1 Standards Chapter 2 (Revised August 2002) Copyright 2003 Prentice-Hall Panko’s Business Data Networks and Telecommunications, 4 th edition

2 Warning: Difficult Material The most difficult chapter in the book Abstract and unfamiliar concepts Concepts are highly interrelated Will require especially diligent study Must be mastered for you to do well in the rest of the course

3 Figure 2.1: Standards Govern Communication Message Client PC Server Message Standards Typically Focus on Message Exchanges: Message Format (Syntax) Message Sequencing (Responses follow Requests) Message Semantics: Meanings of Values in Specific Fields Definition: Standards are rules of operation that govern communication between two (or more) hardware or software processes on different machines.

4 Figure 2.2: Internet Protocol (IP) Packet Version (4 bits) Header Length (4 bits) Diff-Serv (8 bits) Total Length (16 bits) Identification (16 bits) Flags (3 bits) Fragment Offset (13 bits) Protocol (8 bits) 1=ICMP, 6=TCP, 17=UDP Time to Live (8 bits) Header Checksum (16 bits) Bit 0Bit 31 Figure Shows 32 Bits on Each Line

5 Figure 2.2: Internet Protocol (IP) Packet Figure 2.2: Internet Protocol (IP) Packet Source IP Address (32 bits) Data Field (dozens, hundreds, or thousands of bits) Destination IP Address (32 bits) PaddingOptions (if any)

6 Horizontal Layered Message Communication Message Client PC Server

7 Figure 2.3: Message Communication in TCP/IP Application Layer Proc Proc = Process HTTP Msg Application Layer Proc Transport Layer Proc TCP Msg Transport Layer Proc Internet Layer Proc IP Packet Internet Layer Proc Internet Layer Proc Client PCServerEthernet SwitchRouter Data Link Layer Proc Eth Frame Data Link Layer Proc Data Link Layer Proc Data Link Layer Proc Physical Layer Proc Physical Layer Proc Physical Layer Proc Physical Layer Proc

8 Figure 2.3: Message Communication in TCP/IP Application Layer Proc Proc = Process HTTP Msg Application Layer Proc Client PCServerEthernet SwitchRouter Browser Webserver Application Program

9 Figure 2.4: Layer Purposes The Application Layer The purpose of the application layer is to allow two application programs on different hosts to work together. When a browser talks to a webserver application program, the standard for communication is the Hypertext Transfer Protocol (HTTP). This is why website URLs begin with Other application layer services use different application layer standards

10 Transport Layer Proc Transport Layer Proc TCP Msg Transport Layer Proc Host-to-Host Communication HTTP Requires TCP At the Transport Layer Client PCServerEthernet SwitchRouter Figure 2.3: Message Communication in TCP/IP

11 Figure 2.4: Layer Purposes The Transport Layer The purpose of the transport layer is to allow two host computers to talk to one another even if they have very different internal designs, such as a PC and a workstation server. If you use HTTP at the application layer, you are required to use the Transmission Control Protocol (TCP) at the transport layer. Other applications require different transport layer standards

12 Figure 2.6: Physical, Data Link, and Internet Layer Transmission Network X Network Z Network Y Switches Routers Switches Route Network Y

13 Figure 2.3: Message Communication in TCP/IP Internet Layer Proc IP Packet Internet Layer Proc Internet Layer Proc Hop-by-Hop Communication Across an Internet Host-Router-Router-…Router-Host Client PCServerEthernet SwitchRouter

14 Figure 2.4: Layer Purposes The Internet Layer The purpose of the internet layer is to route packets from the source host to the destination host across one or more networks connected by routers. TCP requires the use of the Internet Protocol (IP) at the internet layer.

