CSC 535 Communication Networking I Chapter 2 Layered

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

Protocol Stacks z Typically, communications is achieved via the cooperation of software and hardware z Communication software and hardware grouped into manageable sets called layers z We 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 z OSI (7 layers) vs. TCP/IP (5 layers) 2

Examples of Layering. Web Browsing z A client/server model z A server process waits for incoming requests by listening to a port. z A client process makes requests as desired. z The 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 3

1. 2. 3. 4. 5. 6. 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. Copyright 2000 Mc. Graw-Hill Leon -Garcia and Widjaja Communication Networks 4 Figure 1. 4 - Introduces topic

Request HTTP client HTTP server Response Copyright 2000 Mc. Graw-Hill Leon -Garcia and Widjaja Communication Networks Figure 2. 1 5

HTTP server HTTP client Ephemeral Port 80 Port # GET 80, # TCP #, 80 STATUS Copyright 2000 Mc. Graw-Hill Leon -Garcia and Widjaja Communication Networks Figure 2. 2 6

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

How do layers work together? z A concept called data encapsulation is applied. z In 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. 8

n-PDUs n n entity Copyright 2000 Mc. Graw-Hill Leon -Garcia and Widjaja Communication Networks Figure 2. 3 9

n+1 entity n-SDU n-SAP H n entity H n-SDU n-PDU Copyright 2000 Mc. Graw-Hill Leon -Garcia and Widjaja Communication Networks 10 Figure 2. 4

OSI as Framework for Standardization 11

Layer Specific Standards 12

(a) n-PDU (b) Segmentation Reassembly n-SDU n-PDU Blocking n-SDU n-PDU Unblocking n-SDU n-PDU Copyright 2000 Mc. Graw-Hill Leon -Garcia and Widjaja Communication Networks 13 Figure 2. 5

OSI Layers (1) z Physical y. Physical interface between devices x. Mechanical x. Electrical x. Functional x. Procedural z Data Link y. Means of activating, maintaining and deactivating a reliable link y. Error detection and control y. Higher layers may assume error free transmission 14

OSI Layers (2) z Network y. Transport of information y. Higher layers do not need to know about underlying technology y. Not needed on direct links z Transport y. Exchange of data between end systems y. Error free y. In sequence y. No losses y. No duplicates y. Quality of service 15

OSI Layers (3) z Session y. Control of dialogues between applications y. Dialogue discipline y. Grouping y. Recovery z Presentation y. Data formats and coding y. Data compression y. Encryption z Application y. Means for applications to access OSI environment 16

Use of a Relay 17

Application A Application B Application Layer Presentation Layer Session Layer Transport Layer Communication Network Transport Layer Network Layer Data Link Layer Physical Layer Copyright 2000 Mc. Graw-Hill Leon Electrical and/or Optical Signals -Garcia and Widjaja Communication Networks 18 Figure 2. 6

G net 1 net 3 G G G net 2 net 5 G net 4 G G = gateway/router Copyright 2000 Mc. Graw-Hill Leon -Garcia and Widjaja Communication Networks 19 Figure 2. 8

The OSI Environment 20

PS = packet switch C PS C C = computer PS PS PS C Copyright 2000 Mc. Graw-Hill Leon -Garcia and Widjaja Communication Networks 21 Figure 2. 7

Application A data Application Layer data Transport Layer data Network Layer Physical Layer data dt Presentation Layer ph data Session Layer Application Layer ah data Presentation Layer Data Link Layer Application B data sh Session Layer th Transport Layer Network Layer nh dh bits Copyright 2000 Mc. Graw-Hill Leon -Garcia and Widjaja Communication Networks Data Link Layer Physical Layer 22 Figure 2. 9

TCP/IP Protocol Suite z Dominant commercial protocol architecture z Specified and extensively used before OSI z Developed by research funded US Department of Defense z Used by the Internet 23

Application Layer Transport Layer Internet Layer Network Interface (a) Application Layer Transport Layer Internet Layer Network Interface (b) Copyright 2000 Mc. Graw-Hill Leon -Garcia and Widjaja Communication Networks 24 Figure 2. 10

TCP/IP Protocol Architecture(1) z Application Layer y. Communication between processes or applications z End to end or transport layer (TCP/UDP/…) y. End to end transfer of data y. May include reliability mechanism (TCP) y. Hides detail of underlying network z Internet Layer (IP) y. Routing of data 25

TCP/IP Protocol Architecture(2) z Network Layer y. Logical interface between end system and network z Physical Layer y. Transmission medium y. Signal rate and encoding 26

Machine B Machine A Application Transport Router/Gateway Transport Internet Network Interface Network 1 Network Interface Network 2 Copyright 2000 Mc. Graw-Hill Leon -Garcia and Widjaja Communication Networks 27 Figure 2. 11

HTTP SMTP RTP DNS TCP UDP IP Network Interface 1 Interface 2 Interface 3 Copyright 2000 Mc. Graw-Hill Leon -Garcia and Widjaja Communication Networks 28 Figure 2. 12

Some Protocols in TCP/IP Suite 29

(a) (1, 1) (2, 1) s Ethernet (2, 2) router PPP (1, 3) r w (1, 2) (b) Server HTTP PC HTTP TCP Router IP IP IP Net Interface TCP Copyright 2000 Mc. Graw-Hill Leon. PPP Ethernet -Garcia and Widjaja Communication Networks 30 Figure 2. 13

IP Header contains source and destination physical addresses; network protocol type Frame Check Sequence Ethernet Header Copyright 2000 Mc. Graw-Hill Leon -Garcia and Widjaja Communication Networks 31 Figure 2. 14

PDUs in TCP/IP 32

HTTP Request Header contains source and destination port numbers Header contains source and destination IP addresses; transport protocol type Header contains source and destination physical addresses; network protocol type Ethernet Header TCP Header IP Header Copyright 2000 Mc. Graw-Hill Leon -Garcia and Widjaja Communication Networks Frame Check Sequence 33 Figure 2. 15

Required Reading z Sections 2. 1, 2. 2, 2. 3 z Section 2. 4 is for next semester z Check RFC 2068: go to my homepage and click on “browsing RFCs” 34