Basic telecom

Copyright © 2011 LOGTEL

Basic TelecomIt’s all about signaling

Samuel [email protected]

Copyright © 2011 LOGTEL 2

What are we selling ?

It’s all about customer satisfaction

customer satisfaction !


3

Course Content1. Introduction

• What is telecom ?

2. Telephony history – form Bell to analog switch

3. Telecom Network• Switching• telecom services

4. Moving to Digital

5. Basic Signaling (SS7)

6. ISP / Data network

7. Mobile


Goals

4

• To understand the terminology• To know where did we come from• To understand the need and the various signaling


What is Telecom?

5

Telecommunication is the transmission of information over significant distances to communicate.

Signaling:

the information exchange concerning the establishment and control of a telecommunication circuit and the management of the network, in contrast to user information transfer



Switching Systems

Manual control—Switch/cord boards

Patch CordPairs

Off-Hook Indicator

Manual Ring

TipRing


The Telephone: Tip and Ring


Strowger switch (Step by Step) - 1891

9




Signaling – E&M (Ear and Mouth) inbound

12

• On-hook• Off-hook• Line tone• Dialing• Ringing• Ring back tone• Busy tone


Exchange A Exchange BAlice Bob

ringing tone

Bob answers

off-hook

connection ok

dial tone

Bob number

ringing tone

Setup of a PSTN call(meet Alice and Bob)


Crossbar – 1920’s to 80’s

14

Now we can invent DTMF

and now we can have logic (!)


Tone Dialing

1 2 3 A

4 5 6 B

7 8 9 C

* 0 # D

Dual Tone Multifrequency (DTMF)

1209 1336 1477 1633

697

770

852

941

Timing:60 ms Break40 ms Make



N11 code

17

2-1-1: community services, United Way 3-1-1: municipal government services, non-

emergency 4-1-1: directory assistance 5-1-1: traffic information or police non-emergency

services 6-1-1: telephone company customer service and

repair 7-1-1: TDD relay for the deaf 8-1-1: underground public utility location,[1] in

Canada 8-1-1 is assigned for non-emergency health information and services

9-1-1: emergency services


Telecom Network Elements

18

Core network SDH – Synchronous Digital Hierarchy (Europe) SONET – Synchronous optical networking (USA)

Switches Class 4 – network services Class 5 – Line services

Signaling IN – Intelligent Network SS7 – (Common Channel) Signaling System #7 SIP – Session Initiation Protocol

Access / Last mile Twisted per FTTx – fiber to the X Wireless


Telecom Management – OSS/BSS

19

• Network facing operational support systems

• Run by Network Operations• Typically including service

activation, provisioning, fault management, etc

• Cost-focused

• Customer facing business support systems

• Run by the IT department• Typically including billing

and CRM• Revenue-focused

OSS BSS

Traditional definitions


eTOM – NGOSS - FrameWorX

20


Classes 1-5

21


CLASS (Custom Local Area Signaling Services)

22

• AKA VSC (vertical service code) - developed by AT&T in the 1960s

• a special code dialed prior to (or instead of) a telephone number that engages some type of special telephone service

• Anonymous Call Rejection: start• Anonymous Call Rejection: cancel • Busy Number Redial : start• Busy Number Redial : cancel • Call Forwarding: start• Call Forwarding: cancel• Call Return (incoming)• Call Waiting disable• Caller ID Disable


MDF - Main Distribution Frame

23


MOVING TO DIGITAL

24


Trunks to SDH

25

A trunk line is a circuit connecting telephone switchboards

(local loop circuit which extends from telephone exchange switching equipment to individual telephones)

• DS0 (Digital Signal 0) / T0 / E0 – 64Kb/s• DS1 / T1 – 1.5Mb/s E1 – 2Mb/s

• DS3 / T3 -

Nyquist rate


26

Why 3.4 KHz?

Signal

Energy Distribution forHuman Speech

0 Hz 300 Hz 3,400 Hz 20 kHz

Bandwidth(3.1 kHz)

Bandpass Filtering

The human ear can hear sounds up to 20 kHz,but most sound is between 300 Hz and 3.4 kHz.The bandpass filter only passes this sound to reduce bandwidth.


Time Division Multiplexing (TDM)

27

Used Used Used Used Used

Frame 1 Frame 2 Frame 3

Slot 1forCircuit A

Slot 3forCircuit C

Slot 2forCircuit B

TDM reserves capacityfor each circuit in each frame;assures speed but is wasteful

Time

Slot 1forCircuit A

Slot 1forCircuit A


SONET and SDH

Synchronous Optical Network (SONET) High-speed, fiber optic networks organized in rings

Synchronous Digital Hierarchy (SDH) Fiber ring networks used internationally Essentially the same as SONET


SONET and SDH (cont'd)

The basic measure of SONET speed is the Synchronous Transport Signal level 1 (STS-1) frame, which travels at 51.84 Mbps



The basic unit for SDH is the Synchronous Transport Module (STM)-1 frame, which travels at 155.52 Mbps



Benefits of using SONET/SDH You can use multiplexors and routers to combine

different data lines and streams onto one line One heterogeneous network can communicate with

another distant heterogeneous network via one fiber optic ring


SDH Rings

34 Mb/s 2 Mb/s


Introducing ISDN

Telephone companies developed ISDN (Integrated Services Digital Network) as part of an effort to standardize subscriber services.

This included the User-Network Interface (UNI), better known as the local loop.

The ISDN standards define the hardware and call setup schemes for end-to-end digital connectivity.

These standards help achieve the goal of worldwide connectivity by ensuring that ISDN networks easily communicate with one another.

In an ISDN network, the digitizing function is done at the user site rather than the telephone company.


ISDN Advantages

ISDN also provides more bandwidth than a traditional 56 kbps dialup connection.

ISDN uses bearer channels, also called B channels, as clear data paths.

Each B channel provides 64 kbps of bandwidth. An ISDN connection with two B channels would provide a total

usable bandwidth of 128 kbps. Each ISDN B channel can make a separate serial connection

to any other site in the ISDN network. ISDN lines can be used in conjunction with PPP encapsulation.


