Yelena Yesha Olga Streltchenko

1. Networking Technologies Yelena Yesha Olga Streltchenko

2. Presentation Overview • Evolution of Networks. • Networking Challenges. • Types of Networks. • Network Principles. • Internet Protocols. • Summary.

3. The Network • Built from • Transmission media • Wire, cable, fibre, wireless channels; • Hardware devices • Routers, switches, bridges, hubs, repeaters, network interfaces; • Software components • Protocol stacks, communication handlers, drivers.

4. Evolution of Networking • Batch Environment - 1950s • no direct interaction between users and their programs during execution. • Time Sharing - 1960s • Dumb terminals were connected to a central computer system. • Users were able to interact with the computer and could share its information processing resources. • Marked the beginning of computer communications.

5. Evolution of Networking (cont'd) • Distributed Processing: use of minicomputers - 1970s • Users demanded computing closer to their work areas. • Communication between neighbour processors and applications via networks. • WAN and LAN- 1980s • Internet, broadband and wireless communication, mobile code, ubiquitous computing, etc. - 1990s • 2000s - ?

6. Networking Challenges • Performance • Scalability • Reliability • Mobility • Security • QoS (Quality of Service)

7. Performance • Parameters that determine the speed of message exchange between two nodes • Latency • Delay that occurs after a send operation and before the data becomes available at the target node, i.e. latency=time to transmit an empty message • Data transfer rate • The speed at which data can be transferred between two nodes (bits/sec). • If a message length does not exceed the max determined by the network technology, then Message transmission time=latency+length/data transfer rate

8. Performance (cont'd) • Transfer rate is primarily determined by physical characteristics of the network. • Latency is primarily determined by • software overheads, • routing delays, • load-dependent non-deterministic elements; • E.g., message collision on the Ethernet. • Total system bandwidth of a network • Measure of throughput; • Total volume of traffic that can be transferred across the network in a given time.

9. Scalability • A system is described as scalable if it remains effective when there is a significant increase in the number of resources and the number of users. • Challenges in scalable system design: • Controlling the cost of physical resources as the demand for resources grows; • e.g., for a system with n users the quantity of physical resources should be at mostO(n). • Controlling the performance lost as the number of users/resources grows; • e.g., for a system with n objects the access time should be at mostO(log n).

10. Scalability (cont'd) • Challenges in scalable system design (cont'd): • Preventing software resources running out • Example: 32-bit IP address of the 1970's ran out; current IP address uses 128 bits and is expected to be exhausted by early 2000's. - Keeping up is a serious challenge! • Avoiding performance bottlenecks • Use decentralized algorithms, caching, redundancy and replication; • Example: DNS table maintenance: tables are distributed and replicated.

11. Scalability on the Internet • Potential size of the Internet=world population. • Original network technologies did not anticipate this scope. • Changes to the addressing and routing. • Current average round-trip time= 100-150ms • Individual numbers vary widely. • The ability to scale will depend on the economics of use • Charges to the users • Patterns of communication.

12. Reliability: Failure Models • Communication failures (vs process failures) • Omission failure: communication channel fails to perform prescribed actions; • e.g., loss of messages; • Easiest type of failure to detect and handle, e.g., retransmit the message. • Arbitrary failure: unintended actions occur (any type of error); • e.g., delivery of a corrupted message, delivery of a non-existent message, repeated delivery; • This type of error is rare since communications software is able to detect [and correct] it.

13. Reliability: Failure Models (cont'd) • Communication failures (cont'd) • Timing failure arises in synchronous application where time limits are set on message delivery; • Responses become unavailable to clients after timeout, e.g., ftp; • Asynchronous systems like WWW are not suseptible to this type of error since they do not provide any timing guarantees.

14. Handling failures • Detecting • E.g., use checksum to detect a corrupted message; • Not always possible, e.g., a remote server crash. • Masking • Hide a failure • By means of service/data replication, etc.; • Convert a failure into another type of failure • e.g., dropping a corrupted message turns an arbitrary failure into anomission failure; • We know how to handle it.

15. Handling Failures (cont'd) • Tolerating • Impractical to detect and hide all the failures on the Internet; • Software informs users about failure; • Include redundant components into the system to tolerate failures, e.g. • at least two different routes between two routers; • DNS replication; • operational database replication.

16. Handling failures (cont'd) • Recovery • Involves special software design that allows to recover the state of the permanent data.

17. Reliability of Communications Requirements • Validity • Any message in the outgoing buffer will be eventually delivered to the incoming message buffer. • Integrity • The message received is identical to the message sent, and no messages are delivered twice.

