- A TCP connection is defined by uniquely by the four values (Client Ipaddr, Clientport, ServerIpaddr, Serverport)
- Hub – connects different machines to the internet.
- It simulates a shared cable.
o Analog device, retransmits signals from one segment to the other.
o Used to connect two Ethernets.
- Its retransmits packets but also retransmits noise and collisions.
- connects two Ethernet segments
- It is a digital device.
- It understands packets and it will forward frames from one segment to the other without forwarding noise or collisions.
- It only forwards packets that are destined to the other segment.
o It will forward packet from
IT will not forward packet from
- Bridges need to know which computers are locked in each segment.
- A bridge will start with an empty table and will forward all packets. If a destination his not in list, it will forward.
- White forwarding packets, it will learn what computers are connected in each segment.
- At the end it will forward only the packet when necessary.
- Always forwards broadcast and multicast.
- Bridges also listen the network in promiscuous mode when learning.
It is possible to extend an Ethernet with a bridge and an optical fiber
Why do we use two bridges when using bridge?
Using satellite it has long connection and satellite is more expensive.
Two bridges are necessary because otherwise extra traffic is added t other satellite link.
For Example – if B2 does not exits, traffic from C to D will go across the satellite link.
N ports, R
- Physically similarly to the hub.
- Logically similarly to a bridge
- Operates on packets, understands address
- Only forwards frame if necessary
- Permits separate port of computer to communicate at same time
- Highest “total” throughput considering all connections simultaneous is higher then a hub
Hub – a box that simulates a common shared cable.
- Two computers that communicates will prevent other pair of computers from using the network while C1 & C2 communicate C3 & C4 will have to wait.
- Total throughput: Communication from all the computers to all the computers will be equal to
For 10Mbits/sec : 10 Mbits/sec
- Two pairs of computers can communicate with each other independently.
- An Ethernet switch can be represented as a set of networks equal to the # of computers connected there is a bridge connecting each pair of networks.
- The communication between C1 and C3 can go in parellel with the communications between C4 and CR and so on.
- Total throughput the # of pairs computers * Ethernets
- Total throughput = .5 the ports times speeds = (4/2)*10 = 20Mbits.
- Switch is better (faster).
- Switch is more expansive as the # of ports grow
- More secure, a computer running in promiscuous mode will not be able to get all the packets of the network.
- History of internet
o Double every 9-12 months.
- What is a network?
- Transmission Media
- Types of Encoding
o Analog – continuous
o Digital – Discrete (numbers)
o Send line (Bit are sent at one at a time)
o Start bit/end bit
o Speeds of kbps – 28.8 Kbps
o Limited distance
Carrier wave Modulation
o Long distance
- Network parameters
o Propagation delay
Revolution between bandwidth and throughput
D = 2Blog2K
D = throughput
B = bandwidth
K = # levels used to encode signal
It does not consider noise
C= Blog2 (1+s/N)
C= throughput bps
B= Bandwidth hz
S= Power of Signal
N= Power of Noise
It considers noise
o Sending Multiple signals in a single channel.
o Frequency Division Multiplexor
o Time Division Multiplexor
o Divides data into small units
o Allow a fair acces to the networks
o SOT/EOT characters
o Byte stuffing
Handling of errors
Local Area Network
How it works
o How collisions are handled
o Exponential back off
o Unicast, Broadcast, multicast
o Broadcast in Ethernet works
o Promiscuous Mode
o Ethernet frame
o Thick net
o Thin net
o Twisted Pair
o FDDI, Token Ring,
o How the token parsing works
o FDDI Failure Recovery works
The exam will be 70% theory and 30 % labs.