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Chapter 1: Introduction

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1 Chapter 1: Introduction
Objectives: Types of Networks OSI Reference Model (7 Layers) TCP/IP Model Network Devices Network Topologies

2 Business Applications of Networks
A network with two clients and one server.

3 Business Applications of Networks (2)
The client-server model involves requests and replies.

4 Client/Server In a client/server arrangement, network services are located on a dedicated computer called a server. The server responds to the requests of clients. The client/server model of networking can be used to overcome the limitations of the peer-to-peer network.

5 Home Network Applications (2)
In peer-to-peer system there are no fixed clients and servers.

6 Peer-to-Peer Networks
In a peer-to-peer network, networked computers act as equal partners, or peers. In a peer-to-peer network, individual users control their own resources. The users may decide to share certain files with other users. The users may also require passwords before allowing others to access their resources.

7 Network Hardware Local Area Networks Metropolitan Area Networks
Wide Area Networks Wireless Networks Home Networks

8 Classification of interconnected processors by scale.
Broadcast Networks (2) Classification of interconnected processors by scale.

9 Network Types Local area networks (LANs), which connect over a relatively small geographical area, typically connecting computers within a single office or building. In most cases they connect to a common electronic connection – commonly known as a network backbone. LANs can connect to other networks either directly or through a WAN or MAN. Metropolitan area networks (MANs), which normally connect networks around a town or city based on cable TV. It is smaller than a WAN, but larger than a LAN. Wide area networks (WANs), which connect networks over a large geographical area, such as between different buildings, towns or even countries.

10 Local Area Networks Two broadcast networks (a) Bus (b) Ring

11 Metropolitan Area Networks
A metropolitan area network based on cable TV.

12 Relation between hosts on LANs and the subnet.
Wide Area Networks Relation between hosts on LANs and the subnet.

13 Wireless Networks Categories of wireless networks:
System interconnection Wireless LANs Wireless WANs

14 Network Software Protocol Hierarchies Design Issues for the Layers
Connection-Oriented and Connectionless Services Service Primitives The Relationship of Services to Protocols

15 Protocol Hierarchies (2)
The philosopher-translator-secretary architecture.

16 Design Issues for the Layers
Addressing Error Control Flow Control Multiplexing Routing

17 Connection-Oriented and Connectionless Services
Flow Control Error checking and correction Six different types of service.

18 Service Primitives Five service primitives for implementing a simple connection-oriented service.

19 Service Primitives (2) Packets sent in a simple client-server interaction on a connection-oriented network.

20 Services to Protocols Relationship
The relationship between a service and a protocol.

21 Reference Models The OSI Reference Model The TCP/IP Reference Model
A Comparison of OSI and TCP/IP A Critique of the OSI Model and Protocols A Critique of the TCP/IP Reference Model

22 OSI Model Application Application A Presentation Presentation P A
Sender Virtual data flow Receiver Application Application A Presentation Presentation P A Session Session S P A Transport Transport T S P A Network Network N T S P A Data link Data link D N T S P A D Physical Physical Actual data flow

23 OSI 7-layered Model Example layers
Physical/Data Link: Ethernet/FDDI/ISDN/etc Network: IP (Internet) or IPX (NetWare) Transport: TCP (Internet) or SPX (NetWare) Session-Application: HTTP/FTP/TELNET/SMTP/etc OSI 7-layer Model (International Standards Organisation) Allow manufacturers of different systems to interconnect their equipment through standard interfaces. Allow software and hardware to integrate well and be portable on differing systems. Create a model which all the countries of the world use.

