WAN

WAN technologies

• Frame Relay – old technology, it is replaced by MPLS nowadays
• ISDN
• LAPB
• LAPD
• HDLC
• PPP
• PPPoE
• Cable
• DSL
• MPLS
• ATM

Some facts:

• T1 - 1,544 Mbit/s


• T3 - 44.736 Mbit/s


• Local loop - telco cable between your home and telco central office


• Analog modems and DSL both support symmeric and asymmenric transfers


• Default encapsulation is HDLC


• All HDLC versions are proprietary


• PPP is industry standard. It can be used to create point-to-point links between different vendors’ equipment. It uses a Network Control Protocol field in the Data Link header to identify the Network layer protocol and allows authentication and multi-link connections to be run over asynchronous and synchronous links


• DCE – modems


• DTE – computers, laptops, routers


• DCE side determined by cable


• Add clocking to DCE side only


• A CSU/DSU (Channel Service Unit/Data Service Unit) is a digital-interface device used to connect a Data Terminal Equipment device or DTE, such as a router, to a digital circuit, for example a T1 or T3 line


• A CSU/DSU operates at the physical layer (layer 1) of the OSI model. CSU/DSUs are also made as separate physical products: CSUs and DSUs


• RS-232 end of the cable connets to CSU/DSU, on the router side cable is router specific


• Digital lines require both a channel service unit (CSU) and a data service unit (DSU). The CSU provides termination for the digital signal and ensures connection integrity through error correction and line monitoring. The DSU converts the data encoded in the digital circuit into synchronous serial data for connection to a DTE device.

user#config t

user(config)#interface serial 0

user(config-if)#clock rate 64000

• By default, Cisco routers are all data terminal equipment (DTE) devices, which means that you must configure an interface to provide clocking if you need it to act like a DCE device. Again, you would not provide clocking on a production T1 connection, for example, because you would have a CSU/DSU connected to your serial interface.

Todd(config-if)#clock rate ?

Speed (bits per second)

• To determine the type of the device: DTE or DCE, show controllers command is used:

user#sh controllers s0/2/0

Interface Serial0/2/0

Hardware is GT96K

DCE V.35, clock rate 1000000

• New ISR routers automatically detect DCE connections and set the clock rate to 2000000.


• Setting bandwith:

user#config t

user(config)#int s0/0/0

user(config-if)#bandwidth ?

1-10000000 Bandwidth in kilobits

inherit Specify that bandwidth is inherited

receive Specify receive-side bandwidth

user(config-if)#bandwidth 1000

• Bandwidth command is configured in kilobits.

FastEthernet0/0 is up, line protocol is up

• The first parameter refers to the Physical layer, and it’s up when it receives carrier detect.


• The second parameter refers to the Data Link layer, and it looks for keepalives from the con- necting end. (Keepalives are used between devices to make sure connectivity has not dropped.)


• Default band-width (BW) on all Cisco serial links: 1.544Kbps