Iap lecture 7 and 8
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Transcript of Iap lecture 7 and 8
Lecture 7Lecture 7
ATM Introduction
Instructor:Musfara Farooqui
Lecture ObjectivesLecture ObjectivesIntroduction to ATM technologyDesign Goals of ATMSignificance of small and fixed sized cellsATM network interfaces.Cell structure of UNI and NNI ATM Headers. ATM Virtual ConnectionsIdentify the layers in ATM reference model.
Asynchronous Transfer Mode Asynchronous Transfer Mode (ATM)(ATM)Asynchronous Transfer Mode (ATM)
is an International Telecommunication Union-Telecommunications Standards Section (ITU-T) standard
Also called cell relayIn ATM, information for multiple
service types, such as voice, video, or data, is conveyed in small, fixed-size packets called cells.
ATM Forum (www.atmforum.org) has designed ATM specifications
Basic ConceptsBasic ConceptsIdea is to integrate heterogeneous
sources (different rates, QoS requirements) and provide differentiated services (“to each application according to its needs”)
Asynchronous transmission◦no exclusive reservation of resources (e.g.
pre-assigned slots) to calls◦allocation of resources is possible to provide
minimum quality of service (QoS) guarantees
statistical multiplexing
Basic Concepts …Basic Concepts …Connection-oriented serviceAll information is transmitted in 53-
byte cellsUniform cell format simplifies
broadband switch architecturesStreamlined functionality to support
very high data rates
ATM vs. Telephone ATM vs. Telephone NetworksNetworksCurrent phone networks are synchronous
(periodic) while ATM = Asynchronous Transfer Mode
Phone networks use circuit switching and ATM networks use “Packet” Switching
In phone networks, all rates are multiple of 8 kbps. With ATM service, you can get any rate. You can vary your rate with time.
With current phone networks, all high speed circuits are manually setup. ATM allows dialing any speed.
GoalsGoalsOne objective is to move as many of the
functions to hardware as possible (for speed) and eliminate as many software functions as possible (again for speed)
Optimize use of high data rate transmission media
System must interface with existing systemDesign must be inexpensiveNew system must be connection orientedSystem should be able to work with existing
telecommunication hierarchies.
ATMATMATM is based on ITU-T Broadband ISDN standard
(B-ISDN) It was originally conceived as a high-speed
transfer technology for voice, video, and data over public networks.
It provides scalable bandwidth (Mbps to Gbps) The ATM Forum extended the ITU-T's vision of
ATM for use over public and private networksATM networks are connection-oriented.Asynchronous Transfer Mode (ATM) is the world's
most widely deployed backbone technology
ATM Network EnvironmentATM Network EnvironmentATM is a cell-switching and multiplexing
technologyEfficient than TDM (synchronous). It combines the benefits of both:
◦ circuit switching guaranteed capacity and constant
transmission delay◦ packet switching
flexibility and efficiency for intermittent traffic
ATM; Efficient than TDMATM; Efficient than TDMTDM (synchronous)
◦ Time slots are pre-allocated◦ If a station has much data to send, it can
send only when its time slot comes up◦ If a station has nothing to transmit its time
slot is sent empty and is wasted. ATM is asynchronous, time slots are
available on demand with information identifying the source of the transmission contained in the header of each ATM cell.
ATM DevicesATM DevicesAn ATM network is made up of two general
devices:◦ ATM switch◦ ATM endpoints.
ATM switch◦ responsible for cell transit through an ATM
network. ATM endpoint (or end system)
◦ contains an ATM network interface adapter
ATM Network ATM Network ArchitectureArchitecture
• An ATM Network Comprises:• ATM Switches
• Endpoints • An ATM network consists of a set of ATM switches
interconnected by point-to-point ATM links or interfaces.
ATM Network InterfacesATM Network InterfacesATM switches support two primary types of
interfaces: ◦ UNI
The UNI connects ATM end systems (such as hosts and routers) to an ATM switch.
◦ NNI The NNI connects two ATM switches.
◦ These interfaces are further subdivided into private and public UNIs and NNIs.
