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Lecture #5: Reference Lecture #5: Reference Models and Example Models and Example

NetworksNetworksC o n t e n t s C o n t e n t s The ISO OSI Reference ModelThe ISO OSI Reference Model The TCP Reference ModelThe TCP Reference Model Example Networks:Example Networks:

NovellNovell™™ NetWare NetWare®®

From ARPANET to InternetFrom ARPANET to Internet

Gigabit projectsGigabit projects

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Reference Models - Reference Models - BasicsBasics

Reference models, ISOReference models, ISO OSI = OSI = Open SystemsOpen Systems Interconnection Interconnection Layers:Layers:

Perform similar functionsPerform similar functions Process similar dataProcess similar data Respect internationally standardized protocolsRespect internationally standardized protocols Minimize the information flow though the Minimize the information flow though the

interfacesinterfaces Their number is the smallest possible to mach Their number is the smallest possible to mach

all different levels of protocol abstractionall different levels of protocol abstraction• ExamplesExamples: ISO 7 layers; internet 5 layers: ISO 7 layers; internet 5 layers

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Reference Models - the Reference Models - the OSI ModelOSI Model

The The OSIOSI model: model:

7 layers7 layers

Points out the set of functions of Points out the set of functions of

each layereach layer

Establishes international standard Establishes international standard

for all of the layers but not protocolsfor all of the layers but not protocols

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Protocol stacksProtocol stacks OSI protocol stack OSI protocol stack

OSI-protocols are specified in seven layers. The lower OSI-protocols are specified in seven layers. The lower layers are more hardware and transmission oriented. The layers are more hardware and transmission oriented. The upper layers are oriented to presentation and upper layers are oriented to presentation and synchronization purposes. The middle layers handle synchronization purposes. The middle layers handle network quality, addressing and routing.network quality, addressing and routing.

Layers Layers with example OSI protocols arewith example OSI protocols are::

Application

Presentation

Session

Transport

Network

Data link

Physical

FTAM, ACSE, ROSE

OSI Presentation

OSI Session BSS, BSC, BAS

OSI Transport Class 0,..,4

OSI Network, X.25

HDLC

Voltages as X.24

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Communication Communication Functions according to Functions according to

the OSI Modelthe OSI ModelUser applications ..

Encryption/decryption

compression/expansion

Choice of syntax

Sessioncontrol

Session to transportmapping

Session management

Sessionsynch.

Layer and flowcontrol

Error recovery

Multiplexing

Connection control

Routing Addressing

Errorcontrol

Flowcontrol

Data link establishment

Synch Framing

Access to transm. media

Physical and electrical interface

Activation/ deactivation of con.

Application layer

Presentation layer

Session layer

Transport layer

Network layer

Link layer

Physical layer

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The OSI Model - The The OSI Model - The Physical LayerPhysical Layer

Bit-slice transmission via Bit-slice transmission via some communication channel some communication channel e.g.e.g. Method of bit coding 0/1Method of bit coding 0/1 Physical parameters: Physical parameters:

voltage/amperage etc.voltage/amperage etc. Timing: frequency/period, Timing: frequency/period,

shape of signal front, etc.shape of signal front, etc. Direction[s] of transmissionDirection[s] of transmission Establishment and canceling of Establishment and canceling of

the connection the connection Physical/mechanical interfaces Physical/mechanical interfaces

to the connection medium to the connection medium (e.g. RS234 connector)(e.g. RS234 connector)

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The OSI Model - The The OSI Model - The Data Link LayerData Link Layer

Maintains the Maintains the error-freeerror-free transmission transmission lineline for for data framesdata frames serving the requests of the upper serving the requests of the upper Network Layer.This includes:Network Layer.This includes: braking the upper level data into or braking the upper level data into or

packing the lower level bit stream packing the lower level bit stream into into framesframes

keeping the data keeping the data sequencesequence by by exchange of acknowledgement exchange of acknowledgement framesframes

create or recognize frame create or recognize frame boundaries by bit patterns for boundaries by bit patterns for beginning/end frame boundaries beginning/end frame boundaries

