ATM( Asynchronous
Transfer Mode)
SWITCHING
1. Group 1 WET020022
CHEN SHAN WAN
2. GRACE CHANG POOI KUAN WET020042
3. LIM SEOW FONG WET020072
4. NG SIAO SHAN WET020104
5. TAN PHAIK SEE WET020174
Content of Presentation
Introduction To ATM Switching And Functions of
ATM Switching
Grace Chang Pooi Kuan WET020042
ATM Switching Architecture
Tan Phaik See WET020174
ATM Switching Techniques
Chen Shan Wan WET020022
Switching Element Requirements
Ng Siao Shan WET020104
Queuing Methods
Lim Seow Fong WET020072
Introduction To ATM
Switching And Functions of
ATM Switching
Grace Chang Pooi Kuan
WET020042
Introduction to ATM switching
What is Asynchronous Transfer Mode
(ATM) switching ?
What is ATM Switching ?
A packet switching technology that allows voice, data,
image, and video traffic to be combined into evenly sized
cells for high-speed transmission over one access circuit.
This means that all the information sent over an ATM
network is broken down into discrete packets.
Each 53 byte cell contains 48 bytes of payload and 5
bytes of control information.
Because the cells are all the same size, cell delay at ATM
switches is more predictable and manageable.
An ATM cell
The aim of ATM switch design is to increase speed, capacity
and overall performance.
ATM switching differs from conventional switching because
of the high-speed interfaces (50 Mbps to 2.4 Gbps) to the
switch, with switching rates up to 80 Gbps in the backplane .
ATM was designed specifically to handle broadband
applications efficiently and at the same time let users give
certain types of traffic priority treatment on the network.
For example, voice traffic, which cannot tolerate much
delay, can be marked "high priority" with a guaranteed
bandwidth and minimal delay. Less sensitive traffic, such as
electronic mail, can be marked for lower priority.
ATM networks are linked together by a series of ATM
switches that take in cells from various sources and switch
them out again.
ATM Switch Functions
ATM switch functions :
User Plane
Control Plane
Management Plane
ATM Switch Functions
An ATM switch contains a set of input ports and output
ports, through which it is interconnected to users, other
switches, and other network elements.
There are 3 planes of the switching functions in the context of
the Broadband Integrated Services Digital Network (B-ISDN)
model :
User Plane
Control Plane
Management Plane
User Plane
The main function of an ATM switch is to relay user data
cells from input ports to the appropriate output ports.
The switch processes only the cell headers and the payload
is carried transparently.
As soon as the cell comes in through the input port, the
Virtual Path Identifier/Virtual Channel Identifier (VPI/VCI)
information is derived and used to route the cells to the
appropriate output ports.
Control Plane
This plane represents functions related to the establishment
and control of the Virtual Path/Virtual Channel (VP/VC)
connections.
Unlike the user data cells, information in the control cells
payload is not transparent to the network. The switch
identifies signaling cells, and even generates some itself.
Management Plane
The management plane is concerned with monitoring the
controlling the network to ensure its correct and efficient
operation.
These operations can be subdivided as
fault management functions,
performance management functions,
configuration management functions,
security management functions,
accounting management
traffic management.
ATM Switching Architecture
Tan Phaik See
WET020174
ATM
The generic module consists of the following functional blocks:
Input modules, output models, cell switch fabric, connection
admission control (CAC), and switch management.
Input Module
The input module performs by terminates the incoming signals
and extracts the ATM cell stream.
This task involves signal conversion and recovery and
overhead processing.
Furthermore, the input module performs the following function
on each ATM cell:
Error checking of the header information using Header Error
Control (HEC) field
Determination of the destination output port
Passing signaling cells to CAC and Operations and
Management (OAM) cells to Switch Management
Output Module
It prepares ATM cells into a format for transmission on the physical
network.
It accomplishes this task by:
Removing and processing internal tags
Translating VPI/VCI values
Generating HEC field
Mixing CAC and Switch Management cells with outgoing cell
streams
Mapping cells to physical transmission formats
Converting digital bit stream to optical signal
Cell Switch Fabric
The main task is to perform the routing of data cells, signaling
and management cell.
It receives cells on an incoming port, reads the VPI/VCI value,
and identifies an appropriate outgoing port for the next node
that is to receive the traffic.
Connection Admission Control (CAC)
A set of procedures that include actions taken by the network
to grant or deny a virtual connection.
It establishes, modifies, and terminates virtual path/virtual
channel connections.
It is responsible for:
high-layer signaling protocols
interface with a signaling network
Switch Management
It has the overall responsibility of providing key information for
managing the switch and the network.
It performs tasks that include the following:
Traffic management
Network Management
Security control for switch database
Customer-network management
ATM Switching Techniques
Chen Shan Wan
WET020022
ATM Switching Techniques
Cell Switch Fabric - to relay ATM cells as quickly as
possible and accomplishes this by performing 2 major
functions:
Concentration, expansion, multiplexing/demultiplexing of
traffic
Routing and buffering of traffic
Five ATM Switching Alternatives :
A. Shared Memory Switch
B. Shared Bus Switch
C. Crossbar Switch
D. Multistage Switching
E. Banyan/Delta Switching
A. Shared Memory Switch
B. Shared Bus Switch
C. Crossbar Switch
D. Multistage Switching
E. Banyan/Delta Switching
Switching Element
Requirements
Ng Siao Shan
WET020104
Switching Element Requirements
The ATM switch architectures have to consider above these
requirements.
