What is….. It ?
• A computer network consists of end systems,
which are sources of information, which are
sources of information, which communicate
through the transit systems interconnecting
them. The transit system is also called an
interconnect subsystem or a subnetwork.
– Topology refers to the way the network is laid out,
either physically or logically. Two or more devices
connect to a link, two or more links form a
Asymmetrical DSL (ADSL)
• ADSL divides up the available frequencies in a
line on the assumption that most Internet
users look at, or download, much more
information than they send, or upload.
– Under this assumption, if the connection speed
from the Internet to the user is three to four
times faster than the connection from the user
back to the Internet, then the user will see the
most benefit (most of the time).
Asymmetrical DSL (ADSL)
• ADSL is an adaptive technology.
• The system uses a data rate based on the
condition of the local loop line.
Most existing local loops can handle
bandwidths up to 1.1 MHz.
OTHER TYPES OF DSL:
• Symmetric DSL (SDSL)
• High-bit-rate DSL (HDSL)
• Very high bit-rate DSL (VDSL)
Symmetric DSL (SDSL)
• Used mainly by small businesses & residential
• Bit rate of downstream is higher than
High-bit-rate DSL (HDSL)
• Used as alternative of T-1 line
• Uses 2B1Q encoding
• Less susceptible to attenuation at higher
• Unlike T-1 line (AMI/1.544Mbps/1km), it can
reach 2Mbps @ 3.6Km
Very high bit-rate DSL (VDSL)
• Uses DMT modulation technique
• Effective only for short distances(300-1800m)
downstream : 50 - 55 Mbps
: 1.5-2.5 Mbps
• Starting and ending characters with character
• Starting end ending flags with bit stuffing.
• STOP N WAIT
• SLIDDING WINDOW
– SLIDDING WINDOW GO BACK N ARQ
– SELECTIVE REJECT ARQ
Error control :
• Cyclic redundancy check :
If Original Data to be transmitted is 110101010
Divisor is 10101
The data is appended with 4 zeros and divided by the divisor.
The remainder is added to the dividend in order to obtain the
data to be transmitted.
Therefore, transmitted data : 1101010101011
Broadly HDLC features are as follows:
• Reliable protocol
– selective repeat or go-back-N
• Full-duplex communication
– receive and transmit at the same time
• Bit-oriented protocol
– use bits to stuff flags occurring in data
• Flow control
– adjust window size based on receiver capability
• Uses physical layer clocking and synchronization to
send and receive frames
• Defines three types of stations
• Defines three types of data transfer mode
– Normal Response mode
– Asynchronous Response mode
– Asynchronous Balanced mode
• Three types of frames
• The three stations are :
– Primary station
• Has the responsibility of controlling the operation of data flow the
• Handles error recovery
• Frames issued by the primary station are called commands.
– Secondary station,
• Operates under the control of the primary station.
• Frames issued by a secondary station are called responses.
• The primary station maintains a separate logical link with each
– Combined station,
• Acts as both as primary and secondary station.
• Does not rely on other for sending data
• The three modes of data transfer operations are
– Normal Response Mode (NRM)
• Mainly used in terminal-mainframe networks. In this case,
• Secondaries (terminals) can only transmit when specifically instructed by
the primary station in response to a polling
• Unbalanced configuration, good for multi-point links
– Asynchronous Response Mode (ARM)
• Same as NRM except that the secondaries can initiate transmissions
without direct polling from the primary station
• Reduces overhead as no frames need to be sent to allow secondary nodes
• Transmission proceeds when channel is detected idle , used mostly in
– Asynchronous Balanced Mode (ABM)
• Mainly used in point-to-point links, for communication between
Data Link Control HDLC frame structure
11-7 POINT-TO-POINT PROTOCOL
Although HDLC is a general protocol that can be used
for both point-to-point and multipoint configurations,
one of the most common protocols for point-to-point
access is the Point-to-Point Protocol (PPP). PPP is a
• Link State Routing
– Discover its neighbors and learn their network
– Measure the delay or cost to each of its neighbors.
– Construct a packet telling all it has just learned.
– Send this packet to all other routers.
– Compute the shortest path to every other router.
• Identifying a CIDR block requires both an address and a mask
– Slash notation
– 188.8.131.52/21 for addresses 184.108.40.206 – 220.127.116.11
• Here the /21 indicates a 21 bit mask
– All possible CIDR masks can easily be generated
• /8, /16, /24 correspond to traditional class A, B, C categories
• IP addresses are now arbitrary integers, not classes
• Raises interesting questions about lookups
– Routers cannot determine the division between prefix and suffix just by
looking at the address
• Hashing does not work well
• Interesting lookup algorithms have been developed and analyzed
CIDR – A Couple Details
• ISP’s can further subdivide their blocks of
addresses using CIDR
• Some prefixes are reserved for private
– 10/8, 172.16/12, 192.168/16, 169.254/16
– These are not routable in the Internet
• A repeater (or regenerator) is an electronic device that
operates on only the physical layer of the OSI model.
• A repeater installed on a link receives the signal before it
becomes too weak or corrupted, regenerates the original
pattern, and puts the refreshed copy back on the link.
• A repeater does not actually connect two LANS; it connects
two segments of the same LAN.
