Network Layered Architecture OSI Reference Model & TCP/IP Protocol Suite Professor A. Zahid EE450: Computer Networks A. Zahid, EE450 1 Protocols Human Protocols: Network Protocols: • what’s the time? • Machines rather than • I have a question humans • Introductions • All communication activity in Internet governed by protocols … specific msgs sent … specific actions Protocols define format, order taken when msgs of msgs sent and received received, or other among network entities, and events actions taken on msg transmission, receipt A. Zahid, EE450 2 Human v.s. Network Protocols Hi TCP connection request Hi TCP connection Got the reply time? Get http://www.cnn.com/politics.html 2:00 <file> time A. Zahid, EE450 3 Key Elements of a Protocol • Syntax – Data formats, compression, encryption, etc.. – Signal levels • Semantics – Control information such as flow & congestion – Error detection and control mechanisms • Timing – Speed matching – Sequencing A. Zahid, EE450 4 Standards • Required to allow for interoperability between equipment • Advantages – Ensures a large market for equipment and software – Allows products from different vendors to communicate • Disadvantages – Freeze technology A. Zahid, EE450 5 OSI Reference Model A. Zahid, EE450 6 Data Transmission in OSI Model A. Zahid, EE450 7 Summary of Layer Functions A. Zahid, EE450 8 The Internet is based on TCP/IP A. Zahid, EE450 9 TCP/IP Protocol Suite • Developed by the US Defence Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET) Application Layer Transport (TCP) Layer Network (IP) Layer Network Access (Data Link) Layer Physical Layer A. Zahid, EE450 10 TCP/IP Protocol Suite & OSI A. Zahid, EE450 11 Layer Communications • Peer layers communicate via protocols • Adjacent layers communicate via service interfaces • Protocol control information (PCI) is added to Service data unit (SDU) at each layer to form a Protocol data unit (PDU) –(SDU)N = (PDU)N+1 –(PDU)N = (SDU)N +(PCI)N A. Zahid, EE450 12 Protocol Data Unit (PDU) User/Application Data Transport layer PDU Transport layer header Network layer PDU Network layer header A. Zahid, EE450 13 Layering: Logical Communications Each layer: data application • distributed transporttransport network • “entities” link implement layer physical ack network functions at each application link node transport data physical network • entities perform link data physical actions, application application transport transporttransport exchange network network messages with link link physical physical peers A. Zahid, EE450 14 Layering: Physical Communications data application transport network link physical network application link transport physical network link physical data application application transport transport network network link link physical physical A. Zahid, EE450 15 Layered Architecture & Networks • Each host needs a unique global address referred to as the IP address • Each application on a multitasking computer needs a unique address, referred to as the Port number, within the computer A. Zahid, EE450 16.