We interpret each four-bit pattern as a hexadecimal digit. We then group the hexa- decimal digits with a colon between the pairs: 5AAA:0F The bytes are sent from left to right. However, the bits in each byte are sent from the least significant rightmost to the most significant leftmost. We have shown the bits with spaces between bytes for readability, but we should remember that that bits are sent without gaps.
The arrow shows the direction of movement. The first byte in binary is The least significant bit is 1. This means that the pattern defines a multicast address. A multicast address can be a destination address, but not a source address. Therefore, the receiver knows that there is an error, and discards the packet.
The minimum data size in the Standard Ethernet is 46 bytes. The maximum data size in the Standard Ethernet is bytes. The data of bytes, therefore, must be split between two frames. The standard dictates that the first frame must carry the maximum possible number of bytes ; the second frame then needs to carry only 10 bytes of data it requires padding. The follow- ing shows the breakdown: Data size for the first frame: bytes Data size for the second frame: 46 bytes with padding The smallest Ethernet frame is 64 bytes and carries 46 bytes of data and possible padding.
The largest Ethernet frame is bytes and carries bytes of data. The smallest frame is 64 bytes or bits. A station with no-transition mobility is either stationary or moving only inside a BSS. The orthogonal frequency-division multiplexing OFDM method for signal gen- eration in a 5-GHz ISM band is similar to frequency division multiplexing FDM , with one major difference: All the subbands are used by one source at a given time.
Sources contend with one another at the data link layer for access. Network Allocation Vector NAV forces other stations to defer sending their data if one station acquires access. In other words, it provides the collision avoidance aspect. When a station sends an RTS frame, it includes the duration of time that it needs to occupy the channel. The stations that are affected by this transmission create a timer called a NAV.
A Bluetooth network is called a piconet. A scatternet is two or more piconets. A Bluetooth primary and secondary can be connected by a synchronous connec- tion-oriented SCO link or an asynchronous connectionless ACL link. An ACL link is used when data integrity is more important than avoiding latency. The primary sends on the even-numbered slots; the secondary sends on the odd- numbered slots.
If there is a collision, it will be detected, destroyed, and the frame will be resent. See Table Table An amplifier amplifies the signal, as well as noise that may come with the signal, whereas a repeater regenerates the signal, bit for bit, at the original strength. Bridges have access to station physical addresses and can forward a packet to the appropriate segment of the network. In this way, they filter traffic and help control congestion. If a bridge is added or deleted from the system, reconfigura- tion of the stations is unnecessary.
A signal can only travel so far before it becomes corrupted. A repeater regenerates the original signal; the signal can continue to travel and the LAN length is thus extended. A hub is a multiport repeater. A forwarding port forwards a frame that it receives; a blocking port does not. In a bus backbone, the topology of the backbone is a bus; in a star backbone, the topology is a star. A VLAN saves time and money because reconfiguration is done through software.
Physical reconfiguration is not necessary. Members of a VLAN can send broadcast messages with the assurance that users in other groups will not receive these messages. A VLAN creates virtual workgroups. Each workgroup member can send broadcast messages to others in the workgroup.
This eliminates the need for multicasting and all the overhead messages associated with it. Stations can be grouped by port number, MAC address, IP address, or by a com- bination of these characteristics. We have sorted the table based on the physical address to make the searching faster. We made bridge B1 the root. Although any router is also a bridge, replacing bridges with routers has the follow- ing consequences: a.
Routers are more expensive than bridges. Routers operate at the first three-layers; bridges operates at the first two layers. Routers are not designed to provide direct filtering the way the bridges do.
A router needs to search a routing table which is normally longer and more time consuming than a filtering table. A router needs to decapsulate and encapsulate the frame and change physical addresses in the frame because the physical addresses in the arriving frame define the previous node and the current router; they must be changed to the physical addresses of the current router and the next hop.
A bridge does not change the physical addresses. Changing addresses, and other fields, in the frame means much unnecessary overhead. A filtering table is based on physical addresses; a routing table is based on the logical addresses. We have shown the network, the graph, the spanning tree, and the blocking ports. Network b. Spanning tree d. Blocking ports A router has more overhead than a bridge.
