Transcript Multiple Channel Switches

Characteristics of Multichannel
Switch
* Multichannel Switching
The switch has the ability to group channels arbitrarily and support super-rate switching of
any bandwidth.
* In-Order Cell Sequencing
Guarantee in-order cell sequencing without the use of resequencing mechanism
* Simplicity
Multichannel switching is facilitated without increasing the complexity of the switch
* High Performance
Internal fabric is nonblocking and bufferless
Characteristics of Multichannel
Switch
* Multirate Switching
The Switch can arbitrarily assign the bandwidth to match different rates of the ATM
network.
* Multicast
The Switch supports multipoint connections which is considered an essential function.
* Fairness
Ensure fairness among different I-O pairs by share buffering(recirculation paths).
* Multiple Performance Requirement
Supports two classes of traffic by channel grouping.
Group Switching
0
1
Group x
Group x
0
1
Group x
Group x
2
3
Group x
Group x
3
6
Group x
Group x
4
5
Group x
Group x
7
5
Group x
Group x
6
7
Group x
Group x
4
2
Group x
Group x
(a)
(b)
(c)
Suppose cells had been processed by the input processor
(a) If the two cells are belong to the same group, 0 upward, 1 downward.
If the two cells are belong to different group, 1 upward, 0 downward.
(b) If the two cells belongs to group X 1 upward, 0 downward. Else, 0 upward, 1 downward
(c) The cell belong to group X goes upward, and the other goes downward
ATM Multichannel Switch
Multi-channel Switch
I/P P
Cell
Input
Multi-cast Stage
N
B
G
N
A
E
R
N
B
G
N
Routing Stage
C
N
R
N
B
G
N
N
B
G
N
B
R
Cell
Output
Share Buffering Device & other control logic
Multi-channel Switch Contains Following Components:
* Input Processor---Detect input cell information, sorting, buffering,attributing ...
* Multi-Cast Stage---Maintain the multicast function of this switch.
Contains (R)NBGN/AE/(R)NBGN/CN/Feedback Ckt
* Routing Stage---Maintain the basic or advanced routingfunction of this switch.
Contains RNBGN/NBGN/BR/Feedback Ckt
* Buffering & Traffic Control---Provide share buffer and some other logics for
controlling the entire switch.
Running Adder
SUM 0
AG 0
IP 1
SUM 1
AG 1
IP 2
SUM 2
AG 2
IP 3
SUM 3
AG 3
IP 4
SUM 4
AG 4
IP 5
SUM 5
AG 5
IP 6
SUM 6
AG 6
IP 7
SUM 7
AG 7
X
IP 0
Y
X+Y
Summing Element
(Full Adder)
The running adder can automaticaly generate the packet(cell) output channel address
according to the group it belongs to.
The IP i (input processor) assign 1 to its output line if the targetd channel group is X, and
the other is 0.
Then, after the operation of summing elements, the AG i (address generator) generate the
accurate output channel ID by doing the following operation:
If the packet target group X, the output equals SUM i-1.
If the packet target group X, the output equals N+SUM i-i-1. (N=Total channel no.)
Nonblocking Binary Group Network
Nonblocking Binary Group Network
0
group X
0
group X
0
0
group X
1
group X
1
group X
1
1
group X
2
group X
2
group X
7
3
group X
3
group X
3
group X
2
6
group X
4
group X
4
group X
6
5
group X
5
group X
6
group X
6
7
group X
7
Running
Adder
Flip
Network
7
group X
5
5
group X
group X
3
4
group X
group X
4
2
group X
Input Channel
Number
Channel Group
Destination
Output Channel
Number
The NBGN (Nonblocking Binary Group Network) is made of the combination of
running adder and flip network.
* Note that NBGN can only separate cells into two groups. If more than two groups are
desired, we must use casacde NBGN or Recursive NBGN (RNBGN).
