Kemal AkkayaWireless & Network Security 1 Department of Computer Science Southern Illinois University Carbondale CS591 – Wireless & Network Security Lecture 2: Overview of Computer Networking Dr. Kemal Akkaya

Kemal AkkayaWireless & Network Security 2 What’s the Internet: “nuts and bolts” view  Millions of connected computing devices: hosts = end systems  Running network apps  Communication links  fiber, copper, radio, satellite  transmission rate = bandwidth  Routers: forward packets (chunks of data)  Protocols control sending, receiving of msgs  e.g., TCP, IP, HTTP, FTP, PPP  Internet: “network of networks”  Loosely hierarchical  Public Internet vs Private intranet  Internet standards  RFC: Request for Comments  IETF: Internet Engineering Task Force local ISP company network regional ISP router workstation server mobile

Kemal AkkayaWireless & Network Security 3 The network edge  End systems (hosts)  Run application programs  e.g., Web,  At “edge of network”  Client/Server model  Client host requests, receives service from always-on server  e.g. Web browser/server; client/server  Peer-Peer model  Minimal (or no) use of dedicated servers  e.g., Napster, Gnutella, KaZaA

Kemal AkkayaWireless & Network Security 4 What’s the Internet: a service view  Communication infrastructure enables distributed applications  Network edge: applications and hosts  Network core : routers network of networks  Access networks, physical media: communication links  Applications: Web, , games, e- commerce, file sharing  Communication services provided to apps:  Connectionless unreliable  Connection-oriented reliable  Various protocols are used for communication services

Kemal AkkayaWireless & Network Security 5 What’s a protocol? Human protocols:  “What’s the time?”  “I have a question”  introductions … specific msgs sent … specific actions taken when msgs received, or other events Network protocols:  Machines rather than humans  All communication activity in Internet governed by protocols Protocols define format, order of messages sent and received among network entities, and actions taken on message transmission, receipt

Kemal AkkayaWireless & Network Security 6 What’s a protocol?  A human protocol and a computer network protocol: Q: Other human protocols? Hi Got the time? 2:00 TCP connection req TCP connection response Get time  Timing  Speed matching  Sequencing  Syntax  Data formats  Signal levels  Semantics  Control information  Error handling  Key Elements of a Protocol:

Kemal AkkayaWireless & Network Security 7 Protocol “Layers” Networks are complex!  Many “pieces”:  hosts  routers  links of various media  applications  protocols  hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks? ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing Organization of air travel  Consider the following analogy:  A series of steps

Kemal AkkayaWireless & Network Security 8 Layering of airline functionality  Layers: Each layer implements a service  via its own internal-layer actions  relying on services provided by layer below  Why Layering?  Dealing with complex systems  Explicit structure allows identification, relationship of complex system’s pieces Layered reference model for discussion  Modularization eases maintenance, updating of system Change of implementation of layer’s service transparent to rest of system e.g., change in gate procedure doesn’t affect rest of system ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing departure airport arrival airport intermediate air-traffic control centers airplane routing ticket (complain) baggage (claim gates (unload) runway (land) airplane routing ticket baggage gate takeoff/landing airplane routing

Kemal AkkayaWireless & Network Security 9 Standardized Protocol Architectures  Required for devices to communicate  Vendors have more marketable products  Customers can insist on standards based equipment  Two standards:  OSI Reference model Open Systems Interconnection Developed by the International Organization for Standardization (ISO) Seven layers Never lived up to early promises  TCP/IP protocol suite Most widely used De facto standard  Also: IBM Systems Network Architecture (SNA)

Kemal AkkayaWireless & Network Security 10 OSI - The Model  A layer model  Each layer performs a subset of the required communication functions  Each layer relies on the next lower layer to perform more primitive functions  Each layer provides services to the next higher layer  Changes in one layer should not require changes in other layers  Why OSI did not take over the world  Bad timing  Bad technology  Bad implementations  Bad politics

Kemal AkkayaWireless & Network Security 11 The OSI Environment

Kemal AkkayaWireless & Network Security 12 OSI as Framework for Standardization

Kemal AkkayaWireless & Network Security 13 OSI Layers  Physical  Physical interface between devices Mechanical Electrical Functional Procedural  Data Link  Means of activating, maintaining and deactivating a reliable link  Error detection and control  Higher layers may assume error free transmission  Network  Transport of information  Higher layers do not need to know about underlying technology  Not needed on direct links  Transport  Exchange of data between end systems  Error free  In sequence  No losses  No duplicates  Quality of service  Session  Control of dialogues between applications  Dialogue discipline  Grouping  Recovery  Presentation  Data formats and coding  Data compression  Encryption  Application  Means for applications to access OSI environment

Kemal AkkayaWireless & Network Security 14 Use of a Relay

Kemal AkkayaWireless & Network Security 15 TCP/IP Protocol Architecture  Developed by the US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET)  Used by the global Internet  No official model but a working one.  Application layer  Host to host or transport layer  Internet layer  Data link layer  Physical layer  Problems:  Service, interface, and protocol not distinguished  Not a general model  No exact separate mention of physical and data link layers Sometimes called host-to-network layer  Minor protocols deeply entrenched, hard to replace

Kemal AkkayaWireless & Network Security 16 Layer Descriptions  Physical Layer  Physical interface between data transmission device (e.g. computer) and transmission medium or network  Characteristics of transmission medium  Signal levels  Data rates  Data Link Layer  Exchange of data between neighboring network nodes  Invoking services like priority  Internet (IP) Layer  Systems may be attached to different networks  Routing functions across multiple networks  Implemented in end systems and routers  Transport Layer (TCP)  Reliable delivery of data  Ordering of delivery  Application Layer  Support for user applications: HTTP, SMTP

Kemal AkkayaWireless & Network Security 17 OSI vs TCP/IP

Kemal AkkayaWireless & Network Security 18 Protocols and networks in the TCP/IP model

Kemal AkkayaWireless & Network Security 19 PDUs in TCP/IP

Kemal AkkayaWireless & Network Security 20 message segment datagram frame source application transport network link physical HtHt HnHn HlHl M HtHt HnHn M HtHt M M destination application transport network link physical HtHt HnHn HlHl M HtHt HnHn M HtHt M M network link physical link physical HtHt HnHn HlHl M HtHt HnHn M HtHt HnHn HlHl M HtHt HnHn M HtHt HnHn HlHl M HtHt HnHn HlHl M router switch Encapsulation

Kemal AkkayaWireless & Network Security 21 Some Protocols in TCP/IP Suite