MAC Protocols for High-Speed

LANS, MANs, and Wireless LANs

Wired LANs: Ethernet

• We learned that a local area network (LAN) is a computer network that is

designed for a limited geographic area such as a building or a campus.
• Although a LAN can be used as an isolated network to connect computers in an
organization for the sole purpose of sharing resources, most LANs today are also
linked to a wide area network (WAN) or the Internet.
• The LAN market has several technologies such as Ethernet, Token Ring, Token
Bus, FDDI, and ATM LAN. Some of these technologies survived for a while, but
Ethernet is by far the dominant technology..
IEEE STANDARDS

• 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.
• The relationship of the 802 Standard to the traditional OSI (open source
interconnection )model is shown in Figure.
• The IEEE has subdivided the data link layer into two sublayers: logical link
control (LLC) and media access control (MAC). IEEE has also created several
physical layer standards for different LAN protocols.
IEEE standard for LANs
 Data Link Layer

The data link layer in the IEEE standard is divided into two sublayers: LLC and MAC.
• The data link control handles framing, flow control, and error control.
• In IEEE Project 802, flow control, error control, and part of the framing duties are
collected into one sublayer called the logical link control.
• Framing is handled in both the LLC sublayer and the MAC sublayer.
• The LLC provides one single data link control protocol for all IEEE LANs. In this way,
the LLC is different from the media access control sublayer MAC, which provides
different protocols for different LANs
 Data Link Layer

• The purpose of the LLC is to provide flow and error control for the upper-layer protocols
that actually demand these services. Media Access Control (MAC) is having multiple
access methods including random access, controlled access, and channelization.
• IEEE Project 802 has created a sublayer called media access control that defines the
specific access method for each LAN.
• Some part of the framing function is also handled by the MAC layer.
• In contrast to the LLC sublayer, the MAC sublayer contains a number of distinct
modules; each defines the access method and the framing format specific to the
corresponding LAN protocol.
Figure Ethernet evolution through four generations
MAC frame
 Frame Format

• Preamble. The first field of the 802.3 frame contains 7 bytes (56 bits) of alternating Os
and 1s that alerts the receiving system to the coming frame and enables it to synchronize
its input timing. The pattern provides only an alert and a timing pulse. The 56-bit pattern
allows the stations to miss some bits at the beginning of the frame. The preamble is
actually added at the physical layer and is not (formally) part of the frame.
• Start frame delimiter (SFD). The second field (l byte: 10101011) signals the beginning of
the frame. The SFD warns the station or stations that this is the last chance for
synchronization. The last 2 bits is 11 and alerts the receiver that the next field is the
destination address.
 Frame Format

• Destination address (DA)- The DA field is 6 bytes and contains the physical address of
the destination station or stations to receive the packet. We will discuss addressing
shortly.
• Source address (SA) - The SA field is also 6 bytes and contains the physical address of
the sender of the packet. We will discuss addressing shortly.
• Length or type - This field is defined as a type field or length field. The original Ethernet
used this field as the type field to define the upper-layer protocol using the MAC frame.
The IEEE standard used it as the length field to define the number of bytes in the data
field. Both uses are common today.
 Frame Format

• Data - This field carries data encapsulated from the upper-layer protocols. It is a
minimum of 46 and a maximum of 1500 bytes, as we will see later.
• CRC -The last field contains error detection information, in this case a CRC-32
Minimum and maximum lengths
Note

Frame length:
Minimum: 64 bytes (512 bits)
Maximum: 1518 bytes (12,144 bits)
 Addressing

• Each station on an Ethernet network (such as a PC, workstation, or printer)

has its own network interface card (NIC). The NIC fits inside the station and
provides the station with a 6-byte physical address. As shown in Figure, the
Ethernet address is 6 bytes (48 bits), nonnally written in hexadecimal
notation, with a colon between the bytes.
 Example of an Ethernet MAC address in hexadecimal notation

The way the addresses are sent out online is different from the way they are
written in hexadecimal notation. The transmission is left to right, byte by byte;
however, for each byte, the least significant bit is sent first and the most
significant bit is sent last. This means that the bit that defines an address as
unicast or multicast arrives first at the receiver. This helps the receiver to
immediately know if the packet is unicast or multicast.
 Addressing

Show how the address 47:20:1B:2E:08:EE is sent out online.