Recursive NBGN
RNBGN
NBGN
One Cell
Buffer
Cell Buffering And
Feedback Control Logic
* The RNBGN is the combination of NBGN and the buffer-feedback ckt. The switch with
2^r channel need r+1 recursive channels.
* By the control of buffer-feedback recursion ckt, this switch can provide the variable
channel grouping ability.
* When the size of the switch increase, the use of RNBGN can effectively reduce the logic
complexity rather than adding more and more NBGN.
* The feedback mechanism also provide Fairness and cell output ordering.
Physical Structure of Multicast Stage
Multicast Stage
Twisted
0
PP 0
PP 1
0
0
1
0
1
n-1
0
n-1
BGT 0
BGT 1
Rm-1 Rm-1
0
0
1
1
BGT n-1
CN
PP n-1
n-1
n-1
NBGN
Rm-1
AE
RNBGN
Share Buffer
Memory
(Mapping Table)
* Multicast stage is made of PP (Port Processor), AE (Address Encoder), CN (Copy
Network), NBGN, and NBGN.
* The stage need memory device to work properly.
Details of Port Processor and NBGN
* The PP i is used to:
1. Determine the VPI/VCI and the required number of copies from the input cell.
2. On the other hand, it has to transform the cell list into monotonic form for
further operation.
3. Augment the cell by three additional field: Broadcast Connection ID,
Cardinality, and Sum. These fields are dedscribe follows.
Broadcast Connection ID is used to determine the required information for
all functions of switching.
Cardinality records the required number of copies.
Sum identifies the cell as active one (assign 1) or just an empty one (assign 0).
The Broadcast Connection ID is maintained throughout the entire switch.
* The first NBGN is used to:
1. This NBGN has (n+Rm) inputs, Rm is the number of recirculation.
2. According to the SUM field, this NBGN perform binary grouping, active cells
are concentrated at the upper group, while the empty ones are at the lower
group.
3. The relative ordering is not changed, because of the characteristic of NBGN.
Details of Address Encoder and NBGN
* The Address Encoder functions as follows:
1. Determine the input cells are requested to multicast or not.
2. Determine the multicast interval of the requested cells.
3. Deciding the multicast request is going to be done in the Copy Network or not.
4. The SUM field used by the first NBGN will be assign a new value here. By the
running adders in the AE, these cells are calcuted in Top-Down order to determine
whether the output channel no. is exceed n or not. If exceeded, the cell is remarked 1
in the SUM field, other wise remark 0 instead.
* The second NBGN functions as follows:
1. After processed by AE goes next into the NBGN. These cells are being passed to
CN or the recursive loopback. If the SUM field is 0 after AE, the cell is passed to CN
, otherwise, the cell loopback to the starting of multicast stage, waiting for next time
slot to re-enter again.
2. The re-entered cells have higher priority than the new-entered cells because of the Top
-Down process order of AE.
3. In order to keep the fairness, the feedback twisted. By the way, it also helpful to keep
the relative ordering of the recursive cells.
Multiple Performance Requirement
Multicast Stage
0
PP 0
PP 1
Rm-1
0
1
Twisted
0
0
1
0
1
n-1
0
n-1
BGT 0
BGT 1
Rm-1
0
1
BGT n-1
CN
P P n-1
n-1
n-1
RNBGN
Rm-1
AE
RNBGN
Share Buffer
Memory
(Mapping Table)
•
•
To support two service classes, cells are separate into three groups by the first RNBGN
– group 0: active class 0 cells (delay sensitive)
– group 1: active class 1 cells
– group 2: empty cells
Cells are separate into four groups by the second RNBGN
– group 0: cells to be passed to the CN
– group 1: class 0 cells to be recirculated
– group 2: class 1 cells to be recirculated
– group 3: empty cells
Details of Copy Network and BGT
* The functions of the Copy Network:
1. The basic function of Copy Network is to generate two or more identical cells.
2. The copies made by the CN must be in an interval of several continuous output
channels. In other words, the output channels of copies can’t be aribitary
assigned. If not, the CN may encounter contention problem.
