NETWORKS

• Covering– High speed switching fabrics

– Twisted pair

– Mediums

– Fiber optics

– Radio

– Ethernet Coax

NETWORKS

– Logarithms

– Channel capacity

– Hartley-Shannon Law

– Review of the Layers

– Things you need to get started on a LAN

High Speed Switching Fabrics

• Aside from the Bus topologies, there are many others, with higher throughput, like

• ring

• Transputer Topology

• Torus Topology

• Cray T3D

The Transputer Topology

4 way connectivity

The Torus Topology

4 way connectivity

Torus Topology

5 way connectivity

Cray T3D, Torus Topology

6 way connectivity

MacRadioModemASYNC

SerialSYNC Serial

CPU Memory

TNC

We left out the redundant curcuitry in the gray box to make poor mans packet

Diagram of a typical packet radio setup

Twisted Pair• Typically a balanced digital line

• 2 conductor insulated wire

• Twisting the wire minimizes the electromagnetic interference

• A primary medium for voice traffic

• used as serial cable to hookup networks

Twisted Pair

• The repeat coil (transformer) or Op-Amp can be used

S

-S

I

S+I

-S+I

+-

S+I-(-S+I)=2S

Twisted Pair

• In telephone modem terms this is known as a DAA (Data Access Arrangement).

Mediums

• UTP (unshielded twisted pair)– typical voice line

– Generally good for star LAN short haul 10 Mbps

• STP (shielded twisted pair)– level 5 data grade (100 Mbps)

• RS-422 – balanced serial data communications

• RS-232 – unbalanced serial data communications

Mediums

• Coax– CATV (community antenna TV)

– telephone long line via FDM carries 10,000 voices

– LAN-WAN

– cable TV

Mediums

• Fiber Optics– use total internal reflection

– This occurs in a transparent medium whose index of refraction is higher that surrounding medium

– optic fiber is a wave guide in the 10 raised 14 to 10 raised 15 hz range

Fiber Optics

• multimode– different rays have different path lengths,

loss occurs

• multimode-graded index– variable core index, focuses rays more

efficiently that multimode

• single mode – only the axial ray passes, most efficient.

Fiber Optics

• LED (light emmiting diode)– inexpensive

• ILD (injection laser diode ) – more expensive (more efficient and higher

bandwidth that LED).

• Detectors– Photo Diodes

Fiber Optics

• light propagates best at 850, 1300 and 1500 nm

• 640 nm = wavelength of HE-NE red = .64 micro meters

• ultra pure fused silica is best, plastic is cheapest and worst

Fiber Optics– bandwidth - 2 Gbps (typical)

– smaller size and weight than copper

– lower attenuation than coax

– electromagnetically isolated

– greater repeater spacing, 5 Gbs over 111 km w/o repeater

– phasing out cable.

Jacketcladding, one for each fiber

core, one or more strands

Radio

• Microwave– line-of-sight

– parabolic dishd 7.14 kh distance to horizon

d in meters

h height of antenna in meters

k adjustment factor, microwaves bend with the curature of the earth

Ethernet Coax

• For Ethernet coax – ASIC’s which give a digital interface to a

bus topology LAN

– For example, the Crystal Semiconductor Corporation CS83C92 is a Coaxial Transceiver Interface on a chip

Ethernet Coax

RXICDSTXOGND

RX+RX-CD+CD-TX+TX-

CS83C92

Shield

Ethernet Coax

• CS83C92– Balanced serial inputs

– Uses Manchester codes

– All operations with IEEE 802.3 of the 10Base5 (Ethernet) and 10Base2 (Cheapernet) standard

Ethernet Coax

• CS83C92 have– equalizers

– amplifiers

– idle detectors, receiver squelch circuits

– collision testers

– oscillators

– differential line drivers

– (with other stuff too!!!)

