ZyXEL Communications XMG3512-B10A, Руководство пользователя

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Chapter 6 Broadband
XMG3512-B10A User’s Guide
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continuously require a specific amount of bandwidth. A PCR is specified and if traffic exceeds this rate,
cells may be dropped. Examples of connections that need CBR would be high-resolution video and
voice.
Variable Bit Rate (VBR)
The Variable Bit Rate (VBR) ATM traffic class is used with bursty connections. Connections that use the
Variable Bit Rate (VBR) traffic class can be grouped into real time (VBR-RT) or non-real time (VBR-nRT)
connections.
The VBR-RT (real-time Variable Bit Rate) type is used with bursty connections that require closely
controlled delay and delay variation. It also provides a fixed amount of bandwidth (a PCR is specified)
but is only available when data is being sent. An example of an VBR-RT connection would be video
conferencing. Video conferencing requires real-time data transfers and the bandwidth requirement
varies in proportion to the video image's changing dynamics.
The VBR-nRT (non real-time Variable Bit Rate) type is used with bursty connections that do not require
closely controlled delay and delay variation. It is commonly used for "bursty" traffic typical on LANs. PCR
and MBS define the burst levels, SCR defines the minimum level. An example of an VBR-nRT connection
would be non-time sensitive data file transfers.
Unspecified Bit Rate (UBR)
The Unspecified Bit Rate (UBR) ATM traffic class is for bursty data transfers. However, UBR doesn't
guarantee any bandwidth and only delivers traffic when the network has spare bandwidth. An example
application is background file transfer.
IP Address Assignment
A static IP is a fixed IP that your ISP gives you. A dynamic IP is not fixed; the ISP assigns you a different one
each time. The Single User Account feature can be enabled or disabled if you have either a dynamic or
static IP. However the encapsulation method assigned influences your choices for IP address and
default gateway.
Introduction to VLANs
A Virtual Local Area Network (VLAN) allows a physical network to be partitioned into multiple logical
networks. Devices on a logical network belong to one group. A device can belong to more than one
group. With VLAN, a device cannot directly talk to or hear from devices that are not in the same
group(s); the traffic must first go through a router.
In Multi-Tenant Unit (MTU) applications, VLAN is vital in providing isolation and security among the
subscribers. When properly configured, VLAN prevents one subscriber from accessing the network
resources of another on the same LAN, thus a user will not see the printers and hard disks of another user
in the same building.
VLAN also increases network performance by limiting broadcasts to a smaller and more manageable
logical broadcast domain. In traditional switched environments, all broadcast packets go to each and
every individual port. With VLAN, all broadcasts are confined to a specific broadcast domain.