18. Mobile Code • Code that can be sent from one computer to another; • e.g., Java applets; • Virtual Machine approach • A way of making code executable on any hardware; • VM is middleware, i.e. a layer of software whose purpose is to mask heterogeneity of hardware; • The compiler generates code for a VM; • Used by Java and is not necessarily extendable to other languages.

19. Mobile Code (cont’d) • The advantage of running downloaded code is network delay avoidance during interactions. • Potential security threat to the local resources.

20. Mobile Agents • A running program (code and data) that travels from one computer to another over the network carrying out a task on behalf of a user; • e.g., to perform information retrieval. • The advantage over client-server approach lies in the reduction of communication time and cost; • replaces remote invocations with local ones. • Potential security threat to the host. • MA are vulnerable themselves.

21. Mobile Devices • Proliferation of small and portable computer devices • e.g., laptops, PDAs, mobile phones, digital cameras, etc. • Enabled with wireless networking • Metropolitan or greater ranges • GSM (Global Mobile System), European standard; • CDPD (Cellular Digital Packet Data), in the USA and Canada. • Ranges of l 100m • BlueTooth; • Infra-red; • HomeRF.

22. Spontaneous Networking • The term best describes the integration of mobile devices into a given network. • Encompasses applications that involve connection of mobile and non-mobile devices to networks. • Challenge: enable universal interoperability between mobile devices and local non-mobile services: • e.g., laptops or palmpilots need to detect and be able to use available resources, like printers, fax machines, etc., when they move into different surroundings.

23. Spontaneous Networking (cont’d) • Requirements • Easy connection to a local network: • Avoid the need of pre-installed cabling, inconvenience of plugs and sockets; • Transparently reconfigure a mobile device to obtain connectivity (avoid the need of manually installing drivers). • Easy integration with local services: • Automatic discovery of available services. • Active research area. • Challenge for IP addressing: • Classical IP addressing and routing assumes that computers are located on a particular subnetwork; • if a computer is moved to another subnet it is no longer accessible with its IP address; • Solution: MobileIP (discussed later)

24. Spontaneous Networking (cont’d) • Limited connectivity • Users are intermittently disconnected as they move; • Could be disconnected for long periods of time • Security and Privacy • Security attacks by mobile devices onto the host network or vice versa; • Tracking of physical location of the user; • Access to data otherwise protected by a firewall; • Many other scenarios.

25. Discovery Services • Accept and store details of services that become available on the network and respond to queries from clients about them. • Offer two interfaces: • A registration service accepts registration requests from servers and records the details in the discovery service’s database; • A lookup service accepts and processes queries concerning available services; returns enough details to the client to enable it to choose among similar services and establish a connection. • Example: Jini (discussed later in class).

26. Security Requirements • Confidentiality • protection against disclosure to unauthorized individuals. • Integrity • protection against alteration or corruption. • Availability • protection against interference with the means to access the resource (denial of service attack).

27. Firewalls • Creates a protection boundary between the organization's intranet and the Internet. • Runs on a gateway - a computer that stands at the network entry point to the intranet. • Receives and filters all the incoming and outgoing messages according to the organization‘s security policy.

28. Secure Network Environment • Need to move beyond the restrictions imposed by firewalls. • Need to ensure authentication, privacy and security over unprotected channels. • Use of cryptographic techniques. • Virtual Private Network (VPN) concept: • Use encryption schemes to establish secure tunnels through the Internet.

29. Time and Data Delivery • Most of the data can be delivered within a range of transfer rates; • E.g., e-mail, file transfer. • Time-critical data: streams of data that are required to be transferred at a certain rate. • Multimedia data require guaranteed bandwidth and bounded latency for the communication channels they use.

30. Quality of Service • The ability to meet deadlines when transmitting and processing streams of real-time multimedia data; • provide computing and communication resources. • Currently network performance deteriorates fast with load growth: • no QoS support on the Internet.

31. Types of Networks • Local area networks (LANs). • Wide area networks (WANs). • Metropolitan area networks (MANs). • Wireless networks. • Internetworks.

32. LANs • A collection of hosts connected by a high speed network of a single communication medium; • twisted pair, coaxial cable, optical fibre. • Designed and developed for communications and resource sharing in a local work environment; • room, campus, building.

33. LANs (cont'd) • A segment is a section of a cable serving a floor or a building: • no routing of messages is required since the medium provides direct connection between all of the nodes connected to it. • Larger LANs consist of several segments. • For a LAN, total system bandwidth is high and latency is low.

