CS1302_NOV07

NOV/DEC-�07/CS1302-Answer Key

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B.E/B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2007. Sixth Semester

(Regulation 2004) Electronics and Communication Engineering

CS1302 � COMPUTER NETWORKS - ANSWER KEY

Part : A 1. Differentiate between Logical Address and Physical Address. Logical Address Physical Address (a) It is a 32 bit address (IP v4). 128 bit

address for IP V6. It is a 48 bit address.

(b) It is not permanent, it can be changed when a system moves from one area to another.

It is a permanent one.

(c) It is assigned by an ISP in case of public IP or assigned by network administrator in case of private IP address.

It is assigned by the manufacturer and embedded in the hardware itself.

(d) Used to identify a system uniquely in a network. Routing is performed based on this address.

Link level routing is performed by resolving the IP address to physical address.

2. What is dial up modem technology? List any two of the common modem standard. Dial up modem is used for transmitting data over telephone lines. They act as modulator and demodulator device which converts the binary data to bandpass analog signal and recovers the binary data from the modulated signal. The common modem standards are V.32, V.32 bis, V.34bis, V.90, V.92. 3. Mention the advantages of cyclic codes?

Cyclic codes give very good performance in detecting single bit errors, double errors, an odd number of errors and burst errors.

They can easily be implemented in hardware and software. They are especially fast when implemented in hardware. In a cyclic code if a codeword is cyclically shifted, the result is another code. Cyclic codes can be created to not only to check errors but also to correct errors.

4. What do you mean by Automatic Repeat Request (ARQ)? Error control in the data link layer is based on Automatic repeat request (ARQ), which is done by retransmitting the data in the following 3 cases:

a) Damaged frame b) Lost frame c) Lost acknowledgment.

5. List out the advantages of IPV6.

(a) Has larger address space (128 bits as compared to IPV4 32 bits) (b) Has flexible header format. (c) Has extended address hierarchy. (d) Has improved options which are not available in IPV4. (e) It supports for auto-configuration and renumbering. (f) Support for resource allocation.

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6. What is the broadcast and multicast address for Ethernet? The Internet assigned numbers authority (IANA) allocates number from 01: 00: 5E: 00: 00: 00 through 01:00:5E:7F:FF:FF for Ethernet multicasting. This means there are 23 bits available for the multicast group ID. The Ethernet address for broadcasting is FF:FF:FF:FF:FF:FF.

7. Identify the source port number and destination port number from the following dump

of a UDP header in hexadecimal format. 06 32 00 0D 00 1C E2 17 Source port number - 1586 Destination Port Number - 13 8. Define choke packet. A choke packet is a packet sent by a router to the source to inform it of congestion. This type of control is similar to ICMP�s source quench packet. 9. What kinds of file types can FTP transfer?

A FTP can transfer ASCII file, ABCDIC file and Image file.

10. What is Asymmetric � key cryptography? It is a form of cryptography in which encryption and decryption are performed using two different keys, one of which is referred to as the public key and one of which is referred to as the private key. This is also called as public-key encryption.

Part B

11.(a) Discuss about any two guided transmission media and unguided transmission media in detail with suitable diagram.

Computers and other telecommunication devices use signals to represent data. These signals are transmitted from one device to another in the form of electromagnetic energy. These electromagnetic signals can travel through vaccum, air or other transmission media.

Guided Transmission Media : Coaxial Cable

Pair of conductors separated by insulation


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Offers longer distances and better speeds than twisted pair, due to better shielding. Used for cable TV and local-area networks. Had been widely used in telephone systems,

but optical fibre is now assuming this task.