1. Performance
2. Information Rates
3. Broadcast
Performance
a) Connection Blocking
b) Cell Loss, Cell Insertion
c) Switching Delay
Performance: a) Connection
Blocking
Since ATM is defined to be connection oriented, after
connection set-up, a logical connection must be found between
the logical inlet and the logical outlet.
Cont
Connection blocking is defined as the probability that not
enough resources can be found to allow all the required
physical connections between inlets and outlets at any time.
Performance: b) Cell Loss, Cell Insertion
In an ATM switch it is possible that temporarily too many cells
in the switch have to be transmitted through the same link
(switch internal or external link).
In optimal operational conditions there is an available entry in a
queue to hold all the cells.
But if the queue is currently full, another cell that will require
the same queue will be lost.
The probability of a cell lost must be kept in a specified limits
to assure high semantic transparency.
Some switching architectures are designed such that they will
not suffer from cells competing for the same resources
internally, but only at their inlets and/or outlets.
Cont
It is also possible that from some internal routing
error a cell will be sent to the wrong logical
connection.
If such an error occurs, error impact is doubled by
the fact that one destination will miss a cell and that
a second destination will accept an additional cell.
The switch element has to be designed so that cell
insertion error probability will be about 1000 times
better than a cell loss.
Performance: c) Switching Delay
To allow support of different real time services in an ATM
network, a maximal delay has to be guaranteed and a low
values of jitter.
Typical delay values are between 10 and 1000 usec, with jitter
of 100 nsec or less.
The delay and the jitter in the cell are strongly related to the
queueing in the switching element. A small queue will assure
better delays but will increase the cell loss probability.
Information Rates
A large number of information rates have to be switched in the
same ATM switch.
The maximal bit rate which a future ATM switch has to be able
to switch lies around 150 Mbit/sec.
For such fast services, the switching element can be
implemented as several switching elements in parallel.
Or, several 150Mbit/sec switching elements can be multiplexed
on a single link.
That will require a switching rate in the order of Gbit/sec.
Broadcast
In classical connection oriented packet switching services,
only point to point connections are available, because the
information (cell) can be switched from one logical inlet to one
logical outlet only.
In future broadband networks broadcast and multicast services
are required for different applications from electronic-mail to
network TV services.
Queuing Methods
Lim Seow Fong
WET020072
Queuing Methods: Problems
Many queuing problems in an ATM switch because:
The pre-assigned time slot concept disappears in ATM
switching systems
ATM switch performs statistical multiplexing in the switch
inputs
de-multiplexing in the switch outputs
For example:
Two ATM cells arrived at two inlets at the same time and are
aiming for the same outlet
Queuing Methods: Approaches
Queue of waiting cells has to be implemented in the switch:
Input Buffers
Output Buffers
Central Queuing
Queuing Methods: a) Input Buffers
Add a queue at the switch element inputs
The buffers are located at the input controller (IC)
The switch interconnection network will transfer the cell from
the input buffer to the output buffer without internal conditions
Arbitration logic is needed to determine which of the cells held
in different inlet buffers destined to the same output will be
transferred in the interconnection network
Queuing Methods: a) Input Buffers
(cont’)
Solution:
The FIFO buffer can be replaced by a random access
memory (RAM)
If the first cell in the queue is blocked, the next cell which is
destined for an idle output (or internal switch
interconnection network link) will be selected for
transmission
Queuing Methods: a) Input Buffers
(cont’)
The disadvantage of this solution:
A complex buffering control is required to find a cell
destined to an idle connection to guarantee a correct cell
sequence of cells destined for the same output.
The input buffer approach achieves the worst performance
in the sense of the queue length required to achieve a given
cell-loss rate in various switch loads in comparison to the
other two queuing methods.
Queuing Methods: b) Output Buffers
Add a queue at the switch output
The buffers are located at the output controller (OC) of the
switch element
The assumption is that many cells from the IC can cross the
internal interconnection network and arrive to the outlets
This solution requires use of a very fast internal pass
Queuing Methods: b) Output Buffers
(cont’)
In order to allow a non-blocking switch, the interconnection
network and the output buffer have to be capable of handling N
cells at one cell time (when N in the number of ICs)
When output buffers are in use, no arbitration has to be used.
The control of the output is based on a simple FIFO logic
Queuing Methods: c) Central Queuing
Add a queue between the inputs on the outputs of the switch
The queuing buffers are not dedicated to a single inlet or to a
single outlet, but shared between all inlets and outlets
Each coming cell will be directly stored in the central storing
element
Every outlet will identify the cells destined to it in a FIFO
discipline
Queuing Methods: c) Central Queuing
(cont’)
Advantage:
Most efficient and required the smallest total storage to
allow minimal cell loss in heavy load conditions
Since the available memory on an integrated circuit
switching element is limited, it is possible to achieve low
cell-loss probabilities when using the central queuing
approach
Queuing Methods: c) Central Queuing
(cont’)
Disadvantage:
Very fast memory elements are required to allow all the
coming cells and outgoing cells access to the memory ports
at the same time
Big complexity in the queue management