34. LAN Technologies • Ethernet as a dominant technology for wired LANs; • lacks latency and bandwidth guarantees needed by multimedia applications. • ATM networks were developed to fill the gap; • their high cost inhibited their adoption for LANs. • High-speed Ethernet • is deployed in a switched mode; • overcomes drawbacks of Ethernet; • not as effective as ATM for MM data.

35. WANs • Networks connecting remote communicating entities; • lower speed between nodes; • used to connect LANs. • The communication medium is a set of communication circuits linking a set of routers- dedicated computers that • manage the communication network; • rout messages or packets to their destinations.

36. WANs (cont'd) • Routing operations introduce a delay at each point of routing; • total latency for a transmission depends on the route taken and traffic encountered. • Lower bound on latency is set by physical properties of the medium; • the speed of electronic signals in most media is close to the speed of light.

37. MANs • Network based on the high-bandwidth copper and fibre optic cabling; • installed in metropolitan areas for transmission of video, voice, or other multimedia data over distances up to 50km. • Likely to meet requirements set for LANs while connecting more distant entities. • “Last mile” technology.

38. MAN Technologies • DSL (digital subscriber line) • typically uses ATM switches located in telephone exchange to route digital data onto twisted pair; • limited range: 1.5km from the switch; • speed: 0.25-6.0Mbps. • Cable Modem • uses analog signalling over coaxial cable; • greater range than DSL; • speed: 1.5Mbps.

39. Wireless networks • Digital wireless communication technologies • WaveLAN (IEEE 802.11) • 2-11Mbps over 150m; • wireless local area network designed to replace wired LANs. • other technologies to connect mobile devices to other mobile or fixed devices in the immediate vicinity.

40. WPANs • Wireless personal area networks • infra-red links; • included in laptops and palmtops. • BlueTooth low-power radio network (www.bluetooth.com) • 1-2 Mbps over 10 m.

41. Mobile phone networks • Based on digital wireless network technologies. • Standards • GSM (global System for Mobile communications) used in Europe; • Most mobile phones in the US are based on the analog AMPS cellular radio network with CDPD (Cellular Digital Packet Data) layer over it. • Offer wide-area mobile connections to the Internet for portable devices; • low-data rates: 9.6-19.2 kbps; • successor networks are being designed for 128-384kbps over ~ km and 2Mbps for smaller cells.

42. Internetworks • A communication subsystem in which several networks are linked together to provide common data communication facilities that conceal the technologies and protocols of the individual component networks and the methods used for their interconnection. • Built upon a variety of LAN and WAN technologies; • interconnected by routers (dedicated switching computers) and gateways (general-purpose computers) • a software layer supports addressing and data transmission. • Example: the Internet.

43. Network Principles • Packet transmission. • Data streaming. • Switching schemes. • Protocols. • Routing. • Congestion control. • Internetworking.

44. Packet transmission • Message: sequence of data items (binary). • Messages are subdivided into packets of bounded size • to manage the buffer storage; • to avoid long wait for a window of sufficient size on the communications channel.

45. Data Streaming • Packet transmission is inappropriate for multimedia. • MM applications rely on the transmission of data stream at guaranteed rates with bounded latencies • QoS requirements: • bandwidth, latency, reliability; • availability of a channel from the source to the destination; • buffering where appropriate to cushion flow irregularities.

46. Data Streaming (cont'd) • ATM networks are designed to provide the necessary QoS for MM data. • IPv6 includes feature for recognition and special treatment of MM data packets.

47. Switching Schemes • Broadcast • no switching: everything is transmitted to every node; • Broadcast-based technologies: • Ethernet; • Wireless. • Circuit switching • a channel is created from the source to the destination; • telephone networks are based on circuit switching; • referred to as POST (plain old telephone system).

48. Switching Schemes (cont'd) • Packet switching, or store-and-forward • no direct channel between the source and the destination; • packets are forwarded from node to node along the route and buffered if necessary. • Frame relay • switch very small packets (frames); • switching nodes base their decisions on the first few bits of the packet; • frames are not stored at nodes but streamed through them; • basis for ATM technology.

49. Protocols • Communication protocol: a set of rules and formats; it defines a specification of • the sequence of messages exchanged; • the format of the data in the messages. • Existence of open protocols enables component-based software development. • A protocol is implemented as a pair of software modules on the sender and receiver nodes. • Examples: transport protocol (implements process-to-process channel); network protocol (handles routing).

50. Protocol Layers • Network software=hierarchy of layers. • Each layer provides a service to the layer above it and utilizes the services of the layer below. • Each layer appears to communicate directly to its peer on the other side of the network. • Each layer communicates via local procedure calls to the adjacent layers Layer n Layer 2 Layer1