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Spring 2006
EE 5304/EETS 7304 Internet Protocols
Tom OhDept of Electrical Engineering
Lecture 6
Network Protocol (ATM)
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Administrative Issues
We will have test 1 on Feb. 28.
Test will consists of Lecture 1- 5.
Mutiple choice, true/false, short answers,
We will review for the test today.
DVD students: If you don’t have proctor at your site, please contact Gary McClesky as soon as possible.
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ATM (Comer Ch. 14)
Asynchronous Transfer Mode was ITU standard in late 1980s
Based on fast packet switching research in 1970s-1980s
Objective: streamlined or "lightweight" protocol allows fast packet processing and shorter packet delays
Assumes reliable, high rate digital transmission links Fast packet switching can be suitable for both real-time
traffic (eg, speech) and nonreal-time data
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ATM (cont)
No ACKs or retransmissions (no sequence numbers)
Error control is done end-to-end (in higher protocol layer) as needed
Connection-oriented: virtual circuits
Routing decision is made once, during connection establishment
Simplifies and speeds up packet processing
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ATM Cell Format
In ITU standards, US took position on cell (packet) format: 64 bytes info. + 5 byte header
Data switching was important consideration• More complicated header
Eur. position on cell format: 32 bytes info. + 4 byte header
Speech multiplexing was important consideration• Simple header, shorter packet to minimize packetization delay
and effect of lost speech packet
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ATM Cell Format (cont)
ITU made compromise on cell length: 48 bytes info. + 5 byte header
at UNI at NNI
GFC VPIVPI VCI
VCIVCI PT
HEC
48-byte data
CLP
VPIVPI VCI
VCIVCI PT
HEC
48-byte data
CLP
8 bits 8 bits
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ATM Cell Format (cont)
GFC (4 bits): only at UNI; ignored by network; use is not standardized
VPI/VCI: 24 bits (UNI) or 28 bits (NNI) to identify virtual circuit
Certain values are reserved for signaling cells (VCI=5), OAM cells (VCI=3,4), etc.
PT (payload type): 3 bits for EFCI, AAL5, and type of cell
PT code Meaning
'000' user data, cell type 0, no congestion
'001' user data, cell type 1, no congestion
'010' user data, cell type 0, congestion experienced
'011' user data, cell type 1, congestion experienced
'100' OAM F5 segment cell
'101' OAM F5 end-to-end cell
'110' resource management (RM) cell for ABR
'111' reserved for future use
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ATM Cell Format (cont)
CLP (cell loss priority): 1 bit (CLP=1 cells are discarded before CLP=0)
User may set CLP=1 for less important cells (eg, if layered coding is used)
Network may set CLP=1 for excessive cells (see later)
HEC (header error control): 8 bits to correct single bit errors or detect bit errors
Use CRC code over header only Switches between single bit error correction and error
detection-only
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ATM Cell Format (cont)
Correctionmode
(default)
Detectionmode
No errors detected
Single-bit errordetected and corrected,
or multiple-bit errorsdetected and cell
discarded
No action
Cellsdiscarded
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Quality of Service (QoS)
QoS is a central concept in ATM
ATM is designed to support different services by treating each connection according to its service class
More complicated than traditional packet switching networks
Most networks are designed for best effort or only one type of service (if any), e.g, reliable
QoS parameters describe network performance (impairments) per end-to-end connection oriented to user’s viewpoint
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QoS (cont)
QoS parameter Definition
Accuracy Cell error ratio (CER) fraction of cells delivered with bit errors
Severely errored cellblock ratio (SECBR)
fraction of N-cell blocks delivered with M or more errored cells
QoS aspect
Cell misinsertion rate
rate of appearance of misdirected cells from a different connection
Cell loss ratio (CLR) fraction of cells not deliveredDependability
Speed Cell transfer delay (CTD) maximum delay in delivering cells measured by p-percentile
Cell delay variation (CDV) range between maximum and minimum cell delays, or deviation of cell delivery times from a reference pattern
ATM QoS Parameters
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ATM Services
Constant bit-rate (CBR): for circuit-emulation for real-time applications that need reserved bandwidth
