Presentation is loading. Please wait.

Presentation is loading. Please wait.

Network Layer (3). Node lookup in p2p networks Section 5.2.11 in the textbook. In a p2p network, each node may provide some kind of service for other.

Published byJonah Gardner Modified over 8 years ago

Similar presentations

Presentation on theme: "Network Layer (3). Node lookup in p2p networks Section 5.2.11 in the textbook. In a p2p network, each node may provide some kind of service for other."— Presentation transcript:

1 Network Layer (3)

2 Node lookup in p2p networks Section 5.2.11 in the textbook. In a p2p network, each node may provide some kind of service for other nodes and also will ask other node for service. The problem is to locate a node who provides the service I need. In our project there is a central server who assigns nodes to others.

3 Node lookup in p2p networks P2P networks may have a very large number of nodes, such that a single central server may not be able to handle. Besides, there are legal issues. So, how to design lookup mechanism, such that I can find the node providing the service I need? For simplicity, let’s use the same model as in our project – Each node may have some files, and the job is to find a node with the file I need.

4 Node lookup in p2p networks Any suggestions? Ask the nodes in the network one-by-one? Flood the network? Binary search tree?

5 Node lookup in p2p networks Two costs you have to consider. – The lookup time – The number of messages sent Assume that there is only one node with the file I need, what is the cost for – Linear search? – Flood? – Binary search tree – Are they any good?

6 The key idea There is really not so much you can do if the network does not have a structure. Introduce structure to the network. Distributed Hash Table (DHT).

7 Chord Each node has a unique ID – By hashing its IP address by SHA-1 to get a 160-bit ID. Each file also has a unique ID, called key. – By hashing the file name by SHA-1 to get a 160-bit ID.

8 Chord Successor of a key x or ID x. – Arrange the node as a circle. Start at x and travel clockwise. The first (real) node you visit is the successor of F.

9 Chord successor(F) is the node in charge of telling other people where to get F. If a node has file F, he tells successor(F) that he has F. So, if you can find successor(F), meaning that the IP address of it, you are done.

10 Chord How to find successor(F)? Any suggestions?

11 Chord You know you location on the circle. You know the location of successor(F) on the circle. If every node keeps the IP address of its neighbor on the circle, need to do a linear search.

12 Chord But you control what nodes should remember. What do you want the nodes to remember, such that your searching time is small and your number of message is small?

13 Chord What Chord does is this. He remembers the successors of m locations if the node ID and key are m bits. Consider a node with ID k. The i^{th} entry of his finger table is the IP address of the successor of k+2^i mod 2^m. Given this, how do you design the routing algorithm?

14 Chord Start with k as the routing point (RP). If RP < F < successor(RP), successor(RP) = successor(F) and you are done because you know the IP address of successor(RP). Else, let the next RP be the one in the RP’s finger table that is closest predecessor of F. Repeat.

15 Chord Chord needs m routing steps. The reason is every time, the distance from the RP to the key is at least halved.

16 Internet Protocol (IP) Universal service in a heterogeneous world – IP over everything Globally unique logical address for a host

17 IP Packet

18 IP Addressing A 32-bit number that uniquely identifies a location Written using dotted decimal notation

19 IP Addressing IP address is assigned to each network interface Routers connect two or more physical networks – Each interface has its own address Multi-homed host – A host having multiple connections to Internet – Multiple addresses identify the same host – Does not forward packets between its interfaces

20 IP “Classful” Addressing Scheme Three unicast address classes: A, B, and C One multicast: class D 0 network host 10 network host 110 networkhost 1110 multicast address A B C D class 1.0.0.0 to 127.255.255.255 128.0.0.0 to 191.255.255.255 192.0.0.0 to 223.255.255.255 224.0.0.0 to 239.255.255.255 32 bits

21 Routing IP Packets Get the network address. If local, send the packet to the destination. If not local, send the packet to the next hop based on the network address.

22 Classless Inter-Domain Routing Classful addressing scheme wasteful – IP address space exhaustion – A class B net allocated enough for 65K hosts Even if only 2K hosts in that network Solution: CIDR – Eliminate class distinction No A,B,C – Keep multicast class D

23 Classless Addressing Addresses allocated in contiguous blocks – Number of addresses assigned always power of 2 Network portion of address is of arbitrary length Address format: a.b.c.d/x – x is number of bits in network portion of address 11001000 00010111 00010000 00000000 network part host part 200.23.16.0/23

24 223.1.1.1 223.1.1.2 223.1.1.3 223.1.1.4 223.1.2.9 223.1.2.2 223.1.2.1 223.1.3.2 223.1.3.1 223.1.3.27 LAN first 24 bits are network address IP Addressing

25 223.1.3.2 223.1.3.1 223.1.3.27 223.1.1.1 223.1.1.3 223.1.1.4 223.1.2.2 223.1.2.1 223.1.2.6 223.1.1.2 223.1.7.0 223.1.7.1 223.1.8.0223.1.8.1 223.1.9.1 223.1.9.2 Interconnected system consisting of six networks

26 CIDR A router keeps routing table with entries – IP address, 32-bit mask, outgoing line When an IP packet arrives, the router checks its routing table to find the longest match.

27 NAT – Network Address Translation

28 Virtual Circuit Destination information is large and the table is large – Consider 32 bit IP address. A full table will have 4G entries. If an IP packet is 1250 byte long and the link speed is 10Gbps, how much time do you have for this lookup? (1. You don’t have to implement the full table. 2. You can also use pipeline.)

