Mumbai University EXTC (Third Year) Sem 6 CCTN

1. Asynchronous Transfer Mode (ATM )
Kiran Chhatwani
Shreyas Dighe
Priyanka Holkar
Praveen Menghani

2. ATM – DEFINITION
• Definition: A high-performance, cell-oriented switching and multiplexing
technology that utilizes fixed-length packets to carry different types of traffic.
• Asynchronous Transfer Mode (ATM ) is a switching technique for
telecommunication networks. It uses asynchronous time-division multiplexing, and
it encodes data into small, fixed- sized cells.

4. WHY ATM ?
• Optical fibre offered new transmission media less susceptible to noise with very
high data rates.
• Existing system not utilising its full potential.
• A new system is required which --
Could interface with existing system of packet transmission.
Is inexpensive.
Capable of supporting existing hierarchies as local loop, local service provider
etc.
Is connection oriented / virtual circuit switched.
Has more functions in hardware to get more speed.

5. 7
ATM FEATURES
• Service is connection oriented, with data transferred over a Virtual Circuit.
• A Cell-Switched Network (Architecture).
• Fixed-size cell (53-Bytes).
• Uses Asynchronous Time-division Multiplexing (Asynchronous TDM)
• The Quantity of Service (QoS) enable carriers to transmit voice, data, and video.
• ATM is independent of the transmission medium.
• ATM cells can be sent on a wire or fiber, and can also be packaged inside the
payload of other carrier system.

6. ATM REFERENCE MODEL

7. ATM LAYER
• ATMlayer provides routing, traffic management, switching and multiplexing
services.
• Processes outgoing traffic by accepting 48 bytes segment.
• AAL sublayertransforms them to 53 bytes cell by adding 5 byte header as per
UNI or NNI.

8. ATM ADAPTATION LAYER (AAL)
• Enables ATM to accept any type of
payload, both data frames and streams
of bits
• Fragments them into small and fixed-
size Cells
• Reassembles Cells
• Convergence sub layer (CS): prepares data to ensure their integrity, providing standard interface.
• Segmentation and Reassembly (SAR): Segments the payload into 48-byte cells, and at the destination, reassemble
them to recreate the original payload.

9. ATM defines four versions of the AAL:
 AAL1: Support Constant-bit-rate data (CBR) from upper layer; video and voice.
 AAL2: Used for low-bit-rate and short-frame traffic such as audio (compressed
or uncompressed), video, or fax. AAL2 allows the multiplexing of short frames
into one cell.
 AAL3/4: Supports connection-oriented and connectionless data services.
 AAL5: Assumes that all cells belonging to a single message travel sequentially
and that control functions are included in the layers of the sending application.

10. Constant-bit-rate (CBR): Application that generates and consumes bits at a constant rate.
Real time with minimum td.
Real time voice (telephone) and video (TV).

11. Variable-bit-rate(VBR): Application that generates and consumes bits at variable rates.
Bit rate varies section to section within a limit.
Compressed voice, data and video.

12. Connection Oriented Packet Data:
Conventional packet application.
X.25, TCP protocol of TCP/IP that
uses virtual circuits.
Connection Less Packet Data:
Applications that use Datagram
approach to routing.
IP protocol of TCP/IP AAL3 and
AAL4 overlap hence combined to
AAL3/4.

13. Point-to-point: Cuts across all above data types but for Point-to-Point.
This sublayer is also called SEAL Simple and Efficient Adaptation
Layer.

14. ARCHITECTURE OF AN ATM NETWORK
• User-to-network interface (UNI):
interface between endpoint (user access
devices) and network switches.
• Network-to-network interface (NNIs):
interface between switches insides the
network.
vc
vp vp
vc
vp
vc

15. ATM VIRTUAL CONNECTION
• TP - Transmission path
• VP - Virtual path
• VC - Virtual circuit
• Transmission Path – Physical connection like wire, cable, satellite . (between an end point and a switch or between two switches)
• Virtual Path – Set of connections between two switches. ( combination of VCs bundled together because parts of their path are
same)
• Virtual Circuits – All cells belonging to a single message follow same virtual circuit, in original order till destination. (logical
connections)

16. ATM FRAME AND HEADER
STRUCTURE

17. ATM ROUTING
• A cell of 53 bytes is used as a data unit for transfer.
• ATM uses two types of connections: a Permanent Virtual Circuit (PVC) and a Switch Virtual
• Circuit (SVC).
• ATM uses switches to route the cell from one source endpoint to the destination
• A switch routes the cell using both the VPIs and the VCIs.

18. CONCEPTUAL VIEW OF VPC SWITCH

19. CONCLUSION
• ATM is a flexible and powerful technology which integrates the cell-switching
and multiplexing functions, and enables transmissions over a variety of carrier
system.
• It’s designed for high performance multimedia networking, and suitable for busy
traffic.
• ATM technology is a powerful common platform for LAN and WAN to increase
productivity, to reduce costs and to implement new applications and service.