Μάθηµα Εισαγωγή στις Τηλεπικοινωνίες

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1 Μάθηµα Εισαγωγή στις Τηλεπικοινωνίες Ενότητα 7η Τηλεπικοινωνιακά ίκτυα και ίκτυα εδοµένων - Μάθηµα 8ο Καθ. Θωµάς Σφηκόπουλος thomas@di.uoa.gr Κατσιάνης ηµήτρης, Επιστ. Συνεργάτης dkats@di.uoa.gr Τσίπουρας Άρης, Επιστ. Συνεργάτης aris@di.uoa.gr ΕΘΝΙΚΟ & ΚΑΠΟ ΙΣΤΡΙΑΚΟ ΠΑΝΕΠΙΣΤΗΜΙΟ ΑΘΗΝΩΝ Τοµέας Επικοινωνιών και Επεξεργασίας Σήµατος Τµήµα Πληροφορικής & Τηλεπικοινωνιών

2 Περιεχόµενα Ενότητας Εξέλιξη Τηλεπικοινωνιακών ικτύων Μεταγωγή κυκλώµατος και πακέτων οµή τηλεφωνικού δικτύου Αρχιτεκτονική, πρωτόκολλα, λειτουργία, είδη δικτύων Σηµατοδοσία ίκτυα Επικοινωνιών και το Internet 2

3 Εξέλιξη Τηλεπικοινωνιακών ικτύων Τηλεφωνικά ίκτυα ίκτυα εδοµένων Ασύρµατα Ενσύρµατα Ενοποίησης από τις αρχές του 80 3

4 Λειτουργία Τηλεφωνικού ικτύου 1. Telephone Office The caller picks up the phone triggering the flow of current in wires that connect to the telephone office. 2. Telephone Office The current is detected and a dial tone is transmitted by the telephone office to indicate that it is ready to receive the destination number Telephone Office Telephone Office Telephone Office The caller sends this number by pushing the keys on the telephone set. Each key generates a pair of tones that specify a number. (In the older phone sets the user dials a number which in turn generates a corresponding number of pulses.) The equipment in the telephone office then uses the telephone network to attempt a connection. If the destination telephone busy, then a busy tone is returned to the caller. If the destination telephone is idle, then ringing signals are sent to both the originating and destination telephones. The ringing signals are discontinued when the destination phone is picked up and communication can then proceed. 6. Telephone Office Either of the users terminate the call by putting down a receiver.

5 Internet 1. The user clicks on a link to indicate which document is to be retrieved. 2. The browser must determine the address that contains the document. It does this by sending a query to its local name server. 3. Once the address is known the browser establishes a connection to the specified machine, usually a TCP connection. In order for the connection to be successful, the specified machine must be ready to accept TCP connections. 4. The browser runs a client version of HTTP, which issues a request specifying both the name of the document and the possible document formats it can handle. 5. The machine that contains the requested document runs a server version of HTTP. It reacts to the HTTP request by sending an HTTP response which contains the desired document in the appropriate format. 6. The TCP connection is then closed and the user may view the document.

6 ροµολόγηση-πολυπλέκτης (a) Μεταγωγέας (switch) σε µία οµάδα χρηστών Network Access network (b) Πολυπλέκτης (multiplexer) για τη σύνδεση 2 δικτύων 6

7 Ιεραρχική οµή (α) 2 a 3 c 1* 4 A b d Το Μητροπολιτικό ίκτυο A αποτελείτε από τα υποδίκτυα a, b, c, d. (β) β Metropolitan γ A α Εθνικό δίκτυο που αποτελείται από τοπικά υποδίκτυα a, b, g National 7

8 Ιεραρχική οµή Τηλ. ικτύου Graham Bell 1876 Elisha Gray???? Toll Υπεραστικά Κέντρα Tandem CO CO Tandem Κοµβικά Κέντρα CO CO CO Τοπικά Κέντρα Public Switched Telephone Network Redundant? 8

9 οµή Τηλ. ικτύου 9 (a) Πλήρως. (b) Κεντρικός Μεταγωγέας. (c) Ιεραρχία 2 επιπέδων.

