Residential Gateway - Part 1

I worked for 2 years at a company that manufactures Residential Gateway. I primarily worked on the GUI and Configuration customization of these gateways. At times the work involved debugging functional issues that required understanding of the underlying protocols and standards. This provided me the opportunity to learn about various networking standards.

I referred Wikipedia and RFCs for most of the things I learned. I am going to share my learning through series of blogs. I don't intend to capture the internal details like multiplexing techniques or packet/frame formats as those can be obtained from standards documents. The information here will provide conceptual understanding and some useful facts about the technologies.

In this first installment let's understand what is Residential Gateway.

Residential Gateway is quite a popular term in USA but not a well known term in India. In India people refer it as Modem mostly because:
- It is just a Modem
- If it is not just a Modem then either people don't know about its features and/or they don't use other features.

The primary function of Residential Gateway is to enable broadband Internet connection for home users. It is a combination of modem and router. In addition, it provides other features like:
- Firewall
- NAT
- DHCP
- DNS
- VoIP

Following diagram shows the complete broadband ecosystem. The CPE in the diagram is the residential gateway:
Broadband Network

Following diagrams shows how a typical home network looks like:
Home Network 1
Home Network 2
Following diagram shows the common ports available on a residential gateway and sample devices that can be connected:
Residential Gateway Ports and Devices


If you look at the diagrams available at above links you will notice that the most common interface on the home or LAN side are:
- USB
- Ethernet (RJ-45)
- Wireless (Wifi or 802.11x)
- Coax (For TV or STB)

On the WAN side the most common interfaces are HPNA (DSL) and Cable (this is same as the one on which you get Cable TV service). Out of these the DSL interface is most commonly used, atleast in India. The primary reason for DSL popularity is that the basic infrastructure i.e. the phone line is already present. User just need to buy the modem cum router and he is ready to setup his/her home network.

I will talk about DSL and related technologies in the next part. Stay tuned...