CSE 461: Computer Networks Shyam Gollakota Course Webpage - PowerPoint PPT Presentation

CSE 461: Computer Networks Shyam Gollakota

Course Webpage Cs.washington.edu/461 uter Networks

Textbook https://github.com/SystemsApproach/book uter Networks

Teaching Assistants – Bradford Chen bradchen@cs.washington.edu – Daniel Starikov starikov@cs.washington.edu – John Taggart jwtag@cs.washington.edu – Xinghan Zhao zhaox27@cs.washington.edu – Zetian Chen zetiac@cs.washington.edu uter Networks

Grading • Midterm (15%) • Final (20%) • Assignments (20%) – A recurring SDN programming assignment • Surprise Quizzes (10%) • 3 projects (10%+10%+15%) uter Networks

Protocols and Layers • Protocols and layering is the main structuring method used to divide up network functionality – Each instance of a protocol talks virtually to its peer using the protocol – Each instance of a protocol uses only the services of the lower layer Computer Networks 6

Protocols and Layers (3) • Protocols are horizontal, layers are vertical Instance of Peer Protocol X protocol X instance X X Service provided by Protocol Y Lower layer instance (of Y Y protocol Y) Node 1 Node 2 Computer Networks 7

Protocols and Layers (4) • Set of protocols in use is called a protocol stack Computer Networks 8

Protocols and Layers (6) • Protocols you’ve probably heard of: Browser – TCP, IP, 802.11, Ethernet, HTTP, SSL, DNS, … and many more HTTP • An example protocol stack TCP – Used by a web browser on a host that IP is wirelessly connected to the Internet 802.11 Computer Networks 9

Encapsulation • Encapsulation is the mechanism used to effect protocol layering – Lower layer wraps higher layer content, adding its own information to make a new message for delivery – Like sending a letter in an envelope; postal service doesn’t look inside Computer Networks 10

Encapsulation (3) • Message “on the wire” begins to look like an onion – Lower layers are outermost HTTP HTTP TCP HTTP TCP IP TCP HTTP IP IP TCP HTTP 802.11 802.11 Computer Networks 11

Encapsulation (4) HTTP HTTP HTTP HTTP TCP TCP TCP TCP HTTP HTTP IP IP TCP IP TCP HTTP IP HTTP 802.11 802.11 TCP IP TCP HTTP IP HTTP 802.11 802.11 (wire) IP TCP HTTP 802.11 Computer Networks 12

Advantage of Layering • Information hiding and reuse Browser Server Browser Server HTTP HTTP HTTP HTTP or Computer Networks 13

Advantage of Layering (2) • Information hiding and reuse Browser Server Browser Server HTTP HTTP HTTP HTTP TCP TCP TCP TCP or IP IP IP IP Ethernet 802.11 802.11 Ethernet Computer Networks 14

Advantage of Layering (3) • Using information hiding to connect different systems Browser Server HTTP HTTP TCP TCP IP IP Ethernet 802.11 Computer Networks 15

Advantage of Layering (4) • Using information hiding to connect different systems Browser Server HTTP HTTP IP TCP HTTP TCP TCP IP IP IP IP Ethernet 802.11 802.11 Ethernet 802.11 IP TCP HTTP Ethernet IP TCP HTTP Computer Networks 16

Disadvantage of Layering • ?? Computer Networks 17

Internet Reference Model • A four layer model based on experience; omits some OSI layers and uses IP as the network layer. 4 Application – Programs that use network service 3 Transport – Provides end-to-end data delivery 2 Internet – Send packets over multiple networks 1 Link – Send frames over a link Computer Networks 18

Internet Reference Model (3) • IP is the “narrow waist” of the Internet – Supports many different links below and apps above 4 Application SMTP HTTP RTP DNS 3 Transport TCP UDP 2 Internet IP Ethernet 3G 1 Link Cable DSL 802.11 Computer Networks 19

Layer-based Names (2) • For devices in the network: Repeater (or hub) Physical Physical Link Switch (or bridge) Link Network Network Router Link Link Computer Networks 20

Layer-based Names (3) • For devices in the network: App App Proxy or Transport Transport middlebox Network Network or gateway Link Link But they all look like this! Computer Networks 21