29 Virtual Circuit Circuit means a path between the source and the destination. Real circuit switching has a physical path set up between the source and the destination, like telephone network – When you dial, a request is sent to the network, network finds if there are free links on the path and reserve that link for you. Virtual circuit is different – used in packet switching networks. – No real path set up, because it is packet switching (although link bandwidth can be reserved). – But still has the connection phase. The purpose is to let the routers know how to route the packets of this virtual circuit.

30 Virtual Circuits When setting up the virtual circuit, a VC identifier is picked. The router knows where to forward a packet with a certain VC identifier. Each packet will carry the VC identifier, which is much shorter than the full destination address, so allows more efficient table lookup. Resources can also be reserved. QoS. A practical problem in a distributed environment – different stations may pick the same VC identifier. Labels can be swapped without causing confusion. B E F D C A H1 H2 A’s Table In Out H1, 1 C, 1 H2, 1 C, 2 H3 C’s Table In Out A, 1 E, 1 A, 2 D, 1

Download ppt "Network Layer (3). Node lookup in p2p networks Section 5.2.11 in the textbook. In a p2p network, each node may provide some kind of service for other."

Similar presentations

Delivery and Forwarding of

Delivery and Forwarding of
4 IP Address (IPv4)  A unique 32-bit number  Identifies an interface (on a host, on a router, …)  Represented in dotted-quad notation 0000110000100010.

4 IP Address (IPv4)  A unique 32-bit number  Identifies an interface (on a host, on a router, …)  Represented in dotted-quad notation
Chapter 18 Introduction to Network Layer 18.# 1

Chapter 18 Introduction to Network Layer 18.# 1
© 2007 Cisco Systems, Inc. All rights reserved.Cisco Public 1 Version 4.0 Addressing the Network – IPv4 Network Fundamentals – Chapter 6.

© 2007 Cisco Systems, Inc. All rights reserved.Cisco Public 1 Version 4.0 Addressing the Network – IPv4 Network Fundamentals – Chapter 6.
4: Network Layer4a-1 IP Addressing: introduction r IP address: 32-bit identifier for host, router interface r interface: connection between host, router.

4: Network Layer4a-1 IP Addressing: introduction r IP address: 32-bit identifier for host, router interface r interface: connection between host, router.
Network Layer4-1 Chapter 4: Network Layer r 4. 1 Introduction r 4.2 Virtual circuit and datagram networks r 4.3 What’s inside a router r 4.4 IP: Internet.

Network Layer4-1 Chapter 4: Network Layer r 4. 1 Introduction r 4.2 Virtual circuit and datagram networks r 4.3 What’s inside a router r 4.4 IP: Internet.
Chapter 18. IP: Internet Protocol Addresses

Chapter 18. IP: Internet Protocol Addresses
A supernetwork.

A supernetwork.
Topics in Reliable Distributed Systems 048961 Lecture 2, Fall 2004-2005 Dr. Idit Keidar.

Topics in Reliable Distributed Systems Lecture 2, Fall Dr. Idit Keidar.
11- IP Network Layer4-1. Network Layer4-2 The Internet Network layer forwarding table Host, router network layer functions: Routing protocols path selection.

11- IP Network Layer4-1. Network Layer4-2 The Internet Network layer forwarding table Host, router network layer functions: Routing protocols path selection.
Oct 21, 2004CS573: Network Protocols and Standards1 IP: Addressing, ARP, Routing Network Protocols and Standards Autumn 2004-2005.

Oct 21, 2004CS573: Network Protocols and Standards1 IP: Addressing, ARP, Routing Network Protocols and Standards Autumn
Subnetting and CIDR Textbook Ch 3.2.5

Subnetting and CIDR Textbook Ch 3.2.5
IP Address 0 network host 10 network host 110 networkhost 1110 multicast address A B C D class 1.0.0.0 to 127.255.255.255 128.0.0.0 to 191.255.255.255.

IP Address 0 network host 10 network host 110 networkhost 1110 multicast address A B C D class to to
Chapter 21 IP Addressing “If we all did the things we are capable of doing, we would literally astound ourselves” - Thomas Alva Edison, 1847-1931.

Chapter 21 IP Addressing “If we all did the things we are capable of doing, we would literally astound ourselves” - Thomas Alva Edison,
CS 6401 Efficient Addressing Outline Addressing Subnetting Supernetting.

CS 6401 Efficient Addressing Outline Addressing Subnetting Supernetting.
IP Addressing. Dotted Decimal Notation IP addresses are written in a so-called dotted decimal notation Each byte is identified by a decimal number in.

IP Addressing. Dotted Decimal Notation IP addresses are written in a so-called dotted decimal notation Each byte is identified by a decimal number in.
Types of Addresses in IPv4 Network Range

Types of Addresses in IPv4 Network Range
1 26-Aug-15 Addressing the network using IPv4 Lecture # 2 Engr. Orland G. Basas Prepared by: Engr. Orland G. Basas IT Lecturer.

1 26-Aug-15 Addressing the network using IPv4 Lecture # 2 Engr. Orland G. Basas Prepared by: Engr. Orland G. Basas IT Lecturer.
Fall 2006Computer Networks19-1 Chapter 19. Host-to-Host Delivery: Internetworking, Addressing, and Routing 19.1 Internetworks 19.2 Addressing 19.3 Routing.

Fall 2006Computer Networks19-1 Chapter 19. Host-to-Host Delivery: Internetworking, Addressing, and Routing 19.1 Internetworks 19.2 Addressing 19.3 Routing.
1 Internet Addresses (You should read Chapter 4 in Forouzan) IP Address is 32 Bits Long Conceptually the address is the pair ( NETID, HOSTID ) Addresses.

1 Internet Addresses (You should read Chapter 4 in Forouzan) IP Address is 32 Bits Long Conceptually the address is the pair ( NETID, HOSTID ) Addresses.

Similar presentations

Ads by Google