1. U-V : ISDN & ATM
Dr. D. P.
Mishra
Digitally signed by Dr. D. P. Mishra
DN: cn=Dr. D. P. Mishra, o=durg,
ou=BIT,
email=dpmishra@bitdurg.ac.in,
c=IN
Date: 2023.04.30 00:46:15 +05'30'
2. • ISDN is a set of standards which define an end to end Digital
Network
• WAN Technology
ISDN (Integrated Services Digital
Network)
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3. • Uses Digital Signal
• Uses Existing telephone wiring
• Charges are generally based on the duration of call (How long the
WAN link was used)
• Alternate to using leased lines
• Can transport many types of Network traffic (Voice, Data, Video,
Text, Graphics etc)
• Faster Data transfer rate than modems
• Faster Call setup than Modems
Features of ISDN
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7. • Terminal Equipment type 1 (TE1)
ISDN compatible device (Router with ISDN Interface)
TE1s connect to the ISDN network through a four-wire, twisted-
pair digital link
• Terminal Equipment type 2 (TE2)
ISDN Non-compatible devices.
Will require a terminal adapter.
• Terminal Adapter (TA)
Converts standard electrical signals into the form used by ISDN
Needed for connection with TE2 devices
The ISDN TA can be either a standalone device or a board inside
the TE2
ISDN Components
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9. • Network termination type 1 (NT1)
Network-termination devices that connect the four-wire
Subscriber wiring to the conventional two-wire local loop
Is a customer premises equipment (CPE) device (North America)
• Network termination type 2 (NT2)
Intelligent device that performs switching & concentrating.
Provides multiple ISDN interfaces on an ISDN line.
The NT2 may be as simple as a bridging device connected to an NT1
unit or it may be as complicated as a PBX (Private Branch exchanges)
ISDN Components
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10. ISDN specifies a number of reference points that define logical
interfaces between functional groupings, such as TAs and NT1s.
ISDN reference points include the following:
• R---The reference point between non-ISDN equipment and a TA.
• S---The reference point between user terminals and the NT2.
• T---The reference point between NT1 and NT2 devices.
• U---The reference point between NT1 devices and line-termination
equipment in the carrier network. The U reference point is
relevant only in North America, where the NT1 function is not
provided by the carrier network
ISDN Reference Point
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11. Reference points are a series of specifications that define
the connection between specific devices, depending on their
function in the end-to-end connection
ISDN Reference Point
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15. ISDN Layers for B and D Channels
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• Link Access Procedure, Balanced (LAPB) implements the data link layer as defined in the X.25 protocol suite.
• Link Access Procedures, D channel is part of the network's communications protocol which ensures that messages are
error free and executed in the right sequence. 15
16. BRI Interfaces
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S interface or S reference point, also known as S0, is a User–network interface reference point
for basic rate access in an Integrated Services Digital Network (ISDN)
U interface is the electrical interface for the single twisted pair wire connection from a local phone
company (the central office) to a home or business.
It is a User–network interface reference point that is characterized by a four-wire, 144 kbit/s
(2B+D) user rate.
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19. BRI (Basic Rate Interface)
• Connection from the ISDN office to the user location provides for
access to three channels. The channels are two 64Kb B-
channels and one 16Kb D-channel
• The B-channels and the D-channel provide the user with access
to the circuit switched network
ISDN Services
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20. PRI (Primary Rate Interface)
• ISDN Primary Rate Interface service provides digital
access via a T1 line.
• A T1 line provides a 1.544 bandwidth. This bandwidth is
divided into 24 64Kb channels.
• The ISDN PRI service uses 23 B channel access and
uses the 24th (D) channel for signaling purposes
• B- Channel (Bearer Channel)
• D-channel (Delta Channel) is the channel that carries control and
signaling information.
ISDN Services
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21. Advantages
• To the user : cost savings and flexibility
Integration of voice/data means users do not have to buy
multiple services to meet multiple needs
Single access line to all services
Services tailored to diverse requirements (information
volume, traffic pattern, response time, interface types)
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22. Advantages
• To network providers
Standard support universality and larger potential market for services,
drive down equipment costs
• To manufacturers
Larger potential market, economies of scales standards decrease risk of
obsolescence
• To enhanced service providers
Simplified user access
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24. 24
• Multi-speed network environment that provides a variety of complex
network services
• Can carry voice, data, video separately or simultaneously
• Can be used in LANs, MANs, or WANs
• Fixed-lenth packets (cells)
• Allows multiple logical connections to be multiplexed
• Minimal error and flow control capabilities
• Connection-oriented virtual channel
Asynchronous Transfer Mode (ATM)
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25. A/D AAL
Voice
s1 , s2 …
Digital voice
samples
A/D AAL
Video
… Compressio
n
compressed
frames
picture
frames
AAL
Data
Bursty variable-
length packets
cells
cells
cells
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26. 26
Cell Switched ATM
• Similar to frame relay
• Difference?
