Lecture 8 Modeling & Simulation of Communication Networks.
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Transcript of Lecture 8 Modeling & Simulation of Communication Networks.
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Lecture 8
Modeling & Simulation of Communication Networks
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Layered Tasks
Sender, Receiver, and Carrier
Hierarchy
Services
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Figure 2.1 Sending a letter
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Internet Model
Peer-to-Peer Processes
Functions of Layers
Summary of Layers
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Internet layers
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Figure 2.4 An exchange using the Internet model
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Figure 2.5 Physical layer
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The physical layer is responsible for transmitting individual bits from one
node to the next.
Note:
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Figure 2.6 Data link layer
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The data link layer is responsible for transmitting frames from
one node to the next.
Note:
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Figure 2.7 Node-to-node delivery
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Example 1
In Figure 2.8 a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link. At the data link level this frame contains physical addresses in the header. These are the only addresses needed. The rest of the header contains other information needed at this level. The trailer usually contains extra bits needed for error detection
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Figure 2.8 Example 1
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Figure 2.9 Network layer
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The network layer is responsible for the delivery of packets from the original
source to the final destination.
Note:
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Figure 2.10 Source-to-destination delivery
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Example 2
In Figure 2.11 we want to send data from a node with network address A and physical address 10, located on one LAN, to a node with a network address P and physical address 95, located on another LAN. Because the two devices are located on different networks, we cannot use physical addresses only; the physical addresses only have local jurisdiction. What we need here are universal addresses that can pass through the LAN boundaries. The network (logical) addresses have this characteristic.
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Figure 2.11 Example 2
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Figure 2.12 Transport layer
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The transport layer is responsible for delivery of a message from one process
to another.
Note:
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Figure 2.12 Reliable process-to-process delivery of a message
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Example 3
Figure 2.14 shows an example of transport layer communication. Data coming from the upper layers have port addresses j and k (j is the address of the sending process, and k is the address of the receiving process). Since the data size is larger than the network layer can handle, the data are split into two packets, each packet retaining the port addresses (j and k). Then in the network layer, network addresses (A and P) are added to each packet.
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Figure 2.14 Example 3
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Figure 2.15 Application layer
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The application layer is responsible for providing services to the user.
Note:
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Figure 2.16 Summary of duties
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Link Layer
5-27
Institutional network
to externalnetwork
router
IP subnet
mail server
web server
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Link Layer5-28
Synthesis: a day in the life of a web request
journey down protocol stack complete! application, transport, network, link
putting-it-all-together: synthesis! goal: identify, review, understand protocols
(at all layers) involved in seemingly simple scenario: requesting www page
scenario: student attaches laptop to campus network, requests/receives www.google.com
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A day in the life: scenario
Comcast network 68.80.0.0/13
Google’s network 64.233.160.0/19 64.233.169.105
web server
DNS server
school network 68.80.2.0/24
web page
browser
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router(runs DHCP)
A day in the life… connecting to the Internet
connecting laptop needs to get its own IP address, addr of first-hop router, addr of DNS server: use DHCP
DHCPUDP
IPEthPhy
DHCP
DHCP
DHCP
DHCP
DHCP
DHCPUDP
IPEthPhy
DHCP
DHCP
DHCP
DHCPDHCP
DHCP request encapsulated in UDP, encapsulated in IP, encapsulated in 802.3 Ethernet
Ethernet frame broadcast (dest: FFFFFFFFFFFF) on LAN, received at router running DHCP server Ethernet demuxed to IP demuxed, UDP demuxed to DHCP
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router(runs DHCP)
DHCP server formulates DHCP ACK containing client’s IP address, IP address of first-hop router for client, name & IP address of DNS server
DHCPUDP
IPEthPhy
DHCP
DHCP
DHCP
DHCP
DHCPUDP
IPEthPhy
DHCP
DHCP
DHCP
DHCP
DHCP
encapsulation at DHCP server, frame forwarded (switch learning) through LAN, demultiplexing at client
Client now has IP address, knows name & addr of DNS server, IP address of its first-hop router
DHCP client receives DHCP ACK reply
A day in the life… connecting to the Internet
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router(runs DHCP)
A day in the life… ARP (before DNS, before HTTP)
before sending HTTP request, need IP address of www.google.com: DNS
DNSUDP
IPEthPhy
DNS
DNS
DNS
DNS query created, encapsulated in UDP, encapsulated in IP, encapsulated in Eth. To send frame to router, need MAC address of router interface: ARP
ARP query broadcast, received by router, which replies with ARP reply giving MAC address of router interface client now knows MAC address of first hop router, so can now send frame containing DNS query
ARP query
EthPhy
ARP
ARP
ARP reply
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router(runs DHCP)
DNSUDP
IPEthPhy
DNS
DNS
DNS
DNS
DNS
IP datagram containing DNS query forwarded via LAN switch from client to 1st hop router
IP datagram forwarded from campus network into comcast network, routed (tables created by RIP, OSPF, IS-IS and/or BGP routing protocols) to DNS server
demux’ed to DNS server
DNS server replies to client with IP address of www.google.com
Comcast network 68.80.0.0/13
DNS server
DNSUDP
IPEthPhy
DNS
DNS
DNS
DNS
A day in the life… using DNS
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router(runs DHCP)
A day in the life…TCP connection carrying HTTP
HTTPTCPIP
EthPhy
HTTP
to send HTTP request, client first opens TCP socket to web server
TCP SYN segment (step 1 in 3-way handshake) inter-domain routed to web server
TCP connection established!
64.233.169.105
web server
SYN
SYN
SYN
SYN
TCPIP
EthPhy
SYN
SYN
SYN
SYNACK
SYNACK
SYNACK
SYNACK
SYNACK
SYNACK
SYNACK web server responds with TCP SYNACK (step 2 in 3-way handshake)
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router(runs DHCP)
Link Layer5-35
A day in the life… HTTP request/reply
HTTPTCPIP
EthPhy
HTTP
HTTP request sent into TCP socket
IP datagram containing HTTP request routed to www.google.com
IP datagram containing HTTP reply routed back to client
64.233.169.105
web server
HTTPTCPIP
EthPhy
web server responds with HTTP reply (containing web page)
HTTP
HTTP
HTTPHTTP
HTTP
HTTP
HTTP
HTTP
HTTP
HTTP
HTTP
HTTP
HTTP
web page finally (!!!) displayed
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Questions