FIT3165 / FIT4165 COMPUTER NETWORKS
WEEK 7 – WIRED NETWORKS
Faculty of Information Technology © 2022 Monash University
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WIRED NETWORKS
7.1 INTRODUCTION
7.2 WIRED LANS: ETHERNET PROTOCOL 7.3 OTHER WIRED NETWORKS
7.4 CONNECTING DEVICES
Objectives
❑ We introduce the wired LANs and in particular Ethernet, the dominant LAN protocol today.
❑ We move through different generations of Ethernet and show how it has evolved.
❑ We discuss other wired networks that we encounter in the Internet today, such as
point-to-point networks and switched networks.
❑ We discuss connecting devices used in the lower three layers of the TCP/IP protocol such as hubs, link-layer switches, and routers.
WIRED LANS: ETHERNET PROTOCOL
• TCP/IP protocol stack accepts any data-link protocol at data-link and physical layers. These two layers are actually the territory of the LAN & WAN.
• This means that when we discuss these two layers, we are talking about networks that are using them. We can have wired or wireless networks.
• This lecture we discuss wired networks and wireless networks in the next lecture.
IEEE Project 802
• In 1985, the Computer Society of the IEEE started a project, called Project 802
• To set standards to enable intercommunication among equipment from a variety of manufacturers.
• Project 802 is a way of specifying functions of the physical layer and the data-link layer of major
LAN protocols.
❑ Logical Link Control (LLC)
❑ Media Access Control (MAC)
IEEE standard for LANs
Standard Ethernet
We refer to the original Ethernet technology with the data rate of 10 Mbps as the Standard Ethernet.
Although technology in the Ethernet has evolved, there are some features of the Standard Ethernet that have not changed during the evolution.
We discuss this standard version to pave the way for understanding the other three technologies.
❑ Frame Format
❑ Connectionless and Unreliable Service
❑ Frame Length
❑ Addressing
❖ Transmission of Address Bits
❖ Unicast, Multicast, and Broadcast Addresses
❖ Distinguish between Unicast, Multicast, and
Broadcast Transmission
❑ Access Method
❑ Efficiency of Standard Ethernet
❑ Implementation
A list of the 802 Networking Standards and uses:
802.1: Internetworking
802.2: Logical Link Control
802.3: Ethernet
802.4: Token Bus LAN
802.5: Token Ring LAN
802.6: Metropolitan Area Networks
802.7: Broadband Technical Advisory Group 802.8: Fiber Optic Technical Advisory Group 802.9: Integrated Voice and Data Networks
802.10: Network Security
802.11: Wireless Networking
802.12: High Speed Networking
802.13: Not Currently In Use
802.14: Defunct Working Group
802.15: Wireless Personal Area Networks 802.16: Wireless Metropolitan Area Networks
802.17: Resilient Packet Ring
802.18: Wireless Advisory Group
802.19: Coexistence Advisory Group 802.20: Mobile Broadband Wireless
Ethernet frame
Addressing
• Each station on an Ethernet network has its own network interface card (NIC).
• The NIC fits inside the station and provides the station with a link-layer address.
• The Ethernet address is 6 bytes (48 bits), normally written in hexadecimal notation, with a colon between the bytes. For example, the following shows an Ethernet MAC address:
Implementation of standard Ethernet
Access Methods and Efficiency
• Since the network that uses the standard Ethernet protocol is a broadcast network, we need to use an access method to control access to the sharing medium.
• The standard Ethernet chose CSMA/CD with 1-persistent method. Efficiency of Standard Ethernet:
•The efficiency of the Ethernet is defined as the ratio of the time used by a station to send data to the time the medium is occupied by this station.
•The practical efficiency of standard Ethernet has been measured to be Efficiency = 1 / (1 + 6.4 x a)
in which the parameter “a” is the number of frames that can fit on the medium. It can be calculated as a = (propagation delay)/(transmission delay) because the transmission delay is the time it takes a frame of average size to be sent out and the propagation delay is the time it takes to reach the end of the medium.
•Note that as the value of parameter a decreases, the efficiency increases. This means that if the length of the media is shorter or the frame size longer, the efficiency increases.
•In the ideal case, a = 0 and the efficiency is 1.
Efficiency – Example
• We have Standard Ethernet with the transmission rate of 10 Mbps
• We assume that the length of the medium is 2500 m and
• The size of the frame is 512 bits.
• The propagation speed of a signal in a cable is normally 2 × 108 m/s.
Find the efficiency and interpret this value?
● The example shows that a = 0.24, which means only 0.24 of a frame occupies the whole medium in this case.
● The efficiency is 1/((1+6.4×0.24) = 1 / 2.55 = 39 percent, which is considered moderate; it means that only 61 percent of the time the medium is occupied but not used by a station.
Implementation
The Standard Ethernet defined several implementations, but only four of them became popular during the 1980s. Table shows a summary of Standard Ethernet implementations.