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The OSI Model - The The OSI Model - The Data Link LayerData Link Layer

retransmission of corrupted or retransmission of corrupted or erroneous frameserroneous frames

manages problems of duplicate, manages problems of duplicate, corrupted or lost frames depending on corrupted or lost frames depending on the service (price/speed) level applied the service (price/speed) level applied by the upper layersby the upper layers

low level buffering between upper low level buffering between upper layers peers of different capacitylayers peers of different capacity

support of bi-directional communication: support of bi-directional communication: incoming data frames share the line incoming data frames share the line with outgoing acknowledgement frameswith outgoing acknowledgement frames

for broadcast networks: medium access for broadcast networks: medium access sublayer for shared channel controlsublayer for shared channel control

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The OSI Model - The The OSI Model - The Network LayerNetwork Layer

SubnetSubnet control layer i.e. control layer i.e. routingrouting of of of of the Data Link Layer packets from source the Data Link Layer packets from source to destination. Routing might be:to destination. Routing might be: staticstatic - based on static tables - based on static tables

dynamicdynamic - new route for each session - new route for each session

turboturbo - new revision of the route for each - new revision of the route for each packetpacket

Routing trends to solve problems with Routing trends to solve problems with temporarily bottlenecks temporarily bottlenecks

Network layer also does the following:Network layer also does the following:8

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The OSI Model - The The OSI Model - The Network LayerNetwork Layer

counts (on demand of the upper layers) the counts (on demand of the upper layers) the number of packets/B/b produced by number of packets/B/b produced by customer/network etc.customer/network etc.

interprets addresses from another interprets addresses from another conventionsconventions

adjusts the packet size according to the size adjusts the packet size according to the size of peer networkof peer network

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The OSI Model - The The OSI Model - The Transport LayerTransport Layer

Exchange (“transport”) of data “Exchange (“transport”) of data “point-to-point-to-pointpoint” providing the upper (session) layer ” providing the upper (session) layer with with error-freeerror-free data messages. It cares data messages. It cares for:for: effective communication - for high throughput effective communication - for high throughput

it might open >1 network connections - it might open >1 network connections - ““multiplexingmultiplexing””

fault tolerancefault tolerance opening/closing the connections with named opening/closing the connections with named

parties in the network + support of naming parties in the network + support of naming mechanism needed - “mechanism needed - “flow controlflow control””

different types of services: point-to-point different types of services: point-to-point channel; isolated messages; broadcasting.channel; isolated messages; broadcasting.

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The OSI Model - The The OSI Model - The Session LayerSession Layer

Establishes sessions between network Establishes sessions between network machines. The sessions are extensions machines. The sessions are extensions over the transport layer over the transport layer communication, that support:communication, that support: remote loginremote login file transfer file transfer interactive exchange (dialogue):interactive exchange (dialogue):

bi-directional simultaneousbi-directional simultaneous bi-directional alternativebi-directional alternative uni-directionaluni-directional

dialogue synchronization - by session dialogue synchronization - by session brakes brakes

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The OSI Model - The The OSI Model - The Presentation LayerPresentation Layer

Interprets the exchanged data as Interprets the exchanged data as information considering its syntax and information considering its syntax and semantics. This includes:semantics. This includes:

security coding/decodingsecurity coding/decoding presenting data as presenting data as text stringstext strings, ,

formatted numbersformatted numbers (integers, fixed, (integers, fixed, floating, double, etc.) according floating, double, etc.) according different formatting codes in both different formatting codes in both directions:directions:– local computer standardlocal computer standard– network standardnetwork standard

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The OSI Model - The The OSI Model - The Application LayerApplication Layer

Set of protocols providing network-wide Set of protocols providing network-wide compatibility of the user programs compatibility of the user programs including:including: full-screen terminal compatibility full-screen terminal compatibility file- and directory- structure compatibilityfile- and directory- structure compatibility remote procedure calls/remote evaluationremote procedure calls/remote evaluation electronic mail electronic mail ……………………..

Solution: network virtual standard to Solution: network virtual standard to which to translate local structures/objectswhich to translate local structures/objects

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OSI reference modelOSI reference model

(N)-SAP

(N-1)-SAP (N-1)-SAP(N-1)-SAP

(N)-entity

(N+1)-level

(N-1)-level

(N)-level

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The OSI Model - The OSI Model - example Data example Data TransmissionTransmission

Sender transmits Data to ReceiverSender transmits Data to Receiver The protocols implementing each The protocols implementing each

OSI layer add special header to the OSI layer add special header to the Data (header might be null)Data (header might be null)

The lower level deals with The lower level deals with extended Data (Data+Header) as a extended Data (Data+Header) as a wholewhole

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The OSI Model - The OSI Model - DrawbacksDrawbacks

