CSC 535 Communication Networking I Chapter 2 Layered Architectures Dr. Cheer-Sun Yang

2 Protocol Stacks zTypically, communications is achieved via the cooperation of software and hardware zCommunication software and hardware are grouped into manageable sets called layers zWe use the term network architecture to refer to a set of protocols that specify how every layer is to function z A reference model, called a protocol stack, is used for understanding various networking protocols and their relations zOSI (7 layers) vs. TCP/IP (5 layers)

3 Examples of Layering- Web Browsing zA client/server model zA server process waits for incoming requests by listening to a port. zA client process makes requests as desired. zThe server program usually is executed in the background and is referred to as a daemon. For example, httpd refers to the server daemon for HTTP

Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks4 The user clicks on a link to indicate which document is to be retrieved. The browser must determine the address that contains the document. It does this by sending a query to its local name server. 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. 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. 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. The TCP connection is then closed and the user may view the document Figure Introduces topic

Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks5 HTTP server HTTP client Request Response Figure 2.1

Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks6 HTTP server HTTP client TCP GET 80, # #, 80 STATUS Port 80 Ephemeral Port # Figure 2.2

7 The OSI Reference Model zA layer model defined by the ISO as an effort to develop a seven-layer reference model for open system interconnection (OSI). zEach layer performs a subset of the required communication functions zEach layer relies on the next lower layer to perform more primitive functions zEach layer provides services to the next higher layer zChanges in one layer should not require changes in other layers

8 How do layers work together? zA concept called data encapsulation is applied. zIn each layer, the smallest unit of data is called a Protocol Data Unit (PDU). Each PDU contains a header, which contains protocol control information, and usually user information in the form of a service data unit (SDU). z“Conversations” occur between peer entities on different hosts.

Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks9 n entity n-PDUs n entity Figure 2.3

Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks10 n+1 entity n-SAP n+1 entity n-SAP n entity n-SDU H H n-PDU Figure 2.4

11 OSI as Framework for Standardization

12 Layer Specific Standards

Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks13 n-SDU n-PDU n-SDU n-PDU Segmentation Reassembly n-PDU n-SDU n-PDU Blocking Unblocking n-SDU (a) (b) Figure 2.5

14 OSI Layers (1) zPhysical yPhysical interface between devices xMechanical xElectrical xFunctional xProcedural zData Link yMeans of activating, maintaining and deactivating a reliable link yError detection and control yHigher layers may assume error free transmission

15 OSI Layers (2) zNetwork yTransport of information yHigher layers do not need to know about underlying technology yNot needed on direct links zTransport yExchange of data between end systems yError free yIn sequence yNo losses yNo duplicates yQuality of service

16 OSI Layers (3) zSession yControl of dialogues between applications yDialogue discipline yGrouping yRecovery zPresentation yData formats and coding yData compression yEncryption zApplication yMeans for applications to access OSI environment

17 Use of a Relay

Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks18 Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Network Layer Electrical and/or Optical Signals Application A Application B Data Link Layer Physical Layer Network Layer Data Link Layer Physical Layer Communication Network Figure 2.6

Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks19 G G G G G net 1 net 2 net 3 net 4 net 5 G = gateway/router G Figure 2.8

20 The OSI Environment

Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks21 C PS C C C C PS = packet switch C = computer Figure 2.7

Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks22 Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Application A Application B data ah ph sh th nh dh bits dt Figure 2.9

23 TCP/IP Protocol Suite zDominant commercial protocol architecture zSpecified and extensively used before OSI zDeveloped by research funded US Department of Defense zUsed by the Internet

Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks24 Application Layer Transport Layer Internet Layer Network Interface Application Layer Transport Layer Internet Layer Network Interface (a) (b) Figure 2.10

25 TCP/IP Protocol Architecture(1) zApplication Layer yCommunication between processes or applications zEnd to end or transport layer (TCP/UDP/…) yEnd to end transfer of data yMay include reliability mechanism (TCP) yHides detail of underlying network zInternet Layer (IP) yRouting of data

26 TCP/IP Protocol Architecture(2) zNetwork Layer yLogical interface between end system and network zPhysical Layer yTransmission medium ySignal rate and encoding

Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks27 Application Transport Internet Network Interface Application Transport Internet Network Interface Internet Network Interface Network 1 Network 2 Machine A Machine B Router/Gateway Figure 2.11

Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks28 HTTP SMTP RTP TCP UDP IP Network Interface 1 Network Interface 3 Network Interface 2 DNS Figure 2.12

29 Some Protocols in TCP/IP Suite

Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks30 Net Interface IP TCP HTTP Net Interface IP Net Interface IP TCP HTTP EthernetPPP Router router (1,1) s (1,2) w (2,1) (1,3) r (2,2) PPP Ethernet (a) (b) Server PC Figure 2.13

Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks31 IP Header Header contains source and destination physical addresses; network protocol type Frame Check Sequence Ethernet Header Figure 2.14

32 PDUs in TCP/IP

Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks33 HTTP Request TCP Header Header contains source and destination port numbers Header contains source and destination IP addresses; transport protocol type IP Header Header contains source and destination physical addresses; network protocol type Frame Check Sequence Ethernet Header Figure 2.15

34 Required Reading zSections 2.1, 2.2, 2.3 zSection 2.4 is for next semester zCheck RFC 2068: go to my homepage and click on “browsing RFCs”