Summary of Standard Ethernet implementations
Encoding in standard Ethernet
Standard Ethernet Implementation (1)
10Base5 implementation
10Base2 implementation
Standard Ethernet Implementation (2)
10Base-T implementation 10Base-F implementation
Changes in the Standard Ethernet (1)
➔ Before we discuss higher-rate Ethernet protocols, we need to discuss the changes that occurred to the 10-Mbps Standard Ethernet.
➔ These changes actually opened the road to the evolution of the Ethernet to become compatible with other high-data-rate LANs.
Sharing bandwidth
Changes in the Standard Ethernet (2)
A network with and without bridging
Collision domains
Changes in the Standard Ethernet (3)
Switched Ethernet Full – duplex switched Ethernet
Fast Ethernet
• In the 1990s, Ethernet made a big jump by increasing the transmission rate to 100 Mbps, and the new generation was called the Fast Ethernet.
• The designers of the Fast Ethernet needed to make it compatible with the Standard Ethernet.
• The MAC sublayer was left unchanged.
• But the features of the Standard Ethernet that depend on the transmission rate, had to be changed.
• Fast Ethernet was designed to operate at 100 Mbps.
• The designers of the Fast Ethernet needed to make it compatible with the Standard Ethernet.
• The MAC sublayer was left unchanged, which meant the frame format and the maximum and minimum size could also remain unchanged.
❖ Access Method ❖ Auto-negotiation ❖ Implementation
Encoding for fast Ethernet
Gigabit Ethernet
The need for an even higher data rate resulted in the design of the Gigabit Ethernet Protocol (1000 Mbps). The IEEE committee calls the Standard 802.3z.
The goals of the Gigabit Ethernet were to upgrade the data rate to 1 Gbps, but keep the address length, the frame format, and the maximum and minimum frame length the same.
MAC Sublayer
Implementation
➔ A main consideration in the evolution of Ethernet was to keep the MAC sublayer untouched. However, to achieve a data rate of 1 Gbps, this was no longer possible.
➔ The physical layer in Gigabit Ethernet is more complicated than that in Standard or Fast Ethernet.
➔ We briefly discuss some features of this
➔ Gigabit Ethernet has two distinctive approaches for medium access: half-duplex and full-duplex.
➔ Almost all implementations of Gigabit Ethernet follow the full-duplex approach, so we mostly ignore the half-duplex mode.
Gigabit Ethernet – Encoding
Encoding in Gigabit Ethernet
Summary of Gigabit Ethernet implementations
10-Gigabit Ethernet
● In recent times, there has been another look into the Ethernet for use in metropolitan areas.
● The idea is to extend the technology, the data rate, and the coverage distance so that the Ethernet can be
used as LAN and MAN (metropolitan area network).
● The IEEE committee created 10-Gigabit Ethernet and called it Standard 802.3ae.
● 10 Gigabit Ethernet operates only in full-duplex mode, which means there is no need for contention;
● CSMA/CD is not used in 10 Gigabit Ethernet.
● Four implementations are the most common: 10GBase-SR, 10GBase-LR, 10GBase-EW, and 10GBase-X4.
● Table 13.4 shows a summary of the 10 Gigabit Ethernet implementations.
Summary of standards
Standard Ethernet implementations
Fast Ethernet implementations
Gigabit Ethernet implementations
10-Gigabit Ethernet implementations
Virtual LANs (VLANs)
• 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.
Membership
❖ Interface Numbers
❖ MAC Addresses
❖ IP Addresses
❖ Multicast IP Addresses
❖ Combination
❑ Communication between Switches
❖ Table Maintenance
❖ Frame Tagging
❖ Time-Division Multiplexing (TDM)
❑ IEEE Standard
❑ Advantages
❖ Cost and Time Reduction
❖ Creating Virtual Work Groups
❖ Security
❑ Configuration
❖ Manual Configuration
❖ Automatic Configuration
❖ Semiautomatic Configuration
VLAN Configurations
A switch connecting three LANs without any VLAN’s
A single switch with three VLAN’s configured using software
Two switches in a backbone with three VLAN’s configured using software
Other Wired Networks
• As we discussed in Lecture 1, the networks that we encounter in the Internet are either LANs or WANs.
• However, sometimes the terminology is under dispute.
• For example, some access networks such as dial-up connection or cable connection are
called WANs by some people and MANs by others.
Point to Point
● Digital Subscriber Line (DSL) Using Existing Local Loops •
● Cable Hybrid Fiber Coaxial (HFC) Network
Switched: ATM
Point-to-Point Networks
• Some point-to-point networks, such as dial-up, DSL / ADSL & cable are used to provide internet access from Internet user premises.
• Such networks use a dedicated connection between the two devices, they do not use media access control (MAC).
• The only protocol that is needed is PPP, as we discussed before.
