IT Life: Chapter 2: Connecting to the WAN Part 3

Circuit-Switched Networks/ Packet-Switched Networks

Circuit-Switched Networks

Establish a dedicated circuit/ channel between nodes/terminals before sending data.
Circuit must remain established and unchanged or the connection will fail.
Allows for one pair of nodes to communicate over a single dedicated channel
Activity on the line alternates between running at full capacity and no activity.
Subscribers have sole use of a fixed capacity.
Circuit-switched networks a more expensive to move data.

A telephone call is a good example of a circuit-switched network.

Two circuit-switched WAN technologies are the Public Telephone Network (PSTN) and the Integrated Services Digital Network (ISDN).

Packet-Switched Networks

Split data into packets
Packets are routed over a shared network
Do not require an established circuit
Allows many pairs of nodes to communicated over the same channel
Routers determine the link the packets will take based on addressing in each packet.
There are Two approaches to determine the link, Connectionless systems and Connection-Orientated systems
Links between switches are shared so they are cheaper
Packets must be fully received before moving on causing latency and jitters
Modern Technology allows satisfactory transmission of data

Connectionless Systems requires packets to have full addressing. Routers evaluate addresses to determine where to send the packet. Best known example of a connectionless system is the internet.

Connection-Orientated systems predetermines the route for a packet, which only needs to carry an Identifier. The router looks up the identifier to determine where to send the packet. The table entries the router checks identifies a specific route/circuit. The circuit created, or virtual circuit (VC), is only established when in use then is is broken down. An example of a connection-orientated system is Frame Relay. In Frame Relay the identifiers are called data-link connection identifiers (DLCIs)

Private vs. Public WAN Infrastructures

In Private WAN Infrastructure, service providers may offer dedicated leased lines, circuit-switched lines, and packet-switched lines.

In Public WAN Infrastructure, service providers offer broadband internet access using DSL, cable, and satellite. This option is typically used to connect small offices and telecommuters to corporate networks over the internet. Security need to be address and VPNs should be used.

Service Provider Infrastructure

The data sent over a WAN may need to got to a recipient on the same or different service provider. The service provider network connect to other service providers, cover large distances, handle heavy traffic, and offer high speeds. Service providers mostly use high-speed fiber-optic media to meet their needs.

Fiber-optic standards include, the American-based (ANSI), Synchronous Optical Networking (SONET) or, the European-based (ETSU/ITU), Synchronous Digital Hierarchy (SDH). The standards define how to transfer data/voice/video over fiber using lasers or LEDs over long distances.

Dense Wavelength-Division Multiplexing (DWDM)

DWDM is a newer development in fiber that greatly increases bandwidth of a single fiber by assigning signals specific color wavelengths/frequencies. This allows more signals in one fiber strand. End devices separate the traffic accordingly. DWDM circuits are used in all modern submarine communications cable systems and other long-haul circuits. *Submarine refers to the cables running in the ocean not the vehicle. I looked it up to be sure.*

Why DWDM is good:

Allows bidirectional communications over a single fiber
Assigns signals specific frequencies
Each channel can support 10Gbps multiplexed signal
Multiplex more than 80 different channels of data into a single fiber
Can amplify signal
Supports SONET/SDH

This chapter will be continued in Part 4.

IT Life

Sunday, January 18, 2015

Chapter 2: Connecting to the WAN Part 3