Late appearance (after widespread Late appearance (after widespread application of another models like application of another models like TCP/IP)TCP/IP)

Heavy implementationHeavy implementation– ignores less reliable but prompt ignores less reliable but prompt

connectionless services connectionless services – multiplicates the layer functions multiplicates the layer functions

throughout several layersthroughout several layers Result: slow protocolsResult: slow protocols

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Reference Models - the Reference Models - the TCP/IP ModelTCP/IP Model

Developed for ARPANET (70ties US Developed for ARPANET (70ties US national military network) and national military network) and inherited in the Internetinherited in the Internet

Features:Features: flexible routing - tolerant to loss of flexible routing - tolerant to loss of

network nodes, subnets, route[r]s, network nodes, subnets, route[r]s, connections, etc.connections, etc.

flexible architecture - tolerant to different flexible architecture - tolerant to different throughput and application services (off-throughput and application services (off-line, on-line, real-time)line, on-line, real-time)

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Protocol stacksProtocol stacksTCP/IP stackTCP/IP stack

•Internet networks are based on TCP/IP Internet networks are based on TCP/IP protocols, so the TCP/IP model and protocol protocols, so the TCP/IP model and protocol stack have a growing importance.stack have a growing importance.•TCP/IP is based on TCP/IP is based on fivefive protocol layers protocol layers

instead of seven. The OSI model session and instead of seven. The OSI model session and presentation layers can be considered empty in presentation layers can be considered empty in TCP/IP context.TCP/IP context.•TCP/IP stack with example protocols is shown TCP/IP stack with example protocols is shown

below:below:ApplicationTransportNetworkData link

Telnet, FTP, SMTP, SNMP, HTTP TCP, UDP IP HDLC or LAN frames

Voltage levelsPhysical

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4

3

2

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TCP/IP Layered TCP/IP Layered communicationcommunication

Client Server

Router

Telnet request

TCP segment

IP datagram

Ethernet frame

Voltage

Telnet request

TCP segment

IP datagram

Ethernet frame

Voltage

IP datagram

Ethernet frame

Voltage

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The TCP/IP Model - The The TCP/IP Model - The “Host/Network Layer” “Host/Network Layer”

Corresponds to OSI Physical+Data Corresponds to OSI Physical+Data Link LayersLink Layers

Unspecified strictly as protocolUnspecified strictly as protocol implementations vary in different implementations vary in different

networks and even hosts networks and even hosts only restriction: serving upper only restriction: serving upper

(internet) layer in transmission of (internet) layer in transmission of data packetsdata packets

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The TCP/IP Model - The The TCP/IP Model - The Internet LayerInternet Layer

Connectionless layer (in order to provide Connectionless layer (in order to provide the flexibility needed)the flexibility needed)

Implementation: Implementation: IPIP free independent exchange of packets free independent exchange of packets

(IP datagrams) transparently to the (IP datagrams) transparently to the sender and receiver sender and receiver routingrouting is a key is a key issue in IPissue in IP

standard standard packet formatpacket format (strictly (strictly supported) for proper routingsupported) for proper routing

corresponds to OSI Network Layercorresponds to OSI Network Layer

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The TCP/IP Model - The The TCP/IP Model - The Transport LayerTransport Layer

Supports “point-to-point” connectivity Supports “point-to-point” connectivity between the source and destination (like between the source and destination (like OSI transport layer)OSI transport layer)

Implemented by two protocols:Implemented by two protocols: TCPTCP (Transmission Control Protocol) - (Transmission Control Protocol) -

connection oriented, delivers the byte connection oriented, delivers the byte stream from source to destination by stream from source to destination by fragmentation into discrete messages for fragmentation into discrete messages for transmission by IP. Receiving TCP assembles transmission by IP. Receiving TCP assembles the incoming messages to output streamthe incoming messages to output stream

UDPUDP (User Datagram Protocol) - (User Datagram Protocol) - connectionless, unreliable, non-sequential, connectionless, unreliable, non-sequential, for prompt delivery (multimedia applications)for prompt delivery (multimedia applications)

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The TCP/IP Model - The The TCP/IP Model - The Application LayerApplication Layer

Top level protocols (session and Top level protocols (session and

presentation layer functions are performed presentation layer functions are performed

by the application when needed) like:by the application when needed) like: TELNETTELNET

FTPFTP

SMTPSMTP

DNSDNS

HTTPHTTP

…………......

