Chapter 2 Communicating Over the Network
Elements of Communication
Communicating the Messages Continuous stream of bits 00101010100101010101010101010101010 I have to wait Single communications (e.g. video, e-mail message) could be: Continuous stream of bits Take over (hog) the network. Significant delays Inefficient use Any loss - resend entire message 3
Communicating the Messages Segmentation 001010 001010 001010 001010 001010 001010 Better approach segmentation. Multiplexing: Different conversations can be interleaved. 4
Communicating the Messages X Benefits Reliability (3) Different paths Alternate path Only the missing segments need to be retransmitted 5
Disadvantage of Segmentation Disadvantage added level of complexity. Analogy: 100 page letter one page at a time Separate envelopes Sequencing 6
Components of the Network Devices (hardware) End devices, switch, router, firewall, hub Media (wired, wireless) Cables, wireless mediums Services (software) Network applications, routing protocols, processes, algorithms 7
End devices End devices or hosts: The source or destination of a message. 8
Source Address: 209.67.102.55 Destination Address: 107.16.4.21 209.67.102.55 107.16.4.21 Each host is identified by an address. IP (Internet Protocol) address (later) 9
Servers and Clients Client Server A host Client, Server, or both. Software determines the role. Servers provide information and services to clients e-mail or web pages Clients request information from the server. 10
Intermediary Devices switch or hub routers switch or hub Intermediary devices: Connectivity to and between networks Examples (4): Network Access Devices (Hubs, switches, and wireless access points) Internetworking Devices (routers) Communication Servers and Modems Security Devices (firewalls) 11
Network Media Network media: The medium over which the message travels. Metallic wires - electrical impulses. Fiber optics pulses of light Wireless electromagnetic waves. 12
Network Media Different media considerations (4): Distance it will carry signal Environment it works in Bandwidth (speed) Cost 13
Local Area Network (LAN) Local Area Network (LAN) An individual network usually spans a single geographical area, providing services and applications to people within a common organizational structure, such as a single business, campus or region. 14
Wide Area Network (WAN) T1, DS3, OC3 PPP, HDLC Frame Relay, ATM ISDN, POTS Wide Area Networks (WANs) Leased connections through a telecommunications service provider network. Networks that connect LANs in geographically separated locations Telecommunications service provider (TSP) interconnect the LANs at the different locations. Voice and data on separate networks or converged networks 15
The Internet A Network of Networks ISPs (Internet Service Providers) Often also TSPs Connect their customers to the Internet. The Internet ISPs connected to other ISPs 16
Network Representations Network Interface Card (NIC) Ports and interfaces (used interchangeably) Physical Port Interface - Connect to individual networks. 17
Protocols
Protocol Protocol Rules that govern communications. Protocol suite - A group of inter-related protocols - Example: TCP/IP 19
Message uses Multiple protocols (encapsulated) Protocols HTTP Data Frame IP TCP App Data Frame Trailer Message: Data Multiple protocols 20
Multiple protocols (encapsulated) Protocols HTTP Data Frame IP TCP App Data Frame Trailer Encapsulation Process of adding a header to the data or any previous set of headers. Decapsulation Process of removing a header. 21
Example: Protocol IPv4 Frame IP TCP HTTP Data Frame Trailer 22
209.67.102.55 107.16.4.21 Frame IP TCP HTTP Frame Trailer Data 209.67.102.55 107.16.4.21 23
Protocols Networking protocols suites include rules for: (4) Format Accessing the media Error detection Setup and termination 24
Protocol Suites and Standards Early days proprietary network equipment and protocols. Now Industry standards Institute of Electrical and Electronics Engineers (IEEE) Examples: 802.3 (Ethernet), 802.11 (WLAN) Internet Engineering Task Force (IETF) Internet standards RFCs (Request for Comments) Example: TCP, IP, HTTP, FTP 25
Example: RFC 791 IPv4 26
Interaction of Protocols Protocols HTTP Data Frame IP TCP App Hypertext Transfer Protocol (HTTP) Data Protocol that governs interaction between web server and a web client. Frame Trailer 27
Interaction of Protocols Protocols HTTP Data segment Transmission Control Protocol (TCP) Responsible for controlling the information exchanged between the server and the client: Size of data Flow control Reliability 28
Protocols HTTP Data packet Internetwork Protocol (IP) Assigns the appropriate source and destination addresses, Original source address of host Final destination address of host Used by routers in selecting the best path 29
Interaction of Protocols Protocols HTTP Data frame Network access protocols (Data link and Physical layer protocols) Format and physical transmission of data on the media. 30
Technology-Independent Protocols Frame IP TCP HTTP data Frame Trailer IP Packet Ethernet Ethernet IP Packet T1, DS3, OC3 PPP, HDLC Frame Relay, ATM ISDN, POTS IP is a protocol that will travel over different types of media. 31
Using Layered Protocols
Benefits of a Layered Model Protocols HTTP Data Using a layered model: Fosters competition Prevents changes in one layer from affecting other layers above and below. Provides a common language to describe networking functions and capabilities. 33
Protocol and Reference Models 34
Protocol and Reference Models The Open Systems Interconnection (OSI) model is the most widely known internetwork reference model. The International Organization for Standardization (ISO) released the OSI reference model in 1984, was the descriptive scheme they created. 35
TCP/IP Model TCP/IP Model and Protocol Suite is an open standard. 36
The Communication Process - Encapsulation Data Link IP TCP HTTP Data Data Link Trailer Server HTTP Data Encapsulation Process of adding control information as it passes down through the layered model. 37
The Communication Process - Decapsulation Data Link IP TCP HTTP Data Data Link Trailer HTTP Data Client Decapsulation Process of removing control information as it passes upwards through the layered model. 38
Wireshark will let us examine protocols! 39
The Communication Process Protocol Data Unit (PDU) - The form that a piece of data takes at any layer. PDUs are named according to the protocols of the TCP/IP suite. Data - Application layer PDU Segment - Transport Layer PDU Packet - Internetwork Layer PDU Frame - Network Access Layer PDU Bits - A PDU used when physically transmitting data over the medium 40
Layer 2 Data Link Frame Layer 3 IP Packet Dest. Add MAC 0B-31 FF-FF 0B-20 00-10 Source Add MAC 0A-10 00-20 0C-22 Type 800 Dest. IP 192.168.4.10 Source IP 192.168.1.10 IP fields Data Trailer The sending host builds message with multiple encapsulations. Data Link IP TCP HTTP Data Data Link Trailer The receiving host receives the message with multiple decapsulations. Data Link IP TCP HTTP Data Data Link Trailer 41
Getting Data to the Right Application Protocols HTTP Data Layer 4 (TCP/UDP) contains a port number which represents the application or service carried in the IP packet. Destination port destination application Source port source application 42
Getting Data to the Right Application Destination port number tells the OS (TCP/IP) stack which application to hand the data to. Examples: 80 = HTTP (www) 23 = Telnet 20, 21 = FTP 25 = SMTP 43