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Lecture 1. Advanced Networking CSE 8344 Southern Methodist University Fall 2003 Mark E. Allen. Welcome!. My contact info: Mark E. Allen [email protected] 972 747 1490 phone / messages Email is a great way to reach me. Website engr.smu.edu/cse/8344

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Lecture 1

Lecture 1

Advanced Networking CSE 8344

Southern Methodist University

Fall 2003

Mark E. Allen


Welcome
Welcome!

  • My contact info:

    • Mark E. Allen

    • [email protected]

    • 972 747 1490 phone / messages

    • Email is a great way to reach me.

  • Website

    • engr.smu.edu/cse/8344

    • Will contain syllabus, notes, important dates, etc.


Outline for lecture 1
Outline for Lecture 1

  • Preliminaries

  • Discuss syllabus

  • Course goals and outline for course

  • Get into the content


Intro cont
Intro (cont)

  • Lecture format

    • Power point slides

    • Some written examples

    • Please ask questions! (unless it’s a tape)

  • NOTE:

    • Next two lectures will be pre-taped

      • Aug 29 10 AM (lecture 2)

      • September 5 10 AM (lecture 3)

    • Tapes will play at regular time also.



Motivation
Motivation

  • Purpose of networking: Sharing information between people.

    • Data is “information”

    • Voice is “information”

    • Evolution of networks

      • Teletype (Morse code) was low bit rate.

      • Voice (analog)

      • Video (analog television)

      • FAX

      • Dial-up Modems and DDS circuits

      • High-speed Internet


Network evolution

Voice networks

Analog voice

Digital trunks introduced.

Digital switching

Out of band

SS7, AIN, etc.

Wireless voice

Voice over IP

Data networks

Mainframes connected with SNA

Ethernet, Token ring, Novell IPX

Ethernet wins out

Internet

WWW

TCP/IP wins out

GigE and Wireless Ethernet catching on

Network evolution

Convergence



Data and multimedia now dominate traffic on the network
Data and multimedia now dominate traffic on the network

  • Eventually the network of the future will carry all types of service.

  • IP looks to be the “convergence layer” of the future.

  • Voice, video and data communications will eventually occur over a common network.


Motivation cont
Motivation (cont)

  • What are we really trying to get?

    • 1) Convergence: Voice, data, video, etc. all on the same user terminal

    • 2) Low cost: If we can afford it, we’ll use it.

    • 3) Mobility: We don’t want to be chained to a desk. (wireless, and the internet all give us freedom to access information wherever we are.)

    • 4) High bandwidth: Lots of speed will enable new and useful apps. Games, virtual reality, on demand movies, video conferencing, etc)

    • 5) Consumers want direct access into the data networks (B to B, e-commerce, databases, etc.)


The requirements drive the technology
The requirements drive the technology

  • QoS

    • Bandwidth, Delay, Jitter, etc.

  • Mobility

  • Cost

  • Power consumption

  • These things are all related.

    • More bandwidth usually consumes more power

    • Mobility requires low power.

    • Etc. .. etc.


Functions of network elements
Functions of network elements

  • Signaling / Addressing

    • Allows the users to control how information flows through the network (IP, dialed digits, etc.)

  • Switching

    • Devices necessary for steering information and signaling messages around the network

  • Multiplexing

    • Allows several information “flows” to share the same medium

    • We will discuss this in detail


Public vs enterprise networks

Millions of disparate customers

Distributed control

Usage based billing

911 and public safety concerns

Lots of security concerns

Legacy infrastructure

FCC Issues

Large geography

1 “customer”

Centralized decision making

No billing issues

Limited public safety concerns

Limited legacy concerns

Fewer FCC / regulatory issues.

