?????: ???? ??? [e-mail]

1
?????? ?????? ??????????? ???????

• ???? ??' 202-2-1131
• ????? ???? ??? eyalco_at_cs.bgu.ac.il
• ????? ?????? - ????

2
???????????? 1

• ?????? ?????
• ??? ??? ??? ????? 1810 1900.
• ?????
• Computer Networking A Top-Down Approach
  Featuring the Internet / Kurose-Ross
• Computer Networks / Tanenbaum

3
???????????? 2

• ?????? ??? 5 ???? 34.
• ???? ???? ??? -101 ???? 37, ??? ?' 1600 -1800
  ?? ????? ?????.
• ??????? ????? ????? ????? ?"? ?????.

4
???? ???????

• ????? ?? ????? ?? ?????? ?????? ?????? ????
  (Learn the basics of data communication and
  computer networks).
• ????? ?? ??????? ???????? ??? ????????? ?? ??????
  (To understand the main concepts and principles
  of communication).
• ????? ?? ????? ??????? ????????? ?????????? ????
  (To present modern communication networks and
  their applications).

5
?????? ???????

• ???? (Introduction)
• ???? ?????? ??????? ?????? ???????? ??
  ???? ??????,
• ???? ??? ?????? ((The (OSI) layered
  network architecture.
•   
• ????? ?????? (Physical Layer)
• ?????? ???????? ???????? ?? ?????
  ??????? ???????? ?? ?????? ?????? ?????????
• ???? ????? ?????? (Data Link Layer)
• ????? ???? ??????? ???????? ???????
  ??????, ????? ?????? ??????? ???????????.
• ???? ???? (Network Layer)
• ?????? ?? OSI ??? ?-Internet, ??????
  ?????? ????? ???????????, ???? IP(v4, v6), ,
  routing protocols.
•  
• ???? ?????? (Layer Transport)
• ?????? ?? OSI ??? ?-Internet, ??????
  ?????? ????? ??????,????? ?- TCP, UDP.
•  
• ???? ????????? (Application Layer)
• ?????? ?? OSI ??? ?-Internet, ?????
  ?????????? ???? FTP, SMTP, HTTP, Mail, DNS.

6
??? ?????
??? ?????? ??? ???? ?? ?????? ?????????? ???????
?? ?? ?? ??? ???? ???? A Computer Network is a
collection of autonomous computers,
interconnected through a physical medium
7
???? ?????? ?????
8
???? ?????? ?????? ?????
9
??? ??? ???? ?

• ????? ??????.
• Reliability(????? ?? ?????).
• ?? ?????? ?? ??? ??????.
• ?? ????? ????? ??? ??????.

10

• ?? ??????
• ??????
• ??? ??????
• ???? ?

11
???? ????

• ??? ???
  ??? ???

12
????? ?????
????, ????? ?????? ??????? (CPU - Central
Processing Unit ), ??? ???? ?????? ?????, ?????
?? ??????? ????????? ??????? ?????.
????? (cache) ??? ???? ?????? ???? ??? ??????
?????? ??? ????? ???? ?????? ??????? ?? ????.

• PCI ((Peripheral Component Interconnect- ?????
  ?????? ???????) ??? ??? ????? ???? ????? ?????
  ????? ?????? ?????? ??????? ???? ?? ?? ????.
  ?????? ??? ?????? ????? ?????? ??
• ?????? ??????? ???????? ?? ??? ??? ????.
• ?????? ????? ??? ??????? ??????.

?????? ???? (????? ????? ??????) ??? ????? ????,
?????? ?????? ????? ??????? ???? ?????? ???????
???????? ????? ??? ?????.
??? ??? ??? ????? ?????? ????? ?? ????. ??
??????? ???????? ??????? ?? ????? ????? ??????
??? ???????? ???? ???, ?? ??????? ???? ?????? ???
????? ????? ?????. ?????? ??? ?????? ?? ?????,
???????, ????? ????, ????? ??????? ??????????
????. ?? ??? ?? ????? ?? ???? ????? (Chipset)
??????? ?? ?????? ??? ??????? ?????? ???????? ??
?????. ????? ??????? ???????? ???? ???? ???? ???
?????? ??????, ??????? ????? ????? ?????? ?????
???????? ??? ?????? ???, ?????? ???, ?????? ???,
?????? ???? ??????? ?????.
SCSI (Small Computer System Interface) ??? ??????
?????? ????? ??????? ?????? ???? ????? ??????
?????? ????? ???? ?? ??????? ??????? ??????????
??????? ?????. ??? ????? ?-SCSI ???? ???? ????
????? ??? ????? ??????
ISA (Industry Standard Architecture ) ??? ???
????? ???? ??????? ?????? ?????IBM ??? ????
?-1984, ?????? ?? ?????????? ????? ?? XT ?-16
??????. ??? ?????? ??? ???? ??????? ?? ??????
?????? ???? ???.
13
????? ???? ?? 2 ??????
14
???? ?????? ?????
??? ?? ?????? ??????
15
?????? ?? ????? ?????

