3. LAN
• Standard
– OSI (Open Systems Interconnection)
– IEEE (Institute of Electrical and Electronic Engineers)
– ITU-T (Int’l Telephone Union – Telecom. Sector)
– ISO (International Standards Organization)
– EIA (Electronic Industries Association)
– ETS (European Telecom. Standard)
4. Communications Hardware
• Repeater
– Extends distance limitation on networks (both voice
and data)
– Filters noise
– Regenerates signals
– For twisted pair wire, repeaters are placed every 100
meters
• Amplifier
– Extends distance limitation on networks (both voice
and data)
– Amplifies both signal and noise
5. Communications Hardware
• Bridge
– Connects two LANs using same protocol
– Single path between LANs
– Minimal sophistication
• Router
– Connects multiple LANs using same protocol
– Choice of paths between LANs
– Mainstay of internetworking
6. Communications Hardware
• Gateway
– Connects multiple LANs using any protocol
– Very sophisticated
– Supports today’s internet by providing access
points to several networks
• Hub
– Connects nodes to a network
– Sometimes acts as repeater
7. Communications Hardware
• Switch
– Connects multiple LAN segments using the
same protocol
– Connections may use twisted pair, coaxial
cable, or fiber optics wiring
– Faster than bridges
– Enables simultaneous communication between
multiple network segments
8. Ethernet
• Ethernet was developed jointly by Xerox, Intel,
and DEC in 1980
• DEC (Digital Equipment Corporation) a computer
company that specialized in mini-computers in the
1970s. It was acquired by Compaq and Compaq
merged with HP.
• This was the first commercial LAN system
• Ethernet is a simple protocol to implement
• Ethernet addresses the layers 1 and 2 functionality
for the OSI model
• Ethernet standard is very close to IEEE 802.3
standard, but has some minor differences
9. Ethernet
• Ethernet uses bus topology (which we will discuss
next)
• Ethernet transmits a baseband signal at 10 Mbps
• Baseband signals are digital and bidirectional
• Ethernet allows the user data to have a variable
length up to 1500 bytes
• Unlike HDLC and SDLC protocols, ethernet uses
a length field in the header to identify the length
of the user data in bytes. Because of this, no
special bit pattern is needed to recognize the start
and end of the user data.
10. Ethernet frame format
6-bytes 6-bytes 2-bytes Variable length 4-bytes
Destination Source length User data CRC-32
address address
12. Bus topology
• It is a contention-based topology, which means that each
node on the network must contend for access
• Each node listens to traffic on the network
• When a node has packets to transfer and the bus is not
busy, then the packets are put on the bus in both directions,
with the destination address marked on the packets
• All nodes listen to traffic on the network and the node that
has packets addressed to it, receives the packets
• No routing or switching is involved in data transfer
14. Tree topology
• Tree topology is a variation on bus topology
• A special node is designated as root
• The primary reason for this topology is to
segment nodes so that not all nodes need to
listen to packets broadcast on a segment
• This adds a layer of security in the form of
unwanted nodes not listening to the network
traffic
• Speeds up data transfer since there will be
fewer nodes on each segment
16. Star topology
• This is another variation on bus topology
• This has a central hub, a passive device
• Star is a logical bus and a physical ring
• Hub has ports in multiples of 8. Multiple hubs can be
connected in a daisy chain format
• Easy to add nodes to the network and remove nodes from
the network
• Central node does switching between nodes
• Multiple nodes can communicate simultaneously without
collision
• Potential problem is the single point of failure for the
network when the central node fails
18. Ring topology
• The nodes are connected in a ring pattern
• Unlike bus topology, each node on the ring acts as a
repeater on the network
• Nodes access the network using a token, which eliminates
the need for contention as in bus topology
• Token is a series of bits that identifies the node that has the
right to transmit at any given time
• Example of a token: Assume that there are 6 nodes on the
network. The nodes are labeled 1 through 6 and the token
would consist of 3 bits. The token 100 will indicate that
node 4 has the token.
• Tokens circulate in a single direction from a node to its
neighbor
20. OSI 7-layer model
Source Destination
Application Application
Presentation Presentation
Session Session
Transport Transport
Network Network
Data link Data link
Physical Physical
21. IEEE 802
• 802.1 General LAN management of OSI
layers 3 through 7
• 802.2 LLC sublayer
• 802.3 Ethernet
• 802.4 Token bus
• 802.5 Token ring
• 802.6 MAN
• 802.7 Broadband, in general
25. ATM VPI and VCI
VP I 1 VP I5
VC I 1 VC I 1
VC I 2 VC I 2
VCI 4
VP I6
VCI 7
V C I 2 V P I 2
V C I 6
V C I 2
V C I 6
VP I 3 VP I 3
VCI 4
VCI 7
V P Sw itc h
26. TCP/IP functions
• Establish a connection between nodes
• Manage data flow on the network
• Handle transmission errors
• Terminate connection at the end
• TCP is a connection-oriented protocol, meaning that a
packet sent to the next node is monitored for proper receipt
• IP is a connection-less protocol, meaning that a packet sent
to the next node is not monitored for proper delivery
• Since TCP and IP work together, the packet delivery is
reliable
• Connection-less mode is known as User Datagram
Protocol (UDP)
27. TCP/IP 5-layer model
• TCP/IP protocol is divided into 5 layers
– Application layer
– Transport layer
– Network layer
– Data link layer
– Physical layer
28. IP Addressing
• IP address consists of 4 octets: n.n.n.n
where n is in the range 0 to 255
• This form of IP address is known as IPv4,
denoting IP address Version 4
• A new form of IP address known as IPv6,
denoting IP address Version 6, has been
proposed. It uses 128-bit addressing instead
of 32-bit addressing.
29. IP Address Hierarchy
• There are 3 main classes of IP addresses in use
and two additional classes of IP addresses
available for multicast and testing
• Class A First octet range: 1 – 126
– IBM, AT&T, HP, Merck, Stanford University
• Class B First octet range: 128 – 191
– U of L and most other universities
• Class C First octet range: 192 – 223
– IGLOU, Louisville’s first ISP
30. UDP
• User Datagram Protocol is a ‘best effort’ protocol
• ‘best effort’ means no guarantee of delivery
• This is a connection-less protocol
• UDP does not provide reliability
• UDP sends out packets without first establishing a
connection
• RFC 768 describes UDP
• UDP header consists of source port, destination port,
length, checksum
• Example of UDP: TFTP (Trivial File Transfer Protocol).
TFTP is used when bootsrapping diskless system
• TFTP is on UDP port 69
