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Application (web browser) HTML on HTTP TCP IP Application (web server) HTML on HTTP TCP IP User-space Kernel-space (operating-system) Socket layer (socket.

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Presentation on theme: "Application (web browser) HTML on HTTP TCP IP Application (web server) HTML on HTTP TCP IP User-space Kernel-space (operating-system) Socket layer (socket."— Presentation transcript:

1 Application (web browser) HTML on HTTP TCP IP Application (web server) HTML on HTTP TCP IP User-space Kernel-space (operating-system) Socket layer (socket interface) NIC: Network Interface Card A real layered system End system Physical connector Ethernet (Card and NIC driver) Ethernet (Card and NIC driver)

2 Application (web browser) HTML on HTTP TCP IP Application (web server) HTML on HTTP TCP IP NIC: Network Interface Card A real layered system End system Physical connector Ethernet (data link-layer) Ethernet (Card and NIC driver) Ethernet (Card and NIC driver)

3 NIC: Network Interface Card A real layered system End system Application (web browser) HTML on HTTP TCP IP Ethernet (Card and NIC driver) Physical connector Ethernet (data link-layer) Data-Link (2) Physical (1) Network (3) Transport (4) Session (5) Presentation (6) Application (7) Application (web server) HTML on HTTP TCP IP Physical connector Ethernet (Card and NIC driver) Data-Link (2) Physical (1) Network (3) Transport (4) Session (5) Presentation (6) Application (7) Physical (1) Data-Link (2)

4 Non-Return-to-Zero (NRZ) Non-Return-to-Zero-Mark (NRZM) 1 = transition 0 = no transition Non-Return-to-Zero Inverted (NRZI) (note transitions on the 1) Line Coding Examples where Baud=bit-rate

5 Non-Return-to-Zero (NRZ) (Baud = bit-rate) Manchester example (Baud = 2 x bit-rate) Clock Line Coding Examples - II Quad-level code (2 x Baud = bit-rate) Clock

6 Line Coding Examples - III Name 4b 5b Description hex data hex data hex data hex data hex data hex data hex data hex data hex data hex data 9 A hex data A B hex data B C hex data C D hex data D E hex data E F hex data F Name 4b 5b Description Q -NONE Quiet I -NONE Idle J -NONE SSD #1 K -NONE SSD #2 T -NONE ESD #1 R -NONE ESD #2 H -NONE Halt Block coding transfers data with a fixed overhead: 20% less information per Baud in the case of 4B/5B So to send data at 100Mbps; the line rate (the Baud rate) must be 125Mbps. 1Gbps uses an 8b/10b codec; encoding entire bytes at a time but with 25% overhead Data to send Line-(Wire) representation

7 Line Coding Examples - IV Scrambling Sequence Scrambling Sequence Communications Channel Message XOR Sequence Message XOR Sequence

8 Line Coding Examples - IV Scrambling Sequence Scrambling Sequence Communications Channel Message XOR Sequence Message XOR Sequence δδδδδ e.g. (Self-synchronizing) scrambler

9 Line Coding Examples – V (Hybrid) δδδδδ δδδδδ … … Inserted bits marking “start of frame/block/sequence” … … Scramble / Transmit / Unscramble … … Identify (and remove) “start of frame/block/sequence” This gives you the Byte-delineations for free 64b/66b combines a scrambler and a framer. The start of frame is a pair of bits 01 or 10: 01 means “this frame is data” 10 means “this frame contains data and control” – control could be configuration information, length of encoded data or simply “this line is idle” (no data at all)

10 Rule for adjusting W –If an ACK is received:W ← W+1/W –If a packet is lost:W ← W/2 Single Flow ARQ in operation Only W packets may be outstanding

11 Physical (1) Data-Link (2) Network (3) Transport (4) Session (5) Presentation (6) Application (7) Physical (1) Data-Link (2) Network (3) Transport (4) Session (5) Presentation (6) Application (7)

12 Physical (1) Data-Link (2) Network (3) Transport (4) Session (5) Presentation (6) Application (7) Physical (1) Data-Link (2) Network (3) Transport (4) Session (5) Presentation (6) Application (7)Physical (1) Physical layer interconnect (a connector to the rest of us, in this case it connects male connector to male connector)

13 Physical (1) Data-Link (2) Network (3) Transport (4) Session (5) Presentation (6) Application (7) Physical (1) Data-Link (2) Network (3) Transport (4) Session (5) Presentation (6) Application (7) Data-Link (2) Physical (1) Physical device – media convertor speaks fluent Physical-layer But only a bit of the Data-Link (Ethernet)

