Cisco 2 - Router
Chapter 1
WAN is a data communications network that operates beyond a LAN’s geographic scope.
One must subscribe to a WAN provider such as AT&T, Sprint, RBOC.
They provide network services such as:
• Frame Relay
• Integrated Services Digital Network (ISDN)
• Asynchronous Transfer Mode (ATM)
Which carries traffic type of voice, data and video.
In general , WAN’s operate at the 1st three layers of the OSI . (Though
Frame Relay actually operates at layer 1 and layer 2.) So all of the WAN services have layer 1 & layer 2 in common.
Other characteristics of WAN are:
• operate beyond LAN geographic area
• use serial connections
• provide full-time & part-time connectivity
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Cisco 2 - Router
Router’s Internal Components
The main internal components of the router are:
•
Random Access Memory (RAM)
• Nonvolatile Random-Access Memory (NVRAM)
• flash memory
• Read-Only Memory (ROM)
• Interfaces
Chapter 1
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Cisco 2 - Router
Chapter 1
Router’s Internal Components
RAM:
• stores routing tables
• holds ARP cache
• holds fast-switching cache
• performs packet buffering
• maintains packet-hold queues
• provides temporary memory for the configuration file of the router while the router is powered on
• loses content when router is powered down or restarted
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Cisco 2 - Router
Chapter 1
Router’s Internal Components
NVRAM:
• provides storage for the startup configuration file
• retains content when router is powered down or restarted
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Cisco 2 - Router
Chapter 1
Router’s Internal Components
Flash memory:
• holds the operating system image (IOS)
• allows software to be updated without removing & replacing chips on the processor
• retains content when router is powered down or restarted
• can store multiple versions of IOS software
• is electronically erasable, programmable ROM (EEPROM)
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Cisco 2 - Router
Chapter 1
Router’s Internal Components
ROM:
• maintains instructions for power-on self test (POST) diagnostics
• stores bootstrap program & basic operating system software
• requires replacing pluggable chips on the motherboard for software upgrades
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Cisco 2 - Router
Router’s Internal Components
Interfaces:
• connect router to network for frame entry & exit
• can be on the motherboard or on a separate module
• connect the router to LANs and WANs
Chapter 1
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Cisco 2 - Router
Chapter 1
Subscriber to Provider Interface
Modem
Router
DTE
DCE
A key interface in the customer site occurs between the Data Terminal
Equipment (DTE) such as a router to the Data Circuit-Terminating equipment (DCE) to the WAN network such as a modem.
DTE is on the customer’s side of the network.
The DCE is a modem and in many cases is circuitry in a CO, switch which is made up of a CSU/DSU (Channel Service Unit/Data Service Unit). The major reason for CSU/DSU is to protect the equipment from CPE/DTE from aberrant voltages, and to ‘square’ up the signal.
DCE is usually on the provider’s side.
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Cisco 2 - Router
Subscriber to Provider Interface
Router
EIA/TIA-232, V.35, X.21, HSSI, others
DTE
DCE
Modem
Chapter 1
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Cisco 2 - Router
Routers Physical Characteristics
The 3 basic types of connections on a router are:
1.
LAN interfaces
2.
WAN interfaces
3.
Management ports
• Console
• auxiliary
Chapter 1
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Cisco 2 - Router
Chapter 1
Routers Physical Characteristics
Management ports provide
• Text-based connection
• Configuration, monitoring, password recovery and troubleshooting
The management ports:
•
EIA-232 asynchronous serial ports
• used for non-network connections
• used for initial router configuration
• to connect to a port, a PC must have a terminal emulation program
• rollover cable from PC to the management ports
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Cisco 2 - Router
Chapter 1
Management Ports
The console port, says Cisco is preferred when troubleshooting:
• doesn’t depend on network services
• displays start and error messages by default
To establish a connection between PC and a router, one needs
• terminal emulation software
• rollover cable
• RJ-45 to DB-9 connector
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Cisco 2 - Router
Chapter 1
Routers Physical Characteristics
Cisco says, the terminal emulation software, HyperTerminal, the parameters used to configure a router are:
• Data bits
• Stop bits
• parity
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Cisco 2 - Router
Chapter 1
Router’s connection LAN & WAN
For a PC of a LAN to connect to a router, one
• straight-thru cable from the PC to a HUB or switch
• straightthru cable from the HUB or switch to router’s Ethernet interface
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Cisco 2 - Router
Router’s connection LAN & WAN
An internetwork must include:
• switching
• dynamic or static routing
• consistent end-to-end addressing
Chapter 1
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Cisco 2 - Router
Chapter 1
Router’s connection to LAN & WAN
EIA/TIA-232, V.35, X.21, HSSI, others
Modem
Router
DTE
DCE
The connections to WAN on router is through the serial interface, either as a Smart Serial interface connector or DB-60 connector.
The following devices are used in the construction of a WAN:
• communication servers
• routers
• modems
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Cisco 2 - Router
Chapter 1
Router vs. PC
Cisco says the common components between a router and PC are:
• CPU
• input/output interfaces
• system bus
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