❑ Digital Subscriber Line (DSL) ❖ Using Existing Local Loops
❖ Hybrid Fiber-Coaxial (HFC) Network
Dial-up network to provide Internet access
Point-to-Point Networks – ADSL
ASDL point-to-point network
Using Existing Local Loops: ADSL uses the existing telephone lines (local loop). The telephone lines has bandwidths up to 1.1 MHz, but the filter(splitter) installed at the end office filters the bandwidth to 4 kHz (for voice communication). Typically, an available bandwidth of 1.104 MHz is divided into a voice channel, an upstream channel, and a downstream channel.
Point-to-Point Networks – HFC
The network uses a combination of fiber-optic and coaxial cable
Hybrid Fiber-Coaxial (HFC) Network
• High-speed backbone networks, SONET is used as a transport network to carry loads from other networks.
SONET Data rates
A simple network using SONET equipment
SONET – Layers , Multiplexing and Demultiplexing
The SONET standard includes four functional layers: the photonic, the section, the line, and the path layer. They correspond to both the physical and the data link layers.
Switched Network: ATM
Asynchronous Transfer Mode (ATM) is a switched wide area network based on the cell relay protocol designed by the ATM forum and adopted by the ITU-T.
Architecture
❖ ATM Terminology – Connection address
❖ Virtual channels & Virtual paths
❖ ATM cell Header Formats
❖ ATM service Categories
❖ Applications
▪ Also known as Cell Relay
▪ Operates at high data rates in the WAN
▪ Resembles packet switching
– Involves data transfer in discrete chunks, like
packet switching
– Allows multiple logical connections to be multiplexed over a single physical interface
▪ Minimal error and flow control capabilities reduces overhead processing and size
▪ Fixed-size cells simplify processing at ATM nodes
ATM – Terminology and Connection addresses
▪ Virtual channel connection (VCC)
– Logical connection in ATM
– Basic unit of switching in ATM network
– Analogous to a virtual circuit in packet switching networks
– Exchanges variable-rate, full-duplex flow of fixed-size cells
▪ Virtual path connection (VPC)
– Bundle of VCCs that have the same end points
Advantages of Virtual paths
➢ Simplified network architecture
➢ Increased network performance and
reliability
➢ Reduced processing and short
connection setup time
➢ Enhanced network services
ATM – Service Categories
▪ Real-time service
– Constant bit rate (CBR)
– Real-time variable bit rate (rt-VBR)
▪ Non-real-time service
– Non-real-time variable bit rate (nrt-VBR)
– Available bit rate (ABR)
– Unspecified bit rate (UBR)
▪ Real-time service
– Constant bit rate (CBR)
– Real-time variable bit rate (rt-VBR)
● Videoconferencing
Interactive audio ○ e.g., telephony
Audio/video distribution
○ e.g., television, distance learning,
pay-per-view Audio/video retrieval
○ e.g., video-on-demand, audio library
▪ Non-real-time service
– Non-real-time variable bit rate (nrt-VBR)
– Available bit rate (ABR)
– Unspecified bit rate (UBR)
● Text/data/image
○ transfer, messaging, distribution, retrieval
● Remote terminal
○ e.g., telecommuting
Connecting Devices
• Hosts and networks do not normally operate in isolation. We use connecting devices to connect hosts together to create networks or to connect networks together to make an internet.
• Connecting devices can operate in different layers of the Internet model.
• We discuss three kinds of connecting devices: repeaters, link-layer switches, and routers.
Repeater or Hubs
• A repeater is a device that operates only in the physical layer.
• Signals that carry information within a network can travel a fixed distance before
attenuation endangers the integrity of the data.
• A repeater receives a signal and, before it becomes too weak or corrupted,
regenerates and retimes the original bit pattern.
Link-Layer Switches
➔ A link-layer switch operates in both the physical and the data-link layers.
➔ As a physical layer device, it regenerates the signal it receives. As a link-layer device, the link-layer switch can check the MAC addresses (source and destination) contained in the frame and frame errors.
Link-Layer Switch
❑ Filtering
❑ Transparent Switches
❖ Forwarding
❖ Learning
How switches learn
★ We discussed routers in network layer, here we compare routers with a two-layer switch and a hub.
★ A router is a three-layer device; it operates in the physical, data-link, and network layers.
Routing example
MID SEMESTER TEST
● Date : 11th April 2022 (Monday, Week 7)
● Open time : 4.00pm to 11.55pm AEST
● Time per attempt : 45 minutes
○ Once you have started the quiz, you will get 45 minutes to complete. Therefore, latest time to start the test is 11.10 pm AEST.
● Q’s will cover : Content from week 1 – Week 5
● Attempts allowed : 1
● A Moodle based quiz
● Multiple choice questions only
● Open book test
● Link to access mid semester will be available under week 7 contents on Moodle
● So far we have discussed ○ Ethernet
○ Other wired networks
○ How to connect devices together
● Next week
○ Wireless Networks
Reminder : Mid-Sem Test
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