Analog phone plugged directly into FXS port

DerekAustin26

How does this phone get it's phone # when it's plugged directly into a 2811 series Router's FXS port?

It's one thing when a phone is plugged directly into a 66 block or an MTA that's getting it's phone # from the phone co./ISP, but when plugged directly into the FXS port on a Router?

DexterPark

Dial Peers. Your router might connect back to the PSTN with an FXO Port, PRI, or SIP Trunk via your internet connection. It doesn't really matter how the router has the number(s), only needs to have a place to use them:

dial-peer voice 10 pots
destination-pattern 1234567
port 1/0/1

Your analog phone plugs into port 1/0/1 on the FXS card and any inbound calls for phone number (Area Code) 123-4567 will be sent to that port.

DerekAustin26

Can it also make outbound calls too?

DexterPark

Yes. There are inbound dial peers like the one above and there are outbound:

dial-peer voice 2 pots
destination-pattern [2-9]………
port 0/0/0
forward-digits all

When you dial any number from the analog phone starting with digits 2-9 followed by nine other digits
(example: 987-654-3210) it will match the outbound dial peer above and forward it out port 0/0/0 on your FXO card, which goes out to the PSTN.



This book would be a very good starting point for you: CCNA Voice 640-461 Official Cert Guide

theodoxa

Analog Phone numbers would be manually configured using dial-peers. I set up two 1751s with VIC-2FXS (+ PVDM) on opposite sides of my home. I configured them as follows:

Router 1:

dial-peer voice 101 pots
destination-pattern 101
port 2/0

dial-peer voice 102 pots
destination-pattern 102
port 2/1

dial-peer voice 2 voip
destination-pattern 2..
session target ipv4:172.16.1.200

Router 2:

dial-peer voice 201 pots
destination-pattern 201
port 2/0

dial-peer voice 202 pots
destination-pattern 202
port 2/1

dial-peer voice 1 voip
destination-pattern 1..
session target ipv4:172.16.1.100

............................................

dial-peer voice ID {pots | voip}

Creates a dial peer. For an analog phone plugged directly into an FXS port, it would be "pots", whereas if you want to route a call over your home network to another router, you would use "voip". ID is only locally-significant. It can be anything and does not have to be the same as the destination pattern.

destination-pattern PHONENUMBER

Creates a phone number. You can use wildcards and/or the Pound (#) and Star (*) symbols. A Period (.) represents any number. So, 1.. would be any 3 digit number beginning with a 1. There are other wildcards such as a range of numbers in between [] or a T (Capital T), but a Period (.) is the most basic.

port PORT

Assigns the number to an analog port. In my case, a VIC-2FXS was plugged into Slot 2, so the ports were 2/0 and 2/1.

session target ipv4:IPADDRESS

Forwards the call to an IP ADDRESS. In my case, the IP ADDRESS belonged to another router on the other side of the house. You can also forward to things other than an IP Address, but I only know how to use an IP Address for now.

DexterPark

An excellent breakdown! One more thing to note is that the router will always match the MOST specific dial peer. Lets add my outbound PSTN dial peer to the above example, if I were on the phone attached to router 1 with the extension of 101 and dialed 201 it would be a potential match for both outbound dial peers:

dial-peer voice 2 voip
destination-pattern 2..
session target ipv4:172.16.1.200 <---Router 2

dial-peer voice 3 pots
destination-pattern [2-9]………
port 0/0/0 <---- PSTN
forward-digits all

Since 201 is three digits and not ten, dial peer 2 is the most specific and is used. Alternatively, if I dial 201-123-4567 (New Jersey area code), it would again be a potential match for dial peers 2 & 3 because they both catch the "2" digit, but due to it being a ten digit number, dial peer three will win.