Signaling Categories

Signaling categories: Supervision – detects changes to a particular line Addressing – responsible for routing signals to the correct

switch Alerting – audible alert signals Call progress – signals that maintain calls

Audible call progress tones: Dial tone Busy signal Receiver off hook too long Nonexistent number


In-Band andOut-of-Band Signaling

In-band signaling The process of allowing the control signal to share the

same path as the voice and data AKA CAS (Channel Associated Signaling)

Out-of-band signaling The process of using a separate channel for signaling

purposes AKA CCS (Common Channel Signaling)


Advantage of CCS over CAS

• Faster call setup• No interference between signaling tones by

network and frequency of human speech pattern.• Greater Trunking Efficiency: CCS has shorter call

set up and tear down times that result in less call holding time, thereby reducing the traffic on the network.

• Information Transfer: CCS allows the transfer of additional information along with the signaling traffic providing facilities such as caller identification and voice or data identification


SS7 – Signaling System #7 (80’s)

SS7 network major components include: SSP (Service Switching Point) STP (Signaling Transfer Point) SCP (Service Control Point) SL (signaling link)


SSP (Service Switching Point)

• SSP is the local exchange to the subscriber and the interface to the telephone network.

• The SS7 signaling information is produced at the sending SSP and is handled at the receiving SSP.

• It converts voice (in band) signaling into the SS7 signal units (out band), and vice versa.


STP (Signaling Transfer Point)

• STP is the network node.• It works like a router to perform the routing of

messages to other signaling points.• It is usually paired to provide redundancy for a

reliable message transfer.• It is adjunct to a voice switch, and might stand

alone as a separate machine.(It’s the tandem in class 4/4)


SCP (Service Control Point)

• SCP works as the interface with the databases, which contain the information of the subscribers, such as 800 service, calling cards, fraud data, etc.

• When receiving a request, it is triggered to handle the database queries, and returns a response with the results of the queries to the originating SSP.

Copyright © 2011 LOGTEL Slide 42

IP Formats in INs

SSP – Service Switching PointSS7

STP

STP

SMS

SCP

IP

SSP SSP

SMS – Service Management SystemSCP – Service Control PointSTP – Service Transfer Point

IP – Intelligent Peripheral

Basic Architecture of a IN


Basic Call Setup Example

• Initial address message (IAM): contains all necessary information for a switch to establish a connection

• Address complete message (ACM): acknowledge to IAM; the required circuit is reserved and the “phone is ringing” (ring back tone)

• Answer message (ANM): occurs when the called party picks up the phone

• Release (REL): sent by the switch sensing that the phone hung up• Release complete (RLC): each exchange that receives REL, sends

an RLC message back (this acknowledges receipt of REL)

6,10

9

2

513

1


Exchange A Exchange BTransit exchange Alice Bob

Setup IAMIAM

Setup

Alert

Connect

ACM

ANM

ACM

ANM

Alert

Connect

Charging of call starts now

Link-by-link routing (number analysis)Q.931

Link-by-link signalling (no number analysis)

Setup of a call using ISUP


IAM – Initial Address Message

ACM – Address Complete Message

ANM – Answer Message

REL – Release Message

RLC – Release Complete

user A user B

Some basic ISUP messages


Intelligence Network (90’s)

Before IN?

All services were to be implemented directly in the core switch systems.

Contact Vendors: Headache for service providers.

What actually is IN? An architecture that redistributes a portion of the call

processing, that is traditionally performed by tel-switches, to other nodes.

Two types of IN today:

Intelligence Network (IN) – standardized by ITU. Advanced Intelligent Network (AIN) - standardized by

Bellcore.


Why Intelligent Networking?

Introduce new services rapidly: IN provides the capability to provision new services or modify existing services throughout the network with physical intervention.

Provide Service Customization: Service providers require the ability to change the service logic rapidly and efficiently. Customers are also demanding control of their own services to meet their individual needs.

Establish Vendor Independence: To develop the software for service providers quickly and efficiently, suppliers have to integrate commercially available software to create the applications required by service providers.

Create open interfaces: Open interfaces allow service providers to introduce network elements quickly for individualized customer services.

Capable to act appropriately in a changing environment


IN service family

48

1. Number translating2. Billing modification

Reverse charging (800) Split charging (700) Premium rate (900) Personal services (600)

3. Centralize Voice Mail4. Pre Paid (node)

5. SMS – Short Massaging

in mobile networks IN CAMEL (Customised Applications for Mobile networks Enhanced Logic)


Centrex

49

• Centrex is a PBX-like service providing switching at the central office instead of at the customer's premises. Typically, the telephone company owns and manages all the communications equipment and software necessary to implement the Centrex service and then sells various services to the customer.

• Today we use the terms: Hosted Stickiness Virtual Cloud


PABX (voice) Services (1) Private (automatic) Branch eXchange

50

• Auto attendant• Automatic call distributor• Automated directory services (where callers can be routed to a given

employee by keying or speaking the letters of the employee's name)• Call accounting• Call blocking• Call forwarding on busy or absence• Call park• Call pick-up• Call transfer• Conference call• Custom greetings• Busy Override


PABX service (2)

51

• Direct Inward Dialing (DID) – AKA DDI and DDO• Direct Inward System Access (DISA) (the ability to access internal features

from an outside telephone line)• Do not disturb (DND)• Follow-me, also known as find-me: Determines the routing of incoming calls.

The exchange is configured with a list of numbers for a person. When a call is received for that person, the exchange routes it to each number on the list in turn until either the call is answered or the list is exhausted (at which point the call may be routed to a voice mail system).

• Interactive voice response• Music on hold• Night service


Signaling in VoIP networks

VoIP Network can carry SS7 over IP using protocols defined by Signaling Transport (SIGTRAN).