UNI and NNIUNI and NNI
ATM SW ITCH
ATM SW ITCH
ATM SW ITCH
ATM SW ITCH
NNI NNI
NNINNI
UNI
LAN
UNI
Computer
CompComp
ATM Interface ATM Interface SpecificationsSpecifications
ATM Interface Specifications Differ for Private and Public Networks
ATM InterfacesATM InterfacesUser to Network Interface (UNI):
◦ Public UNI, Private UNINetwork to Node Interface (NNI):
◦ Private NNI (P-NNI)◦ Public NNI =Inter-Switching System
Interface (ISSI)Broadband Inter-Carrier Interface (B-ICI)
◦ Connects two public ATM switches from different service providers
Data Exchange Interface (DXI)◦ Between routers and ATM Digital Service
Units (DSU)
ATM InterfacesATM Interfaces
ATM Cell Basic FormatATM Cell Basic FormatATM transfers information in fixed-size units
called cells. Each cell consists of 53 octets, or bytes.
◦ 5 bytes Header◦ 48 bytes payload (user data)
Small, fixed-length cells are well suited to transferring voice and video traffic at high data rates because such traffic is intolerant of delays that result from having to wait for a large data packet to download, among other things.
Significance of small size Significance of small size ATM HeaderATM HeaderTo guarantee a fast processing in the
network, the ATM header has very limited function.
Its main function is the identification of the virtual connection by an identifier which is selected at call set up and guarantees a proper routing of each packet.
In addition, it allows an easy multiplexing of different virtual connections over a single link
Significance of small size Significance of small size ATM CellATM CellThe Payload/Data field (48 bytes) length is
relatively small:◦ to reduce the internal buffers in the switching node◦ to limit the queuing delays in those buffers
small buffers guarantee a small delay and a small delay jitter as required in real time systems.
The data field of ATM cells is carried transparently through the network. No processing is performed on it inside the network.
◦ All services (voice, video, data) can be transported via ATM , including connectionless services.
ATM Virtual ConnectionsATM Virtual ConnectionsATM networks are fundamentally connection
oriented◦ A virtual circuit is established prior to any
data transferTwo types of ATM connections exist:
◦ virtual paths connections (VPC) identified by virtual path identifiers (VPI)
◦ virtual circuit connections (VCC) identified by the combination of a VPI and
a virtual channel identifier (VCI).
Why two VC identifiers are Why two VC identifiers are used in ATM used in ATM The whole idea behind dividing a virtual
connection identifier into two parts is to allow hierarchical routing
Most switches in a typical ATM network do switching using VPIs.
The switches at the boundaries of the network, those that interconnect directly with the endpoints, use both VPIs and VCIs.
An ATM switch route the cell using both the VPIs and VCIs
Virtual Paths & Virtual Virtual Paths & Virtual CircuitsCircuitsA virtual path is a bundle of virtual channels,
all of which are switched transparently across the ATM network based on the common VPI.
VPIs and VCIs have only local significance across a particular link and are remapped, as appropriate, at each switch.◦ implemented with translation tables◦ allows identifiers to be re-used (a necessity
due to their limited size)◦ Switching can be done based on VP only (VP
switching) or both VP and VC (VC switching)
ATM Connection ATM Connection RelationshipsRelationships
Virtual ConnectionsVirtual ConnectionsSwitches transfer cells from input port to output port
based on Virtual Circuit and Virtual Path identifiers◦ VPI’s and VCI’s are re-usable◦ VPI and VCI are replaced by switches according to
translation table
Advantages of VP and VCAdvantages of VP and VCSimplified Network Architecture
◦ Network Transmission functions can be separated into those related to an individual logical connection (VC) and those related to a group of logical connections (VP)
Increased Performance and Reliability◦ The network deals with fewer aggregated entities
Reduced Processing and Short Connection Setup Time ◦ Much of the work is done, when VP is set up◦ New VC can be established by executing simple
control functions at the end points of VP connection.◦ No call processing is required at the transit nodes◦ The addition of new virtual circuits to an existing
virtual path involves minimal processing
Routing with a switchRouting with a switch
ATM Virtual CircuitsATM Virtual Circuits
ATM Cell Header FormatATM Cell Header FormatAn ATM cell header can be one of
two formats: ◦UNI
The UNI header is used for communication between ATM endpoints and ATM switches in private ATM networks.
