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Dar es Salaam institute of Technology (DIT)
ETU 07420
Switching Systems
Ally, J
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Asynchronous Transfer Mode (ATM)
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To provide a high-speed, low delay
multiplexing and switching network to any type of
user traffic, such as voice support, data,or video
applications.
Why do we need a new technology?
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What is ATM?ATM for Telecommunications is Asynchronous
Transfer Mode, (not Automatic Teller Machine!).ATM is a flexible high bandwidth, low delay
network technology that is capable of handling voice, video and data on a single network; and mostly used in the backbone
In general, ATM means that traffic is carried in small, fixed-length packets called cells.
A technology that integrates advantages of circuit switch and packet switch.
ATM can support any type of user services, such as voice, data, or video service.
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ATM Overview
53byte fixed length cell= 5Bytes cell header+48Bytes payload.
ATM must set up virtual connection before communication.
ATM network will confer with terminal on parameter of QoS before the connection is set up.
Contract
5-Bytes Header
48-Bytes Payload
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ATM can provides both CBR and VBR transport
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Connectionless & Connection-oriented
Setup
Setup
SetupSetu
p
Connectionless: Every packet is transferred from different routes, so the receiving order of packets doesn’t possibly depend on the sending order.
Connection-oriented : All packets are transferred from the same route , so the receiving order of packets depends on the sending order. Time delay is fixed.
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ATM Switch Model’s Characteristic Any user’s cell will not be send
periodically, and bandwidth will be shared and statistically multiplexed.
Many types of service can be transferred in the same time and Quality of Service is supported in an ATM network.
Fixed length cell, so switch can be controlled by hardware and high-speed switching is easy to be realized.
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ATM’s Advantage Integration of various services such as voice, image, video, data and
multimedia.
Standardization of network structures and components. This results in cost savings for network providers.
Transmission that is independent of the medium used PDH, SDH, SONET and other media can be used to transport ATM cells.
ATM is scaleable, i.e. the bandwidth can be adapted extremely flexibly to meet user requirements.
Guaranteed transmission quality to match the service required by the user (quality of service, QoS).
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ATM’s Application In Switching:
Traditional Exchange is evolving into Broadband Exchange by ATM’s application
In Transmission: ATM virtual path exchange node and ATM
Add/Drop Multiplexer
In Internet: ATM router applied in IP Switching, Multi-Protocol
Label Switching
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ATM Network Model
UNI
UNI
UNI
PNNI
PNNI
NNI NNI NNI
NNI
NNI
NNI
NNI
ICI Other Network
NNI : Network Node InterfaceUNI : User Node InterfaceICI : Inter-carrier InterfacePNNI : Private Network Node Interface
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ATM InterfacesThe following ATM interfaces have been defined and standardized Private UNI (user-node interface) –specification of the interface
between a user’s device (e.g. a workstation) and a private ATM switch
Private NNI (network-node interface) –e.g. between private ATM switches needed to support the ATM infrastructure
Public UNI–specification of the interface between the user’s device and a provider of a public ATM service
Public NNI–interface between ATM switches in public carrier networks.
Also referred to as B-ISSI (broadband inter-switching system interface) when applied to the connection between two public
switches of the same carrier Also referred to as B-ICI (broadband inter-carrier interface) when applied to the connection between two carriers networks
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ATM Cell
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ATM Cell GFC ( Generic Flow Control): It is intended for control of a possible
bus system at the user interface and is not used at the moment. VPI ( Virtual Path Identifier): The VPI contains the second part of the
addressing instructions and is of higher priority than the VCI. VCI ( Virtual Channel Identifier): VCI in each case indicates a path
section between switching centers or between the switching center and the subscriber.
PTI ( Payload Type Identifier): Indicates the type of data in the information field.
CLP ( Cell Loss Priority): Determines whether a cell can be preferentially deleted or not in the case of a transmission bottleneck.
HEC ( Header Error Control): Provided in order to control and, to some extent, correct errors in the header data that may occur. The HEC is used to synchronize the receiver to the start of the cell.
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ATM Connection There are two types of ATM connections
Virtual path connections –identified by virtual path identifiers (VPI) Virtual channel connections –identified by a combination of virtual path
and circuit identifiers (VPI and VCI) Virtual channels (VC)
are the basic unit that carry a stream of ATM cells from one user to another are identified by a virtual channel identifier can be configured statically as PVCs (permanent virtual circuits) that are
set up at network configuration time and dynamically as SVCs (switched virtual circuits) that are dynamically configured on-demand
can be bundled together into virtual path connections Virtual paths (VP)
contain one or more virtual channels are identified by a virtual path identifier are routed through a network as a single entity can be used internally for bundling virtual circuits between switches
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Port 1 VPI=2 VCI=37
VPI=3 VCI=39
NNI
UNI
UNI
ATM Cell Switching
ATM Switch
Port VPI VCI 1 2 37 2 1 51
Port 2
Port 1 ATM Switch
Port VPI VCI 1 1 51 2 3 39
Port 2
ATM TerminalUser B
User A
ATM Network Node
Cell and user’s data change each other
VPI=1 VCI=51
ATM Network Node
ATM TerminalCell and user’s data change each other
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Permanent Virtual Channel (PVC): The connections are analogous to leased lines that are switched between certain users. A change can only be made by the network provider. This type of ATM network often forms the initial stage in the introduction of this technology.