DATA NETWORKING

53


OSI 7 Layer Model

OSI - Open Systems Interconnection (Basic Reference Model)

Each level is an independent set of protocols

Each level can be change seamlessly

Application

Presentation

Session

Transport

Network

Data Link

Physical


5 Layer model

Application

Transport

Network

Data Link

Physical

Application

Presentation

Session

Transport

Network

Data Link

Physical


5 Layer model (TCP/IP)

Application – Represent the end user and the application he use (mail, browse, FTP, etc.)

Transport - end-to-end message transfer, along with error control, fragmentation and flow control.

Network (AKA Internet) – responsible on getting packets of data from source to destination.

Link - processes of transmitting receiving packets on a given link layer

Application

Transport - TCP

Network - IP

Link


TCP/IP Connection


TCP - Transmission Control Protocol

Connection oriented - Reliable stream transport Conceptually, two ends communicate to agree

on details After agreeing application notified of connection During transfer, ends communicate continuously

to verify data received correctly When done, ends tear down the connection

Provides buffering and flow control Takes care of lost packets, out of order,

duplicates, long delays Usually used for browsing, FTP, Mail, etc.


read(s1, dataBlock)

Transport (TCP)

Network (IP)

Link (WLAN)

Web serverSamuel

Web Site

send(s2, dataBlock)

1 2 3 4 5

1 2 3 4 5

1 2 3 4 5

Network (IP)

Link

1 2 3

1 2 3

Transport (TCP)

Browser

1 2 3 4 5

Network (IP)

Link (WLAN)

Physical

Router

1 2 3

1 2 3 4 5

1 2 3 4 5

PhysicalPhysical


UDP- User Datagram Protocol

Connectionless Datagram- Not Reliable transport Minimal overhead, high performance No setup/teardown, 1 datagram at a time Application responsible for reliability

Includes datagram loss, duplication, delay, out-of-sequence, multiplexing, loss of connectivity

Usually used for Voice & Video streaming, broadcasting, etc.


TCP vs. UDP data format

Source port Destination port

Sequence number

0 8 16 3124

Acknowledgement number

4

Hlen

Resv

Code Window

Urgent ptrChecksum

Options (if any) Padding

Data if any

…

Source port Destination port

UDP message len

Checksum (opt.)

0 8 16 3124

Data

…


TCP data format

Port - TCP port numbers to ID applications at both ends of connection

Sequence number - ID position in sender’s byte stream

Acknowledgement - identifies the number of the byte the sender of this segment expects to receive next

Hlen - specifies the length of the segment header in 32 bit multiples. If there are no options, the Hlen = 5 (20 bytes)

Code - used to determine segment purpose, e.g. SYN, ACK, FIN, URG


TCP data format (cont.)

Window - Advertises how much data this station is willing to accept. Can depend on buffer space remaining.

Checksum -Verifies the integrity of the TCP header and data. It is mandatory.

Urgent pointer - used with the URG flag to indicate where the urgent data starts in the data stream. Typically used with a file transfer abort during FTP or when pressing an interrupt key in telnet.

Options -used for window scaling, SACK, timestamps, maximum segment size etc.


IP Address

Unique addresses in the world An IP address is 32 bits, noted in dotted decimal

notation: 192.78.32.2

Host and Prefix Part An IP address has a prefix and a host part:

prefix:host Prefix identifies a subnetwork

used for locating a subnetwork – routing Prefix is usually identified in a host using a “subnet mask”


Using a mask: address + mask

the mask is the dotted decimal representation of the string made of : 1 in the prefix, 0 elsewhere

bit wise address & mask gives the prefix example 1: 128.178.156.13 mask

255.255.255.0 here: prefix is 128.178.156.0

example 2: 129.132.119.77 mask 255.255.255.192 Q1: what is the prefix ? Q2: how many host ids can be allocated ?


Address + Mask (example 2)

129.132.119.77 mask 255.255.255.192▪ Q1: what is the prefix ? A: 129.132.119.64

Q2: how many host ids can be allocated ? ▪ A: 64 (minus the reserved addresses: 62)

1000 00011000 01000111 01110100 1101

1111 11111111 11111111 11111100 0000

129

255

132

255

119

255 192

77

64 addresses

26 6

1000 00011000 01000111 01110100 0000129 132 119 64


IP V.6 vs. V.4 Datagram

http://www.networksorcery.com/enp/default1001.htm


IP v.4 header

Version (4 bits) – 6 or 4 Hlen (4 bits) - Header length in 32 bit words,

without options (usual case) = 20 Type of Service (TOS 8 bits): now being used for

QoS Total length (16 bits) - length of datagram in bytes,

includes header and data Time to live (TTL 8bits) - specifies how long

datagram is allowed to remain in internet (how many hops)

Protocol (8 bits) - specifies the format of the data area Protocol numbers administered by central authority to

guarantee agreement, e.g. TCP=6, UDP=17 …68


IP v.6 header

Version (4 bits) – 6 or 4 Traffic Class (8 bits) - traffic priority delivery value. Flow Label. 20 bits.

Used for specifying special router handling from source to destination(s) for a sequence of packets.

Payload Length (16 bits) - Specifies the length of the data

Hop Limit (8 bits) - the same as TTL in the IPv4 Source address. 16 bytes. Destination address. 16 bytes.

69


IPv6 address – 128 bit

IPv6 address is made of two parts: prefix and suffix (I.e interface-ids)

and hierarchical structure (that depends on format prefix, FP) prefix:

suffix:

Link-local address (mandatory) is unique within a "link".

64 bits suffix

64 bits prefixFP TLA NLA SLA

Interface ID

64 bits suffix

54 '0' bits

1111111010

FP – Format prefixTLA - Top-Level Aggregators NLA - Next-Level Aggregators SLA – Service level Agreements


71

IPv6 Autoconfiguration and Renumbering

RFC 2462, IPv6 Stateless Address Autoconfiguration. IPv6 includes stateless address autoconfiguration feature, which

allows a host to determine its own IPv6 address from its Layer 2 address.

