
2000–2002
No
Yes
Yes
No
No
No
Yes Re-Mark to DSCP EF
and Transmit
Re-Mark to DSCP CS1
and Transmit
Servers as well as PCs are subject to attack and infection by worms and viruses, so these should also be
policed as to the amounts of traffic they admit onto the network. The values are greater than PC endpoints
and so network administrators should profile traffic patterns from servers to establish a baseline of
normal and abnormal behavior.
For an example, assume a single server is running multiple applications, in this case SAP (TCP ports
3200–3203 and also 3600), Lotus Notes (TCP port 1352), and IMAP (TCP ports 143 and 220). SAP is
considered a mission-critical application and until call signaling marking on IP telephony equipment
fully migrates from DSCP AF31 to CS3 it should be marked to DSCP 25. Lotus Notes is classed as a
Transactional Data application and should be marked to DSCP AF21. IMAP is considered a Bulk
application and should be marked to DSCP AF11.
Application baselining has shown that 95 percent of the traffic rates for SAP, Lotus Notes and IMAP are
less than 15 Mbps, 35 Mbps and 50 Mbps, respectively. To ensure that no other traffic comes from the
server, a final policer to catch any other type traffic is included. In the event of legitimate traffic that
temporarily exceeds these values, no dropping or re-ordering of packets occurs. However, should this
server become infected and begin sending sustained traffic in excess of these normal rates, the excess is
subject to aggressive dropping in the event of link congestion. The logic of such a policer is shown in
Figure 2-5.
Yes
Yes
Re-Mark to DSCP CS3
and Transmit
Re-Mark to DSCP CS1
and Transmit
Re-Mark to DSCP 0
and Transmit
Re-Mark to DSCP CS1
and Transmit
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