TCOM 509 – Internet Protocols (TCP/IP) Lecture 02_a

1. TCOM 509 – Internet Protocols (TCP/IP)Lecture 02_a Instructor: Dr. Li-Chuan ChenDate: 09/08/2003 Based in part upon slides of Prof. J. Kurose (U Mass), Prof. B. Yener (Rensselaer Polytechnic Institute)

2. Outline • Chapter 2.1 – 2.6 • Packet switching, circuit-switching • WAN, LAN • LAN Technologies • Ethernet • FDDI • ATM • Chapter 4

3. router workstation server mobile local ISP regional ISP company network What is Internet? • The Internet is a technology of interconnecting computing devices via routers in the communication networks through out the world. • Communication networks consist of nodes and communication links. • Computing devices are nodes or end-systems (e.g., PCs, workstations, servers, phones) running network applications. • Communication links • fiber, copper, radio, satellite • Routers forward packets. Source:Computer Networking: A Top Down Approach Featuring the Internet, 2nd edition.

4. network edge: applications and hosts network core: routers network of networks access networks, physical media: communication links A closer look at network structure: Source:Computer Networking: A Top Down Approach Featuring the Internet, 2nd edition.

5. end systems (hosts): run application programs(e.g. Web, email) at the“edge of network” client/server model client host requests, receives service from always-on server(e.g. Web browser/server; email client/server) peer-peer model: minimal (or no) use of dedicated servers The network edge Source:Computer Networking: A Top Down Approach Featuring the Internet, 2nd edition.

6. Network Core • Mesh of interconnected routers • They are either packet switched or circuit switched Source:Computer Networking: A Top Down Approach Featuring the Internet, 2nd edition.

7. Network Core: Circuit Switching • Reserved bandwidth • Call setup required • Guaranteed performance Source:Computer Networking: A Top Down Approach Featuring the Internet, 2nd edition.

8. Packet Switching: Routing • Goals: move packet from source to a router, and from one router to another until reaching the destination. • Datagram network • Destination address determines next hop • Routing can change during the session • Analogy: driving, traffic, take another route Source:Computer Networking: A Top Down Approach Featuring the Internet, 2nd edition.

9. Access Network and Physical Media • Residential Network • Dial up (up to 56Kbps) • ADSL (asymmetric digital subscriber line) • 1.5M – 9Mbps downstream traffic, 64K–1.5M upstream • typical 384K-768K for downstream, 128K-384K for upstream • Cable Modem • up to 40 Mbps. • typical 1-3 Mbps downstream traffic, 250 Kpbs to 2.5 Mpbs upstream. • Wireless Access • Institutional Access (school, company) Source:Computer Networking: A Top Down Approach Featuring the Internet, 2nd edition.

10. Physical Media • Guided media • Copper (twisted pair, co-axial cable) • Fiber links • Unguided media • Radio (microwave, wireless LAN, satellite etc.) Source:Computer Networking: A Top Down Approach Featuring the Internet, 2nd edition.

11. Network Communication Two switching mechanisms: • Circuit-switching • Packet-switching Circuit-switching • connection-oriented technology. • dedicated communication connection between endpoints • use synchronous TDM scheme and provides fixed rate (64 kbps for voice). • designed for voice and used in telephone networks. • pros: provides guarantee bandwidth. • cons: inefficient bandwidth, i.e. you pay even when no one is talking.

12. Network Communications Packet Switching • Computers use packet-switching networks to send data. • Data are divided into packets. • Each packet carries headers to identify the destination and is routed inside the network. • Communication links are shared among computers. • pros: more efficient in utilization, flexibility • cons: longer network delay. As load increases, congestion occurs at the routers.

13. Circuit Switching vs. Packet Switching • Circuit switching • dedicated path, fixed bandwidth • call setup, messages are not stored, data arrives same order as sent. • no overhead once the path is setup. • overload may block call • good for sending large data. • Packet switching • no dedicated path, dynamic bandwidth • no call setup, packets are stored and forward, and delay, data may arrive out of order. • overhead needed for routing info • overload increases packet delay • good for sending small data.

14. Network Types • WANs (Wide Area Networks) • span large geographical distances, e.g., continent • operate at slower speed,1.5M - 155 Mbps • greater delay, < several tenths of sec • e.g., X.25, Arpanet, ISDN, Frame Relay • LANs (Local Area Network) • spans a single building or campus • provide highest speed connections among computers at 10M-2Gbps • lower delay, < 10 ms • e.g., Ethernet, Token Ring, Gigabit Ethernet

15. WAN vs. LAN Scalability • LANs are not scalable – cannot connect many computers at arbitrary sites. • A WAN is scalable - capable of connecting many sites spread across geographical distances with many computers at each site. Performance • WANs are usually slower than LANs. Cost • WANs are much more expensive than LANs. • WANs are usually owned/operated by large public companies

16. Ethernet Technology • Ethernet is the most popular local area network (LAN) technology. • Standardized by Xerox, DEC and Intel in 1978 • Original Ethernet consists of a coaxial cable (ether). • The ether is completely passive, all active electronic components that make up the network function are associated with computers that attach to the network.