◦NNI The NNI header is used for
communication between ATM switches.
An ATM cellAn ATM cell
Generic ATM CellGeneric ATM Cell ATM UNI CellATM UNI Cell ATM NNI CellATM NNI Cell
ATM headersATM headers
Virtual connection Virtual connection identifiers in UNIs and NNIsidentifiers in UNIs and NNIs
ATM Cell Header FieldsATM Cell Header Fields◦Generic Flow Control (GFC)◦Virtual Path Identifier (VPI)◦Virtual Circuit Identifier (VCI)◦Payload Type (PT)◦Cell loss Priority (CLP)◦Header Error Correction (HEC)
ATM Cell Header FieldsATM Cell Header FieldsGeneric Flow Control (GFC)
◦ Provides local functions, such as identifying multiple stations that share a single ATM interface. This field is typically not used and is set to its default value of 0 (binary 0000).
Virtual Path Identifier (VPI)◦ In conjunction with the VCI, identifies the next
destination of a cell as it passes through a series of ATM switches on the way to its destination.
Virtual Channel Identifier (VCI)◦ In conjunction with the VPI, identifies the next
destination of a cell as it passes through a series of ATM switches on the way to its destination.
ATM Cell Header FieldsATM Cell Header Fields Payload Type (PT)
◦ 1st Bit data type Indicates in the first bit whether the cell contains user
data or control data. If the cell contains user data, the bit is set to 0. If it contains control data, it is set to 1.
◦ 2nd Bit Congestion Identifier (CI) The second bit indicates congestion (0 = no
congestion, 1 = congestion)◦ 3rd Bit AAU
The third bit indicates whether the cell is the last in a series of cells that represent a single AAL5 frame (1 = last cell for the frame).
Cell Loss Priority (CLP)◦ Indicates whether the cell should be discarded if it
encounters extreme congestion as it moves through the network. If the CLP bit equals 1, cell should be discarded in preference to cells with the CLP bit equal to 0.
Header Error Control (HEC)◦ Calculates checksum only on the first 4 bytes of the
header. HEC can correct a single bit error in these bytes, thereby preserving the cell rather than discarding it.
ATM ServicesATM ServicesMain types of ATM services:
◦permanent virtual circuits (PVC)◦switched virtual circuits (SVC)
PVCPVCpermanent virtual circuits (PVC)
◦Similar to a leased line◦Guarantees availability of a
connection◦Does not require call setup
procedure between switches◦Disadvantage:
static connectivity Manual setup Non-flexibility
SVCSVCswitched virtual circuits (SVC)
◦Similar to dial-up service/telephone call
◦SVC is created and released dynamically
◦Flexible◦Automatic call setup handling◦Disadvantage:
Extra time and overhead required to set up the connection
ATM Reference ModelATM Reference ModelATM Planes
◦ Control responsible for generating & managing signaling
requests. traffic policing, call control, congestion control, etc.
◦ User responsible for managing the transfer of data.
◦ Management Layer management manages layer specific functions
(manages resources and parameters residing in protocol entities e.g. provisioning for QoS)
Plane management manages functions for system as a whole, coordination between planes
The ATM Reference ModelThe ATM Reference Model
The ATM Reference ModelThe ATM Reference Model
Layers in ATM ModelLayers in ATM ModelThree layers are there in ATM Reference
Model:◦ Physical Layer◦ ATM Layer◦ ATM Adaptation Layer
Physical layerPhysical layerPhysical layer
◦Analogous to the physical layer of the OSI model, it manages the medium-dependent transmission
ATM also support wireless technologyOriginal design of ATM was based on SONET
◦2 Reasons of using SONET High data rates Boundaries of cells are clearly defined.
ATM support any technology of physical layer but the boundaries of the cell should be clearly defined.
