05-07-2013, 02:44 PM
Dynamic synchronous transfer mode (DTM)
Dynamic synchronous.pdf (Size: 145.3 KB / Downloads: 18)
Definition
Dynamic synchronous transfer mode (DTM) is an exciting
networking technology. The idea behind it is to provide high-speed
networking with top-quality transmissions and the ability to adapt the
bandwidth to traffic variations quickly. DTM is designed to be used in
integrated service networks for both distribution and one-to-one
communication. It can be used directly for application-to-application
communication or as a carrier for higher-layer protocols such as
Internet protocol (IP).
DTM, Dynamic synchronous Transfer Mode, is a broadband
network architecture based on circuit switching augmented with
dynamic reallocation of time slots. DTM provides a service based on
multicast, multirate channels with short set-up delay. DTM supports
applications with real-time QoS requirements as well as applications
characterized by bursty, asynchronous traffic
Overview
This tutorial explores the development of DTM in light of the
demand for network-transfer capacity. DTM combines the two basic
technologies used to build high-capacity networks—circuit and packet
switching—and therefore offers many advantages. It also provides
several service-access solutions to city networks, enterprises,
residential and small offices, content providers, video production
networks, and mobile network operators.
WHY DTM?
Over the last few years, the demand for network-transfer
capacity has increased at an exponential rate. The impact of the
Internet; the introduction of network services such as video and
multimedia that require real-time support and multicast; and the
globalization of network traffic enhance the need for cost-efficient
networking solutions with support for real-time traffic and for the
transmission of integrated data, both audio and video. At the same time,
the transmission capacity of optical fibers is today growing
significantly faster than the processing capacity of computers.
Traditionally, the transmission capacity of the network links has been
the main bottleneck in communication systems. Most existing network
techniques are therefore designed to use available link capacity as
efficiently as possible with the support of large network buffers and
elaborate data processing at switch points and interfaces. However,
with the large amount of data-transfer capacity offered today by fiber
networks, a new bottleneck problem is caused by processing and
buffering at switch and access points on the network. This problem has
created a need for networking protocols that are not based on computer
and storage capacity at the nodes but that instead limit complex
operations to minimize processing on the nodes and maximize
transmission capacity.
CIRCUIT SWITCHING vs. PACKET SWITCHING
In principle, two basic technologies are used for building highcapacity
networks: circuit switching and packet switching. In circuitswitched
networks, network resources are reserved all the way from
sender to receiver before the start of the transfer, thereby creating a
circuit. The resources are dedicated to the circuit during the whole
transfer. Control signaling and payload data transfers are separated in
circuit-switched networks. Processing of control information and
control signaling such as routing is performed mainly at circuit setup
and termination. Consequently, the transfer of payload data within the
circuit does not contain any overhead in the form of headers or the like.
Traditional voice telephone service is an example of circuit switching.
Circuit-Switched Networks
An advantage of circuit-switched networks is that they allow for
large amounts of data to be transferred with guaranteed transmission
capacity, thus providing support for real-time traffic. A disadvantage of
circuit switching, however, is that if connections are short-lived—when
transferring short messages, for example—the setup delay may
represent a large part of the total connection time, thus reducing the
network's capacity. Moreover, reserved resources cannot be used by
any other users even if the circuit is inactive, which may further reduce
link utilization.
Packet-Switched Networks
Packet switching was developed to cope more effectively with
the data-transmission limitations of the circuit-switched networks
during bursts of random traffic. In packet switching, a data stream is
divided into standardized packets. Each contains address, size,
sequence, and error-checking information, in addition to the payload
data. The packets are then sent through the network, where specific
packet switches or routers sort and direct each single packet.
Slot Allocation
DTM uses a distributed algorithm for slot reallocation, where
the pool of free slots is distributed among the nodes. At the reception of
a user request, the node first checks its own time slots to see if it has
slots enough to satisfy the request and, if so, immediately sends a
channel establishment message to the next hop. Otherwise, the node
first has to request more slots from the other nodes on the link. Each
node maintains a status table that contains information about free slots
in other nodes, and when more slots are needed the node consults its
status table to decide which node to ask for slots. Every node regularly
sends out status messages with information about its local pool of slots.
Time Slot Reservation
DTM uses a strict time slot reservation scheme. A new channel
is admitted only if there are enough free slots, and a suitable route can
be found. Once a route is established, the user of the route is
guaranteed the reserved bandwidth until the channel is closed. Thus
there can be no congestion in the network. Flow control is only needed
at the access point. DTM may offer the user at least three types of
reservation schemes.
1. For applications requiring constant delay and guaranteed constant bit rate
for their exclusive use through the network, a channel is set up with fixed
capacity for the whole lifetime of the channel.
2. For applications requiring a minimal guaranteed bandwidth with
options for additional bandwidth, a scheme is used where a
guaranteed number of slots are always reserved, while more
bandwidth can be given if time slots are available. The effect is a
non-interrupted traffic that gracefully can be upgraded on demand.
DTM SERVICES
The DTM solution is designed to transport common
communication protocols over optical fibers. DTM provides several
simple and commonly used services in one integrated network. It
results in better utilization of the fiber and of the node equipment and
simple management and operation of the network.
Data communications—particularly IP traffic—are becoming
the main traffic source in the networks. DTM has been specifically
developed for efficient transport of this type of traffic. However, a
large part of the network traffic is still PDH–based (PDH allows
transmission of data streams that are nominally running at the same
rate, but allowing some variation on the speed around a nominal rate),
and, therefore, DTM products also transport PDH traffic.