Baseband Coaxial Cable : 50-ohm cable, commonly used for digital transmission. Broadband Coaxial Cable : 75-ohm cable, commonly used for analog transmission. Coaxial Cable consists of 2 conductors. The inner conductor is held inside an insulator with the other conductor woven around it providing a shield. An insulating protective coating called a jacket covers the outer conductor. The outer shield protects the inner conductor from outside electrical signals. The distance between the outer conductor (shield) and inner conductor plus the type of material used for insulating the inner conductor determine the cable properties or impedance. Typical impedances for coaxial cables are 75 ohms for Cable TV, 50 ohms for Ethernet Thinnet and Thicknet. The excellent control of the impedance characteristics of the cable allow higher data rates to be transferred than Twisted Pair cable. GUIDED MEDIA : OPTICAL FIBER:

Three components: light source, transmission system, and a detector The detector generates an electric pulse when hit by light 1-a pulse of light; 0-missing pulse of light. optical rays travel in glass or plastic core

When light move from one medium to another it bend at the boundary. The amount of bending depends on the properties of the media.

Light at shallow angles propagate along the fibre, and those that are less than critical angle are absorbed in the jacket

The cladding is a glass or plastic with properties that differ from those of the core Used in long distance communication, in locations having small amount of space, and with

reduction in price is starting to get also to LANs. Not affected by external electromagnetic fields, and do not radiate energy. Hence,

providing high degree of security from eavesdropping. Provide for multimode of propagation at different angles of reflections. Cause signal

elements to spread out in time, which limits the rate in which data can be accurately received.


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Reduction of the radius of the core implies less reflected angles. Single mode is achieved with sufficient small radius.

A multimode graded index transmission is obtained by varying the index of reflection of the core to improve on the multi mode option without resolving to the cost of single mode. (index of reflection=speed in vacuum / speed in medium.) .

UNGUIDED TRANSMISSION MEDIA: WIRELESS We have 3 types of wireless communication : Radio wave, Microwave and Infrared. Radiowave : Electromagnetic waves ranging in frequencies between 3 KHz and 1 GHz are normally called radio waves. Radio waves are mostly omni directional it. They are propagated in all directions and the sending and receiving antennas are not to be aligned. Good for long distance broadcasting such as AM radio, television and paging systems. Microwave: Waves ranging in frequencies between 1 and 300 GHz are called microwaves. Microwaves are unidirectional and the sender and receiver antennas need to be aligned. Repeaters are needed for long-distance communication. 11 (b) (i) Explain ISO/OSI reference model in detail with suitable example.

OSI model is nothing but the open systems interconnection(osi)model. Control is passed from one layer to the next, starting at the application layer in one station, proceeding to the bottom layer, over the channel to the next station and back up the hierarchy Application(Layer 7):

This layer supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer. Presentation(Layer 6):

This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.


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Session(Layer 5):

This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination. Transport(Layer 4):

This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer. Network(Layer 3):

This layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling, congestion control and packet sequencing. Data Link(Layer 2):

At this layer, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sublayers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sublayer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control and error checking. Physical(Layer 1): This layer conveys the bit stream - electrical impulse, light or radio signal -- through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.


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11(b) (ii) Briefly discuss about any two recent modem standards in detail.

Modem (from modulate and demodulate) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems can be used over any means of transmitting analog signals, from driven diodes to radio. Modems are generally classified by the amount of data they can send in a given time, normally measured in bits per second, or "bps". They can also be classified by Baud, the number of distinct symbols transmitted per second; these numbers are directly connected, but not necessarily in linear fashion.

V.21 V.22 V.22bis

Voice-band modems generally remained at 300 and 1200 bit/s (V.21 and V.22) into the mid 1980s, although, over this period, the acoustic coupler disappeared, seemingly overnight, as Smart modem-compatible modems flooded the market. A V.22bis 2400-bit/s system similar in concept to the 1200-bit/s Bell 212 signaling was introduced in the U.S., and a slightly different, and incompatible, one in Europe. By the late 1980s, most modems could support all of these standards, and 2400-bit/s operation was becoming common.

V.32

Echo cancellation was the next major advance in modem design. Local telephone lines use the same wires to send and receive, while longer distances use separate wires for the two directions. A small amount of the outgoing signal bounces back. This signal can confuse the modem: is the signal it is "hearing" from the remote modem, or its own transmission bouncing back? This was why earlier modems split the signal frequencies into answer and originate; each modem simply didn't listen to its own transmitting frequencies. Even with improvements to the phone system allowing higher speeds, this splitting of available phone signal bandwidth still imposed a half-speed limit on modems. Echo cancellation got around this problem. Measuring the echo delays and magnitudes allowed the modem to tell if the received signal was from itself or the remote modem, and create an equal and opposite signal to cancel its own. Modems were then able to send at "full speed" in both directions at the same time, leading to the development of the 9600 bit/s V.32 standard.

