1. 1 Fall 2005 Network Characteristics: Ownership, Service Paradigm, Performance Qutaibah Malluhi CSE Department Qatar University

2. 2 Network Characteristics  Previously we classified the Network based on its size –WAN, MAN, and LAN  Other important characteristics –Network ownership –Type of service –Performance

3. 3 Network Ownership  Private network - owned and operated by single organization or company  Public network - owned and operated by common carrier (e.g., phone company)

4. 4 Private Networks  Often LAN technology  Multiple LANs in a building or campus, linked together  Sometimes called intranet  Large organizations may have multiple widely distributed buildings or campuses –Can only install cables on own property –Otherwise, dedicated lines are leased from common carrier  Private network management –Organization buys own equipment and is responsible for all network management –Hires staff to design, implement, maintain and upgrade network

5. 5 Public Networks  Analogous to telephone system  Run as a service available to subscribers  Operated and managed by the service provider –Service provider may own the lines or may use leased lines  Public networks are mostly large WANs  Universal communication: Allow a subscriber to communicate with any other subscriber  Public networks allow private communication between two subscribers or a group of subscribers

6. 6 Virtual Private Network (VPN)  Allows building a private network over a public network –Creates the illusion of a private network over a public network  Use hardware and/or software devices on each site –Devices restrict incoming and outgoing access only to specified sites –Use cryptography techniques for creating what is called a tunnel between the two sites –Encryption guarantees absolute privacy  Connections, sometimes called tunnels, connect sites –Each site sees tunnel as point-to-point link direct to another site

7. 7 VPN Protocols  L2TP: Layer 2 Tunneling protocol –Layer 2 (Data Link layer) Protocol –Microsoft support –Extension of the Internet standard Point-to-Point protocol (PPP) »link layer protocol used to transmit IP packets over serial links  PPTP: Point-to-Point Tunneling Protocol –Layer 2 (Data Link layer) Protocol –Not limited to IP networks (unlike L2TP) –Microsoft, Cisco, and others support –More secure than L2TP  IPSec: IP Security –Layer 2 (Network layer) Protocol –Mostly used for site-to-site VPN (rather than computer to computer or computer to site) »Client requires IPSec software  SSL: Secure Socket Layer –Layer 5 (Session layer) Protocol –Web browser can be the client (no need for client software) –Limit the applications to those running inside the browser

8. 8 Service Paradigm  Connection-oriented –Similar to telephone system; endpoints establish and maintain a connection as long as they have data to exchange  Connectionless –Similar to postal system; endpoint puts data to send into a packet and hands the packet to the network for delivery

9. 9 Connection Oriented Paradigm  One endpoint requests connection from network  Other endpoint agrees to connection  Computers exchange data through connection  Data transmission not necessarily continuous; like telephone, connection remains in place while no data transmitted  One endpoint request network to break connection when transmission is complete

10. 10 Connection Oriented  Typically stream interface –Source delivers stream of data to network –Network breaks into packets for delivery –No packet boundaries – Receiver may receive a block of 100 bytes even thought the sender may have sent 25, 50, 25 chunks. –Notice that it is only a connection-oriented interface »The network at the lower level may still divide data into packets. The interface hides data packets.  Can also provide message interface –Data is delivered in defined chunks  Support continuous (e.g., video and audio) or bursty traffic –Connection stays on when no data is being sent in bursty traffic  Connection duration –Permanent: persists over months or years –Switched: established and created quickly and dynamically

11. 11 Connectionless Paradigm  No connection necessary  Source of data adds destination information to data packets and passes packets to network  Network delivers each data item (packet) individually and independently  Need destination address with every packet –In connection oriented networks, need destination address at connection establishment only. Connection id (smaller than full address) is needed with every transmission.

12. 12 Comparison of Service Paradigms  Connection-oriented –Easier accounting –Application can learn of network problems immediately –More expensive – charged for open connection even if you are not using it  Connectionless –No overhead for establishing connection –Need only be charged by actual usage –Easier to implement network

13. 13 Examples of Service Paradigms

14. 14 Network Performance Criteria  Delay  Throughput  Delay-throughput product  Jitter

15. 15 Network Delay  Delay is measure of time for data to transit network –How long it takes a bit to travel from point A to point B  Delay components –Fixed components »Propagation delay - time to travel across medium »Switching delay - time for network component (hub, bridge, packet switch) to forward data –Variable Components »Access delay - time to get control of medium (CSMA/CD, token) »Queuing delay - time queued in packet switches  Intuition: “length” of the pipe

16. 16 Throughput  Throughput measures rate at which data can be transmitted in network (bits per second) –300 bps (bits per second) - old modems –1 gbps (gigabit [109] bits per second) – among the fastest today  Bandwidth – sometimes use as synonym to throughput –Related to underlying hardware  Effective throughput - real data delivery rate –Consider packet headers for example  Sometimes people use speed as a synonym of throughput –Measure of capacity –Intuition: “width” of the pipe –Consider width of highway versus speed limit of the highway

17. 17 Throughput and Delay  Throughput and delay are not independent –Queuing delay increases with network load –As throughput approaches theoretical maximum, delay increases  Excessive traffic known as congestion  Network utilization is the ratio between throughput and maximum capacity  Effective delay, D, can be approximated: –D = D0 / (1 - U) –D0 is delay when network is idle –U is a value between 0-1 denoting network utilization  Practical consequence: Any network that operates with a utilization approaching 100% of capacity is doomed. –Maintain utilization below a threshold (e.g. 50%, 70%)

18. 18 Delay-Throughput product  Computed as delay time multiplied by effective throughput  Measures amount of data that can be present in the network  In fast networks with long delay times, sending computer can generate large amounts of data before destination receives first bit

19. 19 Jitter  Variance in delay  Important for real time transmission (e.g., audio/video)

20. 20 Summary  Network can be –Public –Private  Virtual Private Network –Uses public network to connect set of private sites  Networks are –Connectionless –Connection-oriented  Network Performance Measures –Delay –Throughput –Delay X Throughput –Jitter Delay and throughput interaction