Packet-Switched Networks and the Internet: A Comprehensive Overview, Essays (university) of Computer Science

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Chapter 7 – Networking Support

Contents

 Packet-switched networks.  The Internet.  Web access and TCP congestion control.  Network management; class-based queuing.  Cloud interconnection networks.  Storage area networks.  Content delivery networks.  Overlay networks.

Dan C. Marinescu^ Cloud Computing: Theory and Practice. Chapter 7^2

The Internet

 Collection of separate and distinct networks.  All networks operate under a common framework consisting of:  globally unique IP addressing.  IP routing.  global Border Gateway Routing (BGP) protocols.  IP only provides best effort delivery - any router on the path from the source to the destination may drop a packet if it is overloaded.  The Internet uses two transport protocols  UDP (User Datagram Protocol) - a connectionless datagram protocol. The UDP transport protocol assumes that error checking and error correction are either not necessary or performed by the application. Datagrams may arrive out of order, duplicated, or may not arrive at all.  TCP (Transport Control Protocol) - a connection-oriented protocol. TCP provides reliable, ordered delivery of a stream of bytes from an application on one system to its peer on the destination system.

Cloud Computing: Theory and Practice.

The Internet protocol stack

Cloud Computing: Theory and Practice.

Teleconferencing

Email

Application Layer Telnet

Transport Layer

Network Layer

Physical and Data Link Layers LANs Wireless Direct Broadcast Sateliite

ATM Dial-up Modems

Videoconferencing WWW FTP

IP

Cable Frame Relay

RealAudio

TCP UDP

IPv4 vs IPv

 IPv4 has an addressing capability of 2^32 , or approximately 4.3 billion addresses, a number that proved to be insufficient.

 IPv6 has an addressing capability of 2^128 , or 3.4x10^38 addresses.

 Other major differences between IPv4 and IPv6:

 IPv6 supports new multicast solutions and but not traditional IP broadcast.  IPv6 hosts can configure themselves automatically when connected to a routed IPv6 network using the Internet Control Message Protocol version 6.  Mandatory support for network security. Internet Network Security(IPsec) is an integral part of the base protocol suite in IPv6.

 Migration from IPv4 to IPv6 is a very challenging and costly proposition.

Cloud Computing: Theory and Practice.

IP and MAC addresses, ports and sockets

 IP address  logical address assigned dynamically by a DHCP server. A host may have multiple IP addresses as it may be connected to more than one network.

 MAC address  unique physical address of each network interface.

 Network interface  hardware connecting a host with a network.

 Port  software abstraction for message delivery to an application.

 Sockets  software abstraction allowing an application to send and receive messages at a given port; implemented as two queues, one for incoming and the other for outgoing messages.

Cloud Computing: Theory and Practice.

The relations between Internet networks

 Three type of relations:  Peering - two networks exchange traffic between each other's customers freely.  Transit - a network pays to another one to access the Internet.  Customer - a network is paid to allow Internet access.  The networks are commonly classified as:  Tier 1 - can reach every other network on the Internet without purchasing IP transit or paying settlements.  Tier 2 - an Internet service provider who engages in the practice of peering with other networks, but who still purchases IP transit to reach some portion of the Internet; the common providers on the Internet.  Tier 3 - purchases transit rights from other networks (typically Tier 2 networks) to reach the Internet.

Cloud Computing: Theory and Practice.

The relation of Internet networks based on the transit and paying settlements. There are three classes of networks, Tier 1, 2, and 3; an IXP is a physical infrastructure allowing ISPs to exchange Internet traffic. Cloud Computing: Theory and Practice.

IXP

Internet – Tier 1 networks

Tier 2 network

POP 1

Tier 2 network

Tier 3 networks

Internet users

The transformation of the Internet. The traffic carried by Tier 3 networks increased from 5.8% in 2007 to 9.4% in 2009; Goggle applications accounted for 5.2% of the traffic in 2009.

Cloud Computing: Theory and Practice.

Sprint, MCI, UUnet,Psnet NAP NAP NAP

BackboneNational Operators RegionalAccess Providers

AccessLocal Providers

(a) Textbook Internet prior to 2007; the global core consists of Tier 1 networks

Customer IPNetworks

ISP 1 ISP 2 ISP 3 ISP n

(b) The 2009 Internet reflects the effect of comoditization of IP hosting and ofcontent-delivery networks (CDNs)

Regional-Tier 2 providers

Customer IPNetworks

IXP IXP IXP ISP 1

National BackbonesGlobal Transit/ Large Content, Consume, Hosting CDN^ “Hyper Giants”

ISP 2

InternetGlobal Core

The average download speed for broadband access advertised by several countries

Cloud Computing: Theory and Practice.

Congestion control in TCP

 Algorithms to control congestion include Tahoe, an algorithm based on: (1) slow start, (2) congestion avoidance, and (3) fast retransmit.

 Slow start means that:

 (a) the sender starts with a window of two times MSS (Maximum Segment Size).  (b) for every packet acknowledged, the congestion window increases by 1 MSS so that the congestion window effectively doubles for every RTT (Round Trip Time).

 To overcame the limitations of the slow start application, strategies have been developed to reduce the time to download data over the Internet. For example,  Firefox 3 and Google Chrome open up to six TCP connections per domain.  Internet Explorer 8 opens 180 connections.

Cloud Computing: Theory and Practice.

Congestion control in TCP (cont’d)

 The strategies used by the browsers to avoid the congestion control mechanisms circumvent the mechanisms for congestion control and incur a considerable overhead.  The TCP latency is dominated by the number of RTTs during the slow start phase.  Given that the average page size is 384 KB, a single TCP connection requires multiple RTTs to download a single page.  It is argued that a better solution is to increase the initial congestion window of TCP. The effects of this solution:  It ensures fairness between short-lived transactions which are a majority of Internet transfers and the long-lived transactions which transfer very large amounts of data, e.g., audio and video streaming.  It allows faster recovery after losses through Fast Retransmission.

Cloud Computing: Theory and Practice.

Class-Based Queuing (CBQ) - packets are first classified into flows and then assigned to a queue dedicated to the flow; queues are serviced one packet at a time in round-robin order and empty queues are skipped Cloud Computing: Theory and Practice.

C L A S S I F I E R S C H E D U L E R Flow 1

Flow 5

Flow 4

Flow 3

Flow 2

Flow 8

Flow 7

Flow 6

Port

Class-Based Queuing (CBQ)

Cloud Computing: Theory and Practice.

CBQ link sharing for two groups: Ashort-lived and Blong-lived traffic, allocated 25% and 75% of the link capacity. There are three classes with priorities 1, 2, and 3: (i) Real-time (RT) and the video streaming have priority 1 and are allocated 3% and 60%, respectively, (ii) Web transactions and audio streaming have priority 2 and are allocated 20% and 10%, respectively; (iii) In interactive (Intr) and file transfer (FTP) applications have priority 3 and are allocated 2% and 5%, respectively.

Link

A B

RT (^) Web Intr Video Audio FTP

25% 75%

Priority: Alloc: 3%

Priority: Alloc: 20%

Priority: Alloc: 2%

Priority: Alloc: 60%

Priority: Alloc: 10%

Priority: Alloc: 5%