The address is sent left to right, byte by byte; for each byte, it is sent right to
left, bit by bit, as shown below:
 Addressing

• Unicast, Multicast, and Broadcast Addresses A source address is always a

unicast address-the frame comes from only one station. The destination
address, however, can be unicast, multicast, or broadcast. Figure shows how
to distinguish a unicast address from a multicast address. If the least
significant bit of the first byte in a destination address is 0, the address is
unicast; otherwise, it is multicast.
Unicast and multicast addresses
Note

The least significant bit of the first byte

defines the type of address.
If the bit is 0, the address is unicast;
otherwise, it is multicast.
Note

The broadcast destination address is a

special case of the multicast address in
which all bits are 1s.
 Example

Define the type of the following destination addresses:

a. 4A:30:10:21:10:1A b. 47:20:1B:2E:08:EE
c. FF:FF:FF:FF:FF:FF

Solution
To find the type of the address, we need to look at the second
hexadecimal digit from the left. If it is even, the address is unicast. If it
is odd, the address is multicast. If all digits are F’s, the address is
broadcast. Therefore, we have the following:
a. This is a unicast address because A in binary is 1010.
b. This is a multicast address because 7 in binary is 0111.
c. This is a broadcast address because all digits are F’s.
Figure Categories of Standard Ethernet
Figure Encoding in a Standard Ethernet implementation
Figure 10Base5 implementation
Figure 10Base2 implementation
Figure 10Base-T implementation
Figure 10Base-F implementation
Table 1 Summary of Standard Ethernet implementations
CHANGES IN THE STANDARD

The 10-Mbps Standard Ethernet has gone through several changes before
moving to the higher data rates. These changes actually opened the road to
the evolution of the Ethernet to become compatible with other high-data-
rate LANs.

Bridged Ethernet
Switched Ethernet
Full-Duplex Ethernet
Figure Sharing bandwidth
Figure A network with and without a bridge
Figure Collision domains in an unbridged network and a bridged network
Figure Switched Ethernet
Figure Full-duplex switched Ethernet
 FAST ETHERNET

Fast Ethernet was designed to compete with LAN protocols such as FDDI or
Fiber Channel. IEEE created Fast Ethernet under the name 802.3u. Fast Ethernet
is backward-compatible with Standard Ethernet, but it can transmit data 10
times faster at a rate of 100 Mbps.
The goals of Fast Ethernet can be summarized as follows:
1. Upgrade the data rate to 100 Mbps.
2. Make it compatible with Standard Ethernet.
3. Keep the same 48-bit address.
4. Keep the same frame format.
Figure Fast Ethernet topology
Figure Fast Ethernet implementations
Figure Encoding for Fast Ethernet implementation
Table Summary of Fast Ethernet implementations
 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 design can be summarized as follows:
1. Upgrade the data rate to 1 Gbps.
2. Make it compatible with Standard or Fast Ethernet.
3. Use the same 48-bit address.
4. Use the same frame format.
5. Keep the same minimum and maximum frame lengths.
6. Support autonegotiation as defined in Fast Ethernet.
Note

In the full-duplex mode of Gigabit

Ethernet, there is no collision;
the maximum length of the cable is
determined by the signal attenuation
in the cable.

13.41
Figure Topologies of Gigabit Ethernet

13.42
Figure Gigabit Ethernet implementations

13.43
Figure Encoding in Gigabit Ethernet implementations

13.44
Table Summary of Gigabit Ethernet implementations
Table Summary of Ten-Gigabit Ethernet implementations

13.46
Types of LANs

• The three most popular types of LANs are:

• Token ring network

• FDDI (Fiber Distributed Data Interface) network

• Ethernet
 Token Ring Network
• Originally developed by IBM in 1970’s
• Still IBM’s primary LAN technology
• In cases of heavy traffic, the token ring network has higher
throughput than ethernet due to the deterministic (non-
random) nature of the medium access
• Is used in applications in which delay when sending data
must be predictable
• Is a robust network i.e. it is fault tolerant through fault
management mechanisms
• Can support data rates of around 16 Mbps
• Typically uses twisted pair
 FDDI (Fiber Distributed Data Interface)
• FDDI is a standard developed by the American
National Standards Institute (ANSI) for
transmitting data on optical fibers
• Supports transmission rates of up to 200 Mbps
• Uses a dual ring
• First ring used to carry data at 100 Mbps
• Second ring used for primary backup in
case first ring fails
• If no backup is needed, second ring can
also carry data, increasing the data rate up
to 200 Mbps
• Supports up to 1000 nodes
• Has a range of up to 200 km
Fiber Distributed Data Interface(FDDI)
• History & Development
• Introduction
• FDDI Features
• Working of FDDI
• FDDI Types
• Frame Format
• Applications of FDDI
• Advantages
• Future of FDDI
• Conclusion
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 History & Development

❑ FDDI was considered an attractive campus backbone

technology in the early to mid 1990s since existing Ethernet
networks only offered 10 Mbit/s transfer speeds and Token
Ring networks only offered 4 Mbit/s or 16 Mbit/s speeds.
❑Thus it was the preferred choice of that era for a high-speed
backbone, but FDDI has since been effectively obsoleted by
fast Ethernet which offered the same 100 Mbit/s speeds, but
at a much lower cost and, since 1998, by Gigabit Ethernet due
to its speed, and even lower cost, and ubiquity.