Traffic control: CAC, UPC
Variable bit-rate (VBR): for applications with time-varying bandwidth, eg, compressed voice/video
Real-time VBR (rt-VBR): need guaranteed end-to-end delay, eg, real-time compressed voice
Nonreal-time VBR (nrt-VBR): do not need end-to-end delay guarantees, eg, nonreal-time data
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ATM Services (cont)
Available bit-rate (ABR): for data applications that can be flow-controlled by feedback control, eg, nonreal-time loss-sensitive rate-adaptable data
Traffic control: CAC, feedback control via RM cells
Unspecified bit-rate (UBR): need only best-effort service, eg, nonreal-time bursty data
No traffic control
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QoS (cont)
Main QOS parameters are max. cell delay, CDV, and CLR
Specified QOS parameters depend on what is important to type of service
CBR rt-VBR nrt-VBR ABR
Cell transfer delay Negotiated Unspecified
Cell loss ratio UnspecifiedNegotiated
UBR
Cell delay variation Negotiated Unspecified
Cell error ratio Implicit
ImplicitCell misinsertion ratio
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Connection Admission Control (CAC)
QoS is sustained mainly by connection admission control
CAC allows network to accept or reject a new connection request
Source provides requested QoS level and traffic rate parameters (eg, peak rate)
If accepted, network guarantees QoS as long as user conforms to given traffic rate parameters
No feedback control during connection
This approach relies on congestion prevention instead of congestion reaction
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Spring 2006
EE 5304/EETS 7304 Internet Protocols
Tom OhDept of Electrical Engineering
Lecture 6
IPv4, ICMP
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Outline
Role of IP in internetworking
IPv4 packet header
Internet Control Message Protocol (ICMP)
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Role of IP in Internetworking
Different networks are owned and operated by independent organizations, but need to work together as internetwork or internet
Two possible approaches
Gateways translate different protocols Each network communicates with other networks using a
common universal protocol
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Gateways
Networks understand their own protocol, and gateways convert packets between networks
NetworkA
NetworkB
NetworkC
A:Bgateway
B:Cgateway
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Gateways
Networks can be simple - support only one protocol
Burden is put on gateways - gateways can be complicated
If many types of networks → many types of gateways
No universal ‘lowest common denominator’
Individual networks many not support virtual connections, QoS, signaling, etc.
Capabilities of one network may be ‘lost in translation’ to another network without same capabilities
Internet has no real structural organization
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Routers
Networks communicate by common Internet protocol
Routers forward IP packets between networks
NetworkA
NetworkB
NetworkC
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Routers
Burden is put on networks to support a common network-to-network protocol, in addition to internal network protocol (which may be anything)
Routers are relatively simple packet switches
Common protocol establishes a universal ‘lowest common denominator’
Common protocol establishes a baseline expectation for capabilities (connection-oriented/connectionless, QoS assurances, minimum packet size, etc.)
Internet has some type of structural organization
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Role of IP (cont)
1978 IP version 4 specified [RFC 791]
1983 mandated by DoD as requirement for any networks to connect to ARPANET
1983 TCP/IP implemented in Unix BSD (Berkeley software distribution)
Design philosophy: IP is designed to be simple to minimize burden on networks
Also economy of scale → inexpensive routers
Best effort service: connectionless datagram delivery
No guarantees on delivery, delays, or sequential order
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IPv4 Datagram Header Format
VERS HLEN TOS TOTAL LENGTH
bits: 4 4 4 4 4 4 4 4
IDENTIFICATION FRAGMENT OFFSETFlags
PROTOCOLTTL HEADER CHECKSUM
SOURCE IP ADDRESS
DESTINATION IP ADDRESS
IP OPTIONS (if any)
Version (4 bits): currently 4, new version 6
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IPv4 Datagram Header Format (cont)
VERS HLEN TOS TOTAL LENGTH
bits: 4 4 4 4 4 4 4 4
IDENTIFICATION FRAGMENT OFFSETFlags
PROTOCOLTTL HEADER CHECKSUM
SOURCE IP ADDRESS
DESTINATION IP ADDRESS
IP OPTIONS (if any)
