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8/3/2019 1-Asynchronous Transfer Mode (ATM)
http://slidepdf.com/reader/full/1-asynchronous-transfer-mode-atm 1/18
Asynchronous Transfer Mode
(ATM)
8/3/2019 1-Asynchronous Transfer Mode (ATM)
http://slidepdf.com/reader/full/1-asynchronous-transfer-mode-atm 2/18
By.
P. Victer Paul
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8/3/2019 1-Asynchronous Transfer Mode (ATM)
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Agenda
Definition
Basic characteristics
Why asynchronous
How to access the network
Service Categories
Connections Protocol Architecture
pros & cons
Troubleshooting
8/3/2019 1-Asynchronous Transfer Mode (ATM)
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ATM – definition
"A transfer mode in which information is
organized into cells; it is asynchronous in the
sense that the recurrence of cells containinginformation from an individual user is not
necessarily periodic".
8/3/2019 1-Asynchronous Transfer Mode (ATM)
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ATM Characteristics
ATM uses packet switching with fixed length packetof 53 bytes – CELLs. Each cell has a 5-byte headerand 48-byte payload
ATM uses Virtual Circuits
ATM can run over any physical layer. Often runsover fiber optics using the SONET standard at speedsof 155.52 Mbps, 622 Mbps and higher
8/3/2019 1-Asynchronous Transfer Mode (ATM)
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ATM Characteristics
A Cell network uses the cell as the basic unit of dataexchange. A cell is defined as a small, fixed-sizedblock of information
ATM uses asynchronous TDM – to multiplex cellscoming 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
8/3/2019 1-Asynchronous Transfer Mode (ATM)
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Asynchronous Transfer Mode
(ATM)
M UX
Wasted bandwidth
4 3 2 1 4 3 2 1 4 3 2 1
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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).
8/3/2019 1-Asynchronous Transfer Mode (ATM)
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STDUCTURE
X
X
X
X
X
X
X
X
X
PrivateUNI
PublicUNI
NNI
PrivateNNI
Private ATMnetwork
Public
UNI B-ICI
Public ATMnetwork A
Public ATMnetwork B
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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
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Physical Link
Virtual Paths
Virtual Channels
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8/3/2019 1-Asynchronous Transfer Mode (ATM)
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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-endconnection
e.g. LAN, router-to-router reliability
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ATM Protocol Architecture
P l a n e m a n
a g e m e n t
Management plane
Control plane User plane
Physical layer
ATM layer
ATM adaptation layer
Higher layers Higher layers
L a y e r m a n a g e m e n t
8/3/2019 1-Asynchronous Transfer Mode (ATM)
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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
Physical layer
ATM layer
AAL user
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Pros & cons higher transmission speeds
quality of service
bandwidth-on-demand
application-independent
Cost
Complexity Availability
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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
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References:
1. Asynchronous Transfer Mode (ATM) fundamentals, white paper from Internation
Engineering Consortium
2. ATM tutorial-fnc educational services
3. Higher Layer Protocols:TCP/IP and ATM- Eytan Modiano,Massachusetts
Institute of Technology
4. ATM Switch Troubleshooting Guide-Cisco