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Service to protocol -Service to protocol -mappingmapping

Ethernet header

Encapsulation between protocol layers

IP header

“Connect”

Telnet request: “Connect”

TCP segment: TCP header

IP datagram: “Connect”TCP header

IP header “Connect”TCP headerEthernetframe:

Voltages:

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The TCP/IP Model - The TCP/IP Model - Drawbacks Drawbacks

Tightly specified, non-general model, Tightly specified, non-general model, oriented to the suspected set of oriented to the suspected set of protocolsprotocols

The lowest “host/network” layer is The lowest “host/network” layer is practically unspecified and this makes practically unspecified and this makes difficulties applying new difficulties applying new communication media and technologiescommunication media and technologies

freeware protocols: freeware protocols: wide application but bad documentation, wide application but bad documentation, bad quality of some and bad quality of some and security security problems (big possibilities for problems (big possibilities for

hackers)hackers)

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Reference Models - OSI Reference Models - OSI vs. TCP/IPvs. TCP/IP

Similarities:Similarities:– structurestructure: stack of protocols: stack of protocols– functionalityfunctionality: routing + point-to-point : routing + point-to-point

connectivity + application supporting connectivity + application supporting functions functions

Dissimilarities (Dissimilarities (OSIOSI)/(TCP):)/(TCP):– conceptualityconceptuality/applicability/applicability– hidden, transparent, replaceable protocolshidden, transparent, replaceable protocols / /

conservative, non-conceptual approachconservative, non-conceptual approach– mostly connection orientedmostly connection oriented / pure / pure

connectionless orientedconnectionless oriented– 7 layers7 layers / 4 layers / 4 layers

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Example Networks - Example Networks - The The ARPANETARPANET

[Defense] [Defense] Advance Research Project Advance Research Project AgencyAgency - consists of subnet and hosts - consists of subnet and hosts

Subnet is based Interface Message Processors Subnet is based Interface Message Processors ((IMPIMP) connected by communication lines.) connected by communication lines.– Software: IMP/IMP- Host/IMP- and Host/Host- Software: IMP/IMP- Host/IMP- and Host/Host-

protocolsprotocols Development - chiefly US universities: 1969, Development - chiefly US universities: 1969,

70, 72, 7370, 72, 73 Extensions: Terminal Interface Processors Extensions: Terminal Interface Processors

((TIPTIP) (Terminal Complexes), LANs, TCP/IP ) (Terminal Complexes), LANs, TCP/IP (protocol stack and model -1974), DNS (1981)(protocol stack and model -1974), DNS (1981)

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Example Networks - Example Networks - The The ARPANETARPANET

[Defense] Advance Research Project Agency - [Defense] Advance Research Project Agency - first to adopt first to adopt packet-switchingpacket-switching replacing replacing traditional circuit-switching. Advantages:traditional circuit-switching. Advantages:– multiple routes rise fault-tolerance (dated)multiple routes rise fault-tolerance (dated)– dense communication channels (actual)dense communication channels (actual)

Structure: Structure: subnetsubnet and and hostshosts Subnet structure: Interface Message Subnet structure: Interface Message

Processors (IMP) connected by communication Processors (IMP) connected by communication lines; Alternative connections for each IMPlines; Alternative connections for each IMP– Software: IMP/IMP- Host/IMP- and Host/Host- Software: IMP/IMP- Host/IMP- and Host/Host-

protocols based on datagram exchange; rerouting protocols based on datagram exchange; rerouting algorithms for lost datagrams. algorithms for lost datagrams.

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Example Networks - The Example Networks - The ARPANETARPANET

Development - chiefly US universities: 1969, 70, Development - chiefly US universities: 1969, 70, 72, 7372, 73

Extensions:Extensions:– Terminal Interface Processors (TIP) (Terminal Terminal Interface Processors (TIP) (Terminal

Complexes) - multiple host per TIP, multiplexed Complexes) - multiple host per TIP, multiplexed access of one host to several TIPsaccess of one host to several TIPs

– LANs LANs – TCP/IP (protocol stack and model -1974) suitable TCP/IP (protocol stack and model -1974) suitable

for mobile networks where a host can be for mobile networks where a host can be switched to different networks of the subnet; switched to different networks of the subnet; since 1983 the only protocol stack of ARPANET since 1983 the only protocol stack of ARPANET

– DNS (1981) organization of host domains, DNS (1981) organization of host domains, namind all the hosts and mapping onto list of IP namind all the hosts and mapping onto list of IP addressesaddresses

Early 90’s ARPANET melted in arising Internet Early 90’s ARPANET melted in arising Internet spacespace

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Internet – a brief prehistoryInternet – a brief prehistory ARPANETARPANET was the first. was the first.

