03 Protocol Layers Introduction 1 1 Chapter 1 Introduction A note on the use of these ppt slides We re making g these slides freely y available to all faculty y students readers They re in PowerPoint form so you can add modify and delete slides including this one and slide content to suit your needs They obviously represent a lot of work on our part In return for use we only ask the following If you use these slides e g in a class in substantially unaltered form th t you mention that ti th their i source after ft all ll we d d lik like people l to t use our book b k If you post any slides in substantially unaltered form on a www site that you note that they are adapted from or perhaps identical to our slides and note our copyright of this material Computer C mp t Networking N t kin A Top Down Approach Featuring the Internet 3rd edition Jim Kurose Keith Ross Addison Wesley July 2004 Thanks and enjoy JFK KWR All material copyright 1996 2004 J F Kurose and K W Ross All Rights Reserved Introduction 1 2 Protocol Layers Layers Networks are complex many pieces i hosts routers links of various media applications protocols hardware software Questions Is there th any h hope of f organizing structure of network Or at least our discussion f networks t k of Introduction 1 3 Organization g of air travel a layered y view ticket purchase ticket complain baggage check baggage claim gates t l load d t unload l d gates runway takeoff runway landing airplane routing airplane routing airplane routing Layers each layer implements a service via its own internal layer actions relying on services provided by layer below Introduction 1 4 ticket purchase ticket complain baggage check baggage claim gates t l load d t unload l d gates runway takeoff runway landing airplane routing airplane routing arrriving a airportt Dep parting g airport Distributed implementation p of layer y functionality y intermediate air traffic sites airplane routing airplane routing airplane routing Introduction 1 5 Why layering layer ng Dealing with complex systems explicit l structure allows ll identification d f 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 e g change in gate procedure doesn doesn tt affect rest of system Introduction 1 6 Internet protocol stack application supporting network applications li ti s FTP SMTP tran transport p rt pr process process c pr c data ata transfer network routing of datagrams from source host h t to t destination d ti ti h hostt IP routing protocols link link data transfer between neighboring network elements application 5 transport 4 network 3 link 2 physical 1 PPP Ethernet physical h i l bits bit on th the wire i Introduction 1 7 Layering y g logical g communication Each layer distributed di ib d entities implement layer functions at each node entities perform actions exchange messages with peers application transport p network link physical application transport network link physical network link physical application transport network link physical application transport network link physical Introduction 1 8 Layering logical communication E g transport take t k data d t f from app add addressing g reliability check info to form datagram send datagram to peer wait for peer to ack receipt data application transport p transport network link physical application transport network link physical ack data network link physical application transport network link physical data application transport transport network link physical Introduction 1 9 Layering y g physical p y communication data application transport network link physical application transport network link physical network link physical application transport network link physical p y data application transport network link physical p y Introduction 1 10 Protocol layering and data Each layer takes data from above adds dd header h d information i f ti to t create t new P Protocol t l Data D t Unit U it PDU may also break into smaller segments passes new data unit to layer below source M Ht M Hn Ht M Hl Hn Ht M application transport network link physical destination application Ht transport Hn Ht network Hl Hn Ht l k link physical M message M segment M datagram M frame Introduction 1 11 Chapter 1 Summary Covered a ton of material Internet overview what s a protocol network edge core access network packet switching packet switching versus circuit switching Internet ISP structure performance loss delay layering and service models d l You now have context overview feel of networking more depth depth detail to follow Introduction 1 12 World Wide Web WWW 2 Application Layer 13 Processes communicating g across network process sends receives messages g to from its socket socket analogous to door host or server sending di process shoves h message out door sending process assumes t transport s t iinfrastructure f st t on other side of door will deliver message to socket at receiving process process host or server se ve controlled by app developer process socket socket TCP with buffers buffers variables Internet TCP with buffers buffers variables controlled by OS 2 Application Layer 14 Addressing g processes p For a process to receive messages g it must have an identifier Every host has a unique 32 bit IP address 32 bit dd ss Q Does the IP address of the th host on which wh ch the process runs suffice for identifying the process Answer No many processes can be p running on same host Identifier includes both the IP address and port numbers associated with the process on the host host Example port numbers HTTP server 80 Mail server 25 More on this later 2 Application Layer 15 What transport p service does an app pp need Data loss some apps e g e g audio can tolerate some loss other apps e g file transfer f telnet l require i 100 reliable data transfer Timing some apps e g Internet telephony telephony interactive games require low delay to be effective ff ti Bandwidth some apps e g multimedia require minimum amount of bandwidth to be effective other apps elastic elastic apps apps make use of whatever bandwidth they get 2 Application Layer 16 Internet transport p protocols p services TCP service connection oriented setup required between client and server p processes reliable transport between sending and receiving process flow control sender won won tt overwhelm receiver congestion control