15 Figure 2.3: Message Communication in TCP/IP Data Link Layer Proc Eth Frame Data Link Layer Proc Data Link Layer Proc Data Link Layer Proc Physical Layer Proc Physical Layer Proc Physical Layer Proc Physical Layer Proc Hop-by-Hop Transmission Across One Network Station-Switch-Switch-…-Switch-Station Propagation Across a Single Wire, Optical Fiber, or Radio Connection Client PCServerEthernet SwitchRouter

16 Figure 2.6: Physical, Data Link, and Internet Layer Transmission Network X Network Z Network Y Switches Routers Switches Data Link Note: There are 3 Data Links. One for each network traversed

17 Figure 2.4: Layer Purposes The Data Link Layer The purpose of the data link layer is to govern the movement of messages from a source station to a destination station or router across a single network containing switches. If the client station is located on an Ethernet LAN, the Ethernet data link layer standard is used.

18 Figure 2.6: Physical, Data Link, and Internet Layer Transmission Network X Network Z Network Y Switches Routers Switches Physical Links Note: There are 7 Physical Links

19 Figure 2.4: Layer Purposes The Physical Layer The purpose of the physical layer is to govern the transmission of bits one at a time over a wire, radio, or other connection between a station and a switch, between pairs of switches, or between a switch and a router. For a station on an Ethernet LAN, an Ethernet physical layer standard will be used. (Ethernet offers multiple physical layer standards.)

20 Figure 2.4: Layer Purposes The Physical Layer Transmission Media Connectors Voltage levels To represent 1s and 0s

21 Figure 2.5: Protocols in Two Examples HTTPPOP Physical Layer Data Link Internet Transport Application TCP IP Ethernet Example 1: Internet Web Access from a LAN Modem (V.92) PPP (Point-to-Point Protocol) IP TCP Example 2: Downloading Internet over a Telephone Line and Modem

22 Layers 1-3: Closer Look Internet Layer Data Link Layer Physical Layer

23 Figure 2.7: Comparing the Physical, Data Link, and Internet Layers Layer Messages are Called PhysicalData LinkInternet None: Bit-by-Bit Transmission FramePacket SwitchRouterRepeater (Hub) Connecting Device 231 Device* Layer *Devices are defined by their highest layer of operation. They also operate on lower layers.

24 Each station on an Ethernet network has a 48-bit network address Frame carries IP packet in its data field like a truck carrying a package Figure 2.8: Ethernet MAC Layer Frame Field Preamble (56 bits) … Start of Frame Delimiter (8 bits) Destination MAC Address (48 bits) Source MAC Address (48 bits) PAD (if needed) Data Field (variable) Contains IP Packet Length (16 bits) Frame Check Sequence (32 bits) LLC Header

25 Figure 2.7: Comparing the Physical, Data Link, and Internet Layers Data LinkInternetPhysicalLayer Format ConversionNone Switches convert between different physical layer connections for different ports UTP Optical Fiber Switch Client PC Server

26 Figure 2.7: Comparing the Physical, Data Link, and Internet Layers Data LinkInternetPhysicalLayer Format ConversionNone Routers convert between different networks— different physical and data link layer standards Ethernet Network ATM Network Router

27 Figure 2.10: All Switches in a Network and All Routers in an Internet Must Follow the Same Standard Network 1 (Ethernet) Network 3 (ATM) Client PC Ethernet Switch Router (IP) ATM Switch Server Network 2

28 Vertical Layered Communication in a Single Host Internet Layer Data Link Layer Physical Layer

29 Figure 2.11: Vertical Communication on the Source Host IP Packet Data Link Process Host A Internet Process Physical Process IP Packet DL-TDL-HIP Packet

30 Figure 2.11: Vertical Communication on the Source Host Internet Layer Process Creates an IP packet Passes the packet down to the data link layer process Data Link Layer Process Creates a new frame Places (encapsulates) the IP packet in the data field of the frame, adding a frame header and perhaps a trailer Passes frame down to the physical layer process

31 Encapsulation Encapsulation is placing a message in the data field of another message. Data Link Layer Trailer IP Packet in Data Field Of the Frame Frame Data Link Layer Header

32 Figure 2.14: Vertical Communication on the Destination Host (Host B) IP Packet DL-T IP Packet DL-H Internet Process Data Link Process Physical Process Host B