CSNETCSNET ("Computer Science Network“, ("Computer Science Network“, 1980-1989) – a non-military alternative to 1980-1989) – a non-military alternative to ARPANET. Running TCP/IP over X.25. ARPANET. Running TCP/IP over X.25.

NSFNETNSFNET (“National Science Foundation (“National Science Foundation Network”, 1985) – provides open access Network”, 1985) – provides open access to supercomputer centers for to supercomputer centers for researchers.researchers.Started from Started from 56 kbps56 kbps speed. speed.1/26

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Example Networks - The Example Networks - The InternetInternet

The Internet arises on base of ARPANET after The Internet arises on base of ARPANET after joining of another regional networks - joining of another regional networks - NSFNET, BITNET, EARN, …, thousands of NSFNET, BITNET, EARN, …, thousands of LANs; early 90’ the term “internet” widely LANs; early 90’ the term “internet” widely accepted as net name accepted as net name “The Internet”“The Internet”

Internet machine is each machine thatInternet machine is each machine that(1)(1) inter-communicates with others under inter-communicates with others under

TCP/IP andTCP/IP and(2)(2) has a specific IP address. has a specific IP address.

Classic applications: mail, news, remote login Classic applications: mail, news, remote login and file transferand file transfer

““New wave”New wave” applications: from gophers to applications: from gophers to WWW surfingWWW surfing

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Example Networks - Example Networks - NovellNovell™™ NetWareNetWare®®

Client-server model based LANs, basically Client-server model based LANs, basically connecting user PCs and server-PCs connecting user PCs and server-PCs

Special protocol stack - 5 layers, closer to Special protocol stack - 5 layers, closer to TCPTCP//IP than OSI:IP than OSI:– Phys./Data layer: different industry standardsPhys./Data layer: different industry standards– Network layer: Network layer: Internet Packet XchangeInternet Packet Xchange (IPX) (IPX)

prototcol: prototcol: connectionlessconnectionless (like IP), IPX packet (like IP), IPX packet has has 12-byte12-byte Source/Destination Address (IP Source/Destination Address (IP datagram : 4 bytes)datagram : 4 bytes)

– Transport layerTransport layer: : •Network Core ProtocolNetwork Core Protocol (NCP) - user data transport (NCP) - user data transport + numerous distributed file system services or + numerous distributed file system services or

•Sequenced Packet XchangeSequenced Packet Xchange (SPX)- simple, (SPX)- simple, compact transport protocol orcompact transport protocol or

•option: option: TCPTCP

4B network # IP Number6B machine # LAN 802 addr.2B local addr. machine socket

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Example Networks - Example Networks - NovellNovell™™ NetWare NetWare®®

– Application layer: includes File system Application layer: includes File system + + SAPSAP (Service Advertising Protocol: (Service Advertising Protocol: broadcasts information about the broadcasts information about the server data and services to routers)server data and services to routers)

3-component client-server model3-component client-server model: : client machine (user workstation), client machine (user workstation), network server (local router) and network server (local router) and remote serverremote server

negotiable IPX packet length (i.e. negotiable IPX packet length (i.e. data field varies) data field varies)

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Example Networks - Example Networks - Gigabit ImplementationsGigabit Implementations

Next step after 100 Mbps Internet Next step after 100 Mbps Internet backbonesbackbones

Specific Applications: Specific Applications: TeleservicesTeleservices (on- (on-line transmission of huge data arrays) line transmission of huge data arrays) especially televideoservices, cable TV to especially televideoservices, cable TV to net, etc.net, etc.

NoteNote: not always faster, but better : not always faster, but better bandwidth - for mass communicationsbandwidth - for mass communications

Implementations: mainly Ethernet LANs Implementations: mainly Ethernet LANs and ATM switches: 3Comand ATM switches: 3Com®® (1000 megabits per (1000 megabits per second (Mbps) Gigabit Ethernet networking infrastructure around second (Mbps) Gigabit Ethernet networking infrastructure around

eleven 3Com CoreBuilder 9000 enterprise switches).eleven 3Com CoreBuilder 9000 enterprise switches).

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44ARPANET growth: 12.1969 – 09.1972

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