Cisco 7925G Administration Guide

Unlike wired networks with dedicated bandwidths, wireless LANs consider traffic direction when implementing
QoS. Traffic is classified as upstream or downstream from the point of view of the AP as shown in the following
figure.
Figure 3: Voice traffic in a wireless network
Beginning with Cisco IOS release 12.2(11)JA, Cisco Aironet APs support the contention-based channel access
mechanism called Enhanced Distributed Coordination Function (EDCF). The EDCF-type of QoS has up to
eight queues for downstream (toward the 802.11b/g clients) QoS. You can allocate the queues based on these
options:
•
Differentiated Services Code Point (DSCP) settings for the packets
•
Layer 2 or Layer 3 access lists
•
VLANs for specific traffic
Different traffic types are sent to different priority queues. The following are the queues:
•
Best Effort (BE) = 0, 3
•
Background (BK) = 1, 2
•
Video (VI) = 4, 5
•
Video (VO) = 6, 7
Call Control (SCCP) is sent on UP4 (VI) and voice is sent as UP6 (VO).
Although 802.11b/g EDCF does not guarantee that voice traffic is protected from data traffic, you should get
the best statistical results by using this queuing model.
The Cisco Unified Wireless IP Phone marks the call control packets with a DSCP value of 24 and voice
packets with DSCP value of 46.
Note
To improve reliability of voice transmissions in a nondeterministic environment, the Cisco Unified Wireless
IP Phone supports the IEEE 802.11e industry standard and is Wi-Fi Multimedia (WMM) capable. WMM
enables differentiated services for voice, video, best effort data and other traffic. However, in order for these
differentiated services to provide sufficient QoS for voice packets, only a certain amount of voice bandwidth
can be serviced or admitted on a channel at one time. If the network can handle “N” voice calls with reserved
bandwidth, when the amount of voice traffic is increased beyond this limit (to N+1 calls), the quality of all
calls suffers.
To help address the problems of VoIP stability and roaming, an initial Call Admission Control (CAC) scheme
is required. With CAC, QoS is maintained in a network overload scenario by ensuring that the number of
active voice calls does not exceed the configured limits on the AP. The Cisco Unified Wireless IP Phone can
integrate layer 2 TSpec admission control with layer 3 Cisco Unified Communications Manager admission
Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G Administration Guide
36
VoIP Wireless Network
Voice QoS in Wireless Networks

Cisco 7925G Specifications

General

Keypad number of keys	12
Display diagonal	2 \
Display resolution	176 x 220 pixels
Call waiting	Yes
Lines quantity	6 lines
Voice codecs	G.711a, G.722, G.729a, iLBC
Security algorithms	128-bit WEP, SSL/TLS, WPA
Supported network protocols	DHCP, TFTP, DNS, SCCP, SRST
Input voltage	100 - 240 V
Dimensions (WxDxH)	52 x 20 x 127 mm
Minimum system requirements	Cisco Unified Communications Manager 4.1, 4.2, 4.3, 5.1, 6.0, 6.1, 7.0 + Cisco Unified Communications Manager Express 4.3 +
Input frequency	50/60 Hz
Storage temperature (T-T)	-30 - 60 °C
Operating temperature (T-T)	0 - 40 °C
Operating relative humidity (H-H)	10 - 95 %
Product type	IP Phone
Product color	Gray
Safety	UL 60950, CSA 22.2 No.60950, EN 60950, IEC 60950, AS/NZS 60950, IEC 60529 (IP 54)
Certification	47 CFR 15 B ICES-003 B EN 55022 B AS/NZS CISPR 22 B CISPR 22 B VCCI B EN 61000-3-2 EN 61000-3-3 KN 22 EN 55024 EN 50082-1 EN 61000-6-1 EN 300386 EN 60601-1-2 KN
Compliance industry standards	IEEE 802.11a, IEEE 802.11b, IEEE 802.11g, IEEE 802.1X, IEEE 802.11e

Weight and Dimensions

Weight	138 g