A router process the packet at three layers; a bridge processes a frame at only two layers. A router needs to search a routing table for finding the output port based on the best route to the final destina- tion; A bridge needs only to consult a filtering table based on the location of sta- tions in a local network. A routing table is normally longer than a filtering table; searching a routing table needs more time than searching a filtering table.
A router changes the physical addresses; a bridge does not. A bridge has more overhead than a repeater. A bridge processes the packet at two layers; a repeater processes a frame at only one layer. A bridge needs to search a table and find the forwarding port as well as to regenerate the signal; a repeater only regenerates the signal. In other words, a bridge is also a repeater and more ; a repeater is not a bridge. A gateway has more overhead than a router.
A gateway processes the packet at five layers; a router processes a packet at only three layers. A gateway needs to worry about the format of the packet at the transport and application layers; a router does not.
In other words, a gateway is also a router but more ; a router is not a gateway. A gateway may need to change the port addresses and application addresses if the gateway connects two different systems together; a router does not change these addresses. A mobile switching center coordinates communications between a base station and a telephone central office. A mobile switching center connects cells, records call information, and is respon- sible for billing.
A high reuse factor is better because the cells that use the same set of frequencies are farther apart separated by more cells. In a hard handoff, a mobile station communicates with only one base station. In a soft handoff, a mobile station communicates with two base stations at the same time.
GSM is a European standard that provides a common second-generation technol- ogy for all of Europe. CDMA encodes each traffic channel using one of the rows in the Walsh table.
The three orbit types are equatorial, inclined, and polar. A GEO satellite has an equatorial orbit since the satellite needs to remain fixed at a certain spot above the earth. A footprint is the area on earth at which the satellite aims its signal. A satellite orbiting in a Van Allen belt would be destroyed by the charged parti- cles. Therefore, satellites need to orbit either above or below these belts. Transmission from the earth to the satellite is called the uplink.
Transmission from the satellite to the earth is called the downlink. GPS is a satellite system that provides land and sea navigation data for vehicles and ships. The system is also used for clock synchronization. The main difference between Iridium and Globalstar is the relaying mechanism. Iridium requires relaying between satellites.
Globalstar requires relaying between satellites and earth stations. In AMPS, there are two separate bands for each direction in communication.
In each band, we have analog channels. Out of this number, 21 channels are reserved for control. Since duplexing is pro- vided at the digital level, this means that analog channels are available in each cell assuming no control channels. In GSM, separate bands are assigned for each direction in communication.
This means analog channels are available in each cell assuming no control chan- nels. Each analog channel carries 1 multiframe. Each multiframe carries 26 frames 2 frames are for control. Each frame allows 8 calls. In IS, separate bands are assigned for each direction in communication. This means 20 analog channels are available in each cell assuming no control chan- nels. Each analog channel carries 64 digital traffic channel 9 channels are for control.
In Exercise 19, we showed that the maximum simultaneous calls per cell for GSM is In Exercise 20, we showed that the maximum simultaneous calls per cell for IS is D-AMPS sends 25 frames per seconds in each channel.
Each frame carries 6 slots. GPS satellites are orbiting at 18, km above the earth surface. Iridium satellites are orbiting at km above the earth surface.
Globalstar satellites are orbiting at km above the earth surface. The standards are nearly identical. An STS multiplexer multiplexes signals from multiple electrical sources and creates the corresponding optical signal.
An STS demultiplexer demultiplexes an optical signal into corresponding electric signals. OCs are the corresponding optical signals. Pointers are used to show the offset of the SPE in the frame or for justification.
A single clock handles the timing of transmission and equipment across the entire network. A regenerator takes a received optical signal and regenerates it.
SONET defines four layers: path, line, section, and photonic. The path layer is responsible for the movement of a signal from its source to its destination.
The line layer is responsible for the movement of a signal across a physical line. The section layer is responsible for the movement of a signal across a physical section. The photonic layer corresponds to the physical layer of the OSI model. It includes physical specifications for the optical fiber channel. A virtual tributary is a partial payload that can be inserted into an STS-1 and com- bined with other partial payloads to fill out the frame. SONET sends frames in each second. How- ever, there is no extra overhead involved in the process of demultiplexing or multi- plexing.