Frame relay switches variable length frames within frame relay cloud from source to
destination
ATM switches fixed-length cells (48 byte information field, 5 byte header)
• Based on packet switching (connection-oriented)
Cell sequence integrity preserved via virtual channel
VCC – virtual channel connection – is set up between end users, variable rate, full duplex
VCC also used for control
• Information field is carried transparently through the network, with
minimal error control
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31. End devices such as routers use all
three layers, while switches use only
the bottom two layers.
Note:
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ATM Physical Layer
• Transports cells via a communications channel (either optical or
electrical)
• LAN support: 25-155 Mbps copper or fiber
• WAN support: SONET rates over fiber
• Physical Medium Sublayer: bit transfer, bit alignment, and
copper/fiber conversions
• Transmission Convergence Sublayer: bit/cell conversion at sending
and receiving nodes
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ATM Layer
• Handles functions of the network layer:
• Connection-oriented without acknowledgements
• Two possible interfaces:
UNI – User-Network Interface: Boundary between an ATM network and host
NNI – Network-Network Interface: Between two ATM switches
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35. ATM Layer ..
• ATM Layer contains various fields such as VPI (Virtual Path Identifier),
VCI (Virtual Circuit Identifier)
• GFC: Generic Flow Control means to arbitrate access to a link on a
shared medium.
• CLP: Cell Loss Priority which indicates that packet may be dropped. A
cell dropped may not cause significant change in video data.
• HEC: Header Error Control which indicates header checksum.
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37. 37
ATM Cell Format
CLP(Cell loss Priority) 1-bit cell loss priority field, which indicates the drop
priority of the cell
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Header Format
• Generic flow control
Only at user to network interface
Controls flow only at this point
• Virtual path identifier
• Virtual channel identifier
• Payload type
e.g. user info or network management
• Cell loss priority
• Header error control
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Generic Flow Control (GFC)
• Control traffic flow at user to network interface (UNI) to alleviate
short term overload
• Two sets of procedures
Uncontrolled transmission
Controlled transmission
• Every connection either subject to flow control or not
• Flow control is from subscriber to network
Controlled by network side
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ATM Adaptation Layer (AAL)
• Maps higher-layer information into ATM cells to be transported over
an ATM network
• Collects information from ATM cells for delivery to higher layers
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Virtual Connections
• Virtual Channel Connection (VCC) – Full duplex virtual circuit with
logical connection between source and destination
• Virtual Path Connection (VPC) – Semi-permanent (or customer
controlled or network controlled) connection
• VPC provides a logical collection of virtual channels that have the
same endpoint
• A single virtual path supports multiple virtual channels (analogy –
highway = VPC, lane = VCC)
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VCI vs VPI
• VPI – Virtual Path Identifier – identified in cell’s header. Cannot
establish a virtual channel before virtual path
• VCI – Virtual Channel Identifier – only have local significance –
different virtual paths reuse VCIs (but VCIs on same path must be
unique)
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What is so special about a virtual
path?
• ATM is connection-oriented, so circuit must be established
before transmission
As route established, VPIs and VCIs are assigned
• VPI and VCI info suffices for addressing info
• Simplified network architecture (based on VC or VP)
• Reduces processing and short connection setup time
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Definition of Terms
• COS – Class of Service – sets a priority of data delivery,
based upon the class.
• Higher priority data get delivered before lower priority
data (example – which should have higher priority –
streaming video or email?)
• QOS – Quality of Service – involves establishing certain
parameters for a specific transmission – e.g. amount of
bandwidth required for a given priority data
transmission, max. amount of latency tolerated, etc
• Both are required to deliver real-time voice and video
traffic
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VP/VC Characteristics
• Quality of service based on VCC
• Switched and semi-permanent channel connections
• Call sequence integrity – packets arrive in order
• Traffic parameter negotiation and usage monitoring
• VPC only
Virtual channel identifier restriction within VPC – some VCCs reserved for
network management
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ATM Cells
• Fixed size – 53 bytes
• 5 octet header
• 48 octet information field
• Small cells reduce queuing delay for high priority cells
• Small cells can be switched more efficiently
• Easier to implement switching of small cells in hardware
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ATM Service Categories
• ATM is designed to transfer many different types of traffic
simultaneously, including real-time voice, video, and bursty TCP
traffic
• Way in which data flow is handled depends on the characteristics of
the traffic flow and requirements of the application (ex. Real-time
video must be delivered within minimum variation in delay)
• Primary service categories – real time service, non-real time service
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ATM Service Categories
• Real time
Constant bit rate (CBR)
Real time variable bit rate (rt-VBR)
• Non-real time
Non-real time variable bit rate (nrt-VBR)
Available bit rate (ABR)
Unspecified bit rate (UBR)
Guaranteed frame rate (GFR)
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ATM versus Frame Relay
• Frame relay uses variable length frames
• ATM fixed length cells
• ATM has higher overhead, but faster speed and traffic management
(better suited for video and voice)
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ATM versus SONET
• SONET is a transport mechanism, transporting data over fiber.
