MULTIMEDIA COMMUNICATION NETWORKS

MULTIMEDIA COMMUNICATION [18EC743]
Amrutha R, Assistant Professor, Dept of ECE, MYCEM 1
MODULE-1
MULTIMEDIA COMMUNICATION
 Multimedia Communication:
Define the term multimedia and give the basic form of representation of each
media. (6 Marks)
Define the following: i) Text ii) Image iii) Audio iv) Video (4 Marks)
The information/data are transferred from source to destination over the network through
single or integration of many media such as text, images, audio and video is called
multimedia communication.
 Types of media:
1. Text: This includes both unformatted text, consisting of strings of characters and
formatted text strings as used for structuring, access and presentation of electronic
documents.
2. Images: These include computer generated images, comprising lines, curves and
circles and digitized images of documents and pictures.
3. Audio: This includes both low fidelity speech as used in telephony and high fidelity
stereophonic music as used with compact discs.
4. Video: This includes short sequence of moving images (video clips) and complete
movies/films.
 Types of communication in multimedia communication:
 The applications may involve either person-to-person communication or person-to-
system communication.
 If two people communicate with each other through suitable terminal equipment
(TE). If a person interacts with a system using either multimedia personal computer
(PC) or workstation.
 Multimedia Networks:
Explain i) Data Network ii) Broadcast multiservice network in detail with
suitable figures. (10 Marks)
List the five basic types of communication network that are used to provide
multimedia services. Explain with a neat diagram i) Telephone network ii)
Integrated services digital network. (10 Marks, 6 Marks)

Discuss the different types of communication networks that are used to provide
multimedia communication service. (8 Marks)
There are five basic types of communication network that are used to provide multimedia
communication services:
1. Telephone networks
2. Data networks
3. Broadcast television networks
4. Integrated Service Digital Networks
5. Broadband Multiservice Networks
1. Telephone networks:
Explain with the aid of the diagram, how a PSTN can support range of
multimedia common applications. (10 Marks)
 Telephone networks are designed to provide a basic switched telephone service which
is known as Plain Old Telephone Service (POTS).
 The term “switched” is used to indicate that a subscriber can make a call to any other
telephone that is connected to the network.
 The main components of the network are shown in the below figure 1.
Figure 1: Telephone networks: (a) Network components (b) Digital transmission
using modems

 Telephone located in the home or in a small business is connected directed to their
nearest Local Exchange (LE)/end office.
 Those located in a medium or large office/site are connected to a private switching
office known as a private branch exchange or PBx.
 The PBx provide a switched service between any two telephones that are connected to
it.
 In addition to this, the PBx is connected to its nearest local exchange which enables
telephones that are connected to PBx also make calls through PSTN.
 Also we have cellular phones network which provide similar services to mobile
subscribers by means of handsets that are linked to the cellular phone network
infrastructure by radio. The switches used in cellular phone network are known as
Mobile Switching Centers (MSCs).
 International calls are routed to switched by International Gateway Exchange (IGE).
 Figure 2 shows digital transmission using modems of telephone networks.
 As a speech signal is an analog signal which varies w.r.t amplitude and frequency
variations of the sound resulting from the speech.
 A microphone is used to convert speech signal into an analog electrical signal to
operate in circuit mode.
 The access circuits that link the telephone handsets to a PSTN or PBx were designed
to carry the two way analog signals associated with a call.
 Hence all switches and the transmission circuits that interconnected to operate in a
digital mode to carry digital signal over analog access circuits requires a device
known as modem.
 In the figure at the sending side the modem converts the digital signal output into an
analog signal. Another modem is again placed at the receiving end in order to convert
analog signal to digital form.
2. Data Networks:
 Data networks were designed to provide basic data communication services such as
electronic mail (email) and file transfer.
 The user equipment connected to these networks is a computer such as PC,
workstation or an email server.
 The two most widely deployed networks are X.25 network and Internet. Because of
its operational mode X.25 network is restricted to low bit rate data applications and
hence unsuitable for most multimedia applications.
 The internet is made up of collection of interconnected networks all of which operate
using same set of communication protocols.Communication protocols are an agreed
set of rules that are applied for the exchange of information.
 In case of a user at home or in a small business, access to internet through an Internet
Service Provider (ISP) network.
 The user devices are connected to ISP network either through a PSTN with modems
or through an ISDN.

