Wide Area Network

What is the primary geographical characteristic of a Wide Area Network (WAN)?

It connects buildings or campuses over long distances spanning cities, regions, or countries.

Which entities typically provide the leased circuits used to build WANs?

Common carriers such as AT&T, Verizon, and BT.

Name three common services used to implement Wide Area Networks.

Dedicated-circuit networks, packet-switched networks, and Virtual Private Networks (VPNs).

How are dedicated-circuit networks billed by common carriers?

They are billed at a flat monthly fee for unlimited use of the circuit.

What is the primary role of a CSU/DSU in a dedicated-circuit network?

It connects a LAN to a leased line provided by a common carrier.

A dedicated-circuit architecture that connects all nodes in a closed loop is a _____ architecture.

Ring

In a Ring architecture with $N$ nodes, what is the cost in relationship to the number of nodes?

$N$

What is the performance of a Ring architecture measured by the number of hops on the longest path?

$\frac{N}{2}$

How does a Ring architecture respond to the loss of a single node or line?

The network remains fully operational.

What is a major disadvantage of long routes in a Ring architecture?

They may increase communication latency.

In a Star architecture, all nodes are connected to a _____.

Central node

What is the cost of a Star architecture in relationship to the number of nodes ($N$)?

$N - 1$

What is the maximum number of hops for a message in a Star architecture?

2

What is the primary risk of the central site in a Star architecture?

Failure of the central site causes complete network failure.

Which dedicated-circuit architecture provides the highest reliability and shortest routes?

Full Mesh architecture

What is the formula for cost (number of circuits) in a Full Mesh network with $N$ nodes?

$\frac{N \times (N - 1)}{2}$

What is the primary disadvantage of a Mesh architecture?

It is expensive due to the high number of circuits required.

Name the two main types of dedicated circuit services.

T-carrier networks and Synchronous Optical Networks (SONET).

What is the data rate of a T1 (DS1) circuit?

1.544 Mbps

Which commercially available T-carrier service provides a speed of approximately 44.736 Mbps?

T3 (DS3)

What is the speed of a DS0 (Fractional T1) signal?

64 Kbps

Which ANSI standard is used for optical fiber transmission in North America?

SONET (Synchronous Optical Network)

What is the speed of an OC-3 SONET designation?

155.52 Mbps

Which SONET designation provides a speed of approximately 9.953 Gbps?

OC-192

How do packet-switched networks differ from dedicated circuits regarding data interleaving?

Packets from separate messages can be interleaved to maximize efficiency.

What device translates messages between protocols to connect a site to a packet-switched carrier?

Packet Assembler/Disassembler (PAD)

What are Permanent Virtual Circuits (PVCs)?

Connections between locations in a packet network that are defined for long-term use.

Virtual circuits that change dynamically based on demand are called _____.

Switched Virtual Circuits (SVCs)

Term: Committed Information Rate (CIR)

Definition: The data rate guaranteed by a packet-switched service provider.

What happens to packets that exceed the Committed Information Rate (CIR) up to the Maximum Allowable Rate (MAR)?

They may be discarded if the network becomes overloaded.

Name three types of packet-switched services.

Frame Relay, Ethernet, and MPLS.

Why is Frame Relay considered an 'unreliable' protocol?

It does not provide error control.

What is the future trend for packet services in WANs?

Many carriers are switching to Ethernet for WANs.

Where is the label applied in Multiprotocol Label Switching (MPLS)?

Between the layer 2 and layer 3 headers.

Why is MPLS sometimes referred to as a layer 2.5 protocol?

Because its label is inserted between the Data Link (Layer 2) and Network (Layer 3) headers.

What is the primary benefit of using labels in MPLS forwarding?

Packets can be switched faster than using complete IP addresses and routing tables.

What is a Virtual Private Network (VPN)?

A service that provides the equivalent of a private packet-switched network over the public Internet.

What is the primary drawback of using a VPN for WAN connectivity?

The organization has no control over speed and security across the public Internet.

An _____ VPN provides virtual circuits between an organization's various locations over the Internet.

Intranet

What is the difference between an Intranet VPN and an Extranet VPN?

An Intranet VPN connects locations within one organization, while an Extranet VPN connects different organizations.

Which type of VPN enables employees to access an organization's network from remote locations?

Access VPN

In public key cryptography, which key is used to decrypt a message encrypted with a public key?

The corresponding private key.

What is the reliability level of VPN services compared to T-Carrier services?

VPNs have moderate reliability, while T-Carriers have high reliability.

For low to moderate traffic where reliability is less important, which service is recommended?

VPN

Which service is recommended for low traffic ($\le 1.5$ Mbps) requiring predictable and stable traffic?

T1

Which packet-switched service is recommended for flexibility at high traffic rates ($1.5$ Mbps to $1$ Gbps)?

Ethernet

For very high traffic ($> 1$ Gbps) that is predictable and stable, which service is recommended?

OC/SONET

What are the two recommended flexible services for very high traffic ($> 1$ Gbps)?

Ethernet and MPLS

Which service type is considered the most inexpensive but least predictable?

VPN

What is the maximum data rate listed for Ethernet WAN services?

40 Gbps

Why are dedicated circuits called 'leased lines' or 'private lines'?

Because they are full duplex circuits leased from common carriers for exclusive point-to-point use.

In a packet-switched network, how is the total cost calculated?

A fixed price for the carrier connection plus a fee for the volume of data transmitted.

What is a 'tunnel' in the context of a VPN?

A virtual circuit created over the public Internet.

Which dedicated circuit architecture is the most susceptible to bottlenecks at a single node?

Star architecture

What is the relationship between SONET's OC-1 and SDH's STM-0 in terms of speed?

They both offer a speed of 51.84 Mbps.

What is the physical topology of a WAN that uses point-to-point links between all sites?

Full Mesh