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Chapter 5 WAN Setup
P-2612HNU-Fx User’s Guide
117
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.
Introduction to IEEE 802.1Q Tagged VLAN
A tagged VLAN uses an explicit tag (VLAN ID) in the MAC header to identify the
VLAN membership of a frame across bridges - they are not confined to the switch
on which they were created. The VLANs can be created statically by hand or
dynamically through GVRP. The VLAN ID associates a frame with a specific VLAN
and provides the information that switches need to process the frame across the
network. A tagged frame is four bytes longer than an untagged frame and
contains two bytes of TPID (Tag Protocol Identifier), residing within the type/
length field of the Ethernet frame) and two bytes of TCI (Tag Control
Information), starts after the source address field of the Ethernet frame).
The CFI (Canonical Format Indicator) is a single-bit flag, always set to zero for
Ethernet switches. If a frame received at an Ethernet port has a CFI set to 1, then