Chapter_01_4

What is a WAN?

A WAN is a data communications network that operates beyond the geographic scope of a LAN.

Here are the three major characteristics of WANs:

WANs generally connect devices that are separated by a broader geographical area than can be served by a LAN.

WANs use the services of carriers, such as telephone companies, cable companies, satellite systems, and network providers.

WANs use serial connections of various types to provide access to bandwidth over large geographic areas.

Sem 4 Chapter 1

A WAN is a data communications network that operates beyond the geographic scope of a LAN.

Here are the three major characteristics of WANs:

WANs generally connect devices that are separated by a broader geographical area than can be served by a LAN.

WANs use the services of carriers, such as telephone companies, cable companies, satellite systems, and network providers.

WANs use serial connections of various types to provide access to bandwidth over large geographic areas.

Why Are WANs Necessary?

LAN technologies provide both speed and cost-efficiency for the transmission of data in organizations over relatively small geographic areas. However, there are other business needs that require communication among remote sites, including the following:

People in the regional or branch offices of an organization need to be able to communicate and share data with the central site.

Organizations often want to share information with other organizations across large distances. For example, software manufacturers routinely communicate product and promotion information to distributors that sell their products to end users.

Employees who travel on company business frequently need to access information that resides on their corporate networks.

metro Ethernet

access server

ATM switches

time-division multiplexing

CSU/DSU

DCE

DTE

data communications equipment

demarcation point

Το DS-HDMOD ειναι μια συσκευή που παρέχει ο ΟΤΕ σε HellasCOM γραμμές με 2 ζευγάρια καλωδίων και τερματίζει σε G.703 interface.

Ερχετε με κάθε σύνδεση HCOM απο 64kbit εως 1940kbit, καθώς και σε PCM 2Mbps.

Στην περίπτωση μετά της HCOM χρησιμοποιείται το MD73 για να σου κάνει interface convertion π.χ. σε X.21 για να συνδέσεις ενα Cisco router πάνω.

Αντίστοιχη συσκευή για την 2Mbps ειναι το Telindus Crocus CVM 2M το οποιο κάνει μετατροπή απο G.703 σε X.21 (υπάρχουν φυσικά και μετατροπείς σε άλλα interface).

Επειδη το MD73 "κόβει" τα κανάλια των 64kbit για να σου δώσει την ταχύτητα που έχεις αγοράσει σε HCOM, καθως και επειδη ειναι αρκετά "αρχαια" συσκευή, προσθέτει αρκετό latency στην γραμμή (για σύνδεση 2-3 χλμ, έχεις 20-30ms ping χαλαρά), ενω ο Telindus interface converter δίνει (απο προσωπική εμπειρία) σε link 45km περίπου 3-4ms round trip.