• ?? ????? ????? ????? (Each envelope is
  individually routed).
• ??? ??? ????? ?????? (No time guarantee for
  delivery).
• ??? ????? ???? ?????? (No guarantee of delivery
  in sequence).
• ??? ??? ????? ?????? ! (No guarantee of delivery
  at all !).
• ????? ?????? ???? ?????? .(Things get lost)
• ???? ??? ?????? ???? ???? ????? ? (How can we
  acknowledge delivery?)
• ????? ????? (Retransmission)
• ?? ???? ??? ????? ???? ? ???-??? ? (How to
  determine when to retransmit? Timeout?).
• ????? ?????? ??????? ?? ???? ?? ????? (Need local
  copies of contents of each envelope).
• ??? ??? ???? ?????? ?? ??? ?? ?????? (How long to
  keep each copy).
• ?? ?? ?????? ???? ? (What if an acknowledgement
  is lost?) .

16
????? ????? ????? ?????? ??????
17
???? ????????
18
?????? ?? ????? ?????? (???????)

• ?? ????? ????? ????? (Each packet is individually
  routed).
• ??? ??? ????? ?????? .(No time guarantee for
  delivery)
• ??? ????? ???? ?????? .(No guarantee of delivery
  in sequence)
• ??? ??? ????? ?????? ! (No guarantee of delivery
  at all!)
• ????? ?????? ???? ?????? (Things get lost).
• ????? ?? ???? Acknowledgements)).
• ????? ????? (Retransmission)
• ?? ???? ??? ????? ???? ? ???-??? ? (How to
  determine when to retransmit? Timeout?).
• ????? ?????? ??????? ?? ???? ?? ????? (Need local
  copies of contents of each envelope).
• ??? ??? ???? ?????? ?? ??? ?? ?????? (How long to
  keep each copy).
• ?? ?? ?????? ???? ? (What if an acknowledgement
  is lost?)

19
?????? ?? ???????? (????)

• ??? ????? ??????? (?? ?????) ??????? (No
  guarantee of integrity of data).
• ?????? ????? ?????? ????? ????? (Packets can be
  fragmented).
• ????? ????? ????? ??????? (Packets may be
  duplicated).
• ?? ??????? ??????? ??"? ?????? ???? ?? ??? ??????
  ????????? ??????? ??????? !

20
?????? ??????

• ???? ?? ???? ??????? ??? ????
• ???? ???? ?????? ???? ??? ?????
• (Out of the computer from one system to
  another).
• ???? ??? ?? ????? ?? ???? .(Usually in a serial
  manner)
• ??????? ????? ?????? ????? ??????, ?????, ????
• (Using a specific medium (fiber, cables,
  radio)).
• ?????? ?? ????? ??? "????? ?????"
• (Option of passing through intermediate
  stations).
• ?????? ??????? ???? ????? ????
• (Possible errors before reaching to the
  destination).

21
?????? ?????? ???????

• ??? ????? ??? ???? ????.
• (?????, ?? ?? ????? ???? ??)
• ?????
• ?????? ????? ??? ????? ?????? (??"?).
• ????? ???? ?? ??????? ?????? ?????? ??? (??????).
  
• ????? ????? ?????? ????? ?????? ????? ??.
• ?? ???? ??? ??????? ????? ???? ????? ?? ????,
  ???? ???? ?? ??? ???? ????? ??????? ??? ???? ????
  ????.

22
??? ?? ????? ?????? ??????

