Cisco Catalyst 4948 User Manual

254 Cisco LAN Switching Configuration Handbook
14-2: Voice QoS
To support proper delivery of voice traffic in a hierarchical switched network, follow sev-
eral QoS rules of thumb. See the basic network diagram in Figure 14-1.
■ Access layer
■ A QoS trust boundary should be established as close to the end devices (at the
access layer) as possible.
■ Let the IP Phone handle the trust boundary for attached PCs; the IP Phone should be
trusted.
■ PCs running Cisco SoftPhone should be untrusted. Instead, the inbound voice traffic
should be classified and the CoS and differentiated services code point (DSCP) val-
ues marked.
CallManager
Server Farm
Access Layer
L2: Trust CoS
L3: Trust CoS, DSCP
Access Laye
r
L2: Trust CoS
L3: Trust CoS, DSCP
L2: Don’t Trust CoS; Mark CoS=0
L3: Don’t Trust CoS, DSCP;
Mark CoS and DSCP=0
L2: Don’t Trust CoS; Mark CoS=0
L3: Don’t Trust CoS, DSCP;
Classify and
Mark Voice Packets
PC
PC
Cisco
IP SoftPhone
IP
Core or Distribution Layer
Cisco IP Phone
Figure 14-1 QoS Trust Considerations in a Switched Network

Cisco Catalyst 4948 Specifications

General

Switching Capacity	136 Gbps
Forwarding Rate	102 Mpps
Rack Units	1U
MAC Address Table Size	32, 000 entries
Authentication Method	RADIUS, TACACS+
RAM	256 MB
Flash Memory	64 MB
Power Device	Internal power supply
Voltage Required	100-240 VAC
Weight	16.5 lbs
Operating Humidity	10% to 85% non-condensing
Ports	48 x 10/100/1000
Power Supply	Internal
Layer Support	Layer 3
Jumbo Frame Support	Yes (up to 9216 bytes)
Routing Protocol	RIP, OSPF, EIGRP, BGP
Remote Management Protocol	SNMP, Telnet, SSH
Features	VLAN support, QoS
Compliant Standards	IEEE 802.3, IEEE 802.3u, IEEE 802.3ab, IEEE 802.1Q, IEEE 802.1p
Operating Temperature	32 °F to 104 °F (0 °C to 40 °C)