 Business users obtain access either through a site/ campus network. If the business
consists only single site or multiple sites the access is done through an enterprise
wide private network.
Figure 2: A selection of the network types connected to the Internet
 In case of single site/ campus, the network is known as Local Area Network (LAN).
Enterprise wide networks consisting multiple sites are interconnected together using
an inter-site backbone network.
 The different types of network are all connected to the Internet backbone network
through an interworking unit called a gateway.
3. Broadcast Television Networks
 Broadcast television networks were designed to support the diffusion of analog
television programs throughout wide geographical areas.
 In case of a large town or city, the broadcast medium is normally a cable distribution
networkwhile for larger areas broadcast medium is a satellite network or terrestrial
broadcast network is used.
 Digital Television services have become available with these networks with a low bit
rate channel for interaction purpose to provide additional services such as games
playing.

 The general architecture of a cable distribution network and a satellite/ terrestrial
broadcast network are shown in the below figure 3 (a) and (b).
Figure 3: Broadcast television networks: (a) cable networks (b) Satellite/ terrestrial
broadcast networks
 In figure 3(a), the set top up box attached to the cable distribution network provides
not only control of the television channels but also access to other services.
 For example, when cable modem is integrated into the STB provides both a low bit
rate channel and a high bit rate channel from the subscriber back to the cable head
end.
 The low bit rate channel is used to connect the subscriber to a PSTN and the high bit
rate channel to connect the subscriber to the internet.
 In figure 3 (b), in case of satellite and terrestrial broadcast networks, when a high
speed PSTN modem is integrated into the STB which provides the subscriber with an
interaction channel. This is the origin of the term “interactive television”.
4. Integrated Services Digital Networks (ISDN)
 ISDN is designed to provide PSTN users with the capability of having additional
services.
 This was achieved firstly by converting the converting the access circuits that connect
user equipment to the network. Secondly by providing two separate communication
channels over these circuits.
 These allows user to have two different calls such as a telephone call and a data call.
This access circuit is known as Digital Subscriber Line (DSL).
 The subscriber telephone can be either a digital phone or analog phone. In case of a
digital phone, the electronics convert the analog voice and call setup signals into

digital form are integrated into the phone handset. Analog phone uses same
electronics are located in the network termination equipment to make the digital
mode of operation.
Figure 4: Alternative services provided by an ISDN
 The digitization of a telephone quality analog speech signal produces a constant bit
rate referred to a bitstreamof 64kbps. Hence the basic DSL of the ISDN is known as
the basic rate access (BRA)which supports two 64kbps channels.
 To combine two separate 64kbps bitstreams into a single 128kbps stream requires an
additional electronics known as aggregation.
 A higher bit rate channel of either 1.5 or 2Mbps is supported to ISDN known as
primary rate access (PRA).
5. Broadcast multiservice network
 Broadband multiservice networks are designed to support a wide range of multimedia
communication application.
 The term “broadband” used to indicate that the circuits associated with a call could
have bits rates of maximum of 2Mbps which is provided by an ISDN. Hence it is also
known as Broadband integrated services digital networks or B-ISDN.

Figure 5: ATM broadband multiservice network
 ISDN is also referred to as Narrowband ISDN or N-ISDN.
 B-ISDN is associated with the digitization of a video signal.
 The switching and transmission methods used within these networks are more flexible
than PSTN or ISDN.
 To achieve this flexibility, all the different multimedia applications are first converted
into digital form.
 The multimedia generates multiple fixed sized packets known as cells. The rate of
transfer of cells through the network is also varies and hence this mode is known as
Asynchronous Transfer Mode (ATM).
 Multimedia Applications
1. Interpersonal communications
2. Interactive applications over the internet
3. Entertainment applications
1. Interpersonal communications
Explain with a neat sketch how voice mail and teleconferencing is supported
in relation To Speech only interpersonal communication. (10 Marks)
 Interpersonal communications may involve speech, image, text or video.
 In some cases just a single type of medium is involved while in others two or more
media types are integrated together.
Speech only
 Interpersonal communications involving speech i.e. telephone have been provided
using telephones that are connected either to a PSTN or PBx.

