Chapter 8

Question 0

Circuit switched services

Answer 0

Oldest and simplest WAN approach
Uses telephone networks
Provided by common carriers

Used for POTS plain old telephone service , and ISDN
today

Question 1

WANs

Answer 1

Connect LANs and bns

Typically built by using leased circuits from common carriers like AT&T
Most organizations cannot afford to build their own WANs

Question 2

Architecture of circuit switched services

Answer 2

Simple design called a cloud architecture

Can be expensive. Payments based on traffic

Creates temp. Circuit until circuit is disconnected

Question 3

Pots

Answer 3

Plain old telephone service

Modem used to call another modem
Connection is made then data transfer begins
Connects to Internet using ISPs access point

Question 4

ISDN based circuit switched services

Integrated services digital network

Answer 4

Combines voice, video, and dat over one circuit
Also called narrowband
Slow acceptance
Provides digital dial up lines which need a Terminal Adapter, a network adapter and profile identifier

Question 5

ISDN service types

Answer 5

Basic rate interface-BRI- 2B+D
Two 64 Kbps B channels
One 16 Kbps control signaling D channel

Primary rate interface-PRI- 23B+D
23. 64 Kbps B channels
One 64 Kbps D channel which is basically T-1 service

Question 6

Circuit switched services pros vs cons

Answer 6

Simple
Flexible
Inexpensive
But
Needs to create connections each time
Low data rates

Question 7

Dedicated circuits

Answer 7

Leased full duplex circuits from common carriers
Create point to point links between organizations locations
Billed a flat rate

Question 8

Dedicated circuit equipment

Answer 8

Channel service unit CSU and data service unit DSU

May include multiplexers

Question 9

Ring architecture

Answer 9

Reliability- data can flow in both direction. But reduced performance

Performance- messages travel many nodes before reaching destination

Question 10

Star architecture

Answer 10

Easy to manage- central computer routes all messages in the network

Reliability- failure of central computer brings network down
Failure of any circuit or computer affects one site only

Performance- central computer becomes bottleneck under high traffic

Question 11

Mesh architectures

Answer 11

Combine benefits of star and ring

Use decentralized routing with each computer performing its own routing

Impact of losing a circuit is minimal
More expensive

Question 12

T-Carrier service

Answer 12

Most common dedicated digital circuit 
Ft1-64kbps
T-1 allows 24 simultaneous 64 Kbps channels at 1.544mbps
T-2 - 6.312 Mbps 
T-3 - 44.376
T-4- 274.176

Question 13

Synchronous optical network

Answer 13

SONET
ANSI standard for optical fiber transmission in gaps

Easily connected with Synchronous digital hierarchy

Optical carrier 1 - 51.84
OC 24 - 1.244 gbps
OC 3072 - 159.25

Question 14

Packet Switched Services

Answer 14

In both switched and dedicated services

Enable multiple connections to exists simultaneously on computers on same physical circuits

User pays fixed rate plus transmission charges

Question 15

Packet switching

Answer 15

Interleaved packers from separate messages for transmission

Short burst data

Interleaving bursts from many users to maximize the use of shared network

Question 16

Connectionless packet routing

Answer 16

Aka data gram

Adds destination and sequence number to each packet
Individual packets can follow different routes
Reassembled at destination

Question 17

Connection oriented routing method

Answer 17

Aka Virtual circuit or VC

Establishes end to end connection
All packets sent over same route
Same physical circuits carry many VCs

Question 18

Permanent virtual circuits

Answer 18

PVC
Established for long durations days or weeks
Changed only by network manager
Common
Behave like dedicated circuit networks

Question 19

Switched virtual circuit

Answer 19

Established dynamically on a per call basis

disconnected when call ends

Question 20

Data rates of virtual circuits

Answer 20

Users specific rates per PVC via negotiations
CIR committed information rate- rates exceeding the CIR add marked discard eligible DE ( discarded if network becomes overloaded)

MAR- maximum allowable rate - sends data only when capacity is available