Smaller geography

Public vs. Enterprise Networks


The layered protocol approach
The layered protocol approach

Applications

Transport

layer

Ex: TCP, UDP ...

defines how data is transported

“layer 4”

Network

layer

“layer 3”

Ex: IP, IPX …

defines the logical structure of the network

Datalink

layer

“layer 2”

Ex: ATM, Ethernet, Token ring…

defines how the media is accessed

Physical

layer

Ex: 10base2, 10baseT, SONET…

defines the voltages and physical connectors

“layer 1”


Limitations of osi model
Limitations of OSI model

  • The layered model

    • Provided clear demarcation points for protocol developers.

      • Physical layer people needn’t be concerned with software.

    • Was intended to be the roadmap for the “OSI” protocol (never materialized)

  • But…

    • Often creates duplication of efforts (error correction, restoration, management, etc.) $$$$

  • More on this later


Defining db
Defining dB

  • dB is a convenient way of describing loss and gain

  • dB can be added where multiplication is normally required

    XdB = 10 log (X)

    Note:

    3dB = 10 log (2)

    6dB = 10 log (4)

    9dB = 10 log (8)

Ex)

6dB

3dB

G=4

G=2

Gtotal= (2)(4) = 8 = 9dB


Defining dbm
Defining dBm

  • dBm describes power

    • YdBm= 10 log(Ymw)

  • Ex, 15 mwatts = 11.8 dBm

    30 mwatts = 14.8 dBm

    (note: 2X the power is 3dBm more)


Types of transmission mediums
Types of transmission mediums

  • Open copper pair

    • Low attenuation (few hundredths of dB per km at Voice frequencies)

    • Takes up lots of space (not used much anymore)

  • Paired wire

    • Many pairs in a bundle (up to a few thousand)

    • Can be buried or put on telephone poles

    • Higher attenuation than Open wire

    • Figure 1 shows the attenuation of copper pairs vs. frequency and wire gauge

    • Example: T1 (~1 MHz signal) experiences 30 dB of attenuation over 1 mile on 22 gauge wire

    • Common in buildings and LAN installs. 100BaseT runs on twisted pair


Types of transmission mediums cont
Types of transmission mediums (cont)

  • Coaxial cable

    • Good for higher bandwidth signals (several hundred MHz) for several km

    • Takes up much more space

    • Digital 50ohm used to carry DS3 signals

    • Analog 75ohm used to carry TV

  • Fiber optic cable

    • Extremely wide bandwidth (several THz)

    • Low attenuation 0.25dB per km


Loops to the home
Loops to the home

  • Transmission from phone to CO occurs on a single pair of wires

    • A “hybrid” on either side of the two wire circuits (one in the phone, on at the subscriber side of the switch)

    • Implemented using specialized transformers

    • Imperfections in the hybrid can cause echos (see figure 2)

  • Loading coils

    • Were installed extensively on long loops (3-15 mile)

    • Reduces attenuation at VF (~3500 Hz) but sharp cutoff at higher frequencies

    • Big problem for DSL installations


Pair gain systems
Pair-gain systems

  • Used to pack several subscribers onto a single loop

    • Acts time division multiplexor

    • Commonly called “subscriber loop carriers”

    • Present a problem when installing DSL

  • Some pair gain systems use Concentration

    • Acts as a statistical multiplexer

    • The terminal that needs the line grabs from the available pool. Some probability exists that the request is blocked.


Multiplexing scheme
Multiplexing scheme

  • FDM – Frequency Division Multiplexing

    • Several analog VF signals are mixed using different local oscillators

    • A5 Channel bank multiplexor was used to mux 12 voice calls into a group

    • See figure 3 for groups, supergroups, etc.

  • This scheme worked well with analog Voice channels and microwave transmission systems.