The concept: A device generates a temporary address until it can determine the characteristics of the network it is on. Then creates a permanent address it can use based on that information. In the case of multi-homed devices: Autoconfiguration is

performed for each interface separately

Stateless address autoconfiguration

No central server needed to aid in address configuration Node forms its own suffix, checks if it is uniqueNode obtains prefix(es) from the nearest router

Stateful address autoconfiguration

Central server allocates full addresses to nodes on requestDHCPv6 is the current protocol for stateful address autoconfiguration


IPv6 Extended Unique Identifier (EUI-64)

RFC 2464 IPv6 link-local addresses and statelessly autoconfigured

addresses on Ethernet networks used in Router Solicitation, Router Advertisement, Neighbor

Solicitation, Neighbor Advertisement and Redirect messages

48-bit MAC address

64-bit IPv6 EUI


IPv6 address Types

73

Unicast (1:1)

Anycast addresses : nearest node of a set of nodes

currently only used to address routers

Multicast (1:n) communicate group of computers

No more broadcast in use

communicate specified one computer

RFC 4291 currently specifies the following restrictions on anycast addresses: An anycast address must not be used as the source address of a packet.Any anycast address can only be assigned to a router


Representation of IPv6 addresses

Colon hexadecimal notation - 805B:2D9D:DC28:0000:0000:FC57:D4C8:1FFF

Leading zeroes can be suppressed in the notation 805B:2D9D:DC28:0:0:FC57:D4C8:1FFF Zero Compression in IPv6 Addresses

805B:2D9D:DC28::FC57:D4C8:1FFF The double-colon can appear only once in any IP address. IPv6 addresses can embed IPv4. The notation has the first

96 bits in colon hex notation, and the last 32 bits in dotted decimal. eg ::212.200.31.255

Prefix notation can be used as with classless IPv4 addressing with CIDR.

Example: 805B:2D9D:DC28::FC57:D4C8:1FFF/48


So why isn’t it here yet?

No clear move to IPv6 Lack of smooth migration plans Investments in IPv4 Software availability - Available from Microsoft Windows XP

sp2 Developments in IP v4

Use of NAT CIDR Planning of Hierarchies and use of Autonomous Areas IPsec implemented in IPv4

Other Points Router Upgrades to handle IPv6 – OSPFv3


Tunneling IPv6 over IPv4

IPv6 can operate within a closed or private network environment Currently across a public networks, such as the Internet, have to

cross an IPv4 domain IPv6 packets can be encapsulated within IPv4 Encapsulated packets can then travel transparently across an IPv4

routing domain Tunneling can be used by routers and hosts

IPv4IPv6 Network

IPv6 Network

Tunnel: IPv6 in IPv4 packet

IPv6 Host

Dual-Stack Router

Dual-Stack Router

IPv6 Host

IPv6 HeaderIPv6 HeaderIPv4 HeaderIPv4 Header

IPv6 HeaderIPv6 Header Transport Header

Transport Header DataData

DataDataTransport Header

Transport Header


MOBILE NETWORKS

77


Cellular Technology Defined :

A communications system which serves users via radio waves (a “radio air interface”) by connecting the user’s mobile terminal to the antennas at the nearest “cell base station”. The cell base station antennas can be tower mounted; rooftop mounted; mounted on water tanks; or hidden from sight for aesthetic purposes. Average base station coverage area today: 2-5 miles radius.

The system functions by re-using frequencies at the low-powered cell base stations throughout a cellular market area, and handing off calls in progress from one cell base station to another as users move throughout the market area.


79

Course Content1. Introduction

• What is telecom ?

2. Telephony history – form Bell to analog switch

3. Telecom Network• Switching• telecom services

4. Moving to Digital

5. Basic Signaling (SS7)

6. ISP / Data network

7. Mobile


Telecom Network Elements

80

Core network SDH – Synchronous Digital Hierarchy (Europe) SONET – Synchronous optical networking (USA)

Switches Class 4 – network services Class 5 – Line services

Signaling IN – Intelligent Network SS7 – (Common Channel) Signaling System #7 SIP – Session Initiation Protocol

Access / Last mile Twisted per FTTx – fiber to the X Wireless


Call Base Station Photos


Stealth Cell Sites


Mobile Telephone (Cellular Technology)

Wireless service is founded on one key concept known as “frequency re-use”

Cellular service launched in Chicago in 1983Traditionally, to engineer a cell network to support millions of

users in a metropolitan area, or thousands in a rural area, markets are broken down into cells. Cells are geographic areas that use their own sets of frequencies (channels) to support dozens of users simultaneously.

Frequency re-use is accomplished by breaking down all available frequencies into groups of 7 (N=7).

Each cell base station has its own transmission system (antennas) and set of assignable channels.


N=7 Frequency Re-Use Cluster. Each hexagon represents a base station with distinct set of frequencies. Note how identicalfrequency sets are laid out symmetrically. This facilitates designand engineering.


Two Antenna Types:

Omnidirectional: propagates radio signal equally 360 degrees, aka “omni”. Also called “stick” antennas. (Lamp With No Shade)

Directional: radio energy is focused in a specific direction at a specific beamwidth, based on a reflector within the antenna housing. (Flashlight)


Five Key Components To Every (Macro) Wireless Network:

Mobile phone, aka “UE” (user equipment) or “mobile terminal”

Cell Base StationFixed network, AKA “backhaul network”Mobile Switching Center (MSC)Interconnection to PSTN and Internet


BTS

BSC

MSC

VLR HLR AuC EIR

PSTN,ISDN...

OMCOMC

NMCX.25 links

GSM interfaces

Voicemail Server

SM-SC

MS (Mobile Station)

BSS (Base Station System)

NSS (Network Switching Subsystem)

OMM (Operations & Maintenance Management)

MS

http://www.nokia-asia.com/nokia/0,,48192,00.html


Key design and engineering concepts that drive cellular technology:

Frequency Re-Use – supports simultaneous use of hundreds or thousands of frequencies (channels) to exponentially increase system capacity

Call Handoffs – seamless transfer of a call / transmission in progress from one base station to an adjacent (neighbor) base station

Frequency Agility: in handsets / terminals – ability of cell phones to operate on any one of dozens or hundreds of possible frequencies. Call handoff cannot occur without this ability.