Header length (4 bits): in units of 4-bytes (commonly 20 bytes → HLEN = 5)
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IPv4 Datagram Header Format (cont)
VERS HLEN TOS TOTAL LENGTH
bits: 4 4 4 4 4 4 4 4
IDENTIFICATION FRAGMENT OFFSETFlags
PROTOCOLTTL HEADER CHECKSUM
SOURCE IP ADDRESS
DESTINATION IP ADDRESS
IP OPTIONS (if any)
Type of service (8 bits): original definition
P P P D T R C 0
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ToS Field
Precedence (3 bits): importance
000: routine 001: priority 010: immediate 110: internetwork control 111: network control
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ToS Field (cont)
D flag (1 bit): minimize delay
T flag (1 bit): maximize throughput
R flag (1bit): maximize reliability
C flag (1 bit): minimize monetary cost
0 (1 bit): reserved
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ToS Field (cont)
ToS field specification not clear and required more work for routers → not widely supported and now obsoleted
Current definitionD D D D D D E E
Explicit congestion notification (2 bits) [RFC 3168]
00: not used01: no congestion10: no congestion11: congestion experienced
Diffserv code point (6 bits) [RFC 2474]
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IPv4 Datagram Header Format (cont)
VERS HLEN TOS TOTAL LENGTH
bits: 4 4 4 4 4 4 4 4
IDENTIFICATION FRAGMENT OFFSETFlags
PROTOCOLTTL HEADER CHECKSUM
SOURCE IP ADDRESS
DESTINATION IP ADDRESS
IP OPTIONS (if any)
Total length (16 bits): of datagram in bytes (max 65,535 bytes)
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IPv4 Datagram Header Format (cont)
VERS HLEN TOS TOTAL LENGTH
bits: 4 4 4 4 4 4 4 4
IDENTIFICATION FRAGMENT OFFSETFlags
PROTOCOLTTL HEADER CHECKSUM
SOURCE IP ADDRESS
DESTINATION IP ADDRESS
IP OPTIONS (if any)
Identification (16 bits): to identify fragments belonging to same original packet
Flags (3 bits): used for fragmentation
Fragment offset (13 bits): used for fragmentation
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Fragmentation
IP datagrams can be fragmented into multiple smaller datagrams, each routed independently, because networks may have limit on packet length
Fragments are reassembled only at dest. host
Intermediate routers do not need to store/reassemble fragments
But fragments can only get smaller and smaller → inefficient
If fragment is lost, entire datagram is lost at dest. Reassembly timer: datagram is discarded if all fragments
do not arrive by timeout from first fragment
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Fragmentation (cont)
Identification field: all fragments belonging to same original datagram should have same Identification number (value has no other meaning)
Flags:
0 (1 bit): reserved DF flag (1 bit): “don’t fragment” prevents datagram from
fragmentation (datagram may be discarded) MF flag (1 bit): all fragments have “more fragments”=1
except last fragment has “more fragments”=0
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Fragmentation (cont)
Fragment offset (13 bits): used for reassembly of fragments into datagram
Indicates where this fragment belongs in original datagram Offset is measured in 8-byte units
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Fragmentation (cont)
DATA
byte 0 byte 600 byte 1200
IP Header
DATAIP Header
DATAIP Header
DATAIP Header
Fragment 1offset = 0
Fragment 2offset = 600
Fragment 3offset = 1200
Datagram
Example: datagram is fragmented into 3 fragments (each becomes a separate IP datagram)
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Fragmentation (cont)
Example: datagram of 288 data bytes is fragmented into 3 fragments of 128, 128, and 32 bytes
Header field Fragment 1
Header length 5
Total length 148
Fragment offset 0
Identification 99
MF 1
Fragment 2
5
148
16
99
1
Fragment 3
5
52
32
99
0
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IPv4 Datagram Header Format (cont)
VERS HLEN TOS TOTAL LENGTH
bits: 4 4 4 4 4 4 4 4
IDENTIFICATION FRAGMENT OFFSETFlags
PROTOCOLTTL HEADER CHECKSUM
SOURCE IP ADDRESS
DESTINATION IP ADDRESS
IP OPTIONS (if any)
Time to live (8 bits): maximum lifetime of packet in seconds, to prevent infinite looping in network
- Should be decremented by time at each router- But since routers forward packets quickly, decrement by 1 sec -- TTL is hop count- Recommended initial value 64- Packet is discarded when TTL=0
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IPv4 Datagram Header Format (cont)
VERS HLEN TOS TOTAL LENGTH
bits: 4 4 4 4 4 4 4 4
IDENTIFICATION FRAGMENT OFFSETFlags
PROTOCOLTTL HEADER CHECKSUM
SOURCE IP ADDRESS
DESTINATION IP ADDRESS
IP OPTIONS (if any)
Protocol (8 bits): identifies higher layer protocol using datagram
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Protocol Field
