Peer-To-Peer (P2P) Network

Technology 12

Peer-to-Peer (P2P) Network  Any node connected to a P2P network can directly connect to any other node on the network.  Limited to approximately ten (10) nodes  Network is decentralized, i.e., each node must provide o security o data backup o software updates

Client-Server Network  Server Computers o stores and provides resources to requests by client computers o serves multiple client computers o restricted to efficient execution of specific tasks, e.g., database requests, email handling, software requests o provides network security o scalable – easy to add additional servers, thus easy to accommodate additional clients, i.e., the network is easy to expand  Client Computers o end-user computer that depends upon a client server for essential resources  Network is centralized, i.e., servers provide o security o data backup o software updates

Local Area Network (LAN)  small groups of computers (clients)  local geographical area  e.g., JD1105, JD1107 & JD1600 computer labs form one LAN

Wide Area Network  large numbers of computers (clients)  separate LANs linked together  e.g., CSUN Network that links all Schools in the University, the Administration & the Student Residence Halls

The Internet is the largest WAN in existence! Metropolitan Area Network (MAN)  city or county wide networks  e.g., San Diego Traffic Management Center www.dott.ca.gov/sdtraffic

Personal Area Networks  Wireless Transmissions  Radio waves – Bluetooth  Limited to 30 feet radius

An internet  private network created by an entity to be used by that entity  uses firewall to prevent unauthorized entry  facilitates information sharing within the entity  uses Transmission Control Protocol/Internet Protocol (TCP

The Internet  collection of individual internets

Client-Server Architecture  Server o at least one computer must be dedicated to act as a server  Net Topology o layout and structure of the network, necessary for efficient communications  Transmission Media o wired o wireless  Network Operating System o specialized operating system o installed on both the servers and the client computers o enables the activation of a client-server network  Network Navigation Devices o Routers o Switches o Bridges Dedicated Servers -- fulfills one specific function  Print Server o print queue o sequence number o priority number  Email Server o process and deliver incoming and outgoing email  Database Server o provides concurrent access to the database by multiple clients  Application Servers o repository of software packages . installation required only on the server . upgrading required only on the server  Web Server o specialized software required to host websites o e.g., Apache or Microsoft Internet Information Server (IIS)  Communications Server o manages access to the Internet o e.g., both the Email Server & Web Servers accesses the Internet via the Communications Server

Network Topologies  Bus Topology o all computers are connected in sequence on a single cable o each computer can connect to any other computer directly o data collisions – two computers transmit data at the same time o access method – controls which computer has access to the bus at any one time o data is broadcast to all computers connected to the network o data can only be broadcast when the network bus is free, i.e., no one else is trying to use it o data is broken into small segments, i.e., packets o packet contains . address of receiving device . data segment . sequence number o each computer connected to the network searches each packet for those that are addressed to them o packets that are not addressed to the receiving computer, are retransmitted to the next computer on the bus (passive technology) o terminator – device attached to end of bus that absorbs signal & prevents its reflection back down the bus o transmission signals degrade as the distance of the cable increases, i.e., not scalable o because only one compute can communicate at a time, size of network is limited o break in bus cable disrupts the network  Ring Topology, Loop Topology, Token-Ring Topology o data flows in a closed ring in one direction o token . specialized data packet . usually only one token exists in the network  passed from computer to computer around the ring  grabbed by a computer if it needs to communicate  holds the token until it is done communicating o data transfer rate (bandwidth) 100Mbps o enables all nodes on the network to have an equal chance to communicate o scalable – easy to add additional computers o break in the data cable disrupts the network

 Star Topology o all nodes connect to a central communications device, i.e., switch o switch receives signal from ending node, retransmits signal to all of the nodes in the network o each network node examines the data and picks up the transmissions directed to them o scalable – easy to add computers to the network o failure of a single computer, not the switch, does not affect the viability of the network o most common topology for client-server networks, i.e., all client computers connect to a centralized server computer

 Ethernet Communications Protocol o set of rules for exchanging communications o transfer rate 1GB o may used on Bus, Ring, & Star Topology Networks o Carrier Sense Multiple Access with Collision Detection . all nodes connected to network have the ability, i.e., carrier sense, to determine that no other nodes are currently transmitting data . if a node determines that no other nodes are currently transmitting data, it may initiate a data transfer operation . if a data collision occurs,  some node will detect the collision and send a jam signal to all the nodes on the network  any node currently transmitting will stop and wait a random time interval before initiating a new data transmission