33 Figure 2.14: Vertical Communication on the Destination Host (Host B) Physical Layer Process Converts the signal into bits of the frame Passes the frame up to the data link layer process Data Link Layer Process Checks the data link layer header (and, if present, trailer) Decapsulates the IP packet Passes the packet up to the internet layer process

34 Figure 2.12: Vertical Communication on Switch X1 Host A Switch X2 A B Frame Switch X1 Port 1 PHY Port 2 PHY Port 3 PHY Port 4 PHY Data Link Layer Process 1234

35 Figure 2.13: Vertical Communication on Router R1 Port 1 DL PHY Internet Layer Process Port 2 DL Port 3 DL Port 4 DL PHY Router R1 Switch X2 Router R1 receives frame from Switch X2 in Port 1. Port 1 DL Process decapsulates packet. Port 1 DL passes packet to internet process. IP Packet DL-TIP PacketDL-H

36 Figure 2.13: Vertical Communication on Router R1 PHY Port 4 DL Port 1 DL PHY Internet Layer Process Port 2 DL Port 3 DL PHY Router R1 Router 2 Internet process sends packet out on Port 4. DL Process on Port 4 encapsulates packet in frame. DL Process passes frame to Port 4 PHY. PHY Process sends the bits out as signals to Router 2 IP Packet DL-TIP PacketDL-H

37 Figure 2.15: Transport and Application Layer Standards Notes:Transport standard can connect computers of different types. Transport standard often is reliable (corrects errors) Transport Layer App 1App 2App 3App 4 Client PC Network or Internet Server

38 Figure 2.15: Transport and Application Layer Standards Notes:Application standard links specific pairs of applications on different multitasking hosts. Application Layer App 1App 2App 3App 4 Client PC Network or Internet Server

39 Figure 2.16: Communication at All Layers on the Source Host HTTP Msg Application Process TCP Hdr HTTP Msg Transport Process Application process creates an HTTP message. Passes HTTP Msg down to next-lower layer (Transport). Transport process encapsulates HTTP message within a TCP message (called a segment) by adding a TCP header. TCP Message (TCP Segment)

40 Figure 2.16: Communication at All Layers on the Source Host HTTP Msg Application Process TCP Hdr HTTP Msg Transport Process TCP Hdr IP Hdr HTTP Msg Internet Process Passes HTTP message (Msg) down to next-lower layer (Internet) Internet process encapsulates TCP segment within an IP packet by adding an IP header

41 Figure 2.16: Communication at All Layers on the Source Host HTTP Msg Application Process TCP Hdr HTTP Msg Transport Process TCP Hdr IP Hdr HTTP Msg Internet Process DL Trlr TCP Hdr IP Hdr DL Hdr HTTP Msg Data Link Process

42 Figure 2.16: Communication at All Layers on the Source Host Test Your Understanding You are on an Ethernet LAN. Your computer wishes to send an SNMP message (Simple Network Management Protocol). SNMP requires the use of UDP at the transport layer UDP uses IP for delivery From beginning to end, name the headers, messages, and trailers you will see in the final frame

43 Figure 2.16: Communication at All Layers on the Source Host Test Your Understanding Your host’s internet layer process sends an ICMP message to another host. ICMP is an internet layer standard. ICMP messages are encapsulated in IP packets You are using a V.90 telephone modem for Internet access. Modems use PPP at the data link layer. From beginning to end, name the headers, messages, and trailers you will see in the final frame

44 Figure 2.16: Communication at All Layers on the Source Host HTTP Msg Application Process TCP Hdr HTTP Msg Transport Process TCP Hdr IP Hdr HTTP Msg Internet Process DL Trlr TCP Hdr IP Hdr DL Hdr HTTP Msg Data Link Process Physical Process Physical layer process converts the frame’s bits into signals and sends them out.