• A manchester code convert chip is also needed

Logarithms

• Log Review

if x ay then y loga x

so

if x 210 then 10 log2 x

Logarithms

• For example

find log2 4096

4096 2y

ln 4096 y ln 2

ln 4096ln 2

y12

Logarithms

so

log2 x ln xln 2

if base = B then

logB x ln xln B

log10 xlog10 B

Logarithms

• Laws of Logarithms

loga (xy) loga x loga y

loga (x / y) loga x loga y

loga xn n loga x

• Intermodulation noise– results when signals at different

frequencies share the same transmission medium

• the effect is to create harmonic interface at

f1 f 2 and / or f1 f 2

f1 frequency of signal 1

f2 frequency of signal 2

• cause– transmitter, receiver of intervening

transmission system nonlinearity

• Crosstalk– an unwanted coupling between signal

paths. i.e hearing another conversation on the phone

• Cause– electrical coupling

• Impluse noise– spikes, irregular pulses

• Cause– lightning can severely alter data

Channel Capacity

• Channel Capacity– transmission data rate of a channel (bps)

• Bandwidth– bandwidth of the transmitted signal (Hz)

• Noise– average noise over the channel

• Error rate– symbol alteration rate. i.e. 1-> 0

Channel Capacity

• if channel is noise free and of bandwidth W, then maximum rate of signal transmission is 2W

• This is due to intersymbol interface

Channel Capacity

• Example

w=3100 Hz

C=capacity of the channel

c=2W=6200 bps (for binary transmission)

m = # of discrete symbols

C = 2Wlog2m

Channel Capacity

• doubling bandwidth doubles the data rate

if m=8c 2(3100 hz)log2 8 18,600 bps

Channel Capacity

• doubling the number of bits per symbol also doubles the data rate (assuming an error free channel)

(S/N):-signal to noise ratio

(S / N)dB 10logsignal powernoise power

Hartley-Shannon Law

• Due to information theory developed by C.E. Shannon (1948)

C:- max channel capacity in bits/second

C w log2 (1SN

)

w:= channel bandwidth in Hz

Hartley-Shannon Law

• Example

W=3,100 Hz for voice grade telco lines

S/N = 30 dB (typically)

30 dB = 10 logPsPn

Hartley-Shannon Law

3 logPsPn

log10

PsPn

3

103 PsPn

1000

C 3100 log2 (11000) 30,898 bps

Hartley-Shannon Law

• Represents the theoretical maximum that can be achieved

• They assume that we have AWGN on a channel

Hartley-Shannon Law

C/W = efficiency of channel utilization

bps/Hz

Let R= bit rate of transmission

1 watt = 1 J / sec

Eb=enengy per bit in a signal

Hartley-Shannon Law

S = signal power (watts)Tb the time required to send a bit

R =1

T b

Eb STb

EbN0

energy per noise power density per hertz

Hartley-Shannon Law

EbN0

S / RN0

SkTR

k=boltzman’s constantby

Eb STb

S EbTb

S / R Eb

N0 kTR

Hartley-Shannon Law

assuming R=W=bandwidth in HzIn Decibel Notation:EbN0

S 10 log R 228.6dbW 10 logT

Hartley-Shannon Law

S=signal powerR= transmission rate and -10logk=228.6So, bit rate error (BER) for digital data is a decreasing function of Eb

N0

For a given , S must increase if R increases

EbN0

Hartley-Shannon Law

• Example

For binary phase-shift keying =8.4 dB is needed for a bit error rate of

EbN0 10 4

let T= k = noise temperature = C, R=2400 bps & Pe 10 4 BER

Hartley-Shannon Law

• Find S

S EbN0

10 logR 228.6dbW 10logT

S 8.4 10 log2400 228.6dbW 10 log 290

S=-161.8 dbw

ADC’s

• typically are related at a convention rate, the number of bits (n) and an accuracy (+- flsb)

• for example– an 8 bit adc may be related to +- 1/2 lsb

• In general an n bit ADC is related to +- 1/2 lsb

ADC’s

• The SNR in (dB) is therefore

SNRdB 10 log10SN

whereS 2n

N 12

2 n 2 n 1

SNRdB 10 log10 22n1 (20n 10)log10 2

SNRdB 6n 3about

Review of the Layers

• Physical Layer (bits)

• The Link Layer (frames)

• The Network Layer (packets)

• The Transport Layer

• Session Layer

• The Presentation Layer

• The Application Layer

Physical Layer

• The function is to send & receive bits (marks & spaces)

• deals with– Physical connections (duplex or half

duplex)

– Physical service data units (PSDU’s) one bit in serial xmission, nbits in parallel xmission

Physical Layer

– circuit identification

– bit sequencing

– notification of false conditions

– deriving quality of service parameters

– modulation and demodulation

– signaling speed

Physical Layer

– transmission of data and handshaking signals

– characterization of communication media

– maintains an actual electrical connection with its peers. Other layers uses virtual connections