Common protocol values [full list in RFC 2780]
ValueValue ProtocolProtocol
1 ICMP
6 TCP
8 Exterior gateway protocol
9 Any private interior gateway protocol
17 UDP
45 Interdomain routing protocol
88 EIGRP
89 OSPF
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IPv4 Datagram Header Format (cont)
VERS HLEN TOS TOTAL LENGTH
bits: 4 4 4 4 4 4 4 4
IDENTIFICATION FRAGMENT OFFSETFlags
PROTOCOLTTL HEADER CHECKSUM
SOURCE IP ADDRESS
DESTINATION IP ADDRESS
IP OPTIONS (if any)
Header checksum (16 bits): to detect errors in packet header
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IP Datagram Header (cont)
Header checksum (16 bits):
Set checksum = 0, take 1's complement sum of all 16-bit words in header
Checksum = 1's complement of result
Recalculated at every switch because header changes
Errored packets are discarded
Applies to header only -- IP tries only to deliver to right destination
Error check of data field is responsibility of higher layers
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Header Checksum
IP header:
2 bytes
2 bytes
+ + + + + + + + =
Checksuminitially 0
ChecksumSummation
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IP Datagram Header (cont)
Source address (32 bits) and destination address (32 bits)
Every host has unique 32-bit address consisting of two parts: (netID, hostID)
NetID allows more efficient routing in internetworking (discussed more later)
NetID assigned by Internet Assigned Number Authority (IANA) through the Internet Network Information Center (INTERNIC)
All hosts on same network have same netID; hostID is assigned locally
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IP Addresses (cont)
Address is usually written as 4 decimal numbers separated by periods, each integer representing a byte of the IP address
eg, 10000000 00001010 00000010 00011110 is written as 128.10.2.30
Bit allocations are different per 5 classes (class is indicated by first few bits of address field)
A: Very large networks• Few networks, each network has many hosts• 7 bits for netID (max. 128), 24 bits to hostID (max. 16.8
million)
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IP Datagram Header (cont)
B: Medium size (campus) networks
More networks, each network has moderate number of hosts
14 bits to netID (max. 16,384), 16 bits to hostID (max. 65,536)
C: Small networks
Many networks, each network has few hosts 21 bits to netID (max. 2 million), 8 bits to hostID (max.
256)
NetID
bits: 7 24
HostID0
NetID
14 16
HostID
NetID
21 8
HostID1
Class A
Class B
Class C
01
1 0
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IP Datagram Header (cont)
Difficulties:
Hosts moving to a different network must get new address Class C network growing into class B network involves
administrative effort
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IP Datagram Header Options
Option = option code (8 bits) + additional data bytes (variable number)
Option code:
Copy flag (1 bit): 1 = copy this option into all fragments; 0 = copy only into first fragment
Option class (2 bits): • 0: datagram or network control• 1: reserved for future use• 2: debugging and measurement• 3: reserved for future use
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IP Datagram Header Options (cont)
Option number (5 bits):
0: end of option list 3: loose source routing 7: record route 9: strict source routing 11: timestamp (if option class = 2)
Complete list of options: www.iana.orgbits: 1 2
COPY OPTION CLASS
5
OPTION NUMBER
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IP Datagram Header Options (cont)
Example: record route (option 7)
Source creates an empty list of IP addresses Each switch adds its IP address to list when it passes
datagram
Example: source route (option 3 or 9)
Allows source to specify a route, eg, to test a network Source writes a list of IP addresses Strict source routing: must follow list exactly Loose source routing: can make detours as long as hit the
addresses on list
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IP Datagram Header (cont)
Example: timestamp (option 11)
Source creates an empty list of addresses and timestamps Each switch adds its IP address and time that datagram
was handled
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ICMP (Internet Control Message Protocol)
Required part of IP, allows reporting of troubles and network conditions
Otherwise, senders may make wrong assumptions and choose wrong actions
ICMP messages are carried in the data portion of IP datagrams
Identified by protocol field = 1 But ICMP is not considered higher layer; same layer as IP
and a part of IP Doesn’t this violate the principles of protocol layering?