45 Figure 2.16: Communication at All Layers on the Source Host HTTP Msg Application Process TCP Hdr HTTP Msg Transport Process TCP Hdr IP Hdr HTTP Msg Internet Process DL Trlr TCP Hdr IP Hdr DL Hdr HTTP Msg Data Link Process Final Frame For HTTP Msg Delivery

46 Figure 2.16: Communication at All Layers on the Source Host TCP Hdr Transport Process TCP Hdr IP Hdr Internet Process DL Trlr TCP Hdr IP Hdr DL Hdr Data Link Process Layered Communication for TCP Supervisory message Delivery Final Message For TCP Supervisory Message

47 Figure 2.17: TCP/IP, OSI, and TCP/IP- OSI Hybrid Architecture Presentation TCP/IPOSIHybrid TCP/IP-OSI Application Session Transport Internet Transport Network Transport Internet Data Link Physical Data Link Physical Use OSI Standards Here

48 Figure 2.17: TCP/IP, OSI, and TCP/IP-OSI Hybrid Architecture The Hybrid TCP/IP-OSI Architecture is used on the Internet and dominates internal corporate networks. The standards agencies for the OSI architecture are ISO and ITU-T. The standards agency for TCP/IP is the IETF. Most IETF documents are called requests for comments (RFCs). Some RFCs—but not all—are Internet Official Protocol Standards.

49 Key Point The most common standards pattern in organizations is to use OSI standards at the physical and data link layers and TCP/IP standards at the internet, transport, and application layers. This is very important for you to keep in mind because this hybrid TCP/IP – OSI standards architecture will form the basis for most of this book.

50 Figure 2.18: OSI Session Layer (5) Transport Layer Client PC Network or Internet Server App 1App 2App 3App 4 Session Layer (Layer 5) Manages Series of Transactions Between Applications Over a Transport Connection

51 Figure 2.18: OSI Session Layer (5) OSI Very useful for applications that need to manage exchanges of application messages closely Few applications need this, however TCP/IP Applications must manage application message exchanges by themselves. No general support in the architecture

52 Figure 2.19: OSI Presentation Layer (6) Presentation Layer (Transfer Syntax C) App 2 Internal Syntax A App 3 Internal Syntax B The presentation layer governs the Syntax of messages Hosts have different data representations, etc. Agree upon a transfer syntax for messages going between them

53 Figure 2.18: OSI Presentation Layer (6) OSI Very useful because it handles differences in data formatting at a general level. Frees application programs from handling data formatting differences TCP/IP Each application must manage presentation differences by themselves MIME message description standards help by letting receiver know the type of file contained in a message

54 Other Standards Architectures IPX/SPX Novell NetWare file servers NetBEUI Small LANs with older Microsoft servers SNA Mainframe computers AppleTalk

55 Mixing Packets from Different Architectures All architectures produce packets that can be carried in frames. Frames do not care what packets they carry, and frames containing packets from different standards architectures can mix freely on a network. IP PacketIPX Packet Ethernet Frames in an Ethernet Network New: Not in Book

56 Figure 2.20: Other Standards Architecture TCP/IPIPX/SPXNetBEUI ApplicationNetBIOSVarious NCP Transport Internet Uses OSI Standards Here SPX IPX Uses OSI Standards Here Uses OSI Standards Here No Internet Layer NetBEUI

57 Figure 2.20: Other Standards Architecture OSISNAAppleTalk Application No Application Layer** Uses OSI Layering but proprietary protocols at each layer above the physical and data link layers Network Addressable Unit (NAU)*** Services Presentation SessionData Flow Control Transport Transmission Control NetworkPath Control Uses OSI Standards Here Uses OSI Standards Here Data Link Physical TCP/IP Application Transport Internet Uses OSI Standards Here

58 Key Point Although this book will focus on OSI at the lower layers and TCP/IP at the upper layer because of the dominance of this combination, real organizations use multiple standards architectures at higher layers (TCP/IP, IPX/SPX, SNA, AppleTalk, Net BEUI, etc). Physical and Data Link Layers: OSI Nearly Absolute Dominance Upper Layers: TCP/IP Dominant but Not Absolute Upper: IPX/SPX Upper: SNA