1. Introduction to Asynchronous Transfer Mode (ATM)
© N. Ganesan, Ph.D.
(Copyrights of sections as acknowledged.)

2. Acknowledgment
This presentation is based on ATM related information provided on the CISCO website, the IEC website and the ATM Forum.
Asynchronous Transfer Mode (ATM) Switching
ATM Fundamentals
ATM Presentations (Good set of PowerPoint presentations).

3. Chapter Objectives

4. Chapter Modules

5. ATM Defined
“ATM is a cell-switching and multiplexing technology that combines the benefits of circuit switching (guaranteed capacity and constant transmission delay) with those of packet switching (flexibility and efficiency for intermittent traffic)” –CISCO.
It utilizes fixed length cells to carry the information

6. Areas of Application Infrastucture
Backbones
LAN
LANsAsynchronous transfer mode (ATM) is a high-performance, cell-oriented switching and multiplexing technology that utilizes fixed-length packets to carry different types of traffic. ATM is a technology that will enable carriers to capitalize on a number of revenue opportunities through multiple ATM classes of services; high-speed local-area network (LAN) interconnection; voice, video, and future multimedia applications in business markets in the short term; and in community and residential markets in the longer term.

7. Infrastructure
Backbones
LAN
Application

8. ATM Connections

9. Circuit Switching and Packet Switching
ATM is circuit switched because it establishes virtual circuits for communication
At the same time, the virtual circuits are established over packet switched networks
As such, it combines the benefits of circuit switched and packet switched technologies

10. ATM Usage and Bandwidth
In theory, ATM can be deployed from small LANs to very large WANs
At present, it is used mostly on backbones, but this may change in the future with declining prices for ATM equipment
ATM deployments can operate at speeds starting in the Mbps range scaling up to Gpbs range
Speed wise, it is very scalable

11. ATM’s Efficiency
It is an asynchronous technology and it uses the links based on the need for information to be transmitted
ATM is based on fixed length cells and the cells are small compared to many other forms of transmission such as frame relay etc.

12. ATM Cell Basics ATM carries information based on fixed length cells
Compare this to the other packet switching technologies such as Frame Relay etc. where each packet may be of a different length
The length of each cell is 53 Bytes
First 5 bytes are used as the cell header
Next 48 bytes are used as the payload carrying the data

13. ATM Cell Format
5 Bytes
48 Bytes
Header
Payload (Data)

14. Fixed Length Cell Advantage
Delay or latency is significantly reduced
ATM is therefore suited for voice and video transmission
Fixed length cells make it easier to switch data across multiple networks
ATM networks are built based on switches and not routers
Fixed length cell is similar to container based road transportation
Some parallels can be drawn with respect to the advantage of fixed length transportation based on the benefits of container transportation

15. ATM Cell Header Format ATM Cell Header—UNI Format
ATM Cell Header—NNI Format

16. ATM Devices ATM networks are built around two categories of devices
ATM Switch
ATM end-point
An ATM switch can be connected to either another ATM switch or and ATM end-point

17. ATM End-Points Will contain and ATM end-point adapter
Examples of ATM end-points
Workstations
LAN switches
Routers
DSU/CSU Units
Video Coder-Decoders (CODECs)

18. Devices on Which ATM Has Been Implemented
PC, workstation, and server network interface cards
switched-Ethernet and token-ring workgroup hubs
workgroup and campus ATM switches
ATM enterprise network switches
ATM multiplexers
ATM–edge switches
ATM–backbone switches
Source:

19. ATM Network Components
Source: CISCO

20. ATM Switches and Interfaces
ATM switch supports two types of interfaces
User-Network Interface (UNI)
Connects an ATM end-point to a switch
Network-Network Interface (NNI)
Connects two ATM switches

21. Public and Private Interfaces
UNI and NNI can further be divided to two types
One is known as the private type and the other is known as the public type

22. Private and Public UNI Private UNI Public UNI
Connects an ATM end-point to a private ATM switch
Public UNI
Connects an ATM end-point or a private ATM switch to a public ATM switch

23. Private and Public NNI Private NNI Public NNI
Connects two ATM switches within the same private organization
Public NNI
Connects two ATM switches within the same public organization

24. A third Type of Interface
Known as Broadband Inter-Carrier Interface (BICI)
Connects two public switches from different service providers

25. Public and Private Interfaces
Source: CISCO

26. ATM Standards UNI 2.0, 3.0, 4.0 P-NNI LAN Emulation (LANE)
For the use of ATM over Ethernet, Token ring etc.
Multi-protocol Over ATM

27. ATM Standards for Digital Lines
Area of Application
Speed
Standard T1
25 Mbps
Yes
T3/E3
155 Mbps
OC-3
622 Mbps Y
OC-12
2.4 Gbps
Check the ATM Forum for approved standards for
further information.