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 Introduction
❑ FDDI LAN standards were developed by subcommittee X3T9.5 of ANSI (American
National Standard Institute)

❑ A networking technology that uses a dual ring topology often with dual networking
equipment (concentrators, etc.)

❑ FDDI facilitates redundancy and protection of the network.

❑ If a device fails, the primary and secondary rings enter a "wrap" state to form a
logical connection and thus maintain the logical ring in the event of a link failure.

❑ FDDI is capable of data rates of 100 Mbps over fiber optic cable (SMF and MMF).
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 FDDI Features
❑Can be implemented over copper (CDDI)
❑The fiber optic cables have clear advantages over the copper cables. There is more
security, and the fiber optic cables are more reliable than any other wire available.
❑The data transfer in the fiber optic cable takes place without any electrical signals
being transmitted.
❑The data flow is undeterred and constant through a fiber optic cable.
❑Long distances can be covered for data flow using the fiber optic cable using a
single node.
❑Maximum of 500 stations
❑Media access - Token passing
❑Speed - 100Mbps
❑Frame Size is large as compared to Ethernet i.e. 4500 bytes
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 Working of FDDI
❑The inside architecture of the FDDI is based on the dual rings where the data is
flowing in the opposite directions.
❑There are two levels of rings the primary and the secondary.
❑Most of the data transmission takes place using the primary ring and the
secondary is idle.
❑However in case the primary does not work the secondary takes over the
primary’s functionalities
❑It also use optical bypass switch for avoiding the wrap

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Wrap condition

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Cont…

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Optical Bypass Switch

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FDDI DAS Ports Attach to the
Primary and Secondary Rings

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Function of Concentrator

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 FDDI TYPES
There are two types of fiber distributed data interface mainly.

• The Single Mode Interface

The single mode uses the laser technology to generate the
light
rays.

• The Multi Mode Interface.

The Multimode fiber uses the LED display to generate the
light rays.

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 Cont…
❑The difference in both these methods is that multi mode as the name
suggests allows many rays at one single point of time to pass and the
single mode laser allows one ray at one time to pass through.
❑The angles at which the light reflects on the cable are all different so
by the time they reach the nodes the time at which they arrive is
different. In a single mode there is no such confusion so the data
arrives at the node in a streamlined fashion.
❑The methodology which the multi mode uses is called modal
dispersion and it is used in an environment which has limited
boundaries.
❑ In comparison with the multi node the single node will be able to
carry more data and deliver at a higher speed along with covering
larger distances.
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Maximum Distance

• 1300nm LED on Multimode fiber

• 50/125 500 Mhz per Km 1.9 miles
• 62.5/125 500 Mhz per Km 2.9 miles
• 85/125 300 Mhz per Km 1.5 miles
• 100/140 200 Mhz per Km 1 mile

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Cont….

• 1300nm Laser on Multimode fiber

• 50/125 1,400 Mhz per Km 16.3 miles
• 62.5/125 1,400 Mhz per Km 16.3 miles
• 85/125 400 Mhz per Km 1.8 miles
• 100/140 600 Mhz per Km 2.7 miles
• 1300nm Laser on Single Mode fiber
• 8/125 100,000 Hhz per Km 29.8 miles

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FDDI frame format

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Applications of FDDI
• FDDI is used mainly in mission critical and high traffic networks where
large amounts of data flow need to flow quickly and efficiently
• FDDI is used anywhere that utilizes a large network in need of high
bandwidth. Businesses, the Government, hospitals and other medical
fields, stock exchanges and money markets etc.

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 Advantages
❑Higher Capacity and Performance than older LANs

❑More Simultaneous Transactions

❑Higher Availability (dual ring topology)

❑Predetermined Performance (adding users have minimal impact on throughput)

❑Longer Distance Loops (2 kilometers to 100 kilometer)

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Future of FDDI
• A newer version of FDDI, called FDDI-2, supports the transmission of
audio and visual information as well as data.
• Another version, FDDI-Full Duplex Technology or FFDT, uses the same
network setup as FDDI but can support twice the data rate, or 200
Mbps.

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 Conclusion
❑After the advent of FDDI internet has advanced to a great extent even with
common day to day users. The internet service providers are able to
provide better services to the people and are able to facilitate internet in a
better fashion.
❑ Since internet has advanced and the number of users has increased, more
and more businesses have started e-commerce applications on the
internet.
❑ Because the fiber distributed data interface is a safe and secure medium
when it comes to cables the ecommerce transactions have found a reliable
media.
❑ FDDI through single node transfers are widely adapted by MNC’s for
communication between different branches.

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Thank You!

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