1. Technical issues in network design IICT-BAS

2. Network Hardware Main Taxonomy Dimensions:  transmission technology  network range (scale, size) Transmission Technology  broadcast links  point-to point links

3. Broadcast Networks Single communication channel shared by all the machines in the network Short messages (packets) with addressing field – sent by any machine – received by all others Target machine interprets current message; the rest ignore it (“Peter, come here/stand up”) Special bits in the address field indicate the transmission mode: broadcast (to all the machines); multicast (to group of machines)

4. Point-to-point Networks Many connections between pairs of machines Packets visit 0, 1, 2 … intermediate machines reaching the target one Alternative routes are possible - routing algorithms Basically for large networks, smaller, geographically localized networks tend to use broadcasting (as a general rule)

5. Network Range Physical Size Data Flow Machines & Multicomputers are Distributed Systems but not Computer Networks Personal Area Network – a wireless network connecting a computer with its mouse, keyboard, and printer Local Area Networks (LANs) Metropolitan Area Networks Wide Area Networks (WANs) Internetworks (connection of more than one network - The Internet) fine grain parallel com- puters; many functional units perform any instruction message passing sys- tems; short and fast com- munication busses

6. Scale of interconnected processors

7. Local Area Networks (LANs) Up to 1-2 km physical range (room, building, campus) Private owned (companies, branches, laboratories, small institutions) Connect PCs, workstations, disk stores, printers and other peripherals Main characteristics:  size  transmission technology  topology

8. Size of the LANs Small, technologically restricted size Bounded and known transmission time allows certain kinds of design Simple network management due to the limited transmission time

9. Transmission Technology of the LANs Usually based on a single cable attaching all the components of the network Communication speed 100 Mb/S, 1 - 10 Gb/s Communication delay 10  S (1  s = 10 -6 S), 1  s, 100 ns

10. Topology of the LANs Topology is the graph of the connectivity of the network components Typical topology of LANs is bus or ring Bus topology is based on linear cable Arbitration management - time-sharing control: 1 master machine at any instant is allowed to transmit; arbitration mechanism is needed to resolve conflicts Centralized or Distributed arbitration Ethernet TM (IEEE 802.3) standard: bus-based, distributed arbitration based on collision detection and random delay for next attempt

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

12. Topology of the LANs - ring topology Network ring forms necklace of the workstations Bit-slice propagation of the packets - each bit propagates around on its own, not waiting for the rest of the packet to which it belongs A rule is needed for arbitrating simultaneous accesses to the ring IBM Token Ring (IEEE 802.5) standard operates at 4-16 Mb/S Fibre Distributed Data Interface (FDDI) is also a ring network – 100 Mbit/s optical standard

13. Local area networks Ethernet LAN technology (IEEE 802.3) has today the largest installed base - types of cabling - thick coaxial (10BASE-5) with AUI connectors and transceivers (not in use any more) - thin coaxial (10BASE-2) with BNC connectors (not in use) - unshielded twisted pair (UTP or 10-base-T) with RJ-45 jacks. The 10BASE-T standard introduced a collision-free full duplex mode of operation that eliminated collisions. Modern Ethernets are entirely collision-free Each station on an Ethernet has an Ethernet network interface card (NIC), which has a special hardware address, assigned to guarantee link layer uniqueness, even across vendors

14. Metropolitan Area Networks A metropolitan area network (MAN), covers a city best-known example of a MAN, available in many cities – the cable television network When Internet became popular, cable TV network operators started to provide two-way Internet service in the unused parts of the spectrum Another MAN – IEEE 802.16 standard(s) - WirelessMAN - commercialized under the name WiMAX (from Worldwide Interoperability for Microwave Access)

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

16. Wide Area Networks (WANs) WAN covers large geographic area (country, continent) Connects different types of machines (for user/application programs) - “hosts” via communication subnet Separation of the services: hosts run application programs and subnet performs the connection tasks Subnet consists of transmission lines and switching elements (“routers”: specialized in connecting 2 or more switching lines)

