Today, I learned about the CSMA collisions, "Taking turns" MAC protocols and Cable Internet. Compared to ALOHA, CSMA is more polite protocol algorithm. CSMA: Carrier Sense Multiple access CSMA: listen before transmit: If channel sensed idle: transmit entire frame. If channel sensed busy, defer transmission. In human analogy, "don't interrupt others!" Collision can still occur: Due to propagation..
Continue to previous review. An ideal multiple access protocol Given: broadcast channel of rate R bps Desiderata: When one node wants to transmit, it can send at rate R. When M nodes want to transmit, each can send at average rate R/M The protocol is fully decentralized: No special node to coordinate transmissions No synchronization of clocks, time slots No master node that represents a single p..
Today, I learned about the MAC protocol. Where is the link layer implemented? At each interface of hosts, routers, switches, access points Link layer implemented mainly in "adoptor" (aka network interface card NIC) or on a chip. e.g. Ethernet card (LAN), 802.11 card (WLAN) NIC implements link layer and physical layer Link layer is implemented in both NIC (hardware) Operating System (software) Fr..
Today, I learned more about the TCP. There are two type of message in TCP: Seq# Byte stream "number" of first byte in segment's data Ack# Seq # of next byte expected from other side So, the packet which is not acknowledged yet is yellow packets. Buffer moves to the next sequence of packets. RTT: Round Trip Time RTT is the length of time it takes for a message to be sent plus the length of time i..
Today, I learned about the TCP. These are the features of TCP. Point-to Point (not Bcast) Single sender, single receiver. Routers don't know TCP con. Reliable, in-order byte stream no "message boundaries" Pipelined TCP congestion and flow control set window size TCP connection state Send and receive buffer Congestion ctrl parameters Sequence number, ACK number for reliability Full duplex data Bi..
Today, I learned about the VLANs. VALNs: Motivation Drawbacks of this configuration: Lack of traffic isolation: Single broadcast domain: all layer-2 broadcast traffic (APR, DHCP, switch flooding to find unknown location of destination MAC address must cross entire LAN. Secuirty/privacy, efficiency issues Inefficient use of swithches: Each small group needs a switch, while a switch has 96 ports M..
Today, I learned about the switch. What is switch?? ๐คจ Features: Hosts have dedicated direct connection to switch. Switches buffer packets. Ethernet protocol used on each incoming link, but no collisions; full duplex. Each link is its own collision domain. Example: 'A-to-A' and 'B-to-B' can transmit simultaneously, without collision. Here is the question: how does switch know A' reachable via int..
Today, I leanred about the NAT: network address translation. Why there is a NAT in the real world?? Motivation: what is the problem? Number of IP addresses required in the internet is much more than the 4 billion available IP addresses. If a subnet grows larger than the ISP's IP address range, no IP address will be available for them. Solution: IPv6: larger IP address, more number of IP addresse..
Today, I learned about the DNS in Network programming class. So, What is DNS?? DNS stands for "Domain Name System." In real world, we identifies people with SSN, their name or passport number. Like this, our network server identifies with IP address and "name" like human. DNS is a distributed database. Implemented in a hierachy of many name servers. DNS is an application-layer protocol. Hosts an..
Today, I reviewed the HTTP connections. HTTP connections Non-persistent HTTP At most one object sent over TCP connection connection then closed Downloading multiple objects required mutiple connections Persistent HTTP Multiple objects can be sent over single TCP connection between client, server. Here is the picture describing Non-persistent HTTP And this is the Persistent HTTP. In the Web serve..