Figure 6: Speech only interpersonal communication network: public and private switched
telephone networks
 The general scheme is shown in the above figure. By using a multimedia PC equipped
with a microphone and speakers, the user can take part in telephone calls through the
PC. This requires a telephone interface card and associated software which is
known as computer telephony integration (CTI).
 In addition to telephony, many public and private networks support additional
services. Two examples are voice mail and teleconferencing.
 Voice mail is used when the called party is being unavailable. A spoken message can
then left in the voice mailbox of the called party. This is located in a central
respiratory known as voice mail server. This message can be read by the owner of the
mailbox the next time he or she contacts the server.
 Teleconferencing calls involve multiple interconnected telephones/PCs. Each person
can hear and talk to all the others involved in the call. This type of call is known as a
conference call or teleconferencing call or audio conferencing call. It requires a
central unit is known as an audio bridge which provides the support to set up a
conference call automatically.
 Telephony over the internet is also known as packet voice or the network protocol
associated with the internet is called Internet Protocol (IP) or Voice Over IP (VOIP).

Figure 7: Telephony over the Internet
Image only
 An alternative form of interpersonal communications over a PSTN or an ISDN is by
exchange of electronic images of documents which is known as facsimile or fax
which is shown in the below figure 8.
Figure 8: Image only interpersonal communication: Facsimile (Fax)
 This involves the use of a pair of fax machines, one at each network termination
point.
 The two fax machines communicate with each other to establish operational
parameters after which the sending machine starts to scan and digitize each page of
the document.
 Both fax machines have an essential modem within them as each page is scanned. Its
digitized image is continuously transmitted over the network and this is received at
the caller side and a printed version of the document is produced.
 Finally after the last page of the document has been sent and received, the connection
through the network.

 PC is also used instead normal fax machine to send an electronic version of a
document that is stored directly within the PC’s memory which is known as PC fax.
 The digital image of each page of the document is sent in the same way as the
scanned image produced by normal fax machine. This requires a telephone interface
card and associated software.
Text only
 Example of interpersonal communication involving just text is Electronic mail (E
mail).
Figure 9: Text only electronic mail: (a) email transfer (b) email message format
 The user terminal is normally workstation or computer. The most widespread network
used is the Internet.
 In case of user at home can access to the internet is through a PSTN/ISDN and an
Internet Service Provider (ISP) network.
 Business user obtains access either through an enterprise network or site/campus
network.

 Each network is a set of one or more server computers. Each known as email server.
Mail server contains a mailbox for each user connected to that network.
 A user can both create and deposit mail into his or her mailbox and read mail from it.
 Bothe email server and internet gateway operate using standard Internet
communication protocols.
Text and images
 An example of an application that involves both text and images integrated together is
Computer supported Cooperative Working (CSCW).
 The network used is an enterprise network, a LAN or the Internet. The general
scheme is shown in the below figure 10.
Figure 10: Text and image computer supported cooperative working (CSCW)
 A distributed group of people in his or her place of work in where all are working on
the same project.
 The user terminal is either a PC or a workstation and window on each person’s
display is used as a shared workspace known as a shared whiteboard and normally
display consists of text and images integrated together.
 The software associated with CSCW consists of a central program is known as the
whiteboard program and it is linked set of supported programs one in each
workstation.
 It is made up of two parts: Change notification part and an update control part.
 Whenever a member of the group updates the contents of his/her whiteboard, the
change notification part sends details of the changes to the whiteboard program. This
give the changes to the update control in each of the other PCs and these in turn
update the contents of their copy of the whiteboard.

Speech and video
 An example application that uses speech and video integrated together is video
telephony which is now supported by all the network types. The general scheme
is shown in the below figure 11.
 In case of the home, the terminals used to provide the videophone service, while
in an office, a single multimedia PC/workstation is used to provide the
videophone service.
 In both the cases, the terminals/PCs consist of a video camera in addition to the
microphone and speaker used for telephony.
 A separate screen is used for the display to display the image of the called party in
a window of the PC/workstation screen.
 Desktop videoconferencing call is the integration of video with speech which
requires higher bandwidth to support this type of service through PCs.
 Large corporations have an enterprise wide network to link the sites together and
in order to support videoconferencing a central unit is called multipoint control
unit (MCU) or videoconferencing server is used (figure 10.b).
 Multicasting is group communication where data transmission is addressed to a
group of destination computers. Multicast can be one to many or many o many
distribution.
 Thus the networks which support multicasting are possible to hold a conferencing
session without an MCU which is shown in figure 10(c).

