CIRCUITS

Circuit Configuration

Logical versus Physical

Network configuration: a "map" of your network wiring, servers and nodes.

Point to point (PtP): 2 computers talking to each other exclusively. 
Primary use is to connect a lan to a backbone network via a gateway router.

Multipoint: 2 or MORE computers talking to each other having access to the 
same circuit.
Primary use is to connect nodes (pcs and end-user devices) on a lan OR in a common enterprise network
VPN is a logical multipoint circuit, but is usually carried over a physical PtP network.

Data Flow

• Full duplex: both directions same time; requires acknowledgement of transmission at a very low level, at every byte or packet.
• Half duplex: both directions, not at same time - faster for file download but slower for interactive - like a walkie-talkie
• Simplex: Can only send or receive (1 way) - television transmission

Asymmetrical: Receive at 1 speed and send at another OR receive on 1 circuit 
and send on another. Examples: aDSL, satellite feed, cable modems.
Advantages: Works well for endusers that are primarily requesting and receiving data.
Disadvantages: Slow uploads. If you need to send large files OR you have a server at your site.

Symmetrical: Upload/download speed the same.
Examples are Local Ethernet, T1 & T3, Fiber Networks, Metro-Ethernet, SDSL (rare).

Definitions:

Medium (media) : What sort of wiring (or waves) is used to form the circuit, e.g. copper such as coax or twisted 
pair, fiber optic, radio such as: 2.4 Ghz wireless, microwave, 4g.

Circuit: The path the data takes, also called the Link.

Line: refers to the physical part of the circuit.

Channel: an electronic link from 1 point to another. Some circuits can carry 
MANY channels thru MULTIPLEXING.

Modem: Modulator/Demodulator: Converts one data link protocol to another, not just analog. Soho DSL routers are usually called DSL modems. Point to Point.

They convert ATM packet switched network packets into Ethernet.

DSL: Digital Subscriber Line. Dedicated (hard wired). Packet Switched Point to Point.

ISDN: Integrated Services Digital Network. No longer common. Circuit Switched Point to Point .

Line: refers to the physical part of the circuit.

Channel: an electronic link from 1 point to another. Some circuits can carry 
MANY channels thru MULTIPLEXING.

MEDIA in detail:
http://en.wikipedia.org/wiki/Twisted_pair

Twisted pair: born from telephone wiring. Twists the receive pairs and transmit pairs of the wires together. 
This reduces electrical interference (RF) by allowing the RF to cancel itself 
out. It can't be run that far, about 500 meters due to signal loss. Ideal for LANS.
cat 3: telephone
cat 5, cat 5e: UTP, or STP, 100-350 Mhz (100 megabits/sec)
cat 6: UTP or STP, 350-500 Mhz, gigabit Ethernet (GigE)
cat 6a, STP, or SSTP, 500-600 Mhz, 10 gig Ethernet
cat7 (unofficial) aka Class Fa. 1000 Mhz, 10 gig Ethernet, longer distances
UTP: unshielded twisted pair, cheapest
STP: shielded twisted pair: metal foil around pairs.
SSTP: screened shielded twisted pair, braided outer shield around 4 separated pairs.
SFTP: screened foiled twisted pair, typically same as SSTP.

Coax Cable: Like your cable tv cable. Single solid copper strand surrounded 
by a metal braided shield. Less susceptable to RF interference. Can run 
for thousands of meters.
Examples of cable type: RG-58, RG-6, RG-192.
Different end connectors! BNC (Arcnet/Radio equipment, F-Connector (cable TV), SMA (antennas)

Fiber Optic: Thin strands of clear glass or plastic surrounded with cladding 
via laser or led light waves. Much faster. Can approach distances of 100s 
of miles. Step Index, Graded Index and Single index fiber types. Very 
secure because it is difficult to "tap in" but also expensive and difficult to repair a cable cut. 
Typically used in backbone or highspeed LONG DISTANCE networks.

The above 3 are called GUIDED media because they are guided by physical 
cable.

There is also RADIATED media:

Infrared media: low frequency light waves. Used for short distances. Its 
inexpensive. Often used to transmit data from keyboards or personal 
information devices (e.g. 3com Palm Pilot) to a desktop PC.

