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 Internet protocol stack  Encapsulation  Connection oriented VS connectionless services  Circuit Switching  Packet Switching  Store-and-forward switches.

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Παρουσίαση με θέμα: " Internet protocol stack  Encapsulation  Connection oriented VS connectionless services  Circuit Switching  Packet Switching  Store-and-forward switches."— Μεταγράφημα παρουσίασης:

1  Internet protocol stack  Encapsulation  Connection oriented VS connectionless services  Circuit Switching  Packet Switching  Store-and-forward switches  Multiplexing: TDM, FDM, Statistical multiplexing, CDMA

2 OSI VS Internet protocol stack application transport network link physical application presentation session transport network link physical  Internet stack “missing” these layers!  these services, if needed, must be implemented in application  needed?

3 Internet protocol stack  application: supporting network applications  FTP, SMTP, HTTP,DNS protocols  transport: process-process data transfer  TCP, UDP protocols  network: routing of datagrams from source to destination  IP, routing protocols  link: data transfer between neighboring network elements  PPP, Media Access Control (Ethernet, DSL, ISDN, FDDI)  physical: bits “on the wire” application transport network link physical

4 Encapsulation source application transport network link physical HtHt HnHn M segment HtHt datagram destination application transport network link physical HtHt HnHn HlHl M HtHt HnHn M HtHt M M network link physical link physical HtHt HnHn HlHl M HtHt HnHn M HtHt HnHn M HtHt HnHn HlHl M router switch message M HtHt M HnHn frame

5 Why layering? Dealing with complex systems:  Abstraction  explicit structure allows identification, relationship of complex system’s pieces  layered reference model for discussion  modularization eases maintenance, updating of system  change of implementation of layer’s service transparent to rest of system  e.g., change in gate procedure doesn’t affect rest of system

6 Connection Oriented services  Establish end to end logical or physical connection before any data are sent  Involves handshaking  Reliable data transfer may be involved (e.g. TCP) Data link layer examples:  Circuit mode communication  Virtual Circuits (packet switching). Same path! We just need a VCI. Transport layer examples:  TCP

7 Transmission Control Protocol (TCP) (belongs to transport layer) A B X B B OK A OK Hi! Hello!

8 Connectionless services  No handshaking!  Each data packet carries information about the destination address (datagram) Network layer example:  IP protocol Transport layer examples:  UDP

9 Connection oriented VS connectionless services  The distinction takes place in several layers  Packet switching examples in both categories  Connection oriented service on connectionless service?? TCP/IP

10 Switched networks Circuit switched networks Packet switched networks Datagram Networks Virtual circuit networks Internet FDM TDM

11 Circuit Switching End-end resources reserved for “call”  link bandwidth, switch capacity  dedicated resources: no sharing (??)  circuit-like (guaranteed) performance  call setup required Introduction 1-11

12 Packet Switching each end-end data stream divided into packets  user A, B packets share network resources  each packet uses full link bandwidth  resources used as needed  Same route?? Introduction 1-12

13 Packet-switching: store-and-forward  takes L/R seconds to transmit (push out) packet of L bits on to link at R bps  store and forward: entire packet must arrive at router before it can be transmitted on next link  delay = 3L/R (assuming zero propagation delay) Example:  L = 7.5 Mbits  R = 1.5 Mbps  transmission delay = 15 sec Introduction 1-13 R R R L

14 Circuit Switching: FDM and TDM Introduction 1-14 FDM frequency time TDM frequency time 4 users Example:

15 Packet Switching: Statistical Multiplexing Sequence of A & B packets does not have fixed pattern, bandwidth shared on demand  statistical multiplexing. TDM: each host gets same slot in revolving TDM frame. Introduction 1-15 A B C 100 Mb/s Ethernet 1.5 Mb/s D E statistical multiplexing queue of packets waiting for output link

16 Πολλαπλή Πρόσβαση Διαίρεσης Κώδικα (CDMA)  Στο CDMA ορίζεται σε κάθε κόμβο ένας διαφορετικός κώδικας  Οι κώδικες είναι ορθογώνιοι μεταξύ τους (δηλ. το εσωτερικό γινόμενο μεταξύ οποιωνδήποτε δύο κωδίκων είναι 0)  Κάθε κόμβος χρησιμοποιεί το δικό του μοναδικό κώδικα για να κωδικοποιήσει τα bits των δεδομένων που στέλνει  Οι κόμβοι μπορούν να εκπέμπουν ταυτόχρονα  Πολλαπλοί κόμβοι σε κάθε κανάλι  Οι αντίστοιχοι προς αυτούς δέκτες  Λαμβάνουν σωστά τα κωδικοποιημένα bits δεδομένων ενός πομπού Θεωρώντας ότι ο δέκτης γνωρίζει τον κώδικα του πομπού, παρά τις παρεμβαλλόμενες μεταδόσεις άλλων κόμβων

17 Παράδειγμα CDMA d 1 =-1 d 0 =1 Sender Data bits Z i,m =d i *c m Time slot 1Time slot Channel output Spread code

18 Παράδειγμα CDMA (συνέχεια)  Όταν δεν υπάρχουν παρεμβάλλοντες πομποί  Ο δέκτης Λαμβάνει τα κωδικοποιημένα bits Ανακτά τα αρχικά bit δεδομένων, d i, υπολογίζοντας το d i = —  Z i,m *c m Τα παρεμβάλλοντα εκπεμπόμενα δυαδικά σήματα είναι προσθετικά m=1 M 1 M


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