COMPUTER COMMUNICATION NETWORKS

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Module-3

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CO-Describe Architecture of Wireless LAN- IEEE 802.11,connecting devices, Virtual LAN and Analyze IPV4 addressing

Module-3

Wireless LANs: Introduction: Architectural Comparison, Characteristics, IEEE 802.11:Architecture, MAC sublayer, Adressing Mechanism, Physical Layer, Bluetooth: Architecture, Layers.

Connecting Devices: Hubs, Switches, Virtual LANs: Membership, Configuration, Communication between Switches, Advantages.

Network Layer: Introduction, Network Layer services: Packetizing, Routing and Forwarding, Other services, Packet Switching: Datagram Approach, Virtual Circuit Approach, IPV4 Addresses: Address Space, Classful Addressing, Classless Addressing, DHCP, Network Address Resolution, Forwarding of IP Packets: Based on destination Address and Label.

Total lecture hours-10

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3.1 WLAN INTRODUCTION

Wireless communication is one of the fastest-growing technologies. The demand for connecting devices without the use of cables is increasing everywhere. Wireless LANs can be found on college campuses, in office buildings, and in many public areas.

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3.1.1Architectural Comparison

i.Medium

When hosts in a wireless LAN communicate with each other, they are sharing the same medium (multiple access). In a very rare situation, we may be able to create a point-to-point communication between two wireless hosts by using a very limited bandwidth and two-directional antennas. Our discussion in this chapter, however, is about the multiple-access medium, which means we need to use MAC protocols.

ii.Hosts

In a wireless LAN, a host is not physically connected to the network; it can move freely (as we’ll see) and can use the services provided by the network. Therefore, mobility in a wired network and wireless network are totally different issues

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3.1.1Architectural Comparison

iii. Isolated LANs

iv. Connection to Other Networks

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3.1.2 Characteristics

• Attenuation
• Interference
• Multipath Propagation
• Error

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3.2 IEEE 802.11

3.2.1 Architecture

Basic Service Set

Extended Service Set

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3.2 IEEE 802.11

3.2.2MAC Sublayer

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3.2 IEEE 802.11

3.2.2MAC Sublayer

CSMA/CA and NAV

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3.2 IEEE 802.11

3.2.2MAC Sublayer

Frame format

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3.2 IEEE 802.11

3.2.3Addressing Mechanism

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3.2 IEEE 802.11

3.2.3Addressing Mechanism

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3.2 IEEE 802.11

3.2.4Physical Layer

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3.3 BLUETOOTH

3.3.1 Architecture

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3.3 BLUETOOTH

3.3.2 Bluetooth Layers

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3.3 BLUETOOTH

3.3.2 Bluetooth Layers

L2CAP

multiplexing, segmentation and reassembly, quality of service (QoS), and group management.

Baseband Layer

The baseband layer is roughly equivalent to the MAC sublayer in LANs. The access method is TDMA

Radio Layer

Band-2.4-GHz ISM band divided into 79 channels of 1 MHz

FHSS-to avoid interference

Modulation-GFSK

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3.3 BLUETOOTH

3.3.2 Bluetooth Layers

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3.3 BLUETOOTH

3.3.2 Bluetooth Layers

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3.3 BLUETOOTH

3.3.2 Bluetooth Layers

Links

SCO A synchronous connection-oriented (SCO) link is used when avoiding

latency

ACL An asynchronous connectionless link (ACL) is used when data integrity is

more important than avoiding latency

Frame Format

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3.4 Connecting Devices

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3.4 Connecting Devices

Hubs

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3.4 Connecting Devices

Switches

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3.5 Virtual LANs

A station is considered part of a LAN if it physically belongs to that LAN. The criterion of membership is geographic. What happens if we need a virtual connection between two stations belonging to two different physical LANs? We can roughly define a virtual local area network (VLAN) as a local area network configured by software, not by physical wiring.

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3.5 Virtual LANs

A switch using VLAN software

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3.5 Virtual LANs

Two switches in a backbone using VLAN software

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3.5 Virtual LANs

3.5.1 Membership

• Interface Numbers
• MAC Addresses
• IP Addresses
• Multicast IP Addresses
• Combination

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3.5 Virtual LANs

3.5.2 Configuration

• Manual Configuration
• Automatic Configuration
• Semiautomatic Configuration

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3.5 Virtual LANs

3.5.3Communication between Switches

• Table Maintenance
• Frame Tagging
• Time-Division Multiplexing (TDM)
• IEEE Standard

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3.5 Virtual LANs

3.5.4 Advantages

• Cost and Time Reduction
• Creating Virtual Work Groups
• Security

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3.5 Virtual LANs

3.5.4 Advantages

• Cost and Time Reduction
• Creating Virtual Work Groups
• Security

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3.6 NETWORK-LAYER SERVICES

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3.6 NETWORK-LAYER SERVICES

3.6.1 Packetizing

The first duty of the network layer is definitely packetizing: encapsulating the payload (data received from upper layer) in a network-layer packet at the source and decapsulating the payload from the network-layer packet at the destination. In other words, one duty of the network layer is to carry a payload from the source to the destination without changing it or using it.