* The functions of the BGT (Broadcast and Group Translator):
1. The function of BGT is used to assign a new group ID to the copies made by the
CN. Then the cells can be switched to proper channel groups in the routing
stage.
2. Assign of the new channel group is based on the Broadcast Connection ID
generated by PP. This field is not changed after the replication of CN.
3. This part of work is done in table which is stored in the memory device of the
switch.
Summary of Multicast Stage
Multicast Stage
0
PP 0
PP 1
Twisted
0
0
1
0
1
n-1
0
n-1
BGT 0
BGT 1
Rm-1 Rm-1
0
0
1
1
BGT n-1
CN
PP n-1
n-1
n-1
RNBGN
Rm-1
AE
RNBGN
Share Buffer
Memory
(Mapping Table)
* Fairness is achieved by virtue of the recirculation path. Cells are delayed in one time
slot, and they gain higher priority in next one.
* Multichannel & Multicast functions are obtained.
* In-order cell sequencing is garenteed by mark the cell index of time. This
index is maintained throughout the entire switch to keep the cell relative ordering.
* No matter are duplicated by the Copy Network or not, the BGT will give them a
group ID. Mulit-rate switching can be done when the routing stage grouping the
channels according to it.
* Multi-performance requirement is discuss in the next page.
The Routing Stage
Routing Stage
0
Twisted
0
0
1
0
1
n-1
0
n-1
Rm-1 Rm-1
0
0
1
1
BN
n-1
n-1
RNBGN
Rm-1
NBGN
* The routing stage is made of RNBGN, NBGN, and BR (Banyan Router).
* The over all function of this unit is
1. The cells enter the RNBGN and targeted for various channel groups. After they
completing the output channels, the excess cells and empty ones were grouped at
the bottom of ouput. ( They are listed according to a Gray code sequence of channel group
address.)
2. Next, the listed cells enter the NBGN, the excess and empty ones are marked for
recirculation. The effective ones ges next into the BR.
( Now, the cells entering the BR are in Monotonic Ascending Order.)
3. At last, the BR route the cells to the right place where they should be.
Simulation Results of the switch
In Multicast Stage, we are interested in
following parameters:
the normalized load ( p )
the cell lost probability
the output channel group N
The amount of the recursive path is very
improtant when the cell lost proability &
p is assured in demands.
In multicast stage:
1. The number of the recirculation
channels (Rm) is the most efficientive
parameter.
2. If Rm is large enough (say Rm>64),
the cell lost proability can as low as
10e-6 and the p is as high as 0.85.
3. If the Rm is small (say Rm<8), the p
droped to 0.6 as the cell lost proability
maintained as 10e-6.
In Routing Stage:
1. Under N output channel groups, the Rr
here is also efficientive as the Rm in the
multicast stage.
2. If N is reduced, i.e., the channels are
grouped, the required number of Rr is
also reduced under the same quality of
cell lost proability and p.
Conclusion
1. Because the optical transmission speed increasing in recent years while
the electrical processing speed remains in the MHz degree, multichannel grouping
becomes more and more important.
2. When the number of users increased, the multicast switching is achieved without
increasing the complexity of the entire switch. Mearly change the output grouping
numbers, the switch can deal with this easily.
3. The switch garentee the cell ordering, switching delay, and high throughput
performance. These connection-oriented characterisitcs are very important for high
speed ATM network.
4. The switch can act according to the different characteristics of the cells. In the ATM
network, there are several kinds of cell like “real time image”, “non-real time image”
, “file transfer”.....and so on. Switching them depend on different proirities is a real
way to deal with high speed ATM network.
5. The multicast, multirate, and multichannel switching functions provides the ATM
network with more variable useage. Especially, time require for the multicast function
can be reduced as compared to the single channel switch.