COP 4930 Computer Network Projects

1. COP 4930Computer Network Projects Summer C 2004 Prof. Roy B. Levow Lecture 3

2. Network Analyzer • Captures, analyses, and reports on all packets at point of attachment to the network • Decodes packets to reveal contents • Can capture all packets or only selected ones • Also known as • Network monitor • Packet analyzer • Network sniffer ™

3. Network Analyzer.2 • Interface operates in promiscuous mode • Can also be implemented in software • Ethereal • http://www.ethereal.com

4. Packet Switching • Packet switch is basic switching element of wide-area networks (WAN) • Has multiple network interfaces • Connects to • Communication lines • Networks • LANs • Computers

5. Packet Switching.2 • Processing at switch • Arriving packet is stored in buffer • Destination address is read • Packet is placed on output queue for next hop to destination • Packet is sent

6. Packet Routing • Hierarchical Addressing • Address is split into two parts • Network identifier • Host identifier • In tcp/ip, net mask indicated bits in network portion of address • Packet switching uses only network address except at destination

7. Packet Routing • Next-Hop Forwarding • Switch only needs to know next step to destination • Routing table • Matches network with outgoing link • Many different ways table can be set and updated

8. Protocols • Protocol defines an interaction between two entities • Specifies the format and meaning of messages • Application program interacts with software that implements a protocol

9. Protocol Suites • Totality of issues are divided into component protocols that work together • Conventional design is layered • Each protocol communicates directly only with those directly above and below • TCP/IP layers (fig. 17.4)

10. TCP/IP Layers 1: Physical – network hardware 2: Network Interface – how frames are formatted and transmitted over the network 3: Internet – how packets are sent across an internet 4: Transport – assures reliable transport 5: Application – interface to applications

11. Protocol Stack • Software at each layer interacts only with adjacent layers (fig. 16.2) • Each frame is nested in next one, from lower layer of stack (fig. 16.4) • Each layer at destination receives frame sent from corresponding layer at origin (fig. 16.5)

12. Sequencing • Adding sequencing numbers to frames allows detection and handling of a variety of error situations • Out-of-order delivery • Duplicate detection and deletion • Recognizing packet loss and prompting retransmission • Send positive acknowledgement (ACK) or negative ack (NAK) with frame number

13. Replay • Delayed, duplicated packets arrive after end of session • Include session ID

14. Flow Control • Data Overrun occurs if data arrives faster than it can be processed • Sliding window • Allows only a limited number of unacknowledged frames in transmission • Sender and receiver agree on a window size, which may be changed by receiver during session

15. Network Congestion • Problem of routers when incoming data, usually from several sources, exceeds outgoing capacity • Congested node sends control messages back requesting that data be sent at a slower rate

16. Internetworking • Provides the ability a collection of different networks as a single network • The networks can run different protocols at the network interface and physical layers • Internally they can be structured entirely differently

17. IP Addressing • Unique 32-bit (4-octet) address for each node • Address space was partitioned into networks of various classes • Class defines the number of nodes the network can support

18. Subnetworks • Network differentiation is enhanced by the use of netmasks • Each network has a network address and netmask that specifies the bits of the IP address that identify that network

19. Classless Internet-Domain Routing CIDR • Uses netmask to define network