1. Asynchronous Transfer Mode (ATM)

2. By.
P. Victer Paul
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3. Agenda Definition Basic characteristics Why asynchronous
How to access the network
Service Categories
Connections
Protocol Architecture
pros & cons
Troubleshooting

4. ATM – definition
"A transfer mode in which information is organized into cells; it is asynchronous in the sense that the recurrence of cells containing information from an individual user is not necessarily periodic".

5. ATM Characteristics
ATM uses packet switching with fixed length packet of 53 bytes – CELLs. Each cell has a 5-byte header and 48-byte payload
ATM uses Virtual Circuits
ATM can run over any physical layer. Often runs over fiber optics using the SONET standard at speeds of Mbps, 622 Mbps and higher

6. ATM Characteristics
A Cell network uses the cell as the basic unit of data exchange. A cell is defined as a small, fixed-sized block of information
ATM uses asynchronous TDM – to multiplex cells coming from different channels
Uses fixed slots (size of cells)
Fills a slot with a cell from any input channel that has a cell
– slot is empty if none of the channels has a cell to send

7. Asynchronous Transfer Mode (ATM)
MUX
Wasted bandwidth

8. ATM Access ATM is a cell-switched network.
The user access devices, called the endpoints, are connected through a user-to-network interface (UNI) to the switches inside the network.
The switches are connected through network-to-network interfaces (NNIs).

9. STDUCTURE Public UNI X X X X X X X X X Private ATM network Private UNI
Private NNI
Public UNI
Public ATM network A X X X
NNI
Public
UNI X
B-ICI
Public ATM network B X
Public UNI X X

10. ATM Connections two levels of ATM connections:
virtual path connections
virtual channel connections
indicated by two fields in the cell header:
virtual path identifier VPI
virtual channel identifier VCI

11. Virtual Paths
Physical Link
Virtual Channels

13. ATM Service Categories
Real-time services
Constant bit rate – uncompressed audio/video info
Videoconferencing, TV, pay-per-view, VOD, etc.
rt-Variable bit rate
Non-real-time services
nrt-VBR – high end system QoS, critical response time
Bank transactions, airline reservations, etc.
Unspecified bit rate – best-effort service
e.g. text/image messaging, telecommuting
Available bit rate – bursty apps requiring reliable end-to-end connection
e.g. LAN, router-to-router reliability

14. ATM Protocol Architecture
Management plane
Plane management
Control plane
User plane
Layer management
Higher layers
Higher layers
ATM adaptation layer
ATM layer
Physical layer

15. adaptation layer: only at edge of ATM network
data segmentation/reassembly
roughly analogous to Internet transport layer
ATM layer: “network” layer
cell switching, routing
physical layer
AAL user
ATM layer
Physical layer

16. Pros & cons higher transmission speeds quality of service
bandwidth-on-demand
application-independent
Cost
Complexity
Availability

17. Troubleshooting Performing Basic Interface Checks
Determining Network Connectivity
Performing Loopback Tests
Troubleshooting 155-Mbps and 622-Mbps Interfaces
Troubleshooting T1 and E1 Interfaces
Troubleshooting DS3 and E3 Interfaces
Troubleshooting CBR T1 and CBR E1 Interfaces
Troubleshooting 25-Mbps Interfaces

18. References:
Asynchronous Transfer Mode (ATM) fundamentals, white paper from Internation Engineering Consortium
ATM tutorial-fnc educational services
Higher Layer Protocols:TCP/IP and ATM- Eytan Modiano,Massachusetts Institute of Technology
ATM Switch Troubleshooting Guide-Cisco