Serial Interface

Introduction

Serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. This is in contrast to parallel communication, where several bits are sent together, on a link with several parallel channels.

A serial interface (E1/V.35) can work in

1. HDLC

2. PPP mode.

Network Diagram

Configuration

Lets take HDLC mode first. Consider a network scenario as shown in fig-3. Router-A and Router-B are connected on V.35 link. Configure Router-A as:

Okapi(config)# interface Serial 0
Okapi(config-if-serial)# encapsulation cisco-hdlc
Okapi(config-if-serial)# ip address 10.5.5.5/16
Okapi(config-if-serial)# no shut

Configure Router-B as:

Router(config)# interface Serial 0
Router(config-if)# encapsulation  hdlc
Router(config-if)# ip address  10.5.5.6 255.255.255.0
Router(config-if)# no shut

With the above configuration serial link is established between two routers.

To work with PPP mode, just change the encapsulation to ppp.

Now lets consider same network scenario with the difference that the two routers are connected through E1 link. Lets assume that the routers are using all 31 timeslots ie 1-31 and not using any crc. The configuration on Router-A for ppp encapsulation would be:

Okapi(config)# interface Serial 0
Okapi(config-if)# encapsulation  ppp
Okapi(config-if)# timeslot 1 31
Okapi(config-if)# ts16
Okapi(config-if)# no crc4
Okapi(config-if)# ip address  10.5.5.5 255.255.255.0
Okapi(config-if)# no shut

The configuration on Router-B for ppp encapsulation would be:

Router(config)#controller e1 0
Router(config-controller)#no channel-group 0
Router(config-controller)#channel-group  0 timeslots 1-31
Router(config-controller)#framing no-crc4

Router(config)#interface  serial  0:0
Router(config-if)# ip address  10.5.5.6 255.255.255.0
Router(config-if)# no shut