• A repeater forwards every frame; it has no filtering capability.
• A Hub is a multiport repeater. It is normally used to create
connections between stations in a physical star topology.
• Bridges operate in both the physical and the data link
layers of the OSI model.
• Bridges can divide a large network into smaller segments. They
contain logic that allows them to keep the traffic on each segment
separate. When a frame (or packet) enters a bridge, the bridge not
only regenerates the signal but checks the destination address and
forwards the new copy only to the segment the address belong.
• A bridge operates in both the physical and the data link layers.
• As a physical layer device, it regenerates the signal it receives.
• As a data link layer device, the bridge can check the physical
(MAC) address (source and destination) contained in the
• A bridge has filtering capability. It can check the destination
address of a frame and decide if the frame should be
forwarded or dropped. If the frame is to be forwarded, the
decision must specify the port.
• A bridge does not change the physical (MAC) addresses in a
• A bridge has a table used in filtering decisions.
Types of Bridges
• To select between segments, a bridge must have a look-up
table that contains the physical addresses of every station
connect to it. The table indicate to which segment each
• The address table must be entered manually, before a
simple bridge can be used.
• Whenever a new station is added or removed, the table
• Installation and maintenance of simple bridges are timeconsuming and potentially more trouble than the cost
savings are worth.
• Routers have access
to network layer
contain software that
enables them to
determine which of
several possible paths
addresses is the best
for a particular
• Routers operate in
the physical, data link,
and network layers of
the OSI model.
• Routers relay packets among multiple interconnected
networks. They route packets from one network to any of
a number of potential destination networks on an
• Gateways potentially operate in all seven layers of the OSI
• A gateway is a protocol converter. A router by itself
transfers, accepts, and relays packets only across networks
using similar protocols.
A gateway can accept a packet formatted for one protocol
(e.g. AppleTalk) and convert it to a packet for another
protocol (e.g. TCP/IP).
• A gateway is generally software installed within a router.
The gateway understands the protocols used by each
network linked into the router and is therefore able to
translate from one to another.
What is SONET?
Synchronous Optical Network standard
Defines a digital hierarchy of synchronous signals
Maps asynchronous signals (DS1, DS3) to synchronous format
Defines electrical and optical connections between equipment
Allows for interconnection of different vendors’ equipment
Provides overhead channels for interoffice OAM&P
= SYNCHRONOUS TRANSPORT SIGNAL
= OPTICAL CARRIER
(“..result of a direct optical conversions of the STS after
synchronous scrambling” - ANSI)
SONET Network Layers
DS3, DS1, etc
• Map Services & POH Into SPE
• Path Protection/Restoration
• Other Path OA&M Functions
• Combine SPE & LOH
• Sync & Mux For Path Layer
• Line Protection/Restoration
• Other Line OA&M Functions
• Add SOH & Create STS Signal
• Framing, Scrambling
• Section OA&M Functions
Physical • E/O Conversion
(Photonic) • Line Code
• Physical Signal
[No additional overhead]
Functional Description of SONET Layers
Transmission over OC-N
Internet Protocol (IP)
– Layer 3 (Network layer)
– Unreliable, Connectionless, Datagram
– Best-effort delivery
• Popular version: IPv4
• Major functions
– Global addressing
– Datagram lifetime
– Fragmentation & Reassembly
• Deficiency of IPv4
• Address space exhaustion
• New types of service Integration
– Quality of Service
– Mobility (MIPv6)
• Header and format limitations
Advantages of IPv6 over IPv4
Larger address space
Better header format
Allowance for extension
Support for resource allocation
Support for more security
Support for mobility
Advantages of IPv6 over IPv4 (1)
Payload ID for QoS in
Resolve IP address to
a link layer address
Using Flow label field
Both router and the
Only supported at the
Advantages of IPv6 over IPv4 (2)
address of the best
Send traffic to all
nodes on a subnet
Link-local scope allnodes multicast
Manually or DHCP
Manage local subnet
• Wireless technology for short-range voice and
• Low-cost and low-power
• Provides a communication platform between
a wide range of “smart” devices
• Not limited to “line of sight” communication
Home Audio System
• Automatic synchronization between mobile
and stationary devices
• Connecting mobile users to the internet using
bluetooth-enabled wire-bound connection
• Dynamic creation of private networks
Ad Hoc Networks
• Up to 8 devices can be actively connected in
• Piconets can be combined to form scatternets
providing unlimited device connectivity
• Uses 2.4 GHz ISM band spread spectrum radio
(2400 – 2483.5 MHz)
– Open to everyone worldwide
– Can be noisy (microwaves, cordless phones,
garage door openers)
In order to mitigate interference, Bluetooth
implements frequency hopping
1600 hops per second through 79 1MHz
Spreads Bluetooth traffic over the entire ISM
All slaves in piconet follow the master for
frequency hop sequence
• Whenever there is a
connection between two
Bluetooth devices, a piconet is
• Always 1 master and up to 7
• Any Bluetooth device can be
either a master or a slave
• Can be a master of one piconet
and a slave of another piconet
at the same time (scatternet)
• All devices have the same
timing and frequency hopping
• Formed by two or
• Master of one piconet
can participate as a
slave in another
• No time or frequency
The socket primitives for TCP.