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3.6 NETWORK-LAYER SERVICES

3.6.2 Routing and Forwarding

• The network layer is responsible for routing the packet from its source to the destination.
• If routing is applying strategies and running some routing protocols to create the decision-making tables for each router, forwarding can be defined as the action applied by each router when a packet arrives at one of its interfaces.

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3.6 NETWORK-LAYER SERVICES

3.6.3 Other Services

• Error Control
• Flow Control
• Congestion Control
• Quality of Service
• Security

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3.7 PACKET SWITCHING

3.7.1 Datagram Approach: Connectionless Service

A connectionless packet-switched network

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3.7 PACKET SWITCHING

3.7.1 Datagram Approach: Connectionless Service

Forwarding process in a router when used in a connectionless network

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3.7 PACKET SWITCHING

3.7.2 Virtual-Circuit Approach: Connection-Oriented Service

A virtual-circuit packet-switched network

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3.7 PACKET SWITCHING

3.7.2 Virtual-Circuit Approach: Connection-Oriented Service

Forwarding process in a router when used in a virtual-circuit network

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3.7 PACKET SWITCHING

3.7.2 Virtual-Circuit Approach: Connection-Oriented Service

Sending request packet in a virtual-circuit network

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3.7 PACKET SWITCHING

3.7.2 Virtual-Circuit Approach: Connection-Oriented Service

Sending acknowledgments in a virtual-circuit network

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3.7 PACKET SWITCHING

3.7.2 Virtual-Circuit Approach: Connection-Oriented Service

Flow of one packet in an established virtual circuit

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3.8 IPV4 ADDRESSES

3.8.1Address Space

A protocol like IPv4 that defines addresses has an address space. An address space is the total number of addresses used by the protocol. If a protocol uses b bits to define an address, the address space is 2b because each bit can have two different values (0 or 1). IPv4 uses 32-bit addresses, which means that the address space is 2^32 or 4,294,967,296

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3.8 IPV4 ADDRESSES

3.8.1Address Space

Notation

Hierarchy in Addressing

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3.8 IPV4 ADDRESSES

3.8.2Classful Addressing

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3.8 IPV4 ADDRESSES

3.8.2Classful Addressing

• Address Depletion
• Subnetting and Supernetting
• Advantage of Classful Addressing

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3.8 IPV4 ADDRESSES

3.8.3 Class less Addressing

Variable-length blocks in classless addressing

Prefix Length: Slash Notation

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3.8 IPV4 ADDRESSES

3.8.3 Class less Addressing

Information extraction in classless addressing

A classless address is given as 167.199.170.82/27

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3.8 IPV4 ADDRESSES

3.8.3 Class less Addressing

Address Mask

Another way to find the first and last addresses in the block is to use the address mask. The address mask is a 32-bit number in which the n leftmost bits are set to 1s and the rest of the bits (32 − n) are set to 0s. A computer can easily find the address mask because it is the complement of (232 − n − 1). The reason for defining a mask in this way is that it can be used by a computer program to extract the information in a block, using the three bit-wise operations NOT, AND, and OR.

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3.8 IPV4 ADDRESSES

3.8.3 Class less Addressing

Address Mask

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3.8 IPV4 ADDRESSES

3.8.3 Class less Addressing

Network address

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3.8 IPV4 ADDRESSES

3.8.3 Class less Addressing

Block Allocation

Subnetting

Address Aggregation

Special Addresses

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3.8 IPV4 ADDRESSES

3.8.4 Dynamic Host Configuration Protocol (DHCP)

DHCP is an application-layer program, using the client-server paradigm, that actually helps TCP/IP at the network layer.

DHCP message format

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3.8 IPV4 ADDRESSES

3.8.4 Dynamic Host Configuration Protocol (DHCP)

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3.8 IPV4 ADDRESSES

3.8.5 Network Address Resolution (NAT)

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3.8 IPV4 ADDRESSES

3.8.5 Network Address Resolution (NAT)

Address translation

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3.8 IPV4 ADDRESSES

3.8.5 Network Address Resolution (NAT)

Translation

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3.9 FORWARDING OF IP PACKETS

3.9.1 Forwarding Based on Destination Address

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3.9 FORWARDING OF IP PACKETS

3.9.1 Forwarding Based on Destination Address

Address Aggregation

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3.9 FORWARDING OF IP PACKETS

3.9.1 Forwarding Based on Destination Address

Longest Mask Matching

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3.9 FORWARDING OF IP PACKETS

3.9.1 Forwarding Based on Destination Address

Hierarchical Routing

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3.9 FORWARDING OF IP PACKETS

3.9.1 Forwarding Based on Destination Address

Geographical Routing

To decrease the size of the forwarding table even further, we need to extend ierarchical

routing to include geographical routing. We must divide the entire address space into a

few large blocks. We assign a block to America, a block to Europe, a block to Asia, a block to Africa, and so on.

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3.9 FORWARDING OF IP PACKETS

3.9.2 Forwarding Based on Label

Multi-Protocol Label Switching (MPLS)

A New Header

Hierarchical Switching