Demultiplexing is done byte by byte; multiplexing is also done byte by byte. To carry a load with a data rate In other words, out of every frames need to allow the H3 byte to carry data. For example, we can have sequences of 16 frames in which the first frame is an overloaded frame and then 15 frames are normal.
In other words, out of every frames need to allow the next byte after H3 to be empty dummy. For example, we can have sequences of 32 frames in which the first three frames are underloaded and the next 29 are normal.
The path layer is responsible for end-to-end communication. The line layer is responsible between multiplexers. The section layer is responsible between devices.
A1 and A2 are used as aligners synchronizers. They perform the same job as a preamble or flag field in other networks. We can call them framing bytes. These bytes are set and renewed at each device to synchronize the two adjacent devices. There is no need for these bytes at the line or path layer. C1 is used at the section layer to identify multiplexed STSs. This idea can be compared to statistical TDM in which each slot needs an address. C2 is like the port numbers in other protocols.
There is no need for C byte at the line layer. SONET requires two separate channels at the section device-to-device and line multiplexer-to-multiplexer layers. No administration is provided at the line layer. E byte creates a voice communication channel between two devices at the ends of a section. F bytes also create a voice communication. F1 is used between two devices at the end of a section; F2 is used between two ends.
No bytes are assigned at the line layer. The only G bytes are used for status reporting. A device at the end of the path reports its status to a device at the beginning of the path. No other layer needs this byte. H bytes are the pointers. H3 is used to compensate for a faster or slower user data.
H4 is used at the path layer to show a multiframe payload. Obviously we do not need an H byte in the section layer because no multiplexing or demulti- plexing happens at this layer.
The only J byte is at the path layer to show the continuous stream of data at the path layer end-to-end. The user uses a pattern that must be repeated to show the stream is going at the right destination.
There is no need for this byte at the other layers. As we discussed, K bytes are used for automatic protection switching, which happens at the line layer multiplexing. Other layers do not need these bytes. Z bytes are unused bytes. The B bytes are error-detection bytes. They are used at all layers. B1 is used at the section layer over the whole frame. Each bit of this byte is calculated over the corresponding bit of all bytes in the previous frame. B2 is used at the line layer.
B3 is used at the path layer calculated over all bits of previous SPE. Frame Relay does not use flow or error control, which means it does not use the sliding window protocol. Therefore, there is no need for sequence numbers. DLCIs are unique only for a particular interface.
A switch assigns a DCLI to each virtual connection in an interface. This way two different connections belonging to two different interfaces may have the same DLCI. T-lines provide point-to-point connections, not many-to-many. In order to connect several LANs together using T-lines, we need a mesh with many lines. In a PVC, two end systems are connected permanently through a virtual connec- tion. In a SVC, a virtual circuit needs to be established each time an end system wants to be connected with another end system.
Frame Relay does not define a specific protocol for the physical layer. Any proto- col recognized by ANSI is acceptable. If data packets are different sizes there might be variable delays in delivery. A TP transmission path is the physical connection between a user and a switch or between two switches. It is divided into several VPs virtual paths , which provide a connection or a set of connections between two switches.
VPs in turn consist of several VCs virtual circuits that logically connect two points together. The ATM layer provides routing, traffic management, switching, and multiplexing services. This means that we can define virtual circuits in an UNI.
This means that we can define virtual circuits in an NNI. We can briefly summarize the most important issues: a. Traditional LANs define the route of a packet through source and destination addresses; ATM defines the route of a cell through virtual connection identifi- ers.
Traditional LANs can do unicast, multicast, and broadcast transmission; ATM is designed only for unicast transmission. We first need to look at the EA bits. In each byte, the EA bit is the last bit the eight bit from the left. If EA bit is 0, the address ends at the current byte; if it 1, the address continues to the next byte.
This means that the address is only two bytes no address extension. DLCI is only 10 bits, bits 1 to 6 and 9 to 12 from left. The address field in Frame Relay is 16 bits. The address given is only 15 bits. It is not valid. If the EA bit is 0, the address ends at the current byte; if it 1, the address continues to the next byte. This means that the address is three bytes address extension.
DLCI is 16 bits, bits 1 to 6, 9 to 12, and 17 to We first change the number to bit binary We then add sepa- rate DLCI into a 6-bit and a 4-bit and add extra bits.
