These computers include the entire spectrum of PCs, through professional workstations up to super-computers. As the performance of computers has increased, so too has the demand for communication between all systems for exchanging data, or between central servers and the associated host computer system.The replacement of copper with fiber and the advancement sin digital communication and encoding are at the heart of several developments that will change the communication infrastructure. The former development has provided us with huge amount of transmission bandwidth. While the latter has made the transmission of all information including voice and video through a packet switched network possible.
With continuously work sharing over large distances, including international communication, the systems must be interconnected via wide area networks with increasing demands for higher bit rates.
For the first time, a single communications technology meets LAN and WAN requirements and handles a wide variety of current and emerging applications. ATM is the first technology to provide a common format for bursts of high speed data and the ebb and flow of the typical voice phone call. Seamless ATM networks provide desktop-to-desktop multimedia networking over single technology, high bandwidth, low latency network, removing the boundary between LAN WAN.
ATM is simply a Data Link Layer protocol. It is asynchronous in the sense that the recurrence of the cells containing information from an individual user is not necessarily periodic. It is the technology of choice for evolving B-ISDN (Board Integrated Services Digital Network), for next generation LANs and WANs. ATM supports transmission speeds of 155Mbits / sec. In the future, Photonic approaches have made the advent of ATM switches feasible, and an evolution towards an all packetized, unified, broadband telecommunications and data communication world based on ATM is taking place.
These computers include the entire spectrum of PCs, through professional workstations upto super-computers. As the performance of computers has increased, so too has the demand for communication between all systems for exchanging data, or between central servers and the associated host computer system.
The replacement of copper with fiber and the advancement sin digital communication and encoding are at the heart of several developments that will change the communication infrastructure. The former development has provided us with huge amount of transmission bandwidth. While the latter has made the transmission of all information including voice and video through a packet switched network possible.
With continuously work sharing over large distances, including international communication, the systems must be interconnected via wide area networks with increasing demands for higher bit rates.For the first time, a single communications technology meets LAN and WAN requirements and handles a wide variety of current and emerging applications. ATM is the first technology to provide a common format for bursts of high speed data and the ebb and flow of the typical voice phone call. Seamless ATM networks provide desktop-to-desktop multimedia networking over single technology, high bandwidth, low latency network, removing the boundary between LAN WAN.
A SEMINAR REPORT ON
ASYNCHRONOUS TRANSFER MODE(ATM)
High performance, cell-oriented switching and multiplexing technology
Utilizes fixed-length packets to carry different types of traffic
Helps in efficient multimedia applications, high-speed LAN connections and used in broad range of networking
BENEFITS OF ATM
high performance via hardware switching
dynamic bandwidth for bursty traffic
class-of-service support for multimedia
scalability in speed and network size
common LAN/WAN architecture
opportunities for simplification via VC architecture
international standards compliance
ATM CELL HEADER FORMAT
ATM REFERENCE MODEL
ATM ADDRESS FORMAT
ATM SERVICE CLASSES
constant bit rate (CBR)
variable bit rateâ€œnon-real time (VBRâ€œNRT)
variable bit rateâ€œreal time (VBRâ€œRT)
available bit rate (ABR)
unspecified bit rate (UBR)
ATM TECHNICAL PARAMETERS
cell loss ratio (CLR)
cell transfer delay (CTD)
cell delay variation (CDV)
peak cell rate (PCR)
burst tolerance (BT)
sustained cell rate (SCR)
A cohesive set of specifications that provide a stable ATM framework.
Provide the end-to-end service definitions
An important ATM standard is interworking between ATM and frame relay
Two ATM networking standards
1)broadband intercarrier interface (Bâ€œICI) 2)public network-to-network interface (Pâ€œNNI)
DATA INSERTION SCHEMES
RFC1483-specifies how interrouter traffic is encapsulated into ATM
LANEMPOA- support dynamic use of ATM SVCs
voice and video adaptation schemes-for efficient traffic that no natural breaks, such as a circuit carrying bits
at a fixed rate
ATM LAN EMULATION(LANE)
VIDEO OVER ATM
Handled by VBRâ€œRT VCs using AALâ€œ5 for MPEG2 on ATM for video-on-demand applications
MPEG2 coding can result in two modes:
program streamsâ€variable-length packets carrying single or multiple programs
transport streamsâ€188-byte packets that contain multiple programs
Time stamps are inserted into MPEG2 packets during the encoding and multiplexing process to make better use of
VOICE OVER ATM
VBRâ€œRT connections is used over ATM which uses silence period.
