Transcript ATM COMPONENT

ATM COMPONENTS
Presented by:
ANG BEE KEE
CHONG SIT MEI
LAI YIN LENG
LEE SEANG LEI
WET 020005
WET 020024
WET 020056
WET 020060
Table of Contents
• ATM Networks
– Presented by Chong Sit Mei
• Virtual Path (VP) Switch
– Presented by Ang Bee Kee
• Virtual Path Connection (VPC) Switch
– Presented by Lai Yin Leng
• ATM Switching Techniques
– Presented by Lee Seang Lei
ATM COMPONENTS
ATM Networks
•ATM contains two basic components: an
endstation, a
computer connected to the ATM network; and an ATM switch,
the device responsible for connecting endstations and making
sure data is transferred successfully.
•ATM is connection-oriented.
•establishes a defined path known as a virtual circuit (VC)
• sends a series of same-size frames called cells along the
virtual circuit towards the destination.
• the ATM endpoint also negotiates a Quality of Service (QoS)
contract for the virtual circuit.
• it spells out the bandwidth, maximum transit delay,
acceptable variance in the transit delay, etc, that the VC
provides, and this contract extends from one endpoint to
the other through all of the intermediate ATM switches.
• ATM traffic is established at the outset, and the switching
hardware merely needs to examine a simple header to
identify the proper path.
• ATM allows a location to establish a full duplex connection
with multiple locations at the same time.
• To travel across the ATM network, data is segmented into
same-size cells, and encapsulated with a header that
contains
switching,
information.
congestion,
and
error-checking
• Cells are transmitted in order, and the ATM network uses
Virtual
Path
Identifier
and
Virtual
Channel
Identifier
(VPI/VCI) numbers in the ATM header to forward them
efficiently.
• A switch reads the header, compares the VPI/VCI to its
switching table to determine the correct output port and
new VPI/VCI, and then forwards the cell.
• All of the addressing information the ATM switch needs is
contained in the header and is always found in the same
place. This makes the forwarding task simple to implement
in hardware, reducing latency.
ATM Virtual Circuit and Packet Transmission
Virtual Path (VP) Switch
• Route the cell using only the VPI
• Check the switching table, which stores 4 pieces
information per row:
•
i.
Arrival interface number
•
ii.
Incoming VPI
•
iii. Corresponding outgoing interface number
•
iv. New VPI
VP Switch (cont.)
VP Switch (cont.)
• The figure shows how a VP switch routes the cell.
• A cell with VPI of 153 arrives at switch interface 1.
• The switch checks its switching table, finds the entry
with interface 1 and VPI 153 and discover that the
combination corresponds to output interface 3 with VPI
140.
• It changes the VPI in the header to 140 and sends the
cell out through interface 3.
VP Switch (cont.)
Virtual Path Connection
(VPC) Switch
• Virtual Path Connection (VPC) means a group of logical
connections between one ATM switch port and another
ATM switch port.
• VPC are provided for the purpose of user-user, usernetwork, network-network information transfer.
• Can be established between :
-end users
-network entities
-end user and network entity
• VPC is established at the time a VC (virtual circuit)
session is activated.
VPC Switch (cont.)
• VPC switch routes the cell using both the VPIs (Virtual
Path Identifier) and VCIs (Virtual Circuits Identifier).
• The routing requires the whole identifier.
• It can assigned within the Virtual Path (VPs).
VPC Switch (cont.)
This diagram shows how a VPC Switch routes the cell.
VPC Switch (cont.)
• Routing with a VPC switch.
– A cell with a VPI of 153 and VCI of 67 arrives at
switch interface 1.
– The switch checks its switching table, which stores
six pieces of information per row.
– The switch finds the entry with the interface 1, VPI
153, and VCI 67 and discovers that the combination
corresponds to output interface 3, VPI 140, and VCI
192.
– It changes the VPI and VCI in the header to 140 and
92.
– Respectively, sends the cell out through interface 3.
VPC Switch (cont.)
• The whole idea behind dividing a virtual connection
identifier into two parts is to allow hierarchical routing.
VC
VCI:92
4
1 VCI:67
3
2
VP
VPC
Advantages
• Simplified network architecture. Network transport
functions can be separated into those related to an
individual logical connection (virtual channel) and those
related to a group of logical connections (virtual path).
• Increased network performance and reliability. The
network deals with aggregated (and therefore fewer)
entities.
Advantages (cont.)
• Reduced processing and short connection setup time.
Much of the work is done when the virtual path is set
up. The addition of new virtual channels to an existing
virtual path involves minimal processing.
• Enhanced network services. The virtual path is used
internal to the network but is also visible to the end
user. Thus, the user may define closed user groups or
closed networks of virtual-channel bundles.
ATM Switching Techniques
• Within an ATM switch, the cell switch fabric plays a very key
role.
• Its main responsibility is to relay ATM cells as quickly as
possible.
• The cell switch fabric accomplishes this by performing 2
major functions:
• -Concentration,
traffic.
expansion,
multiplexing/demultiplexing
• -Routing and buffering of traffic.
of
ATM Switching Techniques
•
•
•
•
•
Shared Memory Switch
Shared Bus Switch
Crossbar Switch
Multistage Switching
Banyan/Delta Switching
Shared Memory Switch
• The Shared Memory Switch is a technique that uses a
common memory for the storage of cells and switching
fabric.
• Incoming cells are multiplexed onto a single line to the
switch and are placed in queues.
• Then, based on cell headers information and internal
tags, the switching function decides the order in which
cells are move from the input queues to the output
queues and ultimately onto the output ports.
Shared Memory Switch
Shared Memory Switch Diagram
Shared Bus Switch
• The Shared Bus Switch approach utilizes a bus or dual
bus architecture to switch cell traffic.
• Cell traffic is carried through the bus for transmission.
With this technique, frame based traffic can also be
supported since the busses operates in cell mode.
• Therefore, the traffic is diced into 48-octet pieces with
5-byte header attached for transmission onto the bus.
• It is easy to see that frame based traffic can be
converted to ATM cells and vice versa with this
approach.
Shared Bus Switch
Shared Bus Switch Diagram
Crossbar Switch
• The Crossbar Switch is a simple matrix-like space
division technique that physically interconnects any of
the N inputs to any of the N outputs at crosspoints.
• Therefore, a crossbar switching fabric consists of N2
crosspoints.
Crossbar Switch
Crossbar Switch Diagram
Multistage Switching
• The Multistage Switching uses a similar concept to the
crossbar switch technique.
• However, it is designed with a more tree-like structure
to reduce the N squared crosspoints requirement
yielding a more economical arrangement.
• Basically, the inputs and output lines are divided into
subgroups of N inputs and N outputs.
Multistage Switching
Multistage Switch Diagram
Banyan/Delta Switching
• The Banyan/Delta Switching is a concept of
interconnection of stages of switching elements.
an
• This technique allows only one path of connection
existing between an input to the final output port.
• With this approach, the routing of traffic is quite simple
and straightforward.
• However, it has one major drawback in that cells may
be blocked if more than one arrives at a switching
element at the same time.
Banyan/Delta Switching
Banyan/Delta Switch Diagram
The End