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Internetworking Basics
Data transmitted in packets
Each packet has:
origination address
destination address
data
error checking
Generally do CSMA/CD - carrier sense multiple access/collision detection (listen before communicating)
HUB - packet data arriving at any port is regenerated and repeated to all parts. one broadcast domain,
one collision domain
Switch - listens to network traffic to learn the MAC address of each port. uses this data to switch
packets. one collision domain per port (many), one broadcast domain. (MAC: media access control)
Router - routes packets - looks at IP address of each packet, uses it to figure out where that packet
should go. has a routing table to figure this out. breaks apart both collision and broadcast domains.
Bridge - 2 port switch
Media Access Control (MAC)
08:00:20:xx:xx:xx - first three segments assigned to manufacturer
this example Sun (Sun has since changed and expanded)
00:03:93:xx:xx:xx
this example is Apple
00:0E:46:xx:xx:xx
this example is Asus
CSMA/CD - Carrier Sense (can tell when other hosts are sending) Media Access (anyone can talk) Collision Detection
(you can tell when you step on someone)
half-duplex - can listen or talk, not both at same time
full duplex - can listen and talk at same time - only possible with switch in two ports
Causes of LAN congestion
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too many hosts in a broadcast domain
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multicasting (sending many packets to many machines) - alternative unicasting
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low bandwidth
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large amount of broadcast traffic - some protocals are really broadcast chatty: ARP, IPX, AppleTalk
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use router to split domains [SOLUTION?]
Routers can do:
- packet switching
- packet filtering
- internetwork communication
- path selection (routing table)
ISO - International Organization for Standardization
- came up with OSI: open source intercommunication in 1984
- 7 layers, why:
- standards let companies make systems that work together
- prevents one layer from affecting other layers
- breaks up things into small chunks for easy implementation
- The 7 layers
- application
- presentation
- session
- transport
- network
- data link
- physical
- --- note: application goes to user; physical goes to wire
Application: supports a spreadsheet, word, Telnet, HTTP
Presentation: translate encryption, decryption; PICT, TIFF, JPEG, MIDI, MPEG
Session: establishes session between two hosts; NFS, Xwindows, RPC, SQL
Transport: segments and reassembles data; does reliable data transport; TCP, UDP, SPX
Network: connects hosts on separate networks; IP, IPX, AppleTalk
Data Link: provides reliable data transfer over a physical link; flow control; PPP, ISDN, frame relay, ethernet, TokenRing,
etc
Physical: electrical, mechanical, voltages, timing, connectors, wire
other notes on layers: Application, Presentation and Session layers are upper layers and are responsible
for communicating from the user interface to an application. The Transport layer provides segmentation,
sequencing and virtual circuits. The Network layer provides logical network addressing and routing
through an internetwork. The Data Link layer provides framing and placing of data on the network medium.
The Physical layer is responsible for taking 1s and 0s and encoding them into a digital signal for
transmission on the network segment.
HW written lab 1.2
fill in the blanks with the appropriate layer of the OSI or hub, switch, or router device.
Description
- This device sends and receives information about the Network layer. Router
- This layer creates a virtual circuit before transmitting between two end stations. Transport
- This layer uses service access points. Data Link (LLC sublayer)
- This device use hardware address to filter a network. Bridge or switch
- Ethernet is defined at these layers. Data Link and Physical
- This layer supports flow control and sequencing. Transport
- This device can measure the distance to a remote network. Router
- Logical addressing is used at this layer. Network
- Hardware addresses are defined at this layer. Data Link (MAC sublayer)
- This device creates one big collision domain and one large broadcast domain. HUB
- This device creates many smaller collision domains, but the network is stll one large broadcast domain. Switch
or bridge
- This device breaks up collision domains and broadcast domains. Router
Ethernet Networking
is contention media access (fight for networking time)
a) popular because its scalable 10M -- 100M -- 1000M
b) simple to implement and troubleshoot
c) uses both specifications at Data Link and Physical Layer
CSMA/CD
- if now signal heard, host transmits
- if collision detected, sends extended jam signal to all hosts. everyone stops sending. everyone waits random
time and tries again
- (backoff algorithm: if another collision, everyone waits longer period. after 15 tries, notes time out.
Heavy traffic produces: delay, low throughput, congestion
Half duplex - 2 wires, for 10Mb/s get about 30 - 40% throughput (~3 - 4 Mb/s)
Full duplex - 4 wires (send on one pair, receive on the other pair) can get close to 10Mb/s on 10M system, etc.
Full duplex
host <--> switch
switch <--> switch
host <--> host (use crossover cable)
Auto Detect ( or auto negotiation): full duplex capable port powers up and negotiates speed and duplex capability
with the other end of the cable. First the port tries 10M, then 100M, then 1000M, stops when it gets no answer back from other
end. If the other end can't do full duplex, it drops back to half duplex.
Most possible error is one end does 100 half and the other end does 100 full; works but very slow (50 - 100 Kb/s)
Ethernet Addressing (MAC)
Organizationally Unique Indentifier (OUI): 08:00:20:xx:xx:xx
Frame sequence
Ethernet II - most common
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Destination
Address
6 bytes
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Frame Check Sequence (FCS)
4 bytes
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IEEE 802.3
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Destination
Address
6 bytes
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Frame Check Sequence (FCS)
4 bytes
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IEEE 802.2 and SNAP
with LLC - logical link control
Preamble - alternate 1 and 0 pattern flag to indicate start of frame and provide clock
Destination Address - 48 bits (MAC), unicast, multicast, broadcast (all 1s)
Source Address - (MAC) no broadcast multicast
Length - length if less than 15360 - 0600H (otherwise practical type of network layer)
Type - always network layer protocol
Data - 64 to 1500 bytes
FCS - Frame Check Sequence
at the data - can add logical link control (LLC)
H.W. Written Lab 1.1
- Which layer chooses and determines the availability of communicating partners, along with the resources necessary to make
the connection; coordinates partnering applications; and forms a consensus on procedures for controlling datat integrity or
error recovery? Application
- Which layer is responsible for converting data packets from the Data Link layer into electrical signals? Physical
- At which layer is routing implemented, enabling connections and path selection between two end systems? Network
- Which layer defines how data is formatted, presented, encoded, and converted for use on the network? Presentation
- Which layer is responsible for creating, managing, and terminating sessions between applications? Session
- Which layer ensures the trusworthy transmission of data across a physical link and is primarily concerned with physical
addressing, line descipline, network topology, error notification, ordered delivery of frames, and flow control? Data
Link
- Which layer isused for reliable communication betwee ned nodes over the network and provides mechanisms for establishing
, maintainings, or terminating virtual cicuites; transport-fault detechtion and recovery; and controlling the flow of information?
- Which layer provides logical addressing that router will use for path determination?
- Which layer specifies voltage, wire speed, and pinout cables and moves bits between devices?
- Which layer combines bits into bytes and bytes into frames, uses MAC addressing, and provides error detection?
- Which layer is responsible for keeping the data from different applications separate on the network?
- Which layer is represented by frames?
- Which layer is represented by segments?
- Which layer is represented by packets?
- Which layer is represented by bits?
- Put the following in order of encapsulation: -packets, -frames, -bits, -segments
- Which layer segments and reassembles datat into a data stream?
- Which layer provides the physical transmission of the data and handles error notification, network topology, and flow
control?
- Which layer manages device addressing, tracks the location of devices on the network, and determines the best way to move
data?
- What is the bit length and expression from of a MAC address?
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