Transmission impairments cont
Transmission impairments (cont)

  • Distortion

    • Envelope delay refers to the delay seen by a particular frequency

    • Loops impose non-uniform envelope delay

    • Voice is not severely impacted but it’s a problem for modems

  • Echos

    • Occur when there is reflection at the opposite end of the line

    • Normally causes by hybrid imbalance (2W to 4 Wire)

    • Attenuation in the circuit helps the problem

    • Not noticed in short circuits less than 1500 miles (10 msec of delay per 1000 mile circuit) which experience 30 msec of delay (round trip)

    • Old echo suppressors used active impedence device in reverse path

    • New echo “cans” are DSP based and use a variant of adaptive filters.


Impairments cont
Impairments (cont)

  • Via Net Loss (VNL) is built-in loss proportional to the length of the circuit.

    • Combats ringing and echo

  • Zero transmission level point (TLP)

    • 0TLP : Reference point in a circuit into the first switch

    • Measurements taken along the path are referenced back to 0TLP

    • (see examples)


Digital signals
Digital Signals

  • Two Symbols: Binary SignalingSymbol is a.k.a. Bit

  • M Symbols: M-Ary SignalingM is usually a power of 2Log2M bits/symbol

  • Baud rates same? Symbol shapes similar? If yes..Bandwidth required is similarM-Ary signaling allows increased bit rate Symbols get closer together if Power fixed Receiver detection errors more likely in presence of noise

  • Bandwidth, Bit Rate, SNR, and BER related


Example binary signal
Example: Binary Signal

  • Serial Bit Stream (a.k.a. Random Binary Square Wave)

    • One of two possible pulses is transmitted every T seconds.Here the symbol is either a positive or negative going pulse.

    • When two symbols are used, a symbol is known as a ‘bit’.

volts

If T = .000001 seconds, then

this signal moves 1 Mbps.

+1

0

time

-1

T


Example m ary signal
Example:M-Ary Signal

  • One of M possible symbols is transmitted every T seconds.EX) 4-Ary signaling. Note each symbol can represent 2 bits.

volts

+1.34

If T = .000001 seconds, then

this 1 MBaud signal moves

2 Mbps.

+.45

time

-.45

-1.34

T


M ary signaling
M-Ary Signaling

  • Bandwidth required

    • Function of symbols/second & symbol shape

    • The more rapidly changing is the symbol, the more bandwidth it requires.

    • An M-Ary signal with the same symbol rate and similar symbol shape as a Binary signal has essentially the same bandwidth.

  • The previous two slides show...

    • Equal Power & Equal Bandwidth Signals

    • M-Ary signal transfers more bits/second BUT detection errors more likely at the receiver


Wired physical links
Wired Physical Links

  • Untwisted Pair Cabling

    • Highly susceptible to EM interference

    • Bad choice for telecom systems

      • Example: Speaker Wires, Power Lines

  • Twisted Pair Cabling

    • Fairly resistant to EM interference

    • Bandwidth typically in 1-2 digit MHz

      • Examples: LAN wiring, Home telephone cables



Wired physical links1
Wired Physical Links

  • Coaxial Cable

    • Resistant to EM interference

    • Bandwidth typically in 2-3 digit MHz

      • Example: Cable TV

  • Fiber Optic Cable

    • Immune to EM interference

    • Bandwidth in GHz to THz


Physical layer ailments
Physical Layer Ailments...

  • AttenuationSignal power weakens with distance

  • DistortionPulse shapes change with distance

    • Copper cablingHigh frequencies attenuate fasterPulses smear

    • Fiber cablingFrequencies propagate at different speedsDispersion


Generating a square wave
Generating a Square Wave...

5 Hz+

15 Hz

+

25 Hz

+

35 Hz

1.5

0

-1.5

1.0

0

cos2*pi*5t - (1/3)cos2*pi*15t

+ (1/5)cos2*pi*25t - (1/7)cos2*pi*35t)


Effects of dispersion
Effects of Dispersion...

5 Hz+

15 Hz

+

25 Hz

+

35 Hz

1.5

0

-1.5

1.0

0

cos2*pi*5t + (1/3)cos2*pi*15t

+ (1/5)cos2*pi*25t + (1/7)cos2*pi*35t)In this example the 15 and 35 Hz signals have suffered a phase shift (which can be caused as a result of different propagation speeds) with respect to the 5 and 25 Hz signals. The pulse shape changes significantly.


