1. COP 4930 Computer 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 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) 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) fig. 16.2fig. 16.2  Each frame is nested in next one, from lower layer of stack (fig. 16.4) fig. 16.4fig. 16.4  Each layer at destination receives frame sent from corresponding layer at origin (fig. 16.5) fig. 16.5fig. 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