Feature Overview
10 Cisco IOS Release 12.0(7)T
Port Address Translation (PAT) is a similar mechanism that enables all internal hosts to share a single
registered IP address (many-to-one translation). NAT/PAT:
•Allows customers to maintain their own private networks while giving them full Internet access
through the use of one or more global IP addresses
•Allows several private IP addresses to use the same global IP address by using address
overloading
•Facilitates configuration and permits a large network of users to reach the network by using one
CiscouBR900 series cable access router and the same DOCSIS cable interface IP address
•Eliminates the need to readdress all hosts with existing private network addresses (one-to-one
translation) or by enabling all internal hosts to share a single registered IP address (many-to-one
translation, also known as Port Address Translation [PAT])
•Enables packets to be routed correctly to and from the outside world by using the Cisco uBR900
series cable access router
•Allows personal computers on the Ethernet interface to have IP addresses to be mapped to the
cable interface’s IP address
Routing protocols will run on the Ethernet interface instead of the cable interface, and all packets
received are translated to the correct private network IP address and routed out the Ethernet
interface. This eliminates the need to run RIP on the cable interface.
To implement NAT on the Cisco uBR900 series, the Ethernet interface is configured with an “inside”
address and the cable interface is configured with an “outside” address. The Cisco uBR900 series
also supports configuration of static connections, dynamic connections, and address pools.
Voice Over IP Operations
Note Voice features are available only on the Cisco uBR924 cable access router.
The Cisco uBR924 cable access router uses packets to transmit and receive digitized voice over an
IP network. Voice signals are packetized and transported in compliance with H.323 or Simple
Gateway Control Protocol (SGCP). H.323 is an International Telecommunications Union (ITU)
standard that specifies call signaling and control protocols for a shared IP data network. SGCP is a
Cisco/Bellcore-developed, out-of-band signaling protocol under review by the Internet Engineering
Task Force (IETF).
Figure4 illustrates a broadband cable system that supports VoIP transmission. Quality of Service
(QoS) and prioritization schemes are used to enable real-time (voice) and non-real-time traffic to
coexist on the same channel. The CMTS routes IP telephony calls intermixed with other data traffic.