Cisco Cisco Unified MeetingPlace Audio Server 安装指南
3-22 Telephony and LAN planning
Cisco MeetingPlace Audio Server Installation Planning Guide
February 27, 2004
About Quality of Service configuration
For IP configuration, either of these two Quality of Service (QOS)
mechanisms can be used:
mechanisms can be used:
•
IP Precedence
•
Differentiated Services Code Point (DSCP)
Technicians must first determine which mechanism a customer’s IP network
uses. Then, with the customer’s IT department, they must determine the
appropriate settings for these values. The following sections provide more
information.
uses. Then, with the customer’s IT department, they must determine the
appropriate settings for these values. The following sections provide more
information.
About Type of Service byte
Within the voice packets, the Type of Service (ToS) byte is an 8-bit field in the
IP header. It is used for either IP Precedence or DSCP. (Another term for byte
is octet.) When this byte is used for IP Precedence, 3 bits are used for the IP
Precedence value, and 4 bits are used for the Type of Service value.
IP header. It is used for either IP Precedence or DSCP. (Another term for byte
is octet.) When this byte is used for IP Precedence, 3 bits are used for the IP
Precedence value, and 4 bits are used for the Type of Service value.
The following shows the bit layout:
I
MPORTANT
Note the differences in terminology: The Type of Service byte
includes all 8 bits; but the Type of Service field is only 4 bits within this byte.
The IP Precedence mechanism partitions the Type of Service byte into an IP
Precedence field and a Type of Service field.
The IP Precedence mechanism partitions the Type of Service byte into an IP
Precedence field and a Type of Service field.
When this byte is used for DSCP, 6 bits are used for DSCP. The following
shows the bit layout:
shows the bit layout:
Notice that the DSCP field overlaps the fields used for IP Precedence.
Therefore, if DSCP values are chosen carefully, then backward compatibility
can be achieved if the customer network has a mixture of devices (some using
IP Precedence, others using DSCP).
Therefore, if DSCP values are chosen carefully, then backward compatibility
can be achieved if the customer network has a mixture of devices (some using
IP Precedence, others using DSCP).
7
6
5
4
3
2
1
0
IP precedence
Type of service
7
6
5
4
3
2
1
0
Differentiated Services Code Point