Figure 10: Speech and video interpersonal communication (a) two party video telephone
call; (b) videoconferencing using MCU; (c) Videoconferencing using a broadcast network
2. Interactive applications over the Internet
 The most widely used for interactions over the internet is World Wide Web (WWW)
or Web server.
 This consists of linked set of multimedia information servers that are geographically
distributed around the internet.
 Each document consists of a linked set of pages and the linkage bewtween the pages
are known as hyperlinks.Documents consisting of only text are created using
hypertextand consisting of multimedia information are created using hypermedia.
 Each document has a unique address known as Uniform Resource Locator (URL).
The first page of the document is known as home page.
 A standard format is used for writing documentsis known as Hypertext Markup
Language (HTML). The client function is called browser.
Figure 11: Schematic of interaction with a World Wide Web server

3. Entertainment applications
Explain in brief interactive applications over internet. (10 Marks)
Explain with neat diagrams, the interactive television application for both cable
and satellite network. (6 Marks)
Explain with neat diagrams the entertainment applications of multimedia. (10
Marks)
Discuss any one entertainment application of multimedia. (4 Marks)
Entertainment applications can be one of two types:
1. Movie/video on demand
2. Interactive television
1. Movie/video on demand
 In general, the video and audio associated with these applications must be a higher
quality /resolution since wide screen televisions and stereophonic sound are often
used.
 A digitized movie/ video with sound require a minimum channel bit rate of 1.5 Mbps.
 The network used support this type of application must be either PSTN with a high bit
rate modem is used. The general operational scheme in both cases is shown in below
figure 12 (a).
Figure 12: Interactions with a video server- networking schematic
 The information stored on the server is a collection of digitized movies/videos.
 By means of suitable menu, the subscriber is able to browse through the set of
movies/videos available and initiate the showing of a selected movie. This type of
application is known as movie on demand (MOD) or video on demand (VOD).

 A key feature of MOD is that a subscriber can initiate the showing of a movie selected
from a large library of movies at any time of the day or night.
2. Interactive television
 Broadcast television networks include cable, satellite and terrestrial networks.
 The basic service provided by these networks is the diffusion of both analog and
digital television programs.
Figure 13: Interactive television: (a) cable distribution network; (b) satellite/terrestrial
broadcast network
 The set top box (STB) associated with these networks also has a modem within it.
 In case of cable network as shown in the figure 13 (a), the STB provides both a low
bit rate connection to the PSTN and high bit rate connection to the Internet.
 Hence by connecting appropriate terminal equipment to the STB, telephone and so
on; the subscriber is able to gain access to all the services provided through PSTN and
the Internet.

 In addition, through the connection to the PSTN, the subscriber is able to actively
respond to the information being broadcast. This is the origin of the term “interactive
television”.
 As shown in the figure 13 (b) a similar set of services are available through satellite
and terrestrial broadcast networks, except that the STB associated with these networks
requires a high speed modem to provide the connections to the PSTN and the Internet.
 Application and Networking terminology
Media Types
 The information flow associated with the different applications can be either
continuous or block mode.
Continuous media
 In the case of continuous media the information stream is generated by the source
continuously in a time dependent way.
 Therefore continuous media is passed directly to the destination as it is generated and
at the destination the information stream is played out directly as it is received. This
mode of operation is called streamingand since continuous media is generated in time
dependent way, it is also known as real time media.
 Two examples of media types that generate continuous streams of information in real
time are audio and video.
 In terms of the bit rate at which the source information stream is generated can be
either a constant bit rate (CBR) or a variable bit rate (VBR).

