Semster 2 Chapters 2-3

    What is and example of a DCE and DTE?

    DCE- (Date Communication Equipment)- provide physcal connections to the network, forwards traffic, and provides
    clocking a clocking signal used to synchronize data transmission between DCE and DTE devices.
            ex.    Modem, Interface Cards

    DTE (Data Treminal Equipment)- Devices at the user end of a user-network interface that serves as a data source,
    destination, or both.  DTE connects to a data network through a DCE.
            ex.    Computer, Protocol Translator, Multiplexers

    Be able to describe:

                    WANs interconnect LANs and allow them to exchange dta packets/frames
                      Physical (Layer 1):  Provide electrical, mechanical, operational, and funcional connections for the WAN
                    Data Link (Layer 2):  Map how frames are carried in a data link
  High-Level Data Link Control (HDLC) -- an IEEE standard; may not be compatible with different vendors because of the way each vendor has chosen to implement it. HDLC supports both point-to-point and multipoint configurations with minimal overhead

Frame Relay -- uses high-quality digital facilities; uses simplified framing with no error correction mechanisms, which means it can send Layer 2 information much more rapidly than other WAN protocols

Point-to-Point Protocol (PPP) -- described by RFC 1661; two standards developed by the IETF; contains a protocol field to identify the network layer protocol

Simple Data Link Control Protocol (SDLC) -- an IBM-designed WAN data link protocol for System Network Architecture (SNA) environments; largely being replaced by the more versatile HDLC

Serial Line Interface Protocol (SLIP) -- an extremely popular WAN data link protocol for carrying IP packets; being replaced in many applications by the more versatile PPP

Link Access Procedure Balanced (LAPB) -- a data link protocol used by X.25; has extensive error checking capabilities

Link Access Procedure D-channel (LAPD) -- the WAN data link protocol used for signaling and call setup on an ISDN

D-channel. Data transmissions take place on the ISDN B channels

Link Access Procedure Frame (LAPF) -- for Frame-Mode Bearer Services; a WAN data link protocol, similar to LAPD, used with frame relay technologies

Cicuit switched services

            POTS, ISDN

Cell switched

            ATM, SMDS

Describe the different kinds of memory used in a router; know what software each type of memory normally contains:

RAM/DRAM -- Stores routing tables, ARP cache, fast-switching cache, packet buffering (shared RAM), and packet hold queues. RAM also provides temporary and/or running memory for the routerís configuration file while the router is powered on. RAM content is lost when you power down or restart.

NVRAM -- nonvolatile RAM; stores a routerís backup/startup configuration file; content remains when you power down or restart.

ROM -- contains power-on diagnostics, a bootstrap program, and operating system software; software upgrades in ROM require replacing pluggable chips on the CPU

Flash -- erasable, reprogrammable ROM; holds the operating system image and microcode; allows you to update software without removing and replacing chips on the processor; content remains when you power down or restart; multiple versions of IOS software can be stored in Flash memory

What protocol does a WAN use to make path determination decisions?


What layer does a router operate at and what kind of addresses does it use to make decisions?

Layer three, IP adresses

What is the difference between Frame relay service and X.25?

Frame relay is becoming more popular because X.25 is older and less efficent

enable-lets you do things
logout/exit-lets you leave the router
?-tells you available commands


User EXEC mode
Priveledged mode
Global configuration
Router configration
Interface configuration (intS0)


Interface- where packets exit and enter the router

Router will hold 22 lines

Space bar to see the more screen.


    WAN Devices

            WANs provide for the exchange of data packets/frames betweeen routers/bridges and the LANs they support.

            A WAN interconnects LANs that usually have a large geographic area between them.


            Routers offer serices including:
                WAN serial interfaces

        Routers can operate as:
                Internal routers
                Backbone routers
                Area border routers
                Autonomous system boundary routers

        WAN bandwidth switches

                Service provider equipment that connects to WAN bandwidth for voice, data, and video communications.


                Also called CSU/DSUs (channel service units/digital service units)

                Interface with voice-grade connection in order to convert analog signal to digital.

                Represents the DCE side of the DTE/DCE connection.

        Communication Servers

                Concentrates dial-in and dial-out services.

                Equipment is usually at the service provider's site.

WAN Standards

              What layers of the OSI layer do the WAN standards describe?
                        Physical and Data Link Layers

        WAN Physical Layer

                Protocols that descrbe how to provide electrical, mechanical, operational, and functional connections for WAN         .               services

                These services ar most often obatained from WAN service providers such as ROBCs, alternate carriers,
                post-telephone, and telegraph (PTT) agencies.

                Describes the interface between the data terminal equipment (DTE) and the data circuit-terminating equipment

                Typically, the DCE in the service provider and the DTE is the attached device.

                Several physical layer standards specefying this interface between the DTE and DCE are...

        Data Link Layer

                Wan data link protocols describe how frames are carried between systems on a single data link

                They include protocols designed to operate over dedicated point to point, multiport, and multiaccess switched

                WAN standards are defined and managed by a number of recognized authorities including ITU-T, ISO, IETF, &

        WAN Data Link Encapsulation

                High-Level Data Link Control (HDLC)
                    Cisco default encapsulation; typically used between running Cisco IOS; replacing SDLC.
                    Streamlined, no windowing or flow control.
                    May not be compatible with each vendor depending on the way each vendor has chosen to implement it
                    HDLC supports both point to point and multipoint configurations with minimal overhead.

                Frame Relay
                    Uses high-quality digital facilities
                    Uses simplified framing with no error correction mechanism (connectionless)
                    It can send layer 2 information much more rapidly than other WAN products

                PPP (point to point protocol)
                    Developed by IETF, replaced SLIP
                    Contains a field to identify the network protocol
                    PPP can check for link qualiy during connection establihment
                    Supports PAP and CHAP

        WAN Technologies Overview

            Dedicated:  xDSL, T1, E1, T3, E3, SONET

            Analog:  Dial-up Modem, Cable Modems, Wireless

            Cicuit Switched:  POTS, ISDN

            Packet Switched:  X25, Frame, Relay

            Cell Switched:  ATM, SMDS

Basic Cisco Router Commands:



User EXEC mode

Router?ena  (enable)
changes to-

Priveledged mode

Type in
config t

global configuration-router donfiguration file

copy, run, start

router configration-chnges the routing protocol

interface configuration (intS0)

WAN=serial (Slower)
LAN=ethernet wire