12.(a) What is the purpose of stop and wait protocol? Discuss it�s design with sender and receiver side algorithm.

Stop and wait protocol is one of the three mechanism used for flow and error control at data link layer level. It is the simplest among all the three mechanisms. Sender side design Sender keeps a copy of the last frame transmitted until it receives an acknowledgement for that frame. It allows the sender to retransmit lost or damaged frames until they are received correctly at the other end. For identification both data frames and acknowledgement frames are numbered alternately 0 and 1. A data 0 frame is acknowledged by an ACK 1 frame indicating that the receiver has received data frame 0 and expecting frame 1. Sender has a control variable S that holds the number of the recently sent frame (0 or 1). The sender starts a timer when it sends a frame. If an ACK s not received within an allotted time period, the sender assumes that the frame was lost or damaged and resends it. Receiver side design Receiver sends only positive ACK for frames received safe and sound; it is silent about the frames damaged or lost. The receiver has a control variable, which we call R that holds the number of the next frame expected (0 or 1). If the receiver receives a frame that is out of


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order (i.e. 0 instead of 1 or 1 instead of 0), it knows that a frame is lost and it discards the out-of-order received frame.

12 (b) (i) Explain the MAC layer frame format in detail with suitable frame design.

The IEEE 802.3 standard defines a basic data frame format that is required for all MAC implementations, plus several additional optional formats that are used to extend the protocol's basic capability. The basic data frame format contains the seven fields shown in Figure below:

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Preamble (PRE)�Consists of 7 bytes. The PRE is an alternating pattern of ones and zeros that tells receiving stations that a frame is coming, and that provides a means to synchronize the frame-reception portions of receiving physical layers with the incoming bit stream.

� Start-of-frame delimiter (SOF)�Consists of 1 byte. The SOF is an alternating pattern of ones and zeros, ending with two consecutive 1-bits indicating that the next bit is the left-most bit in the left-most byte of the destination address.

� Destination address (DA)�Consists of 6 bytes. The DA field identifies which station(s) should receive the frame. The left-most bit in the DA field indicates whether the address is an individual address (indicated by a 0) or a group address (indicated by a 1). The second bit from the left indicates whether the DA is globally administered (indicated by a 0) or locally administered (indicated by a 1). The remaining 46 bits are a uniquely assigned value that identifies a single station, a defined group of stations, or all stations on the network.

� Source addresses (SA)�Consists of 6 bytes. The SA field identifies the sending station. The SA is always an individual address and the left-most bit in the SA field is always 0.

� Length/Type�Consists of 2 bytes. This field indicates either the number of MAC-client data bytes that are contained in the data field of the frame, or the frame type ID if the frame is assembled using an optional format. If the Length/Type field value is less than or equal to 1500, the number of LLC bytes in the Data field is equal to the Length/Type field value. If the Length/Type field value is greater than 1536, the frame is an optional type frame, and the Length/Type field value identifies the particular type of frame being sent or received.

� Data�Is a sequence of n bytes of any value, where n is less than or equal to 1500. If the length of the Data field is less than 46, the Data field must be extended by adding a filler (a pad) sufficient to bring the Data field length to 46 bytes.


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� Frame check sequence (FCS)�Consists of 4 bytes. This sequence contains a 32-bit cyclic redundancy check (CRC) value, which is created by the sending MAC and is recalculated by the receiving MAC to check for damaged frames. The FCS is generated over the DA, SA, Length/Type, and Data fields.

12(b) (ii) Write note about sliding window protocol in detail

Sliding Window Protocol is a bi-directional data transmission protocol used in the data link layer (OSI model) as well as in TCP (transport layer of the OSI model). It is used to keep a record of the frame sequences sent and their respective acknowledgements received by both the users.