• ????? ?? ????? ??????? ??????? ????.
• ????? ?? ????? ?????? "Circuit Switching"
  (?????? ?? ???? ??? ?????? ??????? ????? ??? ???
  ??? ?????? ???).
• ???? ????? ??????? ???? ????? ??? ??? ?? 2 ?????.
• ??? ????? ????? ?? ????? ?????? ??? ??? ?????
  ??????.
• ????? ????

23
Overview
??? ?? ????? ?????? ?????? (????)

• ????? ???? ???? ?????? (configure) ????? ??
  ?????? ????
• ??? ?????? (Local Are Networks (LAN)) ??? ???
  ?????? ??????? ???? ??? ???? ????? ???, ??
  ??????? ??????.
• ??? ??????? (Metropolitan Area Networks (MAN))
  ??? ??? ?????? ?????? ?? ??? ??? ?? ????? (??
  ?????????? ????).
• ??? ?????? (Wide Area Networks (WAN)) - ??? ???
  ?????? ?????? ??? ???? ????? ???????? ??????
  ???????, ??? ???? ??? ??????? ????? ???? ?? ???.
• ?? ??? (Internetworks) - ????? ?? ???? ?????.
• ????? ?? ?? ?????? ???? ????? ???? ?? ?????!
• ???? ???????? ????? ?????? ?? ?????? ??? ??? ??
  ????? ?? ?? ??? (.(internetwork ??? ????? ??? ?
• ?????????? ?????? ??? ??? ????? ??????? ???????
  ?? ????? ???? ??????? ???? ??????.

24
????? ????? ?????? ??? ????
25
??? ?? ????? ?????? ?????? (????)

• ?????? ???? ?? ????? ????? ?????? ?????? ??????.
• ?????? ???? ??? ???? ???? ????? ????? ??????
  ????, ?"? ??? ??????? ?????? ????? ??? ????.
• ???????? ??????? ?? ??? ?????? ??????, ???? ??
  ????? ?????? ????? Open System Interconnection
  OSI, ??? ???? ?"? ????? ?????? ????????? ISO
  )????? ???? ????? ????? ?? ??? ????? ????? ??????
  ??? ?????? ?????), ????? ???? ?????? ?? ????????.

26
????? ??????? ( (LAN

• ??? ?????? ??? ??? ?????? (?? ??? ?? ??????
  ???????) ??????.
• ??? ??????, ??? ??????? ??????? ?? ???? ??????
  ????? ?? ??? ????? ?????????? ????? broadcast ,
  ?????? ??????????? ??????.
• ???? ??? ??????? ????? Shared Media ???? ???
  ???? ???? ??????? ?? ???????.
• ????? Bus ?? ?????? ?????? ?? ??? bus ?????.
  ???? ????? ??? ????, ?? ??? ???????? ?????? ??
  ???? ????, ???? ?? ???? ????? ?????? ?? ?????????
  ??.
• ???? ????? ????????
• 10Mbps 1Gbps

27
????? ??????? ( (LAN

• Token-based ?????? (???? ????? ?? ?????
• (Packet) ????) ???? ??????? ????? ?????.
• ????? ?????
• (1) ????? ?? ???????? ???? ???"? ???? ???.
• (2) ???? ?? ?????? ????? ?????.
• (3) ????? ?? ??? ?????? ?????.
• (4) ????? ???? ?? ???????.
• ???? ??? ?????? ??????? ?

1
2
4
3
28
(WAN) ??? ??????

• WAN ????? ?? ???? ???????? ????, ??? ?????,
  ????????? ?? ???.
• WAN ????? ?????? ???? ??? ????? ???? ????? ????
  LANs .
• ???? ??? ????? ????? (router) ???? ?? ?- LANs ?-
  WAN.
• ??? ????? ??????? 2.5Gbps-10Gbps

29
(Internetworks) ?? ???

• ????? ?? ????? ??? ????? ???????? ?? ????? ???
  ???????? ?? ????? ???????. ???? ?????, ?????
  ?????? ?????? ?? ??????? ?? ??? ????? ?? ????
  ????? ????? --gt ???????.
• ???????
• - ????? ???? ?? ???? LANs ????? (????? Bus ??
  ????? ????)
• ????? ?????.
• - ????? LANs ??? ?????? ?????? ??? WAN. WAN
  ????? ????? ?? ??? ???.
• - ????? WANs ???? ?????? ?????? - ???????

30
?????? ????? -???????