• Can act as a transport carrier for ATM (or FDDI, or ISDN, etc.)
• ATM is a technology and protocol designed to use SONET as its
carrier service
SONET : Synchronous optical networking (SONET) and synchronous
digital hierarchy (SDH) are standardized protocols that transfer
multiple digital bit streams synchronously over optical fiber
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Why is ATM so Efficient?
• Minimal error and flow control
Reduces overhead of processing ATM cells
Reduces number of required overhead bits
• Fixed size simplified processing at each ATM node (can be switched
more efficiently – more efficient use of router)
• Small cells reduce queuing delay
• Minimal addressing info on each cell
• Efficient traffic management
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56. Switch Ports
• Provide the physical connection to other ATM entities
• Dedicated point-to-point links
• Each port (or card) is for a particular type of interface and particular
data rate (e.g., OC-3, DS-3, JPEG, Ethernet,T1,...)
• N inputs, N outputs
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57. Switch Fabric
• Defines the interconnection between the input
ports and the output ports
• Distinguishing characteristic of different types of
ATM switches (e.g., shared memory, banyan,
Benes, hypercube, ...)
• Affects performance (cell delay, cell loss)
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58. Buffering
• Some switches are bufferless
• Some switches are buffered
• Buffers provide physical storage (i.e., memory) to hold
cells that cannot yet be sent on their desired output ports
• Uses RAM, DRAM, or FIFO...
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59. Buffering (Cont’d)
• Buffering can be located at the input ports, at the output
ports, internal to the switch fabric, or any combination
• Buffers are usually limited in size:
e.g., 100 cells per port
e.g., 4096 cells per port
• Buffer size and location affects performance
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60. VPI / VCI Table
• Physical memory that is used to keep track of how to map
cells of different VC’s from input ports to output ports
• Translation table:
1 4 15 1 5 12
3 27 104 2 2 33
Port Port
VPI VPI
VCI VCI
INPUT OUTPUT
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61. Control Unit
• Controls entire operation of switch
• Cell switching
• Signaling (UNI and NNI)
• Call Admission Control (CAC)
• Usage Parameter Control (UPC)
• Accounting statistics
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62. ATM Switch Functionality
• Signalling
participate in UNI signalling protocol (edge switches)
participate in NNI signalling protocol (core switches)
connection setup and teardown
update VPI / VCI table
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63. Summary
• ATM switches form the very heart of ATM networks
• Basic components and functionality are common to all switches
• Switches from different vendors differ in the details (e.g., switch
fabric, buffering, control software, etc.)
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Review Questions
• Describe the basic characteristics of ATM
• Explain the relationship between UNI and NNI interfaces
• What is the difference between a virtual channel and a virtual path?
• What are the advantages of the use of virtual paths?
• What are the characteristics of a virtual channel connection?
• What are the characteristics of a virtual path connection?
• Define the following terms: QOS, COS, CBR, VBR, UBR, GFR, PCR, MCR
• Compare and contrast two methods of transmitting ATM cells.
• How does ATM differ from Frame Relay
• What are the relative advantages of ATM compared to frame relay?
• How does ATM differ for SONET?
• Discuss why ATM is so efficient.
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65. Questions Appeared in University Exam
U-III
Routing
Protocols
-
Unicast
&
Multicast
65
66. U-III
Routing
Protocols
-
Unicast
&
Multicast
66
APRIL- MAY 2019 (Compulsory For all)
1(a) What is ISDN 2M
(b) What is ATM ? Explain the architecture of ATM Network 7M
(c) Explain R-Interface, S-Interface and U-Interface of ISDN 7M
(d) Write short note on following in context to ATM
(i) Logical Subnet Concept
(ii) Connection Management
7M
67. U-III
Routing
Protocols
-
Unicast
&
Multicast
67
APRIL- MAY 2018 (Compulsory For all)
1(a) What are ISDN and B-ISDN ? 2M
(b) How your company is connected by ISDN line to ISP? Explain by drawing suitable block diagram
with indication of special equipments used.
7M
(c) Explain the ATM architecture by giving the details of interfaces TP, VCI and VPL 7M
(d) What do you mean by IP Address binding ? Explain IP address binding in an ATM network. 7M
68. U-III
Routing
Protocols
-
Unicast
&
Multicast
68
APRIL- MAY 2017
1(a) Define Cell Network 2M
(b) Write a note on ATM Layers and their functions 7M
(c) What do you mean by ISDN and B-ISDN ? Compare them 7M
(d) What do you mean by transmission paths , virtual paths and virtual circuits ? 7M
69. U-III
Routing
Protocols
-
Unicast
&
Multicast
69
APRIL- MAY 2016
1(a) Define path vector identifier 2M
(b) Explain the concept of IP Subnet and explain how the binding of IP address is performed in ATM
Network
7M
(c) Explain ATM reference model with suitable block diagram 7M
(d) Write short note on
(i) Packet-type and multiplexing
7M