Block mode media
 In block mode media, the source information consists of a single block of information
that is created in a time independent way.
 Example, a block of text representing an email or computer program, A two
dimensional matrix of pixel values that represents an image and so on.
 Block mode media is created in time independent way and is often stored and
displayed at a time determined by the requesting application program. This mode of
operation is known as down loading.
 When a block is requested, the delay between the request being made and the contents
of the block being displayed at the destination within an acceptable time interval. This
is known as round trip delay (RTD).
Communication modes
Explain the communication modes available to transfer the information stream
(10 Marks)
Briefly explain the communication modes with a simple sketch. (4 Marks)
1. Simplex: This means the information associated with the application flow in one
direction only. An example is the transmission of photographic images involves just a
unidirectional flow of information.
2. Half duplex: This means the information flows in both direction but alternatively.
This mode is also known as two ways alternate. An example is a user making a
request for some information from a server and returning the requested information.
3. Duplex: This means the information flows in both directions simultaneously. It is also
known as two way simultaneous. Example is the two way flow of digitized speech
and video associated with a video telephony applications.
4. Broadcast: This means that the information displayed by a single source node is
received by all the other nodes or computers that are connected to the same network.
An example is the broadcast of a television program over the cable network.
5. Multicast: This is similar to broadcast except that the information displayed by the
source is received by only specific subsets of the nodes that are connected to the
network. An example of this mode is videoconferencing which involves a predefined
group of terminals/computers connected to a network exchanging integrated speech
and video streams.

Figure 14: Communication mode: (a) unicast (b) broadcast (c) multicast
Network Types
Explain the working principle of circuit mode and packet mode of operation of
multimedia networks with a beat diagram. List out salient features of each type
of network. (8 Marks)
 There are two types of communication channels associated with the various network
types, one that operates in a time dependent way known as circuit mode and the other
that operates in a time varying way known as packet mode.
 The circuit mode is also known as synchronous communications channels since it
provides a constant bit rate service at a specified rate. The packet mode is known as
an asynchronous communications channel since it provides a variable bit rate
service.
Circuit mode
 A circuit mode is shown in the below figure 15 consists of an interconnected set of
switching offices/exchanges to which the subscriber terminals/ computers are
connected. This type of network is known a circuit switched network.

Figure 15: Circuit switched network schematic
 In this network before sending any information, the source must first set up a
connection through the network.
 Each subscriber terminal/computer has a unique network wide number/address
associated with it and to make call; the source first enters the number/address of the
intended communication partner.
 The local switching office/exchange then uses this to set up a connection through the
network to the switching office/exchange to which the destination is connected.
 Assume the destination is free and ready to receive a call, a message is returned to the
source indicating that it can now start to transfer/exchange information
 Finally after all the information has been transferred/exchanges, either the source or
the destination requests for the connection to be cleared.
 The message associated with the setting up and clearing of a connection are known as
signaling messages.
 There is a time delay while a connection is being established known as the
call/connection setup delay.
 Networks that operate in this way are PSTN and an ISDN.
Packet mode
 There are two types of packet mode network: connection oriented (CO) and
connectionless (CL).
 Connection oriented network consists of an interconnected set of packet switching
exchanges (PSEs).This type of network is known as a packet switched network.
 In circuit switched network, each terminal/computer is connected to the network that
has a unique network wide number/address associated with it.

Figure 16: Packet switching principles: (a) Connection oriented (b) Connectionless
 In Connection oriented network, as the name implies, prior to sending any
information a connection is first set up through the network using the address of the
source and destination terminals.

 In packet switched network, the connection is set up which utilizes only a variable
portion of the bandwidth of each link and the connection is known as virtual
connection or virtual circuit (VC).
 To set up VC, the source terminal/computer sends a call request control packet to its
local PSE which contains in addition to the address of the source and destination
terminal/computer, a short identifier known as virtual circuit identifier (VCI).
 Each PSE maintains a table that specifies the outgoing link that should be used to
reach each network and on receipt of the call request packet, the PSE uses the
destination address within the packet to determine the outgoing link to be used.
 The next free identifier (VCI) for this link is then selected and two entries are made in
a routing table.
 The first specifies the incoming link/VCI and the corresponding outgoing link/VCI
and the second is used to route packets in the reverse direction as shown in the figure
16(a).
 The call request packet is then forwarded on the selected outgoing link and the same
procedure is followed at each PSE until the destination terminal is reached.
 The destination assuming that the call is accepted and a call accepted packet is
returned to the source over the same VC.
 Each PSEs uses the incoming link/VCI to determine the outgoing link/VCI from the
routing table.
 When all the information has been transferred/exchanged from source to destination,
the VC is cleared and VCIs are released by passing a call clear packet along the VC.
 Multipoint conferencing
What is multipoint conferencing? Explain the various types with diagrams. (6
Marks)
Explain the operational modes of multipoint conferencing with neat diagrams. (6
Marks)
Explain with neat diagram multipoint conferencing modes and type of
conferencing. (6 Marks)
 Multipoint conferencing includes audio and video conferencing, data sharing and
Computer Supported Cooperative Working (CSCW).
 These involve the exchange of information between three or more
terminals/computers.
 Because of different modes of operation of the two network types (circuit and packet
switching networks) multipoint conferencing is implemented in one of three ways:
Centralized, Decentralized and Hybrid mode.