Dynamic synchronous.pdf (Size: 145.3 KB / Downloads: 18)
Definition
Dynamic synchronous transfer mode (DTM) is an exciting
networking technology. The idea behind it is to provide high-speed
networking with top-quality transmissions and the ability to adapt the
bandwidth to traffic variations quickly. DTM is designed to be used in
integrated service networks for both distribution and one-to-one
communication. It can be used directly for application-to-application
communication or as a carrier for higher-layer protocols such as
Internet protocol (IP).
DTM, Dynamic synchronous Transfer Mode, is a broadband
network architecture based on circuit switching augmented with
dynamic reallocation of time slots. DTM provides a service based on
multicast, multirate channels with short set-up delay. DTM supports
applications with real-time QoS requirements as well as applications
characterized by bursty, asynchronous traffic
Overview
This tutorial explores the development of DTM in light of the
demand for network-transfer capacity. DTM combines the two basic
technologies used to build high-capacity networks—circuit and packet
switching—and therefore offers many advantages. It also provides
several service-access solutions to city networks, enterprises,
residential and small offices, content providers, video production
networks, and mobile network operators.
WHY DTM?
Over the last few years, the demand for network-transfer
capacity has increased at an exponential rate. The impact of the
Internet; the introduction of network services such as video and
multimedia that require real-time support and multicast; and the
globalization of network traffic enhance the need for cost-efficient
networking solutions with support for real-time traffic and for the
transmission of integrated data, both audio and video. At the same time,
the transmission capacity of optical fibers is today growing
significantly faster than the processing capacity of computers.
Traditionally, the transmission capacity of the network links has been
the main bottleneck in communication systems. Most existing network
techniques are therefore designed to use available link capacity as
efficiently as possible with the support of large network buffers and
elaborate data processing at switch points and interfaces. However,
with the large amount of data-transfer capacity offered today by fiber
networks, a new bottleneck problem is caused by processing and
buffering at switch and access points on the network. This problem has
created a need for networking protocols that are not based on computer
and storage capacity at the nodes but that instead limit complex
operations to minimize processing on the nodes and maximize
transmission capacity.
CIRCUIT SWITCHING vs. PACKET SWITCHING
In principle, two basic technologies are used for building highcapacity
networks: circuit switching and packet switching. In circuitswitched
networks, network resources are reserved all the way from
sender to receiver before the start of the transfer, thereby creating a
circuit. The resources are dedicated to the circuit during the whole
transfer. Control signaling and payload data transfers are separated in
circuit-switched networks. Processing of control information and
control signaling such as routing is performed mainly at circuit setup
and termination. Consequently, the transfer of payload data within the
circuit does not contain any overhead in the form of headers or the like.
Traditional voice telephone service is an example of circuit switching.
Circuit-Switched Networks
An advantage of circuit-switched networks is that they allow for
large amounts of data to be transferred with guaranteed transmission
capacity, thus providing support for real-time traffic. A disadvantage of
circuit switching, however, is that if connections are short-lived—when
transferring short messages, for example—the setup delay may
represent a large part of the total connection time, thus reducing the
network's capacity. Moreover, reserved resources cannot be used by
any other users even if the circuit is inactive, which may further reduce
link utilization.
Packet-Switched Networks
Packet switching was developed to cope more effectively with
the data-transmission limitations of the circuit-switched networks
during bursts of random traffic. In packet switching, a data stream is
divided into standardized packets. Each contains address, size,
sequence, and error-checking information, in addition to the payload
data. The packets are then sent through the network, where specific
packet switches or routers sort and direct each single packet.
Slot Allocation
DTM uses a distributed algorithm for slot reallocation, where
the pool of free slots is distributed among the nodes. At the reception of
a user request, the node first checks its own time slots to see if it has
slots enough to satisfy the request and, if so, immediately sends a
channel establishment message to the next hop. Otherwise, the node
first has to request more slots from the other nodes on the link. Each
node maintains a status table that contains information about free slots
in other nodes, and when more slots are needed the node consults its
status table to decide which node to ask for slots. Every node regularly
sends out status messages with information about its local pool of slots.
Time Slot Reservation
DTM uses a strict time slot reservation scheme. A new channel
is admitted only if there are enough free slots, and a suitable route can
be found. Once a route is established, the user of the route is
guaranteed the reserved bandwidth until the channel is closed. Thus
there can be no congestion in the network. Flow control is only needed
at the access point. DTM may offer the user at least three types of
reservation schemes.
1. For applications requiring constant delay and guaranteed constant bit rate
for their exclusive use through the network, a channel is set up with fixed
capacity for the whole lifetime of the channel.
2. For applications requiring a minimal guaranteed bandwidth with
options for additional bandwidth, a scheme is used where a
guaranteed number of slots are always reserved, while more
bandwidth can be given if time slots are available. The effect is a
non-interrupted traffic that gracefully can be upgraded on demand.
DTM SERVICES
The DTM solution is designed to transport common
communication protocols over optical fibers. DTM provides several
simple and commonly used services in one integrated network. It
results in better utilization of the fiber and of the node equipment and
simple management and operation of the network.
Data communications—particularly IP traffic—are becoming
the main traffic source in the networks. DTM has been specifically
developed for efficient transport of this type of traffic. However, a
large part of the network traffic is still PDH–based (PDH allows
transmission of data streams that are nominally running at the same
rate, but allowing some variation on the speed around a nominal rate),
and, therefore, DTM products also transport PDH traffic.