In transmit flow control, sliding window is a variable-duration window that allows a sender to transmit a specified number of data units before an acknowledgment is received or before a specified event occurs.

An example of a sliding window is one in which, after the sender fails to receive an acknowledgment for the first transmitted frame, the sender "slides" the window, i.e. resets the window, and sends a second frame. This process is repeated for the specified number of times before the sender interrupts transmission. Sliding window is sometimes (loosely) called acknowledgment delay period. The purpose of the sliding window is to increase throughput

At any instant of time, the sender maintains a set of sequence numbers which correspond to the frames it is permitted to send. Such frames are said to be a set of the sending window. Similarly, the receiver also maintains a receiving window which indicates the set of frames it is allowed to receive. 13(a) (i) What do you mean by sub-netting and masking? Explain them in detail with

suitable example. In subnetting , a network is divided into several smaller subnetworks with each subnetwork having its own subnetwork address. Router takes routing decision based on the network address and subnetwork address. A 32 bit number called the mask is used to extract the network address by doing AND operation with the IP address and the mask. For example a router outside the organization receives a packet with IP address 175.10.2.1. By seeing the first octet, the router will know that it is a Class B address and will use a default mask of 255.255.0.0 to find the network address. While doing AND operation with 175.10.2.1 and 255.255.0.0 we will get 175.10.0.0 which is the network address and with this the routing decision is taken by the router. 13(a) (ii) How to map the logical address into physical address? Explain it in detail with an example. We have two types of address mapping : Static and Dynamic. In static mapping a table is created where the IP address associates with a MAC address. This table is stored in each machine on the network. In dynamic mapping each time a machine knows one of the two address, it can use a protocol to find the other one. Two protocols are designed for this purpose are ARP and RARP. The first one maps an IP address to a MAC address; the second maps a MAC address to an IP address. For example System A having IP address 193.4.1.1. and MAC address 0A:23:45:01:12:01 wants to send data to system N whose IP address is 193.4.1.100. System needs to pass the packet to its


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data link layer for the actual delivery, but it does not know the physical address of the system. So it uses the services of ARP to send a broadcast request packet to ask for the physical address of a system with an IP address 193.4.1.100. This broadcast is received by all the systems on the physical network ie. 193.4.1.x. System N will only answer for this broadcast with its physical address. Now A can send its data. 13 (b) (i) Briefly discuss about link state routing in detail with suitable example. Each router sends information about its neighborhood to every other router

Link cost is usually a weighted sum of various factors e.g. traffic level, security level, packet delay Link cost is from a router to the network connecting it to another router. when a packet is in a LAN (which is typically a broadcast network), every node �including

the router �can receive it . Routers share information by advertising, which means sending link-state packets. Every router builds a link-state packet and floods it through the network, so when all such

packets have been received at a router, it can build its link-state database. Assuming that every router receives the same set of link-state packets (as if the routers

were synchronized),every router builds the same link-state database. Using this database, each router can then calculate its routing table.

To calculate its routing table, a router uses Dijkstra�s Shortest-Path algorithm

First, identify all link costs in the network: either from the link-state database, or using the fact that the cost of any link from a network to a router is 0.

This algorithm builds a shortest-path spanning tree for the router such a tree has a route to all possible destinations, and no loops.

The router running the algorithm is the root of its shortest-path spanning tree. Even if all routers� link-state databases are identical, the trees determined by the routers

are different (since the root of each tree is different) A node is either a network or a router; nodes are connected by arcs. The algorithm keeps track of 2 sets of nodes and arcs �Temporary and Permanent.


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Initially, the Temporary set contains all neighbor nodes of the router itself, and the arcs connecting them to the router; only the router is initially Permanent.

When all nodes and arcs are in the Permanent set, the algorithm has terminated. Identify the Temporary node whose arc has the lowest cumulative cost from the root: this

node and arc are moved into the Permanent set. Any nodes which are connected to the new Permanent node and are not already in the

Temporary set, along with the connecting arcs, are made Temporary. Also, if any node already in the Temporary set has a lower cumulative cost from the root

by using a route passing through the new Permanent node, then this new route replaces the existing one

Repeat until all nodes and arcs are Permanent. 13(b)(ii) Write short note about routing table and router.

