Lecture No. 9
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Sequence Number Space-Advance Computer Networking-Lecture Slides, Slides of Computer Networks
This course is about introduction to network programming. Topics covered in this are direct link networks, packet switching, internetworking, end-to-end protocols, congestion control and resource, allocation, end-to-end data, applications. This lecture includes: Sequence, Number, Space, Wrap, Frames, Outstanding, Sender, Receiver, Window, Advances, Incarnation, Packets, Protocols, Access, Ethernet
Typology: Slides
2011/2012
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- Lecture No.
3
Sequence Number Space
SeqNum
field is finite; sequence
numbers wrap around
- Sequence number space must be
larger than number of outstandingframes (
SWS
5
Required Sequence Number Space ?• Assume SWS=RWS (simplest, and
typical)– Sender transmits full SWS– Two extreme cases at receiver
- None received (waiting for 0…SWS-1)• All received (waiting for
SWS…2*SWS-1)
6
Required Sequence Number Space ?• All possible packets must have unique
SeqNum
SWS
(MaxSeqNum+1)/
or
SWS+RWS
MaxSeqNum+
is the
correct rule
- Intuitively,
SeqNum
“slides” between
two halves of sequence number space
8
Shared Access Networks
Outline
-^
Bus (Ethernet)
-^
Token ring (FDDI)
-^
Wireless (802.11)
-^
Network Adapter
9
Shared Access Media
- Arbitrating
access
to a shared
media– Multiple hosts on a single link
11
Multiple Access Media
- Need method to moderate access
Fair arbitration
Good performance
12
Shared Media
- Communication
needs vary
- Over time– Between hosts
- Network is not fully utilized
14
Shared Media: Problems
- Problem:
demands can conflict
,^
e. g.
two hosts send simultaneously– STDM does not address this problem -
centralized
- Solution is a medium access control
( MAC
) algorithm
15
Shared Media: Solutions
- Three solutions (out of many)
- Carrier sense multiple access with
collision detection (
CSMA / CD
)
- Send only if medium is idle• Stop sending immediately if collision
detected
Token ring
/FDDI pass a token around a
ring; only token holder sends
- Radio /
wireless
(IEEE 802.11)
17
History of Ethernet
- Developed by Xerox PARC in mid-1970s• Roots in
Aloha
packet-radio network
- Standardized by Xerox / DEC / Intel in
- Similar to
IEEE 802.
standard
- IEEE 802.3u standard defines Fast
Ethernet (100 Mbps)
- New switched Ethernet now popular
18
Ethernet Topologies
-^
Bus
— all nodes connected to a
wire
-^
Star
— all nodes connected to a
central repeater
-^
Combinations thereof
...
20
Ethernet – Alternative Technologies•^
Can be constructed from a thinner cable (
10Base
)
rather than 50-ohm coax cable (
10Base
)
-^
Newer technology uses
10BaseT
(twisted pair)
- Several point-to-point segments coming out of a
multiway repeater called “hub”
Hub
Hub
21
Ethernet Components
10Base5 (ThickNet)Controller (Ethernet Card)
Vampire TapTransceiver
Bus Topology