14 Physical (1) Data-Link (2) Network (3) Transport (4) Session (5) Presentation (6) Application (7) Physical (1) Data-Link (2) Network (3) Transport (4) Session (5) Presentation (6) Application (7)Physical (1) Data-Link (2) Data-Link device aka an Ethernet switch speaks fluent Ethernet and often the extra/new Ethernet-related standards (802.1q for VLAN and 802.1x for Network Access Control)

15 Physical (1) Data-Link (2) Network (3) Transport (4) Session (5) Presentation (6) Application (7) Physical (1) Data-Link (2) Network (3) Transport (4) Session (5) Presentation (6) Application (7)Physical (1) Data-Link (2) Data-Link device aka an Ethernet switch speaks fluent Ethernet (two standards: wire and wireless!) Another example with media conversion

16 Physical (1) Data-Link (2) Network (3) Transport (4) Session (5) Presentation (6) Application (7) Physical (1) Data-Link (2) Network (3) Transport (4) Session (5) Presentation (6) Application (7)Physical (1)Data-Link (2)Physical (1) Data-Link (2) Network (3) Network device aka an IP Router speaks fluent IP and can convert between any data-link and any physical standard to any other.

17 Physical (1) Data-Link (2) Network (3) Transport (4) Session (5) Presentation (6) Application (7) Physical (1) Data-Link (2) Network (3) Transport (4) Session (5) Presentation (6) Application (7)Physical (1) Data-Link (2) Network (3)Transport (4)Physical (1) Data-Link (2) Network (3) Transport-layer mapping (pretty uncommon) speaks fluent TCP and ??? ?

18 Physical (1) Data-Link (2) Network (3) Transport (4) Session (5) Presentation (6) Application (7) Physical (1) Data-Link (2) Network (3) Transport (4) Session (5) Presentation (6) Application (7) Physical (1) Data-Link (2) Network (3) Transport (4) Session (5) Physical (1) Data-Link (2) Network (3) Transport (4) Application device aka a Web-load balancer speaks fluent HTTP

19 ARP Recall from the primary slide-stack (slide 8-22) we need a mechanism for higher-layer entities to know what address to utilize in the lower entities. ARP (address resolution protocol) provides a mechanism for establishing a host’s link-layer (e.g. Ethernet) address using only a network-address (e.g. IP address) ARP is not limited to either Ethernet or IP; although that is the most common current use. A linux machine’s ARP table can be shown using the command arp -a

20 Physical (1) Data-Link (2) Network (3) Transport (4) Session (5) Presentation (6) Application (7) Physical (1) Data-Link (2) Network (3) Transport (4) Session (5) Presentation (6) Application (7)Physical (1)Data-Link (2)Physical (1) Consider the following situation:

21 ARP H1 H2H3 H4 H5H6 H7 H8H9 H10 H11H12 Switch D ff.ff.ff.ff.ff.ff SP SH fe d5.29 DP DH H10= IP , Ethernet 44.fe d5 D ff.ff.ff.ff.ff.ff SP SH fe d5.29 DP DH D ff.ff.ff.ff.ff.ff SP SH fe d5.29 DP DH D ff.ff.ff.ff.ff.ff SP SH fe d5.29 DP DH D fe d5.29 SP SH 44.fe d5 DP DH fe d5.29 D fe d5.29 SP SH 44.fe d5 DP DH fe d5.29 D D 44.fe d5 S S fe d5.29 D D 44.fe d5 S S fe d5.29 An Ethernet (switch) example

22 Notes ARP table entries timeout in about 10 minutes ARP table rules: update table with source when you are the target update table if you already have an entry do not refresh table entries upon reference

23 CIDR and Longest Prefix Matches  The IP address space is broken into line segments.  Each line segment is described by a prefix.  A prefix is of the form x/y where x indicates the prefix of all addresses in the line segment, and y indicates the length of the segment.  e.g. The prefix 128.9/16 represents the line segment containing addresses in the range: … / /19 65/

24 Classless Interdomain Routing (CIDR) / / / / /24 Most specific route = “longest matching prefix”

25 HD Display Topology of Routers Video Server

26 Subnet Configuration Video Client Shortest Path Video Server

27 Step 1 – Observe the Routing Tables The router is already configured and running on your machines The routing table has converged to the routing decisions with minimum number of hops Next, break a link …

28 Step 2 - Dynamic Re-routing Break the link between video server and video client Routers re-route traffic around the broken link and video continues playing

29 Working IP Router – Observe PW-OSPF re-routing traffic around a failure – Video is temporarily disrupted then resumes playing as TCP recovers from packet-loss

30 Collision detection can take as long as 2 τ CSMA/CD Ethernet (10Mbps circa 1980) AB AB AB AB Packet starts at time 0 Packet arrives at B at τ-ε Packet starts from B at time τ Collision shortly thereafter Noise (the collision) arrives at A at time 2 τ

31 A User B C D E In pure Aloha, frames are transmitted at arbitrary (and uncoordinated) times Time


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