Transcript ppt3
COP 4930 Computer Network Projects Summer C 2004 Prof. Roy B. Levow Lecture 3 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 ™ Network Analyzer.2 Interface operates in promiscuous mode Can also be implemented in software – Ethereal http://www.ethereal.com Packet Switching Packet switch is basic switching element of wide-area networks (WAN) Has multiple network interfaces Connects to – Communication lines – Networks – LANs – Computers 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 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 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 Protocols Protocol defines an interaction between two entities Specifies the format and meaning of messages Application program interacts with software that implements a protocol 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) 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 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) 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 Replay Delayed, duplicated packets arrive after end of session – Include session ID 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 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 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 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 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 Classless Internet-Domain Routing CIDR Uses netmask to define network