• ????? (Addressing) - ???? ????? ??????? ????
• IP addresses 132.66.48.37, Refer
  to a host interface network number host
  number,
• ???? - ?????? 132.66.48.37 ???? 132.66.48
  ????? ?? ???? ?????? 37 ????? ?? ????? ?????? .
• ????? (Routing) ???? ????? ?????? ????
• ????? ?????? (packet switching) ????
  ?????? ?? ?????? ??? ?????? (routers) ?????? ????
  ????? ?????.
• ?????? ???? (Information Units ) ???? ????
  ?????
• Self-descriptive data packet data
  metadata
• (header).

31
(Protocol Layers) ???? ????????

• ??? ????? ?? ???? ????
• ?????? ????? ?? ????? ?? ????? ????????
  ???????????
• ???????? ??? ????? ?? ????? ??????? ??? ????? ??
  ??????? ??? ?????? ???????.
• ???????? ???? ???? ?? ????? ??? ????? ????? ?????
  ??? ???????.
• ??????? ??????????? ?? ??????
• ???????? ARP (Address Resolution Protocol) ????
  ????? ??? ????? IP ???? ????? MAC .
• ???????? DHCP (Dynamic Host Configuration
  Protocol ) ???? ?????? ???????? ?? ????? IP ????
  ??????? ??? ?????? ??? ???? ????? IP ?????.
• ???????? DNS (Domain Name System) ???? ?????? ??
  ???? ???? ???????? ??????? IP.

32
(Protocol Layers) ???? ?????????

• ???? ??? ????? ???? ?????? (??????,Web, VoIP
  email, games, e-commerce, file sharing) ?????
  ????? ??????????.
• ??? ?? ???????? ?? ???????, ??? ????? ????? ???
  ????.
• ???????? ???? ?????? ????????? ??? ???? ????
  ?????? ???.
• ???? ?? ?? ???? ????? ????? ???? (layering) -
  ???????? ???? ??? "????" (layered) ??? ????????
  ???? ????.

33
Open protocols and systems

• ????? ?? ?????????? ??? ????? ??
• ????? ????????? ?????? ???????.
• ???????? ??????? ?"? ?????? ??? ?????? ??
  ???????????? ?? ??????? ?????? ??????.
• ????? ??? ????? ?????????? ?????? ????? ?????
  ?????.
• International Organization for Standards (ISO)
• ????? ??????????? ?????? ?????? ??????.
• open system interconnect (OSI)
• ?? ????? ????? ?????? ?? ????? ?? ?????????? ???
  ?????.

34
ISO OSI reference model

• ???? ?????
• ????? ????? ?????? ??? ????????? ?????, ??????
  ???'
• ?????????? ??????
• ???? ?? ?????? ?????? ?? ???? ??????? ????? ???
  ?????? ??????.
• ?????????? ???????????
• ????? ?? ?????????? ??? ????? ?? ??????????
  ??????.
• ????? ??? ?? ?? ??????????? ?? ?????? ??????
  ????? "?????? ?????????? - Protocol Stack "

35
???? ??? ??????
36
Physical layer -???? ?????

• ????? ?????? ?????? 4 ?????? ?? ????? ????????
• ??????? ???????? ??????? ?? ???? ???? ???????.
• ??????? ?????? ???????? ???????? ?? ?????
  ???????.
• ??????? ?????? ????? ?? ?????? ??????? ????
  ?????? ?? ??? ?????? ?????? ???? ????.
• ????? ????????? ????? ?? ????? ??????? ?????
  ?????? ????, ??? ?????? ?????? ???? ????? ??????.
• ?????????? ??????
• 802.11x-WiFi- ?????? ?? ????? ??????? ???????
  (Wireless LAN) ?????? ???????.
• 10Base-T - ??? ?????? ?? ?????????? ??Ethernet
  ??? ????? ?????? ??? ?????? ?? ??? ??????? ???
  ????? ??????.
• Bluetooth - ??? ?? ??? ??????? ????? ?????, ????
  ???? ???? 2.45GHz (???? ???? ???? ?????? ????????
  ??????? ??????), ??????? ?????, ?????? ?????,
  ?????? ???? ????, ?????? ????? ???????? ??????,
  ??? ??? ??? ???? ???????? ?????? ???? ???????
  ??????? ????? ????? ???.
• DSL (?? ???? ???????) - ????? ?? ??????????
  ?????? ???? ??????? ??????? ?????? ??????
  ????????.

