ICND2: Frame Relay
Wide Area Networks
A LAN will cover an area in the same building or vicinity; a WAN spans a much larger geographically connected sites. Setting up and maintain a WAN is very expensive, most private companies would rather purchase a WAN connection from the ISP, who will manage the WAN infrastructure and back-end network backbone. Services include T1, T3, E1 and E3, DSL, cable, frame-relay and ATM.
WAN operations cover the Layer 2 Data Link Layer (Metro Ethernet, MPLS, frame-relay, ATM, HDLC)and Layer 1 Physical Layer components (electrical, mechanical, operational connections).
WAN Devices
Equipment required includes a modem CSU/DSU to connect to the service provider, and edge devices modify the Ethernet encapsulation to the serial WAN
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| Wan Ecapsulation Answer Hack. Is this legal? |
Modem - modulates an analog carrier signal to encode the digital signal, and modulates the carrier signal to decode the transmitted information.
CSU/ DSU - Channel Service Unit/ Data Service Unit. CSU is termination for the digital signal ensures integrity, error correction, and line monitoring. DSU converts T Carrier line frames into LAN frames. Provides a clocking signal to the customer equipment interface from the DSU, terminate the channelized transport media of the carrier on the CSU. CSU also provides a loopback test diagnostic.
Demarcation Point, the point where a service provider considers the services delivered, such as the CSU/DSU on customer's premises to the provider's Central Office.
Access Server - I'll check my notes what that is for.
WAN Switch - used in carrier networks to carry Frame Relay, ATM, X.25 and PSTN in the cloud
Router - The router can be a WAN connection device, with serial interface ports to connect to the service provider and the internetwork for the LAN. Basically a router will connect to the POP router of the ISP
Core Router - needs explaining
CPE - Customer Premise Equipment that includes a DCE/ DTE.
DCE - Data Circuit-terminating Equipment or Data Communications Equipment, the device that ports data on the local loop.Configure the clock rate for the DCE interface.
DTE - Data Terminal Equipment, customer equipment that passes data to the DCE such as the routers. Synchronizes to the clock rate.
There is a lengthy description of EIA/ TIA connectors, but the most important part is the router end of the shielded serial transition cable which has a DB-60 connector. The DB-60 port on a serial WAN interface car is a 5 in 1 port. There is a new type of cable called a Smart Serial Cable.
Summary of WAN Links Hierarchy
Three main WAN types: Dedicated, Circuit Switched and Packet Switched.
DEDICATED
Leased Lines: T1/ E1
For companies who constantly send traffic, expensive.
SWITCHED
Circuit Switched: PSTN, ISDN, analog modem
For companies who send occassional traffic, least expensive.
Packet Switched: Frame Relay, x.25
Ideal for companies requiring a minimum constant service without the cost of dedicated lines.
Cell Switched: ATM
INTERNET
Broadband:VPN
Other: DSL Cable, Broadband, Wireless
The Last Mile
This refers to the local loop, the last mile connection that defines how the local user gets to the ISP perhaps? One example is for example, installing a new fiber optic cable from the exchange outside the building into the networking lab perhaps. Another example could be a satellite hop.
Long Range Connectivity
The protocols SONET and Synchronous Digital Hierarchy (SDH) have been around for ages. These are used to move large amounts of data over great distances through fiber optic cables, mostly refering to voice and data. A newer optical technology, Dense Wavelength Division Multiplex (DWDM) provides extremely long range communications by assigning a specific frequency (or wavelength) of light to incoming signals. Equipment can amplify the wavelength to boost signal strength. A single DWDM fiber can have more than 80 different wavelengths or channels multiplexed, each channel carrying up to 10 Gb/s. The other important feature is that DWDM can carry IP, SONET, ATM at the same time on the same optical fiber.
At the receiving end, the router needs the right optical SFP.
Related Topics: PPP Encapsulation, ISDN
Next Topic: DSL two types-ADSL and SDSL
Followed by: Cisco IPSec VPN
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