Note that the first EA bit is 0; the second is 1. In AAL1, each cell carries only 47 bytes of user data. In AAL1, each byte cell carries only 47 bytes of user data. There are 6 bytes of overhead. This means that the total length of the packet in the CS layer should be a multiple of This means we have cells. A larger packet is more efficient than a smaller packet. The minimum number of cells is 1.
Padding is added to make it exactly 36 bytes. Then 8 bytes of header cre- ates a data unit of 44 bytes at the SAR layer. The maximum number of cells can be determined from the maximum number of data units at the CS sublayer. The maxi- mum number of cells is This happens when the data size is between 65, and 65, inclusive bytes. We need to add between 17 to 43 inclu- sive bytes of padding to make the size bytes. The 8 byte overhead at the CS layer makes the total size which means data units of size Padding is added to make it exactly 40 bytes.
Then 8 bytes of header cre- ates a data unit of 48 bytes at the SAR layer. The maximum number of cells is It can be determined from the maxi- mum number of data units at the CS sublayer. We need to add between 25 to 47 inclusive bytes of padding to make the size bytes. The 8 byte overhead at the CS layer makes the total size which means data unit of size AAL1 takes a continuous stream of bits from the user without any boundaries. There are always bits to fill the data unit; there is no need for padding.
The other AALs take a bounded packet from the upper layer. An IPv4 address is 32 bits long. An IPv6 address is bits long. IPv4 addresses are usually written in decimal form with a decimal point dot sep- arating the bytes.
This is called dotted-decimal notation. Each address is 4 bytes. IPv6 addresses are usually written in hexadecimal form with a colon separating the bytes. This is called hexadecimal notation. Each address is 16 bytes or 32 hexa- decimal digits. Classless addressing assigns an organization a block of contiguous addresses based on its needs. Classes A, B, and C are used for unicast communication. Class D is for multicast communication and Class E addresses are reserved for special purposes.
A block in class A address is too large for almost any organization. This means most of the addresses in class A are wasted and not used. A block in class C is probably too small for many organizations. A mask in classful addressing is used to find the first address in the block when one of the addresses is given.
The default mask refers to the mask when there is no subnetting or supernetting. The network address in a block of addresses is the first address.
The mask can be ANDed with any address in the block to find the network address. In subnetting, a large address block could be divide into several contiguous groups and each group be assigned to smaller networks called subnets. In supernetting, several small address blocks can be combined to create a larger range of addresses.
The new set of addresses can be assigned to a large network called a supernet. A subnet mask has more consecutive 1s than the corresponding default mask.
A supernet mask has less consecutive 1s than the corresponding default mask. Multicast addresses in IPv4 are those that start with the pattern.
Multicast addresses in IPv6 are those that start with the pattern. Home users and small businesses may have created small networks with several hosts and need an IP address for each host. With the shortage of addresses, this is a serious problem. A quick solution to this problem is called network address trans- lation NAT.
NAT enables a user to have a large set of addresses internally and one address, or a small set of addresses, externally. The traffic inside can use the large set; the traffic outside, the small set. Class C first byte is between and b. Class D first byte is between and c. Class A first byte is between 0 and d. Class B first byte is between and Class E first four bits are 1s b.
Class B first bit is 1 and second bit is 0 c. Class C first two bits are 1s and the third bit is 0 d. Class D first three bits are 1s and the fourth bit is 0 With the information given, the first address is found by ANDing the host address with the mask Host Address: We can have many small blocks as long as the number of addresses divides this number.
We can have several small blocks as long as the number of addresses divides this number. Subnet 1: The first address in the this address is the beginning address of the block or To find the last address, we need to write 32, one less than the number of addresses in each subnet in base 0. First address in subnet 1: To find the first address in subnet , we need to add net 1. We have Now we can calculate the last address in subnet First address in subnet Subnet 1: The first address is the beginning address of the block or To find the last address, we need to write 63 one less than the number of addresses in each subnet in base 0.
