1. Networks: Introduction1 Course Objectives 1.To introduce the student to the major concepts involved in wide-area networks (WANs) and local area networks (LANs). 2.To develop an understanding of modern network architectures from a design and performance perspective. 3.To expose students to some of the current technologies.

2. Networks: Introduction2 Course Objectives 4. To provide an opportunity to do network programming using TCP/IP. 5. To clarify network terminology. 6. To facilitate an understanding of the current literature.

3. Networks: Introduction3 Definitions computer network :: an interconnected collection of “autonomous” computers. [LG&W] communications network ::a set of equipment and facilities that provide a service. distributed system :: the existence of multiple autonomous computers is transparent.

4. Networks: Introduction4 t0t0 t1t1 Network Figure 1.6 Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies

5. Networks: Introduction5 12 1 11 8 4 7 2 6 9 10 14 5 13 15 3 Host B Host C Host L Host D Host E Host G Host J Host A Host H Host F Host K Host M 16 17 W TX Y Z nodes

6. Networks: Introduction6 Classifying Networks by Transmission Technology broadcast :: a single communications channel shared by all machines (addresses) on the network. Broadcast can be both a logical and a physical concept (e.g. Media Access Control (MAC) layer). multicast :: communications to a specified group. This requires a group address. (example – multimedia multicast). point-to-point :: connections made via links between pairs of nodes.

7. Networks: Introduction7 Network Classification by Size LANs {Local Area Networks} –Typically physically broadcast at the MAC layer (e.g., Ethernet, Token Ring). MANs {Metropolitan Area Networks } –campus networks connecting LANs logically or physically. –often have a backbone (e.g., FDDI, DQDB, and ATM)

8. Networks: Introduction8 (a) (b) transceivers Figure 1.17 Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies LANs

9. Networks: Introduction9 Metropolitan network A consists of access subnetworks a, b, c, d. National network consists of regional subnetworks . Metropolitan network A is part of regional subnetwork . A A Metropolitan 1* a c b d  (a) (b) 2 3 4   Figure 1.8 Copyright ©2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks

10. Networks: Introduction10 Network Classification by Size WANs {Wide Area Networks} –also referred to as “point-to-point” networks. –ARPANET  Internet –usually hierarchical with a backbone. –Enterprise Networks, Autonomous Systems –VPN (Virtual Private Networks).

11. Networks: Introduction11 UCLARANDTINKER USC NBS UCSB HARV SCD BBN STAN AMES McCLELLAN UTAHBOULDERGWCCASE CARN MITRE ETAC MIT ILL LINC RADC Figure 1.16 ARPAnet circa 1972 point-to-point network Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies

12. Networks: Introduction12 G G G G G net 1 net 2 net 3 net 4 net 5 G = gateway G Figure 1.18 Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies

13. Networks: Introduction13 Network Classification by Topology flow of data Repeater Bus

14. Networks: Introduction14 Network Classification by Topology Repeater Ring

15. Networks: Introduction15 Network Classification by Topology Headend Tree

16. Networks: Introduction16 Network Classification by Topology Star hub, switch or repeater

17. Networks: Introduction17 Performance Metrics (General Definitions) Utilization:: the percentage of time a device is busy servicing a “customer”. Throughput:: the number of jobs processed by the “system” per unit time. Response time:: the time required to receive a response to a request (round-trip time). Delay:: the time to traverse from one end to the other in a system.

18. Networks: Introduction18 Network Performance channel utilization – the average fraction of time a channel is busy [e.g. Util = 0.8] –when overhead is taken into account (i.e., excluded from useful bits, channel utilization is often referred to as channel efficiency throughput – bits/sec. successfully transmitted [e.g. Tput = 10 Mbps]

19. Networks: Introduction19 Network Performance end-to-end packet delay :: the time to deliver a packet from source to destination. {most often we are interested in the packet delay within the communications subnet} This delay is the sum of the delays on each subnet link traversed by the packet. Each link delay consists of four components [Bertsekas and Gallager]:

20. Networks: Introduction20 Packet Delay 1.The processing delay [PROC] between the time the packet is correctly received at the head node of the link and the time the packet is assigned to an outgoing link queue for transmission. 2.The queueing delay [QD] between the time the packet is assigned to a queue for transmission and the time it starts being transmitted. During this time, the packet waits while other packets in the transmission queue are transmitted.

21. Networks: Introduction21 Packet Delay 3.The transmission delay [TRANS] between the times that the first and last bits of the packet are transmitted. 4.The propagation delay [PROP] between the time the last bit is transmitted at the head node of the link and the time the last bit is received at the tail node. This is proportional to the physical distance between transmitter and receiver.

22. Networks: Introduction22 End-to-End Packet Delay end-to-end packet delay = sum of ALL link packet delays. Be Careful !! end-to-end can be defined either from Host-to-Host or only within the subnetwork. Link packet delay = PROC + QD + TRANS + PROP.