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ICMP (cont)
IP header ICMP message
Type ChecksumCode Type-specific data
IP payload
8 bits 8 bits 16 bits Variable
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ICMP Message Format (cont)
Type (8 bits) : function of message
0: Echo Reply 3: Destination Unreachable 4: Source Quench 5: Redirect 8: Echo Request 11: Time Exceeded 13: Timestamp Request 14: Timestamp Reply
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ICMP Message Format (cont)
Code (8 bits): more information about message type
0: network unreachable 1: host unreachable 3: port unreachable 5: source route failed 6: destination network unknown 7: destination host unknown
Checksum (16 bits): same as IP checksum but over ICMP message only
Additional fields: type-dependent
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ICMP (cont)
Example: Echo Request and Echo Reply
Used in ping (Packet InterNet Groper) program Host A sends echo request to B B returns echo reply with copy of identifier (sending
process ID), sequence number (packet ID), and optional data in echo request
Tests that IP datagram routing and host software are working properly, and also measures roundtrip delay as estimate of distance
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ICMP (cont)
Example: Destination Unreachable
Returned to source host when a router cannot forward an IP datagram for various reasons
bits: 8
TYPE (3)
8
CODE (0-12) CHECKSUM
IP HEADER + FIRST 64 BITS OF DATAGRAM
8 8
UNUSED (ALL ZERO)
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ICMP (cont)
Example: Source Quench
Optional: congested router or host can return source quench to reduce its transmission rate
No message to relieve source quench Normally, source may decrease its rate until no more
source quench messages are received, then gradually increases rate
Found to be ineffective, unfair, and consume bandwidth during congestion-- not used much
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ICMP (cont)
Example: Time Exceeded
IP datagrams contain Time-to-live (or hop count) in header to prevent looping
Field is decremented at each hop, and datagram is discarded when field is 0
Then time exceeded message is returned to source host (or when dest. host times out waiting for all fragments of a datagram to arrive)
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ICMP (cont)
Used in traceroute program to discover route of IP datagrams (which often take same route)
IP record route option is limited to 9 IP addresses, and not consistently supported
Traceroute begins with datagram with TTL=1; first router will discard and return ICMP time exceeded; traceroute continues with datagram with TTL=2; and so on
Finally reaches host but datagram has unused UDP port number-- host returns ICMP port unreachable
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ICMP (cont)
Example: Timestamp Request and Timestamp Reply
A sends timestamp request (with origination time) to B to get Bs clock reading of time of day
Upon receipt, B adds its clock reading (receive time) When B returns timestamp reply, B adds its clock reading
(transmit time) A uses 3 timestamps in timestamp reply message to
estimate its time difference from Bs clock
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ICMP (cont)
bits: 8
TYPE (13 or 14)
8
CODE (0) CHECKSUM
ORIGINATE TIMESTAMP
8 8
SEQUENCE NUMBERIDENTIFIER
RECEIVE TIMESTAMP
TRANSMIT TIMESTAMP
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TEST 1 Review
Types of networks (size, switching, media, network protocols, services)
Standards
Terminalogy
OSI
TCP/IP
Data Link Layer (synchronization, error control, error detection, hamming distance, hamming code, Bit Interleaved Parity, horizontal/vertical parity checks, ARQ Schemes)
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Review
LANs (general)
MAC protocol (Aloha, CSMA, CSMA/CD, Token Ring)
Bridges (Transparent Learning Bridges)
Network Layer (Routing)
Static routing, Source Routing, Flooding
Dijkstra’s Algorithm, Bellman Ford Algorithm
Distance Vector Routing (RIP, IGRP, EIGRP)
Link State Routing.
X. 25 ( Data and Control Packet, Sliding Window)