Transmission Media  Wired o Criteria . Maximum run length . Bandwidth . Bend radius (flexibility) . Cable Cost . Installation costs . Interference Susceptibility o Twisted Pair Cable . Unshielded Twisted Pair (UTP)  Cat 5E – 200Mbps  Cat 6 – 1Gbps . Shielded Twisted Pair (STP) o Coaxial Cable . ThinNet – residences . ThickNet – industrial settings with high probability of electrical interference  Wireless o WiFi -- IEEE 802.11 Standard . 802.11g  maximum throughput 54 Mbps  maximum throughput 108 Mbps with Super G, Extreme G or Enhanced G Devices . 802.11n  new standard  much higher throughput than 802.11g  greatly increased range over 802.11g

Network Operating Systems  Minor NOS – used on small server systems o Windows Vista o Mac OS/X  Major NOS – used on large servers o Windows Server 2003 o UNIX o Novell NetWare

Network Protocols  Novell Internetwork Packet Exchange (IPX)  Microsoft NetBIOS Extended User Interface (NetBEUI)  Apple file Protocol (AFP)  TCP/IP Network Adapters  device that enables a computer to communicate on a network

Network Interface Cards (NIC)  network adapter expansion card installed inside a computer  generate high-powered signals to enable network transmissions  break data into packets for sending  assemble incoming packets into documents  act as gatekeeper, i.e., o permit or deny access to the computer o controlling the flow of data  Ethernet compliant, RJ-45 connection ports for connection to twisted-pair cable

Wireless Network Interface Cards (Wireless NIC)  Internet connection consists of wireless access points

Network Navigation Devices  MAC Addresses o unique physical address assigned to each network adapter o used for internal identification on a network whereas an IP address is used by external entities to communicate with your network o Media Access Control (MAC) address . six two positions characters, e.g., 01:40:87:44:79:A5, where . 01:40:87 specifies the manufacturer . 44:79:A5 is a sequence which is unique to that specific network adapter o router containing a list of authorized MAC addresses can filter out unauthorized access to the network

 Frame o group of data packets bundled with a single MAC address

 Repeaters o amplifies a signal and retransmits it o used to extend cable runs beyond the maximum run length

 Hubs o contain multiple ports to which devices may be attached o receives a signal from a device o may amplify the signal o retransmits it to all devices attached to the hub

 Switches o hub that uses the MAC address of the connected devices to decide where the signal should be sent; does not broadcast the signal  Bridges o Ethernet networks faced congestion problems as they increased in size. If a large number of stations connected to the same segment and each generated a sizable amount of traffic, many stations may attempt to transmit whenever there was an opportunity. Under these circumstances, collisions would become more frequent and could begin to choke out successful transmissions, which could take inordinately large amounts of time to complete. One way to reduce congestion would be to split a single segment into multiple segments, thus creating multiple collision domains. This solution creates a different problem, as now these now separate segments are not able to share information with each other.

o To alleviate problems with segmentation, Ethernet networks implemented bridges. Bridges connect two or more network segments, increasing the network diameter as a repeater does, but bridges also help regulate traffic. They can send and receive transmissions just like any other node, but they do not function the same as a normal node. The bridge does not originate any traffic of its own; like a repeater, it only echoes what it hears from other stations. (That last statement is not entirely accurate: Bridges do create a special Ethernet frame that allows them to communicate with other bridges, but that is outside the scope of this article.)

o Remember how the multiple access and shared medium of Ethernet meant that every station on the wire received every transmission, whether it was the intended recipient or not? Bridges make use of this feature to relay traffic between segments. In the figure above, the bridge connects segments 1 and 2. If station A or B were to transmit, the bridge would also receive the transmission on segment 1. How should the bridge respond to this traffic? It could automatically transmit the frame onto segment 2, like a repeater, but that would not relieve congestion, as the network would behave like one long segment. o One goal of the bridge is to reduce unnecessary traffic on both segments. It does this by examining the destination address of the frame before deciding how to handle it. If the destination address is that of station A or B, then there is no need for the frame to appear on segment 2. In this case, the bridge does nothing. We can say that the bridge filters or drops the frame. If the destination address is that of station C or D, or if it is the broadcast address, then the bridge will transmit, or forward the frame on to segment 2. By forwarding packets, the bridge allows any of the four devices in the figure to communicate. Additionally, by filtering packets when appropriate, the bridge makes it possible for station A to transmit to station B at the same time that station C transmits to station D, allowing two conversations to occur simultaneously!  Routers o designed to send data between different networks o uses IP addresses to determine which network the data should be sent o if the router detects data with an address that does not belong to one of the devices on the network from which it originated, it sends the data to another network to which it is attached or out onto the Internet o filters data which is not directed to an authorized MAC address

Firewalls  Packet Screening (Router) o Examine incoming packets to ensure that they originate from or are authorized by valid users on the internal network o Examine outgoing packets to ensure that requests for information to the Internet are from legitimate users  Bastion Host (proxy server)

Technology 13