Figure 17: Multipoint conferencing modes: (a) Centralized (b) Decentralized (c)
Hybrid
Centralized mode:
 This mode is used with circuit switched networks such as a PSTN or ISDN as
shown in the above figure 17(a), with this mode a central conference server is used.
 Before sending any information, each terminal/computer to be involved in the
conference must first set up a connection to the server.
 Each terminal/computer then sends its own media stream consisting of audio, video
and data integrated together to the server using established connection.
 The server then distributed either the media streams received from a selected
terminal/computer or a mix of the media streams received from several

terminals/computers back to all the other terminals/computers that are involved in the
conference.
Decentralized mode
 This mode is used with packet switched networks that support multicast
communications.
 Examples include Local Area Networks (LANs), Internet and the Intranet.
 As shown in the above figure 17(b), the output of each terminal/computer is received
by all the other members of the conference/multicast group.
 Hence conference server is not used and instead it is the responsibility of each
terminal/computer to manage the information streams that it received from the other
members.
Hybrid mode
 As shown in the above figure 17(c), this mode is used when the various
terminals/computers that make up the conference are attached to different network
types.
 The conference consisting of four terminals/computers, two attached to a circuit
switched network and two to a packet switched network that support multicasting.
 As in the centralized mode, a conference server is used and the output of each
terminal/computer is sent to the server either individual circuits as terminal A and B
or using multicasting as terminal C and D.
Types of conference
1. Data conferencing: Involves data only and examples include data sharing and
computer supported cooperative working.
2. Audioconferencing: Involves audio (speech) only.
3. Videoconferencing: Involves speech and video integrated together.
4. Multimedia conferencing: Involves speech, video and data integrated together.
 Network QoS
Explain briefly about the network QoS Parameters. (5 Marks)
 The operational parameters associated with a communications channel through a
network are known as network Quality of Service (QoS).
Circuit switched network
The QoS parameters associated with a circuit switched network are:
1. Bit rate
2. Mean bit error rate
3. Transmission delay

1. Bit rate: Bit rate is defined as the number of bits transmitted per second. It is also
referred to as Bits Per Second (BPS).
2. Mean bit error rate: It is the probability of a bits being corrupted during its
transmission across the channel in a defined time interval.
3. Transmission delay: The time taken to transmit a information from host to the
transmission medium is called transmission delay.
Packet switched network
Explain the QoS parameter associated with a packet switched network. (6
Marks)
The QoS parameters associated with a packet switched network are:
1. Maximum packet size
2. Mean packet transfer rate: It is a measure of the average number of packets that are
transferred across the network per second.
3. Mean packet error rate: It is the probability of a received packet containing on or
more bit errors.
4. Mean packet transfer delay: It is the summation of the mean store and forward
delay that experiences in each PSE
5. Worst jitter: It is the variation associated in store and forward delay.
6. Transmission delay: The time taken to transmit a packet from host to the
transmission medium is called transmission delay.2
 Application QoS
Define the key application parameters that relate to the networks. (5 Marks)
The application QoS parameters that a network include:
 The required bit rate or mean packet transfer rate
 Maximum startup delay
 Maximum end to end delay
 Maximum delay variation/ jitter
 Maximum round trip deay

1. Derive the maximum block size that should be used over a channel which
has BER probability of 10-4
if the probability of a block containing an
error and being discarded is to be 10-1
. (2 Marks)
2. Determine the propagation delay associated with the following communication
channels:
i) A connection through a private telephone network of 1km.
ii) A connection through PSTN of 200km.
iii) A connection over a satellite channel of 50,000km.
Assume that the velocity of propagation of a signal in case of i) and ii) is
2x108
ms-1
and in case iii) 3x108
ms-1
(4 Marks, 6 Marks)

MULTIMEDIA COMMUNICATION NETWORKS

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