10 οµή Τηλ. ικτύου(2) A typical circuit route for a medium-distance call. 10

11 Πολιτική LATA (USA) 1500 ανεξάρτητες εταιρίες τηλ/ες IXC υπεραστική κίνηση (1,2 PoP)

12 Computer networks Εφαρµογές. Από το τηλεφωνικό ίκτυο στο ίκτυο εδοµένων 12

13 e-economics e-commerce 13

14 Κανόνες - Βασικές Έννοιες Layers ή levels protocol protocol stack Interface (ανάµεσα στα layers) Network architecture (Ένα σύνολο από layers και protocol) 14

15 Protocol Hierarchies 15

16 Protocol Hierarchies (2) Location A Location B 3 I like rabbits Message Philosopher J'aime bien les lapins 3 2 L: Dutch Ik vind konijnen leuk Information for the remote translator Translator L: Dutch Ik vind konijnen leuk 2 1 Fax #--- L: Dutch Ik vind konijnen leuk Information for the remote secretary Secretary Fax #--- L: Dutch Ik vind konijnen leuk 1 The philosopher-translator-secretary architecture. 16

17 Protocol Hierarchies (3) 17

18 Σχεδιασµός πρωτοκόλλων Addressing Error Control Flow Control (transmission Rate) Multiplexing Routing 18

19 Λογισµικό ικτύων Protocol hierarchies Design issues for the layers Connection-oriented and connectionless services Service primitives (operations) The relationship of services to protocols 19

20 Service Primitive Five service primitives for implementing a simple connection-oriented service. Στοιχεία µιας υπηρεσίας - Λειτουργίες 20

21 Service Primitives (2) Packets sent in a simple client-server interaction on a connection-oriented network. 21

22 Services to Protocols Relationship Από το ένα στρώµα στο άλλο The relationship between a service and a protocol. Από το ένα επίπεδο στο άλλο 22 Service (a set of operations, services relate to the interfaces between layers) Protocol (how these operations are implemented? relate to the packets sent between peer entities on different machines)

23 Μεταγωγή κυκλώµατος και πακέτων Ορισµοί 23

24 Circuit-Switching Definition: Communication in which a dedicated communications path is established between two devices through one or more intermediate switching nodes Dominant in both voice and data communications today e.g. PSTN is a circuit-switched network Relatively inefficient (100% dedication even without 100% utilization) 24

25 Packet-Switching Networks Data is broken into packets, each of which can be routed separately Advantages: better line efficiency, signals can always be routed, prioritization option Disadvantages: transmission delay in nodes, variable delays can cause jitter, extra overhead for packet addresses 25

26 Switching 26 (a) Circuit switching. (b) Packet switching.

27 Message Switching (a) Circuit switching (b) Message switching (c) Packet switching 27

28 Circuit - Packet Switching 28

29 Παράδειγµα Packet Switching Single routing C PS = packet switch C PS PS PS C = computer PS C C C 29 Figure 2.7

30 Packet Switching ιασύνδεση net 1 G net 3 G G G net 5 net 2 G net 4 G 30 G = gateway/router Figure 2.8

31 Reference Models OSI (Open Systems Interconnect ion ) reference model. 31

32 Layers Physical Layer Transmits raw data bits over a channel Design Issues Mechanical Electrical Procedural Physical 32

33 Layers Data Link Layer Handles frames of information Makes line appear to be free from errors Damaged Lost Duplicated Flow Control 33

34 Layers Network Layer Handles subnet operation Routing Billing Information Protocol Transformation 34

35 Layers Transport Layer End to end error-free connection control Point to Point Datagrams Broadcast/Multicast Host addressing/roaming Flow Control 35

36 Layers Session Layer Session Management Token Management Synchronisation Presentation Layer Syntax/Semantics Names Dates Data Compression Cryptography Application Layer e.g. Virtual Terminal software File Transfer 36

37 Reference Models TCP/IP reference model. 37

38 Επικεφαλίδες Headers Application A data Application B Application Layer data ah Application Layer Presentation Layer data ph Presentation Layer Session Layer data sh Session Layer Transport Layer data th Transport Layer Network Layer data nh Network Layer Data Link Layer dt data dh Data Link Layer Physical Layer bits Physical Layer 38 Figure 2.9

39 C End system α Medium A B 1 Network End system β Physical layer entity 3 Network layer entity Data link layer entity 3 4 Network layer entity Transport layer entity Figure 7.3

40 Λειτουργίες ικτύου 40

41 Παράγοντες Επιτυχίας? Technology Standards Regulation Market 41 Figure 1.19

42 υνατότητες Τεχνολογίας Capability Capability Third type of invention Second type of invention Initial class of invention (a) time (b) time 42 Figure 1.20

43 Κακή χρονική Επιλογή? The apocalypse of the two elephants. 43

44 Resources Andrew S. Tanenbaum, Computer Networks, Fourth Edition, Prentice Hall, 2003 ISBN : William Stallings, Business Data Communications, Fifth Edition, ISBN (feb 2004), fourth Edition 2001 ISBN: , Publisher: Prentice Hall A. Leon-Garcia and I. Widjaja, Communication Networks: Fundamental Concepts and Key Architectures, January 2000 ISBN: X 44