Receiver detection
Receiver Detection

  • SNR tends to worsen with distance

  • Digital Receiver Symbol Detectors

    • Examine received symbol intervals (T sec.)

    • Decide which of M symbols was transmitted

    • Single Sample DetectorsSample each symbol once Make decision based on sample value

    • Matched Filter Detectors (Optimal)Sample each symbol effectively an infinite number of timesMake decision based on an average


Snr average signal power average noise power
SNR = (Average Signal Power) Average Noise Power

Binary Signal10 Bits showing


Snr 100
SNR = 100

Sequence = 0011010111


Snr 10
SNR = 10

Signal a sequence +1 and -1 volt pulses




Single sample detector snr 1

4.5

0

4.5

0

20

40

60

80

100

0

k

99

Single Sample Detector: SNR = 1

Threshold is placed midway between nominal Logic 1 and 0 values.

Detected sequence = 0011010111 at the receiver,

but there were some near misses.


Matched filter detector snr 1

4.5

0

4.5

0

20

40

60

80

100

0

k

99

Matched Filter Detector: SNR = 1

Orange Bars are average voltage over that symbol interval.

Averages are less likely to be wrong.


Channel capacity c
Channel Capacity (C)

  • C = W*Log2(1 + SNR) bps

    • W = channel bandwidth (Hz)

    • SNR = channel signal-to-noise ratio

  • Maximum bit rate that can be reliably shoved down a connection

  • EX) Analog Modem (30 dB SNR)C = 3500 *Log2(1 + 1000) = 34,885 bps

  • EX) 6 MHz TV RF Channel (42 dB SNR)C = 6,000,000 *Log2(1 + 15,849) = 83.71 Mbps


Why not just keep amplifying to counter act attenuation
Why not just keep amplifying to counter-act attenuation?

  • Amplifiers add noise as they boost the power.

    • For analog signals, this degrades the signal to noise ratio (SNR)

    • With digital signals, the SNR (Eb/No) is degraded until the system takes errors

  • Low noise and multistage amplifiers are used to combat this problem.


Amplifiers in series
Amplifiers in series

SNRin

SNRout

G2

G1

  • A pre-amp with a low noise figure reduces the overall noise figure while providing high gain

    • For example, using this equation, the effective noise figure of a preamp with a gain of 20dB and noise figure of 3 dB followed by an amplifier of gain 30dB and noise figure 9 dB would be 2+(8-1)/100 = 2.07 or 3.16 dB. The total gain would be 50 dB. (make sure to use non-dB numbers in the equations)

F2

F1


Overview of telephony
Overview of telephony

  • Telecommunication networks were originally designed for voice

    • Analog signals of 4 kHz bandwidth

    • Sampled at 8 kHz with 8 bits of quantizing levels for 64kbps circuit

  • Digital TDM multiplexing has been the technique of choice since the late 70’s.


Multiplexing formats
Multiplexing Formats

  • Why multiplex??

    • Combine several lower bandwidth signals onto a single faster channel

    • Saves running thousands of individual wires

    • Allows single carrier for several signals

  • Frequency division multiplexing

    • Multiple frequencies “stacked”

    • This was done in the analog days.

    • Each voice channel was mixed up to higher center frequency.

    • Doesn’t lend itself to digital technology

    • Requires very (spectrally) flat channels


Fdm hierarchy
FDM Hierarchy

With digital T-Carriers, this is now obsolete

From: Digital Telephony Bellamy, chapter 1


Fdm cont
FDM (cont)

From: Digital Telephony Bellamy, chapter 1


Time division multiplexing
Time division multiplexing

  • With TDM, every low speed signal gets a fixed amount of bandwidth in the high speed signal

Low speed

High speed


Current north american tdm multiplexing scheme
Current North American TDM multiplexing scheme

T1 1.544

Mbps

24

Channel

Bank

44.736

Mbps

DS0

64kbps

M13

2.5

Gbps

28

OC48

48

OC192

10

Gbps

4


What is a t1
What is a T1?

