01 Rn2813-13n 01 Bsssig Overview

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1 Nokia Siemens Networks Presentation / Author / Date / Document Number

BSSSIG: BSS Signalling Overview


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2 Nokia Siemens Networks BSSSIG / Author / May 2008 / Document Number

Module Objectives

After completing the module, the student will be able to:

Explain the need for signaling in telecommunication networks Describe ISO/OSI protocol model

Use protocol analyzer (in practice) to open traces and showsignaling messages


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What is signaling


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The importance of signaling

Signaling is an important part of a telephone call.

In the beginning signaling was just the common language used between

human operators in order to place and manage a voice call. Over the years, signaling methods were developed to properly send

automatic information on who the caller wants to call (the called party) andwho the caller is to the network (identification for billing).


5/385 Nokia Siemens Networks BSSSIG / Author / May 2008 / Document Number

Signaling definition

In telecommunication, signaling isdefined as the exchange of informationbetween involved points in the network(switches or endpoints) that sets up,controls, and terminates each telephonecall.

Signaling is usually transferred from onepoint to the other in separate, dedicatedchannels.



Protocols, Architectures, Interfaces

Signaling standards allow networkelements of different vendors to beconnected together.

Standard = protocols.

Protocols are described byspecifications.

For every telecommunication system

an architecture is defined. Thearchitecture shows the networkelements, their role and theconnections.

Connections between networkelements are called interfaces.

Each interface is a collection ofprotocols



Frames, Messages, Procedures

Every protocol has its own structure,usually made of header, protocol dataand footer

Every protocol is like a differentlanguage with its own dictionary.

Wordsin the dictionaryare calledmessages.

A conversationis called procedure. Conversation can involve different

languages, i.e. procedures can usemessages from different protocols.

Header Protocol data Footer


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What is protocol analyzer used for in everydaymaintenance?

Trouble

shooting

De

bugging

Multi

Vendor

Diagnose

Transmission

Subscriber

Trace

Tool

Network

Perfor

mance

Fault

Finding


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The ISO / OSI protocol stack model


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The importance of the OSI model

The OSI model divides the functions of a protocol into aseries of layers.

Each layer only uses the functions of the layer below,

Each layer only exports functionality to the layer above.

The group of these layers is known as a 'protocol stack' or'stack'.

Exceptions to stacks are called fast path and includeaspects of several layers.

7. Application

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link

1. Physical


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Layer 1: Physical Layer

The Physical layer defines all the electrical and physicalspecifications for devices. This includes the layout of pins,voltages, radio signal and cable specifications. Panels,repeaters, network adapters are physical-layer devices.

The major functions and services performed by the physicallayer are:

Medium synchronization.

Medium sharing. Modulation, or conversion.

In some cases Layer 1 is included in Layer 2 because thelogical link is sometimes strictly related to the way oftransmitting data.

7. Application

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link

1. Physical


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Layer 2: Data Link Layer 1/2

The Data Link layer provides the functional and proceduralmeans to transfer data between network entities.

Functions of the data link layer:

Framing. The data link layer divides the stream of bitsreceived from the network layer into data units called frames.

7. Application

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link

1. Physical


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Physical addressing. If frames are to be distributed todifferent systems on the network, the data link layer adds aheader to the frame to define the physical address of thesender (source address) and/or receiver (destination address)of the frame. If the frame is intended for a system outside thesenders network, the receiver address is the address of thedevice that connects one network to the next.

7. Application

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link

1. Physical


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Physical addressing. If frames are to be distributed todifferent systems on the network, the data link layer adds aheader to the frame to define the physical address of thesender (source address) and/or receiver (destination address)of the frame. If the frame is intended for a system outside thesenders network, the receiver address is the address of thedevice that connects one network to the next.

Flow Control. If the rate at which the data are absorbed bythe receiver is less than the rate produced in the sender, the

data link layer imposes a flow control mechanism to preventoverwhelming the receiver.

7. Application

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link

1. Physical


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Functions of the data link layer (cont.):

Error control. The data link layer adds reliability to the physicallayer by adding mechanisms to detect and retransmit damaged orlost frames. Error control is normally achieved through a trailer tothe end of the frame.

