DOC PREVIEW
Rutgers University CS 417 - Distributed Systems

This preview shows page 1-2-3-23-24-25-26-46-47-48 out of 48 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 48 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 48 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 48 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 48 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 48 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 48 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 48 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 48 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 48 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 48 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 48 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

Distributed Systems 02. Networking Paul Krzyzanowski Rutgers University Fall 2014 1 September 15, 2014 © 2014 Paul KrzyzanowskiConnecting computers • Point-to-point links – Connect one sender with one receiver – No conflict for access to link – Not practical: limits any-any communication September 15, 2014 © 2014 Paul Krzyzanowski 2 Direct linkConnecting computers • Communication network – Share the infrastructure – Collision: when two nodes transmit at the same time, same channel • Both signals get damaged – Multiple access problem • How do you coordinate multiple senders? September 15, 2014 © 2014 Paul Krzyzanowski 3 NetworkMultiple Access Protocols • Ways of enabling devices to share a network • Three approaches 1. Channel partitioning • Time Division Multiplexing (TDM) – each node gets a time slot • Frequency Division Multiplexing (FDM) – each channel gets a frequency band 2. Taking turns • Polling protocol – master polls nodes in sequence • Token passing protocol – node needs a token to transmit 3. Random access • No scheduled time slots • Statistical multiplexing • Retransmit if there’s a collision September 15, 2014 © 2014 Paul Krzyzanowski 4 Bandwidth allocated even if nothing to transmit! Fails badly Complex Sounds like it shouldn’t work well … but it does!Modes of connection Circuit-switching (virtual circuit) – Dedicated path (route) – established at setup – Guaranteed (fixed) bandwidth – routers commit to resources – Typically fixed-length packets (cells) – each cell only needs a virtual circuit ID – Constant latency Packet-switching (datagram) – Shared connection; competition for use with others – Data is broken into chunks called packets – Each packet contains a destination address – available bandwidth  channel capacity – variable latency September 15, 2014 5 © 2014 Paul KrzyzanowskiEthernet • Packet-based protocol • Originally designed for shared (bus-based) links • Each endpoint has a unique ethernet address – MAC address: 48-bit value • Evolution – Ethernet hub • Simulates a bus-based LAN • Every bit received on an interface is transmitted onto every other interface – Ethernet switch • Forwards frames to the correct host • Self-learning (learns from source address) • Switch is transparent to hosts • No collisions! September 15, 2014 © 2014 Paul Krzyzanowski 6Ethernet service guarantees • Each packet (frame) contains a CRC checksum – Recipient will drop the frame if it is bad • No acknowledgement of packet delivery • Unreliable, in-order delivery September 15, 2014 © 2014 Paul Krzyzanowski 7Going beyond the LAN • LAN = Local Area Network – A set of devices connected to the same ethernet network is a LAN – Wi-Fi (802.11) is compatible with ethernet and part of the LAN • We want to communicate beyond the LAN • The Internet – Evolved from ARPANET (1969) – Internet = global network of networks based on the Internet Protocol (IP) family of protocols September 15, 2014 © 2014 Paul Krzyzanowski 8The Internet: Key Design Principles 1. Support interconnection of networks – No changes needed to the underlying physical network – IP is a logical network 2. Assume unreliable communication; design for best effort – If a packet does not get to the destination, software on the receiver will have to detect it and the sender will have to retransmit it 3. Routers connect networks – Store & forward delivery – They need not store information about the flow of packets 4. No global (centralized) control of the network 9 September 15, 2014 © 2014 Paul KrzyzanowskiRouters tie LANs together into one Internet 10 Tier 3 ISP Tier 2 ISP Tier 1 ISP Tier 1 ISP Tier 2 ISP A packet may pass through many networks – within and between ISPs September 15, 2014 © 2014 Paul KrzyzanowskiProtocols September 15, 2014 © 2014 Paul Krzyzanowski 11What’s in the data? • For effective communication – same language, same conventions • For computers: – electrical encoding of data – where is the start of the packet? – which bits contain the length? – is there a checksum? where is it? how is it computed? – what is the format of an address? – byte ordering September 15, 2014 © 2014 Paul Krzyzanowski 12Protocols These instructions & conventions are known as protocols Protocols encompass data formats, order of messages, responses September 15, 2014 © 2014 Paul Krzyzanowski 13Layering To ease software development and maximize flexibility: – Network protocols are generally organized in layers – Replace one layer without replacing surrounding layers – Higher-level software does not have to know how to format an Ethernet packet … or even know that Ethernet is being used September 15, 2014 © 2014 Paul Krzyzanowski 14Protocols September 15, 2014 © 2014 Paul Krzyzanowski 15 Exist at different levels understand format of address and how to compute a checksum request web page humans vs. whales different wavelengths French vs. Hungarian versusLayering Most popular model of guiding (not specifying) protocol layers is OSI reference model Adopted and created by ISO 7 layers of protocols 16 OSI = Open Systems Interconnection From the ISO = International Organization for Standardization September 15, 2014 © 2014 Paul KrzyzanowskiOSI Reference Model: Layer 1 Transmits and receives raw data to communication medium Does not care about contents Media, voltage levels, speed, connectors Physical 1 Examples: USB, Bluetooth, 802.11 17 Deals with representing bits September 15, 2014 © 2014 Paul KrzyzanowskiData Link OSI Reference Model: Layer 2 Detects and corrects errors Organizes data into frames before passing it down. Sequences packets (if necessary) Accepts acknowledgements from immediate receiver Physical 1 2 Examples: Ethernet MAC, PPP 18 Deals with frames September 15, 2014 © 2014 Paul KrzyzanowskiData Link OSI Reference Model: Layer 2 An ethernet switch is an example of a device that works on layer 2 It forwards ethernet frames from one host to another as long as the hosts are connected to the switch (switches may be cascaded) This set of hosts and switches defines the local area network (LAN) 19 Physical 1 2 September 15, 2014 © 2014 Paul KrzyzanowskiNetwork Data Link OSI Reference Model: Layer 3 Relay and route information to destination Manage


View Full Document

Rutgers University CS 417 - Distributed Systems

Download Distributed Systems
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Distributed Systems and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Distributed Systems 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?