  • Four-wire circuit: one pair for transmit, one for receive.

  • Full-duplex: information goes both ways all the time.

  • Digital: transports binary data or voice

  • TDM: Capable of transporting 24 digitized voice channels.

  • Pulse code format: Individual voice channels are normally digitized using PCM.

  • Framed synchronous transmission: samples from each voice channel (8 bits) are taken and sent sequentially. A frame bit is added resulting in 193 bit frames.


Analog to pcm conversion
Analog to PCM conversion

Understanding SONET/SDH, Kartalopoulos


Analog to dso with codec
Analog to DSO with CODEC

Understanding SONET/SDH, Kartalopoulos


Ds0 to ds1 mux channel bank
DS0 to DS1 MUX (channel bank)

Understanding SONET/SDH, Kartalopoulos


European muxing standard
European muxing standard

Understanding SONET/SDH, Kartalopoulos


T1 cont
T1(cont)

  • Note: each voice channel is sampled at 8000 hz, so a T1 must send 193 bits in 125 usec, or 1.544 Mbps.

  • Line coding for T1 is bipolar, AMI. Every other 1 is represented by a positive pulse. 0’s are represented by no pulse.

    • This gives the signal zero average value.

    • The required bandwidth is 770 kHz.

  • T1 uses byte synchronous transmission

    • Receiving end needs to distinguish which channels are which and which 8 bits make up the bytes.

    • Framing bits make this work


Evolution of t1 muxes
Evolution of T1 muxes

  • T1 to DS0 mux commonly called “channel banks”

  • D1 channel bank format

    • Robbed bit signaling

    • LSB of each byte was used to carry signaling for voice channels (no significant degradation)

    • If data was carried, 56k was max amount

  • D2 – D3 channel banks were small improvements

  • D4 channel bank was common and introduced the “superframe” format.


T1 superframe
T1 Superframe

  • Superframe concept: 12 frames together became a “superframe” framing bits occur in a special pattern.

    • Allows only 6th and 12th frames to give up signaling bits.

    • The 24 signaling bits in the 6th frame are called the A bits, 24 in the 12th frame are called the B bits.

    • B8ZS was introduced to solve the “ones density rule” when carrying data: In every 24 bits, there must be at least 3 pulses and no more than 15 consecutive zeros.

      • Recall that 8 zeros are substituted with a pattern then a BPV is generated.


D5 extended superframe esf
D5 Extended superframe (ESF)

  • There was a desire to improve the D4 SF format:

    • More performance monitoring capabilities

      • Customer equipment didn’t pass through Bipolar Violation information

    • 8kbps F bits are redefined to create a 2kbps framing sequence, 4kbps data link channel, and 2kbps CRC channel.

      • Data link channel used to control end equipment

      • 24 rather than 12 frames are now used, framing bits occur in frames 6, 12, 18 and 24. These bits now become the A,B,C,D bits for each channel.


Uses for t1
Uses for T1

  • T1 was primarily used for voice trunks between voice switches.

    • Now many customers use to connect PBX

    • May buy T1 to the internet

      • Connect a Router to ISP’s router

      • Channel Service Unit (CSU) is often used

Central

office

Customer premise

T1

Router

CSU

Internet


Other common tdm rates
Other common TDM rates

  • E1: European version of the DS1, contains 32 voice channels

  • DS3: multiplexed version of 28 DS1’s

    • DS3 uses “bit-interleaving” rather than byte-interleaving in DS1 format.

    • DS3 is 44.736 Mbps

    • B3ZS is used to maintain 1’s density.