Working together, these concepts support basic cellular operation.


Generations Of WirelessWireless Service(s)

Cellular service first launched in 1983 in Chicago, Illinois by Illinois Bell.

First generation (1G) service: All analog, more prone to noise, crosstalk, call drops Limited system capacity Used 850 Mhz frequency spectrum 1983 – 1994 KEY DIFFERENTIATOR: first instance of frequency re-use to

exponentially increase capacity over previous mobile systems

Second generation (2G) service: Also known as “PCS” (Personal Communication Service) Co-existed with analog service for 15 years Used different frequency spectrum (1900 Mhz / 1.9 Ghz) KEY DIFFERENTIATOR: all digital service


Wireless Service(s) Continued:Third generation (3G) service:

All digital “Always On” Internet access High-speed access and transmission (> 384 Kbps) Technologies: UMTS (GSM-based), CDMA 1X-EVDO KEY DIFFERENTIATOR: supports sustainable multimedia

transmissions (i.e. voice, video, text, image, video)Fourth generation (4G)

Launching in 2009 with Clearwire WiMax launch Key technologies: WiMax (802.16) and LTE (Long Term

Evolution) KEY DIFFERENTIATOR: super-fast access and transmissions –

tens of Megabits. Technology built into laptops.

Generations Of Wireless


– 1983 – Present: The “NIMBY” phenomenon. “Not In My Backyard”. Wireless subscribers desire – demand – great cellular coverage but protest when base station towers are installed in areas where “ugly towers” are not desired.

– 2006 – Present: Backhaul network congestion and bottlenecking due to proliferation and popularity of wireless data technologies and services, based on 3G rollouts.• Traditionally, base station-to-MSC (switch) connections

have been one or two DS-1 circuits. This traditional model is quickly becoming outmoded as the backhaul network now has huge potential to become a bottleneck. Adding more and more DS-1 circuits becomes expensive. Solution? Ethernet in the backhaul network: simple, known technology. Ultimately less expensive than multiple DS-1 circuits.

– 2010: Radio spectrum is becoming a precious and increasingly scarce commodity. Also, data traffic vs. revenue dichotomy.

Major Challenges:


INCREASED CAPACITY

• number of cells in the reuse patteThe GSM system provides a greater subscriber capacity than analogue systems.

• GSM allows 25 kHz per user, that is, eight conversations per 200 kHz channel pair (a pair comprising one transmit channel and one receive channel).

• Digital channel coding and the modulation used makes the signal resistant to interference from cells where the same frequencies are re-used (co-channel interference); a Carrier to Interference Ratio (C/I) level of 12 dB is achieved, as opposed to the 18 dB typical with analogue cellular.

• This allows increased geographic reuse by permitting a reduction in the rn.

FEATURES OF GSM (1)


AUDIO QUALITY

• Digital transmission of speech and high performance digital signal processors provide good quality speech transmission.

• Since GSM is a digital technology, the signals passed over a digital air interface can be protected against errors by using better error detection and correction techniques.

• In regions of interference or noise-limited operation the speech quality is noticeably better than analogue.

USE OF STANDARDISED OPEN INTERFACES• Standard interfaces such as C7 and X25 are used throughout the

system. Hence different manufacturers can be selected for different parts of the PLMN.

• There is a high flexibility in where the Network components are situated.

FEATURES OF GSM (2)


IMPROVED SECURITY AND CONFIDENTIALITY

• GSM offers high speech and data confidentiality.• Subscriber authentication can be performed by the system to check if

a subscriber is a valid subscriber or not.• The GSM system provides for high degree of confidentiality for the

subscriber. Calls are encoded and ciphered when sent over air. • The mobile equipment can be identified independently from the mobile

subscriber. The mobile has a identity number hard coded into it when it is manufactured. This number is stored in a standard database and whenever a call is made the equipment can be checked to see if it has been reported stolen.

FEATURES OF GSM (3)


CLEANER HANDOVERS

• GSM uses Mobile assisted handover technique.• The mobile itself carries out the signal strength and quality

measurement of its server and signal strength measurement of its neighbors.

• This data is passed on the Network which then uses sophisticated algorithms to determine the need of handover.

SUBSCRIBER IDENTIFICATION• In a GSM system the mobile station and the subscriber are

identified separately.• The subscriber is identified by means of a smart card known as a

SIM. • This enables the subscriber to use different mobile equipment

while retaining the same subscriber number.

FEATURES OF GSM (4)


GSM Voice and Data Call Architecture

Voice Calls Path

Data Calls PathPacket Data


MS Mobile Station = phone + SIM card

BTS Base Transceiver Station BSC Base Station Controller HLR Home Location Register MSC Mobile services Switching

Centre VLR Visitor Location Register AUC Authentication Centre

Stand-alone or integrated in HLR

EIR Equipment Identity RegisterFor blacklisting stolen and

unwanted equipment SMSC Short Message Service

”Support” Centre VMS Voice Messaging System PrePaid Node Hosting prepaid service

system IN Intelligent Network services PSTN Public Switched Telephone

Network PABX Private Automatic Branch

Exchange

MSC/VLR

IN

BSC

SMSC

EIR

INTERNET

MobilinkPSTN

BSC

PrePaidNode

VMS

HLR

MSCw

AUC

NETWORK COMPONENTS


• The Mobile services Switching Centre (MSC) co-ordinates the setting up of calls to and from GSM users.

• It is the telephone switching office for MS originated or terminated traffic and provides the appropriate bearer services, teleservices and supplementary services.

• It controls a number of Base Station Sites (BSSs) within a specified geographical coverage area and gives the radio subsystem access to the subscriber and equipment databases.

• The MSC carries out several different functions depending on its position in the network.

• When the MSC provides the interface between PSTN and the BSS in the GSM network it is called the Gateway MSC.

