CSU
Channel Service Unit
DSU
Data Service Unit
DCE
Data Connecting Equipment Provides clocking Has the equivalent task of an crossover cable by swapping the transmit and receive wire pairs
DTE
Data Terminating Equipment Used between Routers and CSU/DSU
HDLC
High Level Data Link Control Default encapsulation type for a serial connection
Clocking
CSU/DSU tells the router when to exactly send each bit through signaling over the serial cable

Implenting in a Lab

Serial connections

Commands

1

r1 (config)# show ip interface brief

you will get

Method Protocol Issue
down down Layer 1
up down Layer 2

With Layer 2 issues

Lab

/30 is used only for point-to-point serial connections.

Router 1: 200.200.200.1* DCE device

Router 2: 200.200.200.2

/30 will have a block size of 4. So first network will be between 200.200.200.1 - 200.200.200.3 where 200.200.200.3 is the broadcast address.

router r201

1

r201# show interfaces serial 0/1/0

Serial interfaces have no MAC addresses.

Sign IP address:

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2
3
4
5
6
7

r201# show ip interface brief
r201# configure terminal
r201(config)# interface serial 0/1/0

# /30 network mask
r201(config-if)# ip address 200.200.200.255.255.255.252
r201(config-f)# no shutdown

router 1

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2
3
4
5

r1# conf
r1# configure terminal
r1(config)# interface serial 0/0/0
r1(config-if)# ip address 200.200.200.1 255.255.255.252
r1(config-if)# no shutdown

Make sure interface is up:

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2

r1# show ip interface brief
r1#ping 200.200.200.2

Change clock rate:

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2
3
4
5
6
7

r1#configure t
r1(config)# interface serial 0/0/0

# 128k bit/s
r1(config-if)# clock rate 128000

r1(config-if)# do show controllers serial 0/0/0

DTE/DCE

Figure out which side is the DCE/DTE side:

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2
3
4

r1# show controllers serial 0/0/0
...
DCE V.35, clock rate 2000000
...

Check the other end:

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2
3
4

r201# controllers serial 0/1/0
...
DTE V.35 TX and RX clocks detected
...