    • Multiplexing is done in two stages:

      • 4 DS1 signals are muxed using pulse stuffing synchronization to form a DS2

      • 7 DS2 are muxed using a fixed pulse stuffing synchronization to form a DS3 signal.


Ds3 muxing cont
DS3 muxing (cont)

  • In DS1 to DS2 muxing, stuffing is used to get rate to 1.545796 Mbps (with overhead).

    • Each DS1 can be running at a different speed ranging from 1.540 to 1.545 Mbps

    • Bit interleaving and bit stuffing allow all the DS1s to maintain their independent rates.

    • 48 bits are collected to make a block, 6 blocks to make a subframe, 4 subframes to make DS2 frame. (subframes are not individual DS1s)”

  • See figures 1 and 2 in TTC “Fundamentals of DS3”


Ds3 muxing cont1
DS3 muxing (cont)

  • For DS2 to DS3 muxing, 84 bits make a block, 8 blocks make a subframe, 7 subframes make a frame.

    • Bit stuffing may again be used incase DS2s are not at the same rates.

  • Note that C-bits are used in both stages 1>2 and 2>3 to control bit stuffing.

    • If all DS2s are in sync, this is not necessary for second stage

    • C-bit format uses C bits in DS2>DS3 stage for other purposes.


Drawbacks to ds3 based transport
Drawbacks to DS3 based transport

  • Difficult to drop individual voice or DS1 channels

    • Bit muxing and bit stuffing makes channels locations unknown

  • Not fast enough for some applications

    • No standard Proprietary muxing schemes were developed to transport 12 or 24 DS3 on a fiber link.

    • Interconnects between carriers at rates higher than 45 Mbps were complex

      • Required them to purchase same type of fiber muxes.

  • Runs on Coax vs. unshielded twisted pair (UTP) or fiber.


Sonet is defined to address these problems
Sonet is defined to address these problems

  • Standardized rates beyond 10Gbps on fiber

  • “Synchronous” for improved add/drop capability

  • Standards for both Electrical and Optical interfaces.

  • Backward compatible with T1, DS3, E1, E3, and other “async” standards.


Traditional multiplexing hierarchy
Traditional multiplexing hierarchy

DS0

64 kbps

T1 1.544

Mbps

24

Channel

Bank

44.736

Mbps

M13

2.5

Gbps

28

OC48

10

Gbps

48

OC192

4



Sonet
SONET

  • SONET byte oriented frame format

    • Path, line, and section

    • Multiplexing format

  • Virtual Containers

  • Synchronous payload envelope (SPE)

  • Pointers

    • Timing issues

    • This is what makes SONET synchronous -- the payload can float in the SONET frame.

  • Overhead

    • Line, Section, and Path

  • Performance monitoring



Sonet network
SONET Network

LINE

SECTION

Terminal

(LTE)

ADM

or

DCS

(LTE)

Terminal

(LTE)

REG

REG

REG

Router

(PTE)

Router

(PTE)

PATH


Sonet networking
SONET Networking

810 bytes x 8000 frame/sec x 8 bits = 51,840,000 bps

OH PAYLOAD

OH PAYLOAD

OH PAYLOAD

STS-1

Synchronous

Payload

Envelope

9 rows

90 columns (87 columns of payload)

3 columns of

transport overhead:

Section overhead

Line overhead

Path overhead


Sts 1 frame

9 Rows

90 Columns

BIP-8/BI: Parity Checking

Section Trace/Growth

STS-1 Frame

A1

A2

J1

JO/Z0

B1

E1

F1

B3

D1

D2

D3

C2

87 Columns of Payload

STS-1 Synchronous

Payload Envelope

(STS-1 SPE)

H1

H2

H3

G1

B2

K1

K2

F2

D4

D5

D6

H4

D7

D8

D9

Z3

BIP-8/B2: Error Monitoring

D10

D11

D12

Z4

S/Z1

E2

Z5

M0/M1

Z2


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