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TCP - Networking - Lecture Slides, Slides of Computer Networks
A lecture from Networking with following key points: TCP, TCp Header, Sequence Numbers, Stream of Bytes, Sequence Numbers, Timing Illustration, Karels Algorithm, Initial Sequence Number
Typology: Slides
2013/2014
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TCP
TCP Header
2
Source port Destination port
Sequence number
Acknowledgment
HdrLen (^) Flags Advertised window 0
Checksum Urgent pointer
Options (variable)
Data
Used to mux
and demux
What does TCP do?
Many of our previous ideas, but some key differences
- Checksum
TCP Header
5
Source port Destination port
Sequence number
Acknowledgment
HdrLen (^) Flags Advertised window 0
Checksum Urgent pointer
Options (variable)
Data
Computed
over header
and data
TCP: Segments and
Sequence Numbers
TCP “Stream of Bytes” Service…
Application @ Host A
Application @ Host B
TCP Segment
- IP packet
- No bigger than Maximum Transmission Unit (MTU)
- E.g., up to 1500 bytes with Ethernet
- TCP packet
- IP packet with a TCP header and data inside
- TCP header 20 bytes long
- TCP segment
- No more than Maximum Segment Size (MSS) bytes
- E.g., up to 1460 consecutive bytes from the stream
- MSS = MTU – (IP header) – (TCP header)
IP Hdr
IP Data
TCP Data (segment) TCP Hdr
Sequence Numbers
Host A
ISN (initial sequence number)
Sequence number
= 1
st
byte in segment =
ISN + k
k bytes
TCP Header
Source port Destination port
Sequence number
Acknowledgment
HdrLen (^) Flags Advertised window 0
Checksum Urgent pointer
Options (variable)
Data
Starting byte
offset of data
carried in this
segment
What does TCP do?
Most of our previous tricks, but a few differences
- Checksum
- Sequence numbers are byte offsets
- Receiver sends cumulative acknowledgements (like GBN)
Normal Pattern
- Sender: seqno=X, length=B
- Receiver: ACK=X+B
- Sender: seqno=X+B, length=B
- Receiver: ACK=X+2B
- Sender: seqno=X+2B, length=B
- Seqno of next packet is same as last ACK field
TCP Header
17
Source port Destination port
Sequence number
Acknowledgment
HdrLen (^) Flags Advertised window 0
Checksum Urgent pointer
Options (variable)
Data
Acknowledgment
gives seqno just
beyond highest
seqno received in
order
( “ What Byte
is Next ” )
Loss with cumulative ACKs
- Sender sends packets with 100B and seqnos.:
- 100, 200, 300, 400, 500, 600, 700, 800, 900, …
- Assume the fifth packet (seqno 500) is lost, but no others
- Stream of ACKs will be:
- 200, 300, 400, 500, 500, 500, 500,…
What does TCP do?
Most of our previous tricks, but a few differences
- Checksum
- Sequence numbers are byte offsets
- Receiver sends cumulative acknowledgements (like GBN)
- Receivers may not drop out-of-sequence packets (like SR)
- Introduces fast retransmit: optimization that uses duplicate