• Some important functions carried out by MSC are Call processing including control of data/voice call setup, inter BSS & inter MSC handovers, control of mobility management, Operation & maintenance support including database management, traffic metering and man machine interface & managing the interface between GSM & PSTN N/W.

Mobile Switching Centre (MSC)


Mobile Station (MS)The Mobile Station consists of the Mobile Equipment (ME) and the

Subscriber Identity Module (SIM). Mobile EquipmentThe Mobile Equipment is the hardware used by the subscriber to

access the network. The mobile equipment can be Vehicle mounted, with the antenna

physically mounted on the outside of the vehicle or portable mobile unit, which can be handheld.

Mobiles are classified into five classes according to their power rating.

CLASS POWER OUTPUT1 20W2 8W3 5W4 2W5 0.8W

MS & ME


The SIM is a removable card that plugs into the ME.It identifies the mobile subscriber and provides information about the

service that the subscriber should receive.The SIM contains several pieces of information

– International Mobile Subscribers Identity (IMSI) - This number identifies the mobile subscriber. It is only transmitted over the air during initializing.

– Temporary Mobile Subscriber Identity ( TMSI ) - This number also identifies the subscriber. It can be alternatively used by the system. It is periodically changed by the system to protect the subscriber from being identified by someone attempting to monitor the radio interface.

– Location Area Identity ( LAI ) - Identifies the current location of the subscriber.

– Subscribers Authentication Key ( Ki ) - This is used to authenticate the SIM card.

– Mobile Station International Standard Data Number ( MSISDN ) - This is the telephone number of the mobile.

SIM (1)


• Most of the data contained within the SIM is protected against reading (eg Ki ) or alterations after the SIM is issued.

• Some of the parameters ( eg. LAI ) will be continuously updated to reflect the current location of the subscriber.

• The SIM card can be protected by use of Personal Identity Number( PIN ) password.

• The SIM is capable of storing additional information such as accumulated call charges.

G S M

FULL SIZE SIM CARD MINI SIM CARD

SIM (2)


98 XXX 12345CCNDCSN

CC NDC SN

= Country code= National Destination Code= Subscriber Number

Mobile Station International Subscribers Dialling Number ( MSISDN ) :Human identity used to call a MSThe Mobile Subscriber ISDN (MSISDN) number is the telephone number

of the MS.This is the number a calling party dials to reach the subscriber.It is used by the land network to route calls toward the MSC.

MSISDN


MCC MNC MSIN

404 XX 12345..10

MCCMNCMSIN

= Mobile Country Code ( 3 Digits )= Mobile Network Code ( 2 Digits )= Mobile Subscriber Identity Number

International Mobile Subscribers Identity ( IMSI ) :Network Identity Unique to a MSThe International Mobile Subscriber Identity (IMSI) is the primary identity

of the subscriber within the mobile network and is permanently assigned to that subscriber.

The IMSI can be maximum of 15 digits.

IMSI


TAC FAC SNR

6 2 6 1

TACFACSNRSP

SP

= Type Approval Code= Final Assembly Code= Serial Number= Spare

International Mobile Equipment Identity ( IMEI ) :IMEI is a serial number unique to each mobileEach MS is identified by an International Mobile station Equipment Identity

(IMEI) number which is permanently stored in the Mobile Equipment. On request, the MS sends this number over the signaling channel to the

MSC.The IMEI can be used to identify MSs that are reported stolen or operating

incorrectly.

IMEI


• The HLR contains the master database of all subscribers in the PLMN.• This data is remotely accessed by the MSC´´s and VLRs in the network.

The data can also be accessed by an MSC or a VLR in a different PLMN to allow inter-system and inter-country roaming.

• A PLMN may contain more than one HLR, in which case each HLR contains a portion of the total subscriber database. There is only one database record per subscriber.

• The subscribers data may be accessed by the IMSI or the MSISDN.• The parameters stored in HLR are

– Subscribers ID (IMSI and MSISDN )– Current subscriber VLR.– Supplementary services subscribed to.– Supplementary services information (eg. Current forwarding

address ).– Authentication key and AUC functionality.– TMSI and MSRN

HOME LOCATION REGISTER (HLR)


• The Visited Location Register (VLR) is a local subscriber database, holding details on those subscribers who enter the area of the network that it covers.

• The details are held in the VLR until the subscriber moves into the area serviced by another VLR.

• The data includes most of the information stored at the HLR, as well as more precise location and status information.

• The additional data stored in VLR are– Mobile status ( Busy / Free / No answer etc. )– Location Area Identity ( LAI )– Temporary Mobile Subscribers Identity ( TMSI )– Mobile Station Roaming Number ( MSRN )

• The VLR provides the system elements local to the subscriber, with basic information on that subscriber, thus removing the need to access the HLR every time subscriber information is required.

VISITOR LOCATION REGISTER (VLR)


• The AUC is a processor system that perform authentication function.

• It is normally co-located with the HLR.• The authentication process usually takes place each time

the subscriber initializes on the system.• Each subscriber is assigned an authentication key (Ki) which

is stored in the SIM and at the AUC.• A random number of 128 bits is generated by the AUC &

sent to the MS.• The authentication algorithm A3 uses this random number

and authentication key Ki to produce a signed response SRES( Signed Response ).

• At the same time the AUC uses the random number and Authentication algorithm A3 along with the Ki key to produce a SRES.

• If the SRES produced by AUC matches the one produced by MS is the same, the subscriber is permitted to use the network.

Authentication Centre (AUC)


HLR AUC

TRIPLESRAND, Kc , SRESVLR

RAND Kc SRES

RAND

SRES

SRES

SRES = SRESBTS

A5 , HYPERFRAME NUM

Kc

AIR INTERFACE ENCRYPTION

MS

A3 , A8 , A5 , Ki

SRES = A3 (RAND , Ki )

Kc = A8 (RAND , Ki )

Ki, A3, A8A3 ( RAND, Ki ) = SRES

A8 ( RAND, Ki ) = KcTriples

Generated

AUTHENTICATION PROCESS


HANDOVER


• The GSM handover process uses a mobile assisted technique for accurate and fast handovers, in order to:

– Maintain the user connection link quality.