17. Wide Area Networks (WANs) WAN covers large geographic area (country, continent) Connects different types of machines - “hosts” via communication subnet Separation of the services: hosts (owned by customers) run application programs and subnet (owned by telephone company or ISP) performs the connection tasks Subnet consists of transmission lines and switching elements (“routers”: specialized in connecting 2 or more switching lines)

18. WANs & Routers Router is specialized switching element in the WAN subnet Switching is the process of: 1) receiving data on the incoming channel[s]; 2) interpreting it; 3) choosing an outgoing line and 4) forwarding the data on it Typical structure of WAN: hosts connected by LANs; LANs connected by the subnet

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

20. WANs & Subnets Subnet consists of routers and connection lines The subnet lines are based on cables (telephone lines) that connects pairs of routers (point-to-point network) in a connected graph. Exception: wireless/satellite based subnets are of broadcast type (for WANs specialized in broadcasting communication) Non connected routers communicate via intermediate routers in store-and-forward (store until required output line is free, then forward) mode (or packet-switch) Subnet topology - usually irregular Subnet acquired a second, rather different meaning in conjunction with network addressing (discussed later)

21. WANs & Subnets a host process sending a message to a process on some other host, first cuts the message into packets, each one bearing its number in the sequence packets are then injected into the network one at a time in quick succession packets are transported individually over the network and deposited at the receiving host, where they are reassembled into the original message and delivered to the receiving process

22. A stream of packets sender - receiver

23. Routing Routing decisions are made locally When a packet arrives at router A, A decides if this packet should be sent on the line to B or the line to C The way A makes the decision - routing algorithm Many routing algorithm exist – shall study some of them later

24. Satellite WANs Some WANs are not packet switched With satellite systems each router has an antenna through which it can send and receive Routers can hear the output from the satellite, in some cases they can also hear the upward transmissions of other routers to the satellite Sometimes the routers are connected to a substantial point-to-point subnet, with only some of them having a satellite antenna Satellite networks are inherently broadcast and are most useful when the broadcast property is important

25. Wireless Networks Categories of wireless networks: System interconnection Wireless LANs Wireless WANs

26. System interconnection Interconnecting the components of a computer using short-range radio Some computers connect their components ( keyboard, mouse, printer, etc) by short-range wireless network called Bluetooth Bluetooth allows digital cameras, headsets, scanners, and other devices to connect to a computer by merely being brought within range No cables, no driver installation, just put them down, turn them on, and they work - ease of operation

27. System interconnection Interconnection networks use the master-slave paradigm The system unit is normally the “master”, talking to the mouse, keyboard, etc. – they are “slaves” The master tells the slaves what addresses to use, when they can broadcast, how long they can transmit, what frequencies they can use, and so on

28. Wireless Networks (a) Bluetooth configuration (b) Wireless LAN

29. Wireless LANs Systems in which every computer has a radio modem and antenna with which the computer can communicate with other systems The antenna may be on the ceiling so that the machines talk to it If the systems are close enough, they can communicate directly with one another in a peer-to-peer configuration Wireless LANs - common in small offices and homes, avoiding Ethernet installation The standard for wireless LANs is called IEEE 802.11 - very widespread

30. Wireless WANs Radio network used for cellular telephones is an example of a low-bandwidth wireless system – four generations: 1G - first generation - analog and for voice only 2G - second generation - digital and for voice only 3G - third generation – digital for both voice and data 4G – fourth generation - provides mobile ultra- broadband Internet access; designed to deliver speed - on average from four to ten times faster than 3G

31. Internetworks Internetwork (or internet) = communication between LANs, MANs and WANs with different internal standards (hardware, software) Compatibility requires gateways – machine/device to make the connection and provide the necessary translation, both in terms of hardware and software Typical architecture: collection of LANs connected by a WAN: (WAN differs from the subnet just by presence of hosts and not only routers) The Internet = biggest internetwork connecting universities, public and private offices, persons etc. – we always capitalize