Network Protocols and Layering Models in Computer Networks
Learn about network protocols, protocol suites, layering models, and protocol design in computer networks. Understand how protocols facilitate communication, address hardware-related issues, and organize communication solutions into layers. Explore the OSI 7-Layer Model and the concept of protocol stacks.
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CECS 474 Computer Network Interoperability CHAPTER 1 Network Protocols Tracy Bradley Maples, Ph.D. Computer Engineering & Computer Science Cal ifornia State University, Long Beach Notes for Douglas E. Comer, Computer Networks and Internets (5th Edition)
Protocol Suites and Layering Models Defn: Protocols are agreements about how communication should take place. They specify: Format of messages Meaning of messages Rules for exchanging messages Procedures for handling problems Network hardware functions at a very low level. Hardware related problems can occur that need to be addressed by protocols: Bits can be corrupted or destroyed Entire packets can be lost Packets can be duplicated Packets can be delivered out of order 2
Protocols can also be used to distinguish among: Multiple computers on a network Multiple applications on a computer Multiple copies of a single application on a computer Sets of Protocols Sets of protocols are designed to work together. Each protocol solves a small part of the communications problem Sets of protocols are known as: -- Protocol Suites -- Protocol families They are designed in layers. 3
Protocol Design Protocols are divided into layers Each layer is devoted to one sub-problem Example: The ISO (International Standards Organization) OSI (Open System Interconnection) 7- layer Reference Model The OSI 7-Layer Model The 7-Layer Model: Was defined fairly early in the development of networks Is now somewhat dated Does not include the internet layer 4
The OSI 7-Layers Layer 1: Physical The underlying hardware Layer 5: Session Login and passwords Layer 2: Data Link (media access) Hardware frame definitions Layer 6: Presentation Data representation Layer 3: Network Packet forwarding Layer 7:Application Individual application programs Layer 4: Transport Reliability 5
The Layering Model Protocol software follows the layering model, with: One software module per layer Modules that work together Incoming or outgoing data passing from one module to another The entire set of protocol layers (or modules) is known as a stack. 6
Layers and Packet Headers Each layer: Prepends a header to the outgoing packet Removes a header from the incoming packet This process is known as data encapsulation. 7
Layering Principle Software implementing layer N at the destination receives exactly the message sent by software implementing layer N at the source. --Comer 8
TCP/IP Layering Notwithstanding the push by researchers to adopt the OSI model, it became clear that TCP/IP was technically more flexible and superior. TCP/IP is the primary protocol stack used today. Note: This TCP/IP layering is an actual implementation of protocols, unlike the ISO model. 9
TCP/IP Layers Layer 4: Transport Specifies how to provide reliable transfer from one application on one computer to an application on another Similar to OSI Layer 4 Layer 1: Physical Basic network hardware Similar to OSI Layer 1 Layer 2: Network Interface MAC frame format MAC addressing Interface between computer and the network (i.e., the NIC) Similar to OSI Layer 2 Layer 5:Application Everything else (i.e., how one application uses the Internet) Similar to OSI Layer 6 and 7 Layer 3: Internet Format of packets Mechanisms for forwarding packets Not in the OSI Model 10