ATM LayerATM LayerCombined with the ATM adaptation layer,
the ATM layer is roughly analogous to the data link layer of the OSI model.
The ATM layer is responsible for◦cell multiplexing
the simultaneous sharing of virtual circuits over a physical link
◦cell relay passing cells through the ATM network
◦To do this, it uses the VPI and VCI information in the header of each ATM cell.
ATM LayerATM LayerProvides routing, switching, multiplexing and
traffic management.Transmission/ReceptionCell header generation/removal at
source/destination◦ Header format is different for UNI and NNI
Cell address translationCongestion Control/Buffer managementSequential delivery
ATM Adaptation LayerATM Adaptation LayerATM adaptation layer (AAL)
◦ Breaks messages to cells◦ Combined with the ATM layer, the AAL is
roughly analogous to the data link layer of the OSI model.
◦ The AAL is responsible for isolating higher-layer protocols from the details of the ATM processes.
◦ The adaptation layer prepares user data for conversion into cells and segments the data into 48-byte cell payloads
ATM layersATM layers
ATM layers in endpoint ATM layers in endpoint devices and switchesdevices and switches
ATM layerATM layer
ATM Adaptation LayerATM Adaptation LayerServices:
◦ handling of transmission errors◦ segmentation and reassembly (enables
large blocks of data to be carried in payload field of ATM cells)
◦ handling of lost cells◦ flow control
Several AAL protocols have been specified to meet the needs of different types of application
ATM Adaptation LayerATM Adaptation LayerSubdivided into two logical layers:
◦ Convergence Sublayer (CS) upper-layer frames are basic data units concerned with flow and error control for
connection-oriented traffic◦ Segmentation and Reassembly Sublayer
(SAR) segments of upper-layer frames are basic
data units concerned with segmenting frames at the
source and reconstructing frames at the destination
ATM Adaptation LayerATM Adaptation LayerFour versions
◦ AAL1 (for constant-bit-rate stream)◦ AAL2 (for short packets)◦ AAL3/4 (3 for connection oriented services
and 4 for connection less services)◦ AAL5 (for packets requiring no sequence
and no error control mechanism)
ATM Adaptation Layers ATM Adaptation Layers (AAL)(AAL)AAL1
◦Connection-oriented service◦suitable for handling constant bit rate
sources (CBR)◦Such as voice and videoconferencing◦AAL1 requires timing synchronization
between the source and the destination
◦Thus, AAL1 depends on a medium, such as SONET, that supports clocking.
AAL2◦Connection-oriented service◦suitable for handling bursty traffic
with variable bit rate sources (VBR)◦Also has timing requirements like
AAL1◦Traffic such as packetized voice or
video That do not have a constant data transfer
speed But require service similar to CBR
AAL3/4◦ AAL3/4 supports both connection-oriented and
connectionless data. ◦ It was designed for network service providers
and is closely aligned with Switched Multimegabit Data Service (SMDS).
◦ AAL3/4 is used to transmit SMDS packets over an ATM network.
AAL5◦AAL5 is the primary AAL for data and
supports both connection-oriented and connectionless data.
◦It is used to transfer most non-SMDS data, such as classical IP over ATM and LAN Emulation (LANE).
◦AAL5 also is known as the simple and efficient adaptation layer (SEAL)
The ATM Reference Model The ATM Reference Model (2)(2)
AAL1AAL1
AAL2AAL2
AAL3/4AAL3/4
AAL5AAL5
ReferencesReferencesData and Computer Communications
◦7th Edition, William StallingsData Communications and Networking
◦3rd Edition, Behrouz A. ForouzanInternetworking Technologies
Handbook◦3rd Edition, Cisco Systems
Data Communications and Computer Networks◦Curt M. White
www.atmforum.org
Question BankQuestion BankGroup Activity
◦ Submit 5 questions related to the lectures and topics discussed in class per week.
◦ Questions format: (use both)
4 MCQs with 4 options and correct answer MCQs options should be written horizontally
like: (a) 10 (b) 100 (c) 1000 (d)
10000
1 Short conceptual or logical question◦ Submission will be done in soft form via group
email to CR