– Manage traffic distribution• The overall handover process is implemented in the

MS,BSS & MSC. • Measurement of radio subsystem downlink performance

and signal strengths received from surrounding cells, is made in the MS.

• These measurements are sent to the BSS for assessment. • The BSS measures the uplink performance for the MS being

served and also assesses the signal strength of interference on its idle traffic channels.

• Initial assessment of the measurements in conjunction with defined thresholds and handover strategy may be performed in the BSS. Assessment requiring measurement results from other BSS or other information resident in the MSC, may be perform. in the MSC.

HANDOVER


• The MS assists the handover decision process by performing certain measurements.

• When the MS is engaged in a speech conversation, a portion of the TDMA frame is idle while the rest of the frame is used for uplink (BTS receive) and downlink (BTS transmit) timeslots.

• During the idle time period of the frame, the MS changes radio channel frequency and monitors and measures the signal level of the six best neighbor cells.

• Measurements which feed the handover decision algorithm are made at both ends of the radio link.

HANDOVER (Cont)


• At the MS end, measurements are continuously signalled, via the associated control channel, to the BSS where the decision for handover is ultimately made.

• MS measurements include:

– Serving cell downlink quality (bit error rate (BER) estimate).

– Serving cell downlink received signal level, and six best neighbor cells downlink received signal level.

• The MS also decodes the Base Station ID Code (BSIC) from the six best neighbor cells, and reports the BSICs and the measurement information to the BSS.

MS END

HANDOVER


The BTS measures the uplink link quality, received signal level, and MS to BTS site distance.

The MS RF transmit output power budget is also considered in the handover decision.

If the MS can be served by a neighbor cell at a lower power, the handover is recommended.

From a system perspective, handover may be considered due to loading or congestion conditions. In this case, the MSC or BSC tries to balance channel usage among cells.

BTS END

HANDOVER


During the conversation, the MS only transmits and receives for one eighth of the time, that is during one timeslot in each frame.

During its idle time (the remaining seven timeslots), the MS switches to the BCCH of the surrounding cells and measures its signal strength.

The signal strength measurements of the surrounding cells, and the signal strength and quality measurements of the serving cell, are reported back to the serving cell via the SACCH once in every SACCH multiframe.

This information is evaluated by the BSS for use in deciding when the MS should be handed over to another traffic channel.

This reporting is the basis for MS assisted handovers.

MS IDLE TIME REPORTING

HANDOVER


MEASUREMENT IN ACTIVE MODE

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2

Frame 24 Frame 25 Idle Frame Frame 0

Frame 24 Frame 25 Idle Frame Frame 0

1 2 3 1 2 1 2

1. MS receives and measures signal strength on serving cell(TS2).

2. MS transmits3. MS measures signsl strength for at least one neighbor

cell.4. MS reads BSIC on SCH for one of the 6 strongest

neighbor.

4

Downlink

Uplink

HANDOVER


Maximum 32 averaging of RSS takes place.Practically a cell neighbors can be equipped for a cell.If high numbers of neighbors are equipped, then the accuracy

of RSS is decreased as should have 8 to 10 neighbors.

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NUMBER OF NEIGHBORS

HANDOVER


NUMBER OF NEIGHBORS

In one SACCH multiframe there are 104 TDMA frames.Out of this 104 frames 4 frames are idle and are used to

decode the BSIC.Remaining 100 TDMA frames are used to measure

RSS( Received Signal Strength) of the neighbor.If 25 neigbors are equipped, then in one SACCH multiframe

each neigbor is measured 100/25 = 4 times and averaged out. This produces a less accurate value.

If 10 neigbors are equipped, then in one SACCH multiframe each neigbor is measured 100/10 = 10 times and averaged out. This produces a more accurate value.

HANDOVER


GSM causes its own time interference.

The MS has a omni-directional antenna. Much of the MS power goes to the server but a lot is interfering with surrounding cells using the same channel.

The TDMA frames of adjacent cell are not aligned since they are not synchronised. Hence the uplink in the surrounding cell suffers from interference.

INTERFERENCE ON IDLE CHANNEL

Channel 10Cell 1

1 2 3 4 5

1 2 3 4 5

UPLINK CELL1

UPLINK CELL2

Channel 10Cell 2

HANDOVER


The BSS keeps on measuring the interference on the idle timeslots.

Ambient noise is measured and recorded 104 times in one SACCH multiframe.

These measurements are averaged out to produce one figure.

The BSS then distributes the idle timeslots into band 0 to band 5.

Since the BSS knows the interference level on idle timeslots, it uses this data to allocate the best channel first and the worst last.

INTERFERENCE ON IDLE CHANNEL

0 1 2 3 4 5 6 7

Inteference on idle channel measured on Idle Timeslot by BSS

HANDOVER


The following measurements is be continuously processed in the BSS :i) Measurements reported by MS on SACCH - Down link RXLEV - Down link RXQUAL - Down link neighbor cell RXLEV ii) Measurements performed in BSS - Uplink RXLEV - Uplink RXQUAL - MS-BS distance - Interference level in unallocated time slots

Every SACCH multiframe (480 ms) a new processed value for each of the measurements is calculated..

HANDOVER

HANDOVER


Handover is done on five conditions– Interference– RXQUAL– RXLEV– Distance or Timing Advance– Power Budget

Interference - If signal level is high and still there is RXQUAL problem, then the RXQUAL problem is because of interference.RXQUAL - It is the receive quality. It ranges from 0 to 7 , 0 being the best and 7 the worstRXLEV - It is the receive level. It varies from -47dBm to -110dBm.Timing Advance - Ranges from 0 to 63.Power budget - It is used to save the power of the MS.

HANDOVER CONDITIONS

HANDOVER


Handover takes place in the same cell from one timeslot to another timeslot of the same carrier or different carriers( but the same cell).