A router is a hardware component used to interconnect networks. A router has interfaces on multiple networks. Router forwards packets between networks. To make forwarding decision a router needs to keep a routing table. A routing table contains information about the network address, the cost, the address of the

next hop and so on which are needed to route a packet.

14. (a) (i) Mention the responsibilities of Transport layer. The transport layer is responsible to ensure messages are delivered error-free, in sequence, and with no losses or duplications. It relieves the higher layer protocols from any concern with the transfer of data between them and their peers. The size and complexity of a transport protocol depends on the type of service it can get from the network layer. For a reliable network layer with virtual circuit capability, a minimal transport layer is required. If the network layer is unreliable and/or only supports datagrams, the transport protocol should include extensive error detection and recovery. The transport layer is responsible to provide:

Message segmentation: accepts a message from the (session) layer above it, splits the message into smaller units (if not already small enough), and passes the smaller units down to the network layer. The transport layer at the destination station reassembles the message.

Message acknowledgment: provides reliable end-to-end message delivery with acknowledgments.

Message traffic control: tells the transmitting station to "back-off" when no message buffers are available.

Session multiplexing: multiplexes several message streams, or sessions onto one logical link and keeps track of which messages belong to which sessions (see session layer).

14 (a) (ii) Compare connection oriented protocol and connectionless protocol.

A connection oriented protocol involves a connection or session between the endpoints. In other words, each host is aware of the other and can maintain information about the state of communication between them. The connection needs to be initialized and destroyed. The shared state that is possible with a connection-oriented protocol is essential to a reliable protocol. In particular, the notion of a sequence number or serial number is a practical necessity, if not a theoretical necessity.

A connectionless protocol does not involve a connection or session between the endpoints. So need to initialize or destroy the connection. It just send packets to the destination as and when data is ready.


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14(a) (iii) Discuss briefly about UDP. UDP is a connectionless, unreliable protocol that has no flow and error control. It uses port numbers to multiplex data from the application layer.

The calculation of checksum and its inclusion in the user datagram are optional. UDP is a convenient transport-layer protocol for applications that provide flow and error control. It is also used by multimedia applications. 14 (b) (i) Explain how connection has been established and terminated in TCP in detail. Connection Establishment : A three way handshake is needed to establish a connection.

Connection Termination : A four way handshake is used to terminate a TCP connection.

14(b)(ii) How to avoid the congestion in TCP? Explain it in detail. Congestion in a network may occur if the load on the network�the number of packets sent to the network�is greater than the capacity of the network�the number of packets a network can handle. Congestion control refers to the mechanisms and techniques to control the congestion and


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keep the load below the capacity. TCP uses slow start and congestion avoidance algorithms which work in two phases to avoid the congestion. In the slow-start algorithm, the size of the congestion window increases exponentially until it reaches a threshold In the congestion avoidance algorithm, the size of the congestion window increases additively until congestion is detected. An implementation reacts to congestion detection in one of the following ways:

If detection is by time-out, a new slow start phase starts If detection is by three ACKs, a new congestion avoidance phase starts.

Slow start, exponential increase


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Congestion avoidance, additive increase

15. (a) Briefly discuss about Domain Name space in detail with an example.

The Domain Name System (DNS) is a hierarchical naming system for computers, services, or any resource participating in the Internet. It associates various information with the domain names assigned to each of the participants.

Domain Name Service (DNS) is the service used to convert human readable names of hosts to IP addresses. Host names are not case sensitive and can contain alphabetic or numeric letters or the hyphen. Avoid the underscore. A fully qualified domain name (FQDN) consists of the host name plus domain name as in the following example:

computername.domain.com

The part of the system sending the queries is called the resolver and is the client side of the configuration. The nameserver answers the queries. Read RFCs 1034 and 1035. These contain the bulk of the DNS information and are superceded by RFCs 1535-1537. Naming is in RFC 1591. The main function of DNS is the mapping of IP addresses to human readable names. Three main components of DNS

1. resolver 2. name server 3. database of resource records(RRs)

Domain Name System

The Domain Name System (DNS) is basically a large database which resides on various computers and it contains the names and IP addresses of various hosts on the internet and various domains.


