session 4. transmission systems and the telephone network
DESCRIPTION
Session 4. Transmission Systems and the Telephone Network. Dongsoo S. Kim Electrical and Computer Engineering Indiana U. Purdue U. Indianapolis. A. A. A. A. Trunk group. B. B. B. MUX. MUX. B. C. C. C. C. Multiplexing. - PowerPoint PPT PresentationTRANSCRIPT
Session 4. Transmission Systems and the Telephone Network
Dongsoo S. KimElectrical and Computer EngineeringIndiana U. Purdue U. Indianapolis
ECE/IUPUI
Intro to Computer Communication Networks
4-2
Multiplexing
Sharing of expensive network resources – wire, bandwidth, computation power, …Types of Multiplexing
Frequency-Division Multiplexing Time-Division Multiplexing Wavelength Division Multiplexing Code-Division Multiplexing Statistical Multiplexing
B
C
A
B
C
A
B
C
A
B
C
A
MUXMUX
Trunkgroup
ECE/IUPUI
Intro to Computer Communication Networks
4-3
Frequency Division MultiplexingBandwidth is divided into a number of frequency slotsThe very old technology
AM – 10 kHz/channel FM – 200 kHz/channel TV – 60 MHz/channel Voice – 4 kHz/channel
How It works Each channel is raised in frequency by a different amount from
others. Combine them. No two channels occupy the sample portion of the frequency
spectrum
Standards (almost) group – 12 voice channel (60-108 KHz) supergroup – 5 groups, or 60 voice channels mastergroup – 5 or 10 supergroups.
ECE/IUPUI
Intro to Computer Communication Networks
4-4
Time-Division MultiplexingA single high-speed digital transmissionEach connection produces a digital informationThe high-speed multiplexor picks the digital data in round-robin fashion. Each connection is assigned a fixed time-slot during connection setup.
A2 A1
B2 B1
C2 C1
MUXA2 A1B2 B1C2 C1
DEMUX
A2 A1
B2 B1
C2 C1
ECE/IUPUI
Intro to Computer Communication Networks
4-5
Time-Division Multiplexing – Standards
T-1 Carrier : 24 digital telephone A frame consists of 24 slots, 8-bit per slot. Each frame has a single bit overhead for framing. Each connection 8K pulses. Bandwidth = (24*8+1)*8000 = 1.544 Mbps
TDM Jargon in US and Canada DS1 – output of T-1 multiplexer DS2 – 4 DS1s DS3 – 7 DS2s (28 DS1s)
44.736 Mbps ( not 28*1.544=43.232 Mbps!)
TDM Jargon in Europe E1 – 30/32 voice channels
1 channel for signalling 1 channel for framing and maintenance
E2 – 4 E1s E3 – 4 E2s E4 – 4 E3s, 139.264 Mbps ( not 32*64*64Kbps = 131.072Mbps!)
ECE/IUPUI
Intro to Computer Communication Networks
4-6
SONET – Synchronous Optical Networks
to handle lower-level digital signalsGoals
support different carrier internationalization multiplex different digital channels OAM (Operation, Administration and Maintenance)
It is synchronous – controlled by a master clock.Components – sub-layer
switches multiplexers repeater
STSPTE LTE
STE
Path
Line
Section Section
Mux RSONET
TerminalSwitch
STE STE
R R Mux
STSPTE
SONETTerminalSwitch
SectionSection
ECE/IUPUI
Intro to Computer Communication Networks
4-7
SONET Frame – 1
Basic SONET: STS-1 8000 frame/second, 9x90 bytes Bandwidth ?
Questions Overheads on each sub-layer? How many voice telephones can be carried by STS-1?
sectionoverhead
lineoverhead
payload (SPE) (87)
path overhead
ECE/IUPUI
Intro to Computer Communication Networks
4-8
SONET Frame – 2Asynchronous payload to Synchronous frame
SPE can begin anywhere within the SONET frame, span two frames. If a payload arrives at the source while a dummy SONET frame is
being constructed, it can be inserted into the current frame. – ADM capability
Pointer – First two bytes of line overhead
ECE/IUPUI
Intro to Computer Communication Networks
4-9
Self Healing Ring in SONETDouble ring, bi-directional ring in a normal operation.When the fibers b/w two nodes are broken, the ring wraps around.How about a node failure?Fault tolerance
What is the resource to provide the additional service? What has been sacrificed?
