ATM

1. DIT
Dar es Salaam institute of Technology (DIT)
ETU 07420
Switching Systems
Ally, J
jumannea@gmail.com

2. DIT
Asynchronous Transfer Mode
(ATM)

3. DIT
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?

4. DIT
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.

5. DIT
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

6. DIT
ATM can provides both CBR and VBR
transport

7. DIT
Connectionless & Connection-
oriented
Setup
Setup
Setup
Setup
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.

8. DIT
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.

9. DIT
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).

10. DIT
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

11. DIT
ATM Network Model
UNI
UNI
UNI
PNNI
PNNI
NNI
NNI NNI
NNI
NNI
NNI
NNI
ICI Other
Network
NNI ： Network Node Interface
UNI ： User Node Interface
ICI ： Inter-carrier Interface
PNNI ： Private Network Node
Interface

12. DIT
ATM Interfaces
The 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

13. DIT
ATM Cell

14. DIT
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.

15. DIT
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

16. DIT
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 Terminal
Cell and user’s
data change
each other

17. DIT
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

18. DIT
Types of ATM Virtual Connection
According 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)

19. DIT
UNI cell
VPC and VCC
ATM terminal A C
ATM network node G UNI cell
NNI cell NNI cell
VC
switching
VCC
VPC
VCC
UNI cell UNI cell
B D
For 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

20. DIT
Cells
Voice
Data
Video
 Connection oriented
 Fast packet switching
 Statistical multiplexer
 Supports voice, data and video service
 Provides QoS
Features of ATM

21. DIT
ATM Protocol Structure Model
USER
SAAL
ATM Layer
Physical Layer
AAL
USER
Service and signaling
of user
Information of user
and cell conversion
Cell exchange and
multiplexing or
demultiplexing
Frame structure
physical medium
Impartible
management
of all layer
Independent
management
of every layer
Call connection
and Control
User information 、 Flow
Control and Error Recovery
Interface Management
Layer Management
Control interface User interface

22. DIT
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.

23. DIT
ATM Sublayer Model
ATM Protocol Stack Model OSI Reference Model
User
PMD
TC
PHY
ATM
AAL
CS
SAR
Interface
manage
ment
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data link
1 Physical

24. DIT
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

25. DIT
 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

26. DIT
 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

27. DIT
Function of ATM AAL Overview
Function 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
Constant
Bit Rate
Data
Bursts
Variable
Bit Rate
ATM Cell
Multiplexing
AAL SDU

28. DIT
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 services
AAL type 2–meets the needs of class B services
AAL type 3/4-meets the needs of class C and D services
AAL type 5–meets the needs of class D services
Service type A B C D
Bit rate constant variable variable variable
Real time YES YES NO NO
Connection mode Connection oriented connectionless
AAL AAL1 AAL2 AAL3/4 AAL5

29. DIT
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)

30. DIT
(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

31. DIT
TCP/IP Process
App 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
AAL5
CS
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

32. DIT
Thanks!
Technology changes but communication lasts.