1. CSCI 4550/8556 Computer Networks Comer, Chapter 15: Networking Ownership, Service Paradigm

2. Network Ownership Private network - owned by a single organization or company. Public network - owned by a common carrier (e.g., phone company).

3. Private Networks Often use LAN technology Multiple LANs in a building or campus, linked together Sometimes called an intranet.

4. Private Network Architecture Operates autonomously from other networks (e.g., Internet) Usually includes one or few closely managed external connections May restrict access at connections Example - UNO

5. Managing Private Networks The organization buys its own equipment hires its own staff to design, implement, maintain and upgrade the network is responsible for all network management

6. Extending Private Networks Large organizations may have multiple buildings or campuses The may only install cables on their own property They may contract for leased lines from a common carrier Example – United Parcel Service (UPS)

7. Public Networks Operated by common carrier May be telephone company or other organization that builds network out of leased lines Sometimes called a Public Switched Network (PSN). Multiple organizations subscribe and connect Data transits public network to other organizations Example - AT&T

8. Virtual Private Network (VPN) A VPN (Virtual Private Network) combines features of private and public networks It is limited to a single organization It uses a public network for connectivity Connections, sometimes called tunnels, connect sites Each site sees the tunnel as a point-to-point link direct to another site It cannot be accessed by other users of the public network

9. The Service Paradigm Connection-oriented similar to the telephone system. the endpoints establish and maintain a connection as long as they have data to exchange. Connectionless similar to the postal system the endpoint puts the data to send into a packet and hands it to the network for delivery.

10. Connection-Oriented Service One endpoint requests a connection from the network. The other endpoint agrees to establish the connection. The computers exchange data through the connection. The API typically provides a stream interface. A source (either endpoint) delivers a stream of data to the network. The network breaks the stream into packets for delivery. The data transmission is not necessarily continuous; like the telephone system, the connection remains in place even when no data is being transmitted. Eventually, one endpoint request the network to break the connection when the data exchange is complete.

11. Connectionless Service No connection is established prior to sending or receiving data. The source of the data adds destination information to the data and delivers it to the network. The network delivers each data item individually (note the absence of the stream API).

12. Comparison Connection-oriented accounting is easier the application can learn of network problems immediately fits the stream concept of input/output better than connectionless service Connectionless less overhead than connection-oriented the network is easier to implement

13. Connection Duration and Persistence Connections can be made on-demand or set up permanently. Switched connections or switched virtual circuits Permanent connection or provisioned virtual circuit Permanent connections Originally these were “hard-wired.” They are now configured at system initialization time. Switched connections The computer maintains a permanent connection to the network The network makes each connection on demand. Internal components are switches; network is a switched data network

14. Examples of Service Paradigms

15. Address and Connection Identifiers An address is a complete, unique identifier Connectionless delivery requires an address on each packet Connection-oriented delivery can use a shorthand that identifies the connection rather than the destination ATM - 160-bit address, 28-bit connection identifier Connection identifier includes: 12-bit virtual path identifier (VPI) 16-bit virtual circuit identifier (VCI) Connection identifier local to each computer May be different in different parts of the ATM switch

16. Network Performance Characteristics Delay – how long does it take a frame to go from the source to the destination? Throughput – how many frames can be sent to the network for delivery in a given time interval? Delay  Throughput – how much data can be present (stored) in the network?

17. Network Delay Delay is a measure of the time required for data to transit a network. It is the sum of the following individual delays: Propagation delay – the time to travel across the medium Switching delay – the time required for network components (hub, bridge, packet switch) to forward data Access delay – the time required to get control of the medium (CSMA/CD, token) Queuing delay – the time a frame is queued in packet switches

18. Throughput Throughput measures the rate at which data can be transmitted in a network 300 bps (bits per second) – old modems 1 Gbps (gigabit [10 9 ] bits per second) – typical of the fastest modern networks Bandwidth – the limit of the underlying hardware Effective throughput – the real data delivery rate

19. The Relationship Between Delay and Throughput As throughput approaches the theoretical maximum, delay usually increases. Excessive traffic causes a condition known as congestion. The effective delay, D, can often be approximated as

20. The Delay – Throughput Product This is computed as the delay time multiplied by the effective throughput. It measures the amount of data that can be present, or effectively stored, in the network. In fast networks with long delay times, a sending computer can generate large amounts of data before the destination receives the first bit

21. Summary Public vs. private networks Connection-oriented vs. connectionless service paradigms A connection identifier is a shorthand for a destination address Networks can be measured to determine Delay Throughput Delay-throughput product