37
Data link layer - ???? ?????? ???????

• ???? ?????? ???????? ??????? ???????? ?? ????
  ????? ???? ???????. ???? ????? ?????? ?????
  ????? ????? ???? ????? ?? ???????? ??? ????? ????
  ????? ?????.
• ????? ???? ????? ??????? ??? ????? ?? ?????
  ??????? ???? ????? ????? ?????? ??? ?????
  ???????.
• ???? ????? ??????? ?????? ?????? ???? ???????
  ???????? ??????? ??????, ?????? ??? ?????? ??????
  (frame) .
• ???? ????? ??????? ?????? ???? ??????? ?????? ??
  ??? ?????? ??????.
• ???? ????? ??????? ?????? ???????? ?????? ??
  ????? ?????? ??????? ??????? ???? ????? ???????.
• ?????????? ??????
• ??? ???? ??? ?????? - ?????????? ??????? ??? ????
  ????? ????? ????? ????? ??? ????? ??????, ??????
  ??????? ??????????.
• - Token ring ????? Token ring ????? ????? ???????
  ????? 24 ?????? ?????? ??? ??????? ????, ???? ??
  ???? ??????? ??????? ???? ????.
• FDDI - ???? FDDI ?????? ??? ?????, ????? ??????
  ???????? ?????? (Token ring) ???????? ???????.
  ???? ???? ?????? ??????? ?????? ?? ????? ??????
  ????, ????? ?????? ????? ?????? ???? ?? ???
  ?????? ????? ????.

38
Network layer ???? ???? -

• ???? ???? ?????? ?? ????? ??????? ????? ?????
  ?????? ????.
• ?????? ?? ??????? ???? ???? ?????? ???????.
• ???? ?? ????? ?? ??????? ??????? ??? ??.
• ???? ?? ?????? ?????? ????? ???? ???? ?????
  ??????? ????? ????? ????, ????????? ?????? ??????
  ?????.
• ????? ?? ??????? ???? (??????) ??? ??????? ??????
  (?????).
• ?????????? ??????
• IPv4 - Internet Protocol, ?? ?????? IP, ???
  ???????? ?????? ????? ?????? ?????? ??? ?????
  ???? ?? ????? ??????, ?? ??? ???? ?? ?? ??????
  ???? ????? ?????, ???? ??? ??? ???????????
  ??????? ?????? ?????? ??????, ??????? ????
  ????????.
• IPv6 - ???????? ????? ?????? ?????? ??????
  ??????? ????? ????. ???? 6 ?? ???????? ?-IP ???
  ????? ??????? ?? ????????? ???? ???? 4 ( .(IPv4
• ICMP - ??? ?????? ????????? ?????? ????????.
  ?????? ICMP ?????? ???? ??? ?????? ???????
  ??????? ?? ????????IP , ?? ?????? ????? ??????.
• RIP- ???????? ????? ?????? ?? ????? ????? (Hop
  Count) ?? ??? ???? ?????? ?????.

39
Transport layer - ???? ???????

• ???? ??????? ?????? ???? ??????? ???????????? ??
  ?????? ?????? ??? ??????.
• ???? ?? ????? ????? ?? ???? ?????? ????? ??????
  ???? ????, ????? ?????? ??? ?????? ???, ????
  ?????? ?? ????? ???????, ?????? ??????, ???????
  ???????.
• ???? ??????? ?????? ???? ??????????, ???????? ??
  ????????? ?? ????? ?????? ?????. ?????, ????
  ?????? ????? ?? ?? ????? ???????? ???????.
  ?????? ?? ????????, ?????? ????, ????? ??
  ???????? ??????? ?????? ??, ??? ?????. ??????
  ????? ???????? ???????? HTTP ????? ?????????
  ??????? TCP ??? ????? ???? ????.
• ?????????? ??????
• TCP (Transmission Control Protocol )- ???? ????
  ?????? (error control), ???? ????? (flow control)
  ?????? ???? ?????? ?? ????? ????? ???
  (multiplexing).
• UDP (User Datagram Protocol ) ???? ?? ?????
  ???? ?????? ?? ????? ????? ??? (multiplexing).