The Link Layer

• The Link Layer of data link control arranges the bits into frames

• Most common protocol is ISO high-level Data Link Control Procedures (ISO 3309)

The Link Layer

• This layer– Establishes and releases one or more link

connections

– exchanges data-link service data units (DLSDUs)-frames

– identifies end-points

– keeps DLSDUs / frames in proper sequence

The Link Layer

– notifies the network layer when errors are detected

– controls data flow

– selects optional qualityof service parameters

The Network Layer

• Arranges data into packets– Adds the network information to the

frames to form packets

• SLIP– Serial Line Internet Protocol is network

layer protocol

– uses the EIA-232 Physical layer

– Internet protocol is a network layer protocol

The Network Layer

– keep track of the network node address while routing outgoing packets and recognizing packets that are intended for the local node

The Network Layer

• ARP– Address Resolution Protocol provides

addresses form required by IP

– User may specify the datagram route

– APR will stay aware of manually generated routing tables for the datagram routing function

The Network Layer

•in CCITT x.25 protocol the network layer is called the packet layer.

The Network Layer

• The function provided by the network layer are

– network addressing and identifiers

– network connections and release

– transmission of network service data units NSDU’s (packets)

– quality of service parameters

The Network Layer

– notifies the transport layer of errors

– flow control

– expedited service network

– may provide sequenced delivery

The Network Layer

• Two types of network layer protocols

– connection oriented

– connectionless

Connection Protocol

• set up a virtual circuit (VC) between two end points

• Advantage is that since each packet does not contain complete addressing information, the overhead is lower

Connectionless Protocol

• Uses a datagram (DG) which contains complete addressing information in each packet so that it can use any variable route through the network

Connectionless Protocol

• The advantage is that packets may freely choose the best available routes for the transfer rather than being stuck on a VC with variable quality

The Transport Layer

• uses transport protocol data units (TPDU)

• TPDU = packets + transport layer data

• TCP = transmission control protocol

The Transport Layer

• This layer ensures that– all data send is received completely

– is sequenced

– transmission of TPDU messages

– multiplexing and demultiplexing to share a net connection between two or more Xport connections

The Transport Layer

– error detection

– error recovery

– connection establishment

– data xfer

– release of connections

The Transport Layer

• CCITT transport protocol in X.224 says there are 5 classes of transport classes

– 0. simple class

– 1. error recovery

– 2. multiplexing

– 3. error recovery and multiplexing

– 4. error detection and recovery class

The Transport Layer

• The amount of work done is dependent on the protocol (VC or datagram) used at the network layer

The Transport Layer

• Datagrams may arrive out of sequence, in a connectionless net, and buffers may be needed to resequence

• connection nets allow a leaner transport layer

Session Layer

• Organizes data into SPDU (session protocol data units)

Session Layer

• This layer does– dialog management

– Data flow control

– mapping address with name (domain name service)

– graceful or abrupt disconnection

– buffering data until delivery time

Session Layer

• has phases of service– connection establishment

– data xfer

– connection release

Presentation Layer

• responsible for the terminal management

• Performs – transfer of syntax for character sets, text

strings data display format, graphics file organization and data types

Presentation Layer

– data encoding, decoding and compacting

– interpret character sets ( i.e. ASCII)

– code conversion

Application Layer

• The only layer which does not interface with a higher one

• It does– log in identification of communication

partners

– password checking and authority to communicate

Application Layer

– determine adequacy of resources

– determine acceptable quality of service

– synchronization of application programs

– selecting the dialog procedures

– agreement on error-recovery responsibility

– procedures for control of data integrity

– identifying data syntax constraints

Application Layer

• has 5 groups– 1. System management protocols

– 2. Application management protocols

– 3. System protocols

– 4. Industry specific protocols

– 5. Enterprise protocols

Things you need to get started on a LAN

• IP ADDRESS– this a 32 bit number issued by your local IP

coordinator

– it is expressed as 4 numbers separated by periods

– looks like 44.112.0.200.

Things you need to get started on a LAN

• HOST TABLE– A file that list all the folks around you that

also have IP addresses

– It must have your IP address and hostname (call sign) at least

Things you need to get started on a LAN

• HOST TABLE– you can get this from your coordinator

– It looks like this

44.112.0.1 unix.n3cv1

44.112.0.2 w3vc

44.112.0.3 darth.wa3yoa