Switch Virtual Channel (SVC): Users connected to this type of network can set up a connection to the user of their own choice by means of signaling procedures. This can be compared with the process of dialing a telephone number.
Signaling In ATM
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Types of ATM Virtual ConnectionAccording to the switching mode, ATM Virtual Connection can be classified :
VPC (Virtual Path Connection)
VCC (Virtual Channel Connection)
According to connection establishment, ATM Virtual Connection can be classified:
SVC(Switching Virtual Connection)
PVC(Permanent Virtual Connection)
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UNI cell
VPC and VCCATM terminal A C
ATM network node G UNI cell
NNI cell NNI cellVC
switching
VCC
VPC
VCC
UNI cell UNI cell
B DFor example: When E receives cells from A or B, which would be transferred to C or D, the VPI of these cells would be set to uniform value in E. These cells would be received by G and switched to F by VP switching. Then the cells will be delivered to C or D at F. It means that VPC has been set up between E and F, while VCC has been set up among A, B, C and D.
E F
VP switching
VC switching
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Cells
Voice
Data
Video
Connection oriented Fast packet switching Statistical multiplexer Supports voice, data and video service Provides QoS
Features of ATM
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ATM Protocol Structure Model
USER
SAAL
ATM Layer
Physical Layer
AAL
USERService and signaling of user
Information of user and cell conversion
Cell exchange and multiplexing or demultiplexing
Frame structure physical medium
Impartiblemanagement of all layer
Independent management of every layer
Call connection and Control
User information 、 Flow Control and Error Recovery
Interface ManagementLayer Management
Control interface User interface
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Three Communications Planes The user plane transports the user data for an
application. It uses the physical, ATM and ATM adaptation layers to do this.
The control plane takes care of establishing, maintaining and clearing down user connections in the user plane. The key word here is signaling.
The management plane includes layer management and plane management. Layer management monitors and coordinates the individual layer tasks. Plane management handles monitoring and coordination tasks in the network.
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ATM Sublayer ModelATM Protocol Stack Model OSI Reference Model
User
PMD
TCPHY
ATM
AALCS
SARInterface manage
ment
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data link
1 Physical
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Two sublayers:
Transmission Convergence Sublayer (TC)
transmission frame generation/recovery Processing HEC (Header Error Control) cell delimiting transmission frame adaptation
Physical Medium Dependent Sublayer (PMD)
Link coding Network physical medium
Function of ATM Physical Layer
AAL
ATM
PHY
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Cell switch
Quality of Service
Processing the cell header
Types of payload
Multiplexing /Demultiplexing of different connection cell
Function of ATM Layer
AAL
ATM
PHY
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Support services for user
Segment and reassemble
Complete the change between User-PDU and ATM payload
Function of ATM Adaptation Layer (AAL)
AAL
ATM
PHY
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Function of ATM AAL OverviewFunction of ATM AAL:
Provide a high-speed,
low delay multiplexing
and switching network
to support any type of
user service, such as
voice, data,or video
applications.
ATM Payload
ConstantBit Rate
Data Bursts
Variable Bit Rate
ATM Cell
Multiplexing
AAL SDU
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Types of AAL
In order to support different types of user services, there are five types of AAL. AAL type 1–meets the needs of class A servicesAAL type 2–meets the needs of class B servicesAAL type 3/4-meets the needs of class C and D servicesAAL type 5–meets the needs of class D services
Service type A B C DBit rate constant variable variable variable
Real time YES YES NO NOConnection mode Connection oriented connectionless
AAL AAL1 AAL2 AAL3/4 AAL5
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Service Types of ATM layer CBR (Constant bit rate) Intended to support real-time applications requiring tightly constrained delay variation (e.g. voice, video) VBR-NRT (Variable bit rate-non real time) Intended for non-real-time applications with bursty traffic (e.g. multimedia-email) VBR-RT (VBR-real time) intended for real-time applications with bursty traffic (e.g. compressed video/voice) UBR (Unspecified bit rate) Represents a “best-effort service intended for non-real-time applications that do not require tightly constrained delay or delay variation and are tolerant to cell loss ( widely used today for TCP/IP) ABR (Available bit rate) similar to UBR but enhanced to handle applications that require a minimum bandwidth requirement (e.g. email and file transfer)
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(IP over ATM) IPOA Protocol Stack
ATM network Physical layer
IP address is mapped to PVC or SVC
User application
ATM
AAL
IP
TCP/UDP
ATM
AAL
IP
TCP/UDP
IP packet is transferred to ATM Payload
User application
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TCP/IP ProcessApp DataTCP Header
TCP header App DataIP Header
IP Header TCP Header App DataLLC
SAR-SDU#1 SAR-SDU#2 SAR-SDU#3 SAR-PDU#4 SAR-PDU#5
TCP
IP
SNAP/LLC
AAL5CS
SAR
ATM
PHY
Cell header will be added to SAR-PDU, whose VPI and VCI depends on the map table of IP address to PVC/SVC. Then ,the cells will be sent to Physical Layer.
Perform the transmission of ATM cells via physical media.
LLC IP Header TCP Header App Data PAD CPCS-PDU Tail
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Thanks!
Technology changes but communication lasts.
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