28. ATM Services There are basically three types of ATM services
Permanent Virtual Circuits (PVC)
Switched Virtual Circuits (SVC)
Connectionless Service
Note: SVC is the most widely used service

29. ATM Virtual Connections
Two types of connections exist
One is known as the Virtual Path (VP)
The other is known as the Virtual Circuit (VC)

30. Virtual Connection Composition
There can be a number of virtual paths along a physical connection and there can be a number of virtual circuits within a virtual path

31. Virtual Circuits and Paths
Source: CISCO

32. Transmission Path (Physical Media)
Physical medium standards to carry ATM include the following:
Synchronous Digital Hierarchy/Synchronous Optical Network (SDH/SONET)
DS3/E3
Over Multi-Mode Fiber (MMF) at 155 Mbps
Over Shielded Twisted Pair (STP) at 155 Mbps

33. ISO-OSI and ATM Models

34. LAN Emulation (LANE)
Defined by the ATM forum to emulate popular LAN protocols such as Ethernet and Token Ring
In other words, “the LANE protocol makes an ATM network look and behave like either the Ethernet or the Token Ring network” – CISCO
An emulated LAN is known as ELAN

35. Multi-Protocol Over ATM (MPOA)
Enables the transmission of data between ELANs without having to continuously go through certain routers
After the initial flow of data through routers known as Multi-Protocol Servers (MPS), it would be directed along the path of ATM switches (See next slide and CISCO documentation)

36. Data Flow Between ELANs with and without MPOA

37. ATM Quality of Service (QoS)
ATM’s advantage over competing technologies is that it is able to offer a specified QOS
For example, ATM providers can guarantee to their customers that the end-to-end latency will not exceed a specified level

38. QoS Offered by ATM Constant Bit Rate (CBR) Variable Bit Rate (VBR)
Unspecified Bit Rate (UBR)
Available Bit Rate (ABR)

39. Constant Bit Rate (CBR)
Highest grade service (Grade A)
A constant bandwidth is available for the virtual channel
Suitable for voice-over-IP (Transfer fixed rate uncompressed video), and other traffic that requires steady, guaranteed throughput

40. Variable Bit Rate (VBR)
Second in the level of service (Grade B)
It is divide into to categories
Variable Bit Rate Non-Real Time (VBR-NRT)
Variable Bit Rate Real Time (VBR-RT)

41. Variable Bit Rate Non-Real Time VBR-NRT
Provides bandwidth only as needed
Traffic that is not very sensitive to cell-delay or latency is handled by this service
An example use would be to send multimedia

42. Variable Bit Rate Real Time VBR-RT
Again, this is similar to VBR-RT in providing bandwidth as needed
But VBR-RT is designed for applications where cell-delay or latency cannot be accommodated

43. Sample Applications for VBR-RT
Voice with speech activity detection
Telephony
Compressed interactive video
Video conferencing

44. Available Bit Rate (ABR)
Third in the level of service (Grade C)
Bandwidth is adjusted based on the amount of traffic in the network
Suitable for data traffic such as file transfer and that are basically not time sensitive

45. Unspecified Bit Rate (UBR)
Fourth in the level of service (Grade D)
Dose not offer any fixed values for the traffic parameters

46. QoS Enforcement Traffic contract Traffic shaping Traffic policing
(See CISCO document for more details)

47. Competing Technologies
Frame Relay competes at the backbone
Eventually, ATM will be the choice for backbone technology
Gigabit Ethernet
ATM’s competition on the desktop area and LANs will be challenged effectively by high speed and proven Ethernet technologies

48. End of Module

49. Practical ATM Networks
© N. Ganesan, Ph.D.

50. Chapter Objectives

51. ATM Interfaces
ATM
ATM and other technologies.
Source: CISCO

52. ATM Network Building Block
The main building block of ATM networks is the ATM switch
Workgroup switch
Campus switch
Enterprise switch
Multi-service access switch

53. ATM Network Hierarchy
Source: CISCO

54. Work Group Switch These switches will have Ethernet and ATM ports
Used for connecting Ethernet networks to ATM switches
Note: At the desktop level Ethernet still remains as the leading network technology

55. Campus Switch Used for designing small-scale ATM backbones
Can be used for connecting various campus backbone technologies
FDDI
Gigabit Ethernet etc.

56. Move from Traditional to New Backbones

57. Enterprise ATM Switch Used in building large enterprise backbones
Can be used for integrating different services and technologies on the backbone

58. Multi-Service Access Switch
A common ATM infrastructure can be used in a public network to support disparate services
Frame relay
LAN interconnection
Public ATM services
Their use usually extends beyond a private network to a public network
Used by service providers to connect MANs and WANs for example

59. ATM Interface Types User-to-Network Interface (UNI)
Network-to-Network Interface (NNI)

60. Interface Types in a Network
Source: CISCO

61. ATM Interfaces
LAN interfaces
Backbone interfaces

62. ATM to LAN Interface
Source:

63. LAN Emulation Issues Emulate an Ethernet LANs
Map traditional LAN addresses to ATM addresses

64. ATM to WAN Interface Source: CISCO DXI – Data Exchange Interface
HSSI – High Speed Serial Interface
DSU – Data Service Unit

65. Load Balancing with ATM Switches
Source: CISCO

66. Summary ATM networks are basically built around ATM switches
ATM interfaces can be used for integrating disparate WAN technologies
At the desktop LAN, ATM can be used for emulating the traditional Ethernet environment for example
But, in general, the Ethernet technology is very popular in terms of ease of use and speed
Therefore, ATM at the LAN front is likely to be used for connecting Ethernet LANs to the backbone if the backbone is based on ATM
For the backbone and large public backbones, ATM is bound to become the technology of choice

67. References At CISCO ATM Forum
ATM Forum