Chapter 1/Lecture 1 Introduction Flashcards
What are the three elements in networking?
Hosts(end systems), Communication Links(fiber, copper, radio) and Forwarding/network nodes(routers and switches)
What is the internet, and what is its value?
Network of networks(interconnected ISPs). Value increase with connectivity.
What is a packet, and what is packet-switching?
A packet is a part of an application-layer message, which is broken down into several packets. Packet-switching is the process of sending packets from A to B, where each packet can take a different route.
What’s the difference between routing and forwarding?
Routing; the act of determining route for packet(s)(source->destination). Forwarding; move packets from input to output.
What is the difference between peering and transit link?
In peering, two networks connect together for connectivity without paying one or the other. With a transit link, one network pays the other for the connection/link.
What does POP and IXP stand for, and what are they?
POP; Point of presence, IXP; Internet eXchange Point. Conceptually they are the same(both concern with peering links), but they differ in that POP is concerned with one connectionpoint for one ISP(the connection where the ISP peers with other networks), while IXP is the place where several ISPs connect together.
What’s the difference between Tier 1, 2 and 3 networks?
Tier 1: A network that can reach every other network on the Internet without purchasing IP transit or paying settlements.
Tier 2: A network that peers with some networks, but still purchases IP transit or pay settlements to reach at least some portion of the Internet. Some are larger than the tier-1 networks, via massive peering.
Tier 3: A network that solely purchases transit from other networks to reach the Internet. Pure resellers of Internet connectivity.
What’s a protocol?
Protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt
What are the layers/stack of Internet?
Application(L5, http, ftp etc), Transport(L4, TCP, UDP etc), Network(L3, IP, RIP, BGP etc), Link(L2, Ethernet, WiFi/802.11), Physical(L1, bits on the wire).
ISO splits Application into Application(L7), Presentation(L6) and Sesson(L5).
What happens with messages moved down/up the stack? What’s it for? Does anyone change during transit?
It’s (encapsulated/multiplexed)/(decapsulated/demultiplexed) with headers from/to the current level of the stack, before it’s passed to the next layer. The headers decides what happens next(ex: if going from L3 to L4, decided on TCP or UDP).
Application(L5) and Transport(L4) is not changed, TTL and Checksum differs from node to node in Network(L3), Link(L2) can vary greatly due to different link technologies.