Subnet base 0. Now we can calculate the last address in subnet as we did for the first address. To find the last address, we need to write 7 one less than the number of addresses in each subnet in base 0. Subnet 0. Now we can calculate the last address in subnet 32 as we did for the first address. The mask We need to add 7 one less addresses 0. From: We need to add 31 one less addresses 0. We need to add one less addresses 0.
We need to add 3 one less addresses 0. The ISP can divide this large block in several ways depending on the predicted needs of its customers in the future. We assume that the future needs follow the present pattern.
In other words, we assume that the ISP will have customers that belong to one of the present groups. We design four ranges: group 1, group 2, group 3, and one reserved range of addresses as shown in Figure We augment this number to the in the future. The addresses are: each customer needs addresses. Reserved: , which can be assigned to 56 businesses of this size.
Group 2 In the second group, we have business. We augment this number to the the future. For this group, next number after that is a power of 2 to let more customer of this kind in each customer needs 16 addresses. The addresses are: 1st customer: Group 3 In the third group, we have households. We augment this number to kind in the future. For this the next number after that is a power of 2 to let 48 more customer of this 2.
The addresses are: group, each customer needs 4 addresses. Reserved Range In the reserved range, we have address that are totally unused.
Note that we have unused addresses in each group and a large range of unused addresses in the reserved range. One solution would be to divide this block into 8-address sub-blocks as shown in Figure The ISP can assign the first sub-blocks to the current customers and keep the remaining 28 sub-blocks. Of course, this does not mean the future customer have to use 8-address subblocks.
Each sub-block has 8 addresses. Each customer has only 1 address and, therefore, only one device. Since we defined a network as 2 or more connected devices, this is not a network Link local address b. Site local address c. Multicast address permanent, link local d. Loopback address Unspecified address b. Mapped address c. FE or FE b. The node identifier is The delivery of a frame in the data link layer is node-to-node.
The delivery of a packet at the network layer is host-to-host. In a connectionless service, there is no setup and teardown phases. Each packet is independent from every other packet.
Communication has only one phase: data transfer. In connection-oriented service, a virtual connection is established between the sender and the receiver before transferring data. Layer 2 takes the plaintext from layer 3, encrypts it, and delivers it to layer 1. Layer 2 takes the ciphertext from layer 1, decrypts it, and delivers it to layer 3. In 10 years, the number of hosts becomes about six times 1.
This means the number of hosts connected to the Internet is more than three billion. The system transmits bytes for a byte message. The advantage of using large packets is less overhead. When using large packets, the number of packets to be sent for a huge file becomes small. Since we are adding three headers to each packet, we are sending fewer extra bytes than in the case in which the number of packets is large.
The disadvantage manifests itself when a packet is lost or corrupted during the transmission; we need to resend a large amount of data. The network layer is responsible for route determination.
The physical layer is the only layer that is connected to the transmission media. The application layer provides services for the end users. User datagrams are created at the transport layer.
The data-link layer is responsible for handling frames between adjacent nodes. The physical layer is responsible for transforming bits to electromagnetic signals. There should be an upper-layer identifier in the header of the IP protocol to define to which upper-layer protocol the encapsulated packet belongs.
The identifier is called the protocol field See Figure The following shows the situation. If we think about multiplexing as many-toone and demultiplexing as one-to-many, we have demultiplexing at the source node and multiplexing at the destination node in the data-link layer. However, some purists call these two inverse multiplexing and inverse demultiplexing. At the destination node P Every time any packet at any layer is encapsulated inside another packet at the same layer, we can think of this as a new layer being added under that layer.
The following shows the new suite. The following shows the layers. This book starts with a detailed account on network models, thus providing the user with an ideal introduction on data transmission. Review Questions1. The five components of a data communication system are the sender, receiver, transmission medium, message, and protocol.
The three criteria are performance, reliability, and security. Line configurations or types of connections are point-to-point and multipoint.
To browse Academia. Skip to main content. By using our site, you agree to our collection of information through the use of cookies. To learn more, view our Privacy Policy. Log In Sign Up. Embed Size px x x x x The five components of a data communication system are the sender, receiver,. The advantages of distributed processing are security, access to distributed data-. Advantages of a multipoint over a point-to-point configuration type of connec-.
Questions Q To make the communication bidirectional, each layer needs to be able to pro- vide two opposite tasks, one in each direction.
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