Microwave: very small (high frequency waves) that are close in frequency to 
the light spectrum. Lots of data can be transmitted quickly. However, since it 
behaves like light, towers need line of sight, susceptible to rain, reflections, 
physical blockage, curvature of the earth. Used most often for telephone 
communications between metropolitan and rural areas 75 miles or less away.

Satellite: similar to Microwave except signal is bounced off a satellite 
anywhere from 500 to 22,500 miles above the earth. Received with a 
parabolic dish. Ku Band is very short satellite waves that can be caught with 
a disk as small as 12". This is what DirecTV and DirecPC is. Satellites that 
are 22,300 miles up are geosynchronous (stay in 1 place - relatively), 
problem is that they are very far away and add .5 secs to the transmission. 
VLEO satellites (very low earth orbit) are starting to get used more, but they 
are more difficult to maintain, plus the ground hardware must constantly 
"track" the satellite as it must MOVE to keep from falling to the earth.

Media Selection:
Take into consideration:

Data volume needs (type of data)

Symmetry of data

Availability
Security

Cost

Acceptable error rates

Distance

Number of senders/receivers

DIGITAL TRANSMISSION OF DIGITAL DATA

Analog: electrical, looks at varying degrees of frequency, waves, voltage, etc. 
used mostly for audio and video signals

Digital: binary, on-off, looks more like a square wave if you were to draw it.

Which is better for data? DIGITAL 
        Fewer errors - ON OR OFF, nothing in between 
        More efficient - easier to multiplex 
        Higher throughput 
        More secure - easier to encrypt 
        Integration of voice, data, video is possible
Easier to store and duplicate, the 1000^th copy of digital data = the original.

Is digital always better for everything?  No. Digital data is discrete numbers, and 
can only be expressed in steps, whereas analog can be infinitely variable. 
Use analog to go to speakers/sound equipment.

To more closely approximate analog, digital data increases, i.e. more kbits per second of audio or video. Media capacity must be higher for digital data that approximates analog data.

Coding: All the characters on the keyboard, plus the numbers, plus lowercase 
versions and special characters like the RETURN, DEL, etc... are all coded into 
bytes. The most common is the ASCII code scheme. IBM mainframes use 
EBCDIC.

Analog transmission of digital data. Modems (modulator/demodulator). Used to 
convert digital signals into high and low frequencies of sound. Required to 
transmit data over phone systems.

North American Telephone system. 
Primarily the end user (customer) has a POTS line (Plain old telephone service) 
which is analog and limited to a 4000 Hz range. 
ISDN (integrated services digital network) , still available but rare. Uses same phone wiring but transmits digital signal. Limited distance.
 
BANDWDTH: 
Typical sound wave - sine wave - it has a peak, a valley and a 
midpoint or zero point.

Amplitude: height of the wave 
Frequency: # of waves transmitted in a specific time slot. 
Phase: Where the wave begins. A 0-degree phase starts up and to the right. 
Down and to the right is a 180-degree phase.

Modulation: controlling the amplitude, frequency and phase to DIFFER it in order 
to  transmit signals.

Analog Telephone equipment allocates 4000 Hz (height of the wave) to voice lines. This 
would mean that 2400 baud is about the MAX you could get on a modem. Its 
actual max is 3000 but 2400 became an acceptable standard. How 
do we get 56k modems? PHASE MODULATON. You cut the wave in half and 
phase it a a a few degrees for 4800, cut it in half again and phase it again for 
9600 baud, etc, etc.Usually it is combined with AMPLITUDE MODULATION

The modulation techniques are refered to as CODECs (coder/decoders). Important for VoIP and Video transmission.

# of bits/second, encoding technique, analog data type.

Common Codecs: PCM, MPEG, AVI, JPEG.

VoIP: Voice over IP

2 Session Protocols: SIP and IAX
Protocols for voice and video: RTP (udp)
Common Codecs: G711u (mu-law: USA), G711a (alaw: Europe)
G729: Highly compressed.
refer to: http://en.wikipedia.org/wiki/Codec

IMPLICATIONS FOR MANAGEMENT

SUMMARY

End of Lecture 3

© 2014 Jake Messinger (all rights reserved)
Dept of Decision and Information Sciences (MIS)
Bauer College of Business
University Of Houston