Computer Networks

Computer Networks Chapter One: Overview Prepared By: Dr. Bahjat Qazzaz Book: Computer Networking A Top-Down Approach Featuring the Internet By: James Kurose & Keith Ross Third Edition

Overview: Index • Internet: Services and protocols • Network Edge: End system, client, servers Connection/less services • Network Core: Circuit vs Packet switching Datagram NW & Virtual Circuit NW • ISP and Backbones

Overview: Index • Delay and loss in packet-switched NW • Protocol Layers: Layered architecture • Summary

Overview: Internet • The Internet: Is a worldwide network that interconnects millions of computing devices. (or a collection of different types of networks). • The devices can be: PCs, Workstations, • Also, PDAs, TV, mobile computers, cell phones,

Overview: Internet • Moreover, automobiles, environmental sensing devices, home electrical and security systems. • These devices are referred to as: • Hosts or • End systems • آلآن يجب أن ارسم تخطيط لشبكة

Overview: Internet • End systems are connected together by Communication Links (not directly) of different types: • Copper wire, fiber optics, Coax, radio spectrum • Different links can transmit data at different rates (called Transmission rate and measured in bits/second).

Overview: Internet • End systems (Hosts) are connected through intermediate devices known as: Packet Switches • A packet switch takes a chunk of information arriving on one of its incoming communication link and forward it on one of its outgoing communication link. • The chunk of information is called Packet • Example of packet switches: Routers

Overview: Internet • A Router is an electronic device (e.g. computer) that forwards packets toward their ultimate destination. • The communication links and packet switches between sending host and receiving host is called route or path • Internet uses packet switching technique rather than dedicated path between hosts

Overview: Internet • ISP (Internet Service Provider): End systems access the internet through ISPs. • Examples of ISPs • Local Telephone company (e.g Paltel) • Corporate Company • University…etc • Hosts can access the NW through: Dial-up modem, ADSL, High-speed LAN, Wireless

Overview: Internet • To allow users to access worldwide Internet content: • Local ISP (Lower-tier ISP) is interconnected to National ISP • And the National ISP (Upper-tier ISP) is interconnected to International ISP • An upper-tier ISPs consist of high-speed routers interconnected with high-speed fiber-optic links • Each ISP network is managed independently, runs IP protocols, has name and IP address

Overview: Internet • End systems and packet switches run protocols that control the sending and receiving of information within the Internet • The TCP (transmission Control Protocol) and IP (Internet Protocol) protocols (Known as TCP/IP) are two of the most protocols in the Internet. • IP protocol specifies the format of the packets that are sent and received among routers and end systems.

Internet services • Distributed Applications: The Interenet allows distributed applications running on its end systems to exchange data with each other. Applications include: E-mail, remote login, distributed games, video streaming, …etc • The Internet provides two services to its distributed applications: • Connection oriented reliable service & • Connection unreliable service

TCP/IP Network, and in particular the Internet, provide two types of services to end-system applications • Connection oriented • It guarantees that data transmitted from a sender to a receiver will eventually be delivered to the receiver in order and in its entirety. • Connectionless • It does not make any guarantees about eventual delivery !!! The distributed app. Makes use of one of these applications.

What is a Protocol • A protocol defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on the transmission and/or receipt of a message or other event • Examples:

Protocol examples: • Hardware-implemented protocols in the NIC of two physically connected computers: control the flow of bits on the wire between the two NICs. • Congestion-control protocols in end systems: control the rate at which packets are transmitted between sender and receiver

Protocol examples: • Protocols in routers: determine a packet’s path from source to destination.

Web example!! • What does happens when you request a web page? • You type a URL of a web page into a browser • Your computer will send a connection request message to the web server and wait for rply • The server receives your connection request and return a connection reply message • Your computer now sends the name of the web page it wants to fetch from the web server • The web server sends the web page to your computer

The Network Edge • End Systems, Clients, and Servers • Computers connected to the Internet are called end systems, because they sit at the edge of the Internet. • End systems are referred to as Hosts because they host application programs (e.g. web server prog, e-mail server prog, web browser prog • Hosts are also can be divided to clients and servers

Client/Server paradigm • A client program is a program running on one end system that requests and receives a service from a server program • A server program is a program listening on a connection waiting for a request and replying for the request. • !!!!! Notice the difference between sw & hw

Application examples: • Web, E-mail, File transfer, remote login (Telnet), and many other applications follow the Client / Server Paradigm Since the client program runs on a computer and the server programruns on another, these applications are called Distributed Applications

Application examples: • Notice that: An application may behave as a Client and server at the same time • For example PeerToPeer (P2P) file sharing applications: • It works as a client when it requests a file from another peer, and works as a server when it sends the file to another peer.

Connection and connectionless 1. Connection oriented & hadshaking (by sending control messages) It comes with services: • Reliable data transfer (ack.) • Flow control (No overwhelming) • Congestion control (prevents entering in gridlock) • It has the name: Transmission Control Protocol (TCP)

Connection and connectionless 2. Connectionless • No handshakig (just sending when ready) • E.g. MM App.

Network Core: Circuit switching and Packet switching • Circuit-switched networks: • The resources needed along a path to provide for communication between the end systems are reserved for the duration of the communication session. • So, when two host want to communicate, the network establishes a dedicated end-to-end connection between them.

Network Core: Circuit switching and Packet switching • Packet-switched networks: • The resources are not reserved ahead of the time. Instead, they are resources are allocated on demand. So, a session’s message may have to wait (at the sending buffer) for access to a communication link (suffering a delay)

Network Core: Multiplexing in circuit-switched networks • A circuit in a link can be implemented in one of the two ways: Frequency-Division Multiplexing (FDM) Or Time Division Multiplexing (TDM)

Network Core: Frequency-Division Multiplexing • FDM: The frequency spectrum of a link is shared among the connections. That is, each circuit continuously gets a fraction of the bandwidth.

Network Core: Time-Division Multiplexing • TDM: Time is divided into frames of fixed duration, and each frame is divided into fixed number of time slots, then the networks dedicate the whole bandwidth during the time of the slot to the connection.

Network Core: FDM vs TDM • FDM: • is wasteful during silent period • Is static • TDM: leads to increment in the number of users Example in: end of Page 17

Network Core: Packet switching • In modern networks: • Messages are broken into packet • Each packet travels through communication link and packet switch (router) at full rate (best efforts). • Most packet switches use Store-And-Forwards technique

Network Core: Packet switching • Store-and-forward: • The entire packet is received by the switch • It is checked for errors then, • It is forwarded to its destination. • Of course, this technique introduces some delay. (S&F delay) • Output buffer or output queue (queuing delay) • Packet loss Examples of page: 19+20+21

Network Core:Packet switching • Two classes of packet-switched networks Datagram networks And Virtual-circuit networks They differ in whether their switches use destination address or virtual-circuit numbers to forward packets toward their destination

Network Core:Packet switching • Datagram networks: • The network that forwards packets according to host destination address is called datagram network. • The internet is a datagram network.

Network Core:Packet switching • Virtual circuit networks: • The network that forwards packets according to virtual circuit numbers called virtual-circuit network. • This is done by giving a VC ID to end systems and to each and every switch along the VC’s source-to-destination path. • The x.25, frame relay, and ATM are all examples of packet-switching technologies that use virtual-circuit.

Network Taxonomy

Access Network and Physical Media • Residential Access: connection home end systems to the NW • Dial-up modem • Digital subscriber line (DSL) • Hybrid fiber-coaxial cabe • Company Access • LAN (shared ethernet, now switched ethernet tech). • Wireless Access

Physical Media • Go the layering architecture then back

Computer Networks