Intra-cell handover is triggered only if the cause is interference.Intra-cell handover can be enabled or disabled in a cell.

HANDOVER TYPESIntra-Cell Handover

BSC

BTSCall is handed

from timeslot 3 to timeslot 5

0 1 2 3 4 5 6 7

HANDOVER


Handover takes place between different cell which are controlled by the same BSC.

HANDOVER TYPESIntra-BSC Handover

BSC1

BTS1Call is handed from timeslot 3 of cell1 to timeslot 1 of cell2 . Both the cells are controlled

by the same BSC.

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

HANDOVER


Handover takes place between different cell which are controlled by the different BSC.

HANDOVER TYPESInter-BSC Handover

BSS1


by the different BSC.

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7BSS2

MSC

BTS2

HANDOVER


Handover takes place between different cell which are controlled by the different BSC and each BSC is controlled by different MSC.

HANDOVER TYPESInter-MSC Handover

BSS1


by the different BSC, each BSCbeing controlled by different MSC.

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7BSS2

MSC1

BTS2

MSC2

HANDOVER


LOCATION UPDATE


MSC should always know the location of the MS so that it can contact it by sending pages whenever required.

The mobile keeps on informing the MSC about its current location area or whenever it changes from one LA to another.

This process of informing the MSC is known as location updating.

The new LAI is updated in the VLR.LAI = MCC + MNC + LAC

MCC MNC LAC

3 digits 1-2 digits Max 16 bits

MCC = Mobile country code.MNC = Mobile Network Code.LAC = Location area code. Identifies a location area within a GSM PLMN network. The maximum length of LAC is 16 bits. Thus 65536 different LA can be defined in one GSM PLMN.

LOCATION UPDATE


• Normal location update• Periodic location update• IMSI attach

Normal Location Update1. Mobile powers on and is idle.2. Reads the LAI broadcast on the BCCH.3. Compares with the last stored LAI and if it is different does a

location update.

LOCATION UPDATE TYPES


LTE


The driving forces – The telco point of view

Addressing the trend of declining ARPU Delivery of higher bandwidth services and

capacity Reducing OPEX & Cost/MB Proliferation of emerging devices, with rich

mobile applications and video Quad-play (bundle) Multiple screen offerings

Addressing shortage in bandwidth Leveraging existing 3G infrastructure

Regulation Re-allocation of older spectrum for 4G

technologies Open access & net neutrality

130


Standards bodies

131

IMT-Advanced

802.X – LAN/WLAN


IMT Expected Targets

IMT- Advanced (IMT-2000 – become 3G) high quality mobile services user equipment suitable for worldwide use user‐friendly applications, services and equipment worldwide roaming capability Improve wireless performance

Better signal reception and better coverage Increase spectrum efficiency

More subscribers and more data transfer in the same spectrum Flat all-IP network architecture High mobility up to 500 Km/H enhanced peak data rates to support advanced services

and applications 100 Mbit/s (UL 50 Mbit/s DL) for high mobility 1 Gbit/s for low mobility

Low latency <50ms

132


4G Enabling Technology

Some key technologies made 4G possible

Both WiMAX and LTE use: OFDM, OFDMA and SC-FDMA Channel dependent scheduling Adaptive coding and modulation (ACM) Multiple-In-Multiple-Out (MIMO) antenna

processing Turbo coding and decoding

133


OFDMA Flexibility

With OFDMA the user allocation is flexible Can change from frame to frame Multiple allocations for several applications

Allocation changes In WiMAX every 5 ms In LTE every 1 ms

134

frequency

frequency

time

OFDMA

Burst

Burst Burst


Single Carrier FDMA (SC-FDMA) A major problem with OFDM and OFDMA is

high peak-to-average power ratio (PAPR) Transmitted amplitude with large variation Requires a linear amplifier at transmitter Linear amplifies consumes high power OK at base station For mobile station, this consumes battery

LTE uses a solution for UL: SC-FDMA Single carrier transmission

135


MIMO

Transmit diversity: Same modulation symbols sent from all Tx M

antennas Receiver combines the signal from N antennas Useful to increase performance against fading

Spatial multiplexing: Different modulation symbols sent from M Tx

antennas Receiver received the signal from N antennas Useful to increase data rate if channel is good

WiMAX uses up to 2x2. LTE uses up to 4x4

136


MIMO Radio Channel

Multiple antennas at both the base station and terminal can significantly increase data rates with sufficient multipath

Reduce noise Reduce handoffs and disconnecting


So, What will be the bandwidth?

138


WiMax is dead(?)

139

http://www.networkworld.com/community/blog/wimax-dead


LOCATION UPDATE

MS MSCBSS

RACH

Imme. Assign

Location update request

Authentication request

Authentication response

DTI<CICMD>

DTI<CICMP>

Cipher mode command

Cipher mode complete

Location update accepted


IMSI ATTACHSaves the network from paging a MS which is not active in the system.When MS is turned off or SIM is removed the MS sends a detach signal to

the Network. It is marked as detached.When the MS is powered again it reads the current LAI and if it is same does

a location update type IMSI attach.Attach/detach flag is broadcast on the BCCH sys info.

PERIODIC LOCATION UPDATEMany times the MS enters non-coverage zone.The MS will keep on paging the MS thus wasting precious resources.To avoid this the MS has to inform the MSC about its current LAI in a set

period of time.This time ranges from 0 to 255 decihours.Periodic location timer value is broadcast on BCCH sys info messages.


During conversation user talks alternatively.In DTX mode of operation the transmitter are switched on only for

frames containing useful information.Helps to increase battery life and reduce interference level.

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DISCONTINOUS TRANSMISSION

SID


IMPLEMENTATION OF DTXVoice Activity Detector ( VAD )

Determines which specific block of 20ms from the speech coder contains speech.

Removes stationary noise.Inserts comfort noise.The frames containing this background noise are called SID frames and

are sent in blocks of 8 frames within every 104 frame block.

VAD Speech / No speech20 ms speech

block


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Thank You!!!