Various dynamic compression techniques are used to free bandwidth and alleviate congestion
A further enhancement is to support voice switching over SVCs which interprets PBX (private branch exchange)
signaling and routing voice calls to the appropriate destination PBX
NETWORK TRAFFIC MANAGEMENT
objectives :To deliver quality-of-service (QoS) for multimedia applications and provide overall optimization of
categorized into three distinct elements
nodal-level controls that operate in real time
network-level controls operate in near real time
network engineering capabilities operating in non real time
ATM AND IP INTERWORKING
ATM and IP offer: Scalability, traffic engineering, service differentiation, high availability, value-added
applications such as Virtual Private Networks (VPNs)
Some specifications of ATM and IP
Multi-Protocol over ATM (MPOA) as addition to LAN Emulation (LANE)
Additions to ATM's superior routing protocol PNNI
adoption of Frame-based ATM over Sonet/SDH (FAST)
ATM technology is the only technology that can guarantee a certain and predefined quality of service.
The growth of the Internet, need for broadband access and e-commerce are spurring the need for a reliable,
flexible, scalable, predictable, versatile transport system and that is given by ATM Technology.
For voice, video, data and images together, the next generation network depends on ATM.
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Asynchronous Transfer Mode (ATM)
Issues Driving LAN Changes
• Traffic Integration
– Voice, video and data traffic
– Multimedia became the ‘buzz word’
• One-way batch Web traffic
• Two-way batch voice messages
• One-way interactive Mbone broadcasts
• Two-way interactive video conferencing
• Quality of Service guarantees (e.g. limited jitter, non-blocking streams)
• LAN Interoperability
• Mobile and Wireless nodes
• ATM standard (defined by CCITT) is widely accepted by common carriers as mode of operation for communication – particularly BISDN.
ATM is a form of cell switching using small fixed-sized packets
ATM Conceptual Model Four Assumptions
1. ATM network will be organized as a hierarchy.
User’s equipment connects to networks via a UNI (User-Network Interface).
Connections between provided networks are made through NNI (Network-Network Interface).
2. ATM will be connection-oriented.
A connection (an ATM channel) must be established before any cells are sent.
• 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
3. Vast majority of ATM networks will run on optical fiber networks with extremely low error rates.
4. ATM must support low cost attachments.
• This decision lead to a significant decision – to prohibit cell reordering in ATM networks.
è ATM switch design is more difficult.
Asynchronous Transfer Mode (ATM)
An Overview of ATM
• ATM is Asynchronous Transfer Mode.
• ATM is originally the transfer mode for implementing Broadband ISDN (B-ISDN).
• In 1988, CCITT (from ITU) issued the first two recommendations relating to B-ISDN:
– I.113 Vocabulary of Terms for Broadband Aspects of ISDN
– I.121 Broadband Aspects of ISDN
• In 1911, the ATM Forum was created with the goal of accelerating the development of ATM standards.
• Connection-oriented packet-switched network
• Used in both WAN and LAN settings
• Signaling (connection setup) Protocol:
• Packets are called cells (53 bytes)
– 5-byte header + 48-byte payload
• Commonly transmitted over SONET
– other physical layers possible
• Connections can be switched (SVC), or permanent (PVC).
Variable vs. Fixed-Length Packets
• No Optimal Length
– if small: high header-to-data overhead
– if large: low utilization for small messages
• Fixed-Length Easier to Switch in Hardware
– enables parallelism
Big vs. Small Packets
• Small Improves Queue behavior
– finer-grained pre-emption point for scheduling link
• maximum packet = 4KB
• link speed = 100Mbps
• transmission time = 4096 x 8/100 = 327.68us
• high priority packet may sit in the queue 327.68us
• in contrast, 53 x 8/100 = 4.24us for ATM
– near cut-through behavior
• two 4KB packets arrive at same time
• link idle for 327.68us while both arrive
• at end of 327.68us, still have 8KB to transmit
• in contrast, can transmit first cell after 4.24us
• at end of 327.68us, just over 4KB left in queue
• Small Improves Latency (for voice)
– voice digitally encoded at 64KBps (8-bit samples at 8KHz)
– need full cell’s worth of samples before sending cell
– example: 1000-byte cells implies 125ms per cell (too long)
– smaller latency implies no need for echo cancellors
• ATM Compromise: 48 bytes = (32+64)/2
• ATM operates on a best effort basis.
• ATM guarantees that cells will not be disordered.
• Two types of connections:
– Multipoint (Multicast)
• Four Types of Services:
– CBR (Constant Bit Rate)
– VBR (Variable Bit Rate)
– ABR (Available Bit Rate) Flow Control, Rate-based, Credit- based
– UBR (Unspecific Bit Rate) No Flow control.
• Aggregate Bandwidth vs. Shared Medium (FDDI, Fast Ethernet).
• No error protection or flow control on a link-by-link basis.
• ATM operates in a connection-oriented mode.
• The header functionality is reduced.
The information field length is relatively small and fixed
ATM Layer Service
• Transparent transfer of 48-octet data unit
• Deliver data in sequence on a connection
• Two levels of multiplexing
• Three types of connections
• Transport is best-effort
• Network QoS negotiation
• Traffic control and congestion control