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The Domain Name System is used to provide information to the Domain Name Service to use when queries are made.

The service is the act of querying the database, and the system is the data structure and data itself.

The Domain Name System is similar to a file system in Unix or DOS starting with a root. Branches attach to the root to create a huge set of paths. Each branch in the DNS is called a label. Each label can be 63 characters long, but most are less. Each text word between the dots can be 63 characters in length, with the total domain name (all the labels) limited to 255 bytes in overall length.

The domain name system database is divided into sections called zones. The name servers in their respective zones are responsible for answering queries for their

zones. A zone is a subtree of DNS and is administered separately. There are multiple name servers for a zone. There is usually one primary nameserver and one or more secondary name servers. A name server may be authoritative for more than one zone.

DNS names are assigned through the Internet Registries by the Internet Assigned Number Authority (IANA). The domain name is a name assigned to an internet domain. For example, mycollege.edu represents the domain name of an educational institution. The names microsoft.com and 3Com.com represent the domain names at those commercial companies. Naming hosts within the domain is up to individuals administer their domain.

Generic Domain

Country domains

Inverse domain


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15. (b) Explain the following terms in detail with suitable example. (i) SMTP and HTTP.

SMTP is the TCP/IP mail delivery protocol. It moves mail across the Internet and across your local network. SMTP is defined in RFC 821, A Simple Mail Transfer Protocol. It runs over the reliable, connection-oriented service provided by Transmission Control Protocol (TCP), and it uses well-known port number 25. It is the formal protocol that defines the MTA client and server in the Internet. It simply defines how commands and responses must be sent back and forth. Each network is free to choose a software package for implementation. HTTP is used mainly to access data on the WWW. It functions as the combination of FTP and SMTP. It is similar to FTP because it transfers files and uses the services of TCP. However it is much simpler than FTP because it uses only one TCP connection. There is no separate control connection; only one data are transferred between the client and the server.

(ii) Architecture of WWW

The World Wide Web (known as "WWW', "Web" or "W3") is the universe of network-accessible information, the embodiment of human knowledge. The World Wide Web began as a networked information project at CERN, where Tim Berners-Lee, now Director of the World Wide Web Consortium [W3C], developed a vision of the project. The Web has a body of software, and a set of protocols and conventions. Through the use hypertext and multimedia techniques, the web is easy for anyone to roam, browse, and contribute to. An early talk about the Web gives some more background on how the Web was originally conceived.

How the Web works

Viewing a web page on the World Wide Web normally begins either by typing the URL of the page into a web browser, or by following a hypertext link to that page or resource. The web browser then begins a series of communications, behind the scenes, in order to fetch and display it.

First, the server-name portion of the URL is resolved into an IP address using the global, distributed Internet database known as the domain name system, or DNS. This IP address is necessary to contact and send data packets to the web server.

The browser then requests the resource by sending an HTTP request to the web server at that particular address. In the case of a typical web page, the HTML text of the page is requested first and parsed immediately by the web browser, which will then make additional requests for images and any other files that form a part of the page. Statistics measuring a website's


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popularity are usually based on the number of 'pageviews� or associated server 'hits�, or file requests, which take place.

Having received the required files from the web server, the browser then renders the page onto the screen as specified by its HTML, CSS, and other web languages. Any images and other resources are incorporated to produce the on-screen web page that the user sees.

(iii) Symmetric key cryptography

In symmetric-key cryptography, the same key is used by the sender (for encryption) and the receiver (for decryption). The key is shared. the same key is used in both directions. Symmetric-key cryptography is often used for long messages. Types

Traditional Cipher Block Cipher Operation Modes

CS1302_NOV07

Documents

unguided transmission

automatic

world wide

guided transmission

path spanning

sliding window

data link

cyclic codes