1.Know why shadow copies are used in routers.

A shadow copy is stored because, the forwarding decision is made locally, at each input port,without invoking the centralized routing processor. Also decentralized forwardingavoids creating a forwarding processing bottleneck at a single point within therouter

2.Know the three types of switching fabrics.

Switching via memory: Fabric switching with the use of CPU

Switching via a bus: Fabric switching via shared buses on input and output port

Switching via interconnection network: fragmenting datagrams into fixed length cells switch cells through fabric

3.Know where HOL blocking occurs.

HOL blocking – a queued packet in an input queue must wait for transfer through the fabric because it is blocked by another packet at the head of the line. It occurs at the input port.

4.Know the characteristics of the RIP and OSPF router advertisements.

With OSPF, a router periodically broadcasts routing information to all other routers in the AS, not just to its neighbouring routers. This routing information sent by a router has one entry for each of the router’s neighbours; the entry gives the distance from the router to the neighbour. A RIP advertisement sent by a router contains information about all the networks in the AS, although this information is only sent to its neighbouring routers.

5.Know the advantages and disadvantages of using a virtual circuit architecture versus a datagram architecture.  Understand overheads for each structure.

6.Know when to use a virtual circuit architecture versus a datagram architecture and vice-versa.

7.Know the characteristics of a Delta network self-routing property.  Be able to draw a Delta network.

Delta network has self-routing property

The path for a cell to take to reach its destination can be determined directly from its routing tag (i.e., destination port id)

Stage k of the MIN looks at bit k of the tag

If bit k is 0, then send cell out upper port

If bit k is 1, then send cell out lower port

8.Know how loops in paths can be detected in BGP.

The BGP protocol propagates and obtains reachability of all the neighbouring AS (Autonomous Systems).

The attributes AS-PATH and NEXT-HOP are used for routing.

The router verifies all the AS numbers. If it finds its own number, it will discard the advertisement to prevent the looping. In this way BGP detects the loops and prevents them.

9.Know the limitations of an intra-AS routing algorithm and why different algorithms can be used in the AS networks.

Intra-AS Routing

 Also known as Interior Gateway Protocols (IGP). Most common IGP:

 RIP: Routing Information Protocol

Limits: Limits RIP to networks with a diameter of 15 hops

If no advertisement heard after 180 sec –> neighbor/link declare dead

     Other Intra-AS algorithms include

·OSPF: Open Shortest Path First:      all OSPF messages authenticated (to prevent malicious intrusion)

·IGRP: Interior Gateway Routing Protocol: Distance Vector, like RIP but with advanced features like OSPF. Uses TCP to exchange routing updates

Inter-As algorithms can also be used in these networks such as the Border Gateway protocol (BGP)

·similar to Distance Vector protocol

·Avoids count-to-infinity problem by identifying yourself in a path advertised to you

10.Know why policy plays an important role in routing, both in the LAN and the Internet.  Understand why policy is more important in inter-AS as opposed to intra-AS.

Among ASs, policy issues dominate. It may well be important that traffic originating in a given AS specifically not be able to pass through another specific AS. Similarly, a given AS may well want to control what transit traffic it carries between other ASs. We have seen that BGP specifically carries path attributes and provides for controlled distribution of routing information so that such policy-based routing decisions can be

made. Within an AS, everything is nominally under the same administrative control, and thus policy issues play a much less important role in choosing routes within the AS.

·In Inter-AS: Admin wants control over how its traffic is routed, who routes through its net(work), and hence policy plays a major role in the routing.

·Intra-AS: Single admin, so no policy decisions needed for this network

They also vary is both scale and performance

11.Know the purpose of BGP NEXT-HOP and AS-PATH attributes.

·BGP NEXT HOP attribute tells the receiver of the advertisement the node to send packets to in order to reach the advertised prefix destination

·The BGP AS-Path attribute contains the Autonomous System numbers for each AS that the announcement for the prefix passed through

·It is used to detect and prevent routing loops

12.Know the criteria for routers to connect to multicast groups, including the characteristics of the different tree structures.

13.Know the goal of multicast routing.

·Efficient data distribution – send only one copy of pkt over each link, not n

·Anonymous group addressing – ex. to get a phone number, you call the operator—any operator

14.Know the characteristics of a TCP data stream exchange between a client and server.

·Stream Data transfer: Applications working at the Application Layer transfers a contiguous stream of bytes to the bottom layers. It is the duty of TCP to pack this byte stream to packets, known as TCP segments, which are passed to the IP layer for transmission to the destination device. =

·Reliability: The most important feature of TCP is reliable data delivery.

·Flow control:

·Multiplexing: Multitasking achieved through the use of port numbers.

·Connections: Before application processes can send data by using TCP, the devices must establish a connection. address and port number, which can uniquely identify a connection.

·Full duplex: TCP provides for concurrent data streams in both directions

15.Know that TCP uses a Go-Back-N acknowledgement structure.

The Go-Back-N ack structure is a pipeline protocol

TCP does hop-by hop flow control using a Go-Back-N approach

Steps in Go-Back-N

-pipelined protocol where sender can have up to N unACKed packets in pipeline

-received only sends cumulative ack

-sender has timer for oldest unACKed packet

-when timer expires retransmit all unACKed packe

16.Know the characteristics and be able to explain how a TCP Slow Start process is executed, including what happens when a timeout occurs.

17.Know when a TCP Slow-Start transition ends and congestion avoidance begins in the TCP process.

18.Know the characteristics of the three Application architectures.

19.Know the purpose and characteristics of cookies.

20.Understand the Bit Torrent concept in point-to-point communications.