NEC Univerge SV9100, Manual

Page: 317 / 766

Issue 2.0
SV9100 Networking Manual 5-5

IP Precedence - Layer 3 QoS:
Allows you to specify the class of service for a packet. You use the three
precedence bits in the Ipv4 header type of service (ToS) field for this purpose.
Using the ToS bits, you can define up to six classes of service. Other devices
configured throughout the network can then use these bits to determine how to
treat the packet in regard to the type of service to grant it. These other QoS
features can assign appropriate traffic-handling policies including congestion
management and bandwidth allocation. By setting IP Precedence levels on
incoming traffic and using them in combination with QoS queuing features, you
can create differentiated service. (Refer to Program
84-10 : ToS Setup on page
5-31 for detailed programming information.)

Differentiated service (Diffserv) - Layer 3 QoS:
Provides services differentiated on performance using weighted priority
queuing. DiffServ requires that edge routers classify traffic flows into a member
from a set of categories based on the TCP/IP header fields in what is called a
micro flow. Because the Diffserv is present in every packet header, each node
can provide differentiated services per-hop. Refer to Program
84-10 : ToS
Setup on page 5-31 for detailed programming information.
S
ECTION
3 I
NTERNET
B
ASED
C
ONNECTIONS
(
X
DSL, C
ABLE
,
ETC
.)
Internet-based connections are becoming increasingly popular. This is mainly due to
the speed and cost of xDSL and cable modem connections. For data applications,
these types of connection are generally acceptable. For Voice over IP applications
several issues should be taken into consideration.
Asymmetric Data Rates
On many Internet based connections, there are different data rates for upstream and
downstream. For example 1Mbps down and 256Kbps up. This works well for Internet
access, as generally you download files from the Internet to your PC and transmit
less information in the other direction. For VoIP, speech uses the same amount of
bandwidth in both directions, which means that the amount of simultaneous calls can
not exceed the amount of “upstream” bandwidth available.
Contention
Most Internet based connections specify a contention ratio. This is typically 50:1 for
home users or 20:1 for business users. This specifies the number of users
subscribed to a single connection to the Internet Service Provider (ISP). This
indicates how many users share the bandwidth with other users on the Internet,
which means that the speeds that you are quoted are not necessarily accurate – you
receive less than these figures.
 It is unlikely that all subscribers are using a connection at the same time, so these figures are
not quite as bad as they first seem.