40
Session layer - ???? ?????

• ????? ????????? ???? ??? ?????? ?????? ??????
  ????? ?????? "????".
• ???? ?? ????? ?? ??????? ??? ??????? ?????? ?????
  ???????, ??? ??? ????? ???? ????? ????? ?"? ?????
  ????? ??? ???? ??????? (???? ??????? ???? ?????
  ?????? ?????? ?????? ??? ?? ?? ?????).
• ???? ????? ????? ?? ?????????, ???????? ????
  ?????? (?? ???? ????? ?? ????? ???) ????? ??? ??
  ??? ??? ??????? ??? ????? ?????? ?????, ????? ??,
  ??????? ?????? ?????? ?????? ?????. ?????? ???
  ?????? ????? ?????? ?? ??????? ??????? ?? ??????
  ??? ??????.
• ??????? ?? ????? ???? ????.
• ?????????? ??????
• PPTP - ???????? ?????? ????? ??? ?????
  ?????????VPN) ) ??? ?????? ????? ???? ??????
  ???????? ????? ?????? ??? ??? TCP/IP.
• SSH ???????? ?????? ????? ?????? ?? ???? ?????
  ???? ????? ?????? login) ). ??? ???? ?????? ??
  rlogin ,RSH ??telnet ?????? ?????? ???????
  ??????? ??? ??? ?????? ?? ?????? ?????? ??
  ????????, SSH ???? ??? TCP.
• SSL ???????? ?????? ?????? ??????? ??????? ???
  ??? ??????? ???????.

41
Presentation layer - ???? ??????

• ?????? ????? ?? ????? ??????? (?????) ???????
  ???? ?????? ??????, ??? ???? ??????? ??? ?????
  ?????.
• ?????? ?????? ????? ????? ??? ??????? ??? ?????
  ????? ????? ?? ?????? ??????. ?????? ?? ?????
  ????? ?????? ASCII ????? ?????? EBCDIC ??????
  ???? ?????? ????? ?????? ???? ?? ASCII ?-EBCDIC.
• ???? ?????? ????? ?? ????? ?????? ?? ???????
  (formatting data) ??? ?????? ??? ???? ????? ????
  ??????? ???????? (???, ????? ???').
• ???? ?? ????? ?????? ???? ?????? ??????? ??????
  ?? ????? ?????. ?????? ????? ????? ???? ???? IBM
  ????? ????? ????? ?? ?????? ??? ????? ?????? ??
  ???? ???.
• ??????? ?? ????? ???? ?????.
• ?????????? ??????
• ASCII - ??? ??????? ?? ????? (?????, ??????
  ???????, ????? ????? ????) ??????? ???? ???????
  ????.
• Unicode - ??? ???????? ?????? ???? ??????? ????.
  ???? ????? ????? ????? ?????? ?? ?? ?????? ????
  ??????? ???? ?????? ???? ????? ?????, ??? ??????
  ??? ?????? ?????? ???? ???? ????? ??????? ??????
  ???????.
• MIME - ??? ??? ????? ?? ?????? ????? ????? ?????
  ???????? ?? ??? ????? ??????? ?????
• ???? ????? ?????? ASCII ????.
• ????? ??????? Attachments) ) ????? ??????????.
• ?????? ??????? ????? ????? ?????.
• ?????? ????? (Header-??) ????? ?-ASCII .
• ???? ?? ????? ????????? ???? ???? ?????? MIME.

42
Application layer - ???? ??????

• ???? ?????? ??? ????? ??????? ??? ?????? ????????
  ??????? ??????.
• ??? ?????? ????? ????? ??? ??????? ??? ????????
  ???? ????? ?? ????? ?????, ????? ???? ?????, ????
  ???????? ????.
• ???? ?? ?? ????? ????? ??? ???? ????.
• ?????????? ??????
• HTTP - ???????? ?????? ????? ?????? ??? HTML
  ?????????? ??? ?????? (??? ??????, ????? ???,
  ?????? ???? ???') ???? ????????.
• FTP - ???????? ?????? ????? TCP ?????? ????? ???
  ??????.

43
?????? ????

• ????? ??????
• ??????? ?????? ?? ????? ?????.
• ??? ?????????.
• ??? ??? ??? ????? ????? ?? ????? ??????.
• ??? ?????.
• ??????? ?????? ?? ???? ?????? ??????? ???.
• ????? ???? ?????? ????? ???????? ?????.