24 OSI Layers Transport. Provides for reliable end-to-end error and flow control. The network layer does not validate that the data packet has been successfully received, thus it is up to the transport layer to provide for error and flow control. Network. Defines the protocols that are responsible for delivering the data to the required destination. Data link. Provides for the access to the network media and thus builds on the physical layer. It takes data packets from the upper level and frames it so that it can be transmitted from one node to another. Physical. Defines the electrical characteristics of the communications channel and the transmitted signals, such as voltage levels, connector types, cabling, and so on. Application. Provides application pro­grams, such as file transfer, print access and electronic mail. Presentation. Transforms the data into a form which the session layer and the application layer expect. It can perform encryption, translating character sets (such as converting binary values into text for transmitting a binary program over a text-based system), data compression and network redirections. Session. Setting up, maintaining and closing down of a session. It should not depend on any specific transport or network layer, and should be able to communicate as if the session was created on a stand-alone computer (that is, the network is transparent to the session layer). Session - Application Session HTTP/FTP Session Transport Transport TCP/SPX Transport Network Network IP/IPX Network Data link Data link Ethernet/ ATM/FDDI Data link Physical Physical

25 OSI Layers Socket Application Transport Data stream Network Router
Data link layer Network Data stream Transport Application MAC address in NIC Socket Physical

26 Reference Models The OSI reference model. PDU: Protocol Data Unit

27 The TCP/IP reference model.
TCP/IP Model The TCP/IP reference model.

28 Protocols and networks in the TCP/IP model initially.
Reference Models (3) Protocols and networks in the TCP/IP model initially.

29 Architecture of the Internet
Overview of the Internet.

30 IEEE 802 Standards The 802 working groups. The important ones are marked with *. The ones marked with  are hibernating. The one marked with † gave up.

31 OSI Layer Devices

32 Repeaters, bridges, Switches and routers
Network segment (repeater extends the network segment) Router Bridge only forwards if the station (or MAC) address is not on the connected network segment that it originated from. Broadcasts are also passed over. Bridge Router only forwards if the network address is on another network. It does not forward broadcasts. Network segment bounded by a router or a bridge

33 Network Types Network Data Link Physical Router A router routes with
the network address (such as the IP address) A bridge routes with the MAC address A repeater boosts the signal Repeater Bridge

34 Network / Physical topologies

35 Star Network Star Network Advantages:
Central server Star Network Advantages: Since the data rate is relatively low between central server and the node, a low-specification twisted-pair cable can be used connect the nodes to the server. A fault on one of the nodes will not affect the rest of the network. Typically, mainframe computers use a central server with terminals connected to it. Disadvantages: Network is highly dependent upon the operation of the central server. If it were to slow significantly then the network becomes slow. In addition, if it were to become un-operational then the complete network would shut down.

36 Bus network Bus network Uses a multi-drop transmission medium.
All nodes on the network share a common bus and all share communications. This allows only one device to communicate at a time. A distributed medium access protocol determines which station is to transmit. data frames contain source and destination addresses, where each station monitors the bus and copies frames addressed to itself. Twisted-pair cables give data rates up to 100Mbps, whereas, coaxial and fibre optic cables give higher bit rates and longer transmission distances. Gigabit Ethernet is now available (1Gbps). A typical bus network is Ethernet 2.0. All computers have access to a common bus at the same time Common bus Ethernet hub Advantages: Good compromise over the other two topologies as it allows relatively high data rates. If a node goes down, it does not affect the rest of the network. Disadvantages: Requires a network protocol to detect when two nodes are transmitting at the same time. Does not cope well with heavy traffic rates.

37 Token Ring (example data exchange)
Control token rotates round the ring. Node wishing to transmit data captures the token. Node captures token and transmits a data frame. Data frame rotates round network. All nodes read the frame and determine if the data is for them. Destination node reads the data, and sets an acknowledgement flag. Data frame continues round the network, until the source node receives it. Source node puts the control token back on the ring. Control Token (a) Data Frame (b) Ack. A D C B (c) Control Token (d)

38 Tree topology Network backbone Concentrator (or hub) Workgroup
Resources should be grouped logically when attached to hubs, such as local file servers, printers, and so on. Advantages: Nodes local to a hub can communicate with each other without the data traffic going onto other network segments. A fault on a single computer or a hub does not bring the whole network down. Communication between the hub and the computer has relatively low data transfers, as opposed to the transfer connected hubs to hubs. Easy to connect and disconnect to. Disadvantages: Network may suffer from slow data transfer if the network is not planned to reflect tree topology. Typically network is created with workgroups. Most networking technologies now use hubs to connect to.Typically for Ethernet and Token Ring networks. Concentrator (or hub) Network backbone Concentrator (or hub) Workgroup - with printer - file server - etc

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