Introduction to the Hotwire DSLAM
1-15
8000-A2-GB21-30
April 1998
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 into 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).
H If WAN-C is a router, the WAN must be a routed IP network (i.e., a network
of interconnected IP routers).
In this case:
— The router at the wire 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. The packets are routed to the
subscribed service providers’ POP based on the source IP address.
— The routing tables in the DSLAM are configured such that the next-hop
router is the IP address of the wire center router for all authorized
subscriber IP source addresses. (See the discussion on source-based
routing in Chapter 6,
IP Routing
.)
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.
— Packets flowing from the NSP network to the end-user systems are
routed within the NAP network based on the packet destination IP
address.
H If WAN-C is a VLAN switch, the WAN must be a layer 2 switching network
supporting a Virtual LAN overlay.
In this case:
— Each NSP would be a member of a different Virtual LAN.
— The VLAN switch at the wire center would support either port-based
VLAN switching (i.e., switching all MAC frames received on a specific
port to a specific NSP VLAN on the WAN) or port-based VLAN switching
with MAC-based attributes (i.e., switching frames received on a specific
port to a specific NSP VLAN on the WAN based on the destination MAC
address) for packets sent from the DSLAMs.
— The router at the NSP premises would either be front ended by a VLAN
switch or have an integrated VLAN card that supports protocols
consistent with the wire center VLAN switch (e.g., ATM Forum LAN
Emulation Protocol).
— The routing tables in the DSLAM are configured such that the next-hop
address field points to the IP address of the NSP premises router for all
authorized subscriber IP source addresses. (See the discussion on
source-based routing in Chapter 6,
IP Routing
.)