7. Application

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link

1. Physical


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Functions of the data link layer (cont.):

Error control. The data link layer adds reliability to the physicallayer by adding mechanisms to detect and retransmit damaged orlost frames. Error control is normally achieved through a trailer tothe end of the frame.

Access Control. When two or more devices are connected to thesame link, data link layer protocols are necessary to determinewhich device has control over the link at any time.

The data link layer is usually divided into two sublayers The MAC (Media Access Control) sublayer controls how a

computer on the network gains access to the data and permissionto transmit it.

The LLC (Logical Link Control) sublayer controls framesynchronization, flow control and error checking.

7. Application

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link

1. Physical


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Layer 3: Network Layer

The Network layer is responsible for the source-to-destination delivery of a packet possible across multiple

networks, adding a proper header.

Functions of the network layer:

Logical addressing: usually independent from thephysical (hardware) address

Routing: i.e. finding the way to reach the destination.

Internetworking A typical example is the IP (Internet Protocol)

7. Application

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link

1. Physical

L T L


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Layer 4: Transport Layer 1/2

The transport layer is responsible for process-to-processdelivery of the entire message, that is from software to

software at the two ends of the communication.

The functions of the transport layer are:

Port or protocol addressing: computer or networkelements often run several processes (running programs)at the same time. Process-to-process delivery meansdelivery from a specific process on one computer to a

specific process on the other.

7. Application

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link

1. Physical

L 4 T L 1/2


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specific process on the other. Flow control: the transport layer performs a flow control

end to end. The data link layer performs flow controlacross a single link.

7. Application

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link

1. Physical

L 4 T t L 1/2


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specific process on the other. Flow control: the transport layer performs a flow control

end to end. The data link layer performs flow controlacross a single link.

Error control: the transport layer performs error controlend to end. The data link layer performs control across a

single link.

7. Application

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link

1. Physical

L 4 T t L 2/2


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Functions of Transport Layer (cont.):

Segmentation and reassembly: a message is divided intotransmittable segments, each having a sequence number.

Connection control: The transport layer can be eitherconnectionless or connection-oriented.

A connectionless transport layer treats each segment as anindependent packet and delivers it to the transport layer at thedestination machine.

A connection-oriented transport layer makes a connection withthe transport layer at the destination machine first beforedelivering the packets.

7. Application

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link

1. Physical

Layer 5 Session Layer


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Layer 5: Session Layer

The Session layer controls the dialogues (sessions)between computers.

It establishes, manages and terminates the connectionsbetween the local and remote application.

It provides for either duplex or half-duplex operation andestablishes check pointing, update, termination, and restartprocedures.

This layer is often removed or merged with Layer 5 or withLayer 7

7. Application

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link

1. Physical

Layer 6: Presentation Layer


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Layer 6: Presentation Layer

The presentation layer was designed to handle the syntaxand semantics of the information exchanged between the

two systems. It was designed for data translation, encryption, decryption,

and compression.

The Presentation layer transforms data to provide astandard interface for the Application layer.

MIME encoding, data compression, data encryption andsimilar manipulation of the presentation is done at this layerto present the data as a service or protocol developer seesfit.

Examples: converting an EBCDIC-coded text file to anASCII-coded file, or serializing objects and other data

structures into and out of XML. This layer is often removed or merged in Layer 7

7. Application

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link

1. Physical

Layer 7: Application Layer


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Layer 7: Application Layer

The Application layer is closest to the end user (human orautomatic).

It provides a means for the user to access information onthe network through an application.

This layer is the main interface for the user(s) to interactwith the application and therefore the network.

Some examples of application layer protocols include

Telnet, File Transfer Protocol (FTP), Simple Mail TransferProtocol (SMTP) and Hypertext Transfer Protocol (HTTP).

7. Application

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link

1. Physical

The stack of layers


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The stack of layers

The seven layers weredesigned as a stack of

layers. Data flows from user to

user through all thelayers (if present)

Every entity at thesame layer is virtuallyconnected to the samelayer at the other end.