17. Ethernet Technology • Thick Ethernet or 10Base5 (IEEE 802.3) • max. distance is 500 meters (m) per segment, up to 200 transceivers, at least 2.5 m between transceivers. • Thin Ethernet (thinnet) or 10Base2 • Cheaper, but max. distance is 200 m. • Differ only in electrical connection characteristics, not protocol. • Twisted-pair Ethernet or category 5 • Cheapest and easiest to install. Max distance is 100 m.

18. Ethernet 0.5” diameter Thick Ethernet cable(10Base5) transceiver AUI cable transceiver mux AUI cables Time

19. Thinnet & Hubs 0.25” diameter Thin Ethernet cable(10-Base2) BNC connector terminator Twisted-pair Ethernet (10Base-T) Category 5 cable hub < 100 meter RJ45 connector

20. Variants of Ethernet • Ethernet • up to10 Mbps • Fast Ethernet or 100Base-T • up to 100 Mbps. • Dual-speed Ethernet or 10/100 Ethernet • either 10 or 100 Mbps (auto detects). • Gigabit Ethernet or 1000Base-T • up to 1 Gbps • All of the above Ethernet technologies use the same packet format and maximum packet size.

21. Properties of Ethernet • Broadcast bus technology with best-effort delivery. • All stations in the network read each packet. • Protocol: carrier sense multiple access with collision detect (CSMA/CD) • listen before sending packets (carrier sense), stops when someone is using. • when both stations by chance transmit at the same time (collision occurs by comparing data), use an exponential random time delay before retransmit.

22. Ethernet Hardware Addresses • Each host is assigned a 48-bit integer known as Ethernet address (hardware address, or physical address). • Ethernet addresses are associated with the Ethernet interface card. • IEEE distributes the unique Ethernet addresses to the manufacturers. • Each interface receives a copy of every packet, the interface filters packets based on the destination address field.

23. Ethernet address • 48-bit Ethernet address specify • physical address of one network interface • network broadcast address • a multicast address • When machine boots, the OS initializes the Ethernet interface giving it a set of addresses to recognize. • A host interface usually accepts the following packets • those addressed to the interface’s unicast physical address. • network broadcast address (all 1’s) • multicast group address

24. Ethernet Frame Format 4 bytes 8 bytes 6 bytes 6 bytes 2 bytes 46 - 1500 bytes CRC Frame type - identifies type of data being carried. Also called self-identifying frames Dest. address Source address Preamble: alternating 0s and 1s to help receiving nodes synchronize (not part of Ethernet Frame) • minimum frame size: 64 octets • maximum frame size: 1518 octets • header size: 18 (6+6+2+4) octets Example: B9.5C.01.88.FE.52

25. Example of Ethernet Frame Type

26. Repeaters and Bridges Repeater • Operates at layer 1 (physical layer). • Used to restore (amplify or regenerated if digital signal) the electrical signals and relay them from one cable to another with the same physical characteristics • Works at layer 1 (physical) • Connect segments of a LAN together. Extends Ethernetfrom 500 m to 1000 m. At most two repeaters can be placed between any two transceivers (host machines). • Why not use repeaters to extend Ethernet indefinitely? CSMA/CD requires low delay and can’t support long medium. A repeater also propagates noise. Bridge • Operates on frames rather than signals. • Works at layer 2 (data link) • Performs frame filtering, i.e. forward only if necessary and does not forward noise, errors, or malformed frames. • Make larger networks by connecting arbitrary number of Ethernets together with bridges. • adaptive or learning bridges make intelligent decisions about which frames to forward. • Multiple Ethernet segments connected by bridges & repeaters act as single physical network system.

27. FDDI and ATM Fiber Distributed Data Interconnect (FDDI) • Data rate of 100 Mbps, up to 100 km in length. • Use optical fibers for backbone networks. • Token ring technology • Large frame size - up to 4500 octets. • Efficient for large file transfer.

28. FDDI and ATM Asynchronous Transfer Mode (ATM) • Data rate of Gbps at the ATM network, and 155 Mbps between user’s PC and ATM network. • Scalable: Use optical fibers for both LANs and WANs. • Designed for multimedia (data, audio, and video) transmission. • Packet switching with connection-oriented service. • Fixed packet size of 53 octets, called a cell, with 5 octets of header size. • Efficient due to its fixed packet size, but expensive.