Layer Architecture of Network Protocols Chapter 2 of Leon-Garcia

Outline 2.1 Examples of Layering 2.2 OSI Reference Model (Continued from last time) 2.3. TCP/IP Architecture 2.4 Berkeley API (Skip) 2.5 Application Protocols and TCP/IP Utilities

Problems for Chapter 2 2.6 2.10 2.13 2.19 2.20 2.27 2.37 2.41 2.46 Find, install, test an Internet tool. Write a paragraph on who, what, when, where -- on it.

Overall ISO Model 7-layer cake model discussed last time At end of class, I have some terms for you to define, including what each of these layers do, so think about it Specific network architectures don’t fit this model exactly; they are divided into modules that may perform part of the functions of two or more ISO layers

Application A Application B Application Layer Application Layer Presentation Layer Presentation Layer Session Layer Session Layer Transport Layer Transport Layer Communication Network Network Layer Network Layer Network Layer Network Layer Data Link Layer Data Link Layer Data Link Layer Data Link Layer Physical Layer Physical Layer Physical Layer Physical Layer Electrical and/or Optical Signals Figure 2.6

The big picture for accessing Web page The Internet is a true distributed (democratic) system in that every host is equal However, in discussing dialog between two hosts, it is usually helpful to think of one as client, the other as server. In accessing a Web page, actually two servers are often used. (What are they?)

Request HTTP server HTTP client Response Figure 2.1

Figure 1.4 - Introduces topic 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. 2. 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. Figure 1.4 - Introduces topic

HTTP HTTP server client Ephemeral Port # Port 80 TCP TCP GET 80, # #, 80 STATUS Figure 2.2

n-PDUs n entity n entity Figure 2.3

n+1 n+1 entity entity n entity n entity n-SDU n-SDU n-SAP n-SAP n-SDU H n entity n entity H n-SDU n-PDU Figure 2.4

Segmentation Reassembly n-SDU n-SDU n-PDU n-PDU n-PDU n-PDU n-PDU Blocking Unblocking n-SDU n-SDU n-SDU n-SDU n-SDU n-SDU n-PDU n-PDU Figure 2.5

C PS = packet switch C = computer PS C PS PS PS C C C Figure 2.7

net 3 G net 1 G G G net 5 net 2 net 4 G G G = gateway/router Figure 2.8

ISO Model, including PDUs at Each Level All computer systems consist of hardware, programs, and data. The information data structures used in network protocols consist of PDU exchanged at each layer A PDU generally consists of the information bits from the next higher layer (the SDU) plus a header that contains the necessary additional info for that layer (+ trailer sometimes) What are the PDUs called at each layer on the next slide?

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

TCP/IP Architecure (5 layers counting physical layer) Application Layer Application Layer Transport Layer Transport Layer Internet Layer Internet Layer Network Interface Network Interface (a) (b) Figure 2.10

TCP/IP in Use Machine B Machine A Application Application Transport Internet Network Interface Transport Router/Gateway Internet Internet Network Interface Network Interface Network 1 Network 2 Figure 2.11

TCP/IP Protocol Graph (There’s More, too) HTTP SMTP DNS RTP TCP UDP IP Network Interface 1 Network Interface 2 Network Interface 3 Figure 2.12

(1,1) (a) (2,1) (2,2) s PPP (1,3) r w Ethernet (1,2) (b) router Server HTTP PC HTTP TCP Router TCP IP IP IP Net Interface Net Interface Net Interface Ethernet PPP Figure 2.13

source and destination physical addresses; network protocol type IP Header Header contains source and destination physical addresses; network protocol type Frame Check Sequence Ethernet Header Figure 2.14

HTTP Request TCP Header IP Header Ethernet Header Frame Check Sequence Header contains source and destination port numbers TCP Header 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

Underlying communication Protocols Underlying communication Protocols socket interface socket interface Application 1 Application 2 user user kernel kernel Socket Socket Underlying communication Protocols Underlying communication Protocols Communications network Figure 2.16

Control Connection Data Connection User Interface Control Connection Server PI User PI Server DTP Data Connection User DTP Server FTP User FTP PI = Protocol interpreter DTP = Data transfer process Figure 2.19

C:\WINDOWS>ping nal.toronto.edu Pinging nal.toronto.edu [128.100.244.3] with 32 bytes of data: Reply from 128.100.244.3: bytes=32 time=118ms TTL=243 C:\WINDOWS> Figure 2.20

Can you define? Application layer Client/server Confirmed service Connectionless service Daemon Data Link layer Physical Layer Encapulation PPP Frame Port Header PDU HTTP Segment ISO SDU Internet layer Internetworking SMTP Layer Socket TCP/IP Architecture Transport Layer Network Architecture UDP Traceroute Telnet FTP The Meaning of Life