User`s guide

Components of the Network Model
4-3
8000-A2-GB21-10
June 1997
When your HotWire DSLAM system is maximally configured, more users can be
supported. With a maximally-configured HotWire DSLAM system (i.e., a HotWire
DSLAM with 18 DSL cards with each DSL card having its four ports connected to
a HotWire 5446 RTU for a total of 72 modem ports, and each modem can
connect via a hub to 32 active end systems), a total of 2304 users can be
supported. Additionally, by setting up structured subnets behind each HotWire
5446 RTU, hundreds of active end systems can be supported by each RTU
instead of 32. Careful network traffic analysis must be performed to determine if
very large networks will have acceptable response times. For information on how
to set up structured subnets, see Chapter 5,
IP Address Allocation .
NOTE:
Usually a user is active only in one domain at a time. However, if the user’s
system can be multihomed, it may be possible to be active in more than one
domain at a time. A multihomed system is a system with connections to two
or more logical networks, which may be assigned to one or more physical
networks.
Proxy ARP
Proxy ARP is supported by the DSL cards and the HotWire 5446 RTU. It allows
the end users to appear to be directly connected to the router providing access to
the ISP network. This is an advantage because routers connected to a device
running proxy ARP require less configuration. The following scenarios show why
this is an advantage.
DSL Card Proxy ARP
When an ARP request is sent by an ISP connected to the DSL card 10BaseT
interface for a downstream ES (one on the same IP network), the DSL card will
proxy ARP for the ES. The following figure shows the packet flow when the ISP
wants to send a packet to the ES.
97-15470-0
1
Local Router
155.1.2.1/24
155.1.3.1/24
ISP
155.1.2.2/16
DSL Card
155.1.3.2/24
RTU
135.1.3.3
Local Router: ARP Request for ES
Local Router: Sends packet to ES
DSL: Proxy ARP (for ES)
ES
155.1.3.4
ISP: Sends packet to
Local Router