User`s guide

Introduction to the HotWire DSLAM
1-9
8000-A2-GB21-10
June 1997
Typically, the NAP network is organized into three components:
— Wiring center
The wiring center is usually a local serving office where the DSLs from
the service subscribers are terminated on the HotWire DSLAM.
— Wide Area Network (WAN)
The WAN concentrates and switches data traffic from multiple wire
centers to one or more Regional Centers.
— Regional center
The NSP’s Point of Presence (POP) is located (i.e., access point to the
NAP network for an NSP) at the regional center. The connection from the
POP to the NSP network is typically across an access link that terminates
on a router on the NSP premises. This router acts as a next-hop location
to the NSP’s network.
 The Network Service Providers (NSPs) can be either public data network
providers (i.e., Internet Service Providers) or private data network providers
(i.e., corporate Intranets) who provide network services based on the Internet
Protocol (IP). In some cases, the NSP and the NAP can be a single network
provider.
One or more HotWire DSLAMs are connected to a Wide Area Network
Concentrator (WAN-C) via a LAN. The WAN-C concentrates data traffic from one
or more DSLAMs onto facilities providing access to the WAN. The WAN-C can be
either a router (a layer 3 networking device) or a VLAN switch (a layer 2
networking device).
 If WAN-C is a router, the WAN must be a routed IP network (i.e., a network
comprised of IP routers interconnected via a point-to-point network, a frame
relay switching network, or an Asynchronous Transfer Mode (ATM) switching
network).
In this case:
— The router at the wiring center is required to support routing policies
which permit packets arriving from the local DSLAMs to be routed based
on the service subscriber source IP address to the appropriate router at
the regional center containing the access to the POP for that NSP.
— The routing tables in the DSLAM are configured such that the next-hop
router points to the IP address of the wiring center router for all
authorized subscriber IP source addresses. (See the discussion on
source-based routing in Chapter 6,
IP Routing .)
If the DSLAM at that instance does not know the Media Access Control
(MAC) address of the wire center router, it uses the Address Resolution
Protocol (ARP) to obtain its MAC address from the wire center router
prior to forwarding the packet. The router at the Regional Center must
also route packets to the appropriate NSP based on the source IP
address of the subscriber packets. In addition, the router at the regional
center may need to participate in an exterior gateway protocol, such as
the Border Gateway Protocol, to exchange routing information between
the NSP and NAP routing networks.