Applied in the FDDI ring architecture.
ECE/IUPUI
Intro to Computer Communication Networks
4-10
Wavelength Division MultiplexingOptical version of FDM
The space b/w wavelengths is wideState-of-art technology can multiplex about 200 wavelengths, called DWDM (Dense WDM)Topology of optical networks
Goal: All optical communication (no conversion to electrical to transmission) Expensive optical devices – wavelength converter, optical switch, … Many wavelengths, still limited Transparent optical networks
Major Difficulties in WDM No storage Difficulty in computation
Optical MUXPrism
Optical deMUXPrism
ECE/IUPUI
Intro to Computer Communication Networks
4-11
Assignment of Wavelengths
CH
IN
NY
DC
SF
LA
DF
Current Paths (Connections) SF-NY, SF-LA, LA-DC, NY-DF, NY-DC
We have only two colors, red and blueEach link can not carry two same colorWant to add a connection between NY and LA. How?
ECE/IUPUI
Intro to Computer Communication Networks
4-12
Networks with SwitchesGeographically widespread networksInformation flow from source to destinationSwitch – Core network componentsUnlike LAN, the wires (links) are the expensive resource.
SwitchLink
U
U
U
Connectionof inputs to outputs
Control
123
N
123
N
.
.
.
.
.
.
ECE/IUPUI
Intro to Computer Communication Networks
4-13
The Very First Switch - Human
person2
Switch
ECE/IUPUI
Intro to Computer Communication Networks
4-14
ECE/IUPUI
Intro to Computer Communication Networks
4-15
First Automatic Switch – Crossbar Switch
N xN array of crosspoints (switch elements)Can connect any input to any available output by closing the correcsponding crosspointsIt is nonblocking - a compatible request is always satisfied.Scalability
N2 crosspoints
N
1 2
1
N
2...
… N-1
ECE/IUPUI
Intro to Computer Communication Networks
4-16
The First Multistage Switch (Clos Switch)
3 stages, or 2k+1 stageN inputs = n x r Input, middle, output stageLink b/w each pair of input and middle switch modulesLink b/w each pair of middle and output switch modulesNonblocking if m=2n-12nr(2n-1)+(2n-1)n2
=O(N1.5) crosspointsWhat if k < 2n-1 ?What if links are multiplexed?Multicast ?
1
2
3
4
m
1
2
3
r
1
2
3
r
ECE/IUPUI
Intro to Computer Communication Networks
4-17
Simple Packet Switch – Knockout Switch
Used in some ATM switchesHeader info in each packet addresses to output portPossible to destine multiple packets to same output simultaneously
Tournament and select one packetMulticastScalability
1
2
3
4
1 2 3 4
Input lines
Output lines
Concentrator
OutputQueue
Broadcast Bus
ECE/IUPUI
Intro to Computer Communication Networks
4-18
Binary Switch – Batcher/Banyan Switch
Rearrangeably nonblocking switchBatcher Network – Sort incoming cell based on destination addressBanyan Network
There exists one path from an input line to an output line, so it is possible to route the packet by itself without a central controller (Self-routing).
Two incoming packets might collide. If the packets are ordered at the input lines, no collision.
BatcherSortingNetwork
BanyanNetwork
ECE/IUPUI
Intro to Computer Communication Networks
4-19
Banyan NetworksSelf-Routing
0 – move to the first port in the switching module 1 – move to the second port in the switching module
Possible to collide if they are out of order
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
6=110
4=100
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
4=1006=110
ECE/IUPUI
Intro to Computer Communication Networks
4-20
Batcher Sorting NetworksEach module sorts two numbers only.The network sorts 8 numbers.n external lines – nlog2n complexity.Test yourself with any combination of 0-7.