Network / User layers


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Network / User layers

Layers from 1 to 3 are usually referredto as

network layers,

sub-network layers, or

media layers.

Implementation of network layers isusually hardware based

Layers from 4 to 7 are referred to as user part layers,

application layers, or

host layers.

Implementation of application layers is

very often software based

Layer 5 to 7


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Layer 5 to 7

Layers 5 to 7 are usually represented and designed together because often theapplication also defines new formats and different ways of keeping track of

sessions. That is the reason why the application layer is often represented near the

transport layer

Headers


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Headers

Every protocol has its own headers and footers (or trailers)

From the application layer to the physical layer, many headers and footers areadded by every layer.

Header DATA Footer

Data units


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Data units

At every layer data units, or PDU(protocol data units) assume a

different name:

Data

Segment

Packet

Frame

Bits

A useful parallel


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A useful parallel

Here is a useful parallelbetween ISO/OSI

network layers andsending a snail mail fromcompany to company.


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The tool to look at signaling

NetHawk Protocol Analyzer

The need for a protocol analyzer


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The need for a protocol analyzer

Telecommunication devices are usually connected by E1 cables where data flows in 32timeslots at a speed of 64kbps each.

In every timeslot flows user data or signaling. In some cases signaling links can havehigher (A or Gb) or lower speed (Abis).

Even at the lowest bit rate (8kbps), the information that flows in a signaling link is toomuch to be understood by a human being.

The signaling flow is therefore decoded and presented by a protocol analyzer.

Protocol analyzers are computer software (usually) or computer hardware that can

intercept and log traffic passing over a digital network or part of a network. As datastreams travel back and forth over the network, the analyzer captures each packet andeventually decodes and analyzes its content according to the appropriate protocol orother specifications.

Protocol analyzers are able to identify and show every message of every protocol fromthe interface they are set up for, without interfering with the actual transmission of thedata.

NetHawk


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et a

Nokia co-operates with anotherFinnish company, vendor of protocol

analyzers: NetHawk. The NetHawk GSM Analyzer is an

effective and easy-to-use PC-basedprotocol analyzer for real-timemonitoring and analysis of GSM,GPRS and EDGE networks.

Learning how to use NetHawk is thebest way to learn signaling for Nokiacustomers because:

The layout is similar to Nokiaservice terminal extension forsignaling.

The software can be used freely inoff-line mode without the NetHawkinterface adapters.

How to start


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For on-line monitoring you need a laptopequipped with a NetHawk N2 or a

desktop equipped with a NetHawk NAPcard.

Cards should be connected to patchpanels (or DDF) with proprietary cables.Extensions can easily deteriorate thesignal.

Impedance of the card should match theone of the monitored cable (75-120).

Impedance is set to HIGH not to disturbthe communication. It is set to LOW todivert signaling to the interface only(simulation).

Every card has its own HW id and SWid.

The software


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Both for on-line monitoring and for off-lineuse, a software is needed.

In case of on-line monitoring, the SW id ofthe installed software should match theSW id of the card in use.

The Protocol Info tab shows thespecifications used to decode themessages. These protocols should matchthe one used in the network element inorder to look at signaling closer to the realone.

User interface


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The user interface is made of

A menu bar

A toolbar with configurablebuttons

A monitoring window

A status bar with clickableindicators.

To work on-line


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The first thing to check when workingon-line is if the signal is good or not

(open the State Monitor window) If not check the cables and the HWoptions of each connection.

Monitoring should be the same as inthe N2 hardware card. HIGH is normaluse.

Interface mode should be E1 in

Europe Condensed mode is not influent

SPEC should be ITU-T in Europe

Pointcode should be 14 in Europe

3GPP should be the same as in NE

Increasing the AGC maximum value

can decrease the CRC warnings. AGC is one per NAP card and is

automatically set.

In any case


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Both for on-line and off-line monitoringit is possible to specify the detail

shown per each layer. Both for on-line and off-line monitoring

it is possible to specify whichconnection to monitor and whatprotocol stack assume is flowingthrough it.

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