ECE/IUPUI
Intro to Computer Communication Networks
4-21
Time Division Switch (TDX)n input lines are scanned in sequence, and build a frame with n slots.Slot of fixed sizeTSI reorder the slots in a frame and produce an output frameex) T-1
a slot is one byte, a frame consists of 24 slots, 8000 frame/sec
7 6 5 4 3 2 1 0
76
5
4
3
21
0
01234567
1 2 5 0 3 6 7 4Time Slot
Interchange
n input lines
input frame
output frame
translation table
ECE/IUPUI
Intro to Computer Communication Networks
4-22
Telephone NetworksArea Code 202Area Code 202
Area Code 317 Local Exchange Carrier
Area Code 317 Local Exchange Carrier
274local telephone office
Pedestal
feeder cable
Switch
distribution cable
Serving Area I/f
881
569
TANDEM
TANDEM
Local loop (local access)
Transport Area
interexchange carriers (IXC)
Dis
trib
uti
on
Fra
me
Serving Area I/f
ECE/IUPUI
Intro to Computer Communication Networks
4-23
Telephone NetworksLocal Loop
Analog grade designed 100 years ago. Where is the largest copper mine? A pair of twisted wires for bi-directional
Separate wires for each direction between central offices. Hybrid transformer – convert two pairs to one pair or vice versa.
Utilization is very low. Fiber to the Home (FTTH) vs. Fiber to the curb (FTTC)
Trunk between central offices Replaced by fiber optic. For the most of communication services.
ECE/IUPUI
Intro to Computer Communication Networks
4-24
ConcentrationNumerous users and expensive trunks.Infrequently used customer linesDual goals
Maximize the utilization of the shared trunks Maintain an acceptable blocking probability
Undeterministic and random manner of connection requests Modeling with mathematic Probability and statistics Infinite number of customers
Poisson Process Independent trial Timely process
FewerTrunks
ManyUserLines
ECE/IUPUI
Intro to Computer Communication Networks
4-25
Principle of Poisson Process, 1
t
N(t)all trunks busy
λ arrival rate (call/second)E[X] expected holding time (second/call)ξ λ*E[X], mead load to the system (Erlang)c the number of trunksμ ξ /c , the probability of a trunk occupiedEk event of k trunk occupiedP(Ec ) blocking probability, PB
ECE/IUPUI
Intro to Computer Communication Networks
4-26
Erlang-B Formula
c
k
k
C
B
kac
aP
0!!
Using M/M/c/c queuing model
where a=λ / μ
ECE/IUPUI
Intro to Computer Communication Networks
4-27
Blocking Probability
0.0001
0.001
0.01
0.1
1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
# trunks
Blo
ckin
g P
rob
ab
ility
1 2 3 4 5 6 7
8
9
10
Erlang
ECE/IUPUI
Intro to Computer Communication Networks
4-28
Routing ControlDirect Trunk: for large traffic flowIndirect Path: for smaller flow thru tandem switchesAlternative Path: Handle overflow
What are the blocking probability of the alternative path? Do not use the Erlang-B formula directly.
Fairness between two paths: A-1-2-F and B-1-2-D
TandemSwitch 1
Switch B
Switch C
Switch A
TandemSwitch 2
Switch F
Switch E
Switch D
Indirect Path Alternative Path
ECE/IUPUI
Intro to Computer Communication Networks
4-29
Overflow Control Causes
Link failure: a cut in a wire (unidirectional failure or bidirectional failure)
Node failure: system failure, or sick components Soft failure: Unexpected flow surge
Symptoms In normal condition: the more offered load, the more utilization In overflow condition: the more offered load, the less utilization
Goal Maximize the system efficiency
How To Allocate more resources Re-routing Control the choke, or terminate non-priority services
Detection and Propagation Need extra features or overheads Using signaling or maintenance resources
offered load
carr
ied
load
ECE/IUPUI
Intro to Computer Communication Networks
4-30
Cellular NetworksFrequency reuse
adjacent cells cannot use the same frequency
# of colors = reuse factor minimize the number of colors
graph coloring problem in a planar graph
Handoff user can move from one cell to another,
while continuing without interruption
Home region area the service provides
Roaming provide a service to out-of-home-region
Signal power measurementFrequency allocation
824-849 MHz for mobile-to-base (25MHz)869-894 MHz for base-to-mobile (25MHz)
832 channels (21 setup channels)
Base Stations
Mobile SwitchingCenter
ECE/IUPUI
Intro to Computer Communication Networks
4-31
Satellite NetworksGeo-synchronous Earth Satellite
36,000 km, 270 ms round-trip time fixed location from the earth above equator Application
Spot beam Directional: focus in small area Equipped with multiple antennas and multiple transponders Frequency re-use Application
Low-earth orbit satellite Cellular networks with 77 satellites (from Motolora) for global
coverage 750Km to 2000 Km, 2hr rotation Each station adjust to the passing